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Sample records for african monsoon wam

  1. Spatio-temporal evolution of the West African monsoon during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Weldeab, Syee; Frank, Martin; Stichel, Torben; Haley, Brian; Sangen, Mark

    2011-07-01

    On the basis of a multi-proxy data set from the Gulf of Guinea (eastern equatorial Atlantic) we reconstruct the spatio-temporal evolution of the West African monsoon (WAM) and present evidence for a decoupling between latitudinal shifts of the rain belt and WAM intensification. The onset of deglacial monsoon invigoration at ˜16,600 years before present lagged northward migration of a weak rainfall zone by ˜2800 years. Conversely, during the Younger Dryas (YD) time interval, WAM precipitation was severely reduced but we find no evidence for a large-scale retreat of the rainfall front. This observation is not in agreement with the hypothesis of a large-scale shift of the intertropical convergence zone south of the tropical WAM region during the YD. Our results can be better reconciled with the newly emerging concept of a strong influence of Tropical Easterly and African Easterly Jets on modern WAM.

  2. Mutual interaction between the West African Monsoon on the summer Mediterranean climate

    NASA Astrophysics Data System (ADS)

    Gaetani, M.; Baldi, M.; Dalu, G. A.

    2009-04-01

    Many studies have show that the West African Monsoon (WAM) is teleconnected with neighbouring regions, as the Mediterranean (Med) basin and the Tropical Atlantic, but also it is sensitive to the perturbations occurring even in remote regions, as the Indian sub-continent and the Tropical Pacific, these teleconnections being active on several time-scales, from intraseasonal to multidecadal. The WAM plays also an active role in the regional atmospheric circulation, inducing significant changes in rainfall, moisture, temperature, and wind distribution up to the North Africa. Within this framework, recent works were focused on the teleconnection between WAM and Med. WAM is strengthened by the north-easterly advection of moisture from the Med Sea, and, since the subsiding monsoonal air often invades the Med, there is a 2-way interaction between WAM and Med summer circulation. We study these interactions, applying SVD analysis to global NCEP Reanalysis and to rainfall data from CMAP, during the extended monsoonal season from May to October, on interannual and on intraseasonal time-scale. Dynamical features are explored using composite analysis, focusing on the role of this connection in the heat waves occurrence in the Med. We find that a strong WAM intensifies the Hadley meridional circulation, with a strengthening of the north Atlantic anticyclone and a weakening, even blocking, of the westerly flow in the Med. A deep inland penetration of WAM produces a northern shift of the Libyan anticyclone, with subsidence and high pressure affecting mainly the western Med. The positive feedback is due to the intensification of north-easterly flow from the eastern Med, which, reaching the Sahara desert, intensifies the intertropical front, favouring abundant monsoonal precipitation because of the added moist air.

  3. Future of West African Monsoon in A Warming Climate

    NASA Astrophysics Data System (ADS)

    Raj, Jerry; Kunhu Bangalath, Hamza; Stenchikov, Georgiy

    2016-04-01

    West Africa is the home of more than 300 million people whose agriculture based economy highly relies on West African Monsoon (WAM), which produces a mean annual rainfall of 150 - 2,500 mm and variability and change of which have devastating impact on the local population. The observed widespread drought in West Africa during the 1970s and 1980s was the most significant drought at regional scale during the twentieth century. In this study, a high resolution AGCM, High Resolution Atmospheric Model (HiRAM), is used to study the effects of anthropogenic greenhouse warming on WAM. HiRAM is developed at GFDL based on AM2 and employs a cubed-sphere finite volume dynamical core and uses shallow convective scheme (for moist convection and stratiform cloudiness) instead of deep convective parameterization. Future projections are done using two representative concentration pathways, RCP 4.5 and RCP 8.5 from 2007 to 2050 at C360 (~25 km) resolution. Both RCP 4.5 and RCP 8.5 scenarios predict warming over West Africa during boreal summer, especially over Western Sahara. Also, both scenarios predict southward shift in WAM rainfall pattern and drying over Southern Sahara, while RCP 8.5 predicts enhanced rainfall over Gulf of Guinea. The intensification of rainfall over tropical latitudes is caused by increased low level winds due to warm SST over Gulf of Guinea.

  4. Understanding the mechanisms behind the West African Monsoon northward extension during Mid-Holocene

    NASA Astrophysics Data System (ADS)

    Gaetani, Marco; Messori, Gabriele; Zhang, Qiong; Flamant, Cyrille; Evan, Amato T.; Pausata, Francesco S. R.

    2016-04-01

    Understanding the West African monsoon (WAM) dynamics in the mid-Holocene (MH) is a crucial issue in climate modelling, because numerical models typically fail to reproduce the extensive precipitation suggested by proxy evidence. This discrepancy is largely due to unrealistic imposed land surface cover and aerosols. Numerical experiments are conducted by imposing a "green Sahara", along with a reduced dust concentration in the atmosphere, coherently with the MH environment in the region, and the atmospheric dynamics response and impact on precipitation are investigated. The response of the WAM system to the imposed conditions shows a dramatic augmentation of the precipitation across West Africa up to the Mediterranean coast. This follows a substantial reorganization of the regional circulation, with some monsoonal circulation features (Saharan heat low, African easterly jet, African easterly waves) weakened in favour of deep convection development over land. The simulated response is dominated by land cover changes, and the reduction in dust concentration further enhances the changes induced by the "green Sahara". The intensity and meridional extent of the WAM is fully consistent with proxy evidence. The results for the MH WAM present important implications for understanding future climate scenarios in the region, in the perspective of projected wetter conditions in West Africa.

  5. Evaluation of West African Monsoon Processes and Feedbacks: Second West African Monsoon Modeling and Evaluation Project Experiment (WAMME II)

    NASA Astrophysics Data System (ADS)

    Xue, Y.; Lau, W. K.; Boone, A. A.; Seidou Sanda, I.; Thiaw, W. M.; Druyan, L.; Team, W.

    2013-12-01

    Despite recent progress in understanding of the West African monsoon (WAM), there are still many unanswered questions regarding to the impact of external forcings: oceans, land, and aerosols, on WAM variability, especially their roles in the Sahel drought. The West African Monsoon Modeling and Evaluation (WAMME) is a project comprised of both general circulation models (GCMs) and regional climate models (RCMs) with the objective to collectively provide best estimation of the relative importance of all those external forcing on WAM on seasonal to multi-decadal time scales. WAMME research activities are closely coordinated with those of AMMA, involving many African institutions. Observational evidence has shown strong decadal climate variabilities in the Sahel from the 1950s to the 2000s, not only in precipitation, but also in SST, vegetation cover, land use and land cover changes (LULCC), and aerosols. In WAMME-2, multi-model intercomparison experiments are designed to test how seasonal and decadal variabilities of WAM precipitation are associated with these forcings, and assess their relative contributions in producing/amplifying the WAM seasonal and decadal climate variability. The sensitivity of the WAM variability to those external forcings is also examined. The WAMME-2 strategy is to apply observational data-based anomaly forcing of SST, land surface and aerosols, i.e., "idealized but realistic" forcing, in GCM and RCM simulations with the specific purpose of estimating the relative impacts of each forcing and feedback mechanisms. In the SST experiment, in addition to the global SST effect, each ocean's role is also evaluated. The preliminary results from most GCMs consistently indicate that SST has a maximum impact on the WAM decadal variability compared with other forcings, and that the effect of the Pacific Ocean is most dominant. The models, however, differ in producing other oceans' contribution. Moreover, the models with specified maximum SST forcing are

  6. Impacts of dust reduction on the northward expansion of the African monsoon during the Green Sahara period

    NASA Astrophysics Data System (ADS)

    Pausata, Francesco S. R.; Messori, Gabriele; Zhang, Qiong

    2016-01-01

    The West African Monsoon (WAM) is crucial for the socio-economic stability of millions of people living in the Sahel. Severe droughts have ravaged the region in the last three decades of the 20th century, highlighting the need for a better understanding of the WAM dynamics. One of the most dramatic changes in the West African Monsoon (WAM) occurred between 15000-5000 yr BP, when increased summer rainfall led to the so-called "Green Sahara" and to a reduction in dust emissions from the region. However, model experiments are unable to fully reproduce the intensification and geographical expansion of the WAM during this period, even when vegetation over the Sahara is considered. Here, we use a fully coupled simulation for 6000 yr BP (Mid-Holocene) in which prescribed Saharan vegetation and dust concentrations are changed in turn. A closer agreement with proxy records is obtained only when both the Saharan vegetation changes and dust decrease are taken into account. The dust reduction strengthens the vegetation-albedo feedback, extending the monsoon's northern limit approximately 500 km further than the vegetation-change case only. We therefore conclude that accounting for changes in Saharan dust loadings is essential for improving model simulations of the WAM during the Mid-Holocene.

  7. The Mid-Holocene West African Monsoon strength modulated by Saharan dust and vegetation

    NASA Astrophysics Data System (ADS)

    Pausata, F. S. R.; Messori, G.; Zhang, Q.

    2015-12-01

    The West African Monsoon (WAM) is crucial for the socio-economic stability of millions of people living in the Sahel. Severe droughts have ravaged the region in the last three decades of the 20th century, highlighting the need for a better understanding of the WAM dynamics. One of the most dramatic changes in the WAM occurred between 15,000-5,000 years BP, when increased summer precipitation led to the so-called "Green Sahara" and to a reduction in dust emissions from the region. Previous studies have shown that variations in vegetation and soil type can have major impacts on precipitation. However, model simulations are still unable to fully reproduce the intensification and geographical expansion of the African monsoon during that period, even when vegetation over the Sahara is simulated. Here, we use a fully coupled simulation for 6000 years BP in which prescribed Saharan vegetation and dust concentrations are changed in turn. A close agreement with proxy records is obtained only when both Saharan vegetation and dust decrease are taken into account (Fig. 1). The dust reduction extends the monsoon's northern limit further than the vegetation-change case only (Fig. 2), by strengthening vegetation-albedo feedbacks and driving a deeper Saharan Heat Low. The dust reduction under vegetated Sahara conditions leads to a northward shift of the WAM extension that is about twice as large as the shift due to the changes in orbital forcing alone. We therefore conclude that accounting for changes in Saharan dust loadings is essential for improving model simulations of the MH WAM. The role of dust is also relevant when looking into the future, since Saharan dust emission may decrease owing to both direct and indirect anthropogenic impacts on land cover.

  8. Significant impacts of radiation physics in the Weather Research and Forecasting model on the precipitation and dynamics of the West African Monsoon

    NASA Astrophysics Data System (ADS)

    Li, R.; Jin, J.; Wang, S.-Y.; Gillies, R. R.

    2015-03-01

    Precipitation from the West African Monsoon (WAM) provides food security and supports the economy in the region. As a consequence of the intrinsic complexities of the WAM's evolution, accurate simulations of the WAM and its precipitation regime, through the application of regional climate models, are challenging. We used the coupled Weather Research and Forecasting (WRF) and Community Land Model (CLM) to explore impacts of radiation physics on the precipitation and dynamics of the WAM. Our results indicate that the radiation physics schemes not only produce biases in radiation fluxes impacting radiative forcing, but more importantly, result in large bias in precipitation of the WAM. Furthermore, the different radiation schemes led to variations in the meridional gradient of surface temperature between the north that is the Sahara desert and the south Guinean coastline. Climate diagnostics indicated that the changes in the meridional gradient of surface temperature affect the position and strength of the African Easterly Jet as well as the low-level monsoonal inflow from the Gulf of Guinea. The net result was that each radiation scheme produced differences in the WAM precipitation regime both spatially and in intensity. Such considerable variances in the WAM precipitation regime and dynamics, resulting from radiation representations, likely have strong feedbacks within the climate system and so have inferences when it comes to aspects of predicted climate change both for the region and globally.

  9. Stratospheric variability of wave activity and parameters in equatorial coastal and tropical sites during the West African monsoon

    NASA Astrophysics Data System (ADS)

    Kafando, P.; Chane-Ming, F.; Petitdidier, M.

    2015-08-01

    Recent numerical studies in stratospheric dynamics and its variability as well as climate, have highlighted the need of more observational analyses to improve simulation of the West African monsoon (WAM). In this paper, activity and spectral characteristics of short-scale vertical waves (wavelengths <4 km) are analysed in equatorial coastal and tropical lower stratosphere during the WAM. A first detailed description of such waves over West Africa is derived from high-resolution vertical profiles of temperature and horizontal wind obtained during Intensive Observation Period of the African Monsoon Multidisciplinary Analyses (AMMA) Campaign 2006. Monthly variation of wave energy density is revealed to trace the progression of the inter-tropical convergence zone (ITCZ) over West Africa. Mesoscale inertia gravity-waves structures with vertical and horizontal wavelengths of 1.5-2.5 and 400-1100 km respectively and intrinsic frequencies of 1.1-2.2 f or periods <2 days are observed in the tropical LS with intense activity during July and August when the WAM is installed over the tropical West Africa. Over equatorial region, gravity waves with intrinsic frequencies of 1.4-4 f or periods <5.2 days, vertical wavelength of 2.1 km and long horizontal wavelengths of 1300 km are intense during the WAM coastal phase. From July to October, gravity waves with intrinsic frequencies of 1.2-3.8 f or periods <6 days, vertical wavelength of 2.1 km and horizontal wavelengths of 1650 km are less intense during the WAM Sahelian phase of the WAM, March-June. Unlike potential energy density, kinetic energy density is observed to be a good proxy for the activity of short-scale vertical waves during the WAM because quasi-inertial waves are dominant. Long-term wave activity variation from January 2001 to December 2009, highlights strong year-to-year variation superimposed on convective activity and quasi-biennial oscillation-like variations especially above tropical stations.

  10. Variability of West African monsoon patterns generated by a WRF multi-physics ensemble

    NASA Astrophysics Data System (ADS)

    Klein, Cornelia; Heinzeller, Dominikus; Bliefernicht, Jan; Kunstmann, Harald

    2015-11-01

    The credibility of regional climate simulations over West Africa stands and falls with the ability to reproduce the West African monsoon (WAM) whose precipitation plays a pivotal role for people's livelihood. In this study, we simulate the WAM for the wet year 1999 with a 27-member multi-physics ensemble of the Weather Research and Forecasting (WRF) model. We investigate the inter-member differences in a process-based manner in order to extract generalizable information on the behavior of the tested cumulus (CU), microphysics (MP), and planetary boundary layer (PBL) schemes. Precipitation, temperature and atmospheric dynamics are analyzed in comparison to the Tropical Rainfall Measuring Mission (TRMM) rainfall estimates, the Global Precipitation Climatology Centre (GPCC) gridded gauge-analysis, the Global Historical Climatology Network (GHCN) gridded temperature product and the forcing data (ERA-Interim) to explore interdependencies of processes leading to a certain WAM regime. We find that MP and PBL schemes contribute most to the ensemble spread (147 mm month-1) for monsoon precipitation over the study region. Furthermore, PBL schemes have a strong influence on the movement of the WAM rainband because of their impact on the cloud fraction, that ranges from 8 to 20 % at 600 hPa during August. More low- and mid-level clouds result in less incoming radiation and a weaker monsoon. Ultimately, we identify the differing intensities of the moist Hadley-type meridional circulation that connects the monsoon winds to the Tropical Easterly Jet as the main source for inter-member differences. The ensemble spread of Sahel precipitation and associated dynamics for August 1999 is comparable to the observed inter-annual spread (1979-2010) between dry and wet years, emphasizing the strong potential impact of regional processes and the need for a careful selection of model parameterizations.

  11. The Impact of the Atlantic Cold Tongue on West African Monsoon Onset in Regional Model Simulations for 1998-2002

    NASA Technical Reports Server (NTRS)

    Druyan, Leonard M.; Fulakeza, Matthew B.

    2014-01-01

    The Atlantic cold tongue (ACT) develops during spring and early summer near the Equator in the Eastern Atlantic Ocean and Gulf of Guinea. The hypothesis that the ACT accelerates the timing of West African monsoon (WAM) onset is tested by comparing two regional climate model (RM3) simulation ensembles. Observed sea surface temperatures (SST) that include the ACT are used to force a control ensemble. An idealized, warm SST perturbation is designed to represent lower boundary forcing without the ACT for the experiment ensemble. Summer simulations forced by observed SST and reanalysis boundary conditions for each of five consecutive years are compared to five parallel runs forced by SST with the warm perturbation. The article summarizes the sequence of events leading to the onset of the WAM in the Sahel region. The representation of WAM onset in RM3 simulations is examined and compared to Tropical Rainfall Measuring Mission (TRMM), Global Precipitation Climatology Project (GPCP) and reanalysis data. The study evaluates the sensitivity of WAM onset indicators to the presence of the ACT by analysing the differences between the two simulation ensembles. Results show that the timing of major rainfall events and therefore theWAM onset in the Sahel are not sensitive to the presence of the ACT. However, the warm SST perturbation does increase downstream rainfall rates over West Africa as a consequence of enhanced specific humidity and enhanced northward moisture flux in the lower troposphere.

  12. Regional analysis of convective systems during the West African monsoon

    NASA Astrophysics Data System (ADS)

    Guy, Bradley Nicholas

    The West African monsoon (WAM) occurs during the boreal summer and is responsible for a majority of precipitation in the northern portion of West Africa. A distinct shift of precipitation, often driven by large propagating mesoscale convective systems, is indicated from satellite observations. Excepting the coarser satellite observations, sparse data across the continent has prevented understanding of mesoscale variability of these important systems. The interaction between synoptic and mesoscale features appears to be an important part of the WAM system. Without an understanding of the mesoscale properties of precipitating systems, improved understanding of the feedback mechanism between spatial scales cannot be attained. Convective and microphysical characteristics of West African convective systems are explored using various observational data sets. Focus is directed toward meso -alpha and -beta scale convective systems to improve our understanding of characteristics at this spatial scale and contextualize their interaction with the larger-scale. Ground-based radar observations at three distinct geographical locations in West Africa along a common latitudinal band (Niamey, Niger [continental], Kawsara, Senegal [coastal], and Praia, Republic of Cape Verde [maritime]) are analyzed to determine convective system characteristics in each domain during a 29 day period in 2006. Ancillary datasets provided by the African Monsoon Multidisciplinary Analyses (AMMA) and NASA-AMMA (NAMMA) field campaigns are also used to place the radar observations in context. Results show that the total precipitation is dominated by propagating mesoscale convective systems. Convective characteristics vary according to environmental properties, such as vertical shear, CAPE, and the degree of synoptic forcing. Data are bifurcated based on the presence or absence of African easterly waves. In general, African easterly waves appear to enhance mesoscale convective system strength

  13. West African Monsoon dynamics in idealized simulations: the competitive roles of SST warming and CO2

    NASA Astrophysics Data System (ADS)

    Gaetani, Marco; Flamant, Cyrille; Hourdin, Frederic; Bastin, Sophie; Braconnot, Pascale; Bony, Sandrine

    2015-04-01

    The West African Monsoon (WAM) is affected by large climate variability at different timescales, from interannual to multidecadal, with strong environmental and socio-economic impacts associated to climate-related rainfall variability, especially in the Sahelian belt. State-of-the-art coupled climate models still show poor ability in correctly simulating the WAM past variability and also a large spread is observed in future climate projections. In this work, the July-to-September (JAS) WAM variability in the period 1979-2008 is studied in AMIP-like simulations (SST-forced) from CMIP5. The individual roles of global SST warming and CO2 concentration increasing are investigated through idealized experiments simulating a 4K warmer SST and a 4x CO2 concentration, respectively. Results show a dry response in Sahel to SST warming, with dryer conditions over western Sahel. On the contrary, wet conditions are observed when CO2 is increased, with the strongest response over central-eastern Sahel. The precipitation changes are associated to modifications in the regional atmospheric circulation: dry (wet) conditions are associated with reduced (increased) convergence in the lower troposphere, a southward (northward) shift of the African Easterly Jet, and a weaker (stronger) Tropical Easterly Jet. The co-variability between global SST and WAM precipitation is also investigated, highlighting a reorganization of the main co-variability modes. Namely, in the 4xCO2 simulation the influence of Tropical Pacific is dominant, while it is reduced in the 4K simulation, which also shows an increased coupling with the eastern Pacific and the Indian Ocean. The above results suggest a competitive action of SST warming and CO2 increasing on the WAM climate variability, with opposite effects on precipitation. The combination of the observed positive and negative response in precipitation, with wet conditions in central-eastern Sahel and dry conditions in western Sahel, is consistent with the

  14. Daily characteristics of West African summer monsoon precipitation in CORDEX simulations

    NASA Astrophysics Data System (ADS)

    Klutse, Nana Ama Browne; Sylla, Mouhamadou Bamba; Diallo, Ismaila; Sarr, Abdoulaye; Dosio, Alessandro; Diedhiou, Arona; Kamga, Andre; Lamptey, Benjamin; Ali, Abdou; Gbobaniyi, Emiola O.; Owusu, Kwadwo; Lennard, Christopher; Hewitson, Bruce; Nikulin, Grigory; Panitz, Hans-Jürgen; Büchner, Matthias

    2016-01-01

    We analyze and intercompare the performance of a set of ten regional climate models (RCMs) along with the ensemble mean of their statistics in simulating daily precipitation characteristics during the West African monsoon (WAM) period (June-July-August-September). The experiments are conducted within the framework of the COordinated Regional Downscaling Experiments for the African domain. We find that the RCMs exhibit substantial differences that are associated with a wide range of estimates of higher-order statistics, such as intensity, frequency, and daily extremes mostly driven by the convective scheme employed. For instance, a number of the RCMs simulate a similar number of wet days compared to observations but greater rainfall intensity, especially in oceanic regions adjacent to the Guinea Highlands because of a larger number of heavy precipitation events. Other models exhibit a higher wet-day frequency but much lower rainfall intensity over West Africa due to the occurrence of less frequent heavy rainfall events. This indicates the existence of large uncertainties related to the simulation of daily rainfall characteristics by the RCMs. The ensemble mean of the indices substantially improves the RCMs' simulated frequency and intensity of precipitation events, moderately outperforms that of the 95th percentile, and provides mixed benefits for the dry and wet spells. Although the ensemble mean improved results cannot be generalized, such an approach produces encouraging results and can help, to some extent, to improve the robustness of the response of the WAM daily precipitation to the anthropogenic greenhouse gas warming.

  15. The West African Monsoon: variability and teleconnection with ENSO during the years 1948-57

    NASA Astrophysics Data System (ADS)

    Stickler, Alexander; Brönnimann, Stefan

    2010-05-01

    The intensity of the West African Monsoon (WAM) has been shown to be influenced by different factors. Most important for the existence of the monsoon system is the land-sea thermal contrast between the North African landmass and the Gulf of Guinea. ENSO plays an important role for its interannual variability via an atmospheric teleconnection bridging the Pacific and Atlantic oceanic basins and favouring either descent/weak low-level monsoon flow or ascent/strong low-level monsoon flow over tropical West Africa. Most published studies on the WAM variability are based on reanalysis datasets. However, while reproducing quite well the interannual variability, reanalysis products have been found to contain major biases in certain tropical regions before 1968. These lead to an unrealistic low frequency behaviour and might be explained by the lack of observations assimilated into the reanalyses, as is the case e.g. for tropical Africa where only the much sparser radiosonde data have been assimilated into the NCEP/NCAR Reanalysis (NNR). Here we present an analysis of the interannual WAM variability and its teleconnection with ENSO for the years 1948-57 which is not based on a reanalysis, but on early pilot balloon observational wind data from the Comprehensive Historical Upper Air Network (CHUAN). We have examined wind data from all 36 stations located in the domain (10°S-30°N, 20°W-20°E) on 5 levels up to the mid troposphere (corresponding roughly to the 925, 850, 700, 600 and 500 hPa pressure levels). This analysis shows that 7 subregions can be defined which are characterised by similar vertical wind profiles as well as seasonality: the NW (Mauritania, northern Senegal), the SW (southern Senegal to coastal Guinea), central sub-Saharan West Africa (SSWA, from interior Guinea in the W to coastal Cameroon and southern Niger in the E), central and eastern Niger, western Chad, the western Central African Republic, and the southern coastal regions east of the Gulf of

  16. The West African monsoon: Contribution of the AMMA multidisciplinary programme to the study of a regional climate system.

    NASA Astrophysics Data System (ADS)

    Lebel, T.; Janicot, S.; Redelsperger, J. L.; Parker, D. J.; Thorncroft, C. D.

    2015-12-01

    The AMMA international project aims at improving our knowledge and understanding of the West African monsoon and its variability with an emphasis on daily-to-interannual timescales. AMMA is motivated by an interest in fundamental scientific issues and by the societal need for improved prediction of the WAM and its impacts on water resources, health and food security for West African nations. The West African monsoon (WAM) has a distinctive annual cycle in rainfall that remains a challenge to understand and predict. The location of peak rainfall, which resides in the Northern Hemisphere throughout the year, moves from the ocean to the land in boreal spring. Around the end of June there is a rapid shift in the location of peak rainfall between the coast and around 10°N where it remains until about the end of August. In September the peak rainfall returns equatorward at a relatively steady pace and is located over the ocean again by November. The fact that the peak rainfall migrates irregularly compared to the peak solar heating is due to the interactions that occur between the land, the atmosphere and the ocean. To gain a better understanding of this complex climate system, a large international research programme was launched in 2002, the biggest of its kind into environment and climate ever attempted in Africa. AMMA has involved a comprehensive field experiment bringing together ocean, land and atmospheric measurements, on timescales ranging from hourly and daily variability up to the changes in seasonal activity over a number of years. This presentation will focus on the description of the field programme and its accomplishments, and address some key questions that have been recently identified to form the core of AMMA-Phase 2.

  17. The West African monsoon: Contribution of the AMMA multidisciplinary programme to the study of a regional climate system.

    NASA Astrophysics Data System (ADS)

    Lebel, T.; Janicot, S.; Redelsperger, J. L.; Parker, D. J.; Thorncroft, C. D.

    2014-12-01

    The AMMA international project aims at improving our knowledge and understanding of the West African monsoon and its variability with an emphasis on daily-to-interannual timescales. AMMA is motivated by an interest in fundamental scientific issues and by the societal need for improved prediction of the WAM and its impacts on water resources, health and food security for West African nations. The West African monsoon (WAM) has a distinctive annual cycle in rainfall that remains a challenge to understand and predict. The location of peak rainfall, which resides in the Northern Hemisphere throughout the year, moves from the ocean to the land in boreal spring. Around the end of June there is a rapid shift in the location of peak rainfall between the coast and around 10°N where it remains until about the end of August. In September the peak rainfall returns equatorward at a relatively steady pace and is located over the ocean again by November. The fact that the peak rainfall migrates irregularly compared to the peak solar heating is due to the interactions that occur between the land, the atmosphere and the ocean. To gain a better understanding of this complex climate system, a large international research programme was launched in 2002, the biggest of its kind into environment and climate ever attempted in Africa. AMMA has involved a comprehensive field experiment bringing together ocean, land and atmospheric measurements, on timescales ranging from hourly and daily variability up to the changes in seasonal activity over a number of years. This presentation will focus on the description of the field programme and its accomplishments, and address some key questions that have been recently identified to form the core of AMMA-Phase 2.

  18. West African monsoon dynamics and precipitation: the competition between global SST warming and CO2 increase in CMIP5 idealized simulations

    NASA Astrophysics Data System (ADS)

    Gaetani, Marco; Flamant, Cyrille; Bastin, Sophie; Janicot, Serge; Lavaysse, Christophe; Hourdin, Frederic; Braconnot, Pascale; Bony, Sandrine

    2016-04-01

    Climate variability associated with the West African monsoon (WAM) has important environmental and socio-economic impacts in the region. However, state-of-the-art climate models still struggle in producing reliable climate predictions. An important cause of this low predictive skill is the sensitivity of climate models to different forcings. In this study, the mechanisms linking the WAM dynamics to the CO2 forcing are investigated, by comparing the effect of the CO2 direct radiative effect with its indirect effect mediated by the global sea surface warming. The July-to-September WAM variability is studied in climate simulations extracted from the Coupled Model Intercomparison Project Phase 5 archive, driven by prescribed sea surface temperature (SST). The individual roles of global SST warming and CO2 atmospheric concentration increase are investigated through idealized experiments simulating a 4 K warmer SST and a quadrupled CO2 concentration, respectively. Results show opposite and competing responses in the WAM dynamics and precipitation. A dry response (-0.6 mm/day) to the SST warming is simulated in the Sahel, with dryer conditions over western Sahel (-0.8 mm/day). Conversely, the CO2 increase produces wet conditions (+0.5 mm/day) in the Sahel, with the strongest response over central-eastern Sahel (+0.7 mm/day). The associated responses in the atmospheric dynamics are also analysed, showing that the SST warming affects the Sahelian precipitation through modifications in the global tropical atmospheric dynamics, reducing the importance of the regional drivers, while the CO2 increase reinforces the coupling between precipitation and regional dynamics. A general agreement in model responses demonstrates the robustness of the identified mechanisms linking the WAM dynamics to the CO2 direct and indirect forcing, and indicates that these primary mechanisms are captured by climate models. Results also suggest that the spread in future projections may be caused by

  19. West African monsoon decadal variability and surface-related forcings: second West African Monsoon Modeling and Evaluation Project Experiment (WAMME II)

    NASA Astrophysics Data System (ADS)

    Xue, Yongkang; De Sales, Fernando; Lau, William K.-M.; Boone, Aaron; Kim, Kyu-Myong; Mechoso, Carlos R.; Wang, Guiling; Kucharski, Fred; Schiro, Kathleen; Hosaka, Masahiro; Li, Suosuo; Druyan, Leonard M.; Sanda, Ibrah Seidou; Thiaw, Wassila; Zeng, Ning; Comer, Ruth E.; Lim, Young-Kwon; Mahanama, Sarith; Song, Guoqiong; Gu, Yu; Hagos, Samson M.; Chin, Mian; Schubert, Siegfried; Dirmeyer, Paul; Ruby Leung, L.; Kalnay, Eugenia; Kitoh, Akio; Lu, Cheng-Hsuan; Mahowald, Natalie M.; Zhang, Zhengqiu

    2016-06-01

    The second West African Monsoon Modeling and Evaluation Project Experiment (WAMME II) is designed to improve understanding of the possible roles and feedbacks of sea surface temperature (SST), land use land cover change (LULCC), and aerosols forcings in the Sahel climate system at seasonal to decadal scales. The project's strategy is to apply prescribed observationally based anomaly forcing, i.e., "idealized but realistic" forcing, in simulations by climate models. The goal is to assess these forcings' effects in producing/amplifying seasonal and decadal climate variability in the Sahel between the 1950s and the 1980s, which is selected to characterize the great drought period of the last century. This is the first multi-model experiment specifically designed to simultaneously evaluate such relative contributions. The WAMME II models have consistently demonstrated that SST forcing is a major contributor to the twentieth century Sahel drought. Under the influence of the maximum possible SST forcing, the ensemble mean of WAMME II models can produce up to 60 % of the precipitation difference during the period. The present paper also addresses the role of SSTs in triggering and maintaining the Sahel drought. In this regard, the consensus of WAMME II models is that both Indian and Pacific Ocean SSTs greatly contributed to the drought, with the former producing an anomalous displacement of the Intertropical Convergence Zone before the WAM onset, and the latter mainly contributes to the summer WAM drought. The WAMME II models also show that the impact of LULCC forcing on the Sahel climate system is weaker than that of SST forcing, but still of first order magnitude. According to the results, under LULCC forcing the ensemble mean of WAMME II models can produces about 40 % of the precipitation difference between the 1980s and the 1950s. The role of land surface processes in responding to and amplifying the drought is also identified. The results suggest that catastrophic

  20. The pace of East African monsoon evolution during the Holocene

    NASA Astrophysics Data System (ADS)

    Weldeab, Syee; Menke, Valerie; Schmiedl, Gerhard

    2014-03-01

    African monsoon precipitation experienced a dramatic change in the course of the Holocene. The pace with which the African monsoon shifted from a strong early to middle to a weak late Holocene is critical for our understanding of climate dynamics, hydroclimate-vegetation interaction, and shifts of prehistoric human settlements, yet it is controversially debated. On the basis of planktonic foraminiferal Ba/Ca time series from the eastern Mediterranean Sea, here we present a proxy record of Nile River runoff that provides a spatially integrated measure of changes in East African monsoon (EAM) precipitation. The runoff record indicates a markedly gradual middle to late Holocene EAM transition that lasted over 3500 years. The timing and pace of runoff change parallels those of insolation and vegetation changes over the Nile basin, indicating orbitally forced variation of insolation as the main EAM forcing and the absence of a nonlinear precipitation-vegetation feedback. A tight correspondence between a threshold level of Nile River runoff and the timing of occupation/abandonment of settlements suggests that along with climate changes in the eastern Sahara, the level of Nile River and intensity of summer floods were likely critical for the habitability of the Nile Valley (Egypt).

  1. Skill, reproducibility and potential predictability of the West African monsoon in coupled GCMs

    NASA Astrophysics Data System (ADS)

    Philippon, N.; Doblas-Reyes, F. J.; Ruti, P. M.

    2010-07-01

    In the framework of the ENSEMBLES FP6 project, an ensemble prediction system based on five different state-of-the-art European coupled models has been developed. This study evaluates the performance of these models for forecasting the West African monsoon (WAM) at the monthly time scale. From simulations started the 1 May of each year and covering the period 1991-2001, the reproducibility and potential predictability (PP) of key parameters of the WAM—rainfall, zonal and meridional wind at four levels from the surface to 200 hPa, and specific humidity, from July to September—are assessed. The Sahelian rainfall mode of variability is not accurately reproduced contrary to the Guinean rainfall one: the correlation between observations (from CMAP) and the multi-model ensemble mean is 0.17 and 0.55, respectively. For the Sahelian mode, the correlation is consistent with a low PP of about ~6%. The PP of the Guinean mode is higher, ~44% suggesting a stronger forcing of the sea surface temperature on rainfall variability over this region. Parameters relative to the atmospheric dynamics are on average much more skillful and reproducible than rainfall. Among them, the first mode of variability of the zonal wind at 200 hPa that depicts the Tropical Easterly Jet, is correlated at 0.79 with its “observed” counterpart (from the NCEP/DOE2 reanalyses) and has a PP of 39%. Moreover, models reproduce the correlations between all the atmospheric dynamics parameters and the Sahelian rainfall in a satisfactory way. In that context, a statistical adaptation of the atmospheric dynamic forecasts, using a linear regression model with the leading principal components of the atmospheric dynamical parameters studied, leads to moderate receiver operating characteristic area under the curve and correlation skill scores for the Sahelian rainfall. These scores are however much higher than those obtained using the modelled rainfall.

  2. Strengthened African summer monsoon in the mid-Piacenzian

    NASA Astrophysics Data System (ADS)

    Zhang, Ran; Zhang, Zhongshi; Jiang, Dabang; Yan, Qing; Zhou, Xin; Cheng, Zhigang

    2016-09-01

    Using model results from the first phase of the Pliocene Model Intercomparison Project (PlioMIP) and four experiments with CAM4, the intensified African summer monsoon (ASM) in the mid-Piacenzian and corresponding mechanisms are analyzed. The results from PlioMIP show that the ASM intensified and summer precipitation increased in North Africa during the mid-Piacenzian, which can be explained by the increased net energy in the atmospheric column above North Africa. Further experiments with CAM4 indicated that the combined changes in the mid-Piacenzian of atmospheric CO2 concentration and SST, as well as the vegetation change, could have substantially increased the net energy in the atmospheric column over North Africa and further intensified the ASM. The experiments also demonstrated that topography change had a weak effect. Overall, the combined changes of atmospheric CO2 concentration and SST were the most important factor that brought about the intensified ASM in the mid-Piacenzian.

  3. Characterization of the impact of land degradation in the Sahel on the West African monsoon using an ensemble of climate models from the WAMME project

    NASA Astrophysics Data System (ADS)

    Boone, A. A.; Xue, Y.; Ruth, C.; De Sales, F.; Hagos, S.; Mahanama, S. P. P.; Schiro, K.; Song, G.; Wang, G.; Koster, R. D.; Mechoso, C. R.

    2014-12-01

    There is increasing evidence from numerical studies that anthropogenic land-use and land-cover changes (LULCC) can potentially induce significant variations on the regional scale climate. However, the magnitude of these variations likely depends on the local strength of the coupling between the surface and the atmosphere, the magnitude of the surface biophysical changes and how the key processes linking the surface with the atmosphere are parameterized within a particular model framework. One key hot-spot which has received considerable attention is the Sahelian region of West Africa, for which numerous studies have reported a significant increase in anthropogenic pressure on the already limited natural resources in this region, notably in terms of land use conversion and degradation. Thus, there is a pressing need to better understand the impacts of potential land degradation on the West African Monsoon (WAM) system. One of the main goals of the West African Monsoon Modeling andEvaluation project phase 2 (WAMMEII) is to provide basic understandingof LULCC on the regional climate over West Africa, and to evaluate thesensitivity of the seasonal variability of the WAM to LULCC. Theprescribed LULCC is based on recent 50 year period which represents amaximum feasible degradation scenario. In the current study, the LULCCis applied to five state of the art global climate models over afive-year period. The imposed LULCC results in a model-average 5-7%increase in surface albedo: the corresponding lower surface netradiation mainly results in a significant reduction in surfaceevaporation (upwards of 1 mm per day over a large part of the Sahel)which leads to less convective heating of the atmosphere, lowermoisture convergence, increased subsidence and reduced cloud coverover the LULCC zone. The overall impact can be characterized as asubstantial drought effect resulting in a reduction in annual rainfallof 20-40% in the Sahel and a southward shift of the monsoon. In

  4. Descriptive Model of Generic WAMS

    SciTech Connect

    Hauer, John F.; DeSteese, John G.

    2007-06-01

    The Department of Energy’s (DOE) Transmission Reliability Program is supporting the research, deployment, and demonstration of various wide area measurement system (WAMS) technologies to enhance the reliability of the Nation’s electrical power grid. Pacific Northwest National Laboratory (PNNL) was tasked by the DOE National SCADA Test Bed Program to conduct a study of WAMS security. This report represents achievement of the milestone to develop a generic WAMS model description that will provide a basis for the security analysis planned in the next phase of this study.

  5. The timing of Mediterranean sapropel deposition relative to insolation, sea-level and African monsoon changes

    NASA Astrophysics Data System (ADS)

    Grant, Katharine; Grimm, Rosina; Mikolajewicz, Uwe; Marino, Gianluca; Rohling, Eelco

    2016-04-01

    The periodic deposition of organic rich layers or 'sapropels' in eastern Mediterranean sediments can be linked to orbital-driven changes in the strength and location of (east) African monsoon precipitation. Sapropels are therefore an extremely useful tool for establishing orbital chronologies, and for providing insights about African monsoon variability on long timescales. However, the link between sapropel formation, insolation variations, and African monsoon 'maxima' is not straightforward because other processes (notably, sea-level rise) may have contributed to their deposition, and because there are uncertainties about monsoon-sapropel phase relationships. For example, different phasings are observed between Holocene and early Pleistocene sapropels, and between proxy records and model simulations. To address these issues, we have established geochemical and ice-volume-corrected planktonic foraminiferal stable isotope records for sapropels S1, S3, S4, and S5 in core LC21 from the southern Aegean Sea. The records have a radiometrically constrained chronology that has already been synchronised with the Red Sea relative sea-level record, and this allows us to examine in detail the timing of sapropel deposition relative to insolation, sea-level, and African monsoon changes. Our records suggest that the onset of sapropel deposition and monsoon run-off was near synchronous, yet insolation-sapropel/monsoon phasings varied, whereby monsoon/sapropel onset was relatively delayed (with respect to insolation maxima) after glacial terminations. We suggest that large meltwater discharges into the North Atlantic modified the timing of sapropel deposition by delaying the timing of peak African monsoon run-off. Hence, the previous assumption of a systematic 3-kyr lag between insolation maxima and sapropel midpoints may lead to overestimated insolation-sapropel phasings. We also surmise that both monsoon run-off and sea-level rise were important buoyancy-forcing mechanisms for

  6. Interactive Aspects of the Indian and the African Summer Monsoon Systems

    NASA Astrophysics Data System (ADS)

    Sanjeeva Rao, P.; Sikka, D. R.

    2007-09-01

    This study addresses an understanding of the possible mutual interactions of sub-seasonal variability of the two neighboring regional monsoon systems through data analysis. The NCEP/NCAR re-analysis and OLR data for three years was used to reveal the large-scale organization of convective episodes on synoptic (~5 days) and low frequency (15 50 day) scales. It is found that synoptic scale organization over both the sectors is influenced by the eastward migration of large-scale convective episodes associated with the Madden Julian Oscillation (MJO) on the low frequency scale. The organization of convection associated with the African monsoon on the synoptic scale is influenced by the pulsatory character of lower mid-troposphere and upper troposphere wind regimes moving westward over the African sector. Over the Indian region formation of low pressure areas and depressions in the monsoon trough occur in an overlapping manner under an envelope of low frequency seasonal oscillation. We have also found some correspondence between the summer monsoon rainfall over tropical North Africa and India on a decadal basis, which would suggest a common mode of multi-decadal variability in the two monsoon systems. The study points out the need to organize simultaneous field campaigns over the Indian and the African monsoon regions so as to bring out observational features of possible interactions between the two neighboring systems, which could then be validated through modeling studies.

  7. The timing of Mediterranean sapropel deposition relative to insolation, sea-level and African monsoon changes

    NASA Astrophysics Data System (ADS)

    Grant, K. M.; Grimm, R.; Mikolajewicz, U.; Marino, G.; Ziegler, M.; Rohling, E. J.

    2016-05-01

    The Mediterranean basin is sensitive to global sea-level changes and African monsoon variability on orbital timescales. Both of these processes are thought to be important to the deposition of organic-rich sediment layers or 'sapropels' throughout the eastern Mediterranean, yet their relative influences remain ambiguous. A related issue is that an assumed 3-kyr lag between boreal insolation maxima and sapropel mid-points remains to be tested. Here we present new geochemical and ice-volume-corrected planktonic foraminiferal stable isotope records for sapropels S1 (Holocene), S3, S4, and S5 (Marine Isotope Stage 5) in core LC21 from the southern Aegean Sea. The records have a radiometrically constrained chronology that has already been synchronised with the Red Sea relative sea-level record, and this allows detailed examination of the timing of sapropel deposition relative to insolation, sea-level, and African monsoon changes. We find that sapropel onset was near-synchronous with monsoon run-off into the eastern Mediterranean, but that insolation-sapropel/monsoon phasings were not systematic through the last glacial cycle. These latter phasings instead appear to relate to sea-level changes. We propose that persistent meltwater discharges into the North Atlantic (e.g., at glacial terminations) modified the timing of sapropel deposition by delaying the timing of peak African monsoon run-off. These observations may reconcile apparent model-data offsets with respect to the orbital pacing of the African monsoon. Our observations also imply that the previous assumption of a systematic 3-kyr lag between insolation maxima and sapropel midpoints may lead to overestimated insolation-sapropel phasings. Finally, we surmise that both sea-level rise and monsoon run-off contributed to surface-water buoyancy changes at times of sapropel deposition, and their relative influences differed per sapropel case, depending on their magnitudes. Sea-level rise was clearly important for

  8. Evaluation of Dynamics of the West African Monsoon Jump Simulated by the MIT Regional Climate Model

    NASA Astrophysics Data System (ADS)

    Eltahir, Elfatih A. B.; Im, Eun-Soon

    2015-04-01

    The seasonal advance and retreat of the West African monsoon behaves abrupt northward jump of maximum rainfall from the Guinean coast to the Sahel region. Both global and regional climate models have difficulties in accurately reproducing such a behavior due to its complexity combined the dynamical and physical processes. In this study, we evaluate the performance of the MIT Regional Climate Model (MRCM) in simulating the West African monsoon. For this, 20-year long-term simulation (1989-2008) is performed using the ERAInterim reanalysis as the initial and boundary condition, and the analysis primarily focuses on the dynamics associated with abrupt phase transitions of the monsoon rainfall. We first examine detailed characteristics in terms of the onset, maximum, and retreat of the monsoon rainfall using daily precipitation. We then present the dynamical explanation behind rainfall variability from the analysis of the absolute vorticity near the tropopause and the meridional gradient of boundary-layer entropy within the dynamical theory proposed by Eltahir and Gong (1996). Acknowledgements : This research was supported by the National Research Foundation Singapore through the Singapore MIT Alliance for Research and Technology's Center for Environmental Sensing and Modeling interdisciplinary research program.

  9. Linkages of Remote Sea Surface Temperatures and Atlantic Tropical Cyclone Activity Mediated by the African Monsoon

    SciTech Connect

    Taraphdar, Sourav; Leung, Lai-Yung R.; Hagos, Samson M.

    2015-01-28

    Warm sea surface temperatures (SSTs) in North Atlantic and Mediterranean (NAMED) can influence tropical cyclone (TC) activity in the tropical East Atlantic by modulating summer convection over western Africa. Analysis of 30 years of observations show that the NAMED SST is linked to a strengthening of the Saharan heat low and enhancement of moisture and moist static energy in the lower atmosphere over West Africa, which favors a northward displacement of the monsoonal front. These processes also lead to a northward shift of the African easterly jet that introduces an anomalous positive vorticity from western Africa to the main development region (50W–20E; 10N–20N) of Atlantic TC. By modulating multiple processes associated with the African monsoon, this study demonstrates that warm NAMED SST explains 8% of interannual variability of Atlantic TC frequency. Thus NAME SST may provide useful predictability for Atlantic TC activity on seasonal-to-interannual time scale.

  10. Instrumental evidence of an unusually strong West African Monsoon in the 19th century

    NASA Astrophysics Data System (ADS)

    Gallego, David; Ordoñez, Paulina; Ribera, Pedro; Peña-Ortiz, Cristina; Garcia-Herrera, Ricardo; Vega, Inmaculada; Gomez, Francisco de Paula

    2016-04-01

    The precipitation in the Sahel -which is mainly controlled by the dynamics of the West African Monsoon-, has been in the spot of the climate community for the last three decades due to the persistence of the drought period that started in the 1970s. Unfortunately, reliable meteorological series in this area are only available since the beginning of the 20th Century, thus limiting our understanding of the significance of this period from a long term perspective. Currently, our knowledge of what happened in times previous to the 20th Century essentially relies in documentary or proxy sources. In this work, we present the first instrumental evidence of a 50 year-long period characterised by an unusually strong West African monsoon in the19th Century. Following the recent advances in the generation of climatic indices based on data from ship's logbooks, we used historical wind observations to compute a new index (the so-called ASWI) for characterising the strength of the West African Monsoon. The ASWI is based in the persistence of the southwesterly winds in the [29°W-17°W;7°N-13°N] area and it has been possible to compute it since 1790 for July and since 1839 for August and September. We show that the ASWI is a reliable measure of the monsoon's strength and the Sahelian rainfall. Our new series clearly shows the well-known drought period starting in the 1970s. During this dry period, the West African Monsoon was particularly weak and interestingly, we found that since then, the correlations with different climatic patterns such as the Pacific and Atlantic "El Niño" changed significantly in relation to those of the previous century. Remarkably, our results also show that the period 1839-1890 was characterised by an unusually strong and persistent monsoon. Notwithstanding, two of the few dry years within this period were concurrent with large volcanic eruptions in the Northern Hemisphere. This latter result supports the recently suggested relationship between major

  11. 155,000 years of West African monsoon and ocean thermal evolution.

    PubMed

    Weldeab, Syee; Lea, David W; Schneider, Ralph R; Andersen, Nils

    2007-06-01

    A detailed reconstruction of West African monsoon hydrology over the past 155,000 years suggests a close linkage to northern high-latitude climate oscillations. Ba/Ca ratio and oxygen isotope composition of planktonic foraminifera in a marine sediment core from the Gulf of Guinea, in the eastern equatorial Atlantic (EEA), reveal centennial-scale variations of riverine freshwater input that are synchronous with northern high-latitude stadials and interstadials of the penultimate interglacial and the last deglaciation. EEA Mg/Ca-based sea surface temperatures (SSTs) were decoupled from northern high-latitude millennial-scale fluctuation and primarily responded to changes in atmospheric greenhouse gases and low-latitude solar insolation. The onset of enhanced monsoon precipitation lags behind the changes in EEA SSTs by up to 7000 years during glacial-interglacial transitions. This study demonstrates that the stadial-interstadial and deglacial climate instability of the northern high latitudes exerts dominant control on the West African monsoon dynamics through an atmospheric linkage. PMID:17540896

  12. Influence of Arctic sea-ice and greenhouse gas concentration change on the West African Monsoon.

    NASA Astrophysics Data System (ADS)

    Monerie, Paul-Arthur; Oudar, Thomas; Sanchez-Gomez, Emilia; Terray, Laurent

    2016-04-01

    The Sahelian precipitation are projected to increase in the CNRM-CM5 coupled climate model due to a strengthening of the land-Sea temperature gradient, the increase in the North Atlantic temperature and the deepening of the Heat Low. Arctic Sea-Ice loss impacts the low-level atmospheric circulation through a decrease in the northward heat transport. Some authors have linked the sea-ice loss to a poleward shift of the InterTropical Convergence Zone. Within the CMIP5 models the effect of these mechanisms are not distinguishable and it is difficult to understand the effect of the Arctic sea-ice loss on the West African Monsoon so far. We performed several sensitivity experiments with the CNRM-CM5 coupled climate models by modifying the arctic sea-ice extent and/or the greenhouse gas concentration. We then investigated separately the impact of Arctic sea-ice loss and greenhouse gas concentration increases on the West African Monsoon. The increase in greenhouse gas explains the northward shift and the strengthening of the monsoon. Its effect is stronger with a sea-ice free Arctic that leads to an increase in North Atlantic temperature and in Sahelian precipitation at the end of the rainy season (September-October). We argue that the decrease in sea-ice extent, in the context of the global warming, may moistens the Sahel during the rainy season by changing the pressure, winds and moisture fluxes at low-level.

  13. Regional Climate Modeling of West African Summer Monsoon Climate: Impact of Historical Boundary Forcing

    NASA Astrophysics Data System (ADS)

    Kebe, I.

    2015-12-01

    In this paper, we analyze and intercompare the performance of an ensemble of three Regional Climate Models (RCMs) driven by three set of Global Climate Models (GCMs), in reproducing seasonal mean climatologies with their annual cycle and the key features of West African summer monsoon over 20 years period (1985-2004) during the present day. The results show that errors in lateral boundary conditions from the GCM members, have an unexpected way on the skill of the RCMs in reproducing regional climate features such as the West African Monsoon features and the annual cycle of precipitation and temperature in terms of outperforming the GCM simulation. It also shows the occurrence of the West African Monsoon jump, the intensification and northward shift of the Saharan Heat Low (SHL) as expressed in some RCMs than the GCMs. Most RCMs also capture the mean annual cycle of precipitation and temperature, including, single and double-peaked during the summer months, in terms of events and amplitude. In a series of RCMs and GCMs experiments between the Sahara region and equatorial Africa, the presence of strong positive meridional temperature gradients at the surface and a strong meridional gradients in the potential temperatures near the surface are obvious, indicating the region of strong vertical shear development enough to establish easterly flow such as the African easterly jet. In addition, the isentropic potential vorticity (IPV) gradient decreases northward in the lower troposphere across northern Africa, with the maximum reversal on the 315-K surface. The region with negative IPV gradient favors the potential instability which has been associated with the growth of easterly waves.

  14. Transport pathways of peroxyacetyl nitrate in the upper troposphere and lower stratosphere from different monsoon systems during the summer monsoon season

    NASA Astrophysics Data System (ADS)

    Fadnavis, S.; Semeniuk, K.; Schultz, M. G.; Mahajan, A.; Pozzoli, L.; Sonbawane, S.; Kiefer, M.

    2014-08-01

    The Asian summer monsoon involves complex transport patterns with large scale redistribution of trace gases in the upper troposphere and lower stratosphere (UTLS). We employ the global chemistry-climate model ECHAM5-HAMMOZ in order to evaluate the transport pathways and the contributions of nitrogen oxide reservoir species PAN, NOx, and HNO3 from various monsoon regions, to the UTLS over Southern Asia and vice versa. The model is evaluated with trace gas retrievals from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS-E) and aircraft campaigns during the monsoon season (June-September). There are three regions which contribute substantial pollution to the UTLS during the monsoon: the Asian summer monsoon (ASM), the North American Monsoon (NAM) and the West African monsoon (WAM). However, penetration due to ASM convection is deeper into the UTLS as compared to NAM and WAM outflow. The circulation in these monsoon regions distributes PAN into the tropical latitude belt in the upper troposphere. Remote transport also occurs in the extratropical upper troposphere where westerly winds drive North American and European pollutants eastward to partly merge with the ASM plume. Strong ASM convection transports these remote and regional pollutants into the lower stratosphere. In the lower stratosphere the injected pollutants are transported westward by easterly winds. The intense convective activity in the monsoon regions is associated with lightning generation and thereby the emission of NOy species. This will affect the distribution of PAN in the UTLS. The estimates of lightning produced PAN, HNO3, NOx and ozone obtained from control and lightning-off simulations shows high percentage changes over the regions of convective transport especially equatorial Africa and America and comparatively less over the ASM. This indicates higher anthropogenic pollution transport from the ASM region into the UTLS.

  15. Circulation Regimes of Rainfall Anomalies in the African-South Asian Monsoon Belt.

    NASA Astrophysics Data System (ADS)

    Bhatt, Uma S.

    1989-10-01

    This study explores the spatial differentiation of climate anomalies and associated circulation mechanisms across the African-South Asian monsoon belt through empirical analyses mainly for the period 1948-83. Observations include surface ship observations in the tropical Atlantic, eastern Pacific, and Indian oceans, and various hydrometeorological and circulation index series, representing the water discharge of the Senegal River (SENEGAL), the rainfall in the West African Sahel (SAHEL), the discharge of rivers in the Nile basin (ROSEIRES, ATBARA), India monsoon rainfall (NIR), and the Southern Oscillation (SO). The field significance of correlation patterns is ascertained through Monte Carlo experiments.There is a strong correlation of hydrometeorological conditions from Senegal to the Sahel, a decrease from each of these domains eastward to the Nile catchment, and even more so to India. Conversely, correlations are remarkably high between the water discharge of the Nile basin (ROSEIRES, ATBARA) and Indian rainfall (NIR). An SO index is correlated positively with the hydrometeorological conditions throughout the monsoon belt, but most strongly in the East (NIR) and least in the West (SENEGAL).Correlation analyses for the July-August height of the boreal summer monsoon indicate that abundant rainfall in the western Sahel is, in the Atlantic sector, associated with weak northeast trades and in the western Indian Ocean with low pressure overlying cool surface waters. By comparison, copious river discharge in the eastern portion of the Subsaharan zone coincides with weakened northeast trades over the Atlantic but more pronounced circulation departures in the Indian Ocean sector, consisting of anomalously low pressure, cold surface waters, and abundant cloudiness in the northern Indian Ocean. This ensemble of atmosphere-ocean anomalies is also characteristic of abundant Indian monsoon rainfall. During the positive SO phase, rainfall tends to be relatively abundant

  16. Observed Oceanic and Terrestrial Drivers of North African Climate

    NASA Astrophysics Data System (ADS)

    Yu, Y.; Notaro, M.; Wang, F.; Mao, J.; Shi, X.; Wei, Y.

    2015-12-01

    Hydrologic variability can pose a serious threat to the poverty-stricken regions of North Africa. Yet, the current understanding of oceanic versus terrestrial drivers of North African droughts/pluvials is largely model-based, with vast disagreement among models. In order to identify the observed drivers of North African climate and develop a benchmark for model evaluations, the multivariate Generalized Equilibrium Feedback Assessment (GEFA) is applied to observations, remotely sensed data, and reanalysis products. The identified primary oceanic drivers of North African rainfall variability are the Atlantic, tropical Indian, and tropical Pacific Oceans and Mediterranean Sea. During the summer monsoon, positive tropical eastern Atlantic sea-surface temperature (SST) anomalies are associated with a southward shift of the Inter-Tropical Convergence Zone, enhanced ocean evaporation, and greater precipitable water across coastal West Africa, leading to increased West African monsoon (WAM) rainfall and decreased Sahel rainfall. During the short rains, positive SST anomalies in the western tropical Indian Ocean and negative anomalies in the eastern tropical Indian Ocean support greater easterly oceanic flow, evaporation over the western ocean, and moisture advection to East Africa, thereby enhancing rainfall. The sign, magnitude, and timing of observed vegetation forcing on rainfall vary across North Africa. The positive feedback of leaf area index (LAI) on rainfall is greatest during DJF for the Horn of Africa, while it peaks in autumn and is weakest during the summer monsoon for the Sahel. Across the WAM region, a positive LAI anomaly supports an earlier monsoon onset, increased rainfall during the pre-monsoon, and decreased rainfall during the wet season. Through unique mechanisms, positive LAI anomalies favor enhanced transpiration, precipitable water, and rainfall across the Sahel and Horn of Africa, and increased roughness, ascent, and rainfall across the WAM region

  17. Holocene Asian and African Monsoon Strength Recorded in O-18 of Atmospheric Oxygen

    NASA Astrophysics Data System (ADS)

    Severinghaus, J. P.; Beaudette, R.; Brook, E. J.

    2008-12-01

    Prior work using trapped gases in ice cores has shown that the oxygen-18/16 ratio of atmospheric molecular oxygen (δ18Oatm) is sensitive to orbital-scale monsoon and ice volume variations (Bender et al., 1994) and millennial-scale monsoon variations during Marine Isotope Stage 4 (Landais et al., 2007). Here we extend these findings with a high-resolution record from the Siple Dome ice core, West Antarctica, covering the last 60 kyr. The early Holocene sample resolution is ~30 yr and precision is ±0.009‰, revealing previously unrecognized centennial-scale variations in δ18Oatm. Removal of the seawater δ18O record (Waelbroeck et al., 2002) yields a record of past changes in the Dole Effect, the difference between the δ18O of air and seawater (+23.8‰ today). A further calculation using the derivative of the δ18Oatm data and an assumed 1000-yr O2 turnover time allows a deconvolution of the implied effective value of δ18O of O2 introduced to the atmosphere by the terrestrial biosphere (δ18Oland). Photosynthesis transfers the δ18O of chloroplast water (H218O/H216O) directly to the O2 that is produced (Guy et al., 1997). Strong monsoons are expected to produce low values of δ18Oland and thus a weak Dole Effect by 1) the low δ18O of heavy rainfall, 2) weak evaporative enrichment of 18O in leaf water due to the high humidity in which monsoon photosynthesis generally occurs, and 3) weak respiratory fractionation in wet tropical soils (Angert et al., 2003). In fact, our calculated δ18Oland correlates surprisingly well with Asian monsoon strength indicators such as the Dongge Cave record (Wang et al., 2005) at periods >0.2 kyr, except at 6 ka, where a prominent increase in δ18Oland coincides with the drying of the Sahara. These observations suggest that δ18Oland from ice cores may be a useful proxy of past Asian and African monsoon variations that integrates over large spatial scales (because the atmosphere is well-mixed, and photosynthesis is ubiquitous

  18. Transport pathways of peroxyacetyl nitrate in the upper troposphere and lower stratosphere from different monsoon systems during the summer monsoon season

    NASA Astrophysics Data System (ADS)

    Fadnavis, S.; Semeniuk, K.; Schultz, M. G.; Kiefer, M.; Mahajan, A.; Pozzoli, L.; Sonbawane, S.

    2015-06-01

    The Asian summer monsoon involves complex transport patterns with large scale redistribution of trace gases in the upper troposphere and lower stratosphere (UTLS). We employ the global chemistry-climate model ECHAM5-HAMMOZ in order to evaluate the transport pathways and the contributions of nitrogen oxide species PAN, NOx, and HNO3 from various monsoon regions, to the UTLS over Southern Asia and vice versa. Simulated long term seasonal mean mixing ratios are compared with trace gas retrievals from the Michelson Interferometer for Passive Atmospheric Sounding aboard ENVISAT(MIPAS-E) and aircraft campaigns during the monsoon season (June-September) in order to evaluate the model's ability to reproduce these transport patterns. The model simulations show that there are three regions which contribute substantial pollution to the South Asian UTLS: the Asian summer monsoon (ASM), the North American Monsoon (NAM) and the West African monsoon (WAM). However, penetration due to ASM convection reaches deeper into the UTLS as compared to NAM and WAM outflow. The circulation in all three monsoon regions distributes PAN into the tropical latitude belt in the upper troposphere. Remote transport also occurs in the extratropical upper troposphere where westerly winds drive North American and European pollutants eastward where they can become part of the ASM convection and be lifted into the lower stratosphere. In the lower stratosphere the injected pollutants are transported westward by easterly winds. The intense convective activity in the monsoon regions is associated with lightning and thereby the formation of additional NOx. This also affects the distribution of PAN in the UTLS. According to sensitivity simulations with and without lightning, increase in concentrations of PAN (~ 40%), HNO3 (75%), NOx (70%) and ozone (30%) over the regions of convective transport, especially over equatorial Africa and America and comparatively less over the ASM. This indicates that PAN in the

  19. Half-precessional dynamics of monsoon rainfall near the East African Equator.

    PubMed

    Verschuren, Dirk; Sinninghe Damsté, Jaap S; Moernaut, Jasper; Kristen, Iris; Blaauw, Maarten; Fagot, Maureen; Haug, Gerald H

    2009-12-01

    External climate forcings-such as long-term changes in solar insolation-generate different climate responses in tropical and high latitude regions. Documenting the spatial and temporal variability of past climates is therefore critical for understanding how such forcings are translated into regional climate variability. In contrast to the data-rich middle and high latitudes, high-quality climate-proxy records from equatorial regions are relatively few, especially from regions experiencing the bimodal seasonal rainfall distribution associated with twice-annual passage of the Intertropical Convergence Zone. Here we present a continuous and well-resolved climate-proxy record of hydrological variability during the past 25,000 years from equatorial East Africa. Our results, based on complementary evidence from seismic-reflection stratigraphy and organic biomarker molecules in the sediment record of Lake Challa near Mount Kilimanjaro, reveal that monsoon rainfall in this region varied at half-precessional ( approximately 11,500-year) intervals in phase with orbitally controlled insolation forcing. The southeasterly and northeasterly monsoons that advect moisture from the western Indian Ocean were strengthened in alternation when the inter-hemispheric insolation gradient was at a maximum; dry conditions prevailed when neither monsoon was intensified and modest local March or September insolation weakened the rain season that followed. On sub-millennial timescales, the temporal pattern of hydrological change on the East African Equator bears clear high-northern-latitude signatures, but on the orbital timescale it mainly responded to low-latitude insolation forcing. Predominance of low-latitude climate processes in this monsoon region can be attributed to the low-latitude position of its continental regions of surface air flow convergence, and its relative isolation from the Atlantic Ocean, where prominent meridional overturning circulation more tightly couples low

  20. Dry intrusions in the West African monsoon mid-troposphere during the AMMA experiment

    NASA Astrophysics Data System (ADS)

    Deme, A.; Roca, R.

    2009-04-01

    Mid-troposphere dry air patches (RH < 10%) have been recently detected over the African monsoon region and in particular over Sahel. At 500 hPa, these dry air features are thought to play a complex role onto convection: inhibition isolated convective cells but favouring already organized convection by feeding rear-inflow currents with dry air. The inhibiting action of the dry air onto convection comes from the temperature inversion induced by radiation at the bottom of the dry layer and/or by entrainment of dry air in ascending parcel that decreases its buoyancy. The organizing effect is associated to mesoscale currents within and around long lasting squall lines. This mid-tropospheric dry air has been shown to originate from the mid-latitudes upper level jets, therefore coined extra-tropical dry intrusions.Among all the forcings that control the dynamics of the West African monsoon, the role of a dry mid-troposphere needs to be clarified. The present study is dedicated to this objective and it is focused on extra-tropical dry air intrusions in the West African mid-troposphere during the AMMA campaign. The low level dynamics is documented (African Easterly Jet, African Easterly Wave) thanks to the NCEP operational analysis. It is completed by the radiosondes especially for the temperature and water vapor distribution. Back-trajectory are computed in order to highlight the origin of the tropospheric air mass. Finally Meteosat Second Generation derived water vapor and cloud and rainfall parameters are used to characterize the convective activity and its moist environment. Dry intrusions in the African mid troposphere during the summer 2006 have been shown to be associated with two major modes of occurrences: a 40-50 days mode and a 10-20 days mode. The long mode exhibits negative anomaly of the rainfall and a very large scale structure covering the whole West Africa region when occurring while the short mode is more restricted to the Sahelian longitude. Similarly

  1. A distal 140 kyr sediment record of Nile discharge and East African monsoon variability

    NASA Astrophysics Data System (ADS)

    Ehrmann, Werner; Schmiedl, Gerhard; Seidel, Martin; Krüger, Stefan; Schulz, Hartmut

    2016-03-01

    Clay mineral assemblages in a sediment core from the distal Nile discharge plume off Israel have been used to reconstruct the late Quaternary Nile sediment discharge into the eastern Mediterranean Sea (EMS). The record spans the last ca. 140 kyr. Smectite abundances indicate the influence of the Blue Nile and the Atbara River that have their headwaters in the volcanic rocks of the Ethiopian Highlands. Kaolinite abundances indicate the influence of wadis, which contribute periodically to the suspension load of the Nile. Due to the geographical position, the climate and the sedimentary framework of the EMS is controlled by two climate systems. The long-term climate regime was governed by the African monsoon that caused major African humid periods (AHPs) with enhanced sediment discharge at 132 to < 126 (AHP 5), 116 to 99 (AHP4), and 89 to 77 ka (AHP3). They lasted much longer than the formation of the related sapropel layers S5 (> 2 kyr), S4 (3.5 kyr), and S3 (5 kyr). During the last glacial period (Marine Isotope Stages (MISs) 4-2), the long-term changes in the monsoonal system were superimposed by millennial-scale changes in an intensified midlatitude glacial system. This climate regime caused short but pronounced drought periods in the Nile catchment, which are linked to Heinrich events and alternate with more humid interstadials. The clay mineral record further implies that feedback mechanisms between vegetation cover and sediment discharge of the Nile are detectable but of minor importance for the sedimentary record in the southeastern Mediterranean Sea during the investigated African humid periods.

  2. KZai 02 pollen record, an insight into West African monsoon fluctuations during the Last Climatic Cycle

    NASA Astrophysics Data System (ADS)

    Dalibard, M.; Popescu, S.; Maley, J.; Suc, J.

    2012-12-01

    Climate of the circum-Atlantic intertropical zone is driven by the ocean/atmosphere dynamics in response to variations of yearly insolation. These latitudes correspond to the convergence of the Hadley cells expressed on earth surface by intense trade winds and in lower troposphere by the African easterly jet making the edges of the intertropical zone relatively dry, while humidity is concentrated near the Equator. This phenomenon generates a precipitation front, known as the InterTropical Convergence Zone (ITCZ), the oscillations of which regulate the latitudinal vegetation distribution. Pollen record of core KZai 02 (Guinea Gulf) allows high resolution reconstruction of variations of past ecosystems over Central Africa during the Last Climatic Cycle. Plant taxa recorded in pollen analyses have been clustered according to their ecological requirements and African phytogeography. Fluctuations of these groups inform on precipitation intensity and their distribution during the last 130 ka. During Glacials, an open vegetation made of Cyperaceae marshes developed in the central Zaire/Congo Basin, surrounded by savannah on borders and afromontane forests on reliefs. Composition and distribution of vegetation indicate a decrease in monsoon activity and the strengthening of the precipitation front in the center of the basin. Interglacial phases are characterized by rain forest expansion over Central Africa in response to a precipitation enhancement associated with a northward shift of the rainfall front. Replacement of afromontane forest and marsh ecosystems by savannah then lowland pioneering, warm-temperate and rain forests characterized glacial/interglacial transitions. This succession suggests the increasing influence of at least two climatic parameters: the water availability and temperature and/or CO2 fluctuation. Spectral analysis applied to vegetation groups evidences the forcing of insolation, mainly driven by precession, on the West African monsoon system. Sub

  3. RAMA: Research Moored Array for African - Asian - Australian Monsoon Analysis and Prediction

    NASA Astrophysics Data System (ADS)

    McPhaden, M. J.

    2008-12-01

    The Indian Ocean is unique among the three tropical oceans in that it is blocked at 25N by the Asian land mass. Seasonal heating and cooling over this land mass sets the stage for dramatic monsoon wind reversals and intense summer rains over areas surrounding the basin. These climate variations have significant societal and economic impacts that affect half the world's population. Despite the importance of the Indian Ocean for both the regional and global climate though, it is the most poorly observed and least well understood of the three tropical oceans. This presentation describes the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA), which has been designed to provide sustained, basin scale time series data in the Indian Ocean for climate research and forecasting. RAMA is intended to complement other satellite and in situ components of the Indian Ocean Observing System and it is being implemented through a coordinated multi- national effort involving institutions in several countries. We will review the scientific rationale, design criteria, and implementation status of RAMA. We will also illustrate some of the important intraseasonal to interannual time scale phenomena in the region observed with new RAMA time series data. Potential applications of the data for forecasting purposes will also be discussed.

  4. RAMA: Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction

    NASA Astrophysics Data System (ADS)

    McPhaden, M. J.

    2009-05-01

    The Indian Ocean is unique among the three tropical ocean basins in that it is blocked at 25°N by the Asian land mass. Seasonal heating and cooling over this land mass sets the stage for dramatic monsoon wind reversals and intense rains over areas surrounding the basin. These climate variations have significant societal and economic impacts that affect half the world's population. Despite the importance of the Indian Ocean for both the regional and global climate though, it is the most poorly observed and least well understood of the three tropical oceans. This presentation describes the Research Moored Array for African-Asian- Australian Monsoon Analysis and Prediction (RAMA), which has been designed to provide sustained, basin scale time series data in the Indian Ocean for climate research and forecasting. RAMA is intended to complement other satellite and in situ components of the Indian Ocean Observing System and it is being implemented through a coordinated multi-national effort involving institutions in several countries. We will review the scientific rationale, design criteria, and implementation status of RAMA. We will also illustrate some of the important intraseasonal to interannual time scale phenomena in the region observed with new RAMA time series data. Potential applications of the data for forecasting purposes will also be discussed.

  5. A distal 145 ka sediment record of Nile discharge and East African monsoon variability

    NASA Astrophysics Data System (ADS)

    Ehrmann, W.; Schmiedl, G.; Seidel, M.; Krüger, S.; Schulz, H.

    2015-09-01

    Clay mineral assemblages in a sediment core from the distal Nile discharge plume off Israel have been used to reconstruct the late Quaternary Nile sediment discharge into the Eastern Mediterranean Sea (EMS). The record spans the last ca. 145 ka. Smectite abundances indicate the influence of the Blue Nile and Atbara that have their headwaters in the volcanic rocks of the Ethiopian highlands. Kaolinite abundances indicate the influence of wadis, which contribute periodically to the suspension load of the Nile. Due to the geographical position, the climate and the sedimentary framework of the EMS is controlled by two climate systems. The long-term climate regime was governed by the African monsoon that caused major humid periods with enhanced sediment discharge at 132 to < 122 ka (AHP 5), 113 to 104 ka (AHP 4), and 86 to 74 ka (AHP 3). They lasted much longer than the formation of the related sapropel layers S5, S4 and S3. During the last glacial period (MIS 4-2) the long-term changes of the monsoonal system were superimposed by millennial-scale changes of an intensified mid-latitude glacial system. This climate regime caused short but pronounced drought periods in the Nile catchment, which are linked to Heinrich Events and alternate with more humid interstadials. The clay mineral record further implies that feedback mechanisms between vegetation cover and sediment discharge of the Nile are detectable but of minor importance for the sedimentary record in the southeastern Mediterranean Sea during the investigated African Humid Periods.

  6. West African monsoon dynamics inferred from abrupt fluctuations of Lake Mega-Chad

    PubMed Central

    Armitage, Simon J.; Bristow, Charlie S.; Drake, Nick A.

    2015-01-01

    From the deglacial period to the mid-Holocene, North Africa was characterized by much wetter conditions than today. The broad timing of this period, termed the African Humid Period, is well known. However, the rapidity of the onset and termination of the African Humid Period are contested, with strong evidence for both abrupt and gradual change. We use optically stimulated luminescence dating of dunes, shorelines, and fluviolacustrine deposits to reconstruct the fluctuations of Lake Mega-Chad, which was the largest pluvial lake in Africa. Humid conditions first occur at ∼15 ka, and by 11.5 ka, Lake Mega-Chad had reached a highstand, which persisted until 5.0 ka. Lake levels fell rapidly at ∼5 ka, indicating abrupt aridification across the entire Lake Mega-Chad Basin. This record provides strong terrestrial evidence that the African Humid Period ended abruptly, supporting the hypothesis that the African monsoon responds to insolation forcing in a markedly nonlinear manner. In addition, Lake Mega-Chad exerts strong control on global biogeochemical cycles because the northern (Bodélé) basin is currently the world’s greatest single dust source and possibly an important source of limiting nutrients for both the Amazon Basin and equatorial Atlantic. However, we demonstrate that the final desiccation of the Bodélé Basin occurred around 1 ka. Consequently, the present-day mode and scale of dust production from the Bodélé Basin cannot have occurred before 1 ka, suggesting that its role in fertilizing marine and terrestrial ecosystems is either overstated or geologically recent. PMID:26124133

  7. West African monsoon dynamics inferred from abrupt fluctuations of Lake Mega-Chad.

    PubMed

    Armitage, Simon J; Bristow, Charlie S; Drake, Nick A

    2015-07-14

    From the deglacial period to the mid-Holocene, North Africa was characterized by much wetter conditions than today. The broad timing of this period, termed the African Humid Period, is well known. However, the rapidity of the onset and termination of the African Humid Period are contested, with strong evidence for both abrupt and gradual change. We use optically stimulated luminescence dating of dunes, shorelines, and fluviolacustrine deposits to reconstruct the fluctuations of Lake Mega-Chad, which was the largest pluvial lake in Africa. Humid conditions first occur at ∼ 15 ka, and by 11.5 ka, Lake Mega-Chad had reached a highstand, which persisted until 5.0 ka. Lake levels fell rapidly at ∼ 5 ka, indicating abrupt aridification across the entire Lake Mega-Chad Basin. This record provides strong terrestrial evidence that the African Humid Period ended abruptly, supporting the hypothesis that the African monsoon responds to insolation forcing in a markedly nonlinear manner. In addition, Lake Mega-Chad exerts strong control on global biogeochemical cycles because the northern (Bodélé) basin is currently the world's greatest single dust source and possibly an important source of limiting nutrients for both the Amazon Basin and equatorial Atlantic. However, we demonstrate that the final desiccation of the Bodélé Basin occurred around 1 ka. Consequently, the present-day mode and scale of dust production from the Bodélé Basin cannot have occurred before 1 ka, suggesting that its role in fertilizing marine and terrestrial ecosystems is either overstated or geologically recent.

  8. Lake Mega-Chad, a West African Monsoon indicator and tipping element

    NASA Astrophysics Data System (ADS)

    Armitage, Simon; Bristow, Charlie; Drake, Nick

    2015-04-01

    From the deglacial period to the mid-Holocene, North Africa was characterised by much wetter conditions than today. The broad timing of this period, termed the African Humid Period, is well known. However, the rapidity of the onset and termination of the African Humid Period are contested, with strong evidence for both abrupt and gradual change. We use optically stimulated luminescence dating of dunes, shorelines and fluvio-lacustrine deposits to reconstruct the fluctuations of Lake Mega-Chad, which was the largest pluvial lake in Africa. Humid conditions first occur at ~15 ka, followed by a return to relatively arid conditions. By 11.5 ka Lake Mega-Chad had reached a highstand, which persisted until 5.0 ka. Lake levels fell rapidly at 5 ka, indicating abrupt aridification across the entire Lake Mega-Chad Basin. This record provides strong terrestrial evidence that the African Humid Period ended abruptly, supporting the hypothesis that the African monsoon responds to insolation forcing in a markedly non-linear manner. In addition, Lake Mega-Chad exerts strong control on global biogeochemical cycles since the northern (Bodélé) basin is currently the World's greatest single dust source, and possibly an important source of limiting nutrients for both the Amazon basin and equatorial Atlantic. However, we demonstrate that the final desiccation of the Bodélé Basin occurred around 1 ka. Consequently, the present-day mode and scale of dust production from Bodélé Basin cannot have occurred prior to 1 ka, suggesting that its role in fertilizing marine and terrestrial ecosystems is either overstated or geologically recent.

  9. Revisiting the role of global SST anomalies and their effects on West African monsoon variability

    NASA Astrophysics Data System (ADS)

    Pomposi, Catherine; Kushnir, Yochanan; Giannini, Alessandra

    2016-04-01

    The West African Monsoon is a significant component of the global monsoon system, delivering the majority of annual precipitation for the Sahel and varying on timescales from seasons to decades and beyond. Much of the internal variability of this system is driven by sea surface temperature (SST) anomalies and their resulting atmospheric teleconnections linking oceanic changes to land-based precipitation. Previous idealized studies have identified the role of particular ocean basins in driving monsoon variations on a number of key timescales, including the Atlantic basin as the main driver behind decadal-scale changes and the Pacific basin for interannual variability. However, understanding of how the monsoon responds to global SSTs remains incomplete because the system can be affected by moisture availability locally as well as tropical atmospheric stability, both of which are influenced by ocean temperatures. Furthermore, the complexity of how the global ocean basins change in relation to one another (what we refer to as superposition of anomalies) can result in Sahel precipitation anomalies that are contrary to what one might posit when considering the state of a single basin alone (e.g. the 2015 El Niño event and a relatively wet Sahel). The aim of this work is to revisit the role of global SSTs in driving Sahel rainfall variability over the recent past using a blending of observations and new model output. We seek to disentangle the state of various basins in combination with each other in driving normal or anomalously dry or wet years, resolving the ways that remote and local ocean forcings affect the movement of convection from the Guinea coast inland and northward into the Sahel, and include the study of circulation and stability components of the atmosphere. Preliminary diagnostic work suggests that varying SST conditions across ocean basins could imprint distinctly different precipitation responses in the Sahel. For example, precipitation anomalies are

  10. Assessment of uncertainties in the response of the African monsoon precipitation to land use change simulated by a regional model

    SciTech Connect

    Hagos, Samson M.; Leung, Lai-Yung Ruby; Xue, Yongkang; Boone, Aaron; de Sales, Fernando; Neupane, Naresh; Huang, Maoyi; Yoon, Jin -Ho

    2014-02-22

    Land use and land cover over Africa have changed substantially over the last sixty years and this change has been proposed to affect monsoon circulation and precipitation. This study examines the uncertainties on the effect of these changes on the African Monsoon system and Sahel precipitation using an ensemble of regional model simulations with different combinations of land surface and cumulus parameterization schemes. Furthermore, the magnitude of the response covers a broad range of values, most of the simulations show a decline in Sahel precipitation due to the expansion of pasture and croplands at the expense of trees and shrubs and an increase in surface air temperature.

  11. Transport pathways of peroxyacetyl nitrate in the upper troposphere and lower stratosphere from different monsoon systems during the summer monsoon season

    NASA Astrophysics Data System (ADS)

    Fadnavis, S.; Semeniuk, K.; Schultz, M. G.; Kiefer, M.; Mahajan, A.; Pozzoli, L.; Sonbawane, S.

    2015-10-01

    The Asian summer monsoon involves complex transport patterns with large-scale redistribution of trace gases in the upper troposphere and lower stratosphere (UTLS). We employ the global chemistry-climate model ECHAM5-HAMMOZ in order to evaluate the transport pathways and the contributions of nitrogen oxide species peroxyacetyl nitrate (PAN), NOx and HNO3 from various monsoon regions, to the UTLS over southern Asia and vice versa. Simulated long-term seasonal mean mixing ratios are compared with trace gas retrievals from the Michelson Interferometer for Passive Atmospheric Sounding aboard ENVISAT(MIPAS-E) and aircraft campaigns during the monsoon season (June-September) in order to evaluate the model's ability to reproduce these transport patterns. The model simulations show that there are three regions which contribute substantial pollution to the South Asian UTLS: the Asian summer monsoon (ASM), the North American monsoon (NAM) and the West African monsoon (WAM). However, penetration due to ASM convection reaches deeper into the UTLS compared to NAM and WAM outflow. The circulation in all three monsoon regions distributes PAN into the tropical latitude belt in the upper troposphere (UT). Remote transport also occurs in the extratropical UT where westerly winds drive North American and European pollutants eastward where they can become part of the ASM convection and lifted into the lower stratosphere. In the lower stratosphere the injected pollutants are transported westward by easterly winds. Sensitivity experiments with ECHAM5-HAMMOZ for simultaneous NOx and non-methane volatile organic compounds (NMVOCs) emission change (-10 %) over ASM, NAM and WAM confirm similar transport. Our analysis shows that a 10 % change in Asian emissions transports ~ 5-30 ppt of PAN in the UTLS over Asia, ~ 1-10 ppt of PAN in the UTLS of northern subtropics and mid-latitudes, ~ 7-10 ppt of HNO3 and ~ 1-2 ppb of ozone in UT over Asia. Comparison of emission change over Asia, North

  12. Bias reduction in decadal predictions of West African monsoon rainfall using regional climate models

    NASA Astrophysics Data System (ADS)

    Paxian, A.; Sein, D.; Panitz, H.-J.; Warscher, M.; Breil, M.; Engel, T.; Tödter, J.; Krause, A.; Cabos Narvaez, W. D.; Fink, A. H.; Ahrens, B.; Kunstmann, H.; Jacob, D.; Paeth, H.

    2016-02-01

    The West African monsoon rainfall is essential for regional food production, and decadal predictions are necessary for policy makers and farmers. However, predictions with global climate models reveal precipitation biases. This study addresses the hypotheses that global prediction biases can be reduced by dynamical downscaling with a multimodel ensemble of three regional climate models (RCMs), a RCM coupled to a global ocean model and a RCM applying more realistic soil initialization and boundary conditions, i.e., aerosols, sea surface temperatures (SSTs), vegetation, and land cover. Numerous RCM predictions have been performed with REMO, COSMO-CLM (CCLM), and Weather Research and Forecasting (WRF) in various versions and for different decades. Global predictions reveal typical positive and negative biases over the Guinea Coast and the Sahel, respectively, related to a southward shifted Intertropical Convergence Zone (ITCZ) and a positive tropical Atlantic SST bias. These rainfall biases are reduced by some regional predictions in the Sahel but aggravated by all RCMs over the Guinea Coast, resulting from the inherited SST bias, increased westerlies and evaporation over the tropical Atlantic and shifted African easterly waves. The coupled regional predictions simulate high-resolution atmosphere-ocean interactions strongly improving the SST bias, the ITCZ shift and the Guinea Coast and Central Sahel precipitation biases. Some added values in rainfall bias are found for more realistic SST and land cover boundary conditions over the Guinea Coast and improved vegetation in the Central Sahel. Thus, the ability of RCMs and improved boundary conditions to reduce rainfall biases for climate impact research depends on the considered West African region.

  13. On the Feasibility of Tracking the Monsoon History by Using Ancient Wind Direction Records

    NASA Astrophysics Data System (ADS)

    Gallego, D.; Ribera, P.; Peña-Ortiz, C.; Vega, I.; Gómez, F. D. P.; Ordoñez-Perez, P.; Garcia-Hererra, R.

    2015-12-01

    In this work, we use old wind direction records to reconstruct indices for the West African Monsoon (WAM) and the Indian Summer Monsoon (ISM). Since centuries ago, ships departing from the naval European powers circumnavigated Africa in their route to the Far East. Most of these ships took high-quality observations preserved in logbooks. We show that wind direction observations taken aboard ships can be used to track the seasonal wind reversal typical of monsoonal circulations. The persistence of the SW winds in the 20W-17W and 7N-13N region is highly correlated with the WAM strength and Sahel's precipitation. It has been possible to build a WAM index back to the 19th Century. Our results show that in the Sahel, the second half of the 19thCentury was significantly wetter than present day. The relation of the WAM with the ENSO cycle, and the Atlantic Multidecadal Oscillation was low and instable from the 1840s to the 1970s, when they abruptly suffered an unprecedented reinforcement which last up to the present day. The persistence of the SSW wind in the 60E-80E and 8N-12N area has been used to track the ISM onset since the 1880s. We found evidences of later than average onset dates during the 1900-1925 and 1970-1990 periods and earlier than average onset between 1940 and 1965. A significant relation between the ISM onset and the PDO restricted to shifts from negative to positive PDO phases has been found. The most significant contribution of our study is the fact that we have shown that it is possible to build consistent monsoon indices of instrumental character using solely direct observations of wind direction. Our indices have been generated by using data currently available in the ICOADS 2.5 database, but a large amount of wind observations for periods previous to the 20thcentury still remain not explored in thousands of logbooks preserved in British archives. The interest of unveil these data to track the monsoons for more than 200 -or even 300 years- it is

  14. Sst and Ghg Impacts On The West African Monsoon Climate: A Superensemble Approach

    NASA Astrophysics Data System (ADS)

    Paeth, H.; Hense, A.

    West African rainfall has been subject to large interdecadal variations during the 20th century. The most prominent feature is a negative trend in annual precipitation after 1960, causing severe drought in the Sahel region and the southern part of West Africa, with some recoverage in recent years. We examine and quantify the influence of ob- served SST changes on low-frequency variability over the subcontinent and compare it with the additional impact of increasing GHG concentrations, as revealed by a su- perensemble of SST-driven experiments. SST is largely responsible for decadal and longer-term variability over the southern part of West Africa, accounting for almost 80 % of monsoonal rainfall variance. The additional impact of the enhanced green- house effect is weak but statistically significant by the year 1980, obviously associ- ated with a positive trend in annual precipitation. This positive trend is also found in GHG-induced coupled climate model projection into the future. The CO2 signal is again weak but statistically significant and consistent with different climate models, as revealed by a superensemble of coupled experiments.

  15. Impact of GCM boundary forcing on regional climate modeling of West African summer monsoon precipitation and circulation features

    NASA Astrophysics Data System (ADS)

    Kebe, Ibourahima; Sylla, Mouhamadou Bamba; Omotosho, Jerome Adebayo; Nikiema, Pinghouinde Michel; Gibba, Peter; Giorgi, Filippo

    2016-05-01

    In this study, the latest version of the International Centre for Theoretical Physics Regional Climate Model (RegCM4) driven by three CMIP5 Global Climate Models (GCMs) is used at 25 km grid spacing over West Africa to investigate the impact of lateral boundary forcings on the simulation of monsoon precipitation and its relationship with regional circulation features. We find that the RegCM4 experiments along with their multimodel ensemble generally reproduce the location of the main precipitation characteristics over the region and improve upon the corresponding driving GCMs. However, the provision of different forcing boundary conditions leads to substantially different precipitation magnitudes and spatial patterns. For instance, while RegCM4 nested within GFDL-ESM-2M and HadGEM2-ES exhibits some underestimations of precipitation and an excessively narrow Intertropical Convergence Zone, the MPI-ESM-MR driven run produces precipitation spatial distribution and magnitudes more similar to observations. Such a superior performance originates from a much better simulation of the interactions between baroclinicity, temperature gradient and African Easterly Jet along with an improved connection between the Isentropic Potential Vorticity, its gradient and the African Easterly Waves dynamics. We conclude that a good performing GCM in terms of monsoon dynamical features (in this case MPI-ESM-MR) is needed to drive RCMs in order to achieve a better representation of the West Africa summer monsoon precipitation.

  16. Assessment of uncertainties in the response of the African monsoon precipitation to land use change simulated by a regional model

    DOE PAGES

    Hagos, Samson M.; Leung, Lai-Yung Ruby; Xue, Yongkang; Boone, Aaron; de Sales, Fernando; Neupane, Naresh; Huang, Maoyi; Yoon, Jin -Ho

    2014-02-22

    Land use and land cover over Africa have changed substantially over the last sixty years and this change has been proposed to affect monsoon circulation and precipitation. This study examines the uncertainties on the effect of these changes on the African Monsoon system and Sahel precipitation using an ensemble of regional model simulations with different combinations of land surface and cumulus parameterization schemes. Furthermore, the magnitude of the response covers a broad range of values, most of the simulations show a decline in Sahel precipitation due to the expansion of pasture and croplands at the expense of trees and shrubsmore » and an increase in surface air temperature.« less

  17. Feedback of observed interannual vegetation change: a regional climate model analysis for the West African monsoon

    NASA Astrophysics Data System (ADS)

    Klein, Cornelia; Bliefernicht, Jan; Heinzeller, Dominikus; Gessner, Ursula; Klein, Igor; Kunstmann, Harald

    2016-06-01

    West Africa is a hot spot region for land-atmosphere coupling where atmospheric conditions and convective rainfall can strongly depend on surface characteristics. To investigate the effect of natural interannual vegetation changes on the West African monsoon precipitation, we implement satellite-derived dynamical datasets for vegetation fraction (VF), albedo and leaf area index into the Weather Research and Forecasting model. Two sets of 4-member ensembles with dynamic and static land surface description are used to extract vegetation-related changes in the interannual difference between August-September 2009 and 2010. The observed vegetation patterns retain a significant long-term memory of preceding rainfall patterns of at least 2 months. The interannual vegetation changes exhibit the strongest effect on latent heat fluxes and associated surface temperatures. We find a decrease (increase) of rainy hours over regions with higher (lower) VF during the day and the opposite during the night. The probability that maximum precipitation is shifted to nighttime (daytime) over higher (lower) VF is 12 % higher than by chance. We attribute this behaviour to horizontal circulations driven by differential heating. Over more vegetated regions, the divergence of moist air together with lower sensible heat fluxes hinders the initiation of deep convection during the day. During the night, mature convective systems cause an increase in the number of rainy hours over these regions. We identify this feedback in both water- and energy-limited regions of West Africa. The inclusion of observed dynamical surface information improved the spatial distribution of modelled rainfall in the Sahel with respect to observations, illustrating the potential of satellite data as a boundary constraint for atmospheric models.

  18. Analyse of direct and indirect effects of Saharan dust on convection and on the African monsoon circulation during the FENNEC project using WRF-CHEM

    NASA Astrophysics Data System (ADS)

    Lavaysse, Christophe; Flamant, Cyrille; Grabowski, Wojciech; Morisson, Hugh; Banks, Jamie

    2013-04-01

    The aim of this study is to analyse the local impacts of dust on convection and on the West African monsoon circulation. Using the regional models WRF-CHEM, different dust schemes have been tested to quantify the impacts of dust on convection and on the main components of the West African monsoon, such as the West African Heat Low (WAHL), African Easterly Waves (AEWs), monsoon and harmatan winds. The specific pre-onset period of the monsoon precipitation over the Sahel has been simulated, in 2011 during the FENNEC project. We have investigated a 15-day period from June 10th to 25th. During this period, high dust concentration over the Sahara has been detected using satellite observations and the WAHL settled in its summer Saharan location. In this study, we have observed that WRF-CHEM is able to reproduce dust outbreaks and transport as detected in the satellite and airborne observations. This study also highlights the two effects of dust on the monsoon circulation over the Sahara: a so-called direct effect associated with dust radiative heating, which increases the WAHL thickness, and a so called indirect effect that modifies mid-level and deep convection over the Sahel.

  19. Bipolar modulation of millennial-scale West African monsoon variability during the last glacial (75,000-25,000 years ago)

    NASA Astrophysics Data System (ADS)

    Weldeab, Syee

    2012-04-01

    Time series of planktonic foraminiferal δ18O and Ba/Ca-based sea surface salinity (SSS) estimates from the eastern Gulf of Guinea (eastern equatorial Atlantic) indicate changes in runoff that reflect variability of spatially integrated precipitation over the equatorial West African monsoon area. Millennial-scale and recurring runoff-induced SSS rises and declines in the range of 1.5 and 2 psu (practical salinity unit) reveal rapid oscillation between dry and wet phases. The timing of decreased runoff coincides with oscillation of Dansgaard-Oeschger stadials and Heinrich events, the most severe monsoon weakening correlating with the latter. δ18Oresidual time series, derived by removing temperature, ice volume, and salinity components from the foraminiferal δ18O record, suggest that weak monsoon precipitation during stadials and Heinrich events was accompanied by significant shifts in δ18Oprecipitation toward higher values. Furthermore, δ18O analysis of individual tests of Globigerinoides ruber pink (δ18Oindiv) during dry episodes show a total range and variance of 2.3‰ and 0.25 (n = 121), indicating that seasonal contrast of sea surface freshening was significantly reduced during Heinrich events relative to that of interstadials which show a total range and variance of 3.35‰ and 0.42 (n = 140). On the basis of the timing and magnitude of changes in the monsoon record, it is evident that northern high latitude climate was the most dominant control on the West African monsoon variability. However, a southern high latitude imprint is also apparent during some episodes. This centennially resolved climate record demonstrates that the equatorial West African monsoon experienced profound changes in the amount, seasonal contrast, and moisture source of summer monsoon precipitation during the last glacial. The most plausible mechanism is a large-scale southward displacement of the monsoon trough, most likely initiated by large-scale reorganization of atmospheric

  20. Sensitivity of the African and Asian Monsoons to Mid-Holocene Insolation and Data-Inferred Surface Changes.

    NASA Astrophysics Data System (ADS)

    Texier, Delphine; de Noblet, Nathalie; Braconnot, Pascale

    2000-01-01

    Orbital forcing alone is not sufficient to explain the massive northward penetration of monsoon rains in Africa shown by data during the mid-Holocene (6000 yr ago). Feedbacks associated with changes in SSTs and land surface cover may be necessary to produce a sufficient increase in the monsoon. A step toward a better understanding of the respective role of oceans and land surfaces is to design sensitivity studies with prescribed forcings, inferred from observations. In the first study, SSTs are lowered in the upwelling regions offshore of West Africa and Somalia, and increased in the Bay of Bengal and South China Sea. In the second simulation, the modern Sahara desert is replaced by a combination of xerophytic woods/scrub and grassland.In both cases the amount of water vapor advected from oceanic sources is increased north of 10°N in Africa in response to the increased land-sea temperature contrast, thereby enhancing rainfall. But the magnitude of the simulated changes is much larger when land surface is modified. The lower albedo (compared to desert) increases the amount of radiation absorbed by the surface in northern Africa and warms it up, and the larger roughness length increases both the sensible and latent heat fluxes. Moreover, vegetation is more efficient in recycling water than a bare soil, and the release of latent heat in the atmosphere increases convection, which in turn helps maintain the onshore oceanic advection. The monsoon season is then lengthened by 1-2 months compared to all other simulations reported in the paper.The intensity of monsoon rains is also modified in Asia in both sensitivity experiments. Warmer SSTs in the Bay of Bengal and South China Sea reduce the land-sea contrast and therefore the inland penetration of monsoon rains. Changes in the position of the main large-scale convergence area in the case of a green Sahara enhances the precipitation in India.Changes are also discussed in terms of atmospheric circulation. For example, the

  1. Sensitivity of the simulated African monsoon of summers 1993 and 1999 to convective parameterization schemes in RegCM3

    NASA Astrophysics Data System (ADS)

    Tchotchou, L. A. Djiotang; Kamga, F. Mkankam

    2010-03-01

    In this study, the International Center for Theoretical Physics Regional Climate Model version 3 (RegCM3) was used to investigate the sensitivity of the simulation of the West African monsoon using four different cumulus and closures parameterization schemes of Anthes Kuo (AK), Grell and Fristish Chappell (GFC), Grell and Arakawa Schubert (GAS), and MIT-Emmanuel (EM) while maintaining other physical packages unchanged. The contrasting monsoon years of 1993 and 1999, which were dry and wet years, respectively, were simulated. The model was integrated from a period of 5 months, starting from May 1 to September 30 of each year using the European Centre for Medium-Range-Weather Forecast (ECMWF) Reanalysis data (ERA40) as input boundary conditions. The 6-hourly reanalysis data were used to provide the lateral boundary conditions, and the observed weekly Reynolds Sea Surface Temperature interpolated to 6 h was used as the lower boundary forcing. The results show that in West Africa, monsoon precipitations are sensitive to the choice of cumulus parameterization and closure schemes. None of the schemes is able to simulate the monsoon rainfall accurately, and furthermore, there is little difference in behavior among schemes between dry and wet years. The spatial features of precipitation are not identical among schemes, although they all show a northward shift of the rain bands, giving a very wet Sahel and dry Guinean Coast. The GFC and EM schemes are able to capture the diurnal cycle of precipitation and the zonal averages of stratiform rain fractions as observed in the Tropical Rainfall Measuring Mission (TRMM), although they overestimated rainfall amounts. The most important deficiencies, however, cannot be attributed to the schemes. In particular, the northward shift of both the rain band and the AEJ in RegCM3 is the result of unrealistic soil moisture resulting from the way albedo is parameterized, leading to an excessive northward penetration of monsoon flow. A

  2. Interannual vs decadal SST forced responses of the West African monsoon

    NASA Astrophysics Data System (ADS)

    Rodríguez-Fonseca, Belen

    2010-05-01

    One of the strongest interdecadal signals on the planet has been observed in the Sahelian rainfall during the second half of the XXth century, from wet conditions in the 50's and 60's to drier conditions after the 70's. Parallel to this, several decadal signals have experienced a change from the 70's, and also the influence of the global warming has increased from this decade. From a global perspective the West African rainfall variability is highly modulated by SST forced signals. Many works have pointed out to the Atlantic and Pacific equatorial modes influence on interannual timescales; and to the AMO and the Pacific and Indian Ocean at multidecadal timescales. In the AMMA-EU context the modulation of the interannual modes by the decadal variability together with the influence of the GW has been studied by analysing the interannual modes of variability before and after the 70's. The results indicate the presence of different interannual telecconections between these two periods and, hence, of different anomalous rainfall responses. The importance of the background state modulated by multidecadal variability in the interannual modes is stated in this work. Also, an interesting discussion appears if we wonder whether or not the background state is affected, in turn, by anthropogenic climate change. Recent observational and GCM studies have shown, following the results of Polo et al. (2008), how the Atlantic and Pacific Niños present a dynamical link during the last decades of the XX century (Rodriguez-Fonseca et al., 2009). In this way, the positive (negative) phase of the summer Pacific Niño signal has been found to be connected with a negative (positive) phase of the Equatorial Atlantic mode (EM or Atlantic Niño, Polo et al., 2008); a pattern which leads the summer Atlantic variability. The determinant impact of this connection on the WA monsoon has been addressed by defining a global summer tropical mode accounting for more than the 60% of the rainfall

  3. Autonomous berthing/unberthing of a Work Attachment Mechanism/Work Attachment Fixture (WAM/WAF)

    NASA Technical Reports Server (NTRS)

    Nguyen, Charles C.; Antrazi, Sami S.

    1992-01-01

    Discussed here is the autonomous berthing of a Work Attachment Mechanism/Work Attachment Fixture (WAM/WAF) developed by NASA for berthing and docking applications in space. The WAM/WAF system enables fast and reliable berthing (unberthing) of space hardware. A successful operation of the WAM/WAF requires that the WAM motor velocity be precisely controlled. The operating principle and the design of the WAM/WAF is described as well as the development of a control system used to regulate the WAM motor velocity. The results of an experiment in which the WAM/WAF is used to handle an orbital replacement unit are given.

  4. The middle Holocene climatic records from Arabia: Reassessing lacustrine environments, shift of ITCZ in Arabian Sea, and impacts of the southwest Indian and African monsoons

    NASA Astrophysics Data System (ADS)

    Enzel, Yehouda; Kushnir, Yochanan; Quade, Jay

    2015-06-01

    A dramatic increase in regional summer rainfall amount has been proposed for the Arabian Peninsula during the middle Holocene (ca. 9-5 ka BP) based on lacustrine sediments, inferred lake levels, speleothems, and pollen. This rainfall increase is considered primarily the result of an intensified Indian summer monsoon as part of the insolation-driven, northward shift of the boreal summer position of the Inter-Tropical Convergence Zone (ITCZ) to over the deserts of North Africa, Arabia, and northwest India. We examine the basis for the proposed drastic climate change in Arabia and the shifts in the summer monsoon rains, by reviewing paleohydrologic lacustrine records from Arabia. We evaluate and reinterpret individual lake-basin status regarding their lacustrine-like deposits, physiography, shorelines, fauna and flora, and conclude that these basins were not occupied by lakes, but by shallow marsh environments. Rainfall increase required to support such restricted wetlands is much smaller than needed to form and maintain highly evaporating lakes and we suggest that rainfall changes occurred primarily at the elevated edges of southwestern, southern, and southeastern Arabian Peninsula. These relatively small changes in rainfall amounts and local are also supported by pollen and speleothems from the region. The changes do not require a northward shift of the Northern Hemisphere summer ITCZ and intensification of the Indian monsoon rainfall. We propose that (a) latitudinal and slight inland expansion of the North African summer monsoon rains across the Red Sea, and (b) uplifted moist air of this monsoon to southwestern Arabia highlands, rather than rains associated with intensification of Indian summer monsoon, as proposed before, increased rains in that region; these African monsoon rains produced the modest paleo-wetlands in downstream hyperarid basins. Furthermore, we postulate that as in present-day, the ITCZ in the Indian Ocean remained at or near the equator all

  5. New approach for aerosol profiling with a lidar onboard an ultralight aircraft: application to the African Monsoon Multidisciplinary Analysis.

    PubMed

    Chazette, Patrick; Sanak, Joseph; Dulac, François

    2007-12-15

    A new airborne instrumental payload has been designed for an ultralight aircraft to determine the vertical profile of aerosol optical properties. It is based on Lidar Aérosols UltraViolet Aéroporté (LAUVA), a compact backscattering lidar system emitting at the wavelength of 355 nm. We operated this airborne configuration in the Sahel from the city of Niamey (Niger) during the first campaign of the African Monsoon Multidisciplinary Analysis (AMMA) in January-February 2006, when aerosols from both soil dust and savannah fires cause large visibility reductions. We take advantage of the lidar capability of pointing in different directions for retrieving the vertical profile of the aerosol backscatter to extinction ratio (BER). A synergy with a scatterometer (880 nm) and a ground-based sunphotometer allows us to further determine the vertical profile of Angström exponent (a). We identify three types of aerosol layers up to about 5 km below the free troposphere, dominated by biomass burning (BB) particles, mineral dust (D) particles, and a mixing between BB and D particles, respectively, associated with BER (a) values close to 0.008 sr(-1) (1.5), 0.025 sr(-1) (0), and 0.015 sr(-1) (0.4-1).

  6. Seasonal Evolution and Variability Associated with the West African Monsoon System

    NASA Technical Reports Server (NTRS)

    Gu, Guojun; Adler, Robert F.

    2003-01-01

    In this study, we investigate the seasonal variations in surface rainfall and associated large-scale processes in the tropical eastern Atlantic and West African region. The 5-yr (1998-2002) high-quality TRMM rainfall, sea surface temperature (SST), water vapor and cloud liquid water observations are applied along with the NCEP/NCAR reanalysis wind components and a 3-yr (2000-2002) Quickscat satellite-observed surface wind product. Major mean rainfall over West Africa tends to be concentrated in two regions and is observed in two different seasons, manifesting an abrupt shift of the mean rainfall zone during June-July. (i) Near the Gulf of Guinea (about 5 degN), intense convection and rainfall are seen during April-June and roughly follow the seasonality of SST in the tropical eastern Atlantic. (ii) Along the latitudes of about 10 deg. N over the interior West African continent, a second intense rain belt begins to develop from July and remains there during the later summer season. This belt co-exists with a northwardmoved African Easterly Jet (AEJ) and its accompanying horizonal and vertical shear zones, the appearance and intensification of an upper tropospheric Tropical Easterly Jet (TEJ), and a strong low-level westerly flow. Westward-propagating wave signals [ i e . , African easterly waves (AEWs)] dominate the synoptic-scale variability during July-September, in contrast to the evident eastward-propagating wave signals during May- June. The abrupt shift of mean rainfall zone thus turns out to be a combination of two different physical processes: (i) Evident seasonal cycles in the tropical eastern Atlantic ocean which modulate convection and rainfall in the Gulf of Guinea by means of SST thermal forcing and SST-related meridional gradient; (ii) The interaction among the AEJ, TEJ, low-level westerly flow, moist convection and AEWs during July-September which modulates rainfall variability in the interior West Africa, primarily within the ITCZ rain band. Evident

  7. Correlative Analysis of GRBs Detected by Swift and Suzaku- WAM

    NASA Technical Reports Server (NTRS)

    Krimm, H.A.; Sakamoto, T.; Yamaoka, K.; Sugita, S.; Ohno, M.; Sato, G.; Hara, R.; Ohmori, N.; Tanaka, H.; Yamauchi, M.; Onda, K.; Tashiro, M.

    2009-01-01

    It is now well known that a complete understanding of the energetics of the prompt phase of gamma-ray bursts (GRBs) requires full knowledge of the spectrum, extending at least as high as the peak energy (Epeak) of the vF(v) spectrum. Since most gamma-ray bursts (GRBs) have Epeak above the energy range (15-150 keV) of the Burst Alert Telescope (BAT) on Swift, a full understanding of the prompt emission from Swift GRBs requires spectral fits over as broad an energy range as possible. This can be completed for bursts which are simultaneously detected by Swift BAT and the Suzaku Wide-band All-Sky Monitor (WAM), which covers the energy range from 50-5000 keV. Between the launch of Suzaku in July 2005 and the end of 2008, there were 44 gamma-ray bursts (GRBs) which triggered both Swift and WAM and an additional 41 bursts which triggered Swift and were detected by WAM, but did not trigger. A joint BAT-WAM team has cross-calibrated the two instruments using GRBs, and we are now able to perform joint fits on these bursts to determine spectral parameters including Epeak. The results of broad spectral fits allows us to understand the distribution of Epeak for Swift bursts and to calibrate Epeak estimators when Epeak is within the BAT energy range. For those bursts with spectroscopic redshifts, we can calculate the isotropic energy and study various correlations between Epeak and other global burst parameters. Here we present the results of joint Swift/BAT-Suzaku/WAM spectral fits for 77 of the bursts jointly detected by the two instruments. We show that the distribution of spectral fit parameters is consistent with distributions from earlier missions and confirm that Swift bursts are consistent with earlier reported relationships between Epeak and isotropic energy. We show through time-resolved spectroscopy that individual burst pulses are also consistent with this relationship.

  8. African monsoon variations and persistence of the Megalake Chad during the late Pliocene

    NASA Astrophysics Data System (ADS)

    Contoux, Camille; Ramstein, Gilles; Jost, Anne; Sepulchre, Pierre; Schuster, Mathieu; Braconnot, Pascale

    2013-04-01

    Megalake Chad (MLC) occurrences are widely documented for the mid-Holocene period but also for the Mio-Pliocene (Schuster et al., 2009). From 7 to 3 Ma, analysis of sedimentary deposits of the Djurab desert region show desertic to full-lacustrine facies, suggesting an alternance of dry to wet climates (Schuster, 2002, Schuster et al., 2009), lacustrine conditions being associated to fauna dispersal and early hominid presence (e.g. Brunet et al., 1995, 2002). Some studies (e.g. Braconnot and Marti, 2003) suggest a control of precession on monsoon. Using late Pliocene climate simulations and different orbital configurations, can we constrain variations of the Megalake and reach the water volume of 350 000 km² proposed by several authors (Ghienne et al., 2002; Leblanc et al., 2006)? Can we propose a timing for the MLC occurrences? First, in order to better characterize the precession role on Megalake Chad occurrences during the late Pliocene, we use the IPSLCM5A coupled ocean atmosphere climate model forced with four different orbital configurations and mid-Pliocene boundary conditions. The four orbital configurations, all around 3 Ma, correspond to maximum and minimum insolations at 30°N at summer solstice or autumn equinox. We find important increases of precipitation in North Africa, controlled by insolation maxima at 30°N at summer solstice and autumn equinox, i.e. related to an angular precession between 270° and 10°. When used to force a surface routing model (HYDRA, Coe, 2000), these precipitation increases lead to MLC episodes, suggesting the MLC could be sustained during at least 5 kyr of a precession cycle. However, this method does not account for the lake feedback on climate. Indeed, during wet phases, the MLC becomes an important evaporation source, modifying the climate of the Chad basin. To investigate this aspect, we use the LMDZ4 atmospheric model including an open water surface module (Krinner, 2003). We find that deep convection is suppressed

  9. The representation of low-level clouds during the West African monsoon in weather and climate models

    NASA Astrophysics Data System (ADS)

    Kniffka, Anke; Hannak, Lisa; Knippertz, Peter; Fink, Andreas

    2016-04-01

    The West African monsoon is one of the most important large-scale circulation features in the tropics and the associated seasonal rainfalls are crucial to rain-fed agriculture and water resources for hundreds of millions of people. However, numerical weather and climate models still struggle to realistically represent salient features of the monsoon across a wide range of scales. Recently it has been shown that substantial errors in radiation and clouds exist in the southern parts of West Africa (8°W-8°E, 5-10°N) during summer. This area is characterised by strong low-level jets associated with the formation of extensive ultra-low stratus clouds. Often persisting long after sunrise, these clouds have a substantial impact on the radiation budget at the surface and thus the diurnal evolution of the planetary boundary layer (PBL). Here we present some first results from a detailed analysis of the representation of these clouds and the associated PBL features across a range of weather and climate models. Recent climate model simulations for the period 1991-2010 run in the framework of the Year of Tropical Convection (YOTC) offer a great opportunity for this analysis. The models are those used for the latest Assessment Report of the Intergovernmental Panel on Climate Change, but for YOTC the model output has a much better temporal resolution, allowing to resolve the diurnal cycle, and includes diabatic terms, allowing to much better assess physical reasons for errors in low-level temperature, moisture and thus cloudiness. These more statistical climate model analyses are complemented by experiments using ICON (Icosahedral non-hydrostatic general circulation model), the new numerical weather prediction model of the German Weather Service and the Max Planck Institute for Meteorology. ICON allows testing sensitivities to model resolution and numerical schemes. These model simulations are validated against (re-)analysis data, satellite observations (e.g. CM SAF cloud and

  10. Impact of the Madden Julian Oscillation on the summer West African monsoon in AMIP simulations

    NASA Astrophysics Data System (ADS)

    Niang, Coumba; Mohino, Elsa; Gaye, Amadou T.; Omotosho, J. Bayo

    2016-06-01

    At intraseasonal timescales, convection over West Africa is modulated by the Madden Julian Oscillation (MJO). In this work we investigate the simulation of such relationship by 11 state-of-the-art atmospheric general circulation models runs with prescribed observed sea surface temperatures. In general, the Atmospheric Model Intercomparison Project simulations show good skill in capturing the main characteristics of the summer MJO as well as its influence on convection and rainfall over West Africa. Most models simulate an eastward spatiotemporal propagation of enhanced and suppressed convection similar to the observed MJO, although their signal over West Africa is weaker in some models. In addition, the ensemble average of models' composites gives a better performance in reproducing the main features and timing of the MJO and its impact over West Africa. The influence on rainfall is well captured in both Sahel and Guinea regions thereby adequately producing the transition between positive and negative rainfall anomalies through the different phases as in the observations. Furthermore, the results show that a strong active convection phase is clearly associated with a stronger African Easterly Jet (AEJ) but the weak convective phase is associated with a much weaker AEJ. Our analysis of the equatorial waves suggests that the main impact over West Africa is established by the propagation of low-frequency waves within the MJO and Rossby spectral peaks. Results from the simulations confirm that it may be possible to predict anomalous convection over West Africa with a time lead of 15-20 day.

  11. Past changes of the North African monsoon intensity between 5 and 6.2 My, impact of the Messinian Salinity Crisis (MSC)

    NASA Astrophysics Data System (ADS)

    Ségueni, F.; Colin, C.; Siani, G.; Frank, N.; Blamart, D.; Kissel, C.; Liu, Z.; Richter, T.; Suc, J.

    2006-12-01

    A high resolution multiproxy study by oxygen isotope record (δ18O) on benthic foraminifera (Cibicides wuellerstorfii), magnetic susceptibility, clay mineralogy (DRX), major - trace elements (XRF core scanner and ICPMS) and Rb/Sr - Nd isotopes was carried out from site ODP 659 along the Cape Verde off Africa. The aim was to reconstruct variations of African Monsoon during the Mio-Pliocene in the time interval from 5 My to 6,2 My. Chronology was established by linear interpolation between 3 bio-events based on calcareous nannoplancton zones, 2 glacial stages TG12 and TG22 identified on δ18O records and by tuning the δ18O and magnetic susceptibility records to the orbital parameter of obliquity and precession. Results indicate that between 5 to 6.2 My variability in the eolian input from Sahara and the coastal upwelling intensity are anti-correlated and make it possible to retrace the evolution of northern African Monsoon. The latter co- varies mainly with the insolation received by the earth at low latitude during the summer. Maximal insolation enhance summer monsoonal effects by increasing wetter conditions on Sahel and NE dominance wind system cause a reduced eolian input and an increased biogenic sea surface productivity by coastal upwelling. On the other hand, minimal insolation reinforce winter monsoon that create a more arid climate on Sahel and stronger westward winds that increase eolian flux on Cap Verde with a reduced upwelling effect on sea surface productivity. At a longer time scale, the end of the MSC is correlated with a major change of the African Monsoon intensity. Finally, the δ18O record on C.wuellerstorfii suggests that global eustatic processes didn't play a key role in the MSC history. Nevertheless, transition between glacial stage TG12 and the interglacial TG11 seems to correspond to a major event within the MSC, and associated to the beginning of the upper evaporite deposits. Thus, the facies of the Lago Mare of the upper evaporites would

  12. A comparison of regional monsoon variability using monsoon indices

    NASA Astrophysics Data System (ADS)

    Yim, So-Young; Wang, Bin; Liu, Jian; Wu, Zhiwei

    2014-09-01

    The present study aims to (a) examine meteorological basis for construction of regional monsoon indices and (b) explore the commonality and differences among tropical regional monsoons, especially the teleconnection and monsoon-ENSO relationship. We show that the area-averaged summer precipitation intensity is generally a meaningful precipitation index for tropical monsoons because it represents very well both the amplitude of annual cycle and the leading mode of year-to-year rainfall variability with a nearly uniform spatial pattern. The regional monsoon circulation indices can be defined in a unified way (measuring monsoon trough vorticity) for seven tropical monsoon regions, viz.: Indian, Australian, western North Pacific, North and South American, and Northern and Southern African monsoons. The structures of the tropical monsoons are commonly characterized by a pair of upper-level double anticyclones residing in the subtropics of both hemispheres; notably the winter hemispheric anticyclone has a barotropic structure and is a passive response. Two types of upper-level teleconnection patterns are identified. One is a zonal wave train emanating from the double anticyclones downstream along the westerly jets in both hemispheres, including Indian, Northern African and Australian monsoons; the other is a meridional wave train emanating from the double anticyclones polewards, such as the South American and western North Pacific monsoons. Over the past 55 years all regional summer monsoons have non-stationary relationship with ENSO except the Australian monsoon. The regional monsoon-ENSO relationship is found to have common changing points in 1970s. The relationships were enhanced for the western North Pacific, Northern African, North American and South American summer monsoons, but weakened for the Indian summer monsoon (with a recovery in late 1990s). Regardless the large regional differences, the monsoon precipitations over land areas of all tropical monsoon regions

  13. Radiative forcing of Sahara dust and its impacts on the hydrological cycle in the West African monsoon system

    NASA Astrophysics Data System (ADS)

    Zhao, C.; Liu, X.; Leung, L.; Hagos, S. M.

    2010-12-01

    The WRF-Chem model is applied to simulate the radiative forcing of dust and its impacts on the hydrological cycle during the monsoon season over West Africa (WA). The GOCART dust emission scheme is coupled into two aerosol models (MADE/SORGAM and MOSAIC) in WRF-Chem. During the monsoon season, dust is a dominant contributor to AOD near the dust source regions. Dust heats the atmosphere, and warms the surface in the nighttime through trapping the longwave radiation but cools the surface in the daytime through reducing the shortwave radiation. Dust modifies the surface energy budget through changing radiation, latent heat, and sensible heat fluxes, and results in large surface cooling effect in the afternoon but warming effect in the early morning during the monsoon season over WA. In the standard model configuration, the dust effect on total daily precipitation is small in both strong and weak monsoon years, but is sensitive to the dust absorbing properties. On the other hand, the dust-driven change of the stability of atmosphere significantly reduces the diurnal variation of precipitation during the monsoon season over WA, and improves the model simulation when compared to available observations.

  14. Projected changes of summer monsoon extremes and hydroclimatic regimes over West Africa for the twenty-first century

    NASA Astrophysics Data System (ADS)

    Diallo, Ismaïla; Giorgi, Filippo; Deme, Abdoulaye; Tall, Moustapha; Mariotti, Laura; Gaye, Amadou T.

    2016-03-01

    We use two CORDEX-Africa simulations performed with the regional model RegCM4 to characterize the projected changes in extremes and hydroclimatic regimes associated with the West African Monsoon (WAM). RegCM4 was driven for the period 1970-2100 by the HadGEM2-ES and the MPI-ESM Global Climate Models (GCMs) under the RCP8.5 greenhouse gas concentration pathway. RegCM4 accurately simulates the WAM characteristics in terms of seasonal mean, seasonal cycle, interannual variability and extreme events of rainfall. Overall, both RegCM4 experiments are able to reproduce the large-scale atmospheric circulation for the reference period (i.e. present-day), and in fact show improved performance compared to the driving GCMs in terms of precipitation mean climatology and extreme events, although different shortcomings in the various models are still evident. Precipitation is projected to decrease (increase) over western (eastern) Sahel, although with different spatial detail between RegCM4 and the corresponding driving GCMs. Changes in extreme precipitation events show patterns in line with those of the mean change. The models project different changes in water budget over the Sahel region, where the MPI projects an increased deficit in local moisture supply (E < P) whereas the rest of models project a local surplus (E > P). The E-P change is primarily precipitation driven. The precipitation increases over the eastern and/or central Sahel are attributed to the increase of moisture convergence due to increased water vapor in the boundary layer air column and surface evaporation. On the other hand, the projected dry conditions over the western Sahel are associated with the strengthening of moisture divergence in the upper level (850-300 hPa) combined to both a southward migration of the African Easterly Jet (AEJ) and a weakening of rising motion between the core of the AEJ and the Tropical Easterly Jet.

  15. Intense hurricane activity over the past 5,000 years controlled by El Niño and the West African monsoon.

    PubMed

    Donnelly, Jeffrey P; Woodruff, Jonathan D

    2007-05-24

    The processes that control the formation, intensity and track of hurricanes are poorly understood. It has been proposed that an increase in sea surface temperatures caused by anthropogenic climate change has led to an increase in the frequency of intense tropical cyclones, but this proposal has been challenged on the basis that the instrumental record is too short and unreliable to reveal trends in intense tropical cyclone activity. Storm-induced deposits preserved in the sediments of coastal lagoons offer the opportunity to study the links between climatic conditions and hurricane activity on longer timescales, because they provide centennial- to millennial-scale records of past hurricane landfalls. Here we present a record of intense hurricane activity in the western North Atlantic Ocean over the past 5,000 years based on sediment cores from a Caribbean lagoon that contain coarse-grained deposits associated with intense hurricane landfalls. The record indicates that the frequency of intense hurricane landfalls has varied on centennial to millennial scales over this interval. Comparison of the sediment record with palaeo-climate records indicates that this variability was probably modulated by atmospheric dynamics associated with variations in the El Niño/Southern Oscillation and the strength of the West African monsoon, and suggests that sea surface temperatures as high as at present are not necessary to support intervals of frequent intense hurricanes. To accurately predict changes in intense hurricane activity, it is therefore important to understand how the El Niño/Southern Oscillation and the West African monsoon will respond to future climate change.

  16. A High-Resolution Late Holocene Record of Rainfall From Lake Edward, Equatorial Africa: Linkages Between the African and Indian Monsoons

    NASA Astrophysics Data System (ADS)

    Russell, J. M.; Johnson, T. C.

    2005-12-01

    High-resolution analyses of the chemical composition of calcite and the biogenic silica content of sediments from piston cores spanning the past 3,500 years from Lake Edward, Uganda-Congo, document multidecadal to millennial-scale climate variability in the heart of equatorial Africa. Major drought events in the Lake Edward record occur at about 500, 850, 1500, ~2000, and 2700 cal yr BP, in addition to numerous other events of lesser magnitude/duration. Comparison of our record to other Holocene records of African lake levels suggests that most of these intervals of drought affected most of equatorial East Africa. However, wet conditions at about 500 cal yrs BP at sites to the east of Lake Edward could indicate spatial heterogeneity within the African continent during the "Little Ice Age", which could have resulted from complex interactions between the African (Atlantic) and Indian Ocean monsoons. Spectral analysis of our drought record, sampled at a 3-year step, shows evidence for numerous multidecadal to century-scale drought periods in the region. The periodicities observed do not appear linked to solar forcing; rather, periods of ~125, ~70, ~28, and ~18 years apparent in our record as well as other records from the Indian Ocean basin may arise from climate variability internal to the tropical oceans, in particular the Indo-Pacific. Lastly, the Lake Edward record suggests that the climate of equatorial Africa has been unusually stable and generally wet for the past ca. 100 years. This stability appears unusual in light of the considerable climate variability suggested by our record for the past several millennia, a finding with clear implications for East African societies.

  17. Cloud properties during active and break spells of the West African summer monsoon from CloudSat-CALIPSO measurements

    NASA Astrophysics Data System (ADS)

    Efon, E.; Lenouo, A.; Monkam, D.; Manatsa, D.

    2016-07-01

    High resolution of daily rainfall dataset from the Tropical Rainfall Measuring Mission (TRMM) was used to identify active and break cloud formation periods. The clouds were characterized based on CloudSat-CALIPSO satellite images over West Africa during the summer monsoon during the period 2006-2010. The active and break periods are defined as the periods during the peak monsoon months of June to August when the normalized anomaly of rainfall over the monsoon core zone is greater than 0.9 or less than -0.9 respectively, provided the criteria is satisfied for at least three consecutive days. It is found that about 90% of the break period and 66.7% of the active spells lasted 3-4 days. Active spells lasting duration of about a week were observed while no break spell had such a long span. Cloud macrophysical (cloud base height (CBH), cloud top height (CTH) and cloud geometric depth (∆H), microphysical (cloud liquid water content, (LWC), liquid number concentration (LNC), liquid effective radius, ice water content (IWC), ice number concentration (INC) and ice effective radius) and radiative (heating rate properties) over South Central West Africa (5-15°N; 15°W-10°E) during the active and break spells were also analyzed. High-level clouds are more predominant during the break periods compared to the active periods. Active spells have lower INC compared to the break spells. Liquid water clouds are observed to have more radiative forcing during the active than break periods while ice phase clouds bring more cooling effect during the break spells compared to the active spells.

  18. On the Origin of Monsoon

    NASA Technical Reports Server (NTRS)

    Chao, Winston C.; Chen, Baode; Einaudi, Franco (Technical Monitor)

    2000-01-01

    It is a long-held fundamental belief that the basic cause of a monsoon is land-sea thermal contrast on the continental scale. Through general circulation model experiments we demonstrate that this belief should be changed. The Asian and Australian summer monsoon circulations are largely intact in an experiment in which Asia, maritime continent, and Australia are replaced by ocean. It is also shown that the change resulting from such replacement is in general due more to the removal of topography than to the removal of land-sea contrast. Therefore, land-sea contrast plays only a minor modifying role in Asian and Australian summer monsoons. This also happens to the Central American summer monsoon. However, the same thing cannot be said of the African and South American summer monsoons. In Asian and Australian winter monsoons land-sea contrast also plays only a minor role. Our interpretation for the origin of monsoon is that the summer monsoon is the result of ITCZ's (intertropical convergence zones) peak being substantially (more than 10 degrees) away from the equator. The origin of the ITCZ has been previously interpreted by Chao. The circulation around thus located ITCZ, previously interpreted by Chao and Chen through the modified Gill solution and briefly described in this paper, explains the monsoon circulation. The longitudinal location of the ITCZs is determined by the distribution of surface conditions. ITCZ's favor locations of higher SST as in western Pacific and Indian Ocean, or tropical landmass, due to land-sea contrast, as in tropical Africa and South America. Thus, the role of landmass in the origin of monsoon can be replaced by ocean of sufficiently high SST. Furthermore, the ITCZ circulation extends into the tropics in the other hemisphere to give rise to the winter monsoon circulation there. Also through the equivalence of land-sea contrast and higher SST, it is argued that the basic monsoon onset mechanism proposed by Chao is valid for all monsoons.

  19. Interactions between Oceanic Saharan Air Layer and African Easterly Jet- African Easterly Waves System

    NASA Astrophysics Data System (ADS)

    Hosseinpour, F.; Wilcox, E. M.

    2013-12-01

    , along with strengthened (weakened) correlative low-level trade winds in northern and southern edges of the Atlantic ITCZ. These result in three-dimensional displacements and changes in circulations and precipitation variability, especially in West African monsoon (WAM) dynamics.

  20. Watchdog activity monitor (WAM) for use wth high coverage processor self-test

    NASA Technical Reports Server (NTRS)

    Tulpule, Bhalchandra R. (Inventor); Crosset, III, Richard W. (Inventor); Versailles, Richard E. (Inventor)

    1988-01-01

    A high fault coverage, instruction modeled self-test for a signal processor in a user environment is disclosed. The self-test executes a sequence of sub-tests and issues a state transition signal upon the execution of each sub-test. The self-test may be combined with a watchdog activity monitor (WAM) which provides a test-failure signal in the presence of a counted number of state transitions not agreeing with an expected number. An independent measure of time may be provided in the WAM to increase fault coverage by checking the processor's clock. Additionally, redundant processor systems are protected from inadvertent unsevering of a severed processor using a unique unsever arming technique and apparatus.

  1. Experiments on exactly computing non-linear energy transfer rate in MASNUM-WAM

    NASA Astrophysics Data System (ADS)

    Jiang, Xingjie; Wang, Daolong; Gao, Dalu; Zhang, Tingting

    2016-07-01

    The Webb-Resio-Tracy (WRT) method for exact computation of the non-linear energy transfer rate was implemented in MASNUM-WAM, which is a third-generation wave model solving the discrete spectral balance equation. In this paper, we describe the transformation of the spectral space in the original WRT method. Four numerical procedures were developed in which the acceleration techniques in the original WRT method, such as geometric scaling, pre-calculating, and grid-searching, are all reorganized. A series of numerical experiments including two simulations based on real data were performed. The availability of such implementation in both serial and parallel versions of the wave model was proved, and a comparison of computation times showed that some of the developed procedures provided good efficacy. With exact computation of non-linear energy transfer, MASNUM-WAM now can be used to perform numerical experiments for research purposes, which augurs well for further developments of the model.

  2. Onset of the summer monsoon during the FGGE 1979 experiment off the East African Coast: A comparison of wind data collected by different means

    SciTech Connect

    Schott, F.; Partagas, J.F.

    1981-05-20

    During FGGE 1979, from March to July, an extensive oceanographic experiment with ships and moored stations was carried out in the Somali Current. The development of the monsoon winds off Somalia during the time of that experiment is described in a comparative analysis of standard ship wind observations, moored buoy wind measurements, low-level cloud winds, and winds from land stations. The onset 1979 is found to be of the multiple type, with northward winds off Somalia beginning around May 5 but dying down into early June; the real onset of sustained high winds starts around June 10. Cloud level wind observation numbers off Somalia decrease drastically with the monsoon onset because of lack of clouds over the quickly developing cold upwelling areas. An intercomparison of cloud level and ship winds for the period May 16 to July 6 at five offshore points shows good agreement in directions but reduction of ship wind speeds against cloud level winds off northern Somalia after the onset, which may explained by the increased vertical wind shear due to high air stability over the upwelled water and by geostrophic shear due to the strong gradients of sea surface temperature. A comparison of 3-day averages of buoy winds measured at 3-m height 30 km offshore, but still inland from the ship lane, with ship winds for the period March 3 to June 10 showed good agreement in directions but lower buoy wind speeds, which could partly be due to sensor height difference and partly due to horizontal wind shear towards the coast. Coastal stations and wind buoys near the coast are found not to be good indicators of the monsoon onset further out in the open ocean.

  3. Opportunities for Increased Physical Activity in the Workplace: the Walking Meeting (WaM) Pilot Study, Miami, 2015

    PubMed Central

    Kling, Hannah E.; Yang, Xuan; Messiah, Sarah E.; Arheart, Kristopher L.; Brannan, Debi

    2016-01-01

    Introduction Despite the positive impact walking has on human health, few opportunities exist for workers with largely sedentary jobs to increase physical activity while at work. The objective of this pilot study was to examine the implementation, feasibility, and acceptability of using a Walking Meeting (WaM) protocol to increase the level of work-related physical activity among a group of sedentary white-collar workers. Methods White-collar workers at a large university were invited to participate in a newly developed WaM protocol. Workers who conducted weekly meetings in groups of 2 or 3 individuals were recruited for the pilot study (n = 18) that took place from January 2015 to August 2015. Seventeen participants wore an accelerometer to measure physical activity levels during 3 consecutive weeks (first week baseline, followed by 2 weeks of organized WaMs) and participated in focus groups conducted during week 3 to document experiences with the WaM protocol. Results The WaM protocol met study criteria on feasibility, implementation, and acceptability among study participants. The average number of minutes (standard deviation) participants engaged in combined work-related moderate/vigorous physical activity per week during the 3 weeks increased from an average of 107 (55) minutes during the baseline week to 114 (67) minutes at week 2 and to 117 (65) minutes at week 3. Conclusion White- collar workers were supportive of transforming regular seated meetings into walking meetings and increased their work-related physical activity levels. PMID:27337560

  4. The monsoon experiment MONEX

    NASA Technical Reports Server (NTRS)

    Das, P. K.

    1979-01-01

    The effects of monsoons in different parts of the world on the Earth's atmosphere were studied by MONEX, India's Monsoon Experiment program. Data were gathered from meteorological satellites, sounding rockets, aircraft, land and shipborne stations.

  5. Global aspects of monsoons

    NASA Technical Reports Server (NTRS)

    Murakami, T.

    1985-01-01

    Recent developments are studied in three areas of monsoon research: (1) global aspects of the monsoon onset, (2) the orographic influence of the Tibetan Plateau on the summer monsoon circulations, and (3) tropical 40 to 50 day oscillations. Reference was made only to those studies that are primarily based on FGGE Level IIIb data. A brief summary is given.

  6. An assessment of monsoon precipitation changes during 1901-2001: Observation and Model Simulation

    NASA Astrophysics Data System (ADS)

    Zhou, T.; Zhang, L.

    2010-12-01

    Changes of global land monsoon precipitation are examined by using three sets of rain-gauge precipitation data for the period of 1901-2001 compiled by GPCC, CRU and Dai, respectively. The three datasets show consistent long-term changes of precipitation over the monsoon region with slightly different amplitudes. During 1901-2001, global land monsoon precipitation (GMI) exhibits multi-decadal variations, with an overall increasing trend from 1901 to 1955, followed by a decreasing trend up to 2001. The upward trends during 1901-1955 of global and northern hemispheric land monsoon precipitation are mainly resulted from the increased precipitation over the North African, Indian and East Asian monsoon domains. For the whole period of 1901-2001, precipitation averaged over the Northern Hemisphere and global land monsoon areas all exhibit a decreasing trends, although it is only statistically significant at the 5% level for the Northern Hemisphere. The robust decreasing trend of northern hemispheric land monsoon precipitations during the 20th century mainly comes from the downward trend of North African and eastern part of Indian monsoon precipitation and occurs mainly after the 1950s. The first leading mode of Empirical orthogonal function (EOF) analyses of precipitation annual range features a coherent change of North African, South Asian, Northeast China, southern South African, eastern Australian and western American monsoon, and a coherent change over the equatorial South African monsoon and eastern American monsoon. The corresponding principal component time series also indicates that the majority of global land monsoon precipitation has experienced an increasing tendency from 1901 to 1950s and a decreasing trend since 1950s. The results of observational data diagnosis are compared with the results of AGCM simulations forced by historical sea surface temperature. Possible mechanisms for global land monsoon changes are discussed.

  7. Use of the WECC WAMS in Wide Area Probing Tests for Validation of System Performance & Modeling

    SciTech Connect

    Hauer, John F.; Mittelstadt, William; Martin, Kenneth E.; Burns, J. W.; Lee, Harry; Pierre, John W.; Trudnowski, Daniel

    2009-02-01

    During 2005 and 2006 the Western Electricity Coordinating Council (WECC) performed three major tests of western system dynamics. These tests used a Wide Area Measurement System (WAMS) based primarily on Phasor Measurement Units (PMUs) to determine response to events including the insertion of the 1400-MW Chief Joseph braking resistor, probing signals, and ambient events. Test security was reinforced through real-time analysis of wide area effects, and high-quality data provided dynamic profiles for interarea modes across the entire western interconnection. The tests established that low-level optimized pseudo-random ±20-MW probing with the Pacific DC Intertie (PDCI) roughly doubles the apparent noise that is natural to the power system, providing sharp dynamic information with negligible interference to system operations. Such probing is an effective alternative to use of the 1400-MW Chief Joseph dynamic brake, and it is under consideration as a standard means for assessing dynamic security.

  8. Testing the E(sub peak)-E(sub iso) Relation for GRBs Detected by Swift and Suzaku-WAM

    NASA Technical Reports Server (NTRS)

    Krimm, H. A.; Yamaoka, K.; Sugita, S.; Ohno, M.; Sakamoto, T.; Barthelmy, S. D.; Gehrels, N.; Hara, R.; Onda, K.; Sato, G.; Tanaka, H.; Tashiro, M.; Yamauchi, M.; Norris, J. P.; Ohmori, N.

    2009-01-01

    One of the most prominent, yet controversial associations derived from the ensemble of prompt-phase observations of gamma-ray bursts (GRBs) is the apparent correlation in the source frame between the peak energy (E(sub peak)) of the nuF(nu) spectrum and the isotropic radiated energy, E(sub iso). Since most gamma-ray bursts (GRBs) have E(sub peak) above the energy range (15-150 keV) of the Burst Alert Telescope (BAT) on Swift, determining accurate E(sub peak) values for large numbers of Swift bursts has been difficult. However, by combining data from Swift/BAT and the Suzaku Wide-band All-Sky Monitor (WAM), which covers the energy range from 50-5000 keV, for bursts which are simultaneously detected ; one can accurately fit E(sub peak) and E(sub iso) and test the relationship between them for the Swift sample. Between the launch of Suzaku in July 2005 and the end of March 2009, there were 45 gamma-ray bursts (GRBs) which triggered both Swift/BAT and WAM and an additional 47 bursts which triggered Swift and were detected by WAM, but did not trigger. A BAT-WAM team has cross-calibrated the two instruments using GRBs, and we are now able to perform joint fits on these bursts to determine spectral parameters. For those bursts with spectroscopic redshifts.. we can also calculate the isotropic energy. Here we present the results of joint Swift/BAT-Suzaku/WAM spectral fits for 86 of the bursts detected by the two instruments. We show that the distribution of spectral fit parameters is consistent with distributions from earlier missions and confirm that Swift, bursts are consistent with earlier reported relationships between Epeak and isotropic energy. We show through time-resolved spectroscopy that individual burst pulses are also consistent with this relationship.

  9. Assimilation of ASAR-ENVISAT directional wave spectra in wave model WAM

    NASA Astrophysics Data System (ADS)

    Aouf, L.; Lefevre, J.-M.; Hauser, D.; Chapron, B.

    2003-04-01

    Better understanding and prediction of sea state are an essential need for many application domains, such as navigation and security of ships, off-shore industrial activities and the survey of the coastal zone... etc. In the framework of SWIMSAT (Surface wave investigations and monitoring from satellite, proposition to spatial mission to European Space Agency), we have shown the significant contribution induced by the assimilation of directional wave spectra in wave model WAM (Aouf et al, 2002). These results can be summarized in one hand by the improvement of the estimation of wave parameters (significant wave height, wave period and direction). In the other hand the duration of the assimilation impact in the forecast period is significantly larger regarding to the assimilation of altimeter data (wave height only). In order to prepare the assimilation scheme for operational use, assimilation tests in wave model WAM are performed with real wave spectra from the radar ASAR of the satellite ENVISAT. In this study, assimilation parameters (estimation of the covariance matrix, cross-assignement and selection of wave trains) are well adapted and the partitioning procedure in the scheme is improved in such a way that the limitation in frequency concerning the observed wave spectra (frequency cut-off of 0.1 Hz) is taken into account. The results show that the assimilation is efficient and works correctly. Furthermore, the root mean square of the analyzed wave parameters (wave height, direction and frequency) is significantly reduced and the impact of the assimilation stays effective in the forecast period. Also it has been shown that the ASAR wave spectra affect much more the low frequency wave parameters (swell). More complete and validated ASAR data will be assimilated and compared with other data sources such as RA2, buoy and RAR as part of VALPARAISO experiment.

  10. Impact of potential large-scale and medium-scale irrigation on the West African Monsoon and its dependence on location of irrigated area

    NASA Astrophysics Data System (ADS)

    Eltahir, E. A. B.; IM, E. S.

    2014-12-01

    This study investigates the impact of potential large-scale (about 400,000 km2) and medium-scale (about 60,000 km2) irrigation on the climate of West Africa using the MIT Regional Climate Model. A new irrigation module is implemented to assess the impact of location and scheduling of irrigation on rainfall distribution over West Africa. A control simulation (without irrigation) and various sensitivity experiments (with irrigation) are performed and compared to discern the effects of irrigation location, size and scheduling. In general, the irrigation-induced surface cooling due to anomalously wet soil tends to suppress moist convection and rainfall, which in turn induces local subsidence and low level anti-cyclonic circulation. These local effects are dominated by a consistent reduction of local rainfall over the irrigated land, irrespective of its location. However, the remote response of rainfall distribution to irrigation exhibits a significant sensitivity to the latitudinal position of irrigation. The low-level northeasterly flow associated with anti-cyclonic circulation centered over the irrigation area can enhance the extent of low level convergence through interaction with the prevailing monsoon flow, leading to significant increase in rainfall. Despite much reduced forcing of irrigation water, the medium-scale irrigation seems to draw the same response as large-scale irrigation, which supports the robustness of the response to irrigation in our modeling system. Both large-scale and medium-scale irrigation experiments show that an optimal irrigation location and scheduling exists that would lead to a more efficient use of irrigation water. The approach of using a regional climate model to investigate the impact of location and size of irrigation schemes may be the first step in incorporating land-atmosphere interactions in the design of location and size of irrigation projects. However, this theoretical approach is still in early stages of development and

  11. Monsoons in a changing world: A regional perspective in a global context

    NASA Astrophysics Data System (ADS)

    Kitoh, Akio; Endo, Hirokazu; Krishna Kumar, K.; Cavalcanti, Iracema F. A.; Goswami, Prashant; Zhou, Tianjun

    2013-04-01

    provide a new view of global and regional monsoonal rainfall, and their changes in the 21st century under RCP4.5 and RCP8.5 scenarios as projected by 29 climate models that participated in the Coupled Model Intercomparison Project phase 5. The model results show that the global monsoon area defined by the annual range in precipitation is projected to expand mainly over the central to eastern tropical Pacific, the southern Indian Ocean, and eastern Asia. The global monsoon precipitation intensity and the global monsoon total precipitation are also projected to increase. Indices of heavy precipitation are projected to increase much more than those for mean precipitation. Over the Asian monsoon domain, projected changes in extreme precipitation indices are larger than over other monsoon domains, indicating the strong sensitivity of Asian monsoon to global warming. Over the American and African monsoon regions, projected future changes in mean precipitation are rather modest, but those in precipitation extremes are large. Models project that monsoon retreat dates will delay, while onset dates will either advance or show no change, resulting in lengthening of the monsoon season. However, models' limited ability to reproduce the present monsoon climate and the large scatter among the model projections limit the confidence in the results. The projected increase of the global monsoon precipitation can be attributed to an increase of moisture convergence due to increased surface evaporation and water vapor in the air column although offset to a certain extent by the weakening of the monsoon circulation.

  12. Sensitivity of The High-resolution Wam Model With Respect To Time Step

    NASA Astrophysics Data System (ADS)

    Kasemets, K.; Soomere, T.

    The northern part of the Baltic Proper and its subbasins (Bothnian Sea, the Gulf of Finland, Moonsund) serve as a challenge for wave modellers. In difference from the southern and the eastern parts of the Baltic Sea, their coasts are highly irregular and contain many peculiarities with the characteristic horizontal scale of the order of a few kilometres. For example, the northern coast of the Gulf of Finland is extremely ragged and contains a huge number of small islands. Its southern coast is more or less regular but has up to 50m high cliff that is frequently covered by high forests. The area also contains numerous banks that have water depth a couple of meters and that may essentially modify wave properties near the banks owing to topographical effects. This feature suggests that a high-resolution wave model should be applied for the region in question, with a horizontal resolution of an order of 1 km or even less. According to the Courant-Friedrich-Lewy criterion, the integration time step for such models must be of the order of a few tens of seconds. A high-resolution WAM model turns out to be fairly sensitive with respect to the particular choice of the time step. In our experiments, a medium-resolution model for the whole Baltic Sea was used, with the horizontal resolution 3 miles (3' along latitudes and 6' along longitudes) and the angular resolution 12 directions. The model was run with steady wind blowing 20 m/s from different directions and with two time steps (1 and 3 minutes). For most of the wind directions, the rms. difference of significant wave heights calculated with differ- ent time steps did not exceed 10 cm and typically was of the order of a few per cents. The difference arose within a few tens of minutes and generally did not increase in further computations. However, in the case of the north wind, the difference increased nearly monotonously and reached 25-35 cm (10-15%) within three hours of integra- tion whereas mean of significant wave

  13. Coherent monsoonal changes in the northern tropics revealed by Chadian lakes (L. Chad and Yoa) sedimentary archives during the African Humid Period

    NASA Astrophysics Data System (ADS)

    Sylvestre, Florence; Kroepelin, Stefan; Pierre, Deschamps; Christine, Cocquyt; Nicolas, Waldmann; Kazuyo, Tachikawa; Amaral Paula, Do; Doriane, Delanghe; Guillaume, Jouve; Edouard, Bard; Camille, Bouchez; Jean-Claude, Doumnang; Jean-Charles, Mazur; Martin, Melles; Guillemette, Menot; Frauke, Rostek; Nicolas, Thouveny; Volkner, Wennrich

    2016-04-01

    In northern African tropics, it is now well established that the Last Glacial Maximum (LGM) was extremely dry followed by a wetter Holocene. Numerous palaeolake records reveal a fairly consistent pattern of a moister early Holocene resulting in a green Sahara followed by the onset of aridification about 4000 years ago. These palaeoenvironmental conditions are deciphered from several continental records distributed over the sub-Saharan zone and including diverse environments. However, pronounced differences in the timing and amplitude of these moisture changes inferred from sedimentary records point to both regional climatic variability change and site-specific influences of local topographic-hydrogeological factors which biased the evolution of water balance reconstructed from individual lacustrine archives. Here we present hydrological reconstructions from Chadian lakes, i.e. Lake Chad (c. 13°N) and Lake Yoa (19°N). Because of their location, both records allow to reconstruct lake level fluctuations and environmental changes according to a gradient from Sahelian to Saharan latitudes. Whereas Lake Chad is considered as a good sensor of climatic changes because of its large drainage basin covering 610,000 km2 in the Sudanian belt, Lake Yoa logs the northern precipitation changes in the Sahara. Combining sedimentological (laser diffraction grain size) and geochemical (XRF analysis) data associated with bio-indicators proxies (diatoms, pollen), we compare lake-level fluctuations and environmental changes during the last 12,000 years. After the hyperarid Last Glacial Maximum period during which dunes covered the Lake Chad basin, both lake records indicate an onset of more humid conditions between 12.5-11 ka cal BP. These resulted in lacustrine transgressions approaching their maximum extension at c. 10.5 ka cal BP. The lacustrine phase was probably interrupted by a relatively short drying event occurring around 8.2 ka cal BP which is well-defined in Lake Yoa by

  14. A case study of combined wave and water levels under storm conditions using WAM and SWAN in a shallow water application

    NASA Astrophysics Data System (ADS)

    Brown, Jennifer M.

    Extreme storm events in Liverpool Bay, UK, are under investigation. A recent storm, 18th January 2007, has been used to investigate different modelling approaches to accurately simulate wave-surge conditions in shallow water. In Liverpool Bay wave and surge influence and their interaction are often considered in many studies. The tide-surge-wave interaction has been modelled in the Irish Sea using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) coupled to the state-of-the-art 3rd generation spectral WAve Model (WAM). Waves are locally generated in Liverpool Bay, while the surge is locally and externally generated. To include the external surge the 1.8 km Irish Sea model has been nested, using a 1-way approach, into the 1/9° by 1/6° operational Continental Shelf surge model. To investigate the performance of POLCOMS-WAM in shallow water a 180 m Liverpool Bay model has been nested within the Irish Sea model. For this high resolution model the state-of-the-art 3rd generation Simulating WAves Nearshore (SWAN) spectral model is used to further develop WAM, modified for shallow water. A POLCOMS-WAM and POLCOMS-SWAN (1-way) coupled model has been implemented to assess the effects of tide-surge-wave interaction at the coast. Investigation of the significant wave height and surge elevation reveals that when modified for shallow water WAM performs as well as SWAN. Two-way coupling between POLCOMS-WAM allows wave-setup to be included in the surge prediction greatly improving the hydrodynamic result. A drawback to using WAM is the computational expense, making SWAN more suitable for simulations exceeding a few days in duration.

  15. Energetics and monsoon bifurcations

    NASA Astrophysics Data System (ADS)

    Seshadri, Ashwin K.

    2016-04-01

    Monsoons involve increases in dry static energy (DSE), with primary contributions from increased shortwave radiation and condensation of water vapor, compensated by DSE export via horizontal fluxes in monsoonal circulations. We introduce a simple box-model characterizing evolution of the DSE budget to study nonlinear dynamics of steady-state monsoons. Horizontal fluxes of DSE are stabilizing during monsoons, exporting DSE and hence weakening the monsoonal circulation. By contrast latent heat addition (LHA) due to condensation of water vapor destabilizes, by increasing the DSE budget. These two factors, horizontal DSE fluxes and LHA, are most strongly dependent on the contrast in tropospheric mean temperature between land and ocean. For the steady-state DSE in the box-model to be stable, the DSE flux should depend more strongly on the temperature contrast than LHA; stronger circulation then reduces DSE and thereby restores equilibrium. We present conditions for this to occur. The main focus of the paper is describing conditions for bifurcation behavior of simple models. Previous authors presented a minimal model of abrupt monsoon transitions and argued that such behavior can be related to a positive feedback called the `moisture advection feedback'. However, by accounting for the effect of vertical lapse rate of temperature on the DSE flux, we show that bifurcations are not a generic property of such models despite these fluxes being nonlinear in the temperature contrast. We explain the origin of this behavior and describe conditions for a bifurcation to occur. This is illustrated for the case of the July-mean monsoon over India. The default model with mean parameter estimates does not contain a bifurcation, but the model admits bifurcation as parameters are varied.

  16. Analysis and Prediction of West African Moist Events during the Boreal Spring of 2009

    NASA Astrophysics Data System (ADS)

    Mera, Roberto Javier

    Weather and climate in Sahelian West Africa are dominated by two major wind systems, the southwesterly West African Monsoon (WAM) and the northeasterly (Harmattan) trade winds. In addition to the agricultural benefit of the WAM, the public health sector is affected given the relationship between the onset of moisture and end of meningitis outbreaks. Knowledge and prediction of moisture distribution during the boreal spring is vital to the mitigation of meningitis by providing guidance for vaccine dissemination. The goal of the present study is to (a) develop a climatology and conceptual model of the moisture regime during the boreal spring, (b) investigate the role of extra-tropical and Convectively-coupled Equatorial Waves (CCEWs) on the modulation of westward moving synoptic waves and (c) determine the efficacy of a regional model as a tool for predicting moisture variability. Medical reports during 2009, along with continuous meteorological observations at Kano, Nigeria, showed that the advent of high humidity correlated with cessation of the disease. Further analysis of the 2009 boreal spring elucidated the presence of short-term moist events that modulated surface moisture on temporal scales relevant to the health sector. The May moist event (MME) provided insight into interplays among climate anomalies, extra-tropical systems, equatorially trapped waves and westward-propagating synoptic disturbances. The synoptic disturbance initiated 7 May and traveled westward to the coast by 12 May. There was a marked, semi-stationary moist anomaly in the precipitable water field (kg m-2) east of 10°E through late April and early May, that moved westward at the time of the MME. Further inspection revealed a mid-latitude system may have played a role in increasing the latitudinal amplitude of the MME. CCEWs were also found to have an impact on the MME. A coherent Kelvin wave propagated through the region, providing increased monsoonal flow and heightened convection. A

  17. Local impacts of Saharan dust on convection and on the monsoon circulation during the pre-onset and the established monsoon periods

    NASA Astrophysics Data System (ADS)

    Lavaysse, C.; Flamant, C.; Grabowski, W. W.; Chaboureau, J.

    2012-12-01

    The aim of this study is to analyze the local impacts of dust on the West African monsoon circulation. Using different regional models (Meso-NH and WRF), dust schemes have been used to quantify the impacts of dust on convection and on the main components of the West African monsoon, such as the West African Heat Low (WAHL), African Easterly Waves (AEWs), monsoon and Harmatan winds. Two different periods have been simulated, one in 2006, during the AMMA campaign, investigated a 6-day pulsation of the West African heat low (WAHL) in summertime (14 to 20 July), with convective rainfall and dust bursts being observed over the Sahel at the beginning and end of the episode. Three Meso-NH simulations were designed which differed in their dust representation. This study highlights two effects of dust on the WAHL over the Sahara: a so-called direct effect associated with dust radiative heating, which increases the WAHL thickness, and a so called indirect effect that intensifies both the African easterly jet and a related African easterly wave. Using the observation provided by the FENNEC international project in June 2011, a second study has been done to better understand the local impacts of the dust during the pre-onset period, when the dust load in the mid-troposphere appears large. Using WRF simulations in an ensemble system, the sensitivity of the monsoon circulation to direct and indirect effects of the dust have been compared to the sensitivity of the large-scale forcings.

  18. Radiative impact of mineral dust on monsoon precipitation variability over West Africa

    SciTech Connect

    Zhao, Chun; Liu, Xiaohong; Leung, Lai-Yung R.; Hagos, Samson M.

    2011-03-01

    The radiative forcing of dust and its impact on precipitation over the West Africa monsoon (WAM) region is simulated using a coupled meteorology and aerosol/chemistry model (WRF-Chem). During the monsoon season, dust is a dominant contributor to AOD over West Africa. In the standard simulation, on 24-hour domain average, dust has a cooling effect (-6.11 W/m2) at the surface, a warming effect (6.94 W/m2) in the atmosphere, and a relatively small TOA forcing (0.83 W/m2). Dust modifies the surface energy budget and atmospheric diabatic heating and hence causes lower atmospheric cooling in the daytime but warming in the nighttime. As a result, atmospheric stability is increased in the daytime and reduced in the nighttime, leading to a reduction of late afternoon precipitation by up to 0.14 mm/hour (30%) and an increase of nocturnal and early morning precipitation by up to 0.04 mm/hour (23%) over the WAM region. Dust-induced reduction of diurnal precipitation variation improves the simulated diurnal cycle of precipitation when compared to measurements. However, daily precipitation is only changed by a relatively small amount (-0.14 mm/day or -4%). On the other hand, sensitivity simulations show that, for weaker-to-stronger absorbing dust, dust longwave warming effect in the nighttime surpasses its shortwave cooling effect in the daytime at the surface, leading to a less stable atmosphere associated with more convective precipitation in the nighttime. As a result, the dust-induced change of daily WAM precipitation varies from a significant reduction of -0.40 mm/day (-12%, weaker absorbing dust) to a small increase of 0.05 mm/day (1%, stronger absorbing dust). This variation originates from the competition between dust impact on daytime and nighttime precipitation, which depends on dust shortwave absorption. Dust reduces the diurnal variation of precipitation regardless of its absorptivity, but more reduction is associated with stronger absorbing dust.

  19. Study of aerosol transport through precipitation chemistry over Arabian Sea during winter and summer monsoons

    NASA Astrophysics Data System (ADS)

    Praveen, P. S.; Rao, P. S. P.; Safai, P. D.; Devara, P. C. S.; Chate, D. M.; Ali, K.; Momin, G. A.

    Precipitation samples over the Arabian Sea collected during Arabian Sea Monsoon Experiment (ARMEX) in 2002-2003 were examined for major water soluble components and acidity of aerosols during the period of winter and summer monsoon seasons. The pH of rain water was alkaline during summer monsoon and acidic during winter monsoon. Summer monsoon precipitation showed dominance of sea-salt components (˜90%) and significant amounts of non-sea salt (nss) Ca 2+ and SO 42-. Winter monsoon precipitation samples showed higher concentration of NO 3- and NH 4+ compared to that of summer monsoon, indicating more influence of anthropogenic sources. The rain water data is interpreted in terms of long-range transport and background pollution. In summer monsoon, air masses passing over the north African and Gulf continents which may be carrying nss components are advected towards the observational location. Also, prevailing strong southwesterly winds at surface level produced sea-salt aerosols which led to high sea-salt contribution in precipitation. While in winter monsoon, it was observed that, air masses coming from Asian region towards observational location carry more pollutants like NO 3-and nss SO 42- that acidify the precipitation.

  20. An assessment of improvements in global monsoon precipitation simulation in FGOALS-s2

    NASA Astrophysics Data System (ADS)

    Zhang, Lixia; Zhou, Tianjun

    2014-01-01

    The performance of Version 2 of the Flexible Global Ocean-Atmosphere-Land System model (FGOALS-s2) in simulating global monsoon precipitation (GMP) was evaluated. Compared with FGOALS-s1, higher skill in simulating the annual modes of climatological tropical precipitation and interannual variations of GMP are seen in FGOALS-s2. The simulated domains of the northwestern Pacific monsoon (NWPM) and North American monsoon are smaller than in FGOALS-s1. The main deficiency of FGOALS-s2 is that the NWPM has a weaker monsoon mode and stronger negative pattern in spring-fall asymmetric mode. The smaller NWPM domain in FGOALS-s2 is due to its simulated colder SST over the western Pacific warm pool. The relationship between ENSO and GMP is simulated reasonably by FGOALS-s2. However, the simulated precipitation anomaly over the South African monsoon region-South Indian Ocean during La Niña years is opposite to the observation. This results mainly from weaker warm SST anomaly over the maritime continent during La Niña years, leading to stronger upper-troposphere (lower-troposphere) divergence (convergence) over the Indian Ocean, and artificial vertical ascent (descent) over the Southwest Indian Ocean (South African monsoon region), inducing local excessive (deficient) rainfall. Comparison between the historical and pre-industrial simulations indicated that global land monsoon precipitation changes from 1901 to the 1970s were caused by internal variation of climate system. External forcing may have contributed to the increasing trend of the Australian monsoon since the 1980s. Finally, it shows that global warming could enhance GMP, especially over the northern hemispheric ocean monsoon and southern hemispheric land monsoon.

  1. Desert Dust and Monsoon Rain

    NASA Technical Reports Server (NTRS)

    Lau, William K. M.; Kim, Kyu-Myong

    2014-01-01

    For centuries, inhabitants of the Indian subcontinent have know that heavy dust events brought on by strong winds occur frequently in the pre-monsoon season, before the onset of heavy rain. Yet scientists have never seriously considered the possibility that natural dust can affect monsoon rainfall. Up to now, most studies of the impacts of aerosols on Indian monsoon rainfall have focused on anthropogenic aerosols in the context of climate change. However, a few recent studies have show that aerosols from antropogenic and natural sources over the Indian subcontinent may affect the transition from break to active monsoon phases on short timescales of days to weeks. Writing in Nature Geoscience, Vinoj and colleagues describe how they have shown that desert dust aerosols over the Arabian Sea and West Asia can strenghten the summer monsoon over the Indial subcontinent in a matter of days.

  2. Holocene Monsoon variability in East Africa: a marine perspective

    NASA Astrophysics Data System (ADS)

    Romahn, S.; Mackensen, A.; Groeneveld, J.; Pätzold, J.

    2012-12-01

    The processes that control past monsoon variability in the East African Tropics during the Holocene are poorly understood. Especially the role of Sea Surface Temperatures (SST) controlling East African Rainfall on millennial timescales, as it is observed on decadal timescales, is currently intensely debated. In addition, it has been suggested recently that the longitudinal migration of the Congo Air Boundary (CAB) modulates East African precipitation on a regional scale as well [Tierney et al., 2011]. Here, we present a high-resolution marine sediment record for the past 12 kyrs from offshore Tanzania, close to the Rufiji River delta, to contribute to the current debate from a marine point of view. We reconstructed past SST and δ18Oseawater, derived from planktic foraminiferal Mg/Ca and δ18O, and past Sea Surface Salinity (SSS) variations, derived from planktic foraminiferal Ba/Ca-ratios. In the vicinity of river deltas, Ba/Ca-ratios have potential to record precipitation changes in the rivers' catchment area. Our records show that East African precipitation, derived from Ba/Ca-ratios, roughly varies in concert with Indian Ocean SST, suggesting higher Indian Ocean SST to be an important prerequisite for stronger precipitation, and hence an intense monsoon episode in East Africa. We calculated the difference (ΔSST) between our record of Indian Ocean SST and SST of the tropical Atlantic [Weldeab et al., 2005], showing that ΔSST variability resembles the isotopic pattern of the Kilimanjaro ice core record [Thompson et al., 2002]. We suggest this to be the consequence of a longitudinal movement of the CAB over the African Continent, changing the trajectory of Indian Ocean moisture into the continent and therefore affecting the δ18O of the East African rainout. Thompson, L. G., et al. (2002), Kilimanjaro Ice Core Records: Evidence of Holocene Climate Change in Tropical Africa, Science, 298, 589-593. Tierney, J. E., et al. (2011), Late Quaternary behavior of the

  3. Surface wave effects on water temperature in the Baltic Sea: simulations with the coupled NEMO-WAM model

    NASA Astrophysics Data System (ADS)

    Alari, Victor; Staneva, Joanna; Breivik, Øyvind; Bidlot, Jean-Raymond; Mogensen, Kristian; Janssen, Peter

    2016-08-01

    Coupled circulation (NEMO) and wave model (WAM) system was used to study the effects of surface ocean waves on water temperature distribution and heat exchange at regional scale (the Baltic Sea). Four scenarios—including Stokes-Coriolis force, sea-state dependent energy flux (additional turbulent kinetic energy due to breaking waves), sea-state dependent momentum flux and the combination these forcings—were simulated to test the impact of different terms on simulated temperature distribution. The scenario simulations were compared to a control simulation, which included a constant wave-breaking coefficient, but otherwise was without any wave effects. The results indicate a pronounced effect of waves on surface temperature, on the distribution of vertical temperature and on upwelling's. Overall, when all three wave effects were accounted for, did the estimates of temperature improve compared to control simulation. During the summer, the wave-induced water temperature changes were up to 1 °C. In northern parts of the Baltic Sea, a warming of the surface layer occurs in the wave included simulations in summer months. This in turn reduces the cold bias between simulated and measured data, e.g. the control simulation was too cold compared to measurements. The warming is related to sea-state dependent energy flux. This implies that a spatio-temporally varying wave-breaking coefficient is necessary, because it depends on actual sea state. Wave-induced cooling is mostly observed in near-coastal areas and is the result of intensified upwelling in the scenario, when Stokes-Coriolis forcing is accounted for. Accounting for sea-state dependent momentum flux results in modified heat exchange at the water-air boundary which consequently leads to warming of surface water compared to control simulation.

  4. Global Monsoon Dynamics and Climate Change

    NASA Astrophysics Data System (ADS)

    Zhisheng, An; Guoxiong, Wu; Jianping, Li; Youbin, Sun; Yimin, Liu; Weijian, Zhou; Yanjun, Cai; Anmin, Duan; Li, Li; Jiangyu, Mao; Hai, Cheng; Zhengguo, Shi; Liangcheng, Tan; Hong, Yan; Hong, Ao; Hong, Chang; Juan, Feng

    2015-05-01

    This article provides a comprehensive review of the global monsoon that encompasses findings from studies of both modern monsoons and paleomonsoons. We introduce a definition for the global monsoon that incorporates its three-dimensional distribution and ultimate causes, emphasizing the direct drive of seasonal pressure system changes on monsoon circulation and depicting the intensity in terms of both circulation and precipitation. We explore the global monsoon climate changes across a wide range of timescales from tectonic to intraseasonal. Common features of the global monsoon are global homogeneity, regional diversity, seasonality, quasi-periodicity, irregularity, instability, and asynchroneity. We emphasize the importance of solar insolation, Earth orbital parameters, underlying surface properties, and land-air-sea interactions for global monsoon dynamics. We discuss the primary driving force of monsoon variability on each timescale and the relationships among dynamics on multiple timescales. Natural processes and anthropogenic impacts are of great significance to the understanding of future global monsoon behavior.

  5. Tohono O'odham Monsoon Climatology

    NASA Astrophysics Data System (ADS)

    Ackerman, G.

    2006-12-01

    The North American monsoon is a summertime weather phenomenon that develops over the southwestern North America. For thousands of years the Tohono O'odham people of this area have depended on the associated rainy season (Jukiabig Masad) to grow traditional crops using runoff agriculture. Today, the high incidence of Type II diabetes among native people has prompted many to return to their traditional agricultural diets. Local monsoon onset dates and the North American Regional Reanalysis dataset were used to develop a 24-year Tohono O'odham Nation (TON) monsoon and pre-monsoon climatology that can be used as a tool for planning runoff agriculture. Using monsoon composite datasets, temporal and spatial correlations between antecedent period meteorological variables, monsoon onset dates and total monsoon precipitation were examined to identify variables that could be useful in predicting the onset and intensity of the monsoon. The results suggest additional research is needed to identify variables related to monsoon onset and intensity.

  6. How well do land surface models reproduce the water and energy cycles in the West African monsoon system ? Evaluation over the Upper Ouémé basin, Benin (ALMIP2 project)

    NASA Astrophysics Data System (ADS)

    Peugeot, C.; Boone, A. A.; Demarty, J.; manuela, G.; Laurent, K.; Cappelaere, B.; Awessou, B.; Cohard, J.; Galle, S.; Gascon, T.; Getirana, A.; Hector, B.; Mamadou, O.; Richard, A.; Seghieri, J.; Séguis, L.

    2013-12-01

    Land surface models (LSMs) are widely used in environmental and climate sciences to simulate matter (water, carbon) and energy exchanges between the continental surface and the atmosphere. They are also increasingly used in a wide range of applications such as impact studies on land use management or climate change. The AMMA project and the associated observation campaigns provided unique data-sets to drive land surface models and to evaluate their results over the West African region, where such high added-value information has been lacking. In the framework of the ALMIP2 project (AMMA Land surface Model Inter-comparison Project - phase 2), simulations from about 20 LSMs were done on three contrasted meso-scale domains in Mali, Niger and Benin, over the period 2005-2008 using the same forcing data sets at 0.05 degree and 30 minutes space-time resolution. This talk analyses the simulated water and energy budget components on the sub-humid upper Ouémé basin (10,000 km2, Benin site), where the high-quality rainfall and runoff datasets allow a detailed and original hydrological evaluation of these meso-scale simulations. As expected, the model inter-comparison shows large differences in the water and energy partitioning, either at the annual (see figure) or intra-seasonal time scale. Most of them do not reproduce the observed runoff, with annual biases ranging from -100% to 200 %. The multi-model mean Evapotranspiration (ET) correctly matches the observations, specially in the rainy season, with contrasted simulations of evaporation vs. transpiration from one model to the other. The identification of the more realistic water and energy partitioning is a key issue addressed by the ALMIP2 project. Previous studies performed in the AMMA framework on the Oueme basin highlighted the key role of below-ground water dynamics in the hydrological cycle (lateral transfer to rivers, groundwater seasonal recharge-discharge, ...). Moreover, field evidences suggested that

  7. Response of the Surface Circulation of the Arabian Sea to Monsoonal Forcing

    NASA Astrophysics Data System (ADS)

    Beal, L. M.; Hormann, V.; Lumpkin, R.; Foltz, G. R.

    2014-12-01

    We use two decades of drifter and satellite data to examine the monthly evolution of the surface circulation of the Arabian Sea, which reverses annually in response to the Indian monsoon winds. Most significantly, we find that in the transition from winter to summer circulations, northward flow appears along the length of the western boundary as early as March or April, one or two months before the onset of the southwest monsoon winds. This reversal is initiated by annual Rossby waves, which in turn are initiated by wind curl forcing during the previous southwest monsoon. These results lead us to speculate that there is an oceanic mechanism through which one monsoon may precondition the next. Previous studies of monsoon circulations with lower temporal resolution have highlighted basin-wide currents and connections that are not found to exist in the monthly fields. In particular, we find that the Northeast Monsoon Current does not reach the western boundary and there is no counter-rotating gyre system during boreal winter. South of the equator, the eastward-flowing South Equatorial Counter Current (SECC) is present year-round, even though equatorial winds are strongly influenced by the monsoons. Semi-annual variability of the SECC is governed by Ekman pumping over the south equatorial gyre (or Seychelles dome) and, surprisingly, it is weakest during the northeast monsoon. This region has important influence on the atmosphere and its link to the monsoons deserves further investigation. The East African Coastal Current feeds into the SECC from the boundary. During the southwest monsoon it overshoots the equator and splits, feeding both northward into the Somali Current and eastward into the SECC after looping back across the equator. This apparent retroflection of the EACC is what was previously known as the southern gyre and is obscured at the surface by strong, locally wind-driven, cross-equatorial Ekman transport. Finally, there is broad, strong eastward flow at

  8. Coupling of WRF meteorological model to WAM spectral wave model through sea surface roughness at the Balearic Sea: impact on wind and wave forecasts

    NASA Astrophysics Data System (ADS)

    Tolosana-Delgado, R.; Soret, A.; Jorba, O.; Baldasano, J. M.; Sánchez-Arcilla, A.

    2012-04-01

    Meteorological models, like WRF, usually describe the earth surface characteristics by tables that are function of land-use. The roughness length (z0) is an example of such approach. However, over sea z0 is modeled by the Charnock (1955) relation, linking the surface friction velocity u*2 with the roughness length z0 of turbulent air flow, z0 = α-u2* g The Charnock coefficient α may be considered a measure of roughness. For the sea surface, WRF considers a constant roughness α = 0.0185. However, there is evidence that sea surface roughness should depend on wave energy (Donelan, 1982). Spectral wave models like WAM, model the evolution and propagation of wave energy as a function of wind, and include a richer sea surface roughness description. Coupling WRF and WAM is thus a common way to improve the sea surface roughness description of WRF. WAM is a third generation wave model, solving the equation of advection of wave energy subject to input/output terms of: wind growth, energy dissipation and resonant non-linear wave-wave interactions. Third generation models work on the spectral domain. WAM considers the Charnock coefficient α a complex yet known function of the total wind input term, which depends on the wind velocity and on the Charnock coefficient again. This is solved iteratively (Janssen et al., 1990). Coupling of meteorological and wave models through a common Charnock coefficient is operationally done in medium-range met forecasting systems (e.g., at ECMWF) though the impact of coupling for smaller domains is not yet clearly assessed (Warner et al, 2010). It is unclear to which extent the additional effort of coupling improves the local wind and wave fields, in comparison to the effects of other factors, like e.g. a better bathymetry and relief resolution, or a better circulation information which might have its influence on local-scale meteorological processes (local wind jets, local convection, daily marine wind regimes, etc.). This work, within the

  9. Three million years of monsoon variability over the northern Sahara

    NASA Astrophysics Data System (ADS)

    Larrasoana, J. C.; Roberts, A. P.; Rohling, E. J.; Winklhofer, M.; Wehausen, R.

    2003-04-01

    We present a 3 million-year record of aeolian dust supply into the eastern Mediterranean Sea, based on hematite contents derived from magnetic properties of sediments form ODP Site 967. Our record has an average temporal resolution of ˜400~years. We deduce that the aeolian hematite in eastern Mediterranean sediments derived from eastern Algerian, Libyan, and western Egyptian lowlands located north of the central Saharan watershed (˜21o~N). We relate dust-flux minima to penetration of the African summer monsoon front to the north of the central Saharan watershed. This would have enhanced soil humidity and vegetation cover in the source regions, in agreement with results from "green Sahara" climate models. Our results indicate that this northward monsoon penetration occured pervasively during insolation maxima throughout the last 3 million years. As would be expected, this orbital precession-scale mechanism is modulated on both short (95 kyr) and long (406 kyr) eccentricity time scales. We also observe a strong expression of the 41-kyr obliquity cycle. There is a marked increase in sub-Milankovitch variability around the Mid-Pleistocene transition (˜0.95~Ma), which suggests a link between millennial-scale variability, including monsoon dynamics, and the size of the northern hemisphere ice sheets.

  10. Indian Monsoon Depression: Climatology and Variability

    SciTech Connect

    Yoon, Jin-Ho; Huang, Wan-Ru

    2012-03-09

    The monsoon climate is traditionally characterized by large seasonal rainfall and reversal of wind direction (e.g., Krishnamurti 1979). Most importantly this rainfall is the major source of fresh water to various human activities such as agriculture. The Indian subcontinent resides at the core of the Southeast Asian summer monsoon system, with the monsoon trough extended from northern India across Indochina to the Western Tropical Pacific (WTP). Large fraction of annual rainfall occurs during the summer monsoon season, i.e., June - August with two distinct maxima. One is located over the Bay of Bengal with rainfall extending northwestward into eastern and central India, and the other along the west coast of India where the lower level moist wind meets the Western Ghat Mountains (Saha and Bavardeckar 1976). The rest of the Indian subcontinent receives relatively less rainfall. Various weather systems such as tropical cyclones and weak disturbances contribute to monsoon rainfall (Ramage 1971). Among these systems, the most efficient rain-producing system is known as the Indian monsoon depression (hereafter MD). This MD is critical for monsoon rainfall because: (i) it occurs about six times during each summer monsoon season, (ii) it propagates deeply into the continent and produces large amounts of rainfall along its track, and (iii) about half of the monsoon rainfall is contributed to by the MDs (e.g., Krishnamurti 1979). Therefore, understanding various properties of the MD is a key towards comprehending the veracity of the Indian summer monsoon and especially its hydrological process.

  11. Evaluation of Global Monsoon Precipitation Changes based on Five Reanalysis Datasets

    SciTech Connect

    Lin, Renping; Zhou, Tianjun; Qian, Yun

    2014-02-01

    With the motivation to identify whether or not a reasonably simulated atmospheric circulation would necessarily lead to a successful reproduction of monsoon precipitation, the performances of five sets of reanalysis data (NCEP2, ERA40, JRA25, ERA-Interim and MERRA) in reproducing the climatology, interannual variation and long-term trend of global monsoon (GM) precipitation are comprehensively evaluated. In order to better understand the variability and long-term trend of GM precipitation, we also examined the major components of water budget, including evaporation, water vapor convergence and the change in local water vapor storage, based on five reanalysis datasets. The results show that all five reanalysis data reasonably reproduce the climatology of GM precipitation. The ERA-Interim (NCEP2) shows the highest (lowest) skill among the five datasets. The observed GM precipitation shows an increasing tendency during 1979-2001 along with a strong interannual variability, which is reasonably reproduced by the five sets of reanalysis data. The observed increasing trend of GM precipitation is dominated by the contribution from the North African, North American and Australian monsoons. All five data fail in reproducing the increasing tendency of North African monsoon precipitation. The wind convergence term in water budget equation dominate the GM precipitation variation, indicating a consistency between the GM precipitation and the seasonal change of prevailing wind.

  12. Monsoon-Enso Relationships: A New Paradigm

    NASA Technical Reports Server (NTRS)

    Lau, K. M.; Einaudi, Franco (Technical Monitor)

    2000-01-01

    This article is partly a review and partly a new research paper on monsoon-ENSO relationship. The paper begins with a discussion of the basic relationship between the Indian monsoon and ENSO dating back to the work of Sir Gilbert Walker up to research results in more recent years. Various factors that may affect the monsoon-ENSO, relationship, including regional coupled ocean-atmosphere processes, Eurasian snow cover, land-atmosphere hydrologic feedback, intraseasonal oscillation, biennial variability and inter-decadal variations, are discussed. The extreme complex and highly nonlinear nature of the monsoon-ENSO relationship is stressed. We find that for regional impacts on the monsoon, El Nino and La Nina are far from simply mirror images of each other. These two polarities of ENSO can have strong or no impacts on monsoon anomalies depending on the strength of the intraseasonal oscillations and the phases of the inter-decadal variations. For the Asian-Australian monsoon (AAM) as a whole, the ENSO impact is effected through a east-west shift in the Walker Circulation. For rainfall anomalies over specific monsoon areas, regional processes play important roles in addition to the shift in the Walker Circulation. One of the key regional processes identified for the boreal summer monsoon is the anomalous West Pacific Anticyclone (WPA). This regional feature has similar signatures in interannual and intraseasonal time scales and appears to determine whether the monsoon-ENSO relationship is strong or weak in a given year. Another important regional feature includes a rainfall and SST dipole across the Indian Ocean, which may have strong impact on the austral summer monsoon. Results are shown indicating that monsoon surface wind forcings may induce a strong biennial signal in ENSO and that strong monsoon-ENSO coupling may translate into pronounced biennial variability in ENSO. Finally, a new paradigm is proposed for the study of monsoon variability. This paradigm provides

  13. Global Monsoon Rainfall - What the future holds?

    NASA Astrophysics Data System (ADS)

    Endo, H.; Kitoh, A.; Kumar, K.; Cavalcanti, I. F.; Goswami, P.; Zhou, T.

    2012-12-01

    We provide a latest view of global as well as regional monsoonal rainfall and their changes in the twenty-first century as projected by state-of-the-art climate models participated in the Coupled Model Intercomparison Project phase 5 (CMIP5). The global monsoon area (GMA) defined based on the annual range in precipitation will expand mainly over the central to eastern tropical Pacific, the southern Indian Ocean, and eastern Asia. The global monsoon intensity (GMI) and the global monsoon total precipitation (GMP) are likely to increase, implying that monsoon-related precipitation will remarkably increase in a warmer climate. Heavy precipitation indices are projected to increase much more than the mean precipitation, and their percentage changes depend more on the emission scenario compared to those for mean precipitation. Over the Asian monsoon domain, median increase rate for precipitation is larger than that over other monsoon domains, indicating that the sensitivity of Asian monsoon to global warming is stronger than that of other monsoons. For seasonal progress of monsoon rainfall, CMIP5 models project that the monsoon retreat dates will delay, while the onset dates will either advance or show no change, resulting in lengthening of the monsoon season. It is found that the increase of the global monsoon precipitation can be attributed to the increases of moisture convergence due to increased water vapor in the air column and surface evaporation, offset to a certain extent by the weakening of the monsoon circulation (Figure 1).Figure 1: Time series of anomalies during summer season (%; 20 years running mean) relative to the base period average (1986-2005) over the land global monsoon domain for (a) precipitation (mm day-1), (b) evaporation (mm day-1), (c) water vapor flux convergence in the lower (below 500hPa) troposphere (mm day-1), and (d) wind convergence in the lower troposphere (10-3 kg m-2 s-1), based on 23 CMIP5 model monthly outputs. Historical (grey

  14. Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoon

    SciTech Connect

    Sperber, K R; Yasunari, T

    2005-12-20

    The Earth's monsoon systems are the life-blood of more than two-thirds of the world's population through the rainfall they provide to the mainly agrarian societies they influence. More than 60 experts gathered to assess the current understanding of monsoon variability and to highlight outstanding problems simulating the monsoon.

  15. Plio-pleistocene African climate

    SciTech Connect

    deMenocal, P.B.

    1995-10-06

    Marine records of African climate variability document a shift toward more arid conditions after 2.8 million years ago (Ma), evidently resulting from remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles. African climate before 2.8 Ma was regulated by low-latitude insolation forcing of monsoonal climate due to Earth orbital precession. Major steps in the evolution of African hominids and other vertebrates are coincident with shifts to more arid, open conditions near 2.8 Ma, 1.7 Ma, and 1.0 Ma, suggesting that some Pliocene (Plio)-Pleistocene speciation events may have been climatically mediated. 65 refs., 6 figs.

  16. Plio-Pleistocene African Climate

    NASA Astrophysics Data System (ADS)

    Demenocal, Peter B.

    1995-10-01

    Marine records of African climate variability document a shift toward more arid conditions after 2.8 million years ago (Ma), evidently resulting from remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles. African climate before 2.8 Ma was regulated by low-latitude insolation forcing of monsoonal climate due to Earth orbital precession. Major steps in the evolution of African hominids and other vertebrates are coincident with shifts to more arid, open conditions near 2.8 Ma, 1.7 Ma, and 1.0 Ma, suggesting that some Pliocene (Plio)-Pleistocene speciation events may have been climatically mediated.

  17. Indian monsoon variations during three contrasting climatic periods: The Holocene, Heinrich Stadial 2 and the last interglacial-glacial transition

    NASA Astrophysics Data System (ADS)

    Zorzi, Coralie; Sanchez Goñi, Maria Fernanda; Anupama, Krishnamurthy; Prasad, Srinivasan; Hanquiez, Vincent; Johnson, Joel; Giosan, Liviu

    2015-10-01

    In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric

  18. Indian monsoon variations during three contrasting climatic periods: the Holocene, Heinrich Stadial 2 and the last interglacial-glacial transition

    NASA Astrophysics Data System (ADS)

    Zorzi, Coralie; Fernanda Sanchez Goñi, Maria; Anupama, Krishnamurthy; Prasad, Srinivasan; Hanquiez, Vincent; Johnson, Joel; Giosan, Liviu

    2016-04-01

    In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4,200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4,200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric

  19. The time-transgressive termination of the African Humid Period

    NASA Astrophysics Data System (ADS)

    Shanahan, Timothy M.; McKay, Nicholas P.; Hughen, Konrad A.; Overpeck, Jonathan T.; Otto-Bliesner, Bette; Heil, Clifford W.; King, John; Scholz, Christopher A.; Peck, John

    2015-02-01

    During the African Humid Period about 14,800 to 5,500 years ago, changes in incoming solar radiation during Northern Hemisphere summers led to the large-scale expansion and subsequent collapse of the African monsoon. Hydrologic reconstructions from arid North Africa show an abrupt onset and termination of the African Humid Period. These abrupt transitions have been invoked in arguments that the African monsoon responds rapidly to gradual forcing as a result of nonlinear land surface feedbacks. Here we present a reconstruction of precipitation in humid tropical West Africa for the past 20,000 years using the hydrogen isotope composition of leaf waxes preserved in sediments from Lake Bosumtwi, Ghana. We show that over much of tropical and subtropical Africa the monsoon responded synchronously and predictably to glacial reorganizations of overturning circulation in the Atlantic Ocean, but the response to the relatively weaker radiative forcing during the African Humid Period was more spatially and temporally complex. A synthesis of hydrologic reconstructions from across Africa shows that the termination of the African Humid Period was locally abrupt, but occurred progressively later at lower latitudes. We propose that this time-transgressive termination of the African Humid Period reflects declining rainfall intensity induced directly by decreasing summer insolation as well as the gradual southward migration of the tropical rainbelt that occurred during this interval.

  20. TIGERZ I: Aerosols, Monsoon and Synergism

    NASA Astrophysics Data System (ADS)

    Holben, B. N.; Tripathi, S. N.; Schafer, J. S.; Giles, D. M.; Eck, T. F.; Sinyuk, A.; Smirnov, A.; Krishnmoorthy, K.; Sorokin, M. G.; Newcomb, W. W.; Tran, A. K.; Sikka, D. R.; Goloub, P.; O'Neill, N. T.; Abboud, I.; Randles, C.; Niranjan, K.; Dumka, U. C.; Tiwari, S.; Devara, P. C.; Kumar, S.; Remer, L. A.; Kleidman, R.; Martins, J. V.; Kahn, R.

    2008-12-01

    The Indo-Gangetic Plain of northern India encompasses a vast complex of urban and rural landscapes, cultures that serve as anthropogenic sources of fine mode aerosols mixed with coarse mode particles transported from SW Asia. The summer monsoon and fall Himalayan snowmelt provide the agricultural productivity to sustain an extremely high population density whose affluence is increasing. Variations in the annual monsoon precipitation of 10% define drought, normal and a wet season; the net effects on the ecosystems and quality of life can be dramatic. Clearly investigation of anthropogenic and natural aerosol impacts on the monsoon, either through the onset, monsoon breaks or end points are a great concern to understand and ultimately mitigate. Many national and international field campaigns are being planned and conducted to study various aspects of the Asian monsoon and some coordinated under the Asian Monsoon Years (AMY) umbrella. A small program called TIGERZ conducted during the pre-monsoon of 2008 in North Central India can serve as a model for contributing significant resources to existing field programs while meeting immediate project goals. This poster will discuss preliminary results of the TIGERZ effort including ground-based measurements of aerosol properties in the I-G from AERONET and synergism with various Indian programs, satellite observations and aerosol modeling efforts.

  1. Monsoon '90 - Preliminary SAR results

    NASA Technical Reports Server (NTRS)

    Dubois, Pascale C.; Van Zyl, Jakob J.; Guerra, Abel G.

    1992-01-01

    Multifrequency polarimetric synthetic aperture radar (SAR) images of the Walnut Gulch watershed near Tombstone, Arizona were acquired on 28 Mar. 1990 and on 1 Aug. 1990. Trihedral corner reflectors were deployed prior to both overflights to allow calibration of the two SAR data sets. During both overflights, gravimetric soil moisture and dielectric constant measurements were made. Detailed vegetation height, density, and water content measurements were made as part of the Monsoon 1990 Experiment. Preliminary results based on analysis of the multitemporal polarimetric SAR data are presented. Only the C-band data (5.7-cm wavelength) radar images show significant difference between Mar. and Aug., with the strongest difference observed in the HV images. Based on the radar data analysis and the in situ measurements, we conclude that these differences are mainly due to changes in the vegetation and not due to the soil moisture changes.

  2. Monsoon 1990: Preliminary SAR results

    NASA Technical Reports Server (NTRS)

    Vanzyl, Jakob J.; Dubois, Pascale; Guerra, Abel

    1991-01-01

    Multifrequency polarimetric synthetic aperture radar (SAR) images of the Walnut Gulch watershed near Tombstone, Arizona were acquired on 28 Mar. 1990 and on 1 Aug. 1990. Trihedral corner reflectors were deployed prior to both overflights to allow calibration of the two SAR data sets. During both overflights, gravimetric soil moisture and dielectric constant measurements were made. Detailed vegetation height, density, and water content measurements were made as part of the Monsoon 1990 Experiment. Preliminary results based on analysis of the multitemporal polarimetric SAR data are presented. Only the C-band data (5.7-cm wavelength) radar images show significant difference between Mar. and Aug., with the strongest difference observed in the HV images. Based on the radar data analysis and the in situ measurements, we conclude that these differences are mainly due to changes in the vegetation and not due to the soil moisture changes.

  3. Multidecadal to multicentury scale collapses of Northern Hemisphere monsoons over the past millennium

    PubMed Central

    Asmerom, Yemane; Polyak, Victor J.; Rasmussen, Jessica B. T.; Burns, Stephen J.; Lachniet, Matthew

    2013-01-01

    Late Holocene climate in western North America was punctuated by periods of extended aridity called megadroughts. These droughts have been linked to cool eastern tropical Pacific sea surface temperatures (SSTs). Here, we show both short-term and long-term climate variability over the last 1,500 y from annual band thickness and stable isotope speleothem data. Several megadroughts are evident, including a multicentury one, AD 1350–1650, herein referred to as Super Drought, which corresponds to the coldest period of the Little Ice Age. Synchronicity between southwestern North American, Chinese, and West African monsoon precipitation suggests the megadroughts were hemispheric in scale. Northern Hemisphere monsoon strength over the last millennium is positively correlated with Northern Hemisphere temperature and North Atlantic SST. The megadroughts are associated with cooler than average SST and Northern Hemisphere temperatures. Furthermore, the megadroughts, including the Super Drought, coincide with solar insolation minima, suggesting that solar forcing of sea surface and atmospheric temperatures may generate variations in the strength of Northern Hemisphere monsoons. Our findings seem to suggest stronger (wetter) Northern Hemisphere monsoons with increased warming. PMID:23716648

  4. Multidecadal to multicentury scale collapses of Northern Hemisphere monsoons over the past millennium.

    PubMed

    Asmerom, Yemane; Polyak, Victor J; Rasmussen, Jessica B T; Burns, Stephen J; Lachniet, Matthew

    2013-06-11

    Late Holocene climate in western North America was punctuated by periods of extended aridity called megadroughts. These droughts have been linked to cool eastern tropical Pacific sea surface temperatures (SSTs). Here, we show both short-term and long-term climate variability over the last 1,500 y from annual band thickness and stable isotope speleothem data. Several megadroughts are evident, including a multicentury one, AD 1350-1650, herein referred to as Super Drought, which corresponds to the coldest period of the Little Ice Age. Synchronicity between southwestern North American, Chinese, and West African monsoon precipitation suggests the megadroughts were hemispheric in scale. Northern Hemisphere monsoon strength over the last millennium is positively correlated with Northern Hemisphere temperature and North Atlantic SST. The megadroughts are associated with cooler than average SST and Northern Hemisphere temperatures. Furthermore, the megadroughts, including the Super Drought, coincide with solar insolation minima, suggesting that solar forcing of sea surface and atmospheric temperatures may generate variations in the strength of Northern Hemisphere monsoons. Our findings seem to suggest stronger (wetter) Northern Hemisphere monsoons with increased warming.

  5. A hemispheric climatology of monsoon depressions

    NASA Astrophysics Data System (ADS)

    Hurley, J. V.; Boos, W.

    2012-12-01

    Monsoon depressions are large (1000-2000 km diameter) cyclonic low pressure systems having organized deep convection, best known for forming in the Bay of Bengal and migrating northwest over northern India in the monsoon trough. About 3 to 5 of these systems occur during each monsoon season, contributing about half of the Indian summer rainfall. Despite their importance as a precipitation source, their dynamics are poorly constrained. Furthermore, although they do occur elsewhere, such as around Australia and in the southern Indian Ocean, there does not exist a collective inventory of these systems outside of the Bay of Bengal region. Here we present a climatology of monsoon depressions produced from the ERA-Interim Reanalysis. Feature tracks are identified using an automated tracking algorithm (K. Hodges' TRACK code) applied to the 850 hPa relative vorticity field for local summer, 1989 to 2003. Using criteria based on relative vorticity and sea level pressure, cyclonic low pressure systems are separated into different intensity categories, one of which corresponds to the definition for monsoon depressions used by the India Meteorological Department. The resultant distribution of storms obtained for the Bay of Bengal region compares well with a previously compiled climatology of monsoon depressions that was limited to the region surrounding India. Having validated our ability to identify monsoon depressions in their classic genesis region near India, we then extend the methods to include the western Pacific, Australia, and the southern Indian Ocean. Track distributions and composite structures of monsoon depressions for these different regions will be presented.

  6. The Influence of Somalia and Oman Upwellings on the Indian Summer Monsoon

    NASA Astrophysics Data System (ADS)

    Izumo, T.; de Boyer Montégut, C.; Luo, J.; Behera, S. K.; Masson, S.; Yamagata, T.

    2006-12-01

    What controls the strength of the Indian summer monsoon is not well known yet. The Somalia and Oman upwellings peak during the summer monsoon and strongly cool the Sea Surface Temperature (SST) in the Western Arabian Sea. A slight change in their strength can thus have strong impacts on the SST and extent of the Indian ocean warm pool, which is the main source of moisture for the monsoon. Here the role of Somalia and Oman upwellings on the strength of the Indian monsoon is evidenced using both observations and the high resolution SINTEX-F Coupled Global Circulation Model (CGCM), which accurately simulates the monsoon. Within the CGCM, the spring increase and summer maximum of the Western Arabian Sea coastal upwellings are removed in a sensitivity experiment (SENS) by imposing over the Indian Ocean the mean windstress, instead of the temporally varying one of the control experiment (CTL). The ocean circulation becomes nearly stationnary. In summer, the main change in SST in SENS is a strong warming (up to 2°C) along the East African coast where coastal upwelling and off-shore horizontal advection of upwelled waters usually cool SST. This SST warming leads to a strong increase in the monsoon extent and strength along the West coast of India up to 5 mm/day (about 25% of CTL). The mechanism is as follow: in SENS, summer SST warming in the upwelling region causes anomalous evaporation, which increases specific humidity of the air masses going over the upwelling region. The humidity transport thus increases all over the Arabian sea towards the coastal Ghats mountains of India. This finally leads to enhanced moisture convergence and precipitations along the West coast of India. This role of coastal upwelling and associated SST variations on the Indian monsoon is confirmed by observations since 1980. Correlation analysis shows that enhanced summer precipitations on the West Indian coast are usually associated with warmer SST in summer East of Somalia-Oman and North

  7. Basic mechanism for abrupt monsoon transitions

    PubMed Central

    Levermann, Anders; Schewe, Jacob; Petoukhov, Vladimir; Held, Hermann

    2009-01-01

    Monsoon systems influence the livelihood of hundreds of millions of people. During the Holocene and last glacial period, rainfall in India and China has undergone strong and abrupt changes. Though details of monsoon circulations are complicated, observations reveal a defining moisture-advection feedback that dominates the seasonal heat balance and might act as an internal amplifier, leading to abrupt changes in response to relatively weak external perturbations. Here we present a minimal conceptual model capturing this positive feedback. The basic equations, motivated by observed relations, yield a threshold behavior, robust with respect to addition of other physical processes. Below this threshold in net radiative influx, R c, no conventional monsoon can develop; above R c, two stable regimes exist. We identify a nondimensional parameter l that defines the threshold and makes monsoon systems comparable with respect to the character of their abrupt transition. This dynamic similitude may be helpful in understanding past and future variations in monsoon circulation. Within the restrictions of the model, we compute R c for current monsoon systems in India, China, the Bay of Bengal, West Africa, North America, and Australia, where moisture advection is the main driver of the circulation. PMID:19858472

  8. Three exceptionally strong East-Asian summer monsoon events during glacial times in the past 470 kyr

    NASA Astrophysics Data System (ADS)

    Rousseau, D.-D.; Wu, N.; Pei, Y.; Li, F.

    2009-04-01

    African summer monsoon with relatively low surface water salinity in the Indian Ocean. Changes in the precipitation regime could correspond to a response to a particular astronomical configuration (low obliquity, low precession, summer solstice at perihelion) leading to an increased summer insolation gradient between the tropics and the high latitudes and resulting in enhanced atmospheric water transport from the tropics to the African and Asian continents. However, other climate drivers such as reorganization of marine and atmospheric circulations, tectonic, and the extent of the Northern Hemisphere ice sheet are also discussed.

  9. Three exceptionally strong East-Asian summer monsoon events during glacial conditions in the past 470 kyr

    NASA Astrophysics Data System (ADS)

    Rousseau, D.-D.; Wu, N.; Pei, Y.; Li, F.

    2008-12-01

    African summer monsoon with relatively low surface water salinity in the Indian Ocean. Changes in the precipitation regime could correspond to a response to a particular astronomical configuration (low obliquity, low precession, summer solstice at perihelion) leading to an increased summer insolation gradient between the tropics and the high latitudes and resulting in enhanced atmospheric water transport from the tropics to the African and Asian continents. However, other climate drivers such as reorganization of marine and atmospheric circulations, tectonic, and the extent of the Northern Hemisphere ice sheet are also discussed.

  10. Eocene precipitation: a global monsoon?

    NASA Astrophysics Data System (ADS)

    Greenwood, D. R.; Huber, M.

    2011-12-01

    The Eocene was the warmest part of the Cenozoic, with warm climates extending across all continents including Antarctica, and extending into the Arctic. Substantive paleobotanical evidence (leaf floras and palynofloras) has demonstrated the existence of broadleaf and coniferous polar forests - a circumpolar rain forest - at both poles. North and South America, Australia, and China in the Eocene were well-forested and humid continents, in contrast to today where 2/3 of these continental areas are arid or semi-arid and lack forests. Each of these regions reflect past climate states - mesothermal moist climates with low thermal seasonality at high latitudes - that have no analog in the modern world. Recent modelling and paleontological proxy data, however, is revealing a high degree of seasonality to precipitation for these continental areas, indicating a monsoon-type precipitation regime may have characterized Eocene 'greenhouse climates'. Paleobotanical proxies offer 2 methods for estimated paleo-precipitation; leaf physiognomy (including both CLAMP and leaf area analysis), and quantitative analysis of nearest living relatives ('NLRs') of macrofloras. Presented here are 1) an updated leaf area analysis calibration with smaller errors of the estimate than previously provided, and 2) analyses of fossil floras from North America, Canada, the Arctic, and Australia. Analysis of the Canadian floras indicate moist climates (MAP >100cm/a) in the early and middle Eocene at middle and high paleolatitudes. Precipitation for western North America at mid-latitudes is also estimated as high, but a seasonally dry interior and south-east is indicated. For Australia, precipitation in the south-east is estimated >120 cm/a, but the macrofloras indicate a drier interior (MAP ~60 cm/a) and seasonal drought, contradicting estimates of ~120 cm/a based on NLR analysis of pollen floras. Recently published data show that north-eastern China in the Eocene had a monsoonal-type seasonality for

  11. Monsoon abrupt change and its dominant factors

    NASA Astrophysics Data System (ADS)

    Yao, Qiang; Fu, Conbin

    2010-05-01

    Abrupt changes of monsoon are apparent in the geological record of climate over various timescales. During Holocene and last glacial period, rainfall in India and China has undergone strong and abrupt changes. In this context, we regard monsoon as dissipative system, which has many characteristic times, to contrive various factors and corresponding mechanism dominated in monsoon's abrupt change. The abrupt change of monsoon over inter-decadal to century timescales may be resulting from different fluctuation's competition, which impose on the inner basic physic processes. In order to find out the key factors which control the monsoon's abrupt change, starting from the seminar works by Leith, who proposed to employ the Fluctuation-dissipation Response theory(FDR) to study the response of climatic systems to changes in the external forcing, many authors applied this relation to different geophysical problems, ranging from simplified models to general circulation models and to the covariance of satellite radiance spectra. The FDR has been originally developed in the framework of statistical mechanics of Hamiltonian systems, nevertheless a generalized FDR holds under rather general hypotheses, regardless of the Hamiltonian, or equilibrium nature of the system. Our work verify the FDR theory' applicability in monsoon systems, which demonstrates that it can reveal clear and fundamental factors that control monsoon's abrupt change. By making use of FDR theory, combined with observational data analysis, we have already seen how monsoon systems with many characteristics times, different correlation functions behave differently and a variety of timescales emerges, which correspond to the different decay times of the correlation functions. Via theoretical and data analysis, it is suggested that each monsoon system has experienced several significant abrupt changes in 20th century. The global main monsoon rainfall has undergone an obvious abrupt jump in the mid- and late 1970s

  12. The First Pan-WCRP Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoons

    SciTech Connect

    Sperber, K R; Yasunari, T

    2005-07-27

    In 2004 the Joint Scientific Committee (JSC) that provides scientific guidance to the World Climate Research Programme (WCRP) requested an assessment of (1) WCRP monsoon related activities and (2) the range of available observations and analyses in monsoon regions. The purpose of the assessment was to (a) define the essential elements of a pan-WCRP monsoon modeling strategy, (b) identify the procedures for producing this strategy, and (c) promote improvements in monsoon observations and analyses with a view toward their adequacy, and addressing any undue redundancy or duplication. As such, the WCRP sponsored the ''1st Pan-WCRP Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoons'' at the University of California, Irvine, CA, USA from 15-17 June 2005. Experts from the two WCRP programs directly relevant to monsoon studies, the Climate Variability and Predictability Programme (CLIVAR) and the Global Energy and Water Cycle Experiment (GEWEX), gathered to assess the current understanding of the fundamental physical processes governing monsoon variability and to highlight outstanding problems in simulating the monsoon that can be tackled through enhanced cooperation between CLIVAR and GEWEX. The agenda with links to the presentations can be found at: http://www.clivar.org/organization/aamon/WCRPmonsoonWS/agenda.htm. Scientific motivation for a joint CLIVAR-GEWEX approach to investigating monsoons includes the potential for improved medium-range to seasonal prediction through better simulation of intraseasonal (30-60 day) oscillations (ISO's). ISO's are important for the onset of monsoons, as well as the development of active and break periods of rainfall during the monsoon season. Foreknowledge of the active and break phases of the monsoon is important for crop selection, the determination of planting times and mitigation of potential flooding and short-term drought. With a few exceptions simulations of ISO are typically poor in all classes of

  13. The Joint Aerosol-Monsoon Experiment: A New Challenge to Monsoon Climate Research

    NASA Technical Reports Server (NTRS)

    Lau, William K. M.

    2008-01-01

    Aerosol and monsoon related droughts and floods are two of the most serious environmental hazards confronting more than 60% of the population of the world living in the Asian monsoon countries. In recent years, thanks to improved satellite and in-situ observations, and better models, great strides have been made in aerosol, and monsoon research respectively. There is now a growing body of evidence suggesting that interaction of aerosol forcing with water cycle dynamics in monsoon regions may substantially alter the redistribution of energy at the earth surface and in the atmosphere, and therefore significantly impact monsoon rainfall variability and long term trends. In this talk, I will describe issues related to societal needs, scientific background, and challenges in studies of aerosol-water cycle interaction in Asian monsoon regions. As a first step towards addressing these issues, the authors call for an integrated observation and modeling research approach aimed at the interactions between aerosol chemistry and radiative effects and monsoon dynamics of the coupled ocean-atmosphere-land system. A Joint Aerosol-Monsoon Experiment (JAMEX) is proposed for 2007-2011, with an enhanced observation period during 2008-09, encompassing diverse arrays of observations from surface, aircraft, unmanned aerial vehicles, and satellites of physical and chemical properties of aerosols, long range aerosol transport as well as meteorological and oceanographic parameters in the Indo-Pacific Asian monsoon region. JAMEX will leverage on coordination among many ongoing and planned national programs on aerosols and monsoon research in China, India, Japan, Nepal, Italy, US, as well as international research programs of the World Climate Research Program (WCRP) and the World Meteorological Organization (WMO).

  14. Global climate and monsoons response to orbital forcing in the Late Miocene

    NASA Astrophysics Data System (ADS)

    Marzocchi, A.; Lunt, D. J.; Flecker, R.; Farnsworth, A.; Bradshaw, C.

    2014-12-01

    Global climate during the Late Miocene (11.61-5.33 Ma) is thought to have been generally warmer and wetter than at present day. The Northern Hemisphere was characterised by nearly ice-free conditions (with respect to the extent of the Greenland ice sheet) and some of the main marine gateways were undergoing opening or closure (e.g. Central American gateway, Bering Strait, and Indonesian Throughflow). Vegetation distribution was also generally more extensive than it is today, both at high and low latitudes. There is geological evidence of orbitally-forced cyclicity in sedimentary sections throughout the globe, especially in marginal basins such as the Mediterranean Sea. In the Late Miocene the entire North African catchment drained in the Eastern Mediterranean, constituting the main fresh water input into the basin, regulated by the North African monsoon. In addition, the Tibetan Plateau underwent substantial uplift throughout this time period, which strengthened the Asian monsoon system. The Late Miocene therefore represents an ideal scenario to investigate the impact of orbital forcing on the North African and Asian monsoon systems, the establishment of their teleconnections, and the associated vegetation changes. There still is considerable uncertainty in the reconstructed atmospheric CO2 levels for this time period, due to the patchy distribution (both spatially and temporally) of the available proxy record. Hence, we also explore the sensitivity of global climate to changing CO2 levels with different orbital configurations. We carried out a new series of 22 fully coupled atmosphere-ocean-vegetation numerical simulations, run at evenly spaced intervals (1kyr) through a full late Miocene precession cycle (~6.5 Ma), using a full-complexity general circulation model (HadCM3L). These model results show substantial changes to sea surface temperatures and regional atmospheric circulation on sub-precessional time scales. This triggers responses in the North African and

  15. Interannual variability of the Indian monsoon and the Southern Oscillation

    SciTech Connect

    Wu, M.; Hastenrath, S.

    1986-01-01

    Years with abundant Southwest monsoon rainfall in India are characterized by anomalously low pressure over South Asia and the adjacent waters, enhanced cross-equatorial flow in the western, and increased cloudiness over the northern portion of the Indian Ocean, continuing from the pre-monsoon through the post-monsoon season; positive temperature anomalies over land and in the Arabian Sea in the pre-monsoon season, changing to negative departures after the monsoon onset. The following causality chain is suggested: the anomalously warm surfaces of south Asia and the adjacent ocean in the pre-monsoon season induce a thermal low, thus enhancing the northward directed pressure gradient, and favoring a vigorous cross-equatorial flow over the Indian Ocean. After the monsoon onset the land surfaces are cooled by evaporation, and the Arabian Sea surface waters by various wind stress effects. However, latent heat release over South Asia can now maintain the meridional topography gradients essential to the monsoon circulation. The positive phase of the Southern Oscillation (high pressure over the Eastern South Pacific) is associated with circulation departures in the Indian Ocean sector similar to those characteristic of years with abundant India monsoon rainfall. Abundant rainfall over India during the northern summer monsoon leads the positive mode of the southern Oscillation, and this in turn leads Java rainfall, whose peak is timed about half a year after that of India. A rising Southern Oscillation tendency presages abundant India Southwest Monsoon rainfall but a late monsoon onset. 46 references, 9 figures, 4 tables.

  16. Multi-Satellite Synergy for Aerosol Analysis in the Asian Monsoon Region

    NASA Technical Reports Server (NTRS)

    Ichoku, Charles; Petrenko, Maksym

    2012-01-01

    Atmospheric aerosols represent one of the greatest uncertainties in environmental and climate research, particularly in tropical monsoon regions such as the Southeast Asian regions, where significant contributions from a variety of aerosol sources and types is complicated by unstable atmospheric dynamics. Although aerosols are now routinely retrieved from multiple satellite Sensors, in trying to answer important science questions about aerosol distribution, properties, and impacts, researchers often rely on retrievals from only one or two sensors, thereby running the risk of incurring biases due to sensor/algorithm peculiarities. We are conducting detailed studies of aerosol retrieval uncertainties from various satellite sensors (including Terra-/ Aqua-MODIS, Terra-MISR, Aura-OMI, Parasol-POLDER, SeaWiFS, and Calipso-CALIOP), based on the collocation of these data products over AERONET and other important ground stations, within the online Multi-sensor Aerosol Products Sampling System (MAPSS) framework that was developed recently. Such analyses are aimed at developing a synthesis of results that can be utilized in building reliable unified aerosol information and climate data records from multiple satellite measurements. In this presentation, we will show preliminary results of. an integrated comparative uncertainly analysis of aerosol products from multiple satellite sensors, particularly focused on the Asian Monsoon region, along with some comparisons from the African Monsoon region.

  17. Warm Indian Ocean, Weak Asian Monsoon

    NASA Astrophysics Data System (ADS)

    Koll Roxy, Mathew; Ritika, Kapoor; Terray, Pascal; Murtugudde, Raghu; Ashok, Karumuri; Nath Goswami, Buphendra

    2015-04-01

    There are large uncertainties looming over the status and fate of the South Asian monsoon in a changing climate. Observations and climate models have suggested that anthropogenic warming in the past century has increased the moisture availability and the land-sea thermal contrast in the tropics, favoring an increase in monsoon rainfall. In contrast, we notice that South Asian subcontinent experienced a relatively subdued warming during this period. At the same time, the tropical Indian Ocean experienced a nearly monotonic warming, at a rate faster than the other tropical oceans. Using long-term observations and coupled model experiments, we suggest that the enhanced Indian Ocean warming along with the suppressed warming of the subcontinent weaken the land-sea thermal contrast throughout the troposphere, dampen the monsoon Hadley circulation, and reduce the rainfall over South Asia. As a result, the summer monsoon rainfall during 1901-2012 shows a significant weakening trend over South Asia, extending from Pakistan through central India to Bangladesh.

  18. Past dynamics of the Australian monsoon: precession, phase and links to the global monsoon concept

    NASA Astrophysics Data System (ADS)

    Beaufort, L.; van der Kaars, S.; Bassinot, F. C.; Moron, V.

    2010-10-01

    Past variations in the dynamics of the Australian monsoon have been estimated from multi-proxy analysis of a core retrieved in the Eastern Banda Sea. Records of coccolith and pollen assemblages, spanning the last 150 000 years, allow reconstruction of past primary production in the Banda Sea, summer moisture availability, and the length of the dry season in northern Australia and southeastern Indonesia. The amount of moisture available during the summer monsoon follows typical glacial/interglacial dynamics with a broad asymmetrical 100-kyr cycle. Primary production and length of the dry season appear to be closely related, given that they follow the precessional cycle with the same phase. This indicates their independence from ice-volume variations. The present inter-annual variability of both parameters is related to El Niño Southern Oscillation (ENSO), which modulates the Australian Winter Monsoon (AWM). The precessional pattern observed in the past dynamics of the AWM is found in ENSO and monsoon records of other regions. A marked shift in the monsoon intensity occurring during the mid Holocene during a period of constant ice volume, suggests that low latitude climatic variation precedes increases in global ice volume. This precessional pattern suggests that a common forcing mechanism underlies low latitude climate dynamics, acting specifically and synchronously on the different monsoon systems.

  19. Past dynamics of the Australian monsoon: precession, phase and links to the global monsoon

    NASA Astrophysics Data System (ADS)

    Beaufort, L.; van der Kaars, S.; Bassinot, F. C.; Moron, V.

    2010-06-01

    Past variations in the dynamics of the Australian monsoon have been estimated from multi-proxy analysis of a core retrieved in the Eastern Banda Sea. Records of coccolith and pollen assemblages, spanning the last 150,000 years, allow reconstruction of past primary production in the Banda Sea, summer moisture availability, and the length of the dry season in Northern Australia and Southeastern Indonesia. The amount of moisture available during the summer monsoon follows typical glacial/interglacial dynamics with a broad asymmetrical 100-kyr cycle. Primary production and length of the dry season appear to be closely related, given that they follow the precessional cycle with the same phase (August insolation). This indicates their independence from ice-volume variations. The present inter-annual variability of both parameters is related to El Niño Southern Oscillation (ENSO), which modulates the Australian Winter Monsoon (AWM). The precessional pattern observed in the past dynamics of the AWM is found in ENSO and monsoon records of other regions. A marked shift in the monsoon intensity occurring during the mid Holocene during a period of constant ice volume, suggest that low latitude climatic variation precedes global ice volume. This precessional pattern suggests that a common forcing mechanism underlies low latitude climate dynamics, acting specifically and synchronically on the different monsoon systems.

  20. Orbital control of the western North Pacific summer monsoon

    NASA Astrophysics Data System (ADS)

    Wu, Chi-Hua; Chiang, John C. H.; Hsu, Huang-Hsiung; Lee, Shih-Yu

    2016-02-01

    Orbital forcing exerts a strong influence on global monsoon systems, with higher summer insolation leading to stronger summer monsoons in the Northern Hemisphere. However, the associated regional and seasonal changes, particularly the interaction between regional monsoon systems, remain unclear. Simulations using the Community Earth System Model demonstrate that the western North Pacific (WNP) summer monsoon responds to orbital forcing opposite to that of other major Northern Hemisphere monsoon systems. Compared with its current climate state, the simulated WNP monsoon and associated lower-tropospheric trough is absent in the early Holocene when the precession-modulated Northern Hemisphere summer insolation is higher, whereas the summer monsoons in South and East Asia are stronger and shift farther northward. We attribute the weaker WNP monsoon to the stronger diabatic heating of the summer Asian monsoon—in particular over the southern Tibetan Plateau and Maritime Continent—that in turn strengthens the North Pacific subtropical high through atmospheric teleconnections. By contrast, the impact of the midlatitude circulation changes on the WNP monsoon is weaker when the solar insolation is higher. Prior to the present WNP monsoon onset, the upper-tropospheric East Asian jet stream weakens and shifts northward; the monsoon onset is highly affected by the jet-induced high potential vorticity intrusion. In the instance of the extreme perihelion-summer, the WNP monsoon is suppressed despite a stronger midlatitude precursor than present-day, and the midlatitude circulation response to the enhanced South Asian precipitation is considerable. These conditions indicate internal monsoon interactions of an orbital scale, implying a potential mechanistic control of the WNP monsoon.

  1. The Monsoon as a Self-regulating Coupled Ocean-Atmosphere System

    NASA Astrophysics Data System (ADS)

    Webster, P. J.; Clark, C.; Cherikova, G.; Fasullo, J.; Han, W.; Loschnigg, J.; Sahami, K.

    INTRODUCTION REGULATION OF THE MONSOON ANNUAL CYCLE The Climatological Annual Cycle Processes Determining the Annual Cycle of the Monsoon Role of Ocean Dynamics in the Annual Heat Balance of the Indian - Ocean Regulation of the Annual Cycle of the Monsoon: an Ocean-Atmosphere - Feedback System INTERANNUAL VARIABILITY OF THE MONSOON Modes of Interannual Variability in the Monsoon Interannual Modes in Ocean Heat Transport Interannual Regulation of the Monsoon GENERAL THEORY OF REGULATION OF THE COUPLED OCEAN-ATMOSPHERIC MONSOON - SYSTEM CONCLUSIONS REFERENCES

  2. Dirtier Air from a Weaker Monsoon

    NASA Technical Reports Server (NTRS)

    Chin, Mian

    2012-01-01

    The level of air pollution in China has much increased in the past decades, causing serious health problems. Among the main pollutants are aerosols, also known as particulate matter: tiny, invisible particles that are suspended in the air. These particles contribute substantially to premature mortality associated with cardiopulmonary diseases and lung cancer1. The increase of the aerosol level in China has been commonly attributed to the fast rise in pollutant emissions from the rapid economic development in the region. However, writing in Geophysical Research Letters, Jianlei Zhu and colleagues2 tell a different side of the story: using a chemical transport model and observation data, they show that the decadal scale weakening of the East Asian summer monsoon has also contributed to the increase of aerosol concentrations in China. The life cycle of atmospheric aerosols starts with its emission or formation in the atmosphere. Some aerosol components such as dust, soot and sea salt are emitted directly as particles to the atmosphere, but others are formed there by way of photochemical reactions. For example, sulphate and nitrate aerosols are produced from their respective precursor gases, sulphur dioxide and nitrogen oxides. Aerosol particles can be transported away from their source locations by winds or vertical motion of the air. Eventually, they are removed from the atmosphere by means of dry deposition and wet scavenging by precipitation. Measurements generally show that aerosol concentrations over Asia are lowest during the summer monsoon season3, because intense rainfall efficiently removes them from the air. The East Asian summer monsoon extends over subtropics and mid-latitudes. Its rainfall tends to concentrate in rain belts that stretch out for many thousands of kilometres and affect China, Korea, Japan and the surrounding area. Observations suggest that the East Asian summer monsoon circulation and precipitation have been in decline since the 1970s4. In

  3. Pre-monsoon/monsoon thunderstorm characteristics over Pune—An investigation using Doppler Sodar observations

    NASA Astrophysics Data System (ADS)

    Murthy, B. S.; Latha, R.; Sreeja, P.; Kalapureddy, M. C. R.; Dharmaraj, T.; Waghmare, R. T.

    2011-10-01

    Doppler sodar observations of three dimensional (3D) wind fields and thermal structure of convective boundary layer (CBL) on a few thunderstorm days of 2009 during pre-monsoon (May and June; June due to delayed arrival of monsoon over Pune) and monsoon (July and August) are analyzed. They reveal the typical signatures of wind fields for the late afternoon thunderstorm (TS) such as deceleration of winds with or without change in direction leading to convergence a few minutes (˜15-30 min) prior to the onset of TS. Pre-monsoon TS are characterized by broad updrafts and narrow downdrafts in CBL in contrast to the narrow updrafts and broad downdrafts of a normal day (i.e. No-TS day). Mean vertical velocity averaged over CBL period shows net updraft on TS days and net downdraft on No-TS day for the pre-monsoon cases. Similarly calm winds are observed in the CBL on TS-days that support enhanced free convection. During the monsoon period updrafts are observed on both TS and No-TS days with higher values on TS days in comparison, due to the dominance of large-scale monsoon flow over local convection. Relatively higher turbulence kinetic energy (TKE) in CBL is observed on all TS days. Analysis shows that TKE maximum for the day is attained about 1.5-2.0 h prior to the onset of afternoon TS. Mixed-layer depth, determined from TKE profile, is higher than lifting condensation level (LCL) on TS days in May and June indicating saturation of air parcels in updrafts.

  4. Spatiotemporal variability of rainfall extremes in monsoonal climates - examples from the South American Monsoon and the Indian Monsoon Systems (Invited)

    NASA Astrophysics Data System (ADS)

    Bookhagen, B.; Boers, N.; Marwan, N.; Malik, N.; Kurths, J.

    2013-12-01

    Monsoonal rainfall is the crucial component for more than half of the world's population. Runoff associated with monsoon systems provide water resources for agriculture, hydropower, drinking-water generation, recreation, and social well-being and are thus a fundamental part of human society. However, monsoon systems are highly stochastic and show large variability on various timescales. Here, we use various rainfall datasets to characterize spatiotemporal rainfall patterns using traditional as well as new approaches emphasizing nonlinear spatial correlations from a complex networks perspective. Our analyses focus on the South American (SAMS) and Indian (ISM) Monsoon Systems on the basis of Tropical Rainfall Measurement Mission (TRMM) using precipitation radar and passive-microwave products with horizontal spatial resolutions of ~5x5 km^2 (products 2A25, 2B31) and 25x25 km^2 (3B42) and interpolated rainfall-gauge data for the ISM (APHRODITE, 25x25 km^2). The eastern slopes of the Andes of South America and the southern front of the Himalaya are characterized by significant orographic barriers that intersect with the moisture-bearing, monsoonal wind systems. We demonstrate that topography exerts a first-order control on peak rainfall amounts on annual timescales in both mountain belts. Flooding in the downstream regions is dominantly caused by heavy rainfall storms that propagate deep into the mountain range and reach regions that are arid and without vegetation cover promoting rapid runoff. These storms exert a significantly different spatial distribution than average-rainfall conditions and assessing their recurrence intervals and prediction is key in understanding flooding for these regions. An analysis of extreme-value distributions of our high-spatial resolution data reveal that semi-arid areas are characterized by low-frequency/high-magnitude events (i.e., are characterized by a ';heavy tail' distribution), whereas regions with high mean annual rainfall have a

  5. The Misnomer of East Asia Summer Monsoon

    NASA Technical Reports Server (NTRS)

    Chao, Winston C.; Chen, Baode

    2004-01-01

    The terminology East Asian summer monsoon is used to refer to the heavy rainfall in southeast China including the Yangtze River Valley starting in May and ending in August (e.g., Chen and Chang 1980, Tao and Chen 1987, Ding 1992, Chang et al. 2000a.) This rainfall region is associated with the Mei-Yu front, which extends to Japan and its neighborhood and is called Baiu there. The Mei-Yu front becomes prominent in May and has a slow northward movement. From May to July the elongated rain belt moves from the southeast coast of China to the Yangtze River Valley. The rain belt extends north-east-ward to south of Japan in May and later covers Korea also. The purpose of this note is to point out that the terminology of East Asian summer monsoon is a misnomer to refer to the portion of this rainbelt residing over East Asia, in the sense that it is not a monsoon.

  6. Pacific freshening drives Pliocene cooling and Asian monsoon intensification.

    PubMed

    Nie, Junsheng; Stevens, Thomas; Song, Yougui; King, John W; Zhang, Rui; Ji, Shunchuan; Gong, Lisha; Cares, Danielle

    2014-01-01

    The monsoon is a fundamental component of Earth's climate. The Pliocene warm period is characterized by long-term global cooling yet concurrent monsoon dynamics are poorly known. Here we present the first fully quantified and calibrated reconstructions of separate Pliocene air temperature and East Asian summer monsoon precipitation histories on the Chinese Loess Plateau through joint analysis of loess/red clay magnetic parameters with different sensitivities to air temperature and precipitation. East Asian summer monsoon precipitation shows an intensified trend, paradoxically at the same time that climate cooled. We propose a hitherto unrecognized feedback where persistently intensified East Asian summer monsoon during the late Pliocene, triggered by the gradual closure of the Panama Seaway, reinforced late Pliocene Pacific freshening, sea-ice development and ice volume increase, culminating in initiation of the extensive Northern Hemisphere glaciations of the Quaternary Ice Age. This feedback mechanism represents a fundamental reinterpretation of the origin of the Quaternary glaciations and the impact of the monsoon.

  7. Tropospheric ozone variability during the monsoon season in Malaysia

    NASA Astrophysics Data System (ADS)

    Ahamad, Fatimah; Latif, Mohd Talib

    2013-11-01

    Vertical ozone (O3) profiles obtained from ozonesondes launched at Kuala Lumpur International Airport (KLIA), Malaysia were analyzed. Results of soundings between January to March 2011 and July to September 2011 are presented along with meteorological parameters (temperature and relative humidity (RH)). The overall O3 concentration range between the soundings made during the northeast monsoon (January - March) and the southwest monsoon (July - September) were not far from each other for altitudes below 8 km. However O3 variability is less pronounced between 2 km and 12 km during the southwest monsoon compared to the northeast monsoon season.

  8. Simulation of South-Asian Summer Monsoon in a GCM

    NASA Astrophysics Data System (ADS)

    Ajayamohan, R. S.

    2007-10-01

    Major characteristics of Indian summer monsoon climate are analyzed using simulations from the upgraded version of Florida State University Global Spectral Model (FSUGSM). The Indian monsoon has been studied in terms of mean precipitation and low-level and upper-level circulation patterns and compared with observations. In addition, the model's fidelity in simulating observed monsoon intraseasonal variability, interannual variability and teleconnection patterns is examined. The model is successful in simulating the major rainbelts over the Indian monsoon region. However, the model exhibits bias in simulating the precipitation bands over the South China Sea and the West Pacific region. Seasonal mean circulation patterns of low-level and upper-level winds are consistent with the model's precipitation pattern. Basic features like onset and peak phase of monsoon are realistically simulated. However, model simulation indicates an early withdrawal of monsoon. Northward propagation of rainbelts over the Indian continent is simulated fairly well, but the propagation is weak over the ocean. The model simulates the meridional dipole structure associated with the monsoon intraseasonal variability realistically. The model is unable to capture the observed interannual variability of monsoon and its teleconnection patterns. Estimate of potential predictability of the model reveals the dominating influence of internal variability over the Indian monsoon region.

  9. A solar variability driven monsoon see-saw: switching relationships of the Holocene East Asian-Australian summer monsoons

    NASA Astrophysics Data System (ADS)

    Eroglu, Deniz; Ozken, Ibrahim; McRobie, Fiona; Stemler, Thomas; Marwan, Norbert; Wyrwoll, Karl-Heinz; Kurths, Juergen

    2016-04-01

    The East Asian-Indonesian-Australian monsoon is the predominant low latitude monsoon system, providing a major global scale heat source. Here we apply newly developed non-linear time series techniques on speleothem climate proxies, from eastern China and northwestern Australia and establish relationships between the two summer monsoon regimes over the last ˜9000 years. We identify significant variations in monsoonal activity, both dry and wet phases, at millennial to multi-centennial time scales and demonstrate for the first time the existence of a see-saw antiphase relationship between the two regional monsoon systems. Our analysis attributes this inter-hemispheric linkage to the solar variability that is effecting both monsoon systems.

  10. The resolution sensitivity of the South Asian monsoon and Indo-Pacific in a global 0.35° AGCM

    NASA Astrophysics Data System (ADS)

    Johnson, Stephanie J.; Levine, Richard C.; Turner, Andrew G.; Martin, Gill M.; Woolnough, Steven J.; Schiemann, Reinhard; Mizielinski, Matthew S.; Roberts, Malcolm J.; Vidale, Pier Luigi; Demory, Marie-Estelle; Strachan, Jane

    2016-02-01

    The South Asian monsoon is one of the most significant manifestations of the seasonal cycle. It directly impacts nearly one third of the world's population and also has substantial global influence. Using 27-year integrations of a high-resolution atmospheric general circulation model (Met Office Unified Model), we study changes in South Asian monsoon precipitation and circulation when horizontal resolution is increased from approximately 200-40 km at the equator (N96-N512, 1.9°-0.35°). The high resolution, integration length and ensemble size of the dataset make this the most extensive dataset used to evaluate the resolution sensitivity of the South Asian monsoon to date. We find a consistent pattern of JJAS precipitation and circulation changes as resolution increases, which include a slight increase in precipitation over peninsular India, changes in Indian and Indochinese orographic rain bands, increasing wind speeds in the Somali Jet, increasing precipitation over the Maritime Continent islands and decreasing precipitation over the northern Maritime Continent seas. To diagnose which resolution-related processes cause these changes, we compare them to published sensitivity experiments that change regional orography and coastlines. Our analysis indicates that improved resolution of the East African Highlands results in the improved representation of the Somali Jet and further suggests that improved resolution of orography over Indochina and the Maritime Continent results in more precipitation over the Maritime Continent islands at the expense of reduced precipitation further north. We also evaluate the resolution sensitivity of monsoon depressions and lows, which contribute more precipitation over northeast India at higher resolution. We conclude that while increasing resolution at these scales does not solve the many monsoon biases that exist in GCMs, it has a number of small, beneficial impacts.

  11. Stable isotopes in monsoon precipitation and water vapour in Nagqu, Tibet, and their implications for monsoon moisture

    NASA Astrophysics Data System (ADS)

    He, Siyuan; Richards, Keith

    2016-09-01

    Understanding climate variations over the Qinghai-Tibetan plateau has become essential because the high plateau sustains various ecosystems and water sources, and impacts on the Asian monsoon system. This paper provides new information from isotopic signals in meteoric water and atmospheric water vapour on the Qinghai-Tibetan Plateau using high frequency observation data over a relatively short period. The aim is to explore temporal moisture changes and annual variations at the onset and during the summer monsoon season at a transitional site with respect to the monsoon influence. Data show that high frequency and short period observations can reveal typical moisture changes from the pre-monsoon to the monsoon seasons (2010), and the large variation in isotopic signals in different years with respect to active/inactive periods during a mature phase of the monsoon (2011), especially inferring from the temporal changes in the d-excess of precipitation and its relationship with δ18O values, when higher d-excess is found in the pre-monsoon precipitation. In this transition zone on a daily basis, δ18O values in precipitation are controlled mainly by the amount of rainfall during the monsoon season, while temperature seems more important before the onset of monsoon. Furthermore, the "amount effect" is significant for night-time rain events. From comparison of signals in both the precipitation and water vapour, an inconsistent relationship between d-excess values suggests various moisture fluxes are active in a short period. The temporal pattern of isotopic signal change from the onset of the monsoon to the mature monsoon phase provides information about the larger circulation dynamics of the Asian monsoon.

  12. Asian Eocene monsoons as revealed by leaf architectural signatures

    NASA Astrophysics Data System (ADS)

    Spicer, Robert A.; Yang, Jian; Herman, Alexei B.; Kodrul, Tatiana; Maslova, Natalia; Spicer, Teresa E. V.; Aleksandrova, Galina; Jin, Jianhua

    2016-09-01

    The onset and development of the Asian monsoon systems is a topic that has attracted considerable research effort but proxy data limitations, coupled with a diversity of definitions and metrics characterizing monsoon phenomena, have generated much debate. Failure of geological proxies to yield metrics capable of distinguishing between rainfall seasonality induced by migrations of the Inter-tropical Convergence Zone (ITCZ) from that attributable to topographically modified seasonal pressure reversals has frustrated attempts to understand mechanisms underpinning monsoon development and dynamics. Here we circumvent the use of such single climate parameter metrics in favor of detecting directly the distinctive attributes of different monsoon regimes encoded in leaf fossils. Leaf form adapts to the prevailing climate, particularly under the extreme seasonal stresses imposed by monsoons, so it is likely that fossil leaves carry a unique signature of past monsoon regimes. Leaf form trait spectra obtained from fossils from Eocene basins in southern China were compared with those seen in modern leaves growing under known climate regimes. The fossil leaf trait spectra, including those derived from previously published fossil floras from northwestern India, were most similar to those found in vegetation exposed to the modern Indonesia-Australia Monsoon (I-AM), which is largely a product of seasonal migrations of the ITCZ. The presence of this distinctive leaf physiognomic signature suggests that although a monsoon climate existed in Eocene time across southern Asia the characteristics of the modern topographically-enhanced South Asia Monsoon had yet to develop. By the Eocene leaves in South Asia had become well adapted to an I-AM type regime across many taxa and points to the existence of a pervasive monsoon climate prior to the Eocene. No fossil trait spectra typical of exposure to the modern East Asia monsoon were seen, suggesting the effects of this system in southern

  13. African Aesthetics

    ERIC Educational Resources Information Center

    Abiodun, Rowland

    2001-01-01

    No single traditional discipline can adequately supply answers to the many unresolved questions in African art history. Because of the aesthetic, cultural, historical, and, not infrequently, political biases, already built into the conception and development of Western art history, the discipline of art history as defined and practiced in the West…

  14. "African Connection."

    ERIC Educational Resources Information Center

    Adelman, Cathy; And Others

    This interdisciplinary unit provides students in grades kindergarten through seventh grade an opportunity to understand diversity through a study of Africa as a diverse continent. The project is designed to provide all elementary students with cultural enrichment by exposing them to African music, art, storytelling, and movement. This project can…

  15. Reconciling societal and scientific definitions for the monsoon

    NASA Astrophysics Data System (ADS)

    Reeve, Mathew; Stephenson, David

    2014-05-01

    Science defines the monsoon in numerous ways. We can apply these definitions to forecast data, reanalysis data, observations, GCMs and more. In a basic research setting, we hope that this work will advance science and our understanding of the monsoon system. In an applied research setting, we often hope that this work will benefit a specific stakeholder or community. We may want to inform a stakeholder when the monsoon starts, now and in the future. However, what happens if the stakeholders cannot relate to the information because their perceptions do not align with the monsoon definition we use in our analysis? We can resolve this either by teaching the stakeholders or learning from them about how they define the monsoon and when they perceive it to begin. In this work we reconcile different scientific monsoon definitions with the perceptions of agricultural communities in Bangladesh. We have developed a statistical technique that rates different scientific definitions against the people's perceptions of when the monsoon starts and ends. We construct a probability mass function (pmf) around each of the respondent's answers in a questionnaire survey. We can use this pmf to analyze the time series of monsoon onsets and withdrawals from the different scientific definitions. We can thereby quantitatively judge which definition may be most appropriate for a specific applied research setting.

  16. Autoencoder-based identification of predictors of Indian monsoon

    NASA Astrophysics Data System (ADS)

    Saha, Moumita; Mitra, Pabitra; Nanjundiah, Ravi S.

    2016-10-01

    Prediction of Indian summer monsoon uses a number of climatic variables that are historically known to provide a high skill. However, relationships between predictors and predictand could be complex and also change with time. The present work attempts to use a machine learning technique to identify new predictors for forecasting the Indian monsoon. A neural network-based non-linear dimensionality reduction technique, namely, the sparse autoencoder is used for this purpose. It extracts a number of new predictors that have prediction skills higher than the existing ones. Two non-linear ensemble prediction models of regression tree and bagged decision tree are designed with identified monsoon predictors and are shown to be superior in terms of prediction accuracy. Proposed model shows mean absolute error of 4.5 % in predicting the Indian summer monsoon rainfall. Lastly, geographical distribution of the new monsoon predictors and their characteristics are discussed.

  17. Asian monsoons in a late Eocene greenhouse world

    NASA Astrophysics Data System (ADS)

    Licht, A.; van Cappelle, M.; Abels, H. A.; Ladant, J.-B.; Trabucho-Alexandre, J.; France-Lanord, C.; Donnadieu, Y.; Vandenberghe, J.; Rigaudier, T.; Lécuyer, C.; Terry, D., Jr.; Adriaens, R.; Boura, A.; Guo, Z.; Soe, Aung Naing; Quade, J.; Dupont-Nivet, G.; Jaeger, J.-J.

    2014-09-01

    The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and their response to enhanced greenhouse conditions such as those in the Eocene period (55-34 Myr ago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 34 Myr ago.

  18. Satellite observations of a monsoon depression

    NASA Technical Reports Server (NTRS)

    Warner, C.

    1984-01-01

    The exploration of a monsoon depression over Burma and the Bay of Bengal is discussed. Aircraft and satellite data were examined, with an emphasis on the Microwave Sounding Unit (MSU) aboard TIROS-N and the Scanning Multichannel Microwave Radiometer (SMMR) aboard Nimbus-7. The structure of the monsoon depression was found to be dominated by cumulus convection. The only systematic large scale behavior discerned was a propagation of the depression westward, and diurnal migration of contours of brightness temperature. These contours in the middle troposphere showed a gradient toward the north with the patterns migrating northward at night. From SMMR and dropwindsonde data, water vapor contents were found to be near 65 mm, increasing to more than 70 mm in the northeast Bay of Bengal. Cloud water contents reached about three mm. Rainfall rates exceeding 5.7 mm/h occurred over a small part of the storm area, while mean rainfall rates in areas of order 20,000 sq km reached approximately 0.5 mm/h. Measured MSU brightness temperatures were reconciled very well with dropwindsonde data and with airborne in situ observations of clouds (by photography) and hydrometeors (by radar). Diffuse scattering was determined to be important in computing brightness temperature.

  19. Annual monsoon rains recorded by Jurassic dunes.

    PubMed

    Loope, D B; Rowe, C M; Joeckel, R M

    2001-07-01

    Pangaea, the largest landmass in the Earth's history, was nearly bisected by the Equator during the late Palaeozoic and early Mesozoic eras. Modelling experiments and stratigraphic studies have suggested that the supercontinent generated a monsoonal atmospheric circulation that led to extreme seasonality, but direct evidence for annual rainfall periodicity has been lacking. In the Mesozoic era, about 190 million years ago, thick deposits of wind-blown sand accumulated in dunes of a vast, low-latitude desert at Pangaea's western margin. These deposits are now situated in the southwestern USA. Here we analyse slump masses in the annual depositional cycles within these deposits, which have been described for some outcrops of the Navajo Sandstone. Twenty-four slumps, which were generated by heavy rainfall, appear within one interval representing 36 years of dune migration. We interpret the positions of 20 of these masses to indicate slumping during summer monsoon rains, with the other four having been the result of winter storms. The slumped lee faces of these Jurassic dunes therefore represent a prehistoric record of yearly rain events.

  20. Obesity and African Americans

    MedlinePlus

    ... Data > Minority Population Profiles > Black/African American > Obesity Obesity and African Americans African American women have the ... ss6304.pdf [PDF | 3.38MB] HEALTH IMPACT OF OBESITY More than 80 percent of people with type ...

  1. Interannual variability of South American monsoon circulation

    NASA Astrophysics Data System (ADS)

    Alonso Gan, Manoel; Rafaele Araújo Lima, Jeane

    2016-04-01

    The South America Monsoon System (SAMS) is responsible for influencing the atmospheric circulation and precipitation over most of tropical South America (SA) during the summer season. Studies for aiming to understand the temporal variability of this system have great value to the scientific community, because the processes that control the monsoon climate are not totally clear. Thus, the main objective of this research is to investigate the possible large-scale climatic factors and the remote interaction mechanisms, which may be associated with summer season interannual variability focusing on identifying the main differences between dry and wet extremes rainy season in the South-eastern Amazon Basin (SAB), Central-West (WC) and Southeast (SE) of Brazil, which are areas influenced by the summer monsoon regime. For such analyzes, Pearson correlations, quantile method and composite analysis were used during the period from 1979 to 2014. The correlation between precipitation anomaly in SAB and the sea surface temperature anomaly (SSTA) and wind at 850hPa and 300hPa indicate El Niño-Southern Oscillation (ENSO) influence. Precipitation anomalies in WC did not show significant correlation with SSTA. However, a pattern similar to ENSO Modoki type was observed in the composite analysis. At 850 hPa, the presence of an anomalous cyclonic (anticyclonic) circulation was observed over the central region of SA during wet (dry) summers seasons. Over SE region of Brazil, a dipole SSTA pattern over the South Atlantic was identified, as well the presence of anomalous circulations with an equivalent barotropic structure over these SSTA areas. This pattern is more evident in case of dry summer on the SE. At 300 hPa, the wave train between 30°S-60°S was observed presenting a feature curvature from 120°W reaching SA, similar to the Pacific-South American pattern (PSA). Analysis of the summer interannual variability indicated the manifestation of wet summers more frequently than dry

  2. Three exceptionally strong East-Asian summer monsoon events during glacial times in the past 470 kyr

    NASA Astrophysics Data System (ADS)

    Rousseau, D.; Wu, N.; Pei, Y.; Li, F.

    2009-12-01

    Chinese loess sequences are interpreted as a reliable record of the past variation of the East Asian monsoon regime through the alternation of loess and paleosols units, dominated by the winter and summer monsoon respectively. Different proxies have been used to describe this system, mostly geophysical, geochemical or sedimentological. Terrestrial mollusks are also a reliable proxy of past environmental conditions and are often preserved in large numbers in loess deposits. The analysis of the mollusk remains in the Luochuan sequence, comprising L5 loess to S0 soil, i.e. the last 500 ka, shows that for almost all identified species, the abundance is higher at the base of the interval (L5 to L4) than in the younger deposits. Using the present ecological requirements of the identified mollusk species in the Luochuan sequence allows the definition of two main mollusk groups varying during the last 500 kyr. In the sequence, three events with exceptionally high abundance of the Asian summer monsoon indicators (thermal-humidiphilous mollusks) are recorded during the L5, L4 and L2 glacial intervals, i.e., at about 470, 360 and 170 kyr respectively. The L5 and L4 events appear to be the strongest (high counts). Similar variations have also been identified in E Asia to suggest that this phenomenon is regional rather than local. The L5 and L2 summer monsoons are coeval with Mediterranean sapropels S12 and S6, which characterize a strong African summer monsoon with relatively low surface water salinity in the Indian Ocean. Changes in the precipitation regime could correspond to a response to a particular astronomical configuration (low obliquity, low precession, summer solstice at perihelion) leading to an increased summer insolation gradient between the tropics and the high latitudes and resulting in enhanced atmospheric water transport from the tropics to the African and Asian continents. However, other climate drivers such as reorganization of marine and atmospheric

  3. Impacts of East Asian aerosols on the Asian monsoon

    NASA Astrophysics Data System (ADS)

    Bartlett, Rachel; Bollasina, Massimo; Booth, Ben; Dunstone, Nick; Marenco, Franco

    2016-04-01

    Over recent decades, aerosol emissions from Asia have increased rapidly. Aerosols are able to alter radiative forcing and regional hydroclimate through direct and indirect effects. Large emissions within the geographical region of the Asian monsoon have been found to impact upon this vital system and have been linked to observed drying trends. The interconnected nature of smaller regional monsoon components (e.g. the Indian monsoon and East Asian monsoon) presents the possibility that aerosol sources could have far-reaching impacts. Future aerosol emissions are uncertain and may continue to dominate regional impacts on the Asian monsoon. Standard IPCC future emissions scenarios do not take a broad sample of possible aerosol pathways. We investigate the sensitivity of the Asian monsoon to East Asian aerosol emissions. Experiments carried out with HadGEM2-ES use three time-evolving future anthropogenic aerosol emissions scenarios with similar time-evolving greenhouse gases. We find a wetter summer over southern China and the Indochina Peninsula associated with increased sulfate aerosol over China. The southern-flood-northern-drought pattern seen in observations is reflected in these results. India is found to be drier in the summer overall, although wetter in June. These precipitation changes are linked to the increase in sulfate through the alteration of large scale dynamics. Sub-seasonal changes are also seen, with an earlier withdrawal of the monsoon over East Asia.

  4. Influence of Aerosols on Monsoon Circulation and Hydroclimate

    NASA Technical Reports Server (NTRS)

    Lau, William K.M.

    2007-01-01

    Long recognized as a major environmental hazard, aerosol is now known to have strong impacts on both regional and global water cycles and climate change. In the Asian monsoon regions, the response of the regional water cycle and climate to aerosol forcing is very complex, not only because of presence of diverse mix of aerosol species with vastly different radiative properties, but also because the monsoon is strongly influenced by ocean and land surface processes, land use, land change, as well as regional and global greenhouse warming effects. Thus, sorting out the impacts of aerosol forcing, and interaction with the monsoon water cycle is a very challenging problem. Up to now, besides the general notion that aerosols may significantly impact monsoon through altering large scale radiative heating gradients, there has been very little information regarding the specific signatures, and mechanisms of aerosol-monsoon water cycle interaction. In this talk, based on preliminary results from observations and climate model experiments, I will offer some insights into how aerosols may impact the Asian monsoon water cycle, in particular the effects of absorbing aerosols (dust and black carbon), and the role of the Tibetan Plateau. The influence of aerosol forcing relative to those due to sea surface temperature and land surface processes, and impact on potential predictability of the monsoon climate system will also be discussed.

  5. Influence of Aerosols on Monsoon Circulation and Hydroclimate

    NASA Technical Reports Server (NTRS)

    Lau, William K.

    2006-01-01

    Long recognized as a major environmental hazard, aerosol is now known to have strong impacts on both regional and global water cycles and climate change. In the Asian monsoon regions, the response of the regional water cycle and climate to aerosol forcing is very complex, not only because of presence of diverse mix of aerosol species with vastly different radiative properties, but also because the monsoon is strongly influenced by ocean and land surface processes, land use, land change, as well as regional and global greenhouse warming effects. Thus, sorting out the impacts of aerosol forcing, and interaction with the monsoon water cycle is a very challenging problem. Up to now, besides the general notion that aerosols may significantly impact monsoon through altering large scale radiative heating gradients, there has been very little information regarding the specific signatures, and mechanisms of aerosol-monsoon water cycle interaction. In this talk, based on preliminary results from observations and climate model experiments, I will offer some insights into how aerosols may impact the Asian monsoon water cycle, in particular the effects of absorbing aerosols (dust and black carbon), and the role of the Tibetan Plateau. The influence of aerosol forcing relative to those due to sea surface temperature and land surface processes, and impact on potential predictability of the monsoon climate system will also be discussed.

  6. Extracting the vegetation phenology of tropical monsoon forest

    NASA Astrophysics Data System (ADS)

    Shang, R.; Xu, M.; Zuo, L.

    2015-12-01

    The monsoon forests cover over 40% of tropical forests, and play a significant role in terrestrial ecosystem carbon exchange and water-use efficiency of tropical ecosystems. The monsoons are changing under the global changes, and then impact the vegetation growth. However, the vegetation phenology in this area are difficult to describe, where the "V"-shaped seasonal growth trajectories of tropical monsoon forests are totally different from the normal seasonal trajectories such as the boreal forests. In this paper, a "V"-shaped curve is proposed to simulate the "V"-shaped seasonal trajectory. Current extractions of the onset of greenness are not suitable for "V"-shaped seasonal trajectory, which are seriously affected by the gaps in the rapid growth stage due to the heavy rain. For its insensitivity to the gaps or noise, the whole "V"-shaped curve was used to determine the phenology of tropical monsoon forest, and the lowest point in "V"-shaped curve was regarded as the phenology. The extracted phenology was showed to be correlated with the precipitation, and the validations with ground observations demonstrated that this new methodology has the ability to extract the phenology of tropical monsoon forest correctly. These phenology maps of tropical monsoon forest assist to understand the impact of climate changes in the monsoon regions.

  7. The North American Monsoon Forecast Forum at CPC/NCEP

    NASA Astrophysics Data System (ADS)

    Schemm, J. E.; Higgins, W.; Long, L.; Shi, W.; Gochis, D. J.

    2009-12-01

    In 2008, CPC introduced a new operational product to provide users a forum to monitor the North American monsoon (NAM). The NAME Forecast Forum (NAME FF) was proposed and endorsed by the North American Monsoon Experiment (NAME) Project Science Working Group as a natural extension to the NAME modeling activities coordinated under the NAME Climate Process Team project. It provided an opportunity to consolidate and assess, in real-time, the skill of intra-seasonal and seasonal monsoon forecasts. The NAME FF has continued in 2009 and three modeling groups collaborate with CPC to provide model simulated seasonal precipitation forecasts in the monsoon region. The website includes spatial maps and accumulated precipitation area-averaged over eight sub-regions of the NAM domain and is updated daily to include the current observed precipitation. A weekly update of the current conditions of the NAM system has been added to CPC’s American Monsoons monitoring webpage at, http://www.cpc.ncep.noaa.gov/products/Global_Monsoons/American_Monsoons/NAME/index.shtml. A highlight for the 2009 season is the inclusion of the NCEP CFS forecasts in T382 horizontal resolution. These special high-resolution runs were made with initial conditions in mid-April to accommodate the CPC’s hurricane season outlook. Some results based on the T382 CFS runs also will be presented with emphasis on the prediction of precipitation and accompanying atmospheric circulation over the NAM region.

  8. Book Review: Late Cenozoic Climate Change in Asia: Loess, Monsoon and Monsoon-arid Environment Evolution

    NASA Astrophysics Data System (ADS)

    Clemens, Steven C.

    2015-01-01

    Loess-Paleosol deposits drape >500,000 km2 of eastern China, spanning environments from the humid, monsoon-influenced regions near the coast to the arid, westerlies-dominated regions inland. Sections, up to hundreds of meters thick, are exposed in deeply incised river valleys and can be accessed as well by drilling. Combined, the high sedimentation rates and extensive geographic coverage make these sections unique among global terrestrial sediment archives. The Chinese loess-paleosol sequences, and the arid interior regions to the northwest, record diverse aspects of geologic and environmental change ranging from the tectonic evolution of the Tibetan Plateau (106 year time scale) through glacial-interglacial scale changes in global ice volume and greenhouse gasses (105 year time scale) on down through the orbital (104 years) to millennial and centennial scale events (103-102 year) relevant to the underpinnings of human interactions with changing environmental pressures. 'Late Cenozoic Climate Chang in Asia: Loess, Monsoon and Monsoon-arid Environment Evolution' is a timely contribution that synthesizes findings derived from the extensive work in these areas, places the findings in the broader context of global climate change and helps to define avenues for future research.

  9. Predictability of global monsoon rainfall in NCEP CFSv2

    NASA Astrophysics Data System (ADS)

    Saha, Subodh Kumar; Sujith, K.; Pokhrel, Samir; Chaudhari, Hemantkumar S.; Hazra, Anupam

    2016-09-01

    This study evaluates the actual and potential prediction skill of the global monsoon rainfall using hindcast simulations by NCEP CFSv2 at zero to three lead forecast months (L0-L3). It is shown that the model has moderate skill in global monsoon rainfall (GMR) prediction, where the boreal summer monsoon rainfall forecast is more skillful than that of the austral summer. In general, the prediction skill of the GMR (actual and potential) increases with the decrease in lead forecast time, which is true for the all major regional monsoons, except the Australian monsoon. Over the Australian monsoon region, both actual and potential prediction skills in rainfall increase with increase in lead forecast. The forecast skill of tropical SST during austral summer is a maximum at 3 months lead forecast (i.e. July initial conditions) and that is associated with spring predictability barrier. Using partial least square (PLS) regression method, it is shown that the major predictor (first latent vector) of the boreal and austral summer monsoon rainfall variability is ENSO, and the influence of ENSO on rainfall variability is much stronger in the model as compared to the observation. The second PLS regression mode is associated with the non-ENSO variability like tropical Atlantic, Indian, subtropical northwest Pacific Ocean variability, midlatitude interactions etc. However, the model has very poor skill in reproducing the second mode, particularly during the boreal summer monsoon season. It is also shown that a significant part of the Indian summer monsoon rainfall variability is controlled by other than ENSO variability and the model has limited success in capturing that.

  10. Land-surface processes and monsoon climate system

    NASA Astrophysics Data System (ADS)

    Xue, Y.

    2014-12-01

    Differential thermal heating of land and ocean and heat release into the atmosphere are important factors that determine the onset, strength, duration and spatial distribution of large-scale monsoons. A global and seasonal assessment of land surface process (LSP) effects on the monsoon system has been made based on general circulation models (GCM) coupled to different benchmark land models, which physically represent either comprehensive, or partial, or minimal LSP representations. Observed precipitation is applied as constrain and differences in simulation error are used to assess the effect of the LSP with different complexity. The AGCM results indicate that the land/atmosphere interaction has substantial impact on global water cycle, while the monsoon regions have had strongest impact at intraseasonal to decadal scales. Among monsoon regions, West Africa, South Asia, East Asia, and Amazon regions have largest impact while some monsoon regions have less impact due to strong air/sea interactions and narrow land mass. LSP reduces the annual precipitation error by 58% over global monsoon regions, about 35% observed precipitation. The partial LSP effect (excluding soil moisture and vegetation albedo) reduces annual precipitation error over monsoon region that equals to about 13% of observed precipitation. It has also been suggested that LSP contribute to the abrupt jump in latitude of the East Asian monsoon as well as general circulation turning in some monsoon regions in its early stages. The LSP effects have also been assessed in the land use land cover change experiment. Based on recently compiled global land-use data from 1948-2005, the GCM simulation results indicate the degradation in Mexico, West Africa, south and East Asia and South America produce substantial precipitation anomalies, some of which are consistent with observed regional precipitation anomalies. More comprehensive studies with multi-models are imperatively necessary.

  11. BOBMEX: The Bay of Bengal Monsoon Experiment.

    NASA Astrophysics Data System (ADS)

    Bhat, G. S.; Gadgil, S.; Hareesh Kumar, P. V.; Kalsi, S. R.; Madhusoodanan, P.; Murty, V. S. N.; Prasada Rao, C. V. K.; Babu, V. Ramesh; Rao, L. V. G.; Rao, R. R.; Ravichandran, M.; Reddy, K. G.; Sanjeeva Rao, P.; Sengupta, D.; Sikka, D. R.; Swain, J.; Vinayachandran, P. N.

    2001-10-01

    The first observational experiment under the Indian Climate Research Programme, called the Bay of Bengal Monsoon Experiment (BOBMEX), was carried out during July-August 1999. BOBMEX was aimed at measurements of important variables of the atmosphere, ocean, and their interface to gain deeper insight into some of the processes that govern the variability of organized convection over the bay. Simultaneous time series observations were carried out in the northern and southern Bay of Bengal from ships and moored buoys. About 80 scientists from 15 different institutions in India collaborated during BOBMEX to make observations in most-hostile conditions of the raging monsoon. In this paper, the objectives and the design of BOBMEX are described and some initial results presented. During the BOBMEX field phase there were several active spells of convection over the bay, separated by weak spells. Observation with high-resolution radiosondes, launched for the first time over the northern bay, showed that the magnitudes of the convective available potential energy (CAPE) and the convective inhibition energy were comparable to those for the atmosphere over the west Pacific warm pool. CAPE decreased by 2-3 kJ kg-1 following convection, and recovered in a time period of 1-2 days. The surface wind speed was generally higher than 8 m s-1. The thermohaline structure as well as its time evolution during the BOBMEX field phase were found to be different in the northern bay than in the southern bay. Over both the regions, the SST decreased during rain events and increased in cloud-free conditions. Over the season as a whole, the upper-layer salinity decreased for the north bay and increased for the south bay. The variation in SST during 1999 was found to be of smaller amplitude than in 1998. Further analysis of the surface fluxes and currents is expected to give insight into the nature of coupling.

  12. MONSOON: Image Acquisition System or "Pixel Server"

    NASA Astrophysics Data System (ADS)

    Starr, Barry M.; Buchholz, Nick C.; Rahmer, Gustavo; Penegor, Gerald; Schmidt, Ricardo E.; Warner, Michael; Merrill, Michael; Claver, Charles F.; Ho, Y.; Chopra, K. N.; Shroff, C.; Shroff, D.

    2003-03-01

    The MONSOON Image Acquisition System has been designed to meet the need for scalable, multichannel, high-speed image acquisition required for the next-generation optical and infared detectors and mosaic projects currently under development at NOAO as described in other papers at this proceeding such as ORION, NEWFIRM, QUOTA, ODI and LSST. These new systems with their large scale (64 to 2000 channels) and high performance (up to 1Gbyte/s) raise new challenges in terms of communication bandwidth, data storage and data processing requirements which are not adequately met by existing astronomical controllers. In order to meet this demand, new techniques for not only a new detector controller, but rather a new image acquisition architecture, have been defined. These extremely large scale imaging systems also raise less obvious concerns in previously neglected areas of controller design such as physical size and form factor issues, power dissipation and cooling near the telescope, system assembly/test/ integration time, reliability, and total cost of ownership. At NOAO we have taken efforts to look outside of the astronomical community for solutions found in other disciplines to similar classes of problems. A large number of the challenges raised by these system needs are already successfully being faced in other areas such as telecommunications, instrumentation and aerospace. Efforts have also been made to use true commercial off the shelf (COTS) system elements, and find truly technology independent solutions for a number of system design issues whenever possible. The Monsoon effort is a full-disclosure development effort by NOAO in collaboration with the CARA ASTEROID project for the benefit of the astronomical community.

  13. The Aerosol-Monsoon Climate System of Asia

    NASA Technical Reports Server (NTRS)

    Lau, William K. M.; Kyu-Myong, Kim

    2012-01-01

    In Asian monsoon countries such as China and India, human health and safety problems caused by air-pollution are worsening due to the increased loading of atmospheric pollutants stemming from rising energy demand associated with the rapid pace of industrialization and modernization. Meanwhile, uneven distribution of monsoon rain associated with flash flood or prolonged drought, has caused major loss of human lives, and damages in crop and properties with devastating societal impacts on Asian countries. Historically, air-pollution and monsoon research are treated as separate problems. However a growing number of recent studies have suggested that the two problems may be intrinsically intertwined and need to be studied jointly. Because of complexity of the dynamics of the monsoon systems, aerosol impacts on monsoons and vice versa must be studied and understood in the context of aerosol forcing in relationship to changes in fundamental driving forces of the monsoon climate system (e.g. sea surface temperature, land-sea contrast etc.) on time scales from intraseasonal variability (weeks) to climate change ( multi-decades). Indeed, because of the large contributions of aerosols to the global and regional energy balance of the atmosphere and earth surface, and possible effects of the microphysics of clouds and precipitation, a better understanding of the response to climate change in Asian monsoon regions requires that aerosols be considered as an integral component of a fully coupled aerosol-monsoon system on all time scales. In this paper, using observations and results from climate modeling, we will discuss the coherent variability of the coupled aerosol-monsoon climate system in South Asia and East Asia, including aerosol distribution and types, with respect to rainfall, moisture, winds, land-sea thermal contrast, heat sources and sink distributions in the atmosphere in seasonal, interannual to climate change time scales. We will show examples of how elevated

  14. Impact of anthropogenic aerosols on Indian summer monsoon

    SciTech Connect

    Wang, Chien; Kim, Dongchul; Ekman, Annica; Barth, Mary; Rasch, Philip J.

    2009-11-05

    Using an interactive aerosol-climate model we find that absorbing anthropogenic aerosols, whether coexisting with scattering aerosols or not, can significantly affect the Indian summer monsoon system. We also show that the influence is reflected in a perturbation to the moist static energy in the sub-cloud layer, initiated as a heating by absorbing aerosols to the planetary boundary layer. The perturbation appears mostly over land, extending from just north of the Arabian Sea to northern India along the southern slope of the Tibetan Plateau. As a result, during the summer monsoon season, modeled convective precipitation experiences a clear northward shift, coincidently in agreement with observed monsoon precipitation changes in recent decades particularly during the onset season. We demonstrate that the sub-cloud layer moist static energy is a useful quantity for determining the impact of aerosols on the northward extent and to a certain degree the strength of monsoon convection.

  15. GPM Sees Slow Start of India's 2015 Monsoon Season

    NASA Video Gallery

    This animation shows the GPM core observatory total rainfall that fell from June 1 to 8. 2015 at the start of India's Monsoon Season as calculated by Integrated Multi-satellitE Retrievals for GPM (...

  16. Asian Summer Monsoon Intraseasonal Variability in General Circulation Models

    SciTech Connect

    Sperber, K R; Annamalai, H

    2004-02-24

    The goals of this report are: (1) Analyze boreal summer Asian monsoon intraseasonal variability general circulation models--How well do the models represent the eastward and northward propagating components of the convection and how well do the models represent the interactive control that the western tropical Pacific rainfall exerts on the rainfall over India and vice-versa? (2) Role of air-sea interactions--prescribed vs. interactive ocean; and (3) Mean monsoon vs. variability.

  17. South Asian Summer Monsoon in CMIP5 GCMs

    NASA Astrophysics Data System (ADS)

    Ashfaq, M.; Rastogi, D.; Touma, D. E.

    2012-12-01

    Many Global Climate Models (GCMs) in the IPCC Fourth Assessment Report (AR4) suffered from substantial biases in their simulation of processes that govern summer monsoon dynamics in South Asia, leading to uncertainties in the simulation of monsoon response to future increases in greenhouse forcing. In order to test the ability of the current generation of GCMs that are part of the Coupled Model Inter-comparison Project Phase 5 (CMIP5) in the simulation of South Asian summer monsoon dynamics, we analyze the outputs from their historic simulations that correspond to 1970-1999 period. The analyses include the comparison of multiple monsoon indices including those representing monsoon onset, local circulations and global teleconnections, at seasonal, intra-seasonal and inter-annual time scales. We find that most of the GCMs are unable to simulate the timing of the summer monsoon onset over land, leading to substantial biases in seasonal precipitation means and variability, and intra-seasonal precipitation distribution. These errors are partly due to the fact that the majority of the GCMs exhibit a shift in the annual monsoon cycle with most of them exhibiting a precipitation peak in August in contrast to the observed peak in July, and that most of the GCMs substantially underestimate the strength of meridional troposhepric temperature gradient and vertical easterly shear during the summer season. We also find many models with low skill in the simulation of intra-seasonal temperature variability, and monsoon connection with local Hadley circulation and ENSO variability. These results have important implications for the reliability of future climate projections and impact assessments over South Asia.

  18. Transient coupling relationships of the Holocene Australian monsoon

    NASA Astrophysics Data System (ADS)

    McRobie, F. H.; Stemler, T.; Wyrwoll, K.-H.

    2015-08-01

    The northwest Australian summer monsoon owes a notable degree of its interannual variability to interactions with other regional monsoon systems. Therefore, changes in the nature of these relationships may contribute to variability in monsoon strength over longer time scales. Previous attempts to evaluate how proxy records from the Indonesian-Australian monsoon region correspond to other records from the Indian and East Asian monsoon regions, as well as to El Niño-related proxy records, have been qualitative, relying on 'curve-fitting' methods. Here, we seek a quantitative approach for identifying coupling relationships between paleoclimate proxy records, employing statistical techniques to compute the interdependence of two paleoclimate time series. We verify the use of complex networks to identify coupling relationships between modern climate indices. This method is then extended to a set of paleoclimate proxy records from the Asian, Australasian and South American regions spanning the past 9000 years. The resulting networks demonstrate the existence of coupling relationships between regional monsoon systems on millennial time scales, but also highlight the transient nature of teleconnections during this period. In the context of the northwest Australian summer monsoon, we recognise a shift in coupling relationships from strong interhemispheric links with East Asian and ITCZ-related proxy records in the mid-Holocene to significantly weaker coupling in the later Holocene. Although the identified links cannot explain the underlying physical processes leading to coupling between regional monsoon systems, this method provides a step towards understanding the role that changes in teleconnections play in millennial-to orbital-scale climate variability.

  19. Recent change of the global monsoon precipitation (1979-2008)

    NASA Astrophysics Data System (ADS)

    Wang, Bin; Liu, Jian; Kim, Hyung-Jin; Webster, Peter J.; Yim, So-Young

    2012-09-01

    The global monsoon (GM) is a defining feature of the annual variation of Earth's climate system. Quantifying and understanding the present-day monsoon precipitation change are crucial for prediction of its future and reflection of its past. Here we show that regional monsoons are coordinated not only by external solar forcing but also by internal feedback processes such as El Niño-Southern Oscillation (ENSO). From one monsoon year (May to the next April) to the next, most continental monsoon regions, separated by vast areas of arid trade winds and deserts, vary in a cohesive manner driven by ENSO. The ENSO has tighter regulation on the northern hemisphere summer monsoon (NHSM) than on the southern hemisphere summer monsoon (SHSM). More notably, the GM precipitation (GMP) has intensified over the past three decades mainly due to the significant upward trend in NHSM. The intensification of the GMP originates primarily from an enhanced east-west thermal contrast in the Pacific Ocean, which is coupled with a rising pressure in the subtropical eastern Pacific and decreasing pressure over the Indo-Pacific warm pool. While this mechanism tends to amplify both the NHSM and SHSM, the stronger (weaker) warming trend in the NH (SH) creates a hemispheric thermal contrast, which favors intensification of the NHSM but weakens the SHSM. The enhanced Pacific zonal thermal contrast is largely a result of natural variability, whilst the enhanced hemispherical thermal contrast is likely due to anthropogenic forcing. We found that the enhanced global summer monsoon not only amplifies the annual cycle of tropical climate but also promotes directly a "wet-gets-wetter" trend pattern and indirectly a "dry-gets-drier" trend pattern through coupling with deserts and trade winds. The mechanisms recognized in this study suggest a way forward for understanding past and future changes of the GM in terms of its driven mechanisms.

  20. Land-surface processes and monsoon climate system

    NASA Astrophysics Data System (ADS)

    Xue, Yongkang; De Sales, Fernando; Lau, William; Boone, Arron; Mechoso, Carlos

    2015-04-01

    Yongkang Xue, F. De Sales, B. Lau, A. Boone, C. R. Mechoso Differential thermal heating of land and ocean and heat release into the atmosphere are important factors that determine the onset, strength, duration and spatial distribution of large-scale monsoons. A global and seasonal assessment of land surface process (LSP) effects on the monsoon system has been made based on general circulation models (GCM) coupled to different benchmark land models, which physically represent either comprehensive, or partial, or minimal LSP representations. Observed precipitation is applied as constrain and differences in simulation error are used to assess the effect of the LSP with different complexity. The AGCM results indicate that the land/atmosphere interaction has substantial impact on global water cycle, while the monsoon regions have had strongest impact at intraseasonal to decadal scales. Among monsoon regions, West Africa, South Asia, East Asia, and Amazon regions have largest impact while some monsoon regions have less impact due to strong air/sea interactions and narrow land mass there. LSP reduces the annual precipitation error by 58% over global monsoon regions, about 35% observed precipitation. The partial LSP effect (excluding soil moisture and vegetation albedo) reduces annual precipitation error over monsoon region that equals to about 13% of observed precipitation. The LSP affects the monsoon evolution through different mechanisms at different scales. It affects the surface energy balance and energy partitioning in latent and sensible heat, the atmospheric heating rate, and general circulation. The LSP effects have also been assessed in the land use land cover change experiment. Based on recently compiled global land-use data from 1948-2005, the GCM simulation results indicate the degradation in Mexico, West Africa, south and East Asia and South America produce substantial precipitation anomalies, some of which are consistent with observed regional precipitation

  1. Africans in America.

    ERIC Educational Resources Information Center

    Hart, Ayanna; Spangler, Earl

    This book introduces African-American history and culture to children. The first Africans in America came from many different regions and cultures, but became united in this country by being black, African, and slaves. Once in America, Africans began a long struggle for freedom which still continues. Slavery, the Civil War, emancipation, and the…

  2. Therapy with African Families.

    ERIC Educational Resources Information Center

    Nwadiora, Emeka

    1996-01-01

    Informs helping professionals about the unique history and challenges of African families to guide them toward providing ethnically sensitive psychological services to African immigrant families in need. African families undergo great stress when faced with the alienation of being Black and African in a Euro-American culture. (SLD)

  3. African Outreach Workshop 1974.

    ERIC Educational Resources Information Center

    Schmidt, Nancy J.

    This report discusses the 1974 African Outreach Workshop planned and coordinated by the African Studies Program at the University of Illinois at Urbana-Champaign. Its major aim was to assist teachers in developing curriculum units on African using materials available in their local community. A second aim was for the African Studies Program to…

  4. Pacific freshening drives Pliocene cooling and Asian monsoon intensification

    PubMed Central

    Nie, Junsheng; Stevens, Thomas; Song, Yougui; King, John W.; Zhang, Rui; Ji, Shunchuan; Gong, Lisha; Cares, Danielle

    2014-01-01

    The monsoon is a fundamental component of Earth's climate. The Pliocene warm period is characterized by long-term global cooling yet concurrent monsoon dynamics are poorly known. Here we present the first fully quantified and calibrated reconstructions of separate Pliocene air temperature and East Asian summer monsoon precipitation histories on the Chinese Loess Plateau through joint analysis of loess/red clay magnetic parameters with different sensitivities to air temperature and precipitation. East Asian summer monsoon precipitation shows an intensified trend, paradoxically at the same time that climate cooled. We propose a hitherto unrecognized feedback where persistently intensified East Asian summer monsoon during the late Pliocene, triggered by the gradual closure of the Panama Seaway, reinforced late Pliocene Pacific freshening, sea-ice development and ice volume increase, culminating in initiation of the extensive Northern Hemisphere glaciations of the Quaternary Ice Age. This feedback mechanism represents a fundamental reinterpretation of the origin of the Quaternary glaciations and the impact of the monsoon. PMID:24969361

  5. Interannual and Interdecadal Variability of Thailand Summer Monsoon Season.

    NASA Astrophysics Data System (ADS)

    Singhrattna, Nkrintra; Rajagopalan, Balaji; Krishna Kumar, K.; Clark, Martyn

    2005-06-01

    Summer monsoon rains are a critical factor in Thailand's water resources and agricultural planning and management. In fact, they have a significant impact on the country's economic health. Consequently, understanding the variability of the summer monsoon rains over Thailand is important for instituting effective mitigating strategies against extreme rainfall fluctuations. To this end, the authors systematically investigated the relationships between summer monsoon precipitation from the central and northern regions of Thailand and large-scale climate features. It was found that Pacific sea surface temperatures (SSTs), in particular, El Niño-Southern Oscillation (ENSO), have a negative relationship with the summer monsoon rainfall over Thailand in recent decades. However, the relationship between summer rainfall and ENSO was weak prior to 1980. It is hypothesized that the ENSO teleconnection depends on the SST configuration in the tropical Pacific Ocean, that is, an eastern Pacific-based El Niño pattern, such as is the case in most of the post-1980 El Niño events, tends to place the descending limb of the Walker circulation over the Thailand-Indonesian region, thereby significantly reducing convection and consequently, rainfall over Thailand. It is believed that this recent shift in the Walker circulation is instrumental for the nonstationarity in ENSO-monsoon relationships in Thailand. El Niños of 1997 and 2002 corroborate this hypothesis. This has implications for monsoon rainfall forecasting and, consequently, for resources planning and management.

  6. What is the timing of orbital-scale monsoon changes?

    NASA Astrophysics Data System (ADS)

    Ruddiman, William F.

    2006-04-01

    A major (but little noted) divergence of opinion has developed among climate scientists over the orbital-scale periodicity and phasing of tropical monsoon variations. Kutzbach (1981. Monsoon climate of the early Holocene: climate experiment with Earth's orbital parameters for 9000 years ago. Science 214, 59-61) proposed that monsoons are driven by northern summer insolation at the precession period, but Clemens and Prell (1990. Late Pleistocene variability of Arabian Sea summer monsoon winds and continental aridity: eolian records from the lithogenic component of deep-sea sediments. Paleoceanography 5, 109-145; 2003. A 350,000-year summer-monsoon multi-proxy stack from the Owen Ridge, Northern Arabian Sea. Marine Geology 201, 35-51) inferred a more complicated response tied to latent heat transfer from the Southern Hemisphere. Because tropical monsoons affect climate over a vast area, resolving this divergence is an important task for the climate community. The purpose of this note is to highlight definitive evidence from high-resolution dating of speleothem calcite that provides unambiguous support for the Kutzbach hypothesis.

  7. Early warnings and missed alarms for abrupt monsoon transitions

    NASA Astrophysics Data System (ADS)

    Thomas, Z. A.; Kwasniok, F.; Boulton, C. A.; Cox, P. M.; Jones, R. T.; Lenton, T. M.; Turney, C. S. M.

    2015-12-01

    Palaeo-records from China demonstrate that the East Asian Summer Monsoon (EASM) is dominated by abrupt and large magnitude monsoon shifts on millennial timescales, switching between periods of high and weak monsoon rains. It has been hypothesized that over these timescales, the EASM exhibits two stable states with bifurcation-type tipping points between them. Here we test this hypothesis by looking for early warning signals of past bifurcations in speleothem δ18O records from Sanbao Cave and Hulu Cave, China, spanning the penultimate glacial cycle. We find that although there are increases in both autocorrelation and variance preceding some of the monsoon transitions during this period, it is only immediately prior to the abrupt monsoon shift at the penultimate deglaciation (Termination II) that statistically significant increases are detected. To supplement our data analysis, we produce and analyse multiple model simulations that we derive from these data. We find hysteresis behaviour in our model simulations with transitions directly forced by solar insolation. However, signals of critical slowing down, which occur on the approach to a bifurcation, are only detectable in the model simulations when the change in system stability is sufficiently slow to be detected by the sampling resolution of the data set. This raises the possibility that the early warning "alarms" were missed in the speleothem data over the period 224-150 kyr and it was only at the monsoon termination that the change in the system stability was sufficiently slow to detect early warning signals.

  8. Causal evidence between monsoon and evolution of rhizomyine rodents

    PubMed Central

    López-Antoñanzas, Raquel; Knoll, Fabien; Wan, Shiming; Flynn, Lawrence J.

    2015-01-01

    The modern Asian monsoonal systems are currently believed to have originated around the end of the Oligocene following a crucial step of uplift of the Tibetan-Himalayan highlands. Although monsoon possibly drove the evolution of many mammal lineages during the Neogene, no evidence thereof has been provided so far. We examined the evolutionary history of a clade of rodents, the Rhizomyinae, in conjunction with our current knowledge of monsoon fluctuations over time. The macroevolutionary dynamics of rhizomyines were analyzed within a well-constrained phylogenetic framework coupled with biogeographic and evolutionary rate studies. The evolutionary novelties developed by these rodents were surveyed in parallel with the fluctuations of the Indian monsoon so as to evaluate synchroneity and postulate causal relationships. We showed the existence of three drops in biodiversity during the evolution of rhizomyines, all of which reflected elevated extinction rates. Our results demonstrated linkage of monsoon variations with the evolution and biogeography of rhizomyines. Paradoxically, the evolution of rhizomyines was accelerated during the phases of weakening of the monsoons, not of strengthening, most probably because at those intervals forest habitats declined, which triggered extinction and progressive specialization toward a burrowing existence. PMID:25759260

  9. Possible role of pre-monsoon sea surface warming in driving the summer monsoon onset over the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Li, Kuiping; Liu, Yanliang; Yang, Yang; Li, Zhi; Liu, Baochao; Xue, Liang; Yu, Weidong

    2016-08-01

    Sea surface temperature (SST) reaches its annual maximum just before the summer monsoon onset and collapses soon after in the central areas of the Bay of Bengal (BoB). Here, the impact of the peak in the pre-monsoon SST on triggering the earliest monsoon onset in the BoB is investigated, with a focus on the role they play in driving the first-branch northward-propagating intra-seasonal oscillations (FNISOs) over the equatorial Eastern Indian Ocean (EIO). During the calm pre-monsoon period, sea surface warming in the BoB could increase the surface equivalent potential temperature (θe) in several ways. Firstly, warming of the sea surface heats the surface air through sensible heating, which forces the air temperature to follow the SST. The elevated air surface temperature accounts for 30 % of the surface θe growth. Furthermore, the elevated air temperature raises the water vapor capacity of the surface air to accommodate more water vapor. Constrained by the observation that the surface relative humidity is maintained nearly constant during the monsoon transition period, the surface specific humidity exhibits a significant increase, according to the Clausius-Clapeyron relationship. Budget analysis indicates that the additional moisture is primarily obtained from sea surface evaporation, which also exhibits a weak increasing trend due to the sea surface warming. In this way, it contributes about 70 % to the surface θe growth. The rapid SST increase during the pre-monsoon period preconditions the summer monsoon onset over the BoB through its contributions to significantly increase the surface θe, which eventually establishes the meridional asymmetry of the atmospheric convective instability in the EIO. The pre-established greater convective instability leads to the FNISO convections, and the summer monsoon is triggered in the BoB region.

  10. The first dominant co-circulation of both dengue and chikungunya viruses during the post-monsoon period of 2010 in Delhi, India.

    PubMed

    Singh, P; Mittal, V; Rizvi, M M A; Chhabra, M; Sharma, P; Rawat, D S; Bhattacharya, D; Chauhan, L S; Rai, A

    2012-07-01

    Independent outbreaks of dengue virus (DENV) infection and sporadic cases of chikungunya virus (CHIKV) have been recorded in the metropolitan city of Delhi on several occasions in the past. However, during a recent 2010 arboviral outbreak in Delhi many cases turned negative for DENV. This prompted us to use duplex reverse transcriptase-polymerase chain reaction (D-RT-PCR) to establish the aetiology of dengue/chikungunya through sequencing of CprM and E1 genes of dengue and chikungunya viruses. Interestingly, for the first time, both DENV and CHIKV co-circulated simultaneously and in equally dominant proportion during the post-monsoon period of 2010. DENV-1 genotype III and the East Central South African genotype of CHIKV were associated with post-monsoon spread of these viruses.

  11. Trends in global monsoon area and precipitation over the past 30 years

    NASA Astrophysics Data System (ADS)

    Hsu, Pang-chi; Li, Tim; Wang, Bin

    2011-04-01

    The analysis of the GPCP and CMAP datasets during the past 30 years (1979-2008) indicates that there are consistent increasing trends in both the global monsoon area (GMA) and the global monsoon total precipitation (GMP). This positive monsoon rainfall trend differs from previous studies that assumed a fixed global monsoon domain. Due to the increasing trends in both the GMA and GMP, a global monsoon intensity (GMI) index, which measures the global monsoon precipitation amount per unit area, is introduced. The GMI measures the strength of the global monsoon. Our calculations with both the GPCP and CMAP datasets show a consistent downward trend in the GMI over the past 30 years. This decreasing trend is primarily attributed to a greater percentage increase in the GMA than in the GMP. A further diagnosis reveals that the decrease of the GMI is primarily attributed to the land monsoon in the GPCP, but to the oceanic monsoon in the CMAP.

  12. A Pleistocene Indian Monsoon record from Heqing Basin, SW China

    NASA Astrophysics Data System (ADS)

    Qiang, X.; An, Z.; Shen, J.; Jin, Z.; Sun, Y.; Tong, G.; Chang, H.; Liu, X.; Liu, W.; Wang, S.; Zhou, W.; Song, Y.; Xiao, X.; Xiao, H.

    2008-12-01

    Heqing Basin (100°06'-100°16'E, 26°28'-26°46'N) is situated in southeastern margin of Tibetan Plateau, a geological conjunction zone of three tectonic units separated by Jinshajiang, Honghe and Xiaojinhe-Lijiang fault belts. Modern climate in this region is mainly influenced by Indian monsoon circulation. In Year 2002, a 665.83 m long core was retrieved from the Heqing basin under the support of Chinese Environmental Scientific Drilling program, which permits a high-resolution reconstruction of the Indian monsoon evolution from a continental perspective. The core mainly consists of gray clay, silty clay and silt. Magnetostratographic result generated by both thermal and alternating-field demagnetization methods indicates that the bottom age of the Heqing core is about 2.78 Myr. Multiple proxies (magnetic susceptibility, grain size, CaCO3 content, loss of ignite, pollen concentrations, and major/trace elements) were generated to reconstruct regional climate change and its dynamical links to Indian summer monsoon and solar insolation forcing. The results suggest that during glacial periods, this region is characterized by reduced vegetation cover (e.g., low total pollen concentration) and enhanced physical weathering (e.g., high Rb/Sr ratio), whereas during interglacial times, vegetation cover was extensive and chemical weathering is relatively strong around Heqing basin. Good correlation between variations in proxy indicators from Heqing core and stacked Indian summer monsoon record from Arabian Sea (Clemens and Prell, 2003) indicates that over the last 0.35 Myr, Heqing basin is predominantly influenced by Indian summer monsoon. Unlike Indian monsoon records from the Arabian Sea and Indian Ocean which resolution is relatively low, our high-resolution proxy variations permit a robust understanding of the Indian summer monsoon variations over the last 2.6 Myr. Comparisons of monsoon proxies from land and ocean indicate that solar insolation is the dominant factor

  13. A new perspective on West African hydroclimate during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Parker, Andrew O.; Schmidt, Matthew W.; Jobe, Zane R.; Slowey, Niall C.

    2016-09-01

    Widespread drought characterized the Heinrich 1 and Younger Dryas cold periods of the last deglaciation throughout much of Africa, causing large increases in dust emissions from the Sahara and Sahel. At the same time, increases in wind strength may have also contributed to dust flux, making it difficult to interpret dust records alone as reflecting changes in rainfall over the region. The Niger River has the third largest drainage basin in Africa and drains most of the Sahara and Sahel and thus preserves and propagates climatic signals. Here, we present new reconstructions of Niger Delta sea surface salinity and Niger River discharge for the last 20,000 years in order to more accurately reconstruct the onset of the Western African Monsoon system. Based on calculated δ18OSEAWATER (δ18OSW) and measured Ba/Ca ratios in planktonic foraminifera, these new records reflect changes in sub-Saharan precipitation across the Niger River Basin in West Africa and reveal that the West African Monsoon system began to intensify several thousand years after the equatorial Monsoon system in Central Africa. We also present new records of primary productivity in the Niger Delta that are related to wind-driven upwelling and show that productivity is decoupled from changes in Niger River discharge. Our results suggest that wind strength, rather than changes in monsoon moisture, was the primary driver of dust emissions from the Sahara and Sahel across the last deglaciation.

  14. Subtropical circulation, Tibetan Plateau, and Asian Summer Monsoon

    NASA Astrophysics Data System (ADS)

    Wu, G. X.

    2015-12-01

    The characteristics of the land-air-sea interaction in summer subtropics and their impacts on climate were revealed. It was shown that different kind of diabatic heating plays different roles in the formation of the subtropical circulation where the surface sensible heating associated with the land-sea distribution plays a fundamentally important role, and the three spatial- scales of atmospheric forcing contribute in various ways to the formation of aridity/desert over the western parts of continents and wet/monsoon over the eastern parts. Thus monsoon and desert coexist as twin features. It was identified that the onset of the Asian summer monsoon (ASM) consists of three dynamically consequential stages: the onset first occurs over the eastern Bay of Bengal (BOB) in early May, which is followed by the onset over the South China Sea in mid-May, and the Indian Monsoon onset in early June. During such an onset progression, the formation, maintenance and evolution of the South Asian High (SAH) play a significant role in generating the upper tropospheric dumping. In the lower troposphere, the development of the BOB monsoon onset vortex, the ASM onset barrier, the cross equatorial SST gradient and the forced convection over the eastern Arabian Sea also regulate the onset evolution. In winter the Tibetan Plateau (TP) can inspire a stationary dipole-type atmospheric wave, forming a specific climate pattern in Asia. In spring, such a dipole circulation forms the unique persistent rainfall over Southern China. The TP forcing can also anchor the ASM onset over the BOB by generating the unique short- life BOB SST warm pool and modulating the SAH in the upper troposphere. In summer the thermal forcing of the Tibetan-Iranian Plateau plays a significant role in controlling the Asian monsoon by transporting water vapor from the sea to the land for the genesis of continental monsoon. The TP thermal forcing also modulates the regional climate variability in different time scales.

  15. Asian Monsoon Variability from the Monsoon Asia Drought Atlas (MADA) and Links to Indo-Pacific Climate

    NASA Astrophysics Data System (ADS)

    Ummenhofer, Caroline; D'Arrigo, Rosanne; Anchukaitis, Kevin; Hernandez, Manuel; Buckley, Brendan; Cook, Edward

    2014-05-01

    Drought patterns across monsoon and temperate Asia over the period 1877-2005 are linked to Indo-Pacific climate variability associated with the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). Using the Monsoon Asia Drought Atlas (MADA) composed of a high-resolution network of hydroclimatically sensitive tree-ring records with a focus on the June-August months, spatial drought patterns during El Niño and IOD events are assessed as to their agreement with an instrumental drought index and consistency in the drought response amongst ENSO/IOD events. Spatial characteristics in drought patterns are related to regional climate anomalies over the Indo-Pacific basin, using reanalysis products, including changes in the Asian monsoon systems, zonal Walker circulation, moisture fluxes, and precipitation. A weakening of the monsoon circulation over the Indian subcontinent and Southeast Asia during El Niño events, along with anomalous subsidence over monsoon Asia and reduced moisture flux, is reflected in anomalous drought conditions over India, Southeast Asia and Indonesia. When an IOD event co-occurs with an El Niño, severe drought conditions identified in the MADA for Southeast Asia, Indonesia, eastern China and central Asia are associated with a weakened South Asian monsoon, reduced moisture flux over China, and anomalous divergent flow and subsidence over Indonesia. Variations in the strength of the South Asian monsoon can also be linked to the Strange Parallels Drought (1756-1768) affecting much of Southeast Asia and the Indian subcontinent in the mid-18th Century. Large-scale climate anomalies across the wider region during years with an anomalously strengthened/weakened South Asian monsoon are discussed with implications for severe droughts prior to the instrumental period. Insights into the relative influences of Pacific and Indian Ocean variability for Asian monsoon climate on interannual to decadal and longer timescales, as recorded in the

  16. The Joint Aerosol-Monsoon Experiment (JAMEX): A Core Element for the Asian Monsoon Year (2008-2009)

    NASA Technical Reports Server (NTRS)

    Lau, WIlliam K. M.

    2007-01-01

    The objective of the Joint Aerosol-Monsoon Experiment (JAMEX) is to unravel the physical mechanisms and multi-scale interactions associated with aerosol-monsoon water cycle in the Asian Indo-Paczj?c region towards improved prediction of rainfall in land regions of the Asian monsoon. JAMEX will be planned as a five-year (2007-201 1) multi-national aerosol-monsoon research project, aimed at promoting collaboration, partnership and alignment of ongoing and planned national and international programs. Two coordinated special observing periods (SOP), covering the pre-monsoon (April-May) and the monsoon (June-August) periods is tentatively targeted for 2008 and 2009. The major work on validation and reference site coordination will take place in 2007 through the spring of 2008. A major science workshop is planned after SOP-I1 in 2010. Modeling and satellite data utilization studies will continue throughout the entire period to help in design of the observation arrays and measurement platforms for SOPS. The tentative time schedule, including milestones and research activities is shown in Fig. 1. One of the unique aspects of JAMEX is that it stems from grass-root scientific and societal imperatives, and it bridges a gap in existing national and international research programs. Currently we have identified 10 major national and international projects/programs separately for aerosols and monsoon research planned in the next five years in China, India, Japan, Italy, and the US, that could be potential contributors or partners with JAMEX. These include the Asian-Indo- Pacific Ocean (AIPO) Project and Aerosol Research Project from China, Monsoon Asian Hydro- Atmospheric Science Research and predication Initiative (MAHASRI) from Japan, Continental Tropical Convergence Zone (CTCZ) and Severe Thunderstorm: Observations and Regional Modeling (STORM) from India, Share-Asia from Italy, Atmospheric Brown Cloud (ABC), Pacific Aerosol-Cloud-Dust Experiment (PACDEX), East Asia Study of

  17. The Joint Aerosol-Monsoon Experiment (JAMEX): A Core Element for the Asian Monsoon Year (2008-2009)

    NASA Technical Reports Server (NTRS)

    Lau, William K.M.

    2007-01-01

    The objective of the Joint Aerosol-Monsoon Experiment (JAMEX) is to unravel the physical mechanisms and multi-scale interactions associated with aerosol-monsoon water cycle in the Asian Indo-Pacific region towards improved prediction of rainfall in land regions of the Asian monsoon. JAMEX will be planned as a five-year (2007-201 1) multi-national aerosol-monsoon research project, aimed at promoting collaboration, partnership and alignment of ongoing and planned national and international programs. Two coordinated special observing periods (SOP), covering the pre-monsoon (April-May) and the monsoon (June-August) periods is tentatively targeted for 2008 and 2009. The major work on validation and reference site coordination will take place in 2007 through the spring of 2008. A major science workshop is planned after SOP-I1 in 2010. Modeling and satellite data utilization studies will continue throughout the entire period to help in design of the observation arrays and measurement platforms for SOPS. The tentative time schedule, including milestones and research activities is shown in Fig. 1. One of the unique aspects of JAMEX is that it stems from grass-root scientific and societal imperatives, and it bridges a gap in existing national and international research programs. Currently we have identified 10 major national and international projects/programs separately for aerosols and monsoon research planned in the next five years in China, India, Japan, Italy, and the US, that could be potential contributors or partners with JAMEX. These include the Asian-Indo- Pacific Ocean (AIPO) Project and Aerosol Research Project from China, Monsoon Asian Hydro- Atmospheric Science Research and predication Initiative (MAHASRI) from Japan, Continental Tropical Convergence Zone (CTCZ) and Severe Thunderstorm: Observations and Regional Modeling (STORM) from India, Share-Asia from Italy, Atmospheric Brown Cloud (ABC), Pacific Aerosol-Cloud-Dust Experiment (PACDEX), East Asia Study of

  18. Modelling Monsoons: Understanding and Predicting Current and Future Behaviour

    SciTech Connect

    Turner, A; Sperber, K R; Slingo, J M; Meehl, G A; Mechoso, C R; Kimoto, M; Giannini, A

    2008-09-16

    The global monsoon system is so varied and complex that understanding and predicting its diverse behaviour remains a challenge that will occupy modellers for many years to come. Despite the difficult task ahead, an improved monsoon modelling capability has been realized through the inclusion of more detailed physics of the climate system and higher resolution in our numerical models. Perhaps the most crucial improvement to date has been the development of coupled ocean-atmosphere models. From subseasonal to interdecadal timescales, only through the inclusion of air-sea interaction can the proper phasing and teleconnections of convection be attained with respect to sea surface temperature variations. Even then, the response to slow variations in remote forcings (e.g., El Nino-Southern Oscillation) does not result in a robust solution, as there are a host of competing modes of variability that must be represented, including those that appear to be chaotic. Understanding the links between monsoons and land surface processes is not as mature as that explored regarding air-sea interactions. A land surface forcing signal appears to dominate the onset of wet season rainfall over the North American monsoon region, though the relative role of ocean versus land forcing remains a topic of investigation in all the monsoon systems. Also, improved forecasts have been made during periods in which additional sounding observations are available for data assimilation. Thus, there is untapped predictability that can only be attained through the development of a more comprehensive observing system for all monsoon regions. Additionally, improved parameterizations - for example, of convection, cloud, radiation, and boundary layer schemes as well as land surface processes - are essential to realize the full potential of monsoon predictability. Dynamical considerations require ever increased horizontal resolution (probably to 0.5 degree or higher) in order to resolve many monsoon features

  19. Linear Prediction of Indian Monsoon Rainfall(.

    NASA Astrophysics Data System (ADS)

    Delsole, Timothy; Shukla, J.

    2002-12-01

    This paper proposes a strategy for selecting the best linear prediction model for Indian monsoon rainfall. In this strategy, a cross-validation procedure first screens out all models that perform poorly on independent data, then the error variance of every remaining model is compared to that of every other model to test whether the difference in error variances is statistically significant. This strategy is shown to produce better forecasts on average than selecting either the model that utilizes all predictors, the model that explains the most variance in the independent data, or the model with the most favorable statistic suggested by Mallow. All of the model selection criteria suggest that regression models based on two to three predictors produce better forecasts on average than regression models using a larger number of predictors. For the period up to 1967, the forecast strategy selected the prior climatology as the best predictor. For the period 1967 to the present, the strategy performed better than forecasts based on the prior climatology and all other methodologies investigated. Indexes of Pacific Ocean temperature in the Tropics (called Niño-3) and indexes of pressure fluctuations in the Northern Atlantic (called NAO), at 1-6 lead months, failed to provide prediction models that performed better on average than a prediction based on the antecedent climatology. Forecasts based on the prior 25-yr climatology had especially high skill during the recent period 1989-2000, a fact that appears to be a mere coincidence, but which may be relevant to interpreting the skill of the power regression model currently used by the India Meteorological Department.

  20. Entrainment and mixing mechanism in monsoon clouds

    NASA Astrophysics Data System (ADS)

    Bera, Sudarsan; Prabhakaran, Thara; Pandithurai, Govindan; Brenguier, Jean-Louis

    2015-04-01

    Entrainment and consequent mixing impacts the cloud microphysical parameters and droplet size distribution (DSD) significantly which are very important for cloud radiative properties and the mechanism for first rain drop formation. The entrainment and mixing mechanisms are investigated in this study using in situ observations in warm cumulus clouds over monsoon region. Entrainment is discussed in the framework of the homogeneous and inhomogeneous mixing concepts and their effects on cloud droplet size distribution, number concentration, liquid water content and mean radius are described. The degree of homogeneity increases with droplet number concentration and adiabatic fraction, indicating homogeneous type mixing in the cloud core where dilution is less. Inhomogeneous mixing is found to be a dominating process at cloud edges where dilution is significant. Cloud droplet size distribution (DSD) is found to shift towards lower sizes during a homogeneous mixing event in the cloud core whereas spectral width of DSD decreases due to inhomogeneous mixing at cloud edges. Droplet size spectra suggests that largest droplets are mainly formed in the less diluted cloud core while diluted cloud edges have relatively smaller droplets, so that raindrop formation occurs mainly in the core of the cloud. The origin of the entrained parcels in deep cumulus clouds is investigated using conservative thermodynamical parameters. The entrained parcels originate from a level close to the observation level or slightly below through lateral edges. Cloud edges are significantly diluted due to entrainment of sub-saturated environmental air which can penetrate several hundred meters inside the cloud before it gets mixed completely with the cloud mass. Less diluted parcels inside the cloud core originates from a level much below the cloud base height. Penetrating downdraft from cloud top is seldom observed at the observation level and strong downdrafts may be attributed to in-cloud oscillation

  1. Numerical Simulation of the Large-Scale North American Monsoon Water Sources

    NASA Technical Reports Server (NTRS)

    Bosilovich, Michael G.; Sud, Yogesh C.; Schubert, Siegfried D.; Walker, Gregory K.

    2002-01-01

    A general circulation model (GCM) that includes water vapor tracer (WVT) diagnostics is used to delineate the dominant sources of water vapor for precipitation during the North American monsoon. A 15-year model simulation carried out with one-degree horizontal resolution and time varying sea surface temperature is able to produce reasonable large-scale features of the monsoon precipitation. Within the core of the Mexican monsoon, continental sources provide much of the water for precipitation. Away from the Mexican monsoon (eastern Mexico and Texas), continental sources generally decrease with monsoon onset. Tropical Atlantic Ocean sources of water gain influence in the southern Great Plains states where the total precipitation decreases during the monsoon onset. Pacific ocean sources do contribute to the monsoon, but tend to be weaker after onset. Evaluating the development of the monsoons, soil water and surface evaporation prior to monsoon onset do not correlate with the eventual monsoon intensity. However, the most intense monsoons do use more local sources of water than the least intense monsoons, but only after the onset. This suggests that precipitation recycling is an important factor in monsoon intensity.

  2. East Asian summer monsoon precipitation variability since the last deglaciation

    NASA Astrophysics Data System (ADS)

    Chen, Fahu; Xu, Qinghai; Chen, Jianhui; Birks, H. John B.; Liu, Jianbao; Zhang, Xiaojian; Jin, Liya

    2016-04-01

    The lack of a precisely-dated, unequivocal climate proxy from northern China, where precipitation variability is traditionally considered as an East Asian summer monsoon (EASM) indicator, impedes our understanding of the behaviour and dynamics of the EASM. Here we present a well-dated, pollen-based, ~20-yr-resolution quantitative precipitation reconstruction (derived using a transfer function) from an alpine lake in North China, which provides for the first time a direct record of EASM evolution since 14.7 ka (ka=thousands of years before present, where the "present" is defined as the year AD 1950). Our record reveals a gradually intensifying monsoon from 14.7-7.0 ka, a maximum monsoon (30% higher precipitation than present) from ~7.8-5.3 ka, and a rapid decline since ~3.3 ka. These insolation-driven EASM trends were punctuated by two millennial-scale weakening events which occurred synchronously to the cold Younger Dryas and at ~9.5-8.5 ka, and by two centennial-scale intervals of enhanced (weakened) monsoon during the Medieval Warm Period (Little Ice Age). Our precipitation reconstruction, consistent with temperature changes but quite different from the prevailing view of EASM evolution, points to strong internal feedback processes driving the EASM, and may aid our understanding of future monsoon behaviour under ongoing anthropogenic climate change.

  3. East Asian summer monsoon precipitation variability since the last deglaciation.

    PubMed

    Chen, Fahu; Xu, Qinghai; Chen, Jianhui; Birks, H John B; Liu, Jianbao; Zhang, Shengrui; Jin, Liya; An, Chengbang; Telford, Richard J; Cao, Xianyong; Wang, Zongli; Zhang, Xiaojian; Selvaraj, Kandasamy; Lu, Houyuan; Li, Yuecong; Zheng, Zhuo; Wang, Haipeng; Zhou, Aifeng; Dong, Guanghui; Zhang, Jiawu; Huang, Xiaozhong; Bloemendal, Jan; Rao, Zhiguo

    2015-01-01

    The lack of a precisely-dated, unequivocal climate proxy from northern China, where precipitation variability is traditionally considered as an East Asian summer monsoon (EASM) indicator, impedes our understanding of the behaviour and dynamics of the EASM. Here we present a well-dated, pollen-based, ~20-yr-resolution quantitative precipitation reconstruction (derived using a transfer function) from an alpine lake in North China, which provides for the first time a direct record of EASM evolution since 14.7 ka (ka = thousands of years before present, where the "present" is defined as the year AD 1950). Our record reveals a gradually intensifying monsoon from 14.7-7.0 ka, a maximum monsoon (30% higher precipitation than present) from ~7.8-5.3 ka, and a rapid decline since ~3.3 ka. These insolation-driven EASM trends were punctuated by two millennial-scale weakening events which occurred synchronously to the cold Younger Dryas and at ~9.5-8.5 ka, and by two centennial-scale intervals of enhanced (weakened) monsoon during the Medieval Warm Period (Little Ice Age). Our precipitation reconstruction, consistent with temperature changes but quite different from the prevailing view of EASM evolution, points to strong internal feedback processes driving the EASM, and may aid our understanding of future monsoon behaviour under ongoing anthropogenic climate change.

  4. Indian monsoon variability on millennial-orbital timescales.

    PubMed

    Kathayat, Gayatri; Cheng, Hai; Sinha, Ashish; Spötl, Christoph; Edwards, R Lawrence; Zhang, Haiwei; Li, Xianglei; Yi, Liang; Ning, Youfeng; Cai, Yanjun; Lui, Weiguo Lui; Breitenbach, Sebastian F M

    2016-04-13

    The Indian summer monsoon (ISM) monsoon is critical to billions of people living in the region. Yet, significant debates remain on primary ISM drivers on millennial-orbital timescales. Here, we use speleothem oxygen isotope (δ(18)O) data from Bittoo cave, Northern India to reconstruct ISM variability over the past 280,000 years. We find strong coherence between North Indian and Chinese speleothem δ(18)O records from the East Asian monsoon domain, suggesting that both Asian monsoon subsystems exhibit a coupled response to changes in Northern Hemisphere summer insolation (NHSI) without significant temporal lags, supporting the view that the tropical-subtropical monsoon variability is driven directly by precession-induced changes in NHSI. Comparisons of the North Indian record with both Antarctic ice core and sea-surface temperature records from the southern Indian Ocean over the last glacial period do not suggest a dominant role of Southern Hemisphere climate processes in regulating the ISM variability on millennial-orbital timescales.

  5. Asian monsoons in a late Eocene greenhouse world.

    PubMed

    Licht, A; van Cappelle, M; Abels, H A; Ladant, J-B; Trabucho-Alexandre, J; France-Lanord, C; Donnadieu, Y; Vandenberghe, J; Rigaudier, T; Lécuyer, C; Terry, D; Adriaens, R; Boura, A; Guo, Z; Soe, Aung Naing; Quade, J; Dupont-Nivet, G; Jaeger, J-J

    2014-09-25

    The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and their response to enhanced greenhouse conditions such as those in the Eocene period (55-34 Myr ago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 34 Myr ago.

  6. Asian summer monsoon variability during the last two millennia

    NASA Astrophysics Data System (ADS)

    Chawchai, Sakonvan; Chabangborn, Akkaneewut; Fritz, Sherilyn; Blaauw, Maarten; Löwemark, Ludvig; Reimer, Paula J.; Krusic, Paul J.; Väliranta, Minna; Mörth, Carl-Magnus; Wohlfarth, Barbara

    2014-05-01

    The Southeast Asian mainland is located in the central path of the Asian summer monsoon, a region where paleoclimatic data are still sparse. Here we report a new detailed reconstruction of monsoon variability during the past 2000 years from a multi-proxy sediment record (TOC, C/N, δ13C, δ15N, Si, K, Ti elemental data, biogenic silica and fossil plant remains) from Lake Pa Kho in northeast Thailand. We infer a stronger summer monsoon between BC 200 - AD 400 and AD 800 - 1350, a weaker summer monsoon AD 400 - 800, and fluctuating moisture availability AD 1350 - 1550. Increased run-off after AD 1750 can be linked to agricultural intensification in the region. Placed in a wider context our high-resolution data set contributes important information regarding abrupt shifts in hydroclimatic conditions, spatial patterns of monsoon variability, and variations in the position of the ITCZ across SE Asia during the last two millennia. These paleoclimatic shifts may have contributed to the rise and fall of Iron Age and Khmer societies.

  7. Asian monsoons in a late Eocene greenhouse world.

    PubMed

    Licht, A; van Cappelle, M; Abels, H A; Ladant, J-B; Trabucho-Alexandre, J; France-Lanord, C; Donnadieu, Y; Vandenberghe, J; Rigaudier, T; Lécuyer, C; Terry, D; Adriaens, R; Boura, A; Guo, Z; Soe, Aung Naing; Quade, J; Dupont-Nivet, G; Jaeger, J-J

    2014-09-25

    The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and their response to enhanced greenhouse conditions such as those in the Eocene period (55-34 Myr ago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 34 Myr ago. PMID:25219854

  8. Indian monsoon variability on millennial-orbital timescales

    PubMed Central

    Kathayat, Gayatri; Cheng, Hai; Sinha, Ashish; Spötl, Christoph; Edwards, R. Lawrence; Zhang, Haiwei; Li, Xianglei; Yi, Liang; Ning, Youfeng; Cai, Yanjun; Lui, Weiguo Lui; Breitenbach, Sebastian F. M.

    2016-01-01

    The Indian summer monsoon (ISM) monsoon is critical to billions of people living in the region. Yet, significant debates remain on primary ISM drivers on millennial-orbital timescales. Here, we use speleothem oxygen isotope (δ18O) data from Bittoo cave, Northern India to reconstruct ISM variability over the past 280,000 years. We find strong coherence between North Indian and Chinese speleothem δ18O records from the East Asian monsoon domain, suggesting that both Asian monsoon subsystems exhibit a coupled response to changes in Northern Hemisphere summer insolation (NHSI) without significant temporal lags, supporting the view that the tropical-subtropical monsoon variability is driven directly by precession-induced changes in NHSI. Comparisons of the North Indian record with both Antarctic ice core and sea-surface temperature records from the southern Indian Ocean over the last glacial period do not suggest a dominant role of Southern Hemisphere climate processes in regulating the ISM variability on millennial-orbital timescales. PMID:27071753

  9. Global monsoon precipitation responses to large volcanic eruptions

    PubMed Central

    Liu, Fei; Chai, Jing; Wang, Bin; Liu, Jian; Zhang, Xiao; Wang, Zhiyuan

    2016-01-01

    Climate variation of global monsoon (GM) precipitation involves both internal feedback and external forcing. Here, we focus on strong volcanic forcing since large eruptions are known to be a dominant mechanism in natural climate change. It is not known whether large volcanoes erupted at different latitudes have distinctive effects on the monsoon in the Northern Hemisphere (NH) and the Southern Hemisphere (SH). We address this issue using a 1500-year volcanic sensitivity simulation by the Community Earth System Model version 1.0 (CESM1). Volcanoes are classified into three types based on their meridional aerosol distributions: NH volcanoes, SH volcanoes and equatorial volcanoes. Using the model simulation, we discover that the GM precipitation in one hemisphere is enhanced significantly by the remote volcanic forcing occurring in the other hemisphere. This remote volcanic forcing-induced intensification is mainly through circulation change rather than moisture content change. In addition, the NH volcanic eruptions are more efficient in reducing the NH monsoon precipitation than the equatorial ones, and so do the SH eruptions in weakening the SH monsoon, because the equatorial eruptions, despite reducing moisture content, have weaker effects in weakening the off-equatorial monsoon circulation than the subtropical-extratropical volcanoes do. PMID:27063141

  10. Global monsoon precipitation responses to large volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Liu, Fei; Chai, Jing; Wang, Bin; Liu, Jian; Zhang, Xiao; Wang, Zhiyuan

    2016-04-01

    Climate variation of global monsoon (GM) precipitation involves both internal feedback and external forcing. Here, we focus on strong volcanic forcing since large eruptions are known to be a dominant mechanism in natural climate change. It is not known whether large volcanoes erupted at different latitudes have distinctive effects on the monsoon in the Northern Hemisphere (NH) and the Southern Hemisphere (SH). We address this issue using a 1500-year volcanic sensitivity simulation by the Community Earth System Model version 1.0 (CESM1). Volcanoes are classified into three types based on their meridional aerosol distributions: NH volcanoes, SH volcanoes and equatorial volcanoes. Using the model simulation, we discover that the GM precipitation in one hemisphere is enhanced significantly by the remote volcanic forcing occurring in the other hemisphere. This remote volcanic forcing-induced intensification is mainly through circulation change rather than moisture content change. In addition, the NH volcanic eruptions are more efficient in reducing the NH monsoon precipitation than the equatorial ones, and so do the SH eruptions in weakening the SH monsoon, because the equatorial eruptions, despite reducing moisture content, have weaker effects in weakening the off-equatorial monsoon circulation than the subtropical-extratropical volcanoes do.

  11. Global monsoon precipitation responses to large volcanic eruptions.

    PubMed

    Liu, Fei; Chai, Jing; Wang, Bin; Liu, Jian; Zhang, Xiao; Wang, Zhiyuan

    2016-01-01

    Climate variation of global monsoon (GM) precipitation involves both internal feedback and external forcing. Here, we focus on strong volcanic forcing since large eruptions are known to be a dominant mechanism in natural climate change. It is not known whether large volcanoes erupted at different latitudes have distinctive effects on the monsoon in the Northern Hemisphere (NH) and the Southern Hemisphere (SH). We address this issue using a 1500-year volcanic sensitivity simulation by the Community Earth System Model version 1.0 (CESM1). Volcanoes are classified into three types based on their meridional aerosol distributions: NH volcanoes, SH volcanoes and equatorial volcanoes. Using the model simulation, we discover that the GM precipitation in one hemisphere is enhanced significantly by the remote volcanic forcing occurring in the other hemisphere. This remote volcanic forcing-induced intensification is mainly through circulation change rather than moisture content change. In addition, the NH volcanic eruptions are more efficient in reducing the NH monsoon precipitation than the equatorial ones, and so do the SH eruptions in weakening the SH monsoon, because the equatorial eruptions, despite reducing moisture content, have weaker effects in weakening the off-equatorial monsoon circulation than the subtropical-extratropical volcanoes do. PMID:27063141

  12. Rethinking the Recent Advance of Asian Summer Monsoon Onset

    NASA Astrophysics Data System (ADS)

    Xiang, B.; Wang, B.

    2012-12-01

    Understanding the monsoon onset change is of utmost importance especially for agriculture planning and water management. In the last three decades, Asian Summer Monsoon (ASM) onset has remarkably advanced, but the physical mechanisms remain elusive. Since the overall ASM onset occurs in May, we focus on the change of mean fields in May and consider enhanced mean precipitation and monsoon westerly winds as signs of advanced onset. Results show that the advanced ASM onset mainly represents a robust decadal shift in the mid-to-late 1990s, which is attributed to the mean state change in the Pacific basin characterized by a grand La Niña-like pattern. The La Niña-like mean state change controls the ASM onset through the westward propagation of Rossby waves and its interaction with the asymmetric background mean states in the Indian Ocean and western Pacific, which facilitates the amplification of the northern hemispheric perturbations as well as intensified westerly winds. Intriguingly, the abrupt decadal shifts of monsoon onset in the Arabian Sea and Bay of Bengal occur in 1999, in contrast to the South China Sea with decadal shift in 1994. Numerical experiments demonstrate that the advanced monsoon onset in the Arabian Sea and Bay of Bengal is governed by the enhanced zonal sea surface temperature (SST) gradients in the equatorial Pacific, while that in the South China Sea is primarily determined by the abrupt SST warming near the Philippine Sea.

  13. Testing a flexible method to reduce false monsoon onsets.

    PubMed

    Stiller-Reeve, Mathew Alexander; Spengler, Thomas; Chu, Pao-Shin

    2014-01-01

    To generate information about the monsoon onset and withdrawal we have to choose a monsoon definition and apply it to data. One problem that arises is that false monsoon onsets can hamper our analysis, which is often alleviated by smoothing the data in time or space. Another problem is that local communities or stakeholder groups may define the monsoon differently. We therefore aim to develop a technique that reduces false onsets for high-resolution gridded data, while also being flexible for different requirements that can be tailored to particular end-users. In this study, we explain how we developed our technique and demonstrate how it successfully reduces false onsets and withdrawals. The presented results yield improved information about the monsoon length and its interannual variability. Due to this improvement, we are able to extract information from higher resolution data sets. This implies that we can potentially get a more detailed picture of local climate variations that can be used in more local climate application projects such as community-based adaptations.

  14. Investigation of summer monsoon rainfall variability in Pakistan

    NASA Astrophysics Data System (ADS)

    Hussain, Mian Sabir; Lee, Seungho

    2016-08-01

    This study analyzes the inter-annual and intra-seasonal rainfall variability in Pakistan using daily rainfall data during the summer monsoon season (June to September) recorded from 1980 to 2014. The variability in inter-annual monsoon rainfall ranges from 20 % in northeastern regions to 65 % in southwestern regions of Pakistan. The analysis reveals that the transition of the negative and positive anomalies was not uniform in the investigated dataset. In order to acquire broad observations of the intra-seasonal variability, an objective criterion, the pre-active period, active period and post-active periods of the summer monsoon rainfall have demarcated. The analysis also reveals that the rainfall in June has no significant contribution to the increase in intra-seasonal rainfall in Pakistan. The rainfall has, however, been enhanced in the summer monsoon in August. The rainfall of September demonstrates a sharp decrease, resulting in a high variability in the summer monsoon season. A detailed examination of the intra-seasonal rainfall also reveals frequent amplitude from late July to early August. The daily normal rainfall fluctuates significantly with its maximum in the Murree hills and its minimum in the northwestern Baluchistan.

  15. Indian monsoon variability on millennial-orbital timescales.

    PubMed

    Kathayat, Gayatri; Cheng, Hai; Sinha, Ashish; Spötl, Christoph; Edwards, R Lawrence; Zhang, Haiwei; Li, Xianglei; Yi, Liang; Ning, Youfeng; Cai, Yanjun; Lui, Weiguo Lui; Breitenbach, Sebastian F M

    2016-01-01

    The Indian summer monsoon (ISM) monsoon is critical to billions of people living in the region. Yet, significant debates remain on primary ISM drivers on millennial-orbital timescales. Here, we use speleothem oxygen isotope (δ(18)O) data from Bittoo cave, Northern India to reconstruct ISM variability over the past 280,000 years. We find strong coherence between North Indian and Chinese speleothem δ(18)O records from the East Asian monsoon domain, suggesting that both Asian monsoon subsystems exhibit a coupled response to changes in Northern Hemisphere summer insolation (NHSI) without significant temporal lags, supporting the view that the tropical-subtropical monsoon variability is driven directly by precession-induced changes in NHSI. Comparisons of the North Indian record with both Antarctic ice core and sea-surface temperature records from the southern Indian Ocean over the last glacial period do not suggest a dominant role of Southern Hemisphere climate processes in regulating the ISM variability on millennial-orbital timescales. PMID:27071753

  16. East Asian summer monsoon precipitation variability since the last deglaciation.

    PubMed

    Chen, Fahu; Xu, Qinghai; Chen, Jianhui; Birks, H John B; Liu, Jianbao; Zhang, Shengrui; Jin, Liya; An, Chengbang; Telford, Richard J; Cao, Xianyong; Wang, Zongli; Zhang, Xiaojian; Selvaraj, Kandasamy; Lu, Houyuan; Li, Yuecong; Zheng, Zhuo; Wang, Haipeng; Zhou, Aifeng; Dong, Guanghui; Zhang, Jiawu; Huang, Xiaozhong; Bloemendal, Jan; Rao, Zhiguo

    2015-01-01

    The lack of a precisely-dated, unequivocal climate proxy from northern China, where precipitation variability is traditionally considered as an East Asian summer monsoon (EASM) indicator, impedes our understanding of the behaviour and dynamics of the EASM. Here we present a well-dated, pollen-based, ~20-yr-resolution quantitative precipitation reconstruction (derived using a transfer function) from an alpine lake in North China, which provides for the first time a direct record of EASM evolution since 14.7 ka (ka = thousands of years before present, where the "present" is defined as the year AD 1950). Our record reveals a gradually intensifying monsoon from 14.7-7.0 ka, a maximum monsoon (30% higher precipitation than present) from ~7.8-5.3 ka, and a rapid decline since ~3.3 ka. These insolation-driven EASM trends were punctuated by two millennial-scale weakening events which occurred synchronously to the cold Younger Dryas and at ~9.5-8.5 ka, and by two centennial-scale intervals of enhanced (weakened) monsoon during the Medieval Warm Period (Little Ice Age). Our precipitation reconstruction, consistent with temperature changes but quite different from the prevailing view of EASM evolution, points to strong internal feedback processes driving the EASM, and may aid our understanding of future monsoon behaviour under ongoing anthropogenic climate change. PMID:26084560

  17. Extratropical anticyclonic Rossby wave breaking and Indian summer monsoon failure

    NASA Astrophysics Data System (ADS)

    Samanta, Dhrubajyoti; Dash, M. K.; Goswami, B. N.; Pandey, P. C.

    2016-03-01

    Interactions between midlatitude disturbances and the monsoonal circulation are significant for the Indian summer monsoon (ISM) rainfall. This paper presents examples of monsoon-midlatitude linkage through anticyclonic Rossby wave breaking (RWB) over West Asia during June, July and August of the years 1998-2010. RWB events over West Asia are identified by the inversion of the potential vorticity air mass at three different isentropic levels (340, 350, and 360 K) using daily NCEP-NCAR reanalysis. It is observed that RWB took place over West Asia before/during breaks in the ISM. Further, these events occur on the anticyclonic shear side of the subtropical jet, where the gradient of the zonal wind is found to be high. RWB is responsible for the southward movement of high potential vorticity air from the westerly jet, leading to the formation of a blocking high over the Arabian region. In turn, this blocking high advects and causes the descent of upper tropospheric cold and dry air towards Central India. Such an air mass with low moist static energy inhibits deep monsoonal convection and thereby leads to a dry spell. In fact, we find that RWB induced blocking over West Asia to be one of the major causes of dry spell/break episodes in ISM. Additionally, the presence of cold air over Central India reduces the north-south thermal contrast over the monsoon region thereby modifying the local Hadley circulation over the region.

  18. Indian monsoon variability on millennial-orbital timescales

    NASA Astrophysics Data System (ADS)

    Kathayat, Gayatri; Cheng, Hai; Sinha, Ashish; Spötl, Christoph; Edwards, R. Lawrence; Zhang, Haiwei; Li, Xianglei; Yi, Liang; Ning, Youfeng; Cai, Yanjun; Lui, Weiguo Lui; Breitenbach, Sebastian F. M.

    2016-04-01

    The Indian summer monsoon (ISM) monsoon is critical to billions of people living in the region. Yet, significant debates remain on primary ISM drivers on millennial-orbital timescales. Here, we use speleothem oxygen isotope (δ18O) data from Bittoo cave, Northern India to reconstruct ISM variability over the past 280,000 years. We find strong coherence between North Indian and Chinese speleothem δ18O records from the East Asian monsoon domain, suggesting that both Asian monsoon subsystems exhibit a coupled response to changes in Northern Hemisphere summer insolation (NHSI) without significant temporal lags, supporting the view that the tropical-subtropical monsoon variability is driven directly by precession-induced changes in NHSI. Comparisons of the North Indian record with both Antarctic ice core and sea-surface temperature records from the southern Indian Ocean over the last glacial period do not suggest a dominant role of Southern Hemisphere climate processes in regulating the ISM variability on millennial-orbital timescales.

  19. Global monsoon precipitation responses to large volcanic eruptions.

    PubMed

    Liu, Fei; Chai, Jing; Wang, Bin; Liu, Jian; Zhang, Xiao; Wang, Zhiyuan

    2016-04-11

    Climate variation of global monsoon (GM) precipitation involves both internal feedback and external forcing. Here, we focus on strong volcanic forcing since large eruptions are known to be a dominant mechanism in natural climate change. It is not known whether large volcanoes erupted at different latitudes have distinctive effects on the monsoon in the Northern Hemisphere (NH) and the Southern Hemisphere (SH). We address this issue using a 1500-year volcanic sensitivity simulation by the Community Earth System Model version 1.0 (CESM1). Volcanoes are classified into three types based on their meridional aerosol distributions: NH volcanoes, SH volcanoes and equatorial volcanoes. Using the model simulation, we discover that the GM precipitation in one hemisphere is enhanced significantly by the remote volcanic forcing occurring in the other hemisphere. This remote volcanic forcing-induced intensification is mainly through circulation change rather than moisture content change. In addition, the NH volcanic eruptions are more efficient in reducing the NH monsoon precipitation than the equatorial ones, and so do the SH eruptions in weakening the SH monsoon, because the equatorial eruptions, despite reducing moisture content, have weaker effects in weakening the off-equatorial monsoon circulation than the subtropical-extratropical volcanoes do.

  20. East Asian summer monsoon precipitation variability since the last deglaciation

    PubMed Central

    Chen, Fahu; Xu, Qinghai; Chen, Jianhui; Birks, H. John B.; Liu, Jianbao; Zhang, Shengrui; Jin, Liya; An, Chengbang; Telford, Richard J.; Cao, Xianyong; Wang, Zongli; Zhang, Xiaojian; Selvaraj, Kandasamy; Lu, Houyuan; Li, Yuecong; Zheng, Zhuo; Wang, Haipeng; Zhou, Aifeng; Dong, Guanghui; Zhang, Jiawu; Huang, Xiaozhong; Bloemendal, Jan; Rao, Zhiguo

    2015-01-01

    The lack of a precisely-dated, unequivocal climate proxy from northern China, where precipitation variability is traditionally considered as an East Asian summer monsoon (EASM) indicator, impedes our understanding of the behaviour and dynamics of the EASM. Here we present a well-dated, pollen-based, ~20-yr-resolution quantitative precipitation reconstruction (derived using a transfer function) from an alpine lake in North China, which provides for the first time a direct record of EASM evolution since 14.7 ka (ka = thousands of years before present, where the “present” is defined as the year AD 1950). Our record reveals a gradually intensifying monsoon from 14.7–7.0 ka, a maximum monsoon (30% higher precipitation than present) from ~7.8–5.3 ka, and a rapid decline since ~3.3 ka. These insolation-driven EASM trends were punctuated by two millennial-scale weakening events which occurred synchronously to the cold Younger Dryas and at ~9.5–8.5 ka, and by two centennial-scale intervals of enhanced (weakened) monsoon during the Medieval Warm Period (Little Ice Age). Our precipitation reconstruction, consistent with temperature changes but quite different from the prevailing view of EASM evolution, points to strong internal feedback processes driving the EASM, and may aid our understanding of future monsoon behaviour under ongoing anthropogenic climate change. PMID:26084560

  1. African vegetation controlled by tropical sea surface temperatures in the mid-Pleistocene period.

    PubMed

    Schefuss, Enno; Schouten, Stefan; Jansen, J H Fred; Sinninghe Damsté, Jaap S

    2003-03-27

    The dominant forcing factors for past large-scale changes in vegetation are widely debated. Changes in the distribution of C4 plants--adapted to warm, dry conditions and low atmospheric CO2 concentrations--have been attributed to marked changes in environmental conditions, but the relative impacts of changes in aridity, temperature and CO2 concentration are not well understood. Here, we present a record of African C4 plant abundance between 1.2 and 0.45 million years ago, derived from compound-specific carbon isotope analyses of wind-transported terrigenous plant waxes. We find that large-scale changes in African vegetation are linked closely to sea surface temperatures in the tropical Atlantic Ocean. We conclude that, in the mid-Pleistocene, changes in atmospheric moisture content--driven by tropical sea surface temperature changes and the strength of the African monsoon--controlled aridity on the African continent, and hence large-scale vegetation changes.

  2. Building resilience to face recurring environmental crisis in African Sahel

    NASA Astrophysics Data System (ADS)

    Boyd, Emily; Cornforth, Rosalind J.; Lamb, Peter J.; Tarhule, Aondover; Lélé, M. Issa; Brouder, Alan

    2013-07-01

    The present food shortages in the Horn of Africa and the West African Sahel are affecting 31 million people. Such continuing and future crises require that people in the region adapt to an increasing and potentially irreversible global sustainability challenge. Given this situation and that short-term weather and seasonal climate forecasting have limited skill for West Africa, the Rainwatch project illustrates the value of near real-time monitoring and improved communication for the unfavourable 2011 West African monsoon, the resulting severe drought-induced humanitarian impacts continuing into 2012, and their exacerbation by flooding in 2012. Rainwatch is now coupled with a boundary organization (Africa Climate Exchange, AfClix) with the aim of integrating the expertise and actions of relevant institutions, agencies and stakeholders to broker ground-based dialogue to promote resilience in the face of recurring crisis.

  3. Anomalies in the South American Monsoon Induced by Aerosols

    NASA Technical Reports Server (NTRS)

    Lau, K. M. William; Kyu-Mong, Kim

    2007-01-01

    We have investigated the direct effects of aerosols on the water cycle of the South American monsoon using the NASA finite-volume general circulation model (fvGCM). Global aerosol forcings are computed from radiative transfer functions derived from global distributions of five species of aerosols, i.e., dust, black carbon, organic carbon, sulphate and sea salt from the Goddard Chemistry Aerosol Radiation Transport (GOCART) model. Comparing fvGCM experiments without aerosol forcing, and with different combinations of aerosol forcing, we evaluate the impacts of aerosol direct heating on the onset, maintenance and evolution of the South American summer monsoon. We find that during the pre-monsoon season (September-October-November) Saharan dust contribute to heating of the atmosphere over the central and eastern equatorial Atlantic/Africa region through the elevated heat pump mechanism. The heating generates an anomalous Walker circulation with sinking motion, and low level northeasterlies over the Caribbean and northwestern South America. The low level flow is blocked by the Andes, and turn south and southeastward, increasing the low level jet (LLJ) along the eastern slope of the Andes. The increased LLJ transports more moisture from the Atlantic and the Amazon, enhancing the moisture convergence over subtropical land regions of South America. The moisture convergence was further accelerated by atmospheric heating by biomass burning over the Amazon. The net results of the dust and biomass heating are: a) an advance of the monsoon rainy season, b) an enhanced LLJ and c) a shifting the South America monsoon land precipitation equatorward, with increased rain over southern Brazil and reduced rain over the La Plata basin. ramifications of this elevated heating heat pump mechanism in aerosol monsoon water cycle on climate variability and change will be discussed. The ramifications of this "elevated heating heat pump" mechanism in aerosol monsoom water cycle on climate

  4. Asian summer monsoon onset barrier and its formation mechanism

    NASA Astrophysics Data System (ADS)

    Liu, Boqi; Liu, Yimin; Wu, Guoxiong; Yan, Jinghui; He, Jinhai; Ren, Suling

    2015-08-01

    The onset process of Asian summer monsoon (ASM) is investigated based on diagnostic analysis of observations of precipitation and synoptic circulation. Results show that after the ASM commences over the eastern Bay of Bengal (BOB) around early May, the onset can propagate eastwards towards the South China Sea and western Pacific but is blocked on its westward propagation along the eastern coast of India. This blocking, termed the "monsoon onset barrier (MOB)", presents a Gill-type circulation response to the latent heating released by BOB monsoon convection. This convective condensation heating generates summertime (wintertime) vertical easterly (westerly) shear to its east (west) and facilitates air ascent (descent). The convection then propagates eastward but gets trapped on its westward path. To the east of the central BOB, the surface air temperature (SAT) cools faster than the underlying sea surface temperature (SST) due to monsoon onset. Thus more sensible heat flux supports the onset convection to propagate eastward. To the west of the central BOB, however, the land surface sensible heating over the Indian Peninsula is strengthened by the enhanced anticyclone circulation and air descent induced by the BOB monsoon heating. The strengthened upstream warm horizontal advection then produces a warm SAT center over the MOB region, which together with the in situ cooled SST reduces the surface sensible heating and atmospheric available potential energy to prevent the occurrence of free convection. Therefore, it is the change in both large-scale circulation and air-sea interaction due to BOB summer monsoon onset that contributes to the MOB formation.

  5. The African Connection

    ERIC Educational Resources Information Center

    Oguntoyinbo, Lekan

    2012-01-01

    From student and faculty exchanges to joint research projects, U.S. universities maintain a broad spectrum of collaborative relationships with African universities. It's unclear how many U.S. colleges and universities have partnerships with African universities. The African Studies Association, an organization of scholars, doesn't keep that kind…

  6. Linguistic Imperialism: African Perspectives.

    ERIC Educational Resources Information Center

    Phillipson, Robert

    1996-01-01

    Responds to an article on aspects of African language policy and discusses the following issues: multilingualism and monolingualism, proposed changes in language policy from the Organization for African Unity and South African initiatives, the language of literature, bilingual education, and whose interests English-language teaching is serving.…

  7. Quaternary Indus River Terraces as Archives of Summer Monsoon Variability

    NASA Astrophysics Data System (ADS)

    Jonell, Tara N.; Clift, Peter D.

    2013-04-01

    If we are to interpret the marine stratigraphic record in terms of evolving continental environmental conditions or tectonics, it is essential to understand the transport processes that bring sediment from mountain sources to its final marine depocenter. We investigate the role that climate plays in modulating this flux by looking at the Indus River system, which is dominated by the strong forcing of the Asian monsoon and the erosion of the western Himalaya. Lake, paleoceanographic, and speleothem records offer high-resolution reconstructions of monsoon intensity over millennial timescales. These proxies suggest the monsoon reached peak intensity at ~9-10 ka in central India, followed by a steady decline after ~7 ka, with a steep decline after 4 ka. New lake core records (Tso Kar and Tso Moriri), however, suggest a more complex pattern of monsoon weakening between 7-8 ka in the Greater Himalayan region, which contrasts with a time of strong monsoon in central India. This indicates that the floodplains of the major river systems may not experience the same climatic conditions as their mountain sources, resulting in different geomorphologic responses to climate change. Earlier research has established that the northern part of the Indus floodplain adjacent to the mountains experienced incision after ~10 ka. Incision and reworking is even more intense in the Himalayas but its timing is not well-constrained. High altitude river valleys, at least north of the Greater Himalaya, appear to be sensitive to monsoon strength because they lie on the periphery of the Himalayan rain shadow. These valleys may be affected by landslide damming during periods of strong monsoonal precipitation, such as slightly after the monsoon maximum from 9-10 ka. Damming of these river valleys provides sediment storage through valley-filling and later sediment release through gradual incision or dam-bursting. Terraces of a major tributary to the Indus, the Zanskar River, indicate valley

  8. Impact of a projected future Antarctic sea-ice reduction on the West African Monsoon

    NASA Astrophysics Data System (ADS)

    Bader, Juergen; Voigt, Aiko; Zanchettin, Davide

    2013-04-01

    Several model and observational studies have demonstrated a strong relationship between Sahel rainfall variability and sea-surface temperatures anomalies during the 20th century. However, this relationship does not explain Sahel rainfall changes in model projections of the 21st century. This raises the possibility that other forcing factors might become predominant at the end of the 21st century. Here, simulations with the atmosphere general circulaton model ECHAM5 are performed to investigate to which extent reductions in Antarctic sea ice affect Sahel rainfall during boreal summer. To this end, the model is forced by the present and a projected future seasonal cycle of Antarctic sea ice with sea-surface temperatures outside tha Antarctic sea-ice region kept constant. Reducing the Antarctic sea ice leads to an equatorward shift of the tropical rainbelt over sub-Saharan Africa. The shift entails a strong decline of summer Sahel rainfall and a substantial rainfall increase along the Guinea Coast. The shift is associated with an atmospheric bridge that does not require changes in tropical sea-surface temperatures. While Antarctic sea-ice reductions clearly impact Sahel rainfall in our idealized ECHAM5 simulatons, they do not seem to substantially influence Sahel rainfall in the ECHAM5 CMIP3 A1B simulation.

  9. a Linear Dynamic Model of the East African Jet in a Stratified Atmosphere

    NASA Astrophysics Data System (ADS)

    Sashegyi, Keith Denis

    The motion forced by prescribed heat sources in the Indian summer monsoon region was investigated using a global linear primitive equations model in a stratified atmosphere. The response, without topography, to steady large-scale latent heating at the latitude of northern India showed broad, weak cross-equatorial flow, with the largest subsidence occurring to the west of the heating. The response to a 14-day oscillation in the heat source, representing the active/break cycle of the monsoon, exhibited a somewhat larger cross-equatorial flow, associated with westward propagating geopotential anomalies in both hemispheres. The north-south topographic barrier formed by the East African Highlands was modeled as a western wall, and the response to the steady and the oscillatory monsoon heat source was investigated using a fine resolution model in a limited longitudinal domain. For the steady monsoon heat source, a western boundary jet was produced, and this separated abruptly from the boundary to flow eastward into the region of the heat source. The oscillating monsoon heat source produced oscillations in the boundary jet in the near equatorial region comprised of jets of alternating sign which propagated westward into the boundary and increased in amplitude as they did so. At the equator this "boundary wave" was nearly out of phase with the monsoon heating. Steady prescribed low-level sensible heating along the coastline of Somalia and Saudi Arabia was found to result in a low-level western boundary jet comparable in strength near the surface to that forced by the steady monsoon heat source. This local-heat-source jet was situated along the western wall at the equator, but separated from the wall to run along the coast at higher tropical latitudes. Superposition of this local heating response onto the response to the steady monsoon heating would result in a departure of the jet from the western wall at a lower latitude and would also provide a more gradual curvature to

  10. Arsenic release from paddy soils during monsoon flooding

    NASA Astrophysics Data System (ADS)

    Roberts, Linda C.; Hug, Stephan J.; Dittmar, Jessica; Voegelin, Andreas; Kretzschmar, Ruben; Wehrli, Bernhard; Cirpka, Olaf A.; Saha, Ganesh C.; Ashraf Ali, M.; Badruzzaman, A. Borhan M.

    2010-01-01

    Bangladesh relies heavily on groundwater for the irrigation of dry-season rice. However, the groundwater used for irrigation often contains high concentrations of arsenic, potentially jeopardizing the future of rice production in the country. In seasonally flooded fields, topsoil arsenic concentrations decrease during the monsoon season, suggesting that flooding attenuates arsenic accumulation in the soils. Here we examine the chemistry of soil porewater and floodwater during the monsoon season in rice paddies in Munshiganj, Bangladesh, to assess whether flooding releases significant quantities of arsenic from the soils. We estimate that between 51 and 250mgm-2 of soil arsenic is released into floodwater during the monsoon season. This corresponds to a loss of 13-62% of the arsenic added to soils through irrigation each year. The arsenic was distributed throughout the entire floodwater column by vertical mixing and was laterally removed when the floodwater receded. We conclude that monsoon floodwater removes a large amount of the arsenic added to paddy soils through irrigation, and suggest that non-flooded soils are particularly at risk of arsenic accumulation.

  11. Monsoonal differences and probability distribution of PM(10) concentration.

    PubMed

    Md Yusof, Noor Faizah Fitri; Ramli, Nor Azam; Yahaya, Ahmad Shukri; Sansuddin, Nurulilyana; Ghazali, Nurul Adyani; Al Madhoun, Wesam

    2010-04-01

    There are many factors that influence PM(10) concentration in the atmosphere. This paper will look at the PM(10) concentration in relation with the wet season (north east monsoon) and dry season (south west monsoon) in Seberang Perai, Malaysia from the year 2000 to 2004. It is expected that PM(10) will reach the peak during south west monsoon as the weather during this season becomes dry and this study has proved that the highest PM(10) concentrations in 2000 to 2004 were recorded in this monsoon. Two probability distributions using Weibull and lognormal were used to model the PM(10) concentration. The best model used for prediction was selected based on performance indicators. Lognormal distribution represents the data better than Weibull distribution model for 2000, 2001, and 2002. However, for 2003 and 2004, Weibull distribution represents better than the lognormal distribution. The proposed distributions were successfully used for estimation of exceedences and predicting the return periods of the sequence year. PMID:19365611

  12. Aerosol impact on the Asian Summer Monsoon oberved by CALIPSO

    NASA Astrophysics Data System (ADS)

    Kuhlmann, J.; Quaas, J.; Devasthale, A.; Kinne, S.

    2009-04-01

    Different, sometimes opposed theories about the impact of aerosols above and around the Tibetan Plateau on the Asian Summer Monsoon exist, one being the "Elevated Heat Pump" (EHP) proposed by Lau et al. (2006) which holds local aerosol induced heating close to the Tibetan Plateau during pre-monsoon season responsible for an advance and intensification of the monsoon. However, observational evidence for mechanisms of aerosols either strengthening or weakening the monsoon are still lacking. CALIPSO satellite data provides a three-dimensional view of aerosols and a classification into six different aerosol types according to their radiative properties. We use this data to examine possible aerosol sources, ways of transportation and patterns of concentration in the region. Combination with wind data shows that especially dusts from Taklamakan and Thar deserts possibly contribute to an EHP-like regime, but long-range transport from the Arabian peninsula cannot be excluded either. Furthermore, we use the CALIPSO aerosol data as an input to a radiative transfer model and compute resulting heating rates in order to quantify aerosol impacts on the atmosphere in the region.

  13. Early warnings and missed alarms for abrupt monsoon transitions

    NASA Astrophysics Data System (ADS)

    Thomas, Z. A.; Kwasniok, F.; Boulton, C. A.; Cox, P. M.; Jones, R. T.; Lenton, T. M.; Turney, C. S. M.

    2015-04-01

    Palaeo-records from China (Cheng et al., 2009; Wang et al., 2008, 2001) demonstrate the East Asian Summer Monsoon (EASM) is dominated by abrupt and large magnitude monsoon shifts on millennial timescales, switching between periods of high and weak monsoon rains. It has been hypothesised that over these timescales, the EASM exhibits two stable states with bifurcation-type tipping points between them (Schewe et al., 2012). Here we test this hypothesis by looking for early warning signals of past bifurcations in speleothem records from Sanbao Cave and Hulu Cave, China (Wang et al., 2008, 2001), spanning the penultimate glacial cycle, and in multiple model simulations derived from the data. We find hysteresis behaviour in our model simulations with transitions directly forced by solar insolation. We detect critical slowing down prior to an abrupt monsoon shift during the penultimate deglaciation consistent with long-term orbital forcing. However, such signals are only detectable when the change in system stability is sufficiently slow to be detected by the sampling resolution of the dataset, raising the possibility that the alarm was missed and a similar forcing drove earlier EASM shifts.

  14. Observational and modeling studies of impacts of the South China Sea monsoon on the monsoon rainfall in the middle-lower reaches of the Yangtze River during summer

    NASA Astrophysics Data System (ADS)

    Jin, Lijun; Zhao, Ping

    2012-04-01

    Based on the ERA-40 and NCEP/NCAR reanalysis data, the NOAA Climate Prediction Center's merged analysis of precipitation (CMAP), and the fifth-generation PSU/NCAR Mesoscale Model version 3 (MM5v3), we defined a monsoon intensity index over the East Asian tropical region and analyzed the impacts of summer (June-July) South China Sea (SCS) monsoon anomaly on monsoon precipitation over the middle-lower reaches of the Yangtze River (MLRYR) using both observational data analysis and numerical simulation methods. The results from the data analysis show that the interannual variations of the tropical monsoon over the SCS are negatively correlated with the southwesterly winds and precipitation over the MLRYR during June-July. Corresponding to stronger (weaker) tropical monsoon and precipitation, the southwesterly winds are weaker (stronger) over the MLRYR, with less (more) local precipitation. The simulation results further exhibit that when changing the SCS monsoon intensity, there are significant variations of monsoon and precipitation over the MLRYR. The simulated anomalies generally consist with the observations, which verifies the impact of the tropical monsoon on the monsoon precipitation over the MLRYR. This impact might be supported by certain physical processes. Moreover, when the tropical summer monsoon is stronger, the tropical anomalous westerly winds and positive precipitation anomalies usually maintain in the tropics and do not move northward into the MLRYR, hence the transport of water vapor toward southern China is weakened and the southwest flow and precipitation over southern China are also attenuated. On the other hand, the strengthened tropical monsoon may result in the weakening and southward shift of the western Pacific subtropical high through self-adjustment of the atmospheric circulation, leading to the weakening of the monsoon flows and precipitation over the MLRYR.

  15. An Assessment of Monsoon Triggered Landslides in Western Nepal

    NASA Astrophysics Data System (ADS)

    Sudan Acharya, Madhu

    2010-05-01

    Due to heavy monsoon rain, rugged topography and very young mountains, frequent slope failures and soil erosion are very common in Nepal but in most of cases the natural slopes are disturbed by men to construct a road through it and the situation further aggravated by the Monsoon rain. Summer usually tests the disaster response capacity of Nepal, when the monsoons trigger water induced disasters. This year Nepal's Western regions were most severely affected by floods and landslides. Every year, sadly, it is the same story of mostly poor people living in remote villages succumbing to landslides and flooding and those who survive facing hardships brought on by the disaster. The tail end of the monsoon in October has triggered flood and landslides in Nepal which affected a total of 14 districts in the mid and far-west regions, of which Kailali, Bardiya, Banke, Dadeldhura, Accham and Kanchapur district are most affected. The affected areas are geographically scattered and remote, and are therefore difficult to access. In this year (2009), flood and landslides have claimed 62 lives, affecting more than 152,000 individuals from 27,000 families. More than 4,000 families are displaced and are taking shelter in schools, open space and forest areas with no protection from the external elements. In the above context the prevention and mitigation measures for landslides is a great challenge for Nepal. Nepal has been investing its huge amount of resources to stabilize landslides and roadside slope failures, still then it has become unmanageable during Monsoon time. Considering the above facts, an assessment of landslides which were occurred during the Monsoon (July-October 2009), along Khodpe - Jhota - Chainpur road in far western region of Nepal has been carried out based on the field observation of various landslides. The paper presents the causes and mechanisms of failures of different landslides which are mostly triggered by Monsoon rain. It also suggests some low cost

  16. Monsoon response of the Somali Current and associated upwelling

    NASA Astrophysics Data System (ADS)

    Schott, Friedrich

    The Somali Current typically develops in different phases in response to the onset of the summer monsoon. Each of these phases exists quasistationary for some time ranging from weeks to months. These periods of rather constant circulation patterns are separated by periods of rapid transition. In the early phase of the monsoon response, during May, with weak southerly winds off Somalia, a cross equatorial inertial current develops which turns offshore a few degrees north of the equator with a coastal upwelling wedge just north of the offshore flow. North of that region, an Ekman upwelling regime exists all the way up the coast. At the onset of strong winds in June, a northern anticyclonic gyre develops north of 5°N and a second cold wedge forms north of 8°-9°N, where that current turns offshore. The most drastic change of upwelling pattern occurs in the late phase of the summer monsoon, August/September, when the southern cold wedge propagates northward, indicating a break-down of the two-gyre pattern and development of a continuous boundary current from south of the equator to about 10°N. The wedge propagation during 1976-1978 is discussed, based on satellite observations (EVANS and BROWN, 1981), moored station data during 1978, 1979 and shipboard hydrographic data during 1979. A simple relation between the decrease of local monsoon winds offshore and wedge propagation cannot be determined. The southward coastal undercurrent, which is part of the Ekman upwelling regime north of 5° during the early summer monsoon, seems to turn offshore between 3° and 5°, probably due to a zonal excursion of depth contours in that area. With the spin-up of the deep-reaching northern gyre the undercurrent is extinguished during July to August but seems to get reestablished after the coalescence of the two gyres.

  17. Monsoon-extratropical circulation interactions in Himalayan extreme rainfall

    NASA Astrophysics Data System (ADS)

    Vellore, Ramesh K.; Kaplan, Michael L.; Krishnan, R.; Lewis, John M.; Sabade, Sudhir; Deshpande, Nayana; Singh, Bhupendra B.; Madhura, R. K.; Rama Rao, M. V. S.

    2016-06-01

    Extreme precipitation and flood episodes in the Himalayas are oftentimes traced to synoptic situations involving connections between equatorward advancing upper level extratropical circulations and moisture-laden tropical monsoon circulation. While previous studies have documented precipitation characteristics in the Himalayan region during severe storm cases, a comprehensive understanding of circulation dynamics of extreme precipitation mechanisms is still warranted. In this study, a detailed analysis is performed using rainfall observations and reanalysis circulation products to understand the evolution of monsoon-extratropical circulation features and their interactions based on 34 extreme precipitation events which occurred in the Western Himalayas (WEH) during the period 1979-2013. Our results provide evidence for a common large-scale circulation pattern connecting the extratropics and the South Asian monsoon region, which is favorable for extreme precipitation occurrences in the WEH region. This background upper level large-scale circulation pattern consists of a deep southward penetrating midlatitude westerly trough, a blocking high over western Eurasia and an intensifying Tibetan anticyclone. It is further seen from our analysis that the key elements of monsoon-midlatitude interactions, responsible for extreme precipitation events over the WEH region, are: (1) midlatitude Rossby wave breaking, (2) west-northwest propagation of monsoon low-pressure system from the Bay of Bengal across the Indian subcontinent, (3) eddy shedding of the Tibetan anticyclone, (4) ageostrophic motions and transverse circulation across the Himalayas, and (5) strong moist convection over the Himalayan foothills. Furthermore, high-resolution numerical simulations indicate that diabatic heating and mesoscale ageostrophic effects can additionally amplify the convective motions and precipitation in the WEH region.

  18. Interactions between Super Typhoon Megi (2010) and the Monsoon Gyre

    NASA Astrophysics Data System (ADS)

    Peng, M.; Li, T.; Bi, M.; Shen, X.

    2015-12-01

    Accurate prediction of tropical cyclone track is critical for high-impact weather preparedness, especially as the storm is near the coastal region. The track prediction for super typhoon Megi (2010) in the western Pacific was notoriously bad as most operational models predicated a mainly westward movement while Megi actually made a northward turning after it has crossed the Philippines islands. In this study, we try to understand this rather irregular motion for Megi. Examination of NCEP reanalyzed fields indicated that during this period a low-frequency (10-60-day) monsoon gyre in the vicinity of Megi may have interactions with the latter. To understand the effect of the low-frequency mode on the movement of Megi, numerical experiments were designed and conducted. The total flow from the analyzed field is separated into 1) a slowly varying background state, 2) a 10-60-day low frequency component representing the monsoon gyre, and 3) a 10-day high-pass filtered component representing Megi. In the control experiment, the total field containing all three components is used as the initial and lateral boundary conditions, and the WRF model is able to simulate Megi's sharp northward turning successfully. In the second experiment, the 10-60-day mode is removed from the initial and lateral boundary fields. In the absence of the low-frequency mode, Megi moves westward and only slightly northwestward without turning north. When the vortex representing Megi was removed, the movement of the monsoon gyre was also affected. These experiments indicated strong interactions between Megi and the monsoon gyre. The interactions and the way the monsoon gyre actually affected the track of Megi will be discussed in the presentation.

  19. 2.1 Pan-WCRP Monsoon Modelling Workshop Summary

    SciTech Connect

    Sperber, K R

    2005-06-28

    Ken Sperber led a discussion of the outcome of the Pan-WCRP Monsoon Modelling Workshop that was held at the University of California at Irvine from 15-17 June 2005. At the workshop presentations from key CLIVAR and GEWEX panels were presented to highlight the outstanding problems in modelling the Earth's monsoons. Additionally, presentations from invited experts were given to highlight important aspects of monsoon phenomena and processes, such as low-level jets, air-sea interaction, predictability, observational networks/studies, and model test beds etc. Since all persons attending the CLIVAR AAMP meeting were present for all, or most, of the monsoon workshop, a detailed description of the workshop presentations was not given. Rather, the discussion was focused on the recommendations of the workshop breakout groups and their relevance to CLIVAR AAMP. CLIVAR AAMP endorsed the near-term workshop recommendation of investigating the diurnal cycle using a hierarchy of models a key way forward for promoting CLIVAR/GEWEX interactions. In GCM studies CLIVAR researchers have identified the diurnal cycle as a forced ''mode'' of variability that is poorly represented in terms of amplitude and phase, especially in the case of precipitation. Typical phase errors of 6-12 hours are noted over both land and ocean in GCMs. CLIVAR views adequate simulation of the diurnal cycle as key aspect of variability in its own right, but also because of its potential rectification on to subseasonal variability (e.g., the Madden-Julian oscillation). It is hypothesized that improvement of diurnal variability may lead to an improved representation of intraseasonal variability and improved skill of monsoon forecasts on medium-range to seasonal time scales.

  20. The South Asian Monsoon Circulation in Moist Isentropic coordinates

    NASA Astrophysics Data System (ADS)

    Thazhe Purayil, Sabin; Pauluis, Olivier

    2016-04-01

    The atmospheric circulation and thermodynamic structure during the South Asian Summer Monsoon season is analyzed in isentropic coordinates through the mass transport represented in terms of the potential temperature and equivalent potential temperature. This approach, originally developed to analyze the global meridional circulation, makes it possible to identify the thermodynamic properties of the inflow and outflow of different air mass. To understand the thermodynamic properties of air mass in south Asian monsoon region, we have used three diagnostics; a) the joint distribution of the mass transport as a function of dry and moist entropy, b) the vertical mass flux over the monsoon domain and c) the mass transport and isentropic thickness for different moist ventilation range of tropical atmosphere. The thermodynamic properties of the various air masses, such as the inflow of warm moist air in the boundary layer, upper tropospheric outflow, and midlatitude dry air intrusion are being systematically identified. The isentropic distribution of the vertical mass flux transport in terms of equivalent potential temperature is used to explain the characteristics of ascending and descending air parcels over the Indian subcontinent. Diagnosis based on the isentropic thickness reveals that the regional monsoon circulation and associated precipitation features can be systematically explained by this method. This technique is used to study the evolution of the monsoon flow in the seasonal scale. We used the data from AMIP-type simulations carried out with prescribed Sea Surface Temperature and sea ice for a 25 year period (1981-2005) from the GFDL High-resolution atmospheric model (HiRAM) with an average grid spacing of ~25km over the globe.

  1. African easterly wave energetics on intraseasonal timescales

    NASA Astrophysics Data System (ADS)

    Alaka, Ghassan J., Jr.

    East Atlantic tropical cyclone generation is associated with positive PKE events than with negative PKE events. Easterly wave activity is then examined in a regional model. The Advanced Research Weather Research and Forecasting (WRF-ARW) simulates West African monsoon climatology more accurately than the WRF Nonhydrostatic Mesoscale Model (WRF-NMM). Although the WRF-NMM produces more realistic boreal summer rainfall than the WRF-ARW, it fails to accurately simulate the AEJ and other key West African monsoon features. Parameterizations within the WRF-ARW are scrutinized as well, with the WRF single-moment 6-class microphysics and the Noah land surface model outperforming Thompson microphysics and the RUC land surface model. Three ten-year WRF-ARW experiments are performed to investigate the role of external forcing on intraseasonal variability in West Africa. In addition to a control simulation, two sensitivity experiments remove 30-90-day variability from the boundary conditions (for all zonal wavenumbers and just for eastward zonal wavenumbers 0-10). Overall, intraseasonal variability of AEWs shows only modest differences after the removal of all 30-90-day input into the model boundary conditions. PKE and PAPE budgets reveal that simulated positive PKE events in West Africa are preceded by extensions of the AEJ into East Africa, which enhance barotropic and baroclinic energy conversions in this region. This jet extension is associated with warm lower-tropospheric temperature anomalies in the eastern Sahara. In West Africa, the amplitude of PKE and PAPE budget terms exhibit a similar evolution (even in the sensitivity experiments) as in the reanalysis products.

  2. Diatom community dynamics in a tropical, monsoon-influenced environment: West coast of India

    NASA Astrophysics Data System (ADS)

    D'Costa, Priya M.; Anil, Arga Chandrashekar

    2010-07-01

    Diatom communities are influenced by environmental perturbations, such as the monsoon system that impact the niche opportunities of species. To discern the influence of the monsoon system on diatom community structure, we sampled during two consecutive post-monsoons (2001 and 2002) and the intervening pre-monsoon at Mumbai and Jawaharlal Nehru ports along the central west coast of India. Characteristic temporal shifts in diatom community structure were observed across the sampling periods; these were mainly driven by temperature, salinity and dissolved oxygen saturation. The nutrient-poor pre-monsoon period supported low abundance yet high species richness and diversity of diatoms. Coscinodiscus, Cyclotella, Thalassiosira, Triceratium, Pleurosigma, Skeletonema and Surirella were the most dominant genera. Both the post-monsoon periods, following dissimilar monsoon events, were dominated by Skeletonema costatum, but differed in some of the residual species . Thalassiosira and Thalassionema spp. dominated mostly during post-monsoon I whereas Triceratium and Pleurosigma spp. dominated during post-monsoon II. To understand the underlying ecological mechanisms involved in such dynamics, we focus on the dominant diatom species in post-monsoon periods, S. costatum, that contributes up to 60% to total diatom cell numbers. This research is relevant in light of the fluctuating monsoon regimes over the Asian continent, the confounding effects of anthropogenic eutrophication and the resulting cascading effects on trophic web dynamics.

  3. Aerosol interactions with African/Atlantic climate dynamics

    NASA Astrophysics Data System (ADS)

    Hosseinpour, F.; Wilcox, E. M.

    2014-07-01

    Mechanistic relationships exist between variability of dust in the oceanic Saharan air layer (OSAL) and transient changes in the dynamics of Western Africa and the tropical Atlantic Ocean. This study provides evidence of possible interactions between dust in the OSAL region and African easterly jet-African easterly wave (AEJ-AEW) system in the climatology of boreal summer, when easterly wave activity peaks. Synoptic-scale changes in instability and precipitation in the African/Atlantic intertropical convergence zone are correlated with enhanced aerosol optical depth (AOD) in the OSAL region in response to anomalous 3D overturning circulations and upstream/downstream thermal anomalies at above and below the mean-AEJ level. Upstream and downstream anomalies are referred to the daily thermal/dynamical changes over the West African monsoon region and the Eastern Atlantic Ocean, respectively. Our hypothesis is that AOD in the OSAL is positively correlated with the downstream AEWs and negatively correlated with the upstream waves from climatological perspective. The similarity between the 3D pattern of thermal/dynamical anomalies correlated with dust outbreaks and those of AEWs provides a mechanism for dust radiative heating in the atmosphere to reinforce AEW activity. We proposed that the interactions of OSAL dust with regional climate mainly occur through coupling of dust with the AEWs.

  4. How can aerosols affect the Asian summer monsoon? Assessment during three consecutive pre-monsoon seasons from CALIPSO satellite data

    NASA Astrophysics Data System (ADS)

    Kuhlmann, J.; Quaas, J.

    2010-05-01

    The impact of aerosols above and around the Tibetan Plateau on the Asian Summer Monsoon during pre-monsoon seasons March-April-May 2007, 2008, and 2009 is investigated by means of remote sensing and radiative transfer modelling. Four source regions are found to be responsible for the high aerosol loading around the Tibetan Plateau: the Taklamakan Desert, the Ganges Plains, the Indus Plains, and the Arabian Sea. CALIPSO lidar satellite data, providing vertically resolved images of aerosols, shows aerosol concentrations to be highest in the lower 5 km of the atmosphere with only little amounts reaching the Tibetan Plateau altitude. Using a radiative transfer model we find that aerosol plumes reduce shortwave radiation throughout the Monsoon region in the seasonal average by between 20 and 30 W/m2. Peak shortwave heating in the lower troposphere reaches 0.2 K/day. In higher layers this shortwave heating is partly balanced by longwave cooling. Although high-albedo surfaces, such as deserts or the Tibetan Plateau, increase the shortwave heating by around 10%, the overall effect is strongest close to the aerosol sources. A strong elevated heating which could influence large-scale monsoonal circulations as suggested by previous studies is not found.

  5. How can aerosols affect the Asian summer monsoon? Assessment during three consecutive pre-monsoon seasons from CALIPSO satellite data

    NASA Astrophysics Data System (ADS)

    Kuhlmann, J.; Quaas, J.

    2010-02-01

    The impact of aerosols above and around the Tibetan Plateau on the Asian Summer Monsoon during pre-monsoon seasons March-April-May 2007, 2008, and 2009 is investigated by means of remote sensing and radiative transfer modelling. Four source regions are found to be responsible for the high aerosol loading around the Tibetan Plateau: the Taklamakan Desert, the Ganges Plains, the Indus Plains, and the Arabian Sea. CALIPSO lidar satellite data, providing vertically resolved images of aerosols, shows aerosol concentrations to be highest in the lower 5 km of the atmosphere with only little amounts reaching the Tibetan Plateau altitude. Using a radiative transfer model we find that aerosol plumes reduce shortwave radiation throughout the Monsoon region in the seasonal average by between 20 and 30 W/m2. Peak shortwave heating in the lower troposphere reaches 0.2 K/day. In higher layers this shortwave heating is partly balanced by longwave cooling. Although high-albedo surfaces, such as deserts or the Tibetan Plateau, increase the shortwave heating by around 10%, the overall effect is strongest close to the aerosol sources. A strong elevated heating which could influence large-scale monsoonal circulations as suggested by previous studies is not found.

  6. High Speed Computing, LANs, and WAMs

    NASA Technical Reports Server (NTRS)

    Bergman, Larry A.; Monacos, Steve

    1994-01-01

    Optical fiber networks may one day offer potential capacities exceeding 10 terabits/sec. This paper describes present gigabit network techniques for distributed computing as illustrated by the CASA gigabit testbed, and then explores future all-optic network architectures that offer increased capacity, more optimized level of service for a given application, high fault tolerance, and dynamic reconfigurability.

  7. Relationship between summer monsoon rainfall and cyclogenesis over Bay of Bengal during post-monsoon (October-December) season

    NASA Astrophysics Data System (ADS)

    Sadhuram, Y.; Maneesha, K.

    2016-09-01

    In this study, an attempt has been made to examine the relationship between summer monsoon rainfall (June-September) and the total number of depressions, cyclones and severe cyclones (TNDC) over Bay of Bengal during the post-monsoon (October-December) season. The seasonal rainfall of the subdivisions (located in south India) (referred as rainfall index - RI), is positively and significantly correlated (r=0.59; significant at >99% level) with the TNDC during the period, 1984-2013. By using the first differences (current season minus previous season), the correlations are enhanced and a remarkably high correlation of 0.87 is observed between TNDC and RI for the recent period, 1993-2013. The average seasonal genesis potential parameter (GPP) showed a very high correlation of 0.84 with the TNDC. A very high correlation of 0.83 is observed between GPP and RI for the period, 1993-2013. The relative vorticity and mid-tropospheric relative humidity are found to be the dominant terms in GPP. The GPP was 3.5 times higher in above (below) normal RI in which TNDC was 4 (2). It is inferred that RI is playing a key role in TNDC by modulating the environmental conditions (low level vorticity and relative humidity) over Bay of Bengal during post-monsoon season which could be seen from the very high correlation of 0.87 (which explains 76% variability in TNDC). For the first time, we show that RI is a precursor for the TNDC over Bay of Bengal during post-monsoon season. Strong westerlies after the SW monsoon season transport moisture over the subdivisions towards Bay of Bengal due to cyclonic circulation. This circulation favours upward motion and hence transport moisture vertically to mid-troposphere which causes convective instability and this in turn favour more number of TNDC, under above-normal RI year.

  8. Environment, Health and Climate: Impact of African aerosols

    NASA Astrophysics Data System (ADS)

    Liousse, C.; Doumbia, T.; Assamoi, E.; Galy-Lacaux, C.; Baeza, A.; Penner, J. E.; Val, S.; Cachier, H.; Xu, L.; Criqui, P.

    2012-12-01

    Fossil fuel and biofuel emissions of particles in Africa are expected to significantly increase in the near future, particularly due to rapid growth of African cities. In addition to biomass burning emissions prevailing in these areas, air quality degradation is then expected with important consequences on population health and climatic/radiative impact. In our group, we are constructing a new integrated methodology to study the relations between emissions, air quality and their impacts. This approach includes: (1) African combustion emission characterizations; (2) joint experimental determination of aerosol chemistry from ultrafine to coarse fractions and health issues (toxicology and epidemiology). (3) integrated environmental, health and radiative modeling. In this work, we show some results illustrating our first estimates of African anthropogenic emission impacts: - a new African anthropogenic emission inventory adapted to regional specificities on traffic, biofuel and industrial emissions has been constructed for the years 2005 and 2030. Biomass burning inventories were also improved in the frame of AMMA (African Monsoon) program. - carbonaceous aerosol radiative impact in Africa has been modeled with TM5 model and Penner et al. (2011) radiative code for these inventories for 2005 and 2030 and for two scenarios of emissions : a reference scenario, with no further emission controls beyond those achieved in 2003 and a ccc* scenario including planned policies in Kyoto protocol and regulations as applied to African emission specificities. In this study we will show that enhanced heating is expected with the ccc* scenarios emissions in which the OC fraction is relatively lower than in the reference scenario. - results of short term POLCA intensive campaigns in Bamako and Dakar in terms of aerosol chemical characterization linked to specific emissions sources and their inflammatory impacts on the respiratory tract through in vitro studies. In this study, organic

  9. The African superswell

    NASA Technical Reports Server (NTRS)

    Nyblade, Andrew A.; Robinson, Scott W.

    1994-01-01

    Maps of residual bathymetry in the ocean basins around the African continent reveal a broad bathymetric swell in the southeastern Atlantic Ocean with an amplitude of about 500 m. We propose that this region of anomalously shallow bathymetry, together with the contiguous eastern and southern African plateaus, form a superswell which we refer to as the African superswell. The origin of the African superswell is uncertain. However, rifting and volcanism in eastern Africa, as well as heat flow measurements in southern Africa and the southeastern Atlantic Ocean, suggest that the superswell may be attributed, at least in part, to heating of the lithosphere.

  10. Active and break spells of the Indian summer monsoon

    NASA Astrophysics Data System (ADS)

    Rajeevan, M.; Gadgil, Sulochana; Bhate, Jyoti

    2010-06-01

    In this paper, we suggest criteria for the identification of active and break events of the Indian summer monsoon on the basis of recently derived high resolution daily gridded rainfall dataset over India (1951-2007). Active and break events are defined as periods during the peak monsoon months of July and August, in which the normalized anomaly of the rainfall over a critical area, called the monsoon core zone exceeds 1 or is less than -1.0 respectively, provided the criterion is satisfied for at least three consecutive days. We elucidate the major features of these events. We consider very briefly the relationship of the intraseasonal fluctuations between these events and the interannual variation of the summer monsoon rainfall. We find that breaks tend to have a longer life-span than active spells. While, almost 80% of the active spells lasted 3-4 days, only 40% of the break spells were of such short duration. A small fraction (9%) of active spells and 32% of break spells lasted for a week or longer. While active events occurred almost every year, not a single break occurred in 26% of the years considered. On an average, there are 7 days of active and break events from July through August. There are no significant trends in either the days of active or break events. We have shown that there is a major difference between weak spells and long intense breaks. While weak spells are characterized by weak moist convective regimes, long intense break events have a heat trough type circulation which is similar to the circulation over the Indian subcontinent before the onset of the monsoon. The space-time evolution of the rainfall composite patterns suggests that the revival from breaks occurs primarily from northward propagations of the convective cloud zone. There are important differences between the spatial patterns of the active/break spells and those characteristic of interannual variation, particularly those associated with the link to ENSO. Hence, the interannual

  11. Space-Time Structure of Monsoon Interannual Variability.

    NASA Astrophysics Data System (ADS)

    Terray, Pascal

    1995-11-01

    The analysis of corrected ship reports [sea level pressure (SLP), sea surface temperature (SST), air temperature (AT)] and corrected land data (SLP, AT, rainfall) in the Indian sector reveals the existence of two low-frequency modes of monsoon variability during the 1900-1970 period. A definite biennial (B) mode exists on the SLP fields. This B oscillation is unambiguously linked with a southwest-northeast SLP anomaly gradient. During the summer monsoon, the B SLP pattern can be interpreted as an expansion/contraction of the monsoon activity since this mode is strongly coupled with rainfall variations over peninsular India. A strong low-frequency (LF) mode with period spanning 4-6 years is also seen on SLP fields over the Indian Ocean and subcontinent. The variance associated with this band is typically more important than the one observed for the B mode, and its spatial mark is also strikingly different since it is linked with a global pattern of variation. This mode has also a strong influence on the Indian summer rainfall fluctuations, particularly on the Ghats and in the Indo-Gangetic plains.The amplitude of these oscillations varies widely during the 1900-1970 period. The LF mode is well defined during 1900-1923 and 1947-1970. There is a tendency for the energy associated with the B mode to decrease on the land while it increases over the Indian Ocean during the whole 1900-1970 interval.Although these two timescales exist also on SST fields, cross-spectral analysis shows that ocean-atmosphere interactions are much stronger at the B timescale. This result stresses the B nature of the monsoon system.The existence of these interannual signals in the Indian areas where the annual cycle is so strong raises difficult problems: How can climatic anomalies persist for several years in spite of strong seasonality? Or, still more intriguing, how can be explained the persistence of climatic anomalies during one year and the appearance of opposite sign climatic anomalies

  12. Recent climatological trend of the Saharan heat low and its impact on the West African climate

    NASA Astrophysics Data System (ADS)

    Lavaysse, Christophe; Flamant, Cyrille; Evan, Amato; Janicot, Serge; Gaetani, Marco

    2015-10-01

    The Saharan heat low (SHL) plays a pivotal role in the West African monsoon system in spring and summer. The recent trend in SHL activity has been analysed using two sets of numerical weather prediction (NWP) model reanalyses and Atmospheric Models Intercomparison Project simulations from 15 climate models performed in the framework of the 5th Coupled Models Intercomparison Project (CMIP5) exercise. A local increase of temperature in the Sahara during the 90s is found in the two sets of NWP models temperature. This increase is stronger within the SHL region than over the surrounding areas. Using different temporal filters (under 25 days, 25-100 days and above 300 days), we show that this is accompanied by a slight but widespread increase of temperature, and a change in the filtered signal under 25 days during the transition period of the 90s. We also show that SHL pulsations occurring at different time scales impact the West Africa climate on a variety of spatial scales, from the regional scale (for the high band pass) to the synoptic scale (for the low band pass signal). Despite a large variability in the temporal trends for 15 climate models from the CMIP5 project, the warming trend in the 90s is observed in the models ensemble mean. Nevertheless, large discrepancies are found between the NWP models reanalyses and the climate model simulations regarding the spatial and temporal evolutions of the SHL as well as its impact on West African climate at the different time scales. These comparisons also reveal that climate models represent the West African monsoon interactions with SHL pulsations quite differently. We provide recommendations to use some of them depending on the time scales of the processes at play (synoptic, seasonal, interannual) and based on key SHL metrics (location, mean intensity, global trend, interaction with the West African monsoon dynamics).

  13. Morphodynamics of rivers strongly affected by monsoon precipitation: Review of depositional style and forcing factors

    NASA Astrophysics Data System (ADS)

    Plink-Björklund, Piret

    2015-06-01

    Rivers that receive significant amounts of their surface water supply from monsoon precipitation characteristically experience seasonal floods, and display seasonally highly variable discharge, controlled by the monsoon trough passage and its related cyclones. The intense summer rainfall causes high-magnitude floods, whereas rivers only transmit a low base flow during the dry winters. For many rivers in the sub-humid to arid subtropics, bordering the monsoon domain, the monsoon rain is also the main source of surface water recharge. However, such rivers may receive monsoon rain and transmit discharge only during abnormal or strengthened monsoon seasons. This annual discharge variability or range, as compared to the mean annual discharge, distinguishes the monsoonal and subtropical rivers from the rivers in equatorial tropics and temperate perennial precipitation zones, where the annual range is relatively small compared to the annual mean discharge. This review explores the effects of this seasonal and yearly variable rainfall, and the resultant highly peaked discharge pattern on river morphodynamics, and presents a comparison of modern and ancient monsoonal and subtropical river deposits. The field datasets and literature analyses discussed herein provide recognition criteria for monsoon-controlled river deposits, by documenting the diversity of the sedimentary facies, macroforms (bar forms), and architectural elements common in ancient and modern monsoon-controlled rivers. The review demonstrates that seasonal and inter-annual precipitation range is a key control on river morphodynamics, and resultant sedimentary facies characteristics, rather than the specific climate zone or average annual precipitation.

  14. Shifting covariability of North American summer monsoon precipitation with antecedent winter precipitation

    USGS Publications Warehouse

    McCabe, G.J.; Clark, M.P.

    2006-01-01

    Previous research has suggested that a general inverse relation exists between winter precipitation in the southwestern United states (US) and summer monsoon precipitation. In addition, it has been suggested that this inverse relation between winter precipitation and the magnitude of the southwestern US monsoon breaks down under certain climatic conditions that override the regional winter/monsoon precipitation relations. Results from this new study indicate that the winter/monsoon precipitation relations do not break down, but rather shift location through time. The strength of winter/monsoon precipitation relations, as indexed by 20-year moving correlations between winter precipitation and monsoon precipitation, decreased in Arizona after about 1970, but increased in New Mexico. The changes in these correlations appear to be related to an eastward shift in the location of monsoon precipitation in the southwestern US. This eastward shift in monsoon precipitation and the changes in correlations with winter precipitation also appear to be related to an eastward shift in July/August atmospheric circulation over the southwestern US that resulted in increased monsoon precipitation in New Mexico. Results also indicate that decreases in sea-surface temperatures (SSTs) in the central North Pacific Ocean also may be associated with th changes in correlations between winter and monsoon precipitation. Copyright ?? 2006 Royal Meteorological Society.

  15. Distribution and sources of particulate organic matter in the Indian monsoonal estuaries during monsoon

    NASA Astrophysics Data System (ADS)

    Sarma, V. V. S. S.; Krishna, M. S.; Prasad, V. R.; Kumar, B. S. K.; Naidu, S. A.; Rao, G. D.; Viswanadham, R.; Sridevi, T.; Kumar, P. P.; Reddy, N. P. C.

    2014-11-01

    The distribution and sources of particulate organic carbon (POC) and nitrogen (PN) in 27 Indian estuaries were examined during the monsoon using the content and isotopic composition of carbon and nitrogen. Higher phytoplankton biomass was noticed in estuaries with deeper photic zone than other estuaries receiving higher suspended matter. The δ13CPOC and δ15NPN data suggest that relatively higher δ13CPOC (-27.9 to -22.6‰) and lower δ15NPN (0.7 to 5.8‰) were noticed in the estuaries located in the northern India, north of 16°N, and lower δ13CPOC (-31.4 to -28.2‰) and higher δ15NPN (5 to 10.3‰) in the estuaries located in the southern India. This is associated with higher Chl a in the northern than southern estuaries suggesting that in situ production contributed significantly to the POC pool in the former, whereas terrestrial sources are important in the latter estuaries. The spatial distribution pattern of δ15NPN is consistent with fertilizer consumption in the Indian subcontinent, which is twice as much in the northern India as in the south whereas δ13CPOC suggests that in situ production is a dominant source in the southern and terrestrial sources are important in the northern estuaries. Based on the Stable Isotope Analysis in R model, 40-90% (70-90%) of organic matter is contributed by C3 plants (freshwater algae) in the estuaries located in the northern (southern) India.

  16. Connections Between Stratospheric Pollution and the Asian Summer Monsoon

    NASA Technical Reports Server (NTRS)

    Bauer, Susanne E.; Tsigaridis, Konstas

    2015-01-01

    The Asian Monsoon leads to rapid vertical transport of gases and aerosols into the upper troposphere. Some of the pollution might be transported above cloud levels, which will allow it to spread globally and possibly at some occasions reach into the stratosphere. In this study we will use the GISS climate model to investigate the interactions between pollution and convective transport as well as secondary aerosol formation. Pollution resulting from anthropogenic activity as well as from natural sources such as small and large volcanic eruptions, dust storms and forest fires will be quantified. This modeling study will be accompanied by satellite observations from space that monitor aerosol optical thickness (AOT), and absorption AOT (AAOT) in two and three dimensions. Our goal is a better process level understanding of the evolution of natural and anthropogenic aerosol plumes in conjunction with the Asian Monsoon. Hence, we aim to explain their large-scale expansion, which eventually determines their impacts on climate.

  17. Connections between Pollution and the Asian Monsoon Circulation

    NASA Astrophysics Data System (ADS)

    Bauer, S.

    2015-12-01

    The Asian Monsoon leads to rapid vertical transport of gases and aerosols into the upper troposphere. Some of the pollution might be transported above cloud levels, which will allow it to spread globally and possibly at some occasions reach into the stratosphere. In this study we will use the GISS climate model to investigate the interactions between pollution and convective transport as well as secondary aerosol formation. Pollution resulting from anthropogenic activity as well as from natural sources such as small and large volcanic eruptions, dust storms and forest fires will be quantified. This modeling study will be accompanied by satellite observations from space that monitor aerosol optical thickness (AOT), and absorption AOT (AAOT) in two and three dimensions. Our goal is a better process level understanding of the evolution of natural and anthropogenic aerosol plumes in conjunction with the Asian Monsoon. Hence, we aim to explain their large-scale expansion, which eventually determines their impacts on climate.

  18. Spatiotemporal patterns and trends of Indian monsoonal rainfall extremes

    NASA Astrophysics Data System (ADS)

    Malik, Nishant; Bookhagen, Bodo; Mucha, Peter J.

    2016-02-01

    In this study, we provide a comprehensive analysis of trends in the extremes during the Indian summer monsoon (ISM) months (June to September) at different temporal and spatial scales. Our goal is to identify and quantify spatiotemporal patterns and trends that have emerged during the recent decades and may be associated with changing climatic conditions. Our analysis primarily relies on quantile regression that avoids making any subjective choices on spatial, temporal, or intensity pattern of extreme rainfall events. Our analysis divides the Indian monsoon region into climatic compartments that show different and partly opposing trends. These include strong trends toward intensified droughts in Northwest India, parts of Peninsular India, and Myanmar; in contrast, parts of Pakistan, Northwest Himalaya, and Central India show increased extreme daily rain intensity leading to higher flood vulnerability. Our analysis helps explain previously contradicting results of trends in average ISM rainfall.

  19. Monsoon oscillations regulate fertility of the Red Sea

    NASA Astrophysics Data System (ADS)

    Raitsos, Dionysios E.; Yi, Xing; Platt, Trevor; Racault, Marie-Fanny; Brewin, Robert J. W.; Pradhan, Yaswant; Papadopoulos, Vassilis P.; Sathyendranath, Shubha; Hoteit, Ibrahim

    2015-02-01

    Tropical ocean ecosystems are predicted to become warmer, more saline, and less fertile in a future Earth. The Red Sea, one of the warmest and most saline environments in the world, may afford insights into the function of the tropical ocean ecosystem in a changing planet. We show that the concentration of chlorophyll and the duration of the phytoplankton growing season in the Red Sea are controlled by the strength of the winter Arabian monsoon (through horizontal advection of fertile waters from the Indian Ocean). Furthermore, and contrary to expectation, in the last decade (1998-2010) the winter Red Sea phytoplankton biomass has increased by 75% during prolonged positive phases of the Multivariate El Niño-Southern Oscillation Index. A new mechanism is reported, revealing the synergy of monsoon and climate in regulating Red Sea greenness.

  20. The East Asian subtropical summer monsoon: Recent progress

    NASA Astrophysics Data System (ADS)

    He, Jinhai; Liu, Boqi

    2016-04-01

    The East Asian subtropical summer monsoon (EASSM) is one component of the East Asian summer monsoon system, and its evolution determines the weather and climate over East China. In the present paper, we firstly demonstrate the formation and advancement of the EASSM rainbelt and its associated circulation and precipitation patterns through reviewing recent studies and our own analysis based on JRA-55 (Japanese 55-yr Reanalysis) data and CMAP (CPC Merged Analysis of Precipitation), GPCP (Global Precipitation Climatology Project), and TRMM (Tropical Rainfall Measuring Mission) precipitation data. The results show that the rainy season of the EASSM starts over the region to the south of the Yangtze River in early April, with the establishment of strong southerly wind in situ. The EASSM rainfall, which is composed of dominant convective and minor stratiform precipitation, is always accompanied by a frontal system and separated from the tropical summer monsoon system. It moves northward following the onset of the South China Sea summer monsoon. Moreover, the role of the land-sea thermal contrast in the formation and maintenance of the EASSM is illustrated, including in particular the effect of the seasonal transition of the zonal land-sea thermal contrast and the influences from the Tibetan Plateau and midlatitudes. In addition, we reveal a possible reason for the subtropical climate difference between East Asia and East America. Finally, the multi-scale variability of the EASSM and its influential factors are summarized to uncover possible reasons for the intraseasonal, interannual, and interdecadal variability of the EASSM and their importance in climate prediction.

  1. Transport pathways from the Asian monsoon anticyclone to the stratosphere

    NASA Astrophysics Data System (ADS)

    Garny, Hella; Randel, William

    2016-04-01

    The upper tropospheric Asian monsoon anticyclone emerges in response to persistent deep convection over India and southeast Asia in northern summer. The monsoon circulation is associated with rapid transport from the surface to the upper troposphere within convective updrafts, leading to tracer anomalies within the anticyclone. Possibly air is transported further into the stratosphere, but the exact pathways of air from the upper tropospheric anticyclone to the stratosphere are currently under debate. While air is thought to be confined to the anticyclone by its surrounding wind jets, large variability in the anticyclone results in shedding of air from the anticyclone to its surrounding, and possibly air might reach the extratropical lower stratosphere by isentropic mixing. On the other hand, positive vertical velocities in the anticyclone region suggests upward transport of air into the tropical lower stratosphere. In this study, we investigate transport pathways of air originating in the upper tropospheric Asian monsoon anticyclone based on isentropic and three-dimensional trajectories. Trajectories are driven by ERA-Interim reanalysis data, and three-dimensional results are based both on kinematic and diabatic transport calculations. Isentropic calculations show that air parcels are typically confined within the anticyclone for 10-20 days, and spread over the tropical belt within a month of their initialization. However, only few parcels (3 % at 360 K, 8 % at 380 K) reach the extratropical stratosphere by isentropic transport. When considering vertical transport we find that 31 % (48 %) of the trajectories reach the stratosphere within 60 days when using vertical velocities or diabatic heating rates to calculate vertical transport, respectively. In both cases, most parcels that reach the stratosphere are transported upward within the anticyclone and enter the stratosphere in the tropics, typically 10-20 days after their initialization at 360 K. This suggests

  2. The impact of natural aerosols on Indian summer monsoon

    NASA Astrophysics Data System (ADS)

    Vinoj, V.; Wang, H.; Yoon, J.; Rasch, P.

    2011-12-01

    Atmospheric aerosols emitted from a variety of natural and anthropogenic sources impact the earth's radiation and water budget. Most of the studies in the recent past have been focusing on anthropogenic aerosols and their impact. However, natural aerosols like sea-salt and dust form the bulk of the aerosol mass loading in the atmosphere. For example, oceans cover about 70% of the earth's surface area and are a major source of sea-salt aerosols in the atmosphere. Sea-salt emission is the single largest contributor to natural aerosols and accounts for nearly half of the global aerosol optical depth. Dust emission, the counterpart over land, also contributes substantially to natural atmospheric aerosols. In addition to their direct effect on solar radiation, these aerosols also actively participate in cloud formation by acting as cloud condensation and ice nuclei and have indirect effects on clouds. Both sea-salt and dust particles are primarily formed by the action of winds that largely determine seasonal/annual variations in their source strength and atmospheric loading. Over the Indian Ocean region, especially the Arabian Sea is characterized by high winds during the monsoon that generate a large amount of sea-salt aerosols. Also these high winds mobilize large amount of dust aerosols in the northern Arabian Sea depending on wind direction. These natural aerosols together with anthropogenic emissions impact Indian monsoon precipitation. We use satellite observation of precipitation and column aerosol loading along with a global climate model (Community Atmosphere Model version 5, CAM5) to show that the variability of natural aerosols (i.e., sea-salt and dust) play an important role in modulating the Indian monsoon precipitation and the response of the monsoon system to anthropogenic aerosols. The effect of dust and sea-salt on precipitation is found to be opposite to each other. Our study suggests that the observed spatial and temporal trends in precipitation

  3. CMIP5/AMIP GCM simulations of East Asian summer monsoon

    NASA Astrophysics Data System (ADS)

    Feng, Jinming; Wei, Ting; Dong, Wenjie; Wu, Qizhong; Wang, Yongli

    2014-07-01

    The East Asian summer monsoon (EASM) is a distinctive component of the Asian climate system and critically influences the economy and society of the region. To understand the ability of AGCMs in capturing the major features of EASM, 10 models that participated in Coupled Model Intercomparison Project/Atmospheric Model Intercomparison Project (CMIP5/AMIP), which used observational SST and sea ice to drive AGCMs during the period 1979-2008, were evaluated by comparing with observations and AMIP II simulations. The results indicated that the multi-model ensemble (MME) of CMIP5/AMIP captures the main characteristics of precipitation and monsoon circulation, and shows the best skill in EASM simulation, better than the AMIP II MME. As for the Meiyu/Changma/Baiyu rainbelt, the intensity of rainfall is underestimated in all the models. The biases are caused by a weak western Pacific subtropical high (WPSH) and accompanying eastward southwesterly winds in group I models, and by a too strong and west-extended WPSH as well as westerly winds in group II models. Considerable systematic errors exist in the simulated seasonal migration of rainfall, and the notable northward jumps and rainfall persistence remain a challenge for all the models. However, the CMIP5/AMIP MME is skillful in simulating the western North Pacific monsoon index (WNPMI).

  4. Aerosols and contrasting monsoon conditions over the Himalayan region

    NASA Astrophysics Data System (ADS)

    Singh, Charu; Ganguly, Dilip; Dash, S. K.

    2016-05-01

    Impact of aerosols on the Indian summer monsoon (ISM) variability is well documented; however there are limited studies which have quantified the role of aerosols in modifying the amount of rainfall. To address this research problem, we make use of the remotely sensed data set of precipitation and aerosols from different observations. In the present study remotely sensed precipitation data set has been utilised to define contrasting monsoon conditions over the Himalayan region. As per the classical definition, active and break spells are defined over the central part of the Indian land region, and during the break spells over the central Indian region, the Himalayan region receives substantial amount of rainfall. It is found that accumulation of more dust over the Uttarakhand region significantly (negative correlation with rainfall; significant at 5% significance level) suppresses the rainfall during break spells. We propose that the substantial aerosol loading and its associated dynamical feedback over the Himalayan foothills may have considerable impact on the amount of rainfall over the mountainous regions of the Indian subcontinent. Results presented in this paper are supported by the statistically robust significance test and would be useful to develop the understanding of the role of aerosols in modulating the rainfall intensity during the summer monsoon season.

  5. On the Structure and Dynamics of Indian Monsoon Depressions

    NASA Astrophysics Data System (ADS)

    Hunt, Kieran; Turner, Andrew; Inness, Peter; Parker, David; Levine, Richard

    2016-04-01

    ERA-Interim reanalysis data from the past 35 years have been used with a newly-developed feature tracking algorithm to identify Indian monsoon depressions originating in or near the Bay of Bengal. These were then rotated, centralised and combined to give a fully three-dimensional 106-depression composite structure - a considerably larger sample than any previous detailed study on monsoon depressions and their structure. Many known features of depression structure are confirmed, particularly the existence of a maximum to the southwest of the centre in rainfall and other fields, and a westward axial tilt in others. Additionally, the depressions are found to have significant asymmetry due to the presence of the Himalayas; a bimodal mid-tropospheric potential vorticity core; a separation into thermally cold- (-1.5K) and neutral- (~0K) cores near the surface with distinct properties; and that the centre has very large CAPE and very small CIN. Variability as a function of background state has also been explored, with land/coast/sea, diurnal, ENSO, active/break and Indian Ocean Dipole contrasts considered. Depressions are found to be markedly stronger during the active phase of the monsoon, as well as during La Nina. Depressions on land are shown to be more intense and more tightly constrained to the central axis. A detailed schematic diagram of a vertical cross-section through a composite depression is also presented, showing its inherent asymmetric structure.

  6. 16 Extraordinary African Americans.

    ERIC Educational Resources Information Center

    Lobb, Nancy

    This collection for children tells the stories of 16 African Americans who helped make America what it is today. African Americans can take pride in the heritage of these contributors to society. Biographies are given for the following: (1) Sojourner Truth, preacher and abolitionist; (2) Frederick Douglass, abolitionist; (3) Harriet Tubman, leader…

  7. African Studies Computer Resources.

    ERIC Educational Resources Information Center

    Kuntz, Patricia S.

    African studies computer resources that are readily available in the United States with linkages to Africa are described, highlighting those most directly corresponding to African content. Africanists can use the following four fundamental computer systems: (1) Internet/Bitnet; (2) Fidonet; (3) Usenet; and (4) dial-up bulletin board services. The…

  8. Understanding African American Males

    ERIC Educational Resources Information Center

    Bell, Edward Earl

    2010-01-01

    The purpose of this study was to assess the socialization skills, self-esteem, and academic readiness of African American males in a school environment. Discussions with students and the School Perceptions Questionnaire provided data for this investigation. The intended targets for this investigation were African American students; however, there…

  9. Africans Away from Home.

    ERIC Educational Resources Information Center

    Clarke, John Henrik

    Africans who were brought across the Atlantic as slaves never fully adjusted to slavery or accepted its inevitability. Resistance began on board the slave ships, where many jumped overboard or committed suicide. African slaves in South America led the first revolts against tyranny in the New World. The first slave revolt in the Caribbean occurred…

  10. Keeping African Masks Real

    ERIC Educational Resources Information Center

    Waddington, Susan

    2012-01-01

    Art is a good place to learn about our multicultural planet, and African masks are prized throughout the world as powerfully expressive artistic images. Unfortunately, multicultural education, especially for young children, can perpetuate stereotypes. Masks taken out of context lose their meaning and the term "African masks" suggests that there is…

  11. Educating African American Males

    ERIC Educational Resources Information Center

    Bell, Edward E.

    2010-01-01

    Background: Schools across America spend money, invest in programs, and sponsor workshops, offer teacher incentives, raise accountability standards, and even evoke the name of Obama in efforts to raise the academic achievement of African American males. Incarceration and college retention rates point to a dismal plight for many African American…

  12. African horse sickness and African carnivores.

    PubMed

    Alexander, K A; Kat, P W; House, J; House, C; O'Brien, S J; Laurenson, M K; McNutt, J W; Osburn, B I

    1995-11-01

    African horse sickness (AHS) is a disease that affects equids, and is principally transmitted by Culicoides spp. that are biological vectors of AHS viruses (AHSV). The repeated spread of AHSV from sub-Saharan Africa to the Middle East, northern Africa and the Iberian peninsula indicate that a better understanding of AHS epizootiology is needed. African horse sickness has long been known to infect and cause mortality among domestic dogs that ingest virus contaminated meat, but it is uncertain what role carnivores play in transmission of the virus. We present evidence of widespread natural AHS infection among a diversity of African carnivore species. We hypothesize that such infection resulted from ingestion of meat and organs from AHS-infected prey species. The effect of AHS on the carnivores is unknown, as is their role in the maintenance cycle of the disease.

  13. Diabetes in African Americans

    PubMed Central

    Marshall, M

    2005-01-01

    African Americans have a high risk for type 2 diabetes. Genetic traits, the prevalence of obesity, and insulin resistance all contribute to the risk of diabetes in the African American community. African Americans have a high rate of diabetic complications, because of poor glycaemic control and racial disparities in health care in the USA. African Americans with diabetes may have an atypical presentation that simulates type 1 diabetes, but then their subsequent clinical course is typical of type 2 diabetes. Culturally sensitive strategies, structured disease management protocols, and the assistance of nurses, diabetic educators, and other health care professionals are effective in improving the outcome of diabetes in the African American community. PMID:16344294

  14. Reduction of uncertainty associated with future changes in Indian summer monsoon projected by climate models and assessment of monsoon teleconnections

    NASA Astrophysics Data System (ADS)

    Rajendran, Kavirajan; Surendran, Sajani; Kitoh, Akio; Varghese, Stella Jes

    2016-05-01

    Coupled Model Intercomparison Project phase 5 (CMIP5) coupled global climate model (CGCM) Representative Concentration Pathway (RCP) simulations project clear future temperature increase but diverse changes in Indian summer monsoon rainfall (ISMR) with substantial inter-model spread. Robust signals of projected changes are derived based on objective criteria and the physically consistent simulations with the highest reliability suggest future reduction in the frequency of light rainfall but increase in high to extreme rainfall. The role of equatorial Indian and Pacific Oceans on the projected changes in monsoon rainfall is investigated. The results of coupled model projections are also compared with the corresponding projections from high resolution AGCM time-slice, multi-physics and multi-forcing ensemble experiments.

  15. Fluctuations in the deficiency of the summer monsoon over India, and their effect on economy

    NASA Astrophysics Data System (ADS)

    Mooley, D. A.; Parthasarathy, B.

    1982-04-01

    To assess the deficiency in the activity of the monsoon over India during the season, an index for the country based on the percentage area with a specified percentage seasonal rainfall deficiency and termed the Monsoon Deficiency Index (MDI), has been utilized. The statistical properties of the MDI series for the period 1871 1978 have been examined. The series which can be taken to be homogeneous and random has a high variability. MDI is generally not observed to persist at a high level; a high value is invariably followed by a low value. The deficiency over the country is considered as largescale and is termed as monsoon failure when the MDI value equals or exceeds the nineth decile viz. 40, of the mixed gamma distribution fitted to the MDI series. Using this criterion, the years of monsoon failure have been identified. The monsoon failures are found to occur randomly. The effect of monsoon deficiency on the Indian economy has been assessed.

  16. Effects of large-scale deforestation on precipitation in the monsoon regions: Remote versus local effects

    PubMed Central

    Devaraju, N.; Bala, Govindasamy; Modak, Angshuman

    2015-01-01

    In this paper, using idealized climate model simulations, we investigate the biogeophysical effects of large-scale deforestation on monsoon regions. We find that the remote forcing from large-scale deforestation in the northern middle and high latitudes shifts the Intertropical Convergence Zone southward. This results in a significant decrease in precipitation in the Northern Hemisphere monsoon regions (East Asia, North America, North Africa, and South Asia) and moderate precipitation increases in the Southern Hemisphere monsoon regions (South Africa, South America, and Australia). The magnitude of the monsoonal precipitation changes depends on the location of deforestation, with remote effects showing a larger influence than local effects. The South Asian Monsoon region is affected the most, with 18% decline in precipitation over India. Our results indicate that any comprehensive assessment of afforestation/reforestation as climate change mitigation strategies should carefully evaluate the remote effects on monsoonal precipitation alongside the large local impacts on temperatures. PMID:25733889

  17. Effects of large-scale deforestation on precipitation in the monsoon regions: remote versus local effects.

    PubMed

    Devaraju, N; Bala, Govindasamy; Modak, Angshuman

    2015-03-17

    In this paper, using idealized climate model simulations, we investigate the biogeophysical effects of large-scale deforestation on monsoon regions. We find that the remote forcing from large-scale deforestation in the northern middle and high latitudes shifts the Intertropical Convergence Zone southward. This results in a significant decrease in precipitation in the Northern Hemisphere monsoon regions (East Asia, North America, North Africa, and South Asia) and moderate precipitation increases in the Southern Hemisphere monsoon regions (South Africa, South America, and Australia). The magnitude of the monsoonal precipitation changes depends on the location of deforestation, with remote effects showing a larger influence than local effects. The South Asian Monsoon region is affected the most, with 18% decline in precipitation over India. Our results indicate that any comprehensive assessment of afforestation/reforestation as climate change mitigation strategies should carefully evaluate the remote effects on monsoonal precipitation alongside the large local impacts on temperatures.

  18. Has the number of Indian summer monsoon depressions decreased over the last 30 years?

    NASA Astrophysics Data System (ADS)

    Cohen, Naftali Y.; Boos, William R.

    2014-11-01

    Monsoon depressions are cyclonic atmospheric vortices with outer radii near 1000 km that form within the larger-scale monsoon circulations of India and other regions. Recent studies have reported a downward trend in recent decades in the number of Indian summer monsoon depressions. In particular, the years 2002, 2010, and 2012 were noted for having the first summers, in over a century, in which no depressions formed. Here satellite and reanalysis data are used to document the existence of multiple storms in the summers of 2002, 2010, and 2012 that meet traditional criteria for classification as monsoon depressions. Furthermore, the number of extreme synoptic events occurring each summer over the Bay of Bengal is estimated from satellite scatterometers and exhibits no statistically significant trend over the last three decades. These results raise questions about the validity of previously claimed large trends in monsoon depression activity in the Indian summer monsoon.

  19. African bees to control African elephants

    NASA Astrophysics Data System (ADS)

    Vollrath, Fritz; Douglas-Hamilton, Iain

    2002-11-01

    Numbers of elephants have declined in Africa and Asia over the past 30 years while numbers of humans have increased, both substantially. Friction between these two keystone species is reaching levels which are worryingly high from an ecological as well as a political viewpoint. Ways and means must be found to keep the two apart, at least in areas sensitive to each species' survival. The aggressive African bee might be one such method. Here we demonstrate that African bees deter elephants from damaging the vegetation and trees which house their hives. We argue that bees can be employed profitably to protect not only selected trees, but also selected areas, from elephant damage.

  20. Pleistocene Indian Monsoon rainfall variability dominated by obliquity

    NASA Astrophysics Data System (ADS)

    Gebregiorgis, D.; Hathorne, E. C.; Giosan, L.; Collett, T. S.; Nuernberg, D.; Frank, M.

    2015-12-01

    The past variability of the Indian Monsoon is mostly known from records of wind strength over the Arabian Sea while Quaternary proxy records of Indian monsoon precipitation are still lacking. Here we utilize scanning x-ray fluorescence (XRF) data from a sediment core obtained by the IODP vessel JOIDES Resolution in the Andaman Sea (Site 17) to investigate changes in sediment supply from the peak monsoon precipitation regions to the core site. We use Ti/Ca and K/Rb ratios to trace changes in terrigenous flux and weathering regime, respectively, while Zr/Rb ratios suggest grain size variations. The age model of Site 17 is based on correlation of benthic C. wuellerstorfi/C. mundulus δ18O data to the LR04 global benthic δ18O stack at a resolution of ~3 kyr (Lisiecki and Raymo, 2005) for the last 2 Myrs. In its youngest part the age model is supported by five 14C ages on planktic foraminifera and the youngest Toba ash layer (Ali et al., 2015) resulting in a nearly constant sedimentation rate of ~6.5 cm/kyr. Frequency analysis of the 4 mm resolution Ti/Ca, K/Rb, and Zr/Rb time series using the REDFIT program (Schulz and Mudelsee, 2002), reveals the three main Milankovitch orbital cycles above the 90% confidence level. Depth domain spectral analysis reveals the presence of significant cyclicity at wavelengths of 28.5 and 2.8 m corresponding to the ~400 kyr and ~41 kyr cycles, respectively, during the last 2 Myr. These records suggest that Indian monsoon variability has varied in the obliquity and eccentricity bands, the latter in particular after the mid Pleistocene transition (MPT), while strong precession forcing is lacking in this super-high resolution record. Northern summer insolation and Southern Hemisphere latent heat export are out of phase during precessional cycles, but in phase in the obliquity band, which indicates that Indian monsoon precipitation has likely been more sensitive to both NH pull and SH push mechanisms (Clemens and Prell, 2003). References Ali

  1. Global sensitivity analysis of the Indian monsoon during the Pleistocene

    NASA Astrophysics Data System (ADS)

    Araya-Melo, P. A.; Crucifix, M.; Bounceur, N.

    2015-01-01

    The sensitivity of the Indian monsoon to the full spectrum of climatic conditions experienced during the Pleistocene is estimated using the climate model HadCM3. The methodology follows a global sensitivity analysis based on the emulator approach of Oakley and O'Hagan (2004) implemented following a three-step strategy: (1) development of an experiment plan, designed to efficiently sample a five-dimensional input space spanning Pleistocene astronomical configurations (three parameters), CO2 concentration and a Northern Hemisphere glaciation index; (2) development, calibration and validation of an emulator of HadCM3 in order to estimate the response of the Indian monsoon over the full input space spanned by the experiment design; and (3) estimation and interpreting of sensitivity diagnostics, including sensitivity measures, in order to synthesise the relative importance of input factors on monsoon dynamics, estimate the phase of the monsoon intensity response with respect to that of insolation, and detect potential non-linear phenomena. By focusing on surface temperature, precipitation, mixed-layer depth and sea-surface temperature over the monsoon region during the summer season (June-July-August-September), we show that precession controls the response of four variables: continental temperature in phase with June to July insolation, high glaciation favouring a late-phase response, sea-surface temperature in phase with May insolation, continental precipitation in phase with July insolation, and mixed-layer depth in antiphase with the latter. CO2 variations control temperature variance with an amplitude similar to that of precession. The effect of glaciation is dominated by the albedo forcing, and its effect on precipitation competes with that of precession. Obliquity is a secondary effect, negligible on most variables except sea-surface temperature. It is also shown that orography forcing reduces the glacial cooling, and even has a positive effect on precipitation

  2. Topographic development in the late Neogene and the impact on African vegetation

    NASA Astrophysics Data System (ADS)

    Jung, Gerlinde; Prange, Matthias; Schulz, Michael

    2014-05-01

    Hominid evolution, specifically the split of the hominid-chimpansee lineages in the late Miocene has long been hypothesized to be linked to the retreat of the tropical rainforest in Africa in the late Miocene. A main cause for the climatic and vegetation change often considered was uplift of Africa but also uplift of the Himalaya and the Tibetan Plateau was suggested to have contributed to an intensification of the African-Asian monsoon system and hence impacted rainfall distribution over Eastern Africa. In contrast, more recent proxy data suggest that open grassland habitats were available to human ancestors and apes long before their divergence and that there is no evidence for a closed rainforest in the late Miocene. We use the coupled global circulation model CCSM3 with an online coupled dynamic vegetation module to investigate the impact of the uplift processes on the African-Asian monsoon circulation and consequent changes in tropical African vegetation. The model is run with a resolution of T85 (~1.4°) for the atmosphere and land surface and a variable resolution for the computation of ocean and sea ice down to a meridional grid spacing of 0.3° around the equator. We performed a set of sensitivity experiments, altering elevations of the Himalaya and the Tibet Plateau and of East and South Africa separately and in combination from half to full present day level. The simulations confirm the dominant impact of the East and South African uplift for climate and vegetation development of the African tropics. Only a weak, but significant, impact of the prescribed Asian Uplift on African monsoon and vegetation development could be detected. Himalaya/Tibet Plateau uplift lead to slightly dryer conditions in Central Africa and small increases in rainfall over East Africa. According to the model simulations topographic uplift of Africa significantly altered rainfall in Central Africa, which coincides with proxy records from the Congo basin showing a change towards

  3. The verification of millennial-scale monsoon water vapor transport channel in northwest China

    NASA Astrophysics Data System (ADS)

    Li, Yu; Zhang, Chengqi; Wang, Yue

    2016-05-01

    Long-term changes of the Asian summer monsoon water vapor transport play a pivotal role in the variability of monsoon precipitation. Paleo-climate simulations have shown that there is an important monsoon vapor transport channel in western China. Previous studies mostly focused on the correlation between monsoon precipitation and intensity. Little research has been done on the verification of the water vapor channel. Compared with speleothem and lacustrine systems, the hydrological cycle of land surface sediments is more directly related to the monsoon water vapor. In this study, we used carbonate δ18O and organic matter δ13C of the surface eolian sediments from the piedmont of the northern Qilian Mountains to verify the monsoon water vapor on the Holocene millennial-scale. Two surface sedimentary sections were selected to study paleo-monsoon water vapor transport. Proxy data, including carbonate δ18O and organic matter δ13C of surface eolian sediments, as well as total organic matter and carbonate content were obtained from the two eolian sections. We also synthesized transient simulations of the CCSM3 and the Kiel climate models. The PMIP 3.0 project and TRACE isotopic simulations were also compared with the reconstructed monsoon water vapor transport. Our findings indicate that the strength of the Holocene Asian summer monsoon is consistent with the water vapor transport in western China that has significant impacts to long-term monsoon precipitation in northern China. This study verifies a significant millennial-scale correlation between the monsoon strength and monsoon water vapor transport intensity along the eastern Qinghai-Tibet Plateau.

  4. Near-linear response of mean monsoon strength to a broad range of radiative forcings.

    PubMed

    Boos, William R; Storelvmo, Trude

    2016-02-01

    Theoretical models have been used to argue that seasonal mean monsoons will shift abruptly and discontinuously from wet to dry stable states as their radiative forcings pass a critical threshold, sometimes referred to as a "tipping point." Further support for a strongly nonlinear response of monsoons to radiative forcings is found in the seasonal onset of the South Asian summer monsoon, which is abrupt compared with the annual cycle of insolation. Here it is shown that the seasonal mean strength of monsoons instead exhibits a nearly linear dependence on a wide range of radiative forcings. First, a previous theory that predicted a discontinuous, threshold response is shown to omit a dominant stabilizing term in the equations of motion; a corrected theory predicts a continuous and nearly linear response of seasonal mean monsoon strength to forcings. A comprehensive global climate model is then used to show that the seasonal mean South Asian monsoon exhibits a near-linear dependence on a wide range of isolated greenhouse gas, aerosol, and surface albedo forcings. This model reproduces the observed abrupt seasonal onset of the South Asian monsoon but produces a near-linear response of the mean monsoon by changing the duration of the summer circulation and the latitude of that circulation's ascent branch. Thus, neither a physically correct theoretical model nor a comprehensive climate model support the idea that seasonal mean monsoons will undergo abrupt, nonlinear shifts in response to changes in greenhouse gas concentrations, aerosol emissions, or land surface albedo. PMID:26811462

  5. Seasonal evolution of the West African heat low: a climatological perspective

    NASA Astrophysics Data System (ADS)

    Lavaysse, C.; Flamant, C.; Janicot, S.; Parker, D. J.; Lafore, J.-P.; Sultan, B.; Pelon, J.

    2009-08-01

    The West African heat low (WAHL), a region of high surface temperatures and low surface pressures, is a key element of the West African monsoon system. In this study, we propose a method to detect the WAHL in order to monitor its climatological seasonal displacement over West Africa during the period 1979-2001, using the European Centre for Medium-range Weather Forecast (ECMWF) ERA-40 reanalyses. The low-level atmospheric thickness (LLAT), a variable defined as the difference of geopotential heights at 700 and 925 hPa, is used to detect the dilatation of these levels generated by an increase of the temperature. We define grid points with 10% highest values of the LLAT as the WAHL. We show that our method reliably positions the WAHL over areas of high surface temperatures and low surface pressures, and that it is effective at detecting heat lows. In the course of the year, the climatological WAHL is shown to migrate north-westward from a position south of the Darfur mountains in the winter (November-March) to a location over the Sahara, between the Hoggar and the Atlas mountains, during the summer (June-September). The temperature tendency equation is used to investigate the processes controlling the displacement of the WAHL, and more particularly the heating at low levels. The specific period of the onset of the WAHL in its summer location over the Sahara (referred to as the Saharan heat low -SHL- onset) is also analysed during the 1984-2001 period, using complementary brightness temperature data from the European Union-funded Cloud Archive User Service (CLAUS). The climatological onset of the SHL occurs around 20 June, i.e. just before the climatological monsoon onset date. The present study suggests that the onset of the WAHL occurs approximately 5 days before the monsoon onset for the 1984-2001 period. This is confirmed independently by comparing the SHL onset date and the monsoon onset date for the 1984-2001 period. The seasonal evolution of the WAHL for the

  6. Modelling Suspended Sediment Transport in Monsoon Season: A Case Study of Pahang River Estuary, Pahang, Malaysia

    NASA Astrophysics Data System (ADS)

    Zakariya, Razak; Ahmad, Zuhairi; Saad, Shahbudin; Yaakop, Rosnan

    2013-04-01

    Sediment transport based on 2-dimensional real time model was applied to Pahang River estuary, Pahang, Malaysia and has been evaluated and verified with time series of tidal elevation, flow and suspended sediment load. Period of modelling was during highest high tide and lowest low tide in Northeast Monsoon (NE) which happened in December 2010 and Southwest Monsoon (SW) in July 2011. Simulated model outputs has been verify using Pearson's coefficient and has showed high accuracy. The validated model was used to simulate hydrodynamic and sediment transport of extreme conditions during both monsoon seasons. Based on field measurement and model simulation, tidal elevation and flow velocity, freshwater discharge of Pahang River were found to be higher during NE Monsoon. Based on the fluxes, the estuary also showed 'ebb-dominant' characteristic during highest high tide and lowest low tide in NE monsoon and normal ebbing-flooding characteristics during SW monsoon. In the Pahang River estuary, inflow and outflow patterns were perpendicular to the open boundary with circular flow formed at the shallow area in the middle of estuary during both monsoons. Referring to sea water intrusion from the river mouth, both seasons show penetration of more than 9 km (upstream input boundary) during higher high water tide. During higher lower water tide, the water intrusion stated varies which 5.6km during NE monsoon and 7.8km during SW monsoon. Regarding to the times lap during high tide, the sea water takes 2.8 hours to reach 9km upstream during NE monsoon compared to 1.9 hour during SW monsoon. The averages of suspended sediment concentration and suspended sediment load were higher during Northeast monsoon which increased the sedimentation potentials.Total of suspended sediment load discharged to the South China Sea yearly from Pahang River is approximately 96727.5 tonnes/day or 3.33 tonnes/km2/day which 442.6 tonnes/day during Northeast Monsoon and 25.3 tonnes/day during Southwest

  7. O the Interannual Variability of the Indian Monsoon and the Southern Oscillation

    NASA Astrophysics Data System (ADS)

    Wu, Ming Chin

    The mechanisms of the interannual variability of the Indian monsoon and the Southern Oscillation are investigated from observations in the Indian Ocean sector. On this diagnostic basis, a statistical forecasting scheme is developed for all-India rainfall anomalies. A good summer monsoon is characterized by the following aspects. (1) Arabian Sea: higher sea surface temperature (SST) in the pre-monsoon season but lower SST in the monsoon and post -monsoon seasons, lower sea level pressure (SLP) throughout the year, strong surface wind and more cloudiness from the pre-monsoon through the post-monsoon seasons; (2) Indian subcontinent: higher surface temperature in the pre-monsoon season but lower surface temperature afterward, decreased lower-tropospheric constant pressure topographies and higher in the North but lower in the South upper-tropospheric topographies, stronger lower-tropospheric inflow from the South and upper-tropospheric outflow toward the South, and more northward position of the upper-air ridge; and (3) Tibetan Plateau: a warm and dry concurrent summer and a warm and wet preceding winter. An early monsoon onset is heralded by oceanic -atmospheric conditions around the Indian subcontinent similar to those for a good monsoon year. However, conditions immediately following an early monsoon onset are characterized in the Arabian Sea by high SST, strong surface wind, less cloudiness, and high SLP, and in India by an anomalously cold and then warm surface environment. A cool equatorial Pacific Ocean episode of the southern Oscillation is characterized in the Indian Ocean by higher SST in the antecedent seasons but lower SST in the concurrent and following seasons, lower SLP from the preceding throughout the following seasons, stronger surface wind in the western part of the ocean but weaker surface wind in the eastern part during the summer, and more cloudiness. Both large positive values of the Southern Oscillation index and its tendency foreshadow a good

  8. Pliocene northeast African vegetation change

    NASA Astrophysics Data System (ADS)

    Liddy, H.; Sieracki, A.; Feakins, S. J.

    2012-12-01

    Plant leaf wax molecular fossils have yielded key insights into forest-grassland transitions in northeast Africa. The stable carbon isotopic composition (δ13C) of sedimentary leaf waxes (including n-alkanoic acids) records variations in the proportions of plants using the C3 (Calvin-Benson) pathway including trees, most shrubs and cool-season grasses versus the C4 (Hatch-Slack) pathway including warm-season grasses and sedges. Here we apply this technique to marine sediments from the Gulf of Aden to characterize northeast African environmental variability during the Pliocene. We sample DSDP Site 231 integrating 3kyr intervals to generate a high-resolution reconstruction spanning 3.7-5.3Ma. The δ13C compositions of downcore C30 n-alkanoic acid analyses average -27.5‰ (σ=1.2, n=177), ranging between -30.2 to -24.3‰ with repeated oscillations in the proportions of C4 biomass, presumably corresponding to the eccentricity and precessional modulation of insolation acting on monsoonal precipitation. Although δ13C values cannot be uniquely translated to C4 biomass given the spread in the C3 'endmember', we find complimentary evidence for proportions of C4 biomass from the isotopic spread of the n-alkanoic homologues (n-C28 to n-C32). Comparison to pollen data indicates that at times of low δ13C values, complete forest cover remains unlikely given the presence of grass pollen - taken together these records indicate the presence of C3 grasses. By evaluating our longer record from this site, as well as the terrestrial soil carbonate record, we find the Pliocene has low C4 proportions in comparison to higher proportions in Pleistocene and even late Miocene times. Intriguingly this drop in C4 plant biomass may correspond to a period of elevated atmospheric pCO2. Our ongoing reconstructions are of interest both for constraining environments of hominin evolution and tropical climate variability prior to the onset of Northern Hemisphere Glaciation, in particular during

  9. African Easterly Waves and Superparameterization

    NASA Astrophysics Data System (ADS)

    McCrary, Rachel; Randall, David; Stan, Cristiana

    2013-04-01

    This study examines the dynamics of African easterly wave (AEW) in the Superparameterized Community Climate System Model (SP-CCSM). Conventional general circulation models (GCMs) have difficulty representing AEW dynamics over West Africa. One reason is that the coarse resolution of these models limits their ability to represent the multi-scale interactions between the large-scale dynamics and individual convective systems, which are important for the origin and development of AEWs. The SP-CCSM has been designed to better simulate the interactions between small-scale circulations and large-scale dynamics, by replacing the conventional parameterizations with a 2D cloud resolving model embedded within each GCM grid column. With this approach we are able to capture the interactions between clouds and the global circulation of the atmosphere. The goal of our work is to improve our understanding of the multi-scale interactions that occur between AEWs and convection over West Africa. The implementation of the superparameterization into the CCSM improves the overall representation of monsoon precipitation over West Africa. Most notably, the region of maximum precipitation is shifted from the Gulf of Guinea in CCSM (not realistic), to over the continent in SP-CCSM. The biases found in precipitation for both models are thought to be linked to anomalously warm sea surface temperatures in the Gulf of Guinea and a misrepresentation of the equatorial Atlantic cold tongue (a common problem for coupled GCMs). AEWs and their relationship with convection are also improved in the SP-CCSM. In the standard model, little to no easterly wave activity is found over West Africa, and the relationship with convection is tenuous at best. SP-CCSM on the other hand produces strong AEWs over the region that exhibit similar horizontal and vertical structures to observations. The simulated waves are also shown to be strongly coupled to convection, and results suggest that barotropic and baroclinic

  10. The use of fractional accumulated precipitation for the evaluation of the annual cycle of monsoons

    NASA Astrophysics Data System (ADS)

    Sperber, Kenneth R.; Annamalai, H.

    2014-12-01

    Using pentad rainfall data we demonstrate the benefits of using accumulated rainfall and fractional accumulated rainfall for the evaluation of the annual cycle of rainfall over various monsoon domains. Our approach circumvents issues related to using threshold-based analysis techniques for investigating the life-cycle of monsoon rainfall. In the Coupled Model Intercomparison Project-5 models we find systematic errors in the phase of the annual cycle of rainfall. The models are delayed in the onset of summer rainfall over India, the Gulf of Guinea, and the South American Monsoon, with early onset prevalent for the Sahel and the North American Monsoon. This, in combination with the rapid fractional accumulation rate, impacts the ability of the models to simulate the fractional accumulation observed during summer. The rapid fractional accumulation rate and the time at which the accumulation begins are metrics that indicate how well the models concentrate the monsoon rainfall over the peak rainfall season, and the extent to which there is a phase error in the annual cycle. The lack of consistency in the phase error across all domains suggests that a "global" approach to the study of monsoons may not be sufficient to rectify the regional differences. Rather, regional process studies are necessary for diagnosing the underlying causes of the regionally-specific systematic model biases over the different monsoon domains. Despite the afore-mentioned biases, most models simulate well the interannual variability in the date of monsoon onset, the exceptions being models with the most pronounced dry biases. Two methods for estimating monsoon duration are presented, one of which includes nonlinear aspects of the fractional accumulation. The summer fractional accumulation of rainfall provides an objective way to estimate the extent of the monsoon domain, even in models with substantial dry biases for which monsoon is not defined using threshold-based techniques.

  11. Astronomy for African development

    NASA Astrophysics Data System (ADS)

    Govender, Kevindran

    2011-06-01

    In recent years there have been a number of efforts across Africa to develop the field of astronomy as well as to reap benefit from astronomy for African people. This presentation will discuss the case of the SALT (Southern African Large Telescope) Collateral Benefits Programme (SCBP) which was set up to ensure societal benefit from astronomy. With African society as the target, the SCBP has embarked on various projects from school level education to public understanding of science to socio-economic development, the latter mainly being felt in the rural communities surrounding the South African Astronomical Observatory (home to SALT). A development plan for ``Astronomy in Africa'' will also be discussed. This plan has been drawn up with input from all over Africa and themed ``Astronomy for Education''. The Africa case stands as a good example for the IYA cornerstone project ``Developing Astronomy Globally'' which focuses on developing regions.

  12. African American Health

    MedlinePlus

    ... specific health concerns. Differences in the health of groups can result from Genetics Environmental factors Access to care Cultural factors On this page, you'll find links to health issues that affect African Americans.

  13. African American Suicide

    MedlinePlus

    ... accounted for 83.8% of Caucasian elderly suicides. • Firearms were the predominant method of suicide among African ... per 100,000 annually. Source: Centers for Disease Control and Prevention. National Vital Statistics System. Mortality Data. ...

  14. Predictability of the 1997 and 1998 South Asian Summer Monsoons

    NASA Technical Reports Server (NTRS)

    Schubert, Siegfred D.; Wu, Man Li

    2000-01-01

    The predictability of the 1997 and 1998 south Asian summer monsoon winds is examined from an ensemble of 10 Atmospheric General Circulation Model (AGCM) simulations with prescribed sea surface temperatures (SSTs) and soil moisture, The simulations are started in September 1996 so that they have lost all memory of the atmospheric initial conditions for the periods of interest. The model simulations show that the 1998 monsoon is considerably more predictable than the 1997 monsoon. During May and June of 1998 the predictability of the low-level wind anomalies is largely associated with a local response to anomalously warm Indian Ocean SSTs. Predictability increases late in the season (July and August) as a result of the strengthening of the anomalous Walker circulation and the associated development of easterly low level wind anomalies that extend westward across India and the Arabian Sea. During these months the model is also the most skillful with the observations showing a similar late-season westward extension of the easterly CD wind anomalies. The model shows little predictability or skill in the low level winds over southeast Asia during, 1997. Predictable wind anomalies do occur over the western Indian Ocean and Indonesia, however, over the Indian Ocean they are a response to SST anomalies that were wind driven and they show no skill. The reduced predictability in the low level winds during 1997 appears to be the result of a weaker (compared with 1998) simulated anomalous Walker circulation, while the reduced skill is associated with pronounced intraseasonal activity that is not well captured by the model. Remarkably, the model does produce an ensemble mean Madden-Julian Oscillation (MJO) response that is approximately in phase with (though weaker than) the observed MJ0 anomalies. This is consistent with the idea that SST coupling may play an important role in the MJO.

  15. Future precipitation extremes during summer monsoon in southern Pakistan

    NASA Astrophysics Data System (ADS)

    Zahid, Maida; Lucarini, Valerio

    2016-04-01

    Extreme precipitation events are considered as a hydro-meteorological hazard resulting in colossal damage worldwide. In Pakistan, the extreme precipitation events have increased in the recent decades particularly in the southern part (Sindh province). This region did not receive substantial amount of precipitation earlier, but now experiencing urban flooding almost every year causing loss of life, property, crops and infrastructure. The region lacks the information regarding the recurrence of extreme precipitation events. Therefore, there is a strong need for a reliable information of extremes over the upcoming decades for better regional planning. Although statistical methods based on extreme value theory (EVT) are the most relevant ones to study the extremes, but they are never been applied in Pakistan. To address this shortcoming, we use the peak over threshold (POT) approach to compute the return levels (RLs) of precipitation extremes, and also identify the regions most prone to them. In this study, we analyzed the summer monsoon daily precipitation measured at nine weather stations of Pakistan Meteorological Department over the period 1980-2013. The summer monsoon (JJAS) is preferred for the analysis, because most of the extreme precipitation occurs during this period. We apply POT approach to model the daily precipitation above a selected threshold for each station. Then, we estimate return levels (RLs) of precipitation extremes during summer monsoon in southern Pakistan (Sindh) for the next 5, 25, 50 and 100-years. Lastly, we compare the 5-years with 100-years RLs to indicate the stations most vulnerable to precipitation extremes in future. This work is funded by the Climate KIC, European Institute of Innovation and Technology, Germany.

  16. Ecosystem Response to Monsoon Rainfall Variability in Southwestern North America

    NASA Astrophysics Data System (ADS)

    Forzieri, Giovanni; Feyen, Luc; Vivoni, Enrique

    2013-04-01

    Due to its marked plant phenology driven by precipitation, the North American Monsoon System (NAMS) can serve to reveal ecological responses to climate variability and change in water-controlled regions. This study attempts to elucidate the effects of monsoon rainfall variability on vegetation dynamics over the North American Monsoon Experiment (NAME) tier I domain (20°-35° N, 105°-115° W). To this end, we analyze long-term dynamics (1982-2004) in seasonal precipitation (Pr), net primary production (NPP) and rain-use efficiency (RUE) based on phenological and biophysical memory metrics from NOAA CPC daily 1° gridded precipitation data and satellite GIMMS semi-monthly NDVI images at 8-km resolution. We focus our analysis on six diverse ecosystems spanning from semi-arid and desert environments to tropical deciduous forests to investigate: 1) the spatially averaged NPP/RUE profiles along the regional Pr gradient, 2) the linkage between NPP and Pr inter-annual variations and 3) the long-term trends of Pr, NPP and RUE. All the biomes show an increase (decrease) in mean NPP (RUE) along the mean seasonal precipitation gradient ranging from 100 to 900 mm. Variations in NPP/RUE profiles differ strongly across ecosystems and show threshold behaviors likely resulting from different physiological responses to climate effects and landscape features. Statistical analysis suggests that the inter-annual variability in NPP is significantly related to the temporal variability in precipitation. In particular, we found that forest biomes are more sensitive to inter-annual variations in precipitation regimes. Semi-arid ecosystems appear to be more resilient, probably because they are more exposed to extreme conditions and consequently better adapted to greater inter and intra-annual climate variability. The long-term positive signal in RUE imposed on its inter-annual variability, which results from a constant NPP under negative long-term trends of Pr, indicates an improved

  17. Seasonal prediction of Indian summer monsoon: Sensitivity to persistent SST

    NASA Astrophysics Data System (ADS)

    Das, Sukanta Kumar; Deb, Sanjib Kumar; Kishtawal, C. M.; Pal, Pradip Kumar

    2013-10-01

    In the present study, the assessment of the Community Atmosphere Model (CAM) developed at National Centre for Atmospheric Research (NCAR) for seasonal forecasting of Indian Summer Monsoon (ISM) with different persistent SST is reported. Towards achieving the objective, 30-year model climatology has been generated using observed SST. Upon successful simulation of climatological features of ISM, the model is tested for the simulation of ISM 2011 in forecast mode. Experiments have been conducted in three different time-phases, viz., April, May and June; using different sets of initial conditions (ICs) and the persistent SSTs of the previous months of the time-phases. The spatial as well as temporal distribution of model simulated rainfall suggest a below normal monsoon condition throughout the season in all the experiments. However, the rainfall anomaly shows some positive signature over north-east part of India in the month of June and August whereas the central Indian landmass had positive anomaly during August and September. The monthly accumulated All-India rainfall (AIR) over land for June to September 2011 are predicted to be 101% (17.6 cm), 86% (24.3 cm), 83% (21.0 cm) and 95% (15.5 cm) of normal AIR, respectively. This makes the seasonal accumulated AIR 78.4 cm which is 11% below the normal rainfall of 87.6 cm. The model prediction for the months of June and July is comparable with the observation; however, the simulation would not be able to capture the high rainfall during August and September. The intention behind this work is to assess the shortcomings in the CAM model prediction, which can later be improved for future monsoon forecast experiments.

  18. Transport pathways from the Asian monsoon anticyclone to the stratosphere

    NASA Astrophysics Data System (ADS)

    Garny, Hella; Randel, William J.

    2016-03-01

    Transport pathways of air originating in the upper-tropospheric Asian monsoon anticyclone are investigated based on three-dimensional trajectories. The Asian monsoon anticyclone emerges in response to persistent deep convection over India and southeast Asia in northern summer, and this convection is associated with rapid transport from the surface to the upper troposphere and possibly into the stratosphere. Here, we investigate the fate of air that originates within the upper-tropospheric anticyclone from the outflow of deep convection, using trajectories driven by ERA-interim reanalysis data. Calculations include isentropic estimates, plus fully three-dimensional results based on kinematic and diabatic transport calculations. Isentropic calculations show that air parcels are typically confined within the anticyclone for 10-20 days and spread over the tropical belt within a month of their initialization. However, only few parcels (3 % at 360 K, 8 % at 380 K) reach the extratropical stratosphere by isentropic transport. When considering vertical transport we find that 31 % or 48 % of the trajectories reach the stratosphere within 60 days when using vertical velocities or diabatic heating rates to calculate vertical transport, respectively. In both cases, most parcels that reach the stratosphere are transported upward within the anticyclone and enter the stratosphere in the tropics, typically 10-20 days after their initialization at 360 K. This suggests that trace gases, including pollutants, that are transported into the stratosphere via the Asian monsoon system are in a position to enter the tropical pipe and thus be transported into the deep stratosphere. Sensitivity calculations with respect to the initial altitude of the trajectories showed that air needs to be transported to levels of 360 K or above by deep convection to likely (≧ 50 %) reach the stratosphere through transport by the large-scale circulation.

  19. Changes in biological productivity along the northwest African margin over the past 20,000 years

    NASA Astrophysics Data System (ADS)

    Bradtmiller, Louisa I.; McGee, David; Awalt, Mitchell; Evers, Joseph; Yerxa, Haley; Kinsley, Christopher W.; deMenocal, Peter B.

    2016-01-01

    The intertropical convergence zone and the African monsoon system are highly sensitive to climate forcing at orbital and millennial timescales. Both systems influence the strength and direction of the trade winds along northwest Africa and thus directly impact coastal upwelling. Sediment cores from the northwest African margin record upwelling-related changes in biological productivity connected to changes in regional and hemispheric climate. We present records of 230Th-normalized biogenic opal and Corg fluxes using a meridional transect of four cores from 19°N-31°N along the northwest African margin to examine changes in paleoproductivity since the last glacial maximum. We find large changes in biogenic fluxes synchronous with changes in eolian fluxes calculated using end-member modeling, suggesting that paleoproductivity and dust fluxes were strongly coupled, likely linked by changes in wind strength. Opal and Corg fluxes increase at all sites during Heinrich Stadial 1 and the Younger Dryas, consistent with an overall intensification of the trade winds, and changes in the meridional flux gradient indicate a southward wind shift at these times. Biogenic fluxes were lowest, and the meridional flux gradients were weakest during the African Humid Period when the monsoon was invigorated due to precessional changes, with greater rainfall and weaker trade winds over northwest Africa. These results expand the spatial coverage of previous paleoproxy studies showing similar changes, and they provide support for modeling studies showing changes in wind strength and direction consistent with increased upwelling during abrupt coolings and decreased upwelling during the African Humid Period.

  20. The meteorology of the Western Indian Ocean, and the influence of the East African Highlands.

    PubMed

    Slingo, Julia; Spencer, Hilary; Hoskins, Brian; Berrisford, Paul; Black, Emily

    2005-01-15

    This paper reviews the meteorology of the Western Indian Ocean and uses a state-of-the-art atmospheric general circulation model to investigate the influence of the East African Highlands on the climate of the Indian Ocean and its surrounding regions. The new 44-year re-analysis produced by the European Centre for Medium range Weather Forecasts (ECMWF) has been used to construct a new climatology of the Western Indian Ocean. A brief overview of the seasonal cycle of the Western Indian Ocean is presented which emphasizes the importance of the geography of the Indian Ocean basin for controlling the meteorology of the Western Indian Ocean. The principal modes of inter-annual variability are described, associated with El Nino and the Indian Ocean Dipole or Zonal Mode, and the basic characteristics of the subseasonal weather over the Western Indian Ocean are presented, including new statistics on cyclone tracks derived from the ECMWF re-analyses. Sensitivity experiments, in which the orographic effects of East Africa are removed, have shown that the East African Highlands, although not very high, play a significant role in the climate of Africa, India and Southeast Asia, and in the heat, salinity and momentum forcing of the Western Indian Ocean. The hydrological cycle over Africa is systematically enhanced in all seasons by the presence of the East African Highlands, and during the Asian summer monsoon there is a major redistribution of the rainfall across India and Southeast Asia. The implied impact of the East African Highlands on the ocean is substantial. The East African Highlands systematically freshen the tropical Indian Ocean, and act to focus the monsoon winds along the coast, leading to greater upwelling and cooler sea-surface temperatures.

  1. Evaluation of daily precipitation statistics and monsoon onset/retreat over western Sahel in multiple data sets

    NASA Astrophysics Data System (ADS)

    Diaconescu, Emilia Paula; Gachon, Philippe; Scinocca, John; Laprise, René

    2015-09-01

    The West Africa rainfall regime constitutes a considerable challenge for Regional Climate Models (RCMs) due to the complexity of dynamical and physical processes that characterise the West African Monsoon. In this paper, daily precipitation statistics are evaluated from the contributions to the AFRICA-CORDEX experiment from two ERA-Interim driven Canadian RCMs: CanRCM4, developed at the Canadian Centre for Climate Modelling and Analysis (CCCma) and CRCM5, developed at the University of Québec at Montréal. These modelled precipitation statistics are evaluated against three gridded observed datasets—the Global Precipitation Climatology Project (GPCP), the Tropical Rainfall Measuring Mission (TRMM), and the Africa Rainfall Climatology (ARC2)—and four reanalysis products (ECMWF ERA-Interim, NCEP/DOE Reanalysis II, NASA MERRA and NOAA-CIRES Twentieth Century Reanalysis). The two RCMs share the same dynamics from the Environment Canada GEM forecast model, but have two different physics' packages: CanRCM4 obtains its physics from CCCma's global atmospheric model (CanAM4), while CRCM5 shares a number of its physics modules with the limited-area version of GEM forecast model. The evaluation is focused on various daily precipitation statistics (maximum number of consecutive wet days, number of moderate and very heavy precipitation events, precipitation frequency distribution) and on the monsoon onset and retreat over the Sahel region. We find that the CRCM5 has a good representation of daily precipitation statistics over the southern Sahel, with spatial distributions close to GPCP dataset. Some differences are observed in the northern part of the Sahel, where the model is characterised by a dry bias. CanRCM4 and the ERA-Interim and MERRA reanalysis products overestimate the number of wet days over Sahel with a shift in the frequency distribution toward smaller daily precipitation amounts than in observations. Both RCMs and reanalyses have difficulties in reproducing

  2. A composite study of onset of the Australian summer monsoon

    NASA Technical Reports Server (NTRS)

    Hendon, Harry H.; Liebmann, Brant

    1990-01-01

    The circulation changes that accompany an onset (defined as the first occurrence of wet 850-mb westerly winds at Darwin, Australia) of the Australian summer monsoon are documented by a composite study for the years 1957-1987. Composites of atmospheric fields at stations in and about the Australian tropics are constructed relative to the onset data at Darwin. It is shown that the composite onset is dominated by a slow eastward migration of a deep-baroclinic convective circulation displaced south of the equator. This propagating anomaly exhibited many features of the so-called 40-50 day oscillation, including an upper level anticyclone that accompanies the convective anomaly.

  3. Extended Range Prediction of Indian Summer Monsoon: Current status

    NASA Astrophysics Data System (ADS)

    Sahai, A. K.; Abhilash, S.; Borah, N.; Joseph, S.; Chattopadhyay, R.; S, S.; Rajeevan, M.; Mandal, R.; Dey, A.

    2014-12-01

    The main focus of this study is to develop forecast consensus in the extended range prediction (ERP) of monsoon Intraseasonal oscillations using a suit of different variants of Climate Forecast system (CFS) model. In this CFS based Grand MME prediction system (CGMME), the ensemble members are generated by perturbing the initial condition and using different configurations of CFSv2. This is to address the role of different physical mechanisms known to have control on the error growth in the ERP in the 15-20 day time scale. The final formulation of CGMME is based on 21 ensembles of the standalone Global Forecast System (GFS) forced with bias corrected forecasted SST from CFS, 11 low resolution CFST126 and 11 high resolution CFST382. Thus, we develop the multi-model consensus forecast for the ERP of Indian summer monsoon (ISM) using a suite of different variants of CFS model. This coordinated international effort lead towards the development of specific tailor made regional forecast products over Indian region. Skill of deterministic and probabilistic categorical rainfall forecast as well the verification of large-scale low frequency monsoon intraseasonal oscillations has been carried out using hindcast from 2001-2012 during the monsoon season in which all models are initialized at every five days starting from 16May to 28 September. The skill of deterministic forecast from CGMME is better than the best participating single model ensemble configuration (SME). The CGMME approach is believed to quantify the uncertainty in both initial conditions and model formulation. Main improvement is attained in probabilistic forecast which is because of an increase in the ensemble spread, thereby reducing the error due to over-confident ensembles in a single model configuration. For probabilistic forecast, three tercile ranges are determined by ranking method based on the percentage of ensemble members from all the participating models falls in those three categories. CGMME further

  4. Land-Climate Feedbacks in Indian Summer Monsoon Rainfall

    NASA Astrophysics Data System (ADS)

    Asharaf, Shakeel; Ahrens, Bodo

    2016-04-01

    In an attempt to identify how land surface states such as soil moisture influence the monsoonal precipitation climate over India, a series of numerical simulations including soil moisture sensitivity experiments was performed. The simulations were conducted with a nonhydrostatic regional climate model (RCM), the Consortium for Small-Scale Modeling (COSMO) in climate mode (CCLM) model, which was driven by the European Center for Medium-Range Weather Forecasts (ECMWF) Interim reanalysis (ERA-Interim) data. Results showed that pre-monsoonal soil moisture has a significant impact on monsoonal precipitation formation and large-scale atmospheric circulations. The analysis revealed that even a small change in the processes that influence precipitation via changes in local evapotranspiration was able to trigger significant variations in regional soil moisture-precipitation feedback. It was observed that these processes varied spatially from humid to arid regions in India, which further motivated an examination of soil-moisture memory variation over these regions and determination of the ISM seasonal forecasting potential. A quantitative analysis indicated that the simulated soil-moisture memory lengths increased with soil depth and were longer in the western region than those in the eastern region of India. Additionally, the subsequent precipitation variance explained by soil moisture increased from east to west. The ISM rainfall was further analyzed in two different greenhouse gas emission scenarios: the Special Report on Emissions Scenario (SRES: B1) and the new Representative Concentration Pathways (RCPs: RCP4.5). To that end, the CCLM and its driving global-coupled atmospheric-oceanic model (GCM), ECHAM/MPIOM were used in order to understand the driving processes of the projected inter-annual precipitation variability and associated trends. Results inferred that the projected rainfall changes were the result of two largely compensating processes: increase of remotely

  5. On the Onset of the Planetary Scale Monsoon

    NASA Astrophysics Data System (ADS)

    Pasch, Richard Joseph

    A hypothesis, concerning the spatial scale of the onset of the Asian southwest monsoon of the Northern Hemispheric summer, is put forth. It is implied, from the large scale climatology of the tropospheric motion and temperature fields in May and June, that the monsoon onset is characterized by radical changes in the tropical circulations on a planetary scale. A suitable framework for the quantitative definition of this phenomenon, i.e., the atmospheric energetics in the zonal wavenumber domain, is reviewed. Global tropospheric wind and temperature data for periods surrounding the Indian monsoon onset cases of 1973, 1977 and 1979 are utilized. It is found that the kinetic and available potential energy of the sum of zonal wavenumbers 1, 2 and 3 (defined as the planetary scale waves) increase by about 30 to 50% on the time scale of about 1 week, corresponding to Indian (regional) onset. This increase characterizes the planetary scale onset. From the point of view of scale interactions, the observational calculations show that the planetary scale eddies, in general, supply available potential and kinetic energy to other (zonal mean and sub-planetary) scales during the onset although there are some interesting time variations. It is concluded that additional mechanisms must play the dominant roles in the planetary scale onset. To determine a more complete energetics for the onset using a dynamically more consistent set of atmospheric observations, an NWP experiment, for the 1979 onset case, is conducted. A global, multi-level, primitive equation spectral model containing a variety of physical effects parameterizations is described in detail. The results of a 96-hour prediction are compared to the observed circulation and rainfall patterns over the Indian Ocean region and the model is seen to reproduce the broad scale synoptic features of the onset fairly well. An analysis of the model diagnosed energetics (for the planetary scale waves) reveals that deep cumulus

  6. The dominant intraseasonal mode of intraseasonal South Asian summer monsoon

    NASA Astrophysics Data System (ADS)

    Shukla, Ravi P.

    2014-01-01

    From June through September, the intraseasonal variability of the Asian summer monsoon is dominated by the so-called "monsoon intraseasonal oscillation (MISO)." This paper provides a comprehensive description of the MISO based on outgoing longwave radiation (OLR) data. The MISO is characterized by alternating active periods, in which the primary rain area of the Asian summer monsoon that stretches from the northern Arabian Sea east southeastward almost all the way to the northwest Pacific Intertropical Convergence Zone is relatively intense, and break periods, in which the heaviest rainfall shifts from south Asia to the central and eastern equatorial Indian Ocean. The MISO is attended by well-defined but weak sea surface temperature (SST) perturbations whose phase is indicative of a negative feedback upon the atmospheric perturbations. Meridional profile of variables on the various regression maps shown in this paper averaged along a set of tilted axes parallel to the west-northwest to east-southeast (WNW-ESE) sloping lines in empirical orthogonal function 1 of OLR have been made, and it is found that the strongest westerly 850 hPa wind anomalies are located two grid points (5° of latitude) to the south of the reference latitude. At the 150 hPa level, the meridional profile of divergence is closely aligned with the OLR profile. SST profile is lowest at approximately 2.5° of latitude to the south of the minimum OLR and 2.5° to the north of the strongest westerly 850 hPa wind anomalies. The sea level pressure profiles and the midlower tropospheric geopotential height profiles are almost in phase. It is observed that in most years, there are two-three bands of intensified and suppressed rainfall that cross the reference line from south to north (northward propagating) at the interval of 30-60 days over South Asia. The degree of correspondence between the MISO and active and break spells of the Indian summer monsoon rainfall is also documented.

  7. Linking hemispheric radiation budgets, ITCZ shifts, and monsoons

    NASA Astrophysics Data System (ADS)

    McGee, D.; Donohoe, A.; Marshall, J.; Ferreira, D.

    2014-12-01

    We explore the relationship between the Intertropical Convergence Zone (ITCZ), hemispheric heat budgets, and monsoon strength in past climates. Modern seasonal and interannual variability in the globally-averaged position of the ITCZ (as estimated by the tropical precipitation centroid) reflects the interhemispheric heat balance, with the ITCZ's displacement toward the warmer hemisphere directly proportional to atmospheric heat transport into the cooler hemisphere. Model simulations suggest that ITCZ shifts are likely to have obeyed the same relationship with interhemispheric heat transport in response to past changes in orbital parameters, ice sheets, and ocean circulation. This relationship implies that even small (±1 degree) shifts in the mean (annually and zonally averaged) ITCZ require large changes in hemispheric heat budgets, placing tight bounds on mean ITCZ shifts in past climates. To test this energetic argument, we use the observed relationship between mean ITCZ position and tropical sea surface temperature (SST) gradients in combination with proxy-based estimates of past SST gradients to show that mean ITCZ shifts for the mid-Holocene, Heinrich Stadial 1 and Last Glacial Maximum are not likely to have been more than 1 degree latitude from its present mean position. In exploring these results, we provide brief descriptions of the estimated radiation budgets of past climates that help demonstrate how different climate forcings change the interhemispheric heat balance and thus the ITCZ's global-mean position. We also address the seeming inconsistency between the small ITCZ shifts indicated by energetic constraints and the large changes in monsoon rainfall suggested by proxy data. We compare global-average and regional-scale tropical precipitation in observations and explore their responses to a variety of forcings (orbital changes, ice sheets, hosing) in models. These comparisons make clear that monsoon precipitation can change substantially even in the

  8. Global sensitivity analysis of Indian Monsoon during the Pleistocene

    NASA Astrophysics Data System (ADS)

    Araya-Melo, P. A.; Crucifix, M.; Bounceur, N.

    2014-04-01

    The sensitivity of Indian Monsoon to the full spectrum of climatic conditions experienced during the Pleistocene is estimated using the climate model HadCM3. The methodology follows a global sensitivity analysis based on the emulator approach of Oakley and O'Hagan (2004) implemented following a three-step strategy: (1) develop an experiment plan, designed to efficiently sample a 5-dimensional input space spanning Pleistocene astronomical configurations (3 parameters), CO2 concentration and a Northern Hemisphere glaciation index, (2) develop, calibrate and validate an emulator of HadCM3, in order to estimate the response of the Indian Monsoon over the full input space spanned by the experiment design, and (3) estimate and interpret sensitivity diagnostics, including sensitivity measures, in order to synthesize the relative importance of input factors on monsoon dynamics, estimate the phase of the monsoon intensity response with respect to that of insolation, and detect potential non-linear phenomena. Specifically, we focus on four variables: summer (JJAS) temperature and precipitation over North India, and JJAS sea-surface temperature and mixed-layer depth over the north-western side of the Indian ocean. It is shown that precession controls the response of four variables: continental temperature in phase with June to July insolation, high glaciation favouring a late-phase response, sea-surface temperature in phase with May insolation, and continental precipitation in phase with July insolation, and mixed-layer depth in antiphase with the latter. CO2 variations controls temperature variance with an amplitude similar to that of precession. The effect of glaciation is dominated by the albedo forcing, and its effect on precipitation competes with that of precession. Obliquity is a secondary effect, negligible on most variables except sea-surface temperature. It is also shown that orography forcing reduces the glacial cooling, and even has a positive effect on

  9. A persistent northern boundary of Indian Summer Monsoon precipitation over Central Asia during the Holocene

    NASA Astrophysics Data System (ADS)

    Ramisch, Arne; Lockot, Gregori; Haberzettl, Torsten; Hartmann, Kai; Kuhn, Gerhard; Lehmkuhl, Frank; Schimpf, Stefan; Schulte, Philipp; Stauch, Georg; Wang, Rong; Wünnemann, Bernd; Yan, Dada; Zhang, Yongzhan; Diekmann, Bernhard

    2016-05-01

    Extra-tropical circulation systems impede poleward moisture advection by the Indian Summer Monsoon. In this context, the Himalayan range is believed to insulate the south Asian circulation from extra-tropical influences and to delineate the northern extent of the Indian Summer Monsoon in central Asia. Paleoclimatic evidence, however, suggests increased moisture availability in the Early Holocene north of the Himalayan range which is attributed to an intensification of the Indian Summer Monsoon. Nevertheless, mechanisms leading to a surpassing of the Himalayan range and the northern maximum extent of summer monsoonal influence remain unknown. Here we show that the Kunlun barrier on the northern Tibetan Plateau [~36°N] delimits Indian Summer Monsoon precipitation during the Holocene. The presence of the barrier relocates the insulation effect 1,000 km further north, allowing a continental low intensity branch of the Indian Summer Monsoon which is persistent throughout the Holocene. Precipitation intensities at its northern extent seem to be driven by differentiated solar heating of the Northern Hemisphere indicating dependency on energy-gradients rather than absolute radiation intensities. The identified spatial constraints of monsoonal precipitation will facilitate the prediction of future monsoonal precipitation patterns in Central Asia under varying climatic conditions.

  10. A persistent northern boundary of Indian Summer Monsoon precipitation over Central Asia during the Holocene.

    PubMed

    Ramisch, Arne; Lockot, Gregori; Haberzettl, Torsten; Hartmann, Kai; Kuhn, Gerhard; Lehmkuhl, Frank; Schimpf, Stefan; Schulte, Philipp; Stauch, Georg; Wang, Rong; Wünnemann, Bernd; Yan, Dada; Zhang, Yongzhan; Diekmann, Bernhard

    2016-05-13

    Extra-tropical circulation systems impede poleward moisture advection by the Indian Summer Monsoon. In this context, the Himalayan range is believed to insulate the south Asian circulation from extra-tropical influences and to delineate the northern extent of the Indian Summer Monsoon in central Asia. Paleoclimatic evidence, however, suggests increased moisture availability in the Early Holocene north of the Himalayan range which is attributed to an intensification of the Indian Summer Monsoon. Nevertheless, mechanisms leading to a surpassing of the Himalayan range and the northern maximum extent of summer monsoonal influence remain unknown. Here we show that the Kunlun barrier on the northern Tibetan Plateau [~36°N] delimits Indian Summer Monsoon precipitation during the Holocene. The presence of the barrier relocates the insulation effect 1,000 km further north, allowing a continental low intensity branch of the Indian Summer Monsoon which is persistent throughout the Holocene. Precipitation intensities at its northern extent seem to be driven by differentiated solar heating of the Northern Hemisphere indicating dependency on energy-gradients rather than absolute radiation intensities. The identified spatial constraints of monsoonal precipitation will facilitate the prediction of future monsoonal precipitation patterns in Central Asia under varying climatic conditions.

  11. A brief survey on climate change effects on the Indian Monsoon

    SciTech Connect

    Bala, G

    2007-02-06

    Each year, Indian summer monsoon season begins in June and ends in September. Surface winds blow from the southwest during this season. The Indian summer monsoon typically covers large areas of India with western and central India receiving more than 90% of their total annual precipitation during this period, and southern and northwestern India receiving 50%-75% of their total annual rainfall. Overall, monthly totals average 200-300 mm over the country as a whole, with the largest values observed during the heart of the monsoon season in July and August. In all total, India receives about 870 mm of rainfall in a normal summer monsoon season. This summary discusses the effects of climate change on the frequency, mean rainfall, duration and the variability of the Indian Monsoon. East Asian Monsoon in the southeastern part of Asia is not discussed in this summary. Changes in monsoon characteristics are mainly inferred from climate model simulations submitted to the Intergovernmental Panel on Climate Change (IPCC)'s Fourth Assessment Report (AR4). It should be cautioned that there is a large range in the results from these models. For instance, the range of mean monsoon precipitation as simulated by the AR4 models over India is from 500 mm to 900 mm for the present-day climate (Kirpalani et al. 2006).

  12. The Response of the North American Monsoon to Increased Greenhouse Gas Forcing

    NASA Technical Reports Server (NTRS)

    Cook, B. I.; Seager, R.

    2013-01-01

    [1] We analyze the response of the North American Monsoon (NAM) to increased greenhouse gas (GHG) forcing (emissions scenario RCP 8.5) using new simulations available through the Coupled Model Intercomparison Project version 5 (CMIP5). Changes in total monsoon season rainfall with GHG warming are small and insignificant. The models do, however, show significant declines in early monsoon season precipitation (June-July) and increases in late monsoon season (September-October) precipitation, indicating a shift in seasonality toward delayed onset and withdrawal of the monsoon. Early in the monsoon season, tropospheric warming increases vertical stability, reinforced by reductions in available surface moisture, inhibiting precipitation and delaying the onset of the monsoon. By the end of the monsoon season, moisture convergence is sufficient to overcome the warming induced stability increases, and precipitation is enhanced. Even with no change in total NAM rainfall, shifts in the seasonal distribution of precipitation within the NAM region are still likely to have significant societal and ecological consequences, reinforcing the need to not only understand the magnitude, but also the timing, of future precipitation changes.

  13. See-saw relationship of the Holocene East Asian-Australian summer monsoon

    NASA Astrophysics Data System (ADS)

    Eroglu, Deniz; McRobie, Fiona H.; Ozken, Ibrahim; Stemler, Thomas; Wyrwoll, Karl-Heinz; Breitenbach, Sebastian F. M.; Marwan, Norbert; Kurths, Jürgen

    2016-09-01

    The East Asian-Indonesian-Australian summer monsoon (EAIASM) links the Earth's hemispheres and provides a heat source that drives global circulation. At seasonal and inter-seasonal timescales, the summer monsoon of one hemisphere is linked via outflows from the winter monsoon of the opposing hemisphere. Long-term phase relationships between the East Asian summer monsoon (EASM) and the Indonesian-Australian summer monsoon (IASM) are poorly understood, raising questions of long-term adjustments to future greenhouse-triggered climate change and whether these changes could `lock in' possible IASM and EASM phase relationships in a region dependent on monsoonal rainfall. Here we show that a newly developed nonlinear time series analysis technique allows confident identification of strong versus weak monsoon phases at millennial to sub-centennial timescales. We find a see-saw relationship over the last 9,000 years--with strong and weak monsoons opposingly phased and triggered by solar variations. Our results provide insights into centennial- to millennial-scale relationships within the wider EAIASM regime.

  14. See–saw relationship of the Holocene East Asian–Australian summer monsoon

    PubMed Central

    Eroglu, Deniz; McRobie, Fiona H.; Ozken, Ibrahim; Stemler, Thomas; Wyrwoll, Karl-Heinz; Breitenbach, Sebastian F. M.; Marwan, Norbert; Kurths, Jürgen

    2016-01-01

    The East Asian–Indonesian–Australian summer monsoon (EAIASM) links the Earth's hemispheres and provides a heat source that drives global circulation. At seasonal and inter-seasonal timescales, the summer monsoon of one hemisphere is linked via outflows from the winter monsoon of the opposing hemisphere. Long-term phase relationships between the East Asian summer monsoon (EASM) and the Indonesian–Australian summer monsoon (IASM) are poorly understood, raising questions of long-term adjustments to future greenhouse-triggered climate change and whether these changes could ‘lock in' possible IASM and EASM phase relationships in a region dependent on monsoonal rainfall. Here we show that a newly developed nonlinear time series analysis technique allows confident identification of strong versus weak monsoon phases at millennial to sub-centennial timescales. We find a see–saw relationship over the last 9,000 years—with strong and weak monsoons opposingly phased and triggered by solar variations. Our results provide insights into centennial- to millennial-scale relationships within the wider EAIASM regime. PMID:27666662

  15. A persistent northern boundary of Indian Summer Monsoon precipitation over Central Asia during the Holocene.

    PubMed

    Ramisch, Arne; Lockot, Gregori; Haberzettl, Torsten; Hartmann, Kai; Kuhn, Gerhard; Lehmkuhl, Frank; Schimpf, Stefan; Schulte, Philipp; Stauch, Georg; Wang, Rong; Wünnemann, Bernd; Yan, Dada; Zhang, Yongzhan; Diekmann, Bernhard

    2016-01-01

    Extra-tropical circulation systems impede poleward moisture advection by the Indian Summer Monsoon. In this context, the Himalayan range is believed to insulate the south Asian circulation from extra-tropical influences and to delineate the northern extent of the Indian Summer Monsoon in central Asia. Paleoclimatic evidence, however, suggests increased moisture availability in the Early Holocene north of the Himalayan range which is attributed to an intensification of the Indian Summer Monsoon. Nevertheless, mechanisms leading to a surpassing of the Himalayan range and the northern maximum extent of summer monsoonal influence remain unknown. Here we show that the Kunlun barrier on the northern Tibetan Plateau [~36°N] delimits Indian Summer Monsoon precipitation during the Holocene. The presence of the barrier relocates the insulation effect 1,000 km further north, allowing a continental low intensity branch of the Indian Summer Monsoon which is persistent throughout the Holocene. Precipitation intensities at its northern extent seem to be driven by differentiated solar heating of the Northern Hemisphere indicating dependency on energy-gradients rather than absolute radiation intensities. The identified spatial constraints of monsoonal precipitation will facilitate the prediction of future monsoonal precipitation patterns in Central Asia under varying climatic conditions. PMID:27173918

  16. A persistent northern boundary of Indian Summer Monsoon precipitation over Central Asia during the Holocene

    PubMed Central

    Ramisch, Arne; Lockot, Gregori; Haberzettl, Torsten; Hartmann, Kai; Kuhn, Gerhard; Lehmkuhl, Frank; Schimpf, Stefan; Schulte, Philipp; Stauch, Georg; Wang, Rong; Wünnemann, Bernd; Yan, Dada; Zhang, Yongzhan; Diekmann, Bernhard

    2016-01-01

    Extra-tropical circulation systems impede poleward moisture advection by the Indian Summer Monsoon. In this context, the Himalayan range is believed to insulate the south Asian circulation from extra-tropical influences and to delineate the northern extent of the Indian Summer Monsoon in central Asia. Paleoclimatic evidence, however, suggests increased moisture availability in the Early Holocene north of the Himalayan range which is attributed to an intensification of the Indian Summer Monsoon. Nevertheless, mechanisms leading to a surpassing of the Himalayan range and the northern maximum extent of summer monsoonal influence remain unknown. Here we show that the Kunlun barrier on the northern Tibetan Plateau [~36°N] delimits Indian Summer Monsoon precipitation during the Holocene. The presence of the barrier relocates the insulation effect 1,000 km further north, allowing a continental low intensity branch of the Indian Summer Monsoon which is persistent throughout the Holocene. Precipitation intensities at its northern extent seem to be driven by differentiated solar heating of the Northern Hemisphere indicating dependency on energy-gradients rather than absolute radiation intensities. The identified spatial constraints of monsoonal precipitation will facilitate the prediction of future monsoonal precipitation patterns in Central Asia under varying climatic conditions. PMID:27173918

  17. Assessment of CMIP5 Model Simulation of the North American Monsoon System

    NASA Astrophysics Data System (ADS)

    Geil, K. L.; Serra, Y.

    2012-12-01

    The ability of Coupled Model Intercomparison Project Phase 5 (CMIP5) models to simulate the North American Monsoon System (NAMS) over the historical period of 1979-2005 is examined using a core NAMS domain centered on the Sierra Madre Occidental in northern Mexico. Root mean square error, bias, and phase lag are used to assess the amplitude and phasing of the annual cycle of precipitation at monthly time resolution and results show some improvement over the CMIP3 suite of models. A more detailed evaluation of monsoon season phasing uses daily precipitation magnitude and duration threshold criteria to define yearly monsoon onset and retreat dates for each model. Results reveal that monsoon onset is generally well-captured, while monsoon retreat is poorly captured, as most models produce excessive fall and winter precipitation causing a muddled transition from the monsoon to post-monsoon season in the daily precipitation field. Large-scale field composites of models with the best and worst simulations of onset and retreat provide insight as to the causes of well-simulated onset and poorly-simulated retreat. Model simulation of the NAMS in the future is briefly discussed with an emphasis on the cautious use of models for monsoon projections.

  18. Relationship between the Indian summer monsoon and the large-scale circulation variability over the Mediterranean

    NASA Astrophysics Data System (ADS)

    Rizou, Despoina; Flocas, Helena A.; Athanasiadis, Panos; Bartzokas, Aristides

    2015-01-01

    In this study the impact of the Indian summer monsoon on the large scale variability of the atmospheric circulation over the Mediterranean is investigated on an inter-annual time scale. Composite and correlation analysis results are presented, outlining different circulation patterns in the upper and lower troposphere for strong and weak monsoon years respectively. For this purpose ERA-40 Reanalysis monthly mean data at various isobaric levels together with the standardized All India Rainfall Index for boreal summer (June-July-August-September) of a 44-year period were employed. During strong monsoon years many atmospheric circulation systems appear strengthened over Eurasia, resembling a well-organized Rossby wave train over the area. In the upper troposphere a meridional shift of the jet streams over the examined area was also identified during extreme monsoon years. On the other hand, in the lower troposphere enhanced northerlies (Etesians) appear to dominate over Eastern Mediterranean along with intensified subsidence during strong monsoon years.

  19. The aerosol-monsoon climate system of Asia: A new paradigm

    NASA Astrophysics Data System (ADS)

    Lau, William K. M.

    2016-02-01

    This commentary is based on a series of recent lectures on aerosol-monsoon interactions I gave at the Beijing Normal University in August 2015. A main theme of the lectures is on a new paradigm of "An Aerosol-Monsoon-Climate-System", which posits that aerosol, like rainfall, cloud, and wind, is an integral component of the monsoon climate system, influencing monsoon weather and climate on all timescales. Here, salient issues discussed in my lectures and my personal perspective regarding interactions between atmospheric dynamics and aerosols from both natural and anthropogenic sources are summarized. My hope is that under this new paradigm, we can break down traditional disciplinary barriers, advance a deeper understanding of weather and climate in monsoon regions, as well as entrain a new generation of geoscientists to strive for a sustainable future for one of the most complex and challenging human-natural climate sub-system of the earth.

  20. Orbital Asian summer monsoon dynamics revealed using an isotope-enabled global climate model.

    PubMed

    Caley, Thibaut; Roche, Didier M; Renssen, Hans

    2014-01-01

    The Asian summer monsoon dynamics at the orbital scale are a subject of considerable debate. The validity of Asian speleothem δ(18)O records as a proxy for summer monsoon intensity is questioned together with the ultimate forcing and timing of the monsoon. Here, using the results of a 150,000-year transient simulation including water isotopes, we demonstrate that Asian speleothem δ(18)O records are not a valid proxy for summer monsoon intensity only at the orbital timescale. Rather, our results show that these records reflect annual variations in hydrologic processes and circulation regime over a large part of the Indo-Asian region. Our results support the role of internal forcing, such as sea surface temperature in the equatorial Pacific, to modulate the timing of monsoon precipitation recorded in paleo-proxies inside the Asian region.

  1. Trend analysis and ARIMA modelling of pre-monsoon rainfall data for western India

    NASA Astrophysics Data System (ADS)

    Narayanan, Priya; Basistha, Ashoke; Sarkar, Sumana; Kamna, Sachdeva

    2013-01-01

    Spatial and temporal variability of rainfall over different seasons influence physical, social and economic parameters. Pre-monsoon (March, April and May - MAM) rainfall over the country is highly variable. Since heat lows and convective rainfall in MAM have an impact on the intensity of the ensuing monsoons, hence the pre-monsoon period was chosen for the study. The pre-whitened Mann Kendall test was used to explore presence of rainfall trend during MAM. The results indicate presence of significant (at 10% level) increasing trend in two stations (Ajmer, Bikaner). The practical significance of the change in rainfall was also explored as percentage changes over long term mean, using Theil and Sen's median slope estimator. Forecast using univariate ARIMA model for pre-monsoon months indicates that there is a significant rise in the pre-monsoon rainfall over the northwest part of the country.

  2. Orbital Asian summer monsoon dynamics revealed using an isotope-enabled global climate model.

    PubMed

    Caley, Thibaut; Roche, Didier M; Renssen, Hans

    2014-01-01

    The Asian summer monsoon dynamics at the orbital scale are a subject of considerable debate. The validity of Asian speleothem δ(18)O records as a proxy for summer monsoon intensity is questioned together with the ultimate forcing and timing of the monsoon. Here, using the results of a 150,000-year transient simulation including water isotopes, we demonstrate that Asian speleothem δ(18)O records are not a valid proxy for summer monsoon intensity only at the orbital timescale. Rather, our results show that these records reflect annual variations in hydrologic processes and circulation regime over a large part of the Indo-Asian region. Our results support the role of internal forcing, such as sea surface temperature in the equatorial Pacific, to modulate the timing of monsoon precipitation recorded in paleo-proxies inside the Asian region. PMID:25373794

  3. Glacial aridity in central Indonesia coeval with intensified monsoon circulation

    NASA Astrophysics Data System (ADS)

    Konecky, Bronwen; Russell, James; Bijaksana, Satria

    2016-03-01

    The Last Glacial Maximum was cool and dry over the Indo-Pacific Warm Pool (IPWP), a key region driving global oceanic-atmospheric circulation. Both low- and high-latitude teleconnections with insolation, ice sheets, and sea level have been suggested to explain the pervasive aridity observed in paleoecological and geomorphic data. However, proxies tracking the H- and O-isotopic composition of rainfall (e.g., speleothems, sedimentary biomarkers) suggest muted aridity or even wetter conditions than the present, complicating interpretations of glacial IPWP climate. Here we use multiproxy reconstructions from lake sediments and modern rainfall isotopic measurements from central Indonesia to show that, contrary to the classical "amount effect," intensified Australian-Indonesian monsoon circulation drove lighter H- and O-isotopic composition of IPWP rainfall during the LGM, while at the same time, dry conditions prevailed. Precipitation isotopes are particularly sensitive to the apparent increase in monsoon circulation and perhaps also decreased moisture residence time implied by our data, explaining contrasts among proxy records while illuminating glacial IPWP atmospheric circulation, a key target for climate models.

  4. Asian monsoon extremes and humanity's response over the past millennium

    NASA Astrophysics Data System (ADS)

    Buckley, B. M.; Lieberman, V. B.; Zottoli, B.

    2012-12-01

    The first decade of the 21st century has seen significant development in the production of paleo proxies for the Asian monsoon, exemplified by the Monsoon Asian Drought Atlas that was comprised of more than 300 tree ring chronologies. Noteworthy among them is the Vietnamese cypress tree-ring record which reveals that the two worst droughts of the past 7 centuries, each more than a decade in length, coincided with the demise of the Khmer civilization at Angkor in the early 15th century CE. The 18th century was nearly as tumultuous a period across Southeast Asia, where several polities fell against a backdrop of epic decadal-scale droughts. At this time all of the region's charter states saw rapid realignment in the face of drought, famine, disease and a raft of related and unrelated social issues. Several other droughts, some more extreme but of lesser duration, punctuate the past millennium, but appear to have had little societal impact. Historical documentation is being used not only to provide corroborative evidence of tree-ring reconstructed climate extremes, but to attempt to understand the dynamics of the coupled human-natural systems involved, and to define what kinds of thresholds need to be reached before societies respond. This paleo perspective can assist our analyses of the role of climate extremes in the collapse or disruption of regional societies, a subject of increasing concern given the uncertainties surrounding projections for future climate across the highly populated areas of Asia.

  5. The abrupt onset of the modern South Asian Monsoon winds.

    PubMed

    Betzler, Christian; Eberli, Gregor P; Kroon, Dick; Wright, James D; Swart, Peter K; Nath, Bejugam Nagender; Alvarez-Zarikian, Carlos A; Alonso-García, Montserrat; Bialik, Or M; Blättler, Clara L; Guo, Junhua Adam; Haffen, Sébastien; Horozal, Senay; Inoue, Mayuri; Jovane, Luigi; Lanci, Luca; Laya, Juan Carlos; Mee, Anna Ling Hui; Lüdmann, Thomas; Nakakuni, Masatoshi; Niino, Kaoru; Petruny, Loren M; Pratiwi, Santi D; Reijmer, John J G; Reolid, Jesús; Slagle, Angela L; Sloss, Craig R; Su, Xiang; Yao, Zhengquan; Young, Jeremy R

    2016-07-20

    The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment's content of particulate organic matter. A weaker 'proto-monsoon' existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system.

  6. Forecasting of monsoon heavy rains: challenges in NWP

    NASA Astrophysics Data System (ADS)

    Sharma, Kuldeep; Ashrit, Raghavendra; Iyengar, Gopal; Bhatla, R.; Rajagopal, E. N.

    2016-05-01

    Last decade has seen a tremendous improvement in the forecasting skill of numerical weather prediction (NWP) models. This is attributed to increased sophistication in NWP models, which resolve complex physical processes, advanced data assimilation, increased grid resolution and satellite observations. However, prediction of heavy rains is still a challenge since the models exhibit large error in amounts as well as spatial and temporal distribution. Two state-of-art NWP models have been investigated over the Indian monsoon region to assess their ability in predicting the heavy rainfall events. The unified model operational at National Center for Medium Range Weather Forecasting (NCUM) and the unified model operational at the Australian Bureau of Meteorology (Australian Community Climate and Earth-System Simulator -- Global (ACCESS-G)) are used in this study. The recent (JJAS 2015) Indian monsoon season witnessed 6 depressions and 2 cyclonic storms which resulted in heavy rains and flooding. The CRA method of verification allows the decomposition of forecast errors in terms of error in the rainfall volume, pattern and location. The case by case study using CRA technique shows that contribution to the rainfall errors come from pattern and displacement is large while contribution due to error in predicted rainfall volume is least.

  7. Impact of irrigation on the South Asian summer monsoon

    NASA Astrophysics Data System (ADS)

    Saeed, Fahad; Hagemann, Stefan; Jacob, Daniela

    2009-10-01

    The Indian subcontinent is one of the most intensely irrigated regions of the world and state of the art climate models do not account for the representation of irrigation. Sensitivity studies with the regional climate model REMO show distinct feedbacks between the simulation of the monsoon circulation with and without irrigation processes. We find that the temperature and mean sea level pressure, where the standard REMO version without irrigation shows a significant bias over the areas of Indus basin, is highly sensitive to the water used for irrigation. In our sensitivity test we find that removal of this bias has caused less differential heating between land and sea masses. This in turns reduces the westerlies entering into land from Arabian Sea, hence creating conditions favorable for currents from Bay of Bengal to intrude deep into western India and Pakistan that have been unrealistically suppressed before. We conclude that the representation of irrigated water is unavoidable for realistic simulation of south Asian summer monsoon and its response under global warming.

  8. Interannual variation of East Asian Winter Monsoon and ENSO

    SciTech Connect

    Zhang, Yi; Sperber, Kenneth R.; Boyle, James S.

    1996-12-01

    This paper examines the interannual variation of the East Asian winter monsoon and its relationship with EJSO based on the 1979-1995 NCEP/NCAR reanalysis. Two stratifications of cold surges are used. The first one, described as the conventional cold surges, indicates that the surge frequency reaches a urn one year after El Nino events. The second one, originated from the same region as the first, is defined as the maximum wind events near the South China Sea. The variation of this stratification of surges is found to be in good agreement with the South Oscillation Index (SOI). Low SOI (high SOI) events coincide with years of low (high) surge frequency. The interannual variation of averaged meridional wind near the South China Sea and western Pacific is dominated by the South China Sea cold surges, and is also well correlated (R--O.82) with the SOI. Strong wind seasons are associated with La Nina and high SOI events; likewise, weak wind years are linked with El Nino and low SOI cases. This pattern is restricted north of the equator within the region of (OON-20 N, 11OOE-1300E), and is confined to the near surface layer. The surface Siberian high, 500 hPa trough and 200 hPa jetstream, all representing the large-scale monsoon flow, are found to be weaker than normal during El Nino years. In particular, the interannual variation of the Siberian high is in general agreement with the SOL.

  9. Transport of sulfonamide antibiotics in small fields during monsoon season

    NASA Astrophysics Data System (ADS)

    Park, J. Y.; Huwe, B.; Kolb, A.; Tenhunen, J.

    2012-04-01

    Transport and fate of 3 sulfonamide antibiotics (sulfamethoxazole, sulfadimethoxine and sulfamethazine) were studied in small agricultural land during monsoon period. The experiment has been conducted in 2 typical sandy loam potato fields of South Korea after application of the veterinary antibiotics and bromide. Precipitation was measured by AWS (Automatic Weather Station) near the fields during the whole monsoon season. Runoff generation was estimated by multislot divisors in combination with pressure sensor. Concentration of the target antibiotics and the conservative tracer in runoff, soil-water and soil was determined using HPLC-MS-MS and Br selected electrode. Transport simulation has been performed with Hydrus-2D program which can consider soil characteristics, climate condition, adsorption/desorption and degradation. Results from the measurements and modeling focus on the role of heavy rainfall, of related the ratio of runoff and infiltration in terms of the selected antibiotics distribution and fate. Bromide on topsoil was moved into soil as increasing rainfall loading. On the contrary, the sulfonamides were relatively retarded in upper soil layer owing to adsorption onto soil particles. Different patterns of runoff were observed, and slope and rain intensity was representative factor in this study. Distribution of target pharmaceuticals was strongly dependent on constitution of furrow and ridge in the agricultural fields. Modeling results positively matched with background studies that describe physico-chemical properties of the sulfonamides, interaction between soil and the antibiotic group, solute transport through vadose zone and runoff induction by storm events.

  10. Earlier North American Monsoon Onset in a Warmer World?

    NASA Astrophysics Data System (ADS)

    Rauscher, S. A.; Seth, A.; Ringler, T.; Rojas, M.; Liebmann, B.

    2009-12-01

    Analysis of twenty-first century projections indicate substantial drying over the American Southwest and the potential for “Dust Bowl” conditions to be the norm by the middle of century. Closer examination of monthly precipitation data from the CMIP3 models indicates that the annual cycle is actually amplified over the North American Monsoon (NAMS) region, with drier conditions during the winter and an increase in monsoon rains during the later part of the rainy season. Importantly, the projected decrease in winter precipitation extends into the spring season, suggesting a delayed onset of the NAMS. Consistent thermodynamic changes, including a decrease in low-level relative humidity and an increase in the vertical gradient of moist static energy, accompany this spring precipitation decrease. Here we examine daily precipitation data from the CMIP3 archive to determine if this reduced spring precipitation represents a true delay in the NAMS onset. We further analyze the hydrological cycle over the NAMS region in several of the CMIP3 models, focusing on changes in net moisture divergence, surface evaporation, and soil moisture in order to fully understand how the hydrological cycle will change in the future based on the CMIP3 simulations, and how these changes may be translated into the timing and intensity of the NAMS. The combination of a delayed NAMS onset and earlier and reduced snowmelt runoff in the western US could substantially change the availability of water resources over the NAMS region.

  11. The abrupt onset of the modern South Asian Monsoon winds.

    PubMed

    Betzler, Christian; Eberli, Gregor P; Kroon, Dick; Wright, James D; Swart, Peter K; Nath, Bejugam Nagender; Alvarez-Zarikian, Carlos A; Alonso-García, Montserrat; Bialik, Or M; Blättler, Clara L; Guo, Junhua Adam; Haffen, Sébastien; Horozal, Senay; Inoue, Mayuri; Jovane, Luigi; Lanci, Luca; Laya, Juan Carlos; Mee, Anna Ling Hui; Lüdmann, Thomas; Nakakuni, Masatoshi; Niino, Kaoru; Petruny, Loren M; Pratiwi, Santi D; Reijmer, John J G; Reolid, Jesús; Slagle, Angela L; Sloss, Craig R; Su, Xiang; Yao, Zhengquan; Young, Jeremy R

    2016-01-01

    The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment's content of particulate organic matter. A weaker 'proto-monsoon' existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system. PMID:27436574

  12. Decadal Prediction and Stochastic Simulation of Hydroclimate Over Monsoonal Asia

    SciTech Connect

    Ghil, Michael; Robertson, Andrew W.; Cook, Edward R.; D’Arrigo, Rosanne; Lall, Upmanu; Smyth, Padhraic J.

    2015-01-18

    We developed further our advanced methods of time series analysis and empirical model reduction (EMR) and applied them to climatic time series relevant to hydroclimate over Monsoonal Asia. The EMR methodology was both generalized further and laid on a rigorous mathematical basis via multilayered stochastic models (MSMs). We identified easily testable conditions that imply the existence of a global random attractor for MSMs and allow for non-polynomial predictors. This existence, in turn, guarantees the numerical stability of the MSMs so obtained. We showed that, in the presence of low-frequency variability (LFV), EMR prediction can be improved further by including information from selected times in the system’s past. This prediction method, dubbed Past-Noise Forecasting (PNF), was successfully applied to the Madden-Julian Oscillation (MJO). Our time series analysis and forecasting methods, based on singular-spectrum analysis (SSA) and its enhancements, were applied to several multi-centennial proxy records provided by the Lamont team. These included the Palmer Drought Severity Index (PDSI) for 1300–2005 from the Monsoonal Asia Drought Atlas (MADA), and a 300-member ensemble of pseudo-reconstructions of Indus River discharge for 1702–2005. The latter was shown to exhibit a robust 27-yr low-frequency mode, which helped multi-decadal retroactive forecasts with no look-ahead over this 300-year interval.

  13. Analysis of Vegetation Index Variations and the Asian Monsoon Climate

    NASA Technical Reports Server (NTRS)

    Shen, Sunhung; Leptoukh, Gregory G.; Gerasimov, Irina

    2012-01-01

    Vegetation growth depends on local climate. Significant anthropogenic land cover and land use change activities over Asia have changed vegetation distribution as well. On the other hand, vegetation is one of the important land surface variables that influence the Asian Monsoon variability through controlling atmospheric energy and water vapor conditions. In this presentation, the mean and variations of vegetation index of last decade at regional scale resolution (5km and higher) from MODIS have been analyzed. Results indicate that the vegetation index has been reduced significantly during last decade over fast urbanization areas in east China, such as Yangtze River Delta, where local surface temperatures were increased significantly in term of urban heat Island. The relationship between vegetation Index and climate (surface temperature, precipitation) over a grassland in northern Asia and over a woody savannas in southeast Asia are studied. In supporting Monsoon Asian Integrated Regional Study (MAIRS) program, the data in this study have been integrated into Giovanni, the online visualization and analysis system at NASA GES DISC. Most images in this presentation are generated from Giovanni system.

  14. Insolation and Abrupt Climate Change Effects on the Western Pacific Maritime Monsoon

    NASA Astrophysics Data System (ADS)

    Partin, J. W.; Quinn, T. M.; Shen, C.; Cardenas, M. B.; Siringan, F. P.; Banner, J. L.; lin, K.; Taylor, F. W.

    2012-12-01

    The response of the Asian-Australian monsoon system to changes in summer insolation over the Holocene is recorded in many monsoon-sensitive paleoclimate reconstructions. The response is commonly direct; more summer insolation leads to increased monsoon rainfall over land as captured in stalagmite δ18O records from Oman and China. We evaluate this direct response using a maritime stalagmite record from the island of Palawan, Philippines (10 N, 119 E). The wet season in Palawan occurs over the same months (June-October) as in Oman, India and China. Therefore, we expected the stalagmite δ18O record from Palawan, a proxy of rainfall, to have a similar trend of decreasing monsoon rainfall over the Holocene. However, the Holocene trend in stalagmite δ18O is opposite to that expected: rainfall increases over the Holocene. Our explanation for the Holocene trend observed at Palawan is that the increase in the maritime monsoon balances the reduction in the land monsoon; an explanation that is consistent with previously published coupled ocean-atmosphere general circulation model results. Seawater δ18O reconstructions from marine sediment cores in the western tropical Pacific contain a freshening trend over the Holocene, also supporting the hypothesis of increase maritime monsoon rainfall. However, the decrease in maritime monsoon rainfall during the Younger Dryas at Palawan matches that observed in Chinese stalagmite records, meeting our original expectation of a similar wet season response in the various Asian-Australian monsoon records. One explanation for the similar Younger Dryas response in these monsoon records is the influence of seasonal changes in sea ice coverage, as previously suggested. A stalagmite δ18O record from Borneo (~800 km SE of Palawan), which lacks evidence of the Younger Dryas, provides supporting evidence for this explanation.

  15. Community level perceptions of the monsoon onset, withdrawal and climatic trends in Bangladesh

    NASA Astrophysics Data System (ADS)

    Reeve, M. A.; Abu Syed, M. D.; Hossain, P. R.; Maainuddi, G.; Mamnun, N.

    2012-04-01

    A structured questionnaire study was carried out in 6 different regions in Bangladesh in order to give insight into how the different communities define the monsoon. The respondents were asked how they define the monsoon onset and withdrawal, and by how much these can vary from year to year. They were also asked about how they perceive changes in onset and withdrawal dates and total monsoonal rainfall during the past 20 years. Bangladesh is a developing country with a large proportion of the population living in rural areas and employed in the agricultural sector. It is foreseen that these communities will be most affected by changes in the climate. These groups were considered to be the main stakeholders when considering climate change, due to the direct influence the monsoon has on their livelihood and the food supply for the entire nation. Agricultural workers were therefore the main group targeted in this study. The main aim of the study was to create a framework for defining the monsoon in order to increase the usability of results in future impact-related studies. Refining definitions according to the perceptions of the main stakeholders helps to achieve this goal. Results show that rainfall is the main parameter used in defining the monsoon onset and withdrawal. This is possibly intuitive, however the monsoon onset was considered to be considerably earlier than previous scientific studies. This could be due to pre-monsoonal rainfall, however the respondents defined this type of rainfall separately to what they called the monsoon. The monsoon is considered to start earliest in the Sylhet region in northeast Bangladesh.

  16. Principal modes of Asian summer monsoon variability: Detection and changes

    NASA Astrophysics Data System (ADS)

    Yasutomi, N.; Kimoto, M.

    2009-12-01

    Principal modes of Asian summer monsoon variability are identified. By using vertically integrated moisture flux, principal modes represent better separation than commonly used variables such as rainfall, winds and outgoing longwave radiation. An empirical orthogonal function of vertically integrated moisture flux within the South, Southeast and East Asia during summertime is analysed. Results of various analyses let us convince that the first and second EOFs of the moisture flux are the principal modes of the Asian monsoon variability. In summer, there are two modes dominant in the Asian monsoon region; one consists of low-level circulation over the subtropical western Pacific near Philippines and associated convective dipole centers located over the western Pacific and Indonesia. The other consists of El Nino-Southern Oscillation (ENSO) signal and the Pacific-Japan (PJ) pattern, called ENSO-PJ mixed mode. This pattern is detected as the first EOF mode of a simulation with an atmospheric general circulation model giving the climatological mean sea surface temperature. Furthermore, the pattern is dominant in both present climate simulation and global warming simulation using coupled GCM. A projected change shows increasing of precipitation over South China and Japan. The Pacific-Indo dipole pattern is found out to be excited without external forcing like a specific sea surface temperature anomaly. Moreover, the Pacific-Indo dipole pattern appears as the preferred structure of variability by giving small perturbations to a three-dimensionally varying basic state in summertime by using a linear baroclinic model. Factors of the basic state which help to excite and maintain the Pacific-Indo dipole pattern are examined. Free, stationary Rossby waves can be excited in the region of low-level westerly extending from the Indian Ocean to the South China Sea which blows as a part of the monsoonal flow in summer. Rossby waves at the eastern end of the low-level westerly where

  17. Monsoonal Variations of Supraglacial Lakes, Langtang Khola, Nepal

    NASA Astrophysics Data System (ADS)

    Miles, E. S.; Willis, I. C.; Arnold, N. S.; Pellicciotti, F.

    2013-12-01

    As Himalayan debris-covered glaciers retreat and thin in response to climate warming, their long, low-gradient tongues and undulating surfaces tend to form supraglacial lakes. The conceptual response of debris-covered valley glaciers progresses from thinning and stagnation to the development of supraglacial ponds, which eventually may coalesce into very large lakes bounded by terminal moraines. Large terminal lakes are a topic of frequent study due to the public safety hazard of glacier lake outburst floods (GLOFs). However, smaller, transient ponds that form on the glacier's surface may play an important role in determining annual mass balance. Development of surpaglacial ponds may be controlled by the magnitudes of surface undulations, meltwater inputs, and the glacier's general surface gradient. These lakes are not necessarily permanent: they enlarge by enhanced ice-cliff ablation, they are advected and deformed by glacial strain, they may disappear due to englacial drainage or prolonged evaporation, and they may not recur in the same locations each year due to changes in surface topography and hydrologic routing. The prevalence and character of such lakes varies greatly throughout the year. In the cold, dry winter (October-March), the debris surface is largely snow-covered and supraglacial lakes are frozen. During the arid premonsoon (April-May), lakes thaw and the debris surface is dry and free of snow. The debris surface becomes nearly-saturated by monsoonal rains (June-September) leading to surface runoff and widespread lake-filling. During this dynamic monsoon period, ponded water substantially alters the glacier's specific energy balance by increasing the effective thermal conductivity between atmosphere and ice, acting as a heat reservoir, and reducing albedo. Additionally, supraglacial ponds often enhance ablation processes in proximal areas by initiating lake-marginal calving and exposing debris-free ice cliffs. Through these processes supraglacial

  18. Fine-scale responses of phytoplankton to freshwater influx in a tropical monsoonal estuary following the onset of southwest monsoon

    NASA Astrophysics Data System (ADS)

    Pednekar, Suraksha M.; Matondkar, S. G. Prabhu; Gomes, Helga Do R.; Goes, Joaquim I.; Parab, Sushma; Kerkar, Vijaya

    2011-06-01

    In May of 2007, a study was initiated by the National Institute of Oceanography (NIO), Goa, India, to investigate the influence of monsoonal rainfall on hydrographic conditions in the Mandovi River of India. The study was undertaken at a location ˜2 km upstream of the mouth of this estuary. During the premonsoon (PreM) in May, when circulation in the estuary was dominated by tidal activity, phytoplankton communities in the high saline (35-37 psu) waters at the study site were largely made up of the coastal neritic species Fragilaria oceanica, Ditylum brightwellii and Trichodesmium erythraeum. During the later part of the intermonsoon (InterM) phase, an abrupt decline in salinity led to a surge in phytoplankton biomass (Chlorophyll a ˜14 mg m - 3), of a population that was dominated by Thalassiosira eccentricus. As the southwest monsoon (SWM) progressed and the estuary freshened salinity and Chlorophyll a (Chl a) concentrations decreased during the MoN, Skeletonema costatum established itself as the dominant form. Despite the low biomass (Chl a <2 mg m - 3), the phytoplankton community of the MoN was the most diverse of the entire study. During the postmonsoon (PostM), the increase in salinity was marked by a surge in dinoflagellate populations comprising of Ceratium furca, Akashiwo sanguinea, and Pyrophacus horologium.

  19. African-Americans and Alzheimer's

    MedlinePlus

    ... Share Plus on Google Plus African-Americans and Alzheimer's alz.org | IHaveAlz Introduction 10 Warning Signs Brain ... African-Americans are at a higher risk for Alzheimer's disease. Many Americans dismiss the warning signs of ...

  20. Indian summer monsoon precipitating clouds: role of microphysical process rates

    NASA Astrophysics Data System (ADS)

    Hazra, Anupam; Chaudhari, Hemantkumar S.; Pokhrel, Samir; Saha, Subodh K.

    2016-04-01

    The budget analysis of microphysical process rates based on Modern Era Retrospective-analysis for Research and Applications (MERRA) products are presented in the study. The relative importance of different microphysical process rates, which is crucial for GCMs, is investigated. The autoconversion and accretion processes are found to be vital for Indian Summer Monsoon (ISM). The map-to-map correlations are examined between observed precipitation and MERRA reanalysis. The pattern correlations connote the fidelity of the MERRA datasets used here. Results of other microphysical parameters (e.g. ice water content from CloudSat, high cloud fraction from CALIPSO and MODIS, latent heating from TRMM, cloud ice mixing ratio from MERRA) are presented in this study. The tropospheric temperature from reanalysis product of MERRA and NCEP are also analyzed. Furthermore, the linkages between cloud microphysics production rates and dynamics, which are important for North-South tropospheric temperature gradient for maintaining the ISM circulation, are also discussed. The study demonstrates the microphysical process rates, which are actually responsible for the cloud hydrometeors and precipitation formation on the monsoon intraseasonal oscillations timescale. Cloud to rain water auto-conversion and snow accretion rates are the dominant processes followed by the rain accretion. All these tendency terms replicates the similar spatial patterns as that of precipitation. The quantification of microphysical process rates and precipitation over different regions are shown here. The freezing rate is also imperative for the formation of cloud ice as revealed by the observation. Freezing rates at upper level and snow accretion at middle level may have effect on latent heating release. Further it can modulate the north-south temperature gradient which can influence the large-scale monsoon dynamics. The rain water evaporation is also considered as a key aspect for controlling the low level

  1. Precipitation and Moisture Sources in North American Monsoon Surges

    NASA Astrophysics Data System (ADS)

    Schiffer, N. J.; Nesbitt, S. W.

    2009-12-01

    Prediction of North American Monsoon (NAM) precipitation plays an important role in decision-making on time scales from minutes for severe weather to seasons and years for agriculture. Gulf of California (GoC) moisture surges are connected to NAM precipitation and play a role in modulating the monsoon. This study aims to improve understanding of the relationship between precipitation, surges, and the larger scale moisture sources of the NAM with the ultimate goal of improving precipitation forecasts over the monsoon region. Although previous studies have relied primarily on dew point temperature to identify surges, relative humidity accounts for the cool and moist qualities of surges simultaneously. Using an updated method to recognize surges, relative humidity, temperature, and dew point from surface observations all show distinct trends that are consistent with surges lasting 1-2 days. The NARR identifies surges more precisely based on a plan view of θe anomalies than a pseudo-surface observation at a single data point near Yuma. With an eye towards climate change, 29 years of surface observations show surge length is not changing, but surges may be growing more frequent, less humid, and warmer. Surges show a pronounced relationship with Tropical Rainfall Measuring Mission (TRMM) 3B42-estimated precipitation. As the surge progresses northward along the GoC, precipitation follows, showing little delay until the surge breaches the northern end of the GoC. Yuma, AZ, surface observations show a one-day delay between surge arrival and precipitation enhancement, probably because surge arrival is defined at the beginning of the rise in atmospheric moisture. This positive precipitation anomaly in the Desert Southwest appears at the same time that negative anomalies dominate the Great Plains, intimating an inverse relationship suggested in previous studies. In terms of surge moisture source, there is no significant connection between the GoC and an outside moisture

  2. South American Monsoon and the Land Surface Processes

    NASA Astrophysics Data System (ADS)

    Xue, Y.; de Sales, F. H.; Li, W.; Mechoso, C. R.; Nobre, C. A.; Juang, H. H.

    2002-12-01

    In this numerical modeling study, the NCEP GCM is applied to investigate the interactions between land surface processes and climate, particularly the effects of land processes on the South American monsoon system (SAMS). A model version with spectral triangular 42 truncation (T42) is used. The corresponding Gaussian grid for T42 is 128 by 64, which is roughly equivalent to 2.8 degrees in latitude and longitude. Two land surface parameterizations are used. One is the Simplified Simple Biosphere Model (SSiB), which includes explicit vegetation representation. The other parameterization is a surface model with two-soil layers (SOIL) and no explicit vegetation scheme. Two 12-month long simulations were performed with the two parameterizations from initial conditions corresponding to May 1, 1987 and identical distributions of soil moisture and surface albedo. The simulations will be referred to as NCEP GCM/SOIL and NCEP GCM/SSiB. The simulations, therefore, differ in the land surface parameterizations and land cover conditions: one with vegetation and the other with only soil layers (but monthly mean vegetation albedo). This experiment aims to test the role of explicit description of vegetation process in the climate model and hence the role of vegetation in the South American hydrometeorology. SAMS starts developing in Central America and then moves southeast towards the Amazons in South America. Afterwards, largest precipitation moves northward and eventually retreats northwest. NCEP GCM/SOIL and NCEP GCM/SSiB produce substantially different evolution and spatial distributions of SAMS. In the NCEP GCM/SOIL, the development of SAMS is too fast and too strong with no clear indication of the southward movement. Rainfall magnitudes are much stronger than in the observation. The NCEP/SSiB, on the other hand, correctly simulates SAMS evolution. To understand the mechanisms that contributed to the differences in the simulations, the surface energy and water balances are

  3. The role of fall season tropical plumes in enhancing Saharan rainfall during the African Humid Period

    NASA Astrophysics Data System (ADS)

    Skinner, Christopher B.; Poulsen, Christopher J.

    2016-01-01

    The early Holocene to mid-Holocene African Humid Period (AHP) is marked by widespread rainfall throughout the present-day arid Sahara. Here we simulate early Holocene and mid-Holocene climate with the Community Atmosphere Model version 5 to explore the role of fall season dynamics in driving Saharan rainfall during the AHP. An enhanced summer monsoon during the AHP results in abundant fall season moisture throughout tropical Africa, particularly during the mid-Holocene. During the fall, extratropical troughs advect tropical moisture toward the Sahara in the form of concentrated plumes of water vapor and extend the Saharan rainy season into October. Fall season tropical plumes contribute up to 30% of annual Saharan rainfall during the mid-Holocene. Our results suggest that tropical plumes serve as an important mechanism for enhancing Saharan rainfall during the late AHP and that further understanding of changes in tropical plumes through time may provide valuable insights into past African hydroclimate change.

  4. LASE Observations of Interactions Between African Easterly Waves and the Saharan Air Layer

    NASA Technical Reports Server (NTRS)

    Ismail, Syed; Ferrare, Richard; Browell, Edward; Kooi, Susan; Biswas, Mrinal; Krishnamurti, T. N.; Notari, Anthony; Heymsfield, Andrew; Butler, Carolyn; Burton, Sharon; Fenn, Marta; Dunion, Jason

    2010-01-01

    The Lidar Atmospheric Sensing Experiment (LASE) participated in the NASA African Monsoon Multidisciplinary Analyses (NAMMA) field experiment in 2006 that was conducted from Sal, Cape Verde to study the Saharan Air Layer (SAL) and its influence on the African Easterly Waves (AEWs) and Tropical Cyclones (TCs). During NAMMA, LASE collected simultaneous water vapor and aerosol lidar measurements from 14 flights onboard the NASA DC- 8. In this paper we present three examples of the interaction of the SAL and AEWs regarding: moistening of the SAL and transfer of latent heat; injection of dust in an updraft; and influence of dry air intrusion on an AEW. A brief discussion is also given on activities related to the refurbishment of LASE to enhance its operational performance and plans to participate in the next NASA hurricane field experiment in the summer of 2010.

  5. English as an African Language.

    ERIC Educational Resources Information Center

    Desai, Gaurav

    1993-01-01

    Discusses the role of the English language in postcolonial African literature, focusing on the politics of language, "Africanized" English, and the social languages used in Chinua Achebe's novels and concludes that English today is as much an African language as a British or American one. (Contains 37 references.) (MDM)

  6. The Struggles over African Languages

    ERIC Educational Resources Information Center

    Maseko, Pam; Vale, Peter

    2016-01-01

    In this interview, African Language expert Pam Maseko speaks of her own background and her first encounter with culture outside of her mother tongue, isiXhosa. A statistical breakdown of South African languages is provided as background. She discusses Western (originally missionary) codification of African languages and suggests that this approach…

  7. An assessment of Indian monsoon seasonal forecasts and mechanisms underlying monsoon interannual variability in the Met Office GloSea5-GC2 system

    NASA Astrophysics Data System (ADS)

    Johnson, Stephanie J.; Turner, Andrew; Woolnough, Steven; Martin, Gill; MacLachlan, Craig

    2016-06-01

    We assess Indian summer monsoon seasonal forecasts in GloSea5-GC2, the Met Office fully coupled subseasonal to seasonal ensemble forecasting system. Using several metrics, GloSea5-GC2 shows similar skill to other state-of-the-art seasonal forecast systems. The prediction skill of the large-scale South Asian monsoon circulation is higher than that of Indian monsoon rainfall. Using multiple linear regression analysis we evaluate relationships between Indian monsoon rainfall and five possible drivers of monsoon interannual variability. Over the time period studied (1992-2011), the El Niño-Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD) are the most important of these drivers in both observations and GloSea5-GC2. Our analysis indicates that ENSO and its teleconnection with Indian rainfall are well represented in GloSea5-GC2. However, the relationship between the IOD and Indian rainfall anomalies is too weak in GloSea5-GC2, which may be limiting the prediction skill of the local monsoon circulation and Indian rainfall. We show that this weak relationship likely results from a coupled mean state bias that limits the impact of anomalous wind forcing on SST variability, resulting in erroneous IOD SST anomalies. Known difficulties in representing convective precipitation over India may also play a role. Since Indian rainfall responds weakly to the IOD, it responds more consistently to ENSO than in observations. Our assessment identifies specific coupled biases that are likely limiting GloSea5-GC2 Indian summer monsoon seasonal prediction skill, providing targets for model improvement.

  8. Deciphering the desiccation trend of the South Asian monsoon hydroclimate in a warming world

    NASA Astrophysics Data System (ADS)

    Krishnan, R.; Sabin, T. P.; Vellore, R.; Mujumdar, M.; Sanjay, J.; Goswami, B. N.; Hourdin, F.; Dufresne, J.-L.; Terray, P.

    2016-08-01

    Rising propensity of precipitation extremes and concomitant decline of summer-monsoon rains are amongst the most distinctive hydroclimatic signals that have emerged over South Asia since 1950s. A clear understanding of the underlying causes driving these monsoon hydroclimatic signals has remained elusive. Using a state-of-the-art global climate model with high-resolution zooming over South Asia, we demonstrate that a juxtaposition of regional land-use changes, anthropogenic-aerosol forcing and the rapid warming signal of the equatorial Indian Ocean is crucial to produce the observed monsoon weakening in recent decades. Our findings also show that this monsoonal weakening significantly enhances occurrence of localized intense precipitation events, as compared to the global-warming response. A 21st century climate projection using the same high-resolution model indicates persistent decrease of monsoonal rains and prolongation of soil drying. Critical value-additions from this study include (1) realistic simulation of the mean and long-term historical trends in the Indian monsoon rainfall (2) robust attributions of changes in moderate and heavy precipitation events over Central India (3) a 21st century projection of drying trend of the South Asian monsoon. The present findings have profound bearing on the regional water-security, which is already under severe hydrological-stress.

  9. Determination of summer monsoon onset and its related large-scale circulation characteristics over Pakistan

    NASA Astrophysics Data System (ADS)

    Latif, M.; Syed, F. S.

    2016-08-01

    The onset of summer monsoon over the Core Monsoon Region of Pakistan (CMRP) has been investigated in this study using observational daily rainfall and Precipitable Water (PW) data sets. An objective criterion is proposed to define monsoon onset dates by employing Precipitation Index and Normalized Precipitable Water Index techniques. The climatological mean summer monsoon onset dates over CMRP based on daily rainfall data sets are observed to be 1 July and 30 June in the station and gridded data sets, respectively. Whereas the daily PW-based climatological mean onset date is 30 June. The year-wise onset dates determined through station and gridded rainfall data sets are very similar but these dates differ in case of PW-based onsets. The evolution of large-scale circulation anomalies and thermodynamic structure leading monsoon onset over Pakistan shows that a strong positive temperature and geopotential height anomalies appear over the northwestern part of the core region in the upper atmosphere. This warm geopotential height anomaly gets strengthen as the monsoon onset approaches. The temperature anomalies are barotropic whereas the geopotential height anomalies are baroclinic with the presence of low level anticyclone over the Tibetan Plateau. A moisture convergence zone along the foothill of Himalayas and low level moisture convergence zone over the north Arabian Sea set the stage for the moisture carrying monsoon winds to blow inland towards CMRP. The moisture is mainly supplied from the Arabian Sea, as the low pressure system approaches CMRP from the Bay of Bengal.

  10. A seamless approach to assessing monsoon simulations in the Met Office Unified Model

    NASA Astrophysics Data System (ADS)

    Levine, R. C.; Boo, K. O.; Martin, G. M.; Milton, S. F.; Mitra, A.; Sellar, A. A.; Willett, M. R.

    2009-04-01

    We present an assessment of monsoons as simulated by the latest configurations of the Met Office Unified Model. These consist of models of varying complexity that are used for Numerical Weather Prediction (NWP), climate, and seasonal prediction. A comparison is made between the model biases in different monsoon regions for the different configurations, giving an insight into the nature of the main systematic errors, and also of the time-scales involved in their development. Both the mean state and the variability are assessed using a metric-based approach. The main model bias in the Indian monsoon region is the relatively low precipitation over Indian land. This has been significantly improved in the latest atmospheric component of the climate model, mainly due to changes in the CAPE closure in the convection scheme, which are aimed at reducing the tendency for strong intermittent deep convection. A more detailed comparison of the model with ERA re-analysis data is made for the onset and the pre-monsoon period of the Indian summer monsoon, giving an insight into the impact of various changes to the model. The emphasis is placed on the impacts of the timing of convection, the development of the monsoon jet, the impact of cyclonic vortices, and the moistening rates over India. The interannual variability is further examined through analysis of the ENSO-monsoon teleconnection, the link between El Nino/La Nina events and below/above average rainfall over India, which is assessed using a metric-based approach.

  11. Non-local Impact of South and East Asian Aerosols on Monsoon Onset and Withdrawal

    NASA Astrophysics Data System (ADS)

    Bollasina, M. A.; Bartlett, R. E.; Booth, B.; Dunstone, N. J.; Marenco, F.

    2015-12-01

    The powerful Asian monsoon is of vital importance to the billions of people who are reliant on its rainfall, especially considering that society within its domain is largely agrarian. This monsoon system comprises smaller regional components, including the Indian monsoon and East Asian monsoon. These components are linked to one another through large scale circulation. The impacts of rapidly increasing anthropogenic aerosols over Asia on the monsoon have been widely studied. However, most studies consider only regional impacts, and not the subsequent effects on other geographical components of the system. We use observational and modelling methods to investigate the links between the regional components of the Asian monsoon and how they are affected by aerosols. Satellite observations of aerosol optical depth are used in conjunction with precipitation and atmospheric reanalysis data to investigate the problem at interannual timescales. Modelling experiments using HadGEM2-ES and GFDL CM3 are used to look at longer timescales and the potential influence of long term feedbacks. The HadGEM2 experiments use three time-evolving future anthropogenic aerosol emissions scenarios with the same time-evolving greenhouse gases. The GFDL CM3 experiments are forced by historical regional anthropogenic aerosol emissions. Using these methods, we look at the separate impact that South and East Asian aerosols have on monsoon onset and withdrawal. We focus on impacts in regions non-local to the aerosol source. We will also present proposed mechanisms for the apparent effects based on analysis of large scale circulation and atmospheric heating.

  12. Leaf unfolding of Tibetan alpine meadows captures the arrival of monsoon rainfall

    PubMed Central

    Li, Ruicheng; Luo, Tianxiang; Mölg, Thomas; Zhao, Jingxue; Li, Xiang; Cui, Xiaoyong; Du, Mingyuan; Tang, Yanhong

    2016-01-01

    The alpine meadow on the Tibetan Plateau is the highest and largest pasture in the world, and its formation and distribution are mainly controlled by Indian summer monsoon effects. However, little is known about how monsoon-related cues may trigger spring phenology of the vast alpine vegetation. Based on the 7-year observations with fenced and transplanted experiments across lower to upper limits of Kobresia meadows in the central plateau (4400–5200 m), we found that leaf unfolding dates of dominant sedge and grass species synchronized with monsoon onset, regardless of air temperature. We also found similar patterns in a 22-year data set from the northeast plateau. In the monsoon-related cues for leaf unfolding, the arrival of monsoon rainfall is crucial, while seasonal air temperatures are already continuously above 0 °C. In contrast, the early-emerging cushion species generally leafed out earlier in warmer years regardless of precipitation. Our data provide evidence that leaf unfolding of dominant species in the alpine meadows senses the arrival of monsoon-season rainfall. These findings also provide a basis for interpreting the spatially variable greening responses to warming detected in the world’s highest pasture, and suggest a phenological strategy for avoiding damages of pre-monsoon drought and frost to alpine plants. PMID:26856260

  13. Near-linear response of mean monsoon strength to a broad range of radiative forcings

    PubMed Central

    Boos, William R.; Storelvmo, Trude

    2016-01-01

    Theoretical models have been used to argue that seasonal mean monsoons will shift abruptly and discontinuously from wet to dry stable states as their radiative forcings pass a critical threshold, sometimes referred to as a “tipping point.” Further support for a strongly nonlinear response of monsoons to radiative forcings is found in the seasonal onset of the South Asian summer monsoon, which is abrupt compared with the annual cycle of insolation. Here it is shown that the seasonal mean strength of monsoons instead exhibits a nearly linear dependence on a wide range of radiative forcings. First, a previous theory that predicted a discontinuous, threshold response is shown to omit a dominant stabilizing term in the equations of motion; a corrected theory predicts a continuous and nearly linear response of seasonal mean monsoon strength to forcings. A comprehensive global climate model is then used to show that the seasonal mean South Asian monsoon exhibits a near-linear dependence on a wide range of isolated greenhouse gas, aerosol, and surface albedo forcings. This model reproduces the observed abrupt seasonal onset of the South Asian monsoon but produces a near-linear response of the mean monsoon by changing the duration of the summer circulation and the latitude of that circulation’s ascent branch. Thus, neither a physically correct theoretical model nor a comprehensive climate model support the idea that seasonal mean monsoons will undergo abrupt, nonlinear shifts in response to changes in greenhouse gas concentrations, aerosol emissions, or land surface albedo. PMID:26811462

  14. Dominating Controls for Wetter South Asian Summer Monsoon in the Twenty-First Century

    SciTech Connect

    Mei, Rui; Ashfaq, Moetasim; Rastogi, Deeksha; Leung, Lai-Yung R.; Dominguez, Francina

    2015-04-01

    We analyze a suite of Global Climate Models from the 5th Phase of Coupled Models Intercomparison Project (CMIP5) archives to understand the mechanisms behind a net increase in the South Asian summer monsoon precipitation in response to enhanced radiative forcing during the 21st century despite a robust weakening of dynamics governing the monsoon circulation. Combining the future changes in the contributions from various sources, which contribute to the moisture supply over South Asia, with those in monsoon dynamics and atmospheric moisture content, we establish a pathway of understanding that partly explains these counteracting responses to increase in radiative forcing. Our analysis suggests that both regional (local recycling, Arabian Sea, Bay of Bengal) and remote (mainly Indian Ocean) sources contribute to the moisture supply for precipitation over South Asia during the summer season that is facilitated by the monsoon dynamics. Increase in radiative forcing fuels an increase in the atmospheric moisture content through warmer temperatures. For regional moisture sources, the effect of excessive atmospheric moisture is offset by weaker monsoon circulation and uncertainty in the response of the evapotranspiration over land, so anomalies in their contribution to the total moisture supply are either mixed or muted. In contrast, weakening of the monsoon dynamics has less influence on the moisture supply from remote sources that not only is a dominant moisture contributor in the historical period, but is also the net driver of the positive summer monsoon precipitation response in the 21st century. Our results also indicate that historic measures of the monsoon dynamics may not be well suited to predict the non-stationary moisture driven South Asian summer monsoon precipitation response in the 21st century.

  15. Impact of East Asian Summer Monsoon on the Air Quality over China: View from space

    SciTech Connect

    Zhao, Chun; Wang, Yuhang; Yang, Qing; Fu, Rong; Cunnold, Derek; Choi, Yunsoo

    2010-05-04

    Tropospheric O3 columns retrieved from OMI and MLS measurements, CO columns from MOPITT, and tropospheric O3 and CO concentrations from TES from May to August in 2006 are analyzed using the Regional chEmical and trAnsport Model (REAM) to investigate the impact of the East Asian summer monsoon on the air quality over China. The observed and simulated migrations of O3 and CO are in good agreement, demonstrating that the summer monsoon significantly affects the air quality over southeastern China and this influence extends to central East China from June to July. Enhancements of CO and O3 over southeastern China disappear after the onset of the summer monsoon and re-emerge in August after the monsoon wanes. The pre-monsoon high O3 concentrations over southern China are due to photochemical production from pollutant emissions and the O3 transport from the stratosphere. In the summer monsoon season, the O3 concentrations are relatively low over monsoon-affected regions because of the transport of marine air masses and weak photochemical activity. We find that the monsoon system strongly modulates the pollution problem over a large portion of East China in summer, depending on its strength and tempo-spatial extension. Model results also suggest that transport from the stratosphere and long-range transport from East China and South/Central Asia all make significant contributions to O3 enhancements over West China. Satellite observations provide valuable information for investigating the monsoon impact on air quality, particularly for the regions with limited in situ measurements.

  16. Global monsoon change during the Last Glacial Maximum: a multi-model study

    NASA Astrophysics Data System (ADS)

    Yan, Mi; Wang, Bin; Liu, Jian

    2016-07-01

    Change of global monsoon (GM) during the Last Glacial Maximum (LGM) is investigated using results from the multi-model ensemble of seven coupled climate models participated in the Coupled Model Intercomparison Project Phase 5. The GM changes during LGM are identified by comparison of the results from the pre-industrial control run and the LGM run. The results show (1) the annual mean GM precipitation and GM domain are reduced by about 10 and 5 %, respectively; (2) the monsoon intensity (demonstrated by the local summer-minus-winter precipitation) is also weakened over most monsoon regions except Australian monsoon; (3) the monsoon precipitation is reduced more during the local summer than winter; (4) distinct from all other regional monsoons, the Australian monsoon is strengthened and the monsoon area is enlarged. Four major factors contribute to these changes. The lower greenhouse gas concentration and the presence of the ice sheets decrease air temperature and water vapor content, resulting in a general weakening of the GM precipitation and reduction of GM domain. The reduced hemispheric difference in seasonal variation of insolation may contribute to the weakened GM intensity. The changed land-ocean configuration in the vicinity of the Maritime Continent, along with the presence of the ice sheets and lower greenhouse gas concentration, result in strengthened land-ocean and North-South hemispheric thermal contrasts, leading to the unique strengthened Australian monsoon. Although some of the results are consistent with the proxy data, uncertainties remain in different models. More comparison is needed between proxy data and model experiments to better understand the changes of the GM during the LGM.

  17. Climatology of monsoon precipitation over the Tibetan Plateau from 13-year TRMM observations

    NASA Astrophysics Data System (ADS)

    Aijuan, Bai; Guoping, Li

    2015-07-01

    Based on the 13-year data from the Tropical Rainfall Measuring Mission (TRMM) satellite during 2001-2013, the influencing geographical location of the Tibetan Plateau (Plateau) monsoon is determined. It is found that the domain of the Plateau monsoon is bounded by the latitude between 27° N and 37° N and the longitude between 60° E and 103° E. According to the annual relative precipitation, the Plateau monsoon can be divided into three sections: the Plateau winter monsoon (PWM) over Iran and Afghanistan, the Plateau summer monsoon (PSM) over the central Plateau, and the transiting zone of the Plateau monsoon (TPM) over the south, west, and east edges of the Plateau. In PWM and PSM, the monsoon climatology has a shorter rainy season with the mean annual rainfall of less than 800 mm. In TPM, it has a longer rainy season with the mean annual rainfall of more than 1800 mm. PWM experiences a single-peak monthly rainfall with the peak during January to March; PSM usually undergoes a multi-peak pattern with peaks in the warm season; TPM presents a double-peak pattern, with a strong peak in late spring to early summer and a secondary peak in autumn. The Plateau monsoon also characterizes an asymmetrical seasonal advance of the rain belt. In the east of the Plateau, the rain belt migrates in a south-north orientation under the impact of the tropical and subtropical systems' oscillation. In the west of the Plateau, the rain belt advances in an east-west direction, which is mainly controlled by the regional Plateau monsoon.

  18. Climatology of monsoon precipitation over the Tibetan Plateau from 13-year TRMM observations

    NASA Astrophysics Data System (ADS)

    Aijuan, Bai; Guoping, Li

    2016-10-01

    Based on the 13-year data from the Tropical Rainfall Measuring Mission (TRMM) satellite during 2001-2013, the influencing geographical location of the Tibetan Plateau (Plateau) monsoon is determined. It is found that the domain of the Plateau monsoon is bounded by the latitude between 27° N and 37° N and the longitude between 60° E and 103° E. According to the annual relative precipitation, the Plateau monsoon can be divided into three sections: the Plateau winter monsoon (PWM) over Iran and Afghanistan, the Plateau summer monsoon (PSM) over the central Plateau, and the transiting zone of the Plateau monsoon (TPM) over the south, west, and east edges of the Plateau. In PWM and PSM, the monsoon climatology has a shorter rainy season with the mean annual rainfall of less than 800 mm. In TPM, it has a longer rainy season with the mean annual rainfall of more than 1800 mm. PWM experiences a single-peak monthly rainfall with the peak during January to March; PSM usually undergoes a multi-peak pattern with peaks in the warm season; TPM presents a double-peak pattern, with a strong peak in late spring to early summer and a secondary peak in autumn. The Plateau monsoon also characterizes an asymmetrical seasonal advance of the rain belt. In the east of the Plateau, the rain belt migrates in a south-north orientation under the impact of the tropical and subtropical systems' oscillation. In the west of the Plateau, the rain belt advances in an east-west direction, which is mainly controlled by the regional Plateau monsoon.

  19. Sea surface height anomaly and upper ocean temperature over the Indian Ocean during contrasting monsoons

    NASA Astrophysics Data System (ADS)

    Gera, Anitha; Mitra, A. K.; Mahapatra, D. K.; Momin, I. M.; Rajagopal, E. N.; Basu, Swati

    2016-09-01

    Recent research emphasizes the importance of the oceanic feedback to monsoon rainfall over the Asian landmass. In this study, we investigate the differences in the sea surface height anomaly (SSHA) and upper ocean temperature over the tropical Indian Ocean during multiple strong and weak monsoons. Analysis of satellite derived SSHA, sea surface temperature (SST) and ocean reanalysis data reveals that patterns of SSHA, SST, ocean temperature, upper ocean heat content (UOHC) and propagations of Kelvin and Rossby waves differ during strong and weak monsoon years. During strong monsoons positive SSH, SST and UOHC anomalies develop over large parts of north Indian Ocean whereas during weak monsoons much of the north Indian Ocean is covered with negative anomalies. These patterns can be used as a standard tool for evaluating the performance of coupled and ocean models in simulating & forecasting strong and weak monsoons. The rainfall over central India is found to be significantly correlated with SSHA over the regions (Arabian Sea and West central Indian Ocean and Bay of Bengal) where SSHA is positively large during strong monsoons. The SST-SSHA correlation is also very strong over the same area. The study reveals that much convection takes place over these regions during strong monsoons. In contrast during weak monsoons, convection takes place over eastern equatorial region. These changes in SST are largely influenced by oceanic Kelvin and Rossby waves. The Rossby waves initiated in spring at the eastern boundary propagate sub-surface heat content in the ocean influencing SST in summer. The SST anomalies modulate the Hadley circulation and the moisture transport thereby contributing to rainfall over central India. Therefore oceanic Kelvin and Rossby waves influence the rainfall over central India.

  20. Dominating Controls for Wetter South Asian Summer Monsoon in the Twenty-First Century

    SciTech Connect

    Mei, Rui; Ashfaq, Moetasim; Rastogi, Deeksha; Leung, L. Ruby; Dominguez, Francina

    2015-04-07

    This study analyzes a suite of global climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) archives to understand the mechanisms behind a net increase in the South Asian summer monsoon precipitation in response to enhanced radiative forcing during the twenty-first century. An increase in radiative forcing fuels an increase in the atmospheric moisture content through warmer temperatures, which overwhelms the weakening of monsoon circulation and results in an increase of moisture convergence and therefore summer monsoon precipitation over South Asia. Moisture source analysis suggests that both regional (local recycling, the Arabian Sea, the Bay of Bengal) and remote (including the south Indian Ocean) sources contribute to the moisture supply for precipitation over South Asia during the summer season that is facilitated by the monsoon dynamics. For regional moisture sources, the effect of excessive atmospheric moisture is offset by weaker monsoon circulation and uncertainty in the response of the evapotranspiration over land, so anomalies in their contribution to the total moisture supply are either mixed or muted. In contrast, weakening of the monsoon dynamics has less influence on the moisture supply from remote sources that not only is a dominant moisture contributor in the historical period but is also the net driver of the positive summer monsoon precipitation response in the twenty-first century. Finally, the results also indicate that historic measures of the monsoon dynamics may not be well suited to predict the nonstationary moisture-driven South Asian summer monsoon precipitation response in the twenty-first century.

  1. Dominating Controls for Wetter South Asian Summer Monsoon in the Twenty-First Century

    DOE PAGES

    Mei, Rui; Ashfaq, Moetasim; Rastogi, Deeksha; Leung, L. Ruby; Dominguez, Francina

    2015-04-07

    This study analyzes a suite of global climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) archives to understand the mechanisms behind a net increase in the South Asian summer monsoon precipitation in response to enhanced radiative forcing during the twenty-first century. An increase in radiative forcing fuels an increase in the atmospheric moisture content through warmer temperatures, which overwhelms the weakening of monsoon circulation and results in an increase of moisture convergence and therefore summer monsoon precipitation over South Asia. Moisture source analysis suggests that both regional (local recycling, the Arabian Sea, the Bay of Bengal)more » and remote (including the south Indian Ocean) sources contribute to the moisture supply for precipitation over South Asia during the summer season that is facilitated by the monsoon dynamics. For regional moisture sources, the effect of excessive atmospheric moisture is offset by weaker monsoon circulation and uncertainty in the response of the evapotranspiration over land, so anomalies in their contribution to the total moisture supply are either mixed or muted. In contrast, weakening of the monsoon dynamics has less influence on the moisture supply from remote sources that not only is a dominant moisture contributor in the historical period but is also the net driver of the positive summer monsoon precipitation response in the twenty-first century. Finally, the results also indicate that historic measures of the monsoon dynamics may not be well suited to predict the nonstationary moisture-driven South Asian summer monsoon precipitation response in the twenty-first century.« less

  2. Toward a 530,000-year Hydroclimate History for the Southern Half of the Australasian Monsoon

    NASA Astrophysics Data System (ADS)

    Gagan, M. K.; Scroxton, N. G.; Kimbrough, A. K.; Krause, C.; Hantoro, W. S.; Ayliffe, L. K.; Dunbar, G. B.; Cheng, H.; Edwards, R. L.; Hellstrom, J. C.; Shen, C. C.; Scott-Gagan, H.; Suwargadi, B. W.; Rifai, H.

    2015-12-01

    Speleothem 18O/16O records have revealed key aspects of past hydroclimates in the northern Australasian monsoon domain on orbital to millennial scales, but much less is known about the southern half of the monsoon system. We aim to develop a hydroclimate history for the southern Australasian monsoon based on speleothems from southwest Sulawesi and Flores, Indonesia (latitudes 5-9oS), which extend back to ~530 kyr BP and 90 kyr BP, respectively. To date, the 18O/16O record for Sulawesi covers glacial terminations TIV (~340 kyr BP), TIII (~245 kyr BP) and TI (~18 kyr BP). The details of each termination are different, however two important hydroclimate patterns are emerging. First, the 18O/16O record shows sharp weakening of the monsoon immediately before each termination. This surprisingly robust pattern marks a southern extension of the northern 'weak monsoon interval', and reinforces the idea that southward monsoon displacement is a fundamental feature of terminations. Second, monsoon intensification around Sulawesi lags the rise in atmospheric CO2 and Antarctic temperature by several thousand years, but parallels the 18O/16O decrease in atmospheric O2. Our finding extends that of Wang et al. (2008) and Cheng et al. (2009) who noted the influence of the low-latitude hydrological cycle on the 18O/16O of tropical transpiration, and its potential for correlating ice core and paleomonsoon records. Further south, the 90-kyr 18O/16O record for Flores shows clear precession-scale antiphasing with China, and southerly positioning of the summer monsoon rainfall belt during Heinrich stadials. Heinrich stadials 5, 4, 2 and 1 occur during wetter intervals in Flores that accompanied relatively high southern summer insolation. Intriguingly, these events are associated with abrupt atmospheric CH4 signals that may be due to increased Southern Hemisphere CH4 production related to intensification of monsoon rainfall over southern tropical land areas (Rhodes et al., 2014).

  3. Falling monsoon depression frequency: A Gray-Sikka conditions perspective

    PubMed Central

    Prajeesh, A. G.; Ashok, K.; Rao, D. V. Bhaskar

    2013-01-01

    In this study, we show that the annual monsoon depression (MD) frequency making landfall on the east coast of India shows a statistically significant decreasing trend for the period 1979–2010. Importantly, about 80% of this fall is confined to the south of 20°N. To understand the plausible reason(s) for the weakening frequency of MDs in the southern Bay of Bengal in recent decades, we examine some of the seasonal average in-situ atmospheric parameters important for tropical cyclogenesis; we use various observational data from the IMD, and three atmospheric climate reanalysis datasets to account for possible quality constraints in them. Our findings suggest that the observed weakening of MD frequency south of 20°N in the Bay of Bengal since 1950s is likely due to a declining trend in the mid-tropospheric relative humidity over the Indian region. Our numerical sensitivity experiments support this finding. PMID:24141862

  4. Holocene biome shifts in the East Asian monsoon margin region

    NASA Astrophysics Data System (ADS)

    Dallmeyer, Anne; Claussen, Martin; Ni, Jian; Wang, Yongbo; Cao, Xianyong; Herzschuh, Ulrike

    2013-04-01

    East Asia is affected by three major atmospheric circulation systems determining the regional climate and vegetation distribution: The moisture advected by the Indian and East Asian monsoon support the growing of forest in large parts of Eastern China. The influence of the monsoon gets weaker further on the continent yielding a transition of forest to steppe and of steppe to desert in Central East Asia (e.g. Inner Mongolia) where the dry westerly winds prevail. Particularly in these transition zones, vegetation is supposed to be very sensitive to climate change and strong feedbacks are expected in case of climate and vegetation shifts due to large environmental changes (Feng et al., 2006). During mid-Holocene, cyclic variations in the Earth's orbit around the sun led to an enhancement of the Asian monsoon system probably causing strong shifts in the biome distribution. According to reconstructions, the steppe-forest margin moved to the northwest by about 500km (Yu et al., 2000) and the desert area in China and Inner Mongolia was substantially reduced compared to today (Feng et al., 2006). However, in the complex environment of Asia, the locally limited reconstructions may not portray the general vegetation change. To get a systematic overview on the spatial pattern of biome shifts in the Asian monsoon - westerly wind transition zone since mid-Holocene, we use the diagnostic vegetation model BIOME4 and force this model with climate anomalies from different transient Holocene climate simulations performed in coupled atmosphere-ocean-vegetation models. The main aims of this study are to a) get a consistent ensemble of possible changes in biome distribution since the mid-Holocene b) test the robustness of the simulated vegetation changes and quantify the differences between the models, and c) allow for a better comparison of simulated and reconstructed vegetation changes. Preliminary results confirm the general trend seen in the reconstructions. The simulations reveal

  5. Cloud distributions in a Bay of Bengal monsoon depression

    NASA Technical Reports Server (NTRS)

    Warner, C.; Grumm, R. H.

    1984-01-01

    Much of the volume of a monsoon depression studied over the Bay of Bengal on July 7, 1979 featured thin, fragmentary layers of stratus, implying an absence of strong vertical motion. Coverage by cumulus updrafts was about 20 times less than coverage by inert cumulus remnants, and a great number density of humilis was found moistening the central area, following subsidence and drying. Detailed observations were made of a cloud line growing out of the southwesterly flow south of the center of the depression, which propagated faster than the low level winds. Aircraft altimetry showed an abrupt height drop from 6097 to 6090 m at 483 hPa, over a distance of 50 km from southeast to northwest through the line. Southwesterly momentum was lifted from 900 to 600 hPa and from southeast to northwest through the line. Other colocated singularities in convection and wind fields were found.

  6. Characterizing the onset and demise of the Indian summer monsoon

    NASA Astrophysics Data System (ADS)

    Noska, Ryne; Misra, Vasubandhu

    2016-05-01

    An objective index of the onset and demise of the Indian summer monsoon (ISM) is introduced. This index has the advantage of simplicity by using only one variable, which is the spatially averaged all-India rainfall, a reliably observed quantity for more than a century. The proposed onset index is shown to be insensitive to all historic false onsets. By definition, now the seasonal mean rainfall anomalies become a function of variations in onset and demise dates, rendering their monitoring to be very meaningful. This new index provides a comprehensive representation of the seasonal evolution of the ISM by capturing the corresponding changes in large-scale dynamic and thermodynamic variables. We also show that the interannual variability of the onset date of the ISM is associated with El Niño-Southern Oscillation (ENSO) with early (late) onsets preceded by cold (warm) ENSO.

  7. Effect of El-Nino on Southwest Monsoon 2015

    NASA Astrophysics Data System (ADS)

    K. U., Vidhulakshmi; Mrudula, G.

    2016-05-01

    Indian Summer Monsoon Rainfall (ISMR) of 2015 showed a deficit of 14% in the seasonal rainfall. Many researchers connected this deficit to the El-Nino which developed in late May. In this study an analysis of major ENSO events and its influence on ISMR during the period 1975 till present have been carried out. The behavior of ISMR during the previous El-Nino/La-Nina years has been compared with that of 2015. Preliminary analysis shows the effects of El-Nino on ISMR of 2015 started mainly from July. This is attributed to Madden Julian Oscillation (MJO) by many scientists. Analysis of spatial and temporal correlations of SST of various Nino regions with the ISMR and of MJO will also be presented in detail.

  8. Remote Sensing of Arizona Monsoons: Application of GOES Infrared Imagery

    NASA Astrophysics Data System (ADS)

    Carter, S.; Christensen, P. R.; Cerveny, R. S.

    2013-12-01

    Large, violent thunder and dust storms occur in the Phoenix area during monsoon season. Currently, the best ways to predict these dangerous and potentially damaging storms are not very accurate. The primary goal of this investigation is to attempt to develop a new technique to identify and predict these storms before they reach Phoenix. In order to address this question, two data sets (remote sensing satellite imagery and ground-based weather information) will be analyzed and compared against one another using time as a corresponding variable. The goal is to discern any correlations between data sets which be used as an indicator of imminent large monsoons. The moisture needed for the storms is carried to Arizona by events known as gulf surges (from the California Gulf); these will be the target of investigation. These chutes of moisture surge through Arizona, primarily up through Yuma in a northeasterly direction towards central/south central Arizona. The main goal is to identify if satellite imagery can be used as an accurate identifier of moisture movements preceding a storm in areas where ground measurements are not available. Presently, ground measurements of dew points are the primary technique by which these moisture surges are identified. However, while these measurements do have a fairly high temporal resolution (once an hour) they cover an awfully poor spacial range. Furthermore, it is suspected that because of interference to the instruments, the ground point data may not be as accurate as is preferred. On the other hand, satellite imagery such as GOES - the instrument used in this investigation - has both a remarkably high temporal resolution and spacial coverage. If a correlation can be demonstrated, then the high temporal resolution of the remote sensing data could be used as an identifier of oncoming monsoon storms. In order to proceed in this research, a software package known as Java Mission-planning and Analysis for Remote Sensing (JMARS) for

  9. Logit-normal mixed model for Indian Monsoon rainfall extremes

    NASA Astrophysics Data System (ADS)

    Dietz, L. R.; Chatterjee, S.

    2014-03-01

    Describing the nature and variability of Indian monsoon rainfall extremes is a topic of much debate in the current literature. We suggest the use of a generalized linear mixed model (GLMM), specifically, the logit-normal mixed model, to describe the underlying structure of this complex climatic event. Several GLMM algorithms are described and simulations are performed to vet these algorithms before applying them to the Indian precipitation data procured from the National Climatic Data Center. The logit-normal model was applied with fixed covariates of latitude, longitude, elevation, daily minimum and maximum temperatures with a random intercept by weather station. In general, the estimation methods concurred in their suggestion of a relationship between the El Niño Southern Oscillation (ENSO) and extreme rainfall variability estimates. This work provides a valuable starting point for extending GLMM to incorporate the intricate dependencies in extreme climate events.

  10. Logit-normal mixed model for Indian monsoon precipitation

    NASA Astrophysics Data System (ADS)

    Dietz, L. R.; Chatterjee, S.

    2014-09-01

    Describing the nature and variability of Indian monsoon precipitation is a topic of much debate in the current literature. We suggest the use of a generalized linear mixed model (GLMM), specifically, the logit-normal mixed model, to describe the underlying structure of this complex climatic event. Four GLMM algorithms are described and simulations are performed to vet these algorithms before applying them to the Indian precipitation data. The logit-normal model was applied to light, moderate, and extreme rainfall. Findings indicated that physical constructs were preserved by the models, and random effects were significant in many cases. We also found GLMM estimation methods were sensitive to tuning parameters and assumptions and therefore, recommend use of multiple methods in applications. This work provides a novel use of GLMM and promotes its addition to the gamut of tools for analysis in studying climate phenomena.

  11. Monsoon drought over Java, Indonesia, during the past two centuries

    NASA Astrophysics Data System (ADS)

    D'Arrigo, Rosanne; Wilson, Rob; Palmer, Jonathan; Krusic, Paul; Curtis, Ashley; Sakulich, John; Bijaksana, Satria; Zulaikah, Siti; Ngkoimani, La Ode

    2006-02-01

    Monsoon droughts, which often coincide with El Niño warm events, can have profound impacts on the populations of Southeast Asia. Improved understanding and prediction of such events can be aided by high-resolution proxy climate records, but these are scarce for the tropics. Here we reconstruct the boreal autumn (October-November) Palmer Drought Severity Index (PDSI) for Java, Indonesia (1787-1988). This reconstruction is based on nine ring-width chronologies derived from living teak trees growing on the islands of Java and Sulawesi, and one coral δ18O series from Lombok. The PDSI reconstruction correlates significantly with El Niño-Southern Oscillation (ENSO)-related sea surface temperatures and other historical and instrumental records of tropical climate, reflecting the strong coupling between the climate of Indonesia and the large scale tropical Indo-Pacific climate system.

  12. The Genetic Structure and History of Africans and African Americans

    PubMed Central

    Tishkoff, Sarah A.; Reed, Floyd A.; Friedlaender, Françoise R.; Ehret, Christopher; Ranciaro, Alessia; Froment, Alain; Hirbo, Jibril B.; Awomoyi, Agnes A.; Bodo, Jean-Marie; Doumbo, Ogobara; Ibrahim, Muntaser; Juma, Abdalla T.; Kotze, Maritha J.; Lema, Godfrey; Moore, Jason H.; Mortensen, Holly; Nyambo, Thomas B.; Omar, Sabah A.; Powell, Kweli; Pretorius, Gideon S.; Smith, Michael W.; Thera, Mahamadou A.; Wambebe, Charles; Weber, James L.; Williams, Scott M.

    2010-01-01

    Africa is the source of all modern humans, but characterization of genetic variation and of relationships among populations across the continent has been enigmatic. We studied 121 African populations, four African American populations, and 60 non-African populations for patterns of variation at 1327 nuclear microsatellite and insertion/deletion markers. We identified 14 ancestral population clusters in Africa that correlate with self-described ethnicity and shared cultural and/or linguistic properties. We observed high levels of mixed ancestry in most populations, reflecting historical migration events across the continent. Our data also provide evidence for shared ancestry among geographically diverse hunter-gatherer populations (Khoesan speakers and Pygmies). The ancestry of African Americans is predominantly from Niger-Kordofanian (~71%), European (~13%), and other African (~8%) populations, although admixture levels varied considerably among individuals. This study helps tease apart the complex evolutionary history of Africans and African Americans, aiding both anthropological and genetic epidemiologic studies. PMID:19407144

  13. Acid Monsoonal Rains in Nepal in August 2008

    NASA Astrophysics Data System (ADS)

    Gazis, C. A.; Best, B.; Johnson, J.; Pratt-Sitaula, B.; Hodges, D.; Johansen, A. M.; Upreti, B.

    2010-12-01

    Monsoonal rains between the months of May and September constitute approximately 80% of Nepal’s annual precipitation, controlling river discharge and flooding patterns, sustaining native vegetation and agriculture, and influencing physical and chemical weathering rates. Acid rain events, if common during the monsoon season, could have significant impact on regional ecosystems as well as chemical weathering rates and patterns. In this study, precipitation samples were collected in August 2008 and August 2009 from a site in the town of Bhulbhule on the Marsyandi River in north-central Nepal. These samples were analyzed for pH, conductivity, major ion chemistry and trace element chemistry. In 2008, daily samples were collected between August 12 and August 25. Of these fourteen samples, eleven were acid rain, with pH between 4.1 and 4.8. The remaining three, collected between August 14 and August 16 had pH vaules between 6.6 and 7.0. In 2009, samples were collected again between August 12 and August 25. During the first four days of this interval, samples were collected after each precipitation event and thereafter they were collected daily. In 2009, all but one sample collected had a pH above 6.1 and five samples had values above 8.0. The lowest pH measured was 5.5. Major ion chemistry reveals a number of differences between the 2008 precipitation samples and the 2009 samples. For example, 2009 samples have higher K and Cl concentrations and thus tend to have lower Ca/K and SO4/Cl ratios. When comparing the acid rain and non-acid rain samples collected in 2008, the most distinct difference is the presence of PO4 in measurable amounts (0.2 to 1.1 ppm) in the acid rain samples. In this poster we discuss these differences in major ion chemistry in terms of local and regional weather patterns and potential ion sources.

  14. IODP Expedition 359: Maldives Monsoon and Sea Level

    NASA Astrophysics Data System (ADS)

    Betzler, Christian; Eberli, Gregor; Zarikian, Carlos

    2016-04-01

    Drilling the carbonate platforms and drifts in the Maldives aimed to recover the marine tropical record of the Neogene sea-level changes and the onset of the monsoon related current system in the Indian Ocean. To reach this goal, eight sites were drilled along two transects in the Kardiva Channel in the Inner Sea of the Maldives during IODP Expedition 359. The recovered cores and log data retrieved the material to achieve all the objectives set for the expedition. The most arresting accomplishment is the documentation of how the sea level controlled the carbonate platform system that was thriving during the Miocene Climate Optimum abruptly transitioned into a current-dominated system in the late Middle Miocene. This transition is linked to the onset of an early intensification of the Indian monsoon and the coeval demise of some of the Maldivian platforms. Cores and downhole logs allowed producing a solid record and reconstructing the Neogene environmental changes in the central Indian Ocean. Preliminary shipboard analyses allow a precise dating of this major paleoclimatological and paleoceanographical changes, as it also applies for the extension of the Oxygen Minimum Zone (OMZ) into this part of the Indian Ocean. Coring produced a solid framework to foster the post-cruise research of these distinct topics. In addition, complete spliced sections and logging at key sites during Expedition 359 provide the potential to assemble a cycle-based astrochronology for the Neogene section in the Maldives. This high-resolution chronology will allow: 1) independent ages to be assigned to key biostratigraphic events in the Maldives for comparison with those from other tropical regions; 2) more precise ages for the major sequence boundaries and unconformities; and 3) evaluation of higher-resolution sedimentation rate variations.

  15. Asian summer monsoon rainfall predictability: a predictable mode analysis

    NASA Astrophysics Data System (ADS)

    Wang, Bin; Lee, June-Yi; Xiang, Baoqiang

    2015-01-01

    To what extent the Asian summer monsoon (ASM) rainfall is predictable has been an important but long-standing issue in climate science. Here we introduce a predictable mode analysis (PMA) method to estimate predictability of the ASM rainfall. The PMA is an integral approach combining empirical analysis, physical interpretation and retrospective prediction. The empirical analysis detects most important modes of variability; the interpretation establishes the physical basis of prediction of the modes; and the retrospective predictions with dynamical models and physics-based empirical (P-E) model are used to identify the "predictable" modes. Potential predictability can then be estimated by the fractional variance accounted for by the "predictable" modes. For the ASM rainfall during June-July-August, we identify four major modes of variability in the domain (20°S-40°N, 40°E-160°E) during 1979-2010: (1) El Niño-La Nina developing mode in central Pacific, (2) Indo-western Pacific monsoon-ocean coupled mode sustained by a positive thermodynamic feedback with the aid of background mean circulation, (3) Indian Ocean dipole mode, and (4) a warming trend mode. We show that these modes can be predicted reasonably well by a set of P-E prediction models as well as coupled models' multi-model ensemble. The P-E and dynamical models have comparable skills and complementary strengths in predicting ASM rainfall. Thus, the four modes may be regarded as "predictable" modes, and about half of the ASM rainfall variability may be predictable. This work not only provides a useful approach for assessing seasonal predictability but also provides P-E prediction tools and a spatial-pattern-bias correction method to improve dynamical predictions. The proposed PMA method can be applied to a broad range of climate predictability and prediction problems.

  16. An Assessment of the Impact of the 1997-98 El Nino on the Asian-Australian Monsoon

    NASA Technical Reports Server (NTRS)

    Lau, K.-M.; Wu, H.-T.

    1999-01-01

    Using state-of-the-art satellite-gauge monthly rainfall estimate and optimally interpolated sea surface temperature (SST) data, we have assessed the 1997-98 AA-monsoon anomalies in terms of three basic causal factors: basin-scale SST, regional coupling, and internal variability. Singular Value Decomposition analyses of rainfall and SST are carried out globally over the entire tropics and regionally over the AA-monsoon domain. Contributions to monsoon rainfall predictability by various factors are evaluated from cumulative anomaly correlation with dominant regional SVD modes. Results reveal a dominant, large-scale monsoon-El Nino coupled mode with well-defined centers of action in the near-equatorial monsoon regions during the boreal summer and winter respectively. The observed 1997-98 AA-monsoon anomalies are found to be very complex with approximately 34% of the anomalies of the Asian (boreal) summer monsoon and 74% of the Australia (austral) monsoon attributable to basin-scale SST influence associated with El Nino. Regional coupled processes contribute an additional 19% and 10%, leaving about 47% and 16% due to internal dynamics for the boreal and austral monsoon respectively. For the boreal summer monsoon, it is noted that the highest monsoon predictability is not necessary associated with major El Nino events (e.g. 1997, 1982) but rather in non-El Nino years (e.g. 1980, 1988) when contributions from the regional coupled modes far exceed those from the basin-scale SST. The results suggest that in order to improve monsoon seasonal-to-interannual predictability, there is a need to exploit not only monsoon-El Nino relationship, but also intrinsic monsoon regional coupled processes.

  17. The Other African Americans.

    ERIC Educational Resources Information Center

    Matory, J. Lorand

    Black North America is ethnically and culturally diverse. It contains many groups who do not call themselves or have not always called themselves "Negro,""Black,""African-American," and so forth, such as Louisiana Creoles of color and many of the Indian tribes east of the Mississippi. There are also numerous North American ethnic groups of African…

  18. African Oral Tradition Literacy.

    ERIC Educational Resources Information Center

    Green, Doris

    1985-01-01

    Presents the basic principles of two systems for notating African music and dance: Labanotation (created to record and analyze movements) and Greenotation (created to notate musical instruments of Africa and to parallel Labanotation whereby both music and dance are incorporated into one integrated score). (KH)

  19. Elective: African Literature.

    ERIC Educational Resources Information Center

    Jenkins, Kenneth V.

    The make-up of a course in African literature for high school students is discussed. It is pointed out that the course can be constructed on already familiar lines. High school students will be able to describe clearly, for example, the relationship between environment and character or the dilemma of characters caught between traditional values…

  20. West Indian Ocean variability and East African fish catch.

    PubMed

    Jury, M; McClanahan, T; Maina, J

    2010-08-01

    We describe marine climate variability off the east coast of Africa in the context of fish catch statistics for Tanzania and Kenya. The time series exhibits quasi-decadal cycles over the period 1964-2007. Fish catch is up when sea surface temperature (SST) and atmospheric humidity are below normal in the tropical West Indian Ocean. This pattern relates to an ocean Rossby wave in one phase of its east-west oscillation. Coastal-scale analyses indicate that northward currents and uplift on the shelf edge enhance productivity of East African shelf waters. Some of the changes are regulated by the south equatorial current that swings northward from Madagascar. The weather is drier and a salty layer develops in high catch years. While the large-scale West Indian Ocean has some impact on East African fish catch, coastal dynamics play a more significant role. Climatic changes are reviewed using 200 years of past and projected data. The observed warming trend continues to increase such that predicted SST may reach 30 degrees C by 2100 while SW monsoon winds gradually increase, according to a coupled general circulation model simulation with a gradual doubling of CO(2). PMID:20471674

  1. Influence of 21st century atmospheric and sea surface temperature forcing on West African climate

    SciTech Connect

    Skinner, Chris B; Ashfaq, Moetasim; Diffenbaugh, Noah

    2011-01-01

    he persistence of extended drought events throughout West Africa during the 20th century has motivated a substantial effort to understand the mechanisms driving African climate variability, as well as the possible response to elevated greenhouse gas (GHG) forcing. We use an ensemble of global climate model experiments to examine the relative roles of future direct atmospheric radiative forcing and SST forcing in shaping potential future changes in boreal summer precipitation over West Africa. We find that projected increases in precipitation throughout the Western Sahel result primarily from direct atmospheric radiative forcing. The changes in atmospheric forcing generate a slight northward displacement and weakening of the African easterly jet (AEJ), a strengthening of westward monsoon flow onto West Africa and an intensification of the tropical easterly jet (TEJ). Alternatively, we find that the projected decreases in precipitation over much of the Guinea Coast region are caused by SST changes that are induced by the atmospheric radiative forcing. The changes in SSTs generate a weakening of the monsoon westerlies and the TEJ, as well as a decrease in low-level convergence and resultant rising air throughout the mid levels of the troposphere. Our experiments suggest a potential shift in the regional moisture balance of West Africa should global radiative forcing continue to increase, highlighting the importance of climate system feedbacks in shaping the response of regional-scale climate to global-scale changes in radiative forcing.

  2. Prediction and monitoring of monsoon intraseasonal oscillations over Indian monsoon region in an ensemble prediction system using CFSv2

    NASA Astrophysics Data System (ADS)

    Abhilash, S.; Sahai, A. K.; Borah, N.; Chattopadhyay, R.; Joseph, S.; Sharmila, S.; De, S.; Goswami, B. N.; Kumar, Arun

    2014-05-01

    An ensemble prediction system (EPS) is devised for the extended range prediction (ERP) of monsoon intraseasonal oscillations (MISO) of Indian summer monsoon (ISM) using National Centers for Environmental Prediction Climate Forecast System model version 2 at T126 horizontal resolution. The EPS is formulated by generating 11 member ensembles through the perturbation of atmospheric initial conditions. The hindcast experiments were conducted at every 5-day interval for 45 days lead time starting from 16th May to 28th September during 2001-2012. The general simulation of ISM characteristics and the ERP skill of the proposed EPS at pentad mean scale are evaluated in the present study. Though the EPS underestimates both the mean and variability of ISM rainfall, it simulates the northward propagation of MISO reasonably well. It is found that the signal-to-noise ratio of the forecasted rainfall becomes unity by about 18 days. The potential predictability error of the forecasted rainfall saturates by about 25 days. Though useful deterministic forecasts could be generated up to 2nd pentad lead, significant correlations are found even up to 4th pentad lead. The skill in predicting large-scale MISO, which is assessed by comparing the predicted and observed MISO indices, is found to be ~17 days. It is noted that the prediction skill of actual rainfall is closely related to the prediction of large-scale MISO amplitude as well as the initial conditions related to the different phases of MISO. An analysis of categorical prediction skills reveals that break is more skillfully predicted, followed by active and then normal. The categorical probability skill scores suggest that useful probabilistic forecasts could be generated even up to 4th pentad lead.

  3. Prediction and Monitoring of Monsoon Intraseasonal Oscillations over Indian Monsoon Region in an Ensemble Prediction System using CFSv2

    NASA Astrophysics Data System (ADS)

    Borah, N.; Abhilash, S.; Sahai, A. K.; Chattopadhyay, R.; Joseph, S.; Sharmila, S.; de, S.; Goswami, B.; Kumar, A.

    2013-12-01

    An ensemble prediction system (EPS) is devised for the extended range prediction (ERP) of monsoon intraseasonal oscillations (MISOs) of Indian summer monsoon (ISM) using NCEP Climate Forecast System model version2 at T126 horizontal resolution. The EPS is formulated by producing 11 member ensembles through the perturbation of atmospheric initial conditions. The hindcast experiments were conducted at every 5-day interval for 45 days lead time starting from 16th May to 28th September during 2001-2012. The general simulation of ISM characteristics and the ERP skill of the proposed EPS at pentad mean scale are evaluated in the present study. Though the EPS underestimates both the mean and variability of ISM rainfall, it simulates the northward propagation of MISO reasonably well. It is found that the signal-to-noise ratio becomes unity by about18 days and the predictability error saturates by about 25 days. Though useful deterministic forecasts could be generated up to 2nd pentad lead, significant correlations are observed even up to 4th pentad lead. The skill in predicting large-scale MISO, which is assessed by comparing the predicted and observed MISO indices, is found to be ~17 days. It is noted that the prediction skill of actual rainfall is closely related to the prediction of amplitude of large scale MISO as well as the initial conditions related to the different phases of MISO. Categorical prediction skills reveals that break is more skillfully predicted, followed by active and then normal. The categorical probability skill scores suggest that useful probabilistic forecasts could be generated even up to 4th pentad lead.

  4. Prediction and Monitoring of Monsoon Intraseasonal Oscillations over Indian Monsoon Region in an Ensemble Prediction System using CFSv2

    NASA Astrophysics Data System (ADS)

    Borah, Nabanita; Sukumarpillai, Abhilash; Sahai, Atul Kumar; Chattopadhyay, Rajib; Joseph, Susmitha; De, Soumyendu; Nath Goswami, Bhupendra; Kumar, Arun

    2014-05-01

    An ensemble prediction system (EPS) is devised for the extended range prediction (ERP) of monsoon intraseasonal oscillations (MISO) of Indian summer monsoon (ISM) using NCEP Climate Forecast System model version2 at T126 horizontal resolution. The EPS is formulated by producing 11 member ensembles through the perturbation of atmospheric initial conditions. The hindcast experiments were conducted at every 5-day interval for 45 days lead time starting from 16th May to 28th September during 2001-2012. The general simulation of ISM characteristics and the ERP skill of the proposed EPS at pentad mean scale are evaluated in the present study. Though the EPS underestimates both the mean and variability of ISM rainfall, it simulates the northward propagation of MISO reasonably well. It is found that the signal-to-noise ratio becomes unity by about18 days and the predictability error saturates by about 25 days. Though useful deterministic forecasts could be generated up to 2nd pentad lead, significant correlations are observed even up to 4th pentad lead. The skill in predicting large-scale MISO, which is assessed by comparing the predicted and observed MISO indices, is found to be ~17 days. It is noted that the prediction skill of actual rainfall is closely related to the prediction of amplitude of large scale MISO as well as the initial conditions related to the different phases of MISO. Categorical prediction skills reveals that break is more skillfully predicted, followed by active and then normal. The categorical probability skill scores suggest that useful probabilistic forecasts could be generated even up to 4th pentad lead.

  5. Monsoon rainfall interannual variability over China and its association with the Euasian circulation

    SciTech Connect

    Samel, A.N.; Wang, Wei-Chyung

    1997-11-01

    This study has two goals. The first is to determine annual observed initial and final dates of east Asian summer monsoon rainfall. To accomplish this, a semi-objective analysis is developed and applied to daily rainfall station data throughout China. The resulting values are used to calculate monsoon duration and total rainfall. The second goal is to identify relationships between these rainfall characteristics and circulation features in the Eurasian sea level pressure. The analysis of the duration of monsoon rainfall events produced results that are consistent with those found in previous studies. Total monsoon rainfall over south China, the Yangtze River valley, and north China was then correlated with the Eurasian sea level pressure and 500 millibar height fields. The results indicate that summer rainfall interannual variability over each region is governed by the interaction of several circulation features. These findings are also consistent with those of other studies. 18 refs., 5 figs.

  6. Role of transport in elevated CO levels over Delhi during onset phase of monsoon

    NASA Astrophysics Data System (ADS)

    Srinivas, Reka; Beig, Gufran; Peshin, Sunil K.

    2016-09-01

    While local anthropogenic emission sources contribute significantly to pollutant levels in a megacity Delhi, meteorology can significantly modulate carbon monoxide (CO) levels. We hereby demonstrate that the concentration of CO during the unusual onset of monsoon 2013 was dramatically elevated and crossed the permissible limit (1.7 ppmv) for about a month long-period as against normal onset of monsoon where CO concentration generally drops down significantly. We compare level of CO in 2013 with normal monsoon year 2012. We provide a hypothesis to interpret this long lasting high concentration CO episode and validate using interactive high resolution WRF-Chem model. The model indicates that the high CO episode was caused by an unusually active Bay of Bengal branch of monsoon which bounces off from the east and transports CO rich air from the eastern part of the Indo Gangetic Plains to Delhi.

  7. Observational Evidence of Impacts of Aerosols on Seasonal-to-Interannual Variability of the Asian Monsoon

    NASA Technical Reports Server (NTRS)

    Lau, K.-M.; Kim, K.-M.; Hsu, N. C.

    2006-01-01

    Observational evidences are presented showing that the Indian subcontinent and surrounding regions are subject to heavy loading of absorbing aerosols (dust and black carbon), with strong seasonality closely linked to the monsoon annual rainfall cycle. Increased loading of absorbing aerosols over the Indo-Gangetic Plain in April-May is associated with a) increased heating of the upper troposphere over the Tibetan Plateau, b) an advance of the monsoon rainy season, and c) subsequent enhancement of monsoon rainfall over the South Asia subcontinent, and reduction over East Asia. Also presented are radiative transfer calculations showing how differential solar absorption by aerosols over bright surface (desert or snow cover land) compared to dark surface (vegetated land and ocean), may be instrumental in triggering an aerosol-monsoon large-scale circulation and water cycle feedback, consistent with the elevated heat pump hypothesis (Lau et al. 2006).

  8. Precipitation-aerosol relationship over the Indian region during drought and excess summer monsoon years

    NASA Astrophysics Data System (ADS)

    Surendran, Sajani; Rajendran, Kavirajan; V. B., Arya

    2016-05-01

    This study investigates the aerosols-rainfall interaction during Indian summer monsoon and characterizes their difference in drought and excess summer monsoon years, based on MODIS (MODerate Resolution Imaging Spectro-radiometer) derived Aerosol Optical Depth (AOD) at 550 nm. AOD has been estimated using Level-2 MODIS Terra Data Version 6. AOD in drought years is found to be higher over India compared to excess monsoon years. The total effect of aerosols causes reduction of summer rainfall but with distinct differences in their impact during strong and weak summer monsoon years, due to the changes in clouds, radiation, large-scale circulation, and convection. Aerosol and cloud characteristics exhibit strong association to rainfall variability in interannual time scales. Variability in cloud effective radius and cloud optical thickness is found to be consistent with aerosol effect.

  9. GCM Simulation of the Large-Scale North American Monsoon Including Water Vapor Tracer Diagnostics

    NASA Technical Reports Server (NTRS)

    Bosilovich, Michael G.; Walker, Gregory; Schubert, Siegfried D.; Sud, Yogesh; Atlas, Robert M. (Technical Monitor)

    2002-01-01

    The geographic sources of water for the large scale North American monsoon in a GCM (General Circulation Model) are diagnosed using passive constituent tracers of regional water sources (Water Vapor Tracers, WVT). The NASA Data Assimilation Office Finite Volume (FV) GCM was used to produce a 10-year simulation (1984 through 1993) including observed sea surface temperature. Regional and global WVT sources were defined to delineate the surface origin of water for precipitation in and around the North American Monsoon. The evolution of the mean annual cycle and the interannual variations of the monsoonal circulation will be discussed. Of special concern are the relative contributions of the local source (precipitation recycling) and remote sources of water vapor to the annual cycle and the interannual variation of monsoonal precipitation. The relationships between soil water, surface evaporation, precipitation and precipitation recycling will be evaluated.

  10. Orographic insulation in the South Asian summer monsoon: mean state and model bias

    NASA Astrophysics Data System (ADS)

    Boos, W.; Kuang, Z.; Hurley, J. V.

    2012-12-01

    Monsoons are thermally direct, continental-scale circulations that supply water to billions of people, so controls on the intensity and location of monsoons are widely studied. Here we discuss several aspects of the interaction of orography with the South Asian summer monsoon. We begin by reviewing the observed thermodynamic mean state of this monsoon, and explain how it motivates the hypothesis that orography creates a strong monsoon by preventing the intrusion of cold and dry extratropical air into the monsoon thermal maximum. This hypothesis contrasts sharply with the long-standing view that the South Asian summer monsoon is driven by elevated heating from the Tibetan Plateau, but numerical model results confirm that the monsoon remains largely unchanged when the plateau heat source is eliminated. Next we show that almost all models participating in the Coupled Model Intercomparison Project (CMIP) exhibit a common bias in the thermodynamic structure of the South Asian summer monsoon that is caused by a poor representation of orography. In most CMIP models, the simulated Asian upper-tropospheric temperature maximum is too weak during summer and is displaced southeast of its observed location over northwest India; maxima of surface air moist static energy are also too weak and displaced to the southeast. The spatial structure of this bias and its relation to low-level wind suggest that it is caused by an overly smoothed representation of topography west of the Tibetan Plateau, which allows dry air from the deserts of western Asia to pass over topography and penetrate the thermal maximum. A model with a decent representation of the thermodynamic state of the Asian monsoon is integrated with standard topography and then with truncated topography just west of the Tibetan Plateau. This relatively minor modification recreates the thermodynamic bias seen in the CMIP models; it also reduces precipitation over India in simulations of modern climate and reduces the next

  11. Spacebased Observations of the Oceanic Responses to Monsoons in South China Sea and Arabian Sea

    NASA Technical Reports Server (NTRS)

    Xie, Xiao-Su; Liu, W. Timothy

    2000-01-01

    A large percentage of the world's population and their agrarian economy must endure the vagaries of the monsoons over the tropical oceans between Africa and the Philippines. We know very little about the oceanic responses to changes of the monsoon in the South China Sea (SCS), which is under the influence of the East Asian Monsoon System, and the Arabian Sea (AS), which is dominated by the Indian Monsoon System; oceanic observations are sparse in both regions. Data from spaceborne microwave scatterometers and radiometers have been used to estimate the two major atmospheric forcing, momentum flux and latent heat flux (LHF), which change with the monsoon winds. Spaceborne sensors also observed the surface signatures of the oceanic response: SST and sea level changes (SLC. Sufficient durations of these data have recently become available to allow the meaningful studies of the annual cycles and interannual anomalies. In SCS, the winter monsoon is strong and steady but the summer monsoon is weak and has large intraseasonal fluctuations. In AS, the summer monsoon is much stronger than the winter monsoon. Significant correlations between LHF and SST tendency, and between curl of wind stress and SLC are found in both oceans. In the north SCS, winds are strong and dry, LHF is high, and ocean cooling is also large in fall; LHF is low and the ocean warms up in spring. In AS, LHF and SST tendency have a semi annual period; LHF is high in summer when the wind is strong and in winter when the wind is dry. Along the coast of Oman, the strong summer southwest monsoon causes intense upwelling, low SST and LHF in summer; such wind-driven SST changes is not as obvious along the Vietnam coast because of the weaker summer monsoon. The negative correlation between curl of wind stress and SLC found in the central basins of both SCS and AS agrees with a simple Ekman pumping scenario. Cyclonic winds drive surface divergence and upwelling in the ocean; the rise of the thermocline causes

  12. The concept of global monsoon applied to the last glacial maximum: A multi-model analysis

    NASA Astrophysics Data System (ADS)

    Jiang, Dabang; Tian, Zhiping; Lang, Xianmei; Kageyama, Masa; Ramstein, Gilles

    2015-10-01

    The last glacial maximum (LGM, ca. 21,000 years ago) has been extensively investigated for better understanding of past glacial climates. Global-scale monsoon changes, however, have not yet been determined. In this study, we examine global monsoon area (GMA) and precipitation (GMP) as well as GMP intensity (GMPI) at the LGM using the experiments of 17 climate models chosen from the Paleoclimate Modelling Intercomparison Project (PMIP) according to their ability to reproduce the present global monsoon climate. Compared to the reference period (referring to the present day, ca. 1985, for three atmospheric plus two atm-slab ocean models and the pre-industrial period, ca. 1750, for 12 fully coupled atmosphere-ocean or atmosphere-ocean-vegetation models), the LGM monsoon area increased over land and decreased over the oceans. The boreal land monsoon areas generally shifted southward, while the northern boundary of land monsoon areas retreated southward over southern Africa and South America. Both the LGM GMP and GMPI decreased in most of the models. The GMP decrease mainly resulted from the reduced monsoon precipitation over the oceans, while the GMPI decrease was derived from the weakened intensity of monsoon precipitation over land and the boreal ocean. Quantitatively, the LGM GMP deficit was due to, first, the GMA reduction and, second, the GMPI weakening. In response to the LGM large ice sheets and lower greenhouse gas concentrations in the atmosphere, the global surface and tropospheric temperatures cooled, the boreal summer meridional temperature gradient increased, and the summer land-sea thermal contrast at 40°S - 70°N decreased. These are the underlying dynamic mechanisms for the LGM monsoon changes. Qualitatively, simulations agree with reconstructions in all land monsoon areas except in the western part of northern Australia where disagreements occur and in South America and the southern part of southern Africa where there is uncertainty in reconstructions

  13. The timing and duration of the Last Interglacial Asian Monsoon

    NASA Astrophysics Data System (ADS)

    Yuan, D.; Cheng, H.; Edwards, R.; Kelly, M.; Qing, J.; Lin, Y.; Zhang, M.

    2002-12-01

    An accurate estimate for the timing and duration of regional and global climate change associated with the Last Interglacial is important for elucidating climate change mechanisms. We present a 230Th-dated δ18O record of 2 stalagmites (D3 and D4) from Dongge Cave, southern China (25°N, 109°E, an area affected by East Asian and Indian Monsoons), which record Asian Monsoon history over 3 periods, 160-110 ka, 65-43 ka and 15.5 ka - present. The stalagmites have different precipitation environments and water flow paths as indicated by different growth histories, growth rates and δ234U values. D3 grew faster between 123-118 ka (12 vs. 0.4 cm/ka), but D4 grew faster between 138-126 ka (3.4 vs. 0.7 cm/ka). The mean initial δ234U value of D3 is -272 (range of -261 to -287). D4 values are higher (mean = -78, range of -27 to -160). Despite these differences, both have similar large δ18O variations for the interval over which both were active (148 to 113 ka), suggesting that water-rock interactions and kinetic fractionation did not affect δ18O values significantly. Dongge Cave stalagmites exhibit features similar to the Younger Dryas (YD) and the Bolling/Allerod as recorded in Greenland ice cores (GISP, 1997) and stalagmites from Hulu Cave, eastern China (Wang et al., 2001). The Dongge YD lies between 12640 +/-140 and 11550 +/-80 years BP, synchronous with Greenland and Hulu Cave YD analogues. Similar to Hulu Cave, light Dongge Cave δ18O excursions correspond to heavy isotopic excursions in Greenland, consistent with a positive correlation between the intensity of the Asian summer monsoon and Greenland temperature. The most prominent feature in the Dongge record is a peak that approximates a square wave and is contemporaneous with at least portions of the Last Interglacial sea level high. Dongge Termination II is a large, abrupt negative shift in δ18O (>3 per mil). The mid-point is at 129.3 +/-0.9 ka, based on direct dating of D4. D3 gives an age indistinguishable

  14. Empirical Orthogonal Function (EOF) analysis of monsoon rainfall and satellite-observed outgoing long-wave radiation for Indian monsoon: a comparative study

    NASA Astrophysics Data System (ADS)

    Singh, C. V.

    The present study involves the use of Empirical Orthogonal Function (EOF) analysis/Principal Component Analysis (PCA) to compare the dominant rainfall patterns from normal rainfall records over India, coupled with the major modes of the Outgoing Long-wave Radiation (OLR) data for the period (1979-1988) during the monsoon period (June-September). To understand the intraseasonal and interannual variability of the monsoon rainfall, daily and seasonal anomalies have been obtained by using the (EOF) analysis. Importantly, pattern characteristics of seasonal monsoon rainfall covering 68 stations in India are highlighted. The purpose is to ascertain the nature of rainfall distribution over the Indian continent. Based on this, the percentage of variance for both the rainfall and OLR data is examined. OLR has a higher spatial coherence than rainfall. The first principal component of rainfall data shows high positive values, which are concentrated over northeast as well as southeast, whereas for the OLR, the area of large positive values is concentrated over northwest and lower value over south India apart from the Indian ocean. The first five principal components explain 92.20% of the total variance for the rainfall and 99.50% of the total variance for the outgoing long-wave radiation. The relationship between monsoon rainfall and Southern Oscillations has also been examined and for the Southern Oscillations, it is 0.69 for the monsoon season. The El-Niño events mostly occurred during Southern Oscillations, i.e. Walker circulation. It has been found that the average number of low pressure system/low pressure system days play an important role during active (flood) or inactive (drought) monsoon year, but low pressure system days play more important role in comparison to low pressure systems and their ratio are (16:51) and (13:25) respectively. Significantly, the analysis identifies the spatial and temporal pattern characteristics of possible physical significance.

  15. GMMIP (v1.0) contribution to CMIP6: Global Monsoons Model Inter-comparison Project

    NASA Astrophysics Data System (ADS)

    Zhou, Tianjun; Turner, Andrew G.; Kinter, James L.; Wang, Bin; Qian, Yun; Chen, Xiaolong; Wu, Bo; Wang, Bin; Liu, Bo; Zou, Liwei; He, Bian

    2016-10-01

    The Global Monsoons Model Inter-comparison Project (GMMIP) has been endorsed by the panel of Coupled Model Inter-comparison Project (CMIP) as one of the participating model inter-comparison projects (MIPs) in the sixth phase of CMIP (CMIP6). The focus of GMMIP is on monsoon climatology, variability, prediction and projection, which is relevant to four of the "Grand Challenges" proposed by the World Climate Research Programme. At present, 21 international modeling groups are committed to joining GMMIP. This overview paper introduces the motivation behind GMMIP and the scientific questions it intends to answer. Three tiers of experiments, of decreasing priority, are designed to examine (a) model skill in simulating the climatology and interannual-to-multidecadal variability of global monsoons forced by the sea surface temperature during historical climate period; (b) the roles of the Interdecadal Pacific Oscillation and Atlantic Multidecadal Oscillation in driving variations of the global and regional monsoons; and (c) the effects of large orographic terrain on the establishment of the monsoons. The outputs of the CMIP6 Diagnostic, Evaluation and Characterization of Klima experiments (DECK), "historical" simulation and endorsed MIPs will also be used in the diagnostic analysis of GMMIP to give a comprehensive understanding of the roles played by different external forcings, potential improvements in the simulation of monsoon rainfall at high resolution and reproducibility at decadal timescales. The implementation of GMMIP will improve our understanding of the fundamental physics of changes in the global and regional monsoons over the past 140 years and ultimately benefit monsoons prediction and projection in the current century.

  16. Late Miocene Pliocene intensification of the East Asian monsoon linked to Antarctic ice-sheet development

    NASA Astrophysics Data System (ADS)

    Ao, H.; An, Z.; Dekkers, M. J.; Liu, X.

    2013-12-01

    Recent evidence indicates that an East Asian monsoon broadly similar to the present may have occurred in China as early as the late Oligocene or early Miocene, but its variability and possible driving forces prior to the Quaternary epoch remain poorly known, due to rare reconstructions of continuous long-term East Asian monsoon records extending to the earlier periods. Here we report Late MiocenePliocene records of magnetic property variations of an eolian red clay sequence on the eastern Chinese Loess Plateau, which is dated using magnetostratigraphy. The high-resolution magnetic records indicate a long-term increasing trend in the East Asian summer monsoon intensity from ca 8 to 2.6 Ma. This is supported by studies from central Chinese Loess Plateau and South China Sea. We further find that this Late MiocenePliocene monsoon intensification is broadly correlated the long-term increasing trend in the Southern Hemisphere ice volume, suggesting a possible linkage between them. Combing a numerical climate-model experiment that simulates the East Asian summer monsoonal responses to the idealized stepwise increases of ice sheets from East to West Antarctic, we suggested that the Southern Hemisphere ice-sheet development is a driver of this late MiocenePliocene intensification of the East Asian summer monsoon. The Southern Hemisphere ice-sheet development could have intensified the East Asian monsoon mainly via weakening the low pressures over Asia and enhancing the high pressures over western Pacific Ocean and Australia, implying sensitivity of the Asian monsoon to the interhemispheric temperature gradient modulated by Southern Hemisphere climate.

  17. Propagation of Mesoscale Convective Systems over India in the Boreal Summer Monsoon Season

    NASA Astrophysics Data System (ADS)

    Phadtare, J. A.; Bhat, G. S.

    2015-12-01

    With an automated cloud tracking algorithm, we have analysed the propagation of mesoscale convective systems (MCSs) over Indian region in the boreal summer monsoon season (June-September). We used half hourly infrared images of a geostationary satellite KALPANA-I for the study. The data covers four monsoon seasons (2010,12,13,and 14). Mesoscale convective systems (MCSs) over the Indian land show a prominent westward propagation, which is opposite to the lower tropospheric monsoonal westerlies. The mechanism associated with these propagations seems robust, i.e. it appears in all the events. The propagation seems to be a result of internal dynamics of MCS, and not forced by any external agent. The mechanism is prevalent through out the monsoon season, but absent in pre- and post-monsoon season. The zonal convective streaks associated with the large MCSs have a spatial and temporal scales of 1000 km and 1 day respectively, with a westward speed of 18 m/s. These streaks resemble the westward propagating inertial-gravity (WIG) type of wave propagation. Thus, we speculate that, the MCSs over India in the summer monsoon season trigger WIG waves. And the subsequent propagation of MCS is coupled to this wave signal. Most of the large MCSs are associated with the synoptic scale monsoon depressions. Mean propagation of MCSs over Bay of Bengal (BoB) is of more complex nature. There seems to be more than one propagation mechanism which are active over BoB in the summer monsoon season. The selection of propagation mechanism by the BoB MCSs might depend on the phase of diurnal cycle or intra-seasonal oscillation, MCS size, and its location over the bay.

  18. Southern Hemisphere forcing of Pliocene δ18O and the evolution of Indo-Asian monsoons

    NASA Astrophysics Data System (ADS)

    Clemens, Steven C.; Prell, Warren L.; Sun, Youbin; Liu, Zhengyu; Chen, Guangshan

    2008-12-01

    The Milankovitch paradigm links the timing (phase) of ice volume minima to summer insolation maxima in the hemisphere where ice volume dominates; consistent application of this paradigm dictates that Pliocene ice volume minima should lag Southern Hemisphere summer insolation maxima. We infer the magnitude of this lag on the basis of the phase relationship between equatorial sea surface temperature and benthic δ18O. We infer that Pliocene δ18O minima should lag obliquity maxima by 19° (2.2 ka), broadly consistent with the current global marine δ18O chronology, and precession maxima by 32° (2 ka), a difference of 160° (10.2 ka) relative to the current global marine δ18O chronology. Only in the context of this revision are Pliocene summer and winter monsoon phase relationships consistent with direct orbital forcing across the entire Indo-Asian region, including marine and terrestrial proxies from the Chinese Loess Plateau, the South China Sea, and the Arabian Sea. Strong Pliocene summer and winter monsoons were in phase with one another, strengthened at obliquity minima and precession minima; the summer monsoon was also strengthened at precession maxima, yielding a semiprecession spectral signal. Strong Pliocene monsoons at orbital extremes indicate a direct response to fast physics processes including sensible heating and cooling of the Asian landmass and, for the summer monsoon, the export of latent heat from the southern Indian Ocean. As Northern Hemisphere ice volume grew into the Pleistocene, the timing of strong winter and summer monsoons drifted apart becoming influenced by the combined effects of fast physics and slow physics (ice volume) variables. The phase of strong winter monsoons shifted toward ice maxima, and the phase of strong summer monsoons shifted toward ice minima.

  19. Cyclone trends constrain monsoon variability during Late Oligocene sea level highstands (Kachchh Basin, NW India)

    NASA Astrophysics Data System (ADS)

    Reuter, M.; Piller, W. E.; Harzhauser, M.; Kroh, A.

    2013-01-01

    Important concerns about the consequences of climate change for India are the potential impact on tropical cyclones and the monsoon. Herein we present a sequence of fossil shell beds from the shallow-marine Maniyara Fort Formation (Kachcch Basin) as an indicator of tropical cyclone activity along the NW Indian coast during the Late Oligocene warming period (~27-24 Ma). Direct proxies providing information about the atmospheric circulation dynamics over the Indian subcontinent at this time are important since it corresponds to a major climate reorganization in Asia that ends up with the establishment of the modern Asian monsoon system in the Early Miocene. The vast shell concentrations comprise a mixture of parautochthonous and allochthonous assemblages indicating storm-generated sediment transport from deep to shallow water during third-order sea level highstands. Three distinct skeletal assemblages were distinguished each recording a relative storm wave base depth. (1) A shallow storm wave base is shown by nearshore mollusks, corals and Clypeaster echinoids; (2) an intermediate storm wave base depth is indicated by lepidocyclind foraminifers, Eupatagus echinoids and corallinaceans; and (3) a deep storm wave base is represented by an Amussiopecten-Schizaster echinoid assemblage. Vertical changes in these skeletal associations give evidence of gradually increasing tropical cyclone intensity in line with third-order sea level rise. The intensity of cyclones over the Arabian Sea is primarily linked to the strength of the Indian monsoon. Therefore and since the topographic boundary conditions for the Indian monsoon already existed in the Late Oligocene, the longer-term cyclone trends were interpreted to reflect monsoon variability during the initiation of the Asian monsoon system. Our results imply an active monsoon over the Eastern Tethys at ~26 Ma followed by a period of monsoon weakening during the peak of the Late Oligocene global warming (~24 Ma).

  20. Cyclone trends constrain monsoon variability during late Oligocene sea level highstands (Kachchh Basin, NW India)

    NASA Astrophysics Data System (ADS)

    Reuter, M.; Piller, W. E.; Harzhauser, M.; Kroh, A.

    2013-09-01

    Climate change has an unknown impact on tropical cyclones and the Asian monsoon. Herein we present a sequence of fossil shell beds from the shallow-marine Maniyara Fort Formation (Kachcch Basin) as a recorder of tropical cyclone activity along the NW Indian coast during the late Oligocene warming period (~ 27-24 Ma). Proxy data providing information about the atmospheric circulation dynamics over the Indian subcontinent at this time are important since it corresponds to a major climate reorganization in Asia that ends up with the establishment of the modern Asian monsoon system at the Oligocene-Miocene boundary. The vast shell concentrations are comprised of a mixture of parautochthonous and allochthonous assemblages indicating storm-generated sediment transport from deeper to shallow water during third-order sea level highstands. Three distinct skeletal assemblages were distinguished, each recording a relative storm wave base. (1) A shallow storm wave base is shown by nearshore molluscs, reef corals and Clypeaster echinoids; (2) an intermediate storm wave base depth is indicated by lepidocyclinid foraminifers, Eupatagus echinoids and corallinacean algae; and (3) a deep storm wave base is represented by an Amussiopecten bivalve-Schizaster echinoid assemblage. These wave base depth estimates were used for the reconstruction of long-term tropical storm intensity during the late Oligocene. The development and intensification of cyclones over the recent Arabian Sea is primarily limited by the atmospheric monsoon circulation and strength of the associated vertical wind shear. Therefore, since the topographic boundary conditions for the Indian monsoon already existed in the late Oligocene, the reconstructed long-term cyclone trends were interpreted to reflect monsoon variability during the initiation of the Asian monsoon system. Our results imply an active monsoon over the Eastern Tethys at ~ 26 Ma followed by a period of monsoon weakening during the peak of the late

  1. Future change of the global monsoon revealed from 19 CMIP5 models

    NASA Astrophysics Data System (ADS)

    Hsu, Pang-Chi; Li, Tim; Murakami, Hiroyuki; Kitoh, Akio

    2013-02-01

    The variability of global monsoon area (GMA), global monsoon precipitation (GMP), and global monsoon intensity (GMI) in the present climate (1979-2003) and the future warmer climate (2075-2099) under Representative Concentration Pathways 4.5 (RCP4.5) scenario was examined based on 19 Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations. In the present-day simulations, the ensemble mean precipitation reproduces the observed GMA, GMP, and GMI, although the spread of individual models is large. In the RCP4.5 simulations, most (17 of 19) of the CMIP5 models project enhanced global monsoon activity, with the increases of GMA, GMP, and GMI by 1.9%, 3.2%, and 1.3%, respectively, per 1 K of surface warming. The diagnosis of a column-integrated moisture budget indicates that the increase in GMP is primarily attributed to the increases of moisture convergence and surface evaporation, whereas horizontal moisture advection has little effect. A further separation of dynamic and thermodynamic factors shows that increase of the moisture convergence comes mainly from the increase of water vapor, but is partly offset by the convergence effect. The increase of the surface evaporation is caused by the increase of sea-air specific humidity difference, while the change in surface wind speed plays a minor role. The GMP experiences a great year-to-year variation, and it is significantly negatively correlated with the Niño3.4 index averaged over a typical monsoon year (defined from May to the following April) in the pre-industrial control and present-day simulations, similar to observations. Under the RCP4.5 warming, such rainfall variability is intensified, and the relationship between monsoon and El Niño strengthens. A large proportion of intensification in the year-to-year monsoon rainfall variability arises from the land monsoon region.

  2. Seasonally asymmetric transition of the Asian monsoon in response to ice age boundary conditions

    NASA Astrophysics Data System (ADS)

    Ueda, Hiroaki; Kuroki, Harumitsu; Ohba, Masamichi; Kamae, Youichi

    2011-12-01

    Modulation of a monsoon under glacial forcing is examined using an atmosphere-ocean coupled general circulation model (AOGCM) following the specifications established by Paleoclimate Modelling Intercomparison Project phase 2 (PMIP2) to understand the air-sea-land interaction under different climate forcing. Several sensitivity experiments are performed in response to individual changes in the continental ice sheet, orbital parameters, and sea surface temperature (SST) in the Last Glacial Maximum (LGM: 21 ka) to evaluate the driving mechanisms for the anomalous seasonal evolution of the monsoon. Comparison of the model results in the LGM with the pre-industrial (PI) simulation shows that the Arabian Sea and Bay of Bengal are characterized by enhancement of pre-monsoon convection despite a drop in the SST encompassing the globe, while the rainfall is considerably suppressed in the subsequent monsoon period. In the LGM winter relative to the PI, anomalies in the meridional temperature gradient (MTG) between the Asian continents minus the tropical oceans become positive and are consistent with the intensified pre-monsoon circulation. The enhanced MTG anomalies can be explained by a decrease in the condensation heating relevant to the suppressed tropical convection as well as positive insolation anomalies in the higher latitude, showing an opposing view to a warmer future climate. It is also evident that a latitudinal gradient in the SST across the equator plays an important role in the enhancement of pre-monsoon rainfall. As for the summer, the sensitivity experiments imply that two ice sheets over the northern hemisphere cools the air temperature over the Asian continent, which is consistent with the reduction of MTG involved in the attenuated monsoon. The surplus pre-monsoon convection causes a decrease in the SST through increased heat loss from the ocean surface; in other words, negative ocean feedback is also responsible for the subsequent weakening of summer

  3. Climatic controls on central African hydrology during the past 20,000 years.

    PubMed

    Schefuss, Enno; Schouten, Stefan; Schneider, Ralph R

    2005-10-13

    Past hydrological changes in Africa have been linked to various climatic processes, depending on region and timescale. Long-term precipitation changes in the regions of northern and southern Africa influenced by the monsoons are thought to have been governed by precessional variations in summer insolation. Conversely, short-term precipitation changes in the northern African tropics have been linked to North Atlantic sea surface temperature anomalies, affecting the northward extension of the Intertropical Convergence Zone and its associated rainbelt. Our knowledge of large-scale hydrological changes in equatorial Africa and their forcing factors is, however, limited. Here we analyse the isotopic composition of terrigenous plant lipids, extracted from a marine sediment core close to the Congo River mouth, in order to reconstruct past central African rainfall variations and compare this record to sea surface temperature changes in the South Atlantic Ocean. We find that central African precipitation during the past 20,000 years was mainly controlled by the difference in sea surface temperatures between the tropics and subtropics of the South Atlantic Ocean, whereas we find no evidence that changes in the position of the Intertropical Convergence Zone had a significant influence on the overall moisture availability in central Africa. We conclude that changes in ocean circulation, and hence sea surface temperature patterns, were important in modulating atmospheric moisture transport onto the central African continent.

  4. Short-term modulation of Indian summer monsoon rainfall by West Asian dust

    SciTech Connect

    Vinoj, V.; Rasch, Philip J.; Wang, Hailong; Yoon, Jin-Ho; Ma, Po-Lun; Landu, Kiranmayi; Singh, Balwinder

    2014-03-16

    The Indian summer monsoon is the result of a complex interplay between radiative heating, dynamics and cloud and aerosol interactions. Despite increased scientific attention, the effect of aerosols on monsoons still remains uncertain. Here we present both observational evidence and numerical modeling results demonstrating a remote aerosol link to Indian summer monsoon rainfall. Rainfall over central India is positively correlated to natural aerosols over the Arabian Sea and West Asia. Simulations using a state-of-the-art global climate model support this remote aerosol link and indicate that dust aerosols induce additional moisture transport and convergence over Central India, producing increased monsoon rainfall. The convergence is driven through solar heating and latent heating within clouds over West Asia that increases surface winds over the Arabian Sea. On the other hand, sea-salt aerosol tends to counteract the effect of dust and reduces rainfall. Our findings highlight the importance of natural aerosols in modulating the strength of the Indian summer monsoon, and motivate additional research in how changes in background aerosols of natural origin may be influencing long-term trends in monsoon precipitation.

  5. Catastrophic drought in East Asian monsoon region during Heinrich event 1

    NASA Astrophysics Data System (ADS)

    Zhou, Xin; Sun, Liguang; Chu, Yangxi; Xia, Zehui; Zhou, Xinying; Li, Xiangzhong; Chu, Zhuding; Liu, Xiangjun; Shao, Da; Wang, Yuhong

    2016-06-01

    Heinrich event 1 (H1) is an important millennial climate event during the last deglaciation. The substantial decreasing of monsoon strength in the East Asian monsoon region during the H1, as shown by stalagmite δ18O records, has been attributed to the southward shift of the intertropical convergence zone (ITCZ), which is caused by the slowdown/collapse of the Atlantic meridional overturning circulation (AMOC). However, records from different Asian monsoon regions show various trends in precipitation changes during the H1, and these trends cannot be solely interpreted by the southward shift of the ITCZ. In the present study, we reconstructed time-series of East Asian monsoon precipitation between 25,000 and 10,000 a BP from floodplain sediments in the Huai River Basin. A white sediment layer, distinct from other layers in the profile, contains significantly low TOC, tree pollen and fern spore contents, and more positive δ13Corg, and it is deposited during the H1 event. The determined TOC, pollen and δ13Corg time-series, together with previously reported stalagmite δ18O, indicate a catastrophic (severe) drought in Jianghuai Region, one of the East Asian monsoon regions, during the H1. The La Niña condition in tropical Pacific likely also contributes to the catastrophic drought in Jianghuai Region and the precipitation variations in the Asian monsoon region during the H1.

  6. Indian monsoon and the elevated-heat-pump mechanism in a coupled aerosol-climate model

    NASA Astrophysics Data System (ADS)

    D'Errico, Miriam; Cagnazzo, Chiara; Fogli, Pier Giuseppe; Lau, William K. M.; Hardenberg, Jost; Fierli, Federico; Cherchi, Annalisa

    2015-09-01

    A coupled aerosol-atmosphere-ocean-sea ice climate model is used to explore the interaction between aerosols and the Indian summer monsoon precipitation on seasonal-to-interannual time scales. Results show that when increased aerosol loading is found on the Himalayas slopes in the premonsoon period (April-May), intensification of early monsoon rainfall over India and increased low-level westerly flow follow, in agreement with the elevated-heat-pump mechanism. The increase in rainfall during the early monsoon season has a cooling effect on the land surface. In the same period, enhanced surface cooling may also be amplified through solar dimming by more cloudiness and aerosol loading, via increased dust transported by low-level westerly flow. The surface cooling causes subsequent reduction in monsoon rainfall in July-August over India. The time-lagged nature of the reasonably realistic response of the model to aerosol forcing suggests that absorbing aerosols, besides their potential key roles in impacting monsoon water cycle and climate, may influence the seasonal variability of the Indian summer monsoon.

  7. Record of the North American southwest monsoon from Gulf of Mexico sediment cores

    USGS Publications Warehouse

    Poore, R.Z.; Pavich, M.J.; Grissino-Mayer, H. D.

    2005-01-01

    Summer monsoonal rains (the southwest monsoon) are an important source of moisture for parts of the southwestern United States and northern Mexico. Improved documentation of the variability in the southwest monsoon is needed because changes in the amount and seasonal distribution of precipitation in this semiarid region of North America influence overall water supply and fire severity. Comparison of abundance variations in the planktic foraminifer Globigerinoides sacculifer in marine cores from the western and northern Gulf of Mexico with terrestrial proxy records of precipitation (tree-ring width and packrat-midden occurrences) from the southwestern United States indicate that G. sacculifer abundance is a proxy for the southwest monsoon on millennial and submillennial time scales. The marine record confirms the presence of a severe multicentury drought centered ca. 1600 calendar (cal.) yr B.P. as well as several multidecadal droughts that have been identified in a long tree-ring record spanning the past 2000 cal. yr from westcentral New Mexico. The marine record further suggests that monsoon circulation, and thus summer rainfall, was enhanced in the middle Holocene (ca. 6500-4500 14C yr B.P.; ca. 6980-4710 cal. yr B.P.). The marine proxy provides the potential for constructing a highly resolved, well-dated, and continuous history of the southwest monsoon for the entire Holocene. ?? 2005 Geological Society of America.

  8. 250 years of SW Indian Monsoon Variability from Red Sea Corals

    NASA Astrophysics Data System (ADS)

    Bryan, S.; Hughen, K. A.; Karnauskas, K. B.; Farrar, J. T.

    2015-12-01

    During the northern hemisphere summer, strong dust storms develop in the Tokar Delta region of Sudan. These massive dust storms are funneled through a gap in the coastal mountains and blow out across the Red Sea. The generation and transport of these dust storms is driven by the large-scale atmospheric pressure gradient across the Red Sea, which is a component of the Southwest Indian Monsoon. Dust deposited on the Red Sea is recorded in skeletal geochemistry of corals that live on the Saudi Arabian coast, and provides an opportunity to reconstruct variability in the monsoon system prior to instrumental records. We have generated annually-resolved records of coral Ba/Ca, which display strong correlations to the zonal pressure gradient across the Red Sea during the instrumental period. Our coral-based monsoon records show an increasing trend in the strength of SW Indian Monsoon circulation since the Little Ice Age, in agreement with lower-resolution Arabian Sea upwelling based records. Our records also show strong decadal-scale variability, which was strongest during the late 19th century and has declined during the past century. In this presentation, we will discuss the decadal-scale variability in the SW Indian Monsoon circulation over the past 250 years as revealed by Red Sea Corals and the implications of the relationships and trends observed in this study for projections of future monsoon variability.

  9. Late Miocene-Pliocene Asian monsoon intensification linked to Antarctic ice-sheet growth

    NASA Astrophysics Data System (ADS)

    Ao, Hong; Roberts, Andrew P.; Dekkers, Mark J.; Liu, Xiaodong; Rohling, Eelco J.; Shi, Zhengguo; An, Zhisheng; Zhao, Xiang

    2016-06-01

    Environmental conditions in one of Earth's most densely populated regions, East Asia, are dominated by the monsoon. While Quaternary monsoon variability is reasonably well understood, pre-Quaternary monsoon variability and dynamics remain enigmatic. In particular, little is known about potential relationships between northern hemispheric monsoon response and major Cenozoic changes in Antarctic ice cover. Here we document long-term East Asian summer monsoon (EASM) intensification through the Late Miocene-Pliocene (∼8.2 to 2.6 Ma), and attribute this to progressive Antarctic glaciation. Our new high-resolution magnetic records of long-term EASM intensification come from the Late Miocene-Pliocene Red Clay sequence on the Chinese Loess Plateau; we identify underlying mechanisms using a numerical climate-model simulation of EASM response to an idealized stepwise increase in Antarctic ice volume. We infer that progressive Antarctic glaciation caused intensification of the cross-equatorial pressure gradient between an atmospheric high-pressure cell over Australia and a low-pressure cell over mid-latitude East Asia, as well as intensification of the cross-equatorial sea-surface temperature (SST) gradient. These combined atmospheric and oceanic adjustments led to EASM intensification. Our findings offer a new and more global perspective on the controls behind long-term Asian monsoon evolution.

  10. Mid-Holocene global monsoon area and precipitation from PMIP simulations

    NASA Astrophysics Data System (ADS)

    Jiang, Dabang; Tian, Zhiping; Lang, Xianmei

    2015-05-01

    Towards a better insight into orbital-scale changes in global monsoon, here we examine global monsoon area (GMA) and precipitation (GMP) as well as GMP intensity (GMPI) in the mid-Holocene, approximately 6,000 years ago, using all available numerical experiments from the Paleoclimate Modelling Intercomparison Project. Compared to the reference period, both the mid-Holocene GMA and GMP increased in the majority of the 35 models chosen for analysis according to their ability, averaging 5.5 and 4.2 %, respectively, which were mainly due to the increase in monsoon area and precipitation over the boreal land and austral ocean. The mid-Holocene GMPI decreased in most models and by an average of 1.2 %, mainly due to the decrease in monsoon precipitation intensity over the boreal ocean and austral land. The mid-Holocene GMA, GMP, and GMPI all showed opposite changes both between the land and ocean in the northern or southern hemisphere and between the boreal and austral land or ocean. Orbital-induced changes in large-scale meridional temperature gradient and land-sea thermal contrast are the underlying mechanisms, and the presence of an interactive ocean has an amplifying effect in the boreal land monsoon areas overall. Qualitatively, the model-data comparison indicates agreement in the boreal land monsoon areas and South America but disagreement in southern Africa and northern Australia.

  11. The South American Monsoon Variability over the Last Millennium in CMIP5/PMIP3 simulations

    NASA Astrophysics Data System (ADS)

    Rojas, M.; Arias, P. A.; Flores-Aqueveque, V.; Seth, A.; Vuille, M.

    2015-12-01

    In this paper we assess South American Monsoon System (SAMS) variability throughout the Last Millennium as depicted by the Coupled Modelling Intercomparison Project version 5/Paleo Modelling Intercomparison Project version 3 (CMIP5/PMIP3) simulations. High-resolution proxy records for the South American monsoon over this period show a coherent regional picture of a weak monsoon during the Medieval Climate Anomaly period and a stronger monsoon during the Little Ice Age (LIA). Due to the small forcing during the past 1000 years, CMIP5/PMIP3 model simulations do not show very strong temperature anomalies over these two specific periods, which in turn do not translate into clear precipitation anomalies, as suggested by rainfall reconstructions in South America. However, with an ad-hoc definition of these two periods for each model simulation, several coherent large-scale atmospheric circulation anomalies were identified. The models feature a stronger Monsoon during the LIA associated with: (i) an enhancement of the rising motion in the SAMS domain in austral summer, (ii) a stronger monsoon-related upper-troposphere anticyclone, (iii) activation of the South American dipole, which results to a certain extent in a poleward shift in the South Atlantic Convergence Zone and (iv) a weaker upper-level sub tropical jet over South America, this providing important insights into the mechanisms of these climate anomalies over South America during the past millennium.

  12. The South American monsoon variability over the last millennium in climate models

    NASA Astrophysics Data System (ADS)

    Rojas, Maisa; Arias, Paola A.; Flores-Aqueveque, Valentina; Seth, Anji; Vuille, Mathias

    2016-08-01

    In this paper we assess South American monsoon system (SAMS) variability in the last millennium as depicted by global coupled climate model simulations. High-resolution proxy records for the South American monsoon over this period show a coherent regional picture of a weak monsoon during the Medieval Climate Anomaly and a stronger monsoon during the Little Ice Age (LIA). Due to the small external forcing during the past 1000 years, model simulations do not show very strong temperature anomalies over these two specific periods, which in turn do not translate into clear precipitation anomalies, in contrast with the rainfall reconstructions in South America. Therefore, we used an ad hoc definition of these two periods for each model simulation in order to account for model-specific signals. Thereby, several coherent large-scale atmospheric circulation anomalies are identified. The models feature a stronger monsoon during the LIA associated with (i) an enhancement of the rising motion in the SAMS domain in austral summer; (ii) a stronger monsoon-related upper-tropospheric anticyclone; (iii) activation of the South American dipole, which results in a poleward shift of the South Atlantic Convergence Zone; and (iv) a weaker upper-level subtropical jet over South America. The diagnosed changes provide important insights into the mechanisms of these climate anomalies over South America during the past millennium.

  13. Increase of global monsoon area and precipitation under global warming: A robust signal?

    NASA Astrophysics Data System (ADS)

    Hsu, Pang-chi; Li, Tim; Luo, Jing-Jia; Murakami, Hiroyuki; Kitoh, Akio; Zhao, Ming

    2012-03-01

    Monsoons, the most energetic tropical climate system, exert a great social and economic impact upon billions of people around the world. The global monsoon precipitation had an increasing trend over the past three decades. Whether or not this increasing trend will continue in the 21st century is investigated, based on simulations of three high-resolution atmospheric general circulation models that were forced by different future sea surface temperature (SST) warming patterns. The results show that the global monsoon area, precipitation and intensity all increase consistently among the model projections. This indicates that the strengthened global monsoon is a robust signal across the models and SST patterns explored here. The increase of the global monsoon precipitation is attributed to the increases of moisture convergence and surface evaporation. The former is caused by the increase of atmospheric water vapor and the latter is due to the increase of SST. The effect of the moisture and evaporation increase is offset to a certain extent by the weakening of the monsoon circulation.

  14. Tipping Elements in Earth Systems Special Feature: Basic mechanism for abrupt monsoon transitions

    NASA Astrophysics Data System (ADS)

    Levermann, Anders; Schewe, Jacob; Petoukhov, Vladimir; Held, Hermann

    2009-12-01

    Monsoon systems influence the livelihood of hundreds of millions of people. During the Holocene and last glacial period, rainfall in India and China has undergone strong and abrupt changes. Though details of monsoon circulations are complicated, observations reveal a defining moisture-advection feedback that dominates the seasonal heat balance and might act as an internal amplifier, leading to abrupt changes in response to relatively weak external perturbations. Here we present a minimal conceptual model capturing this positive feedback. The basic equations, motivated by observed relations, yield a threshold behavior, robust with respect to addition of other physical processes. Below this threshold in net radiative influx, R c, no conventional monsoon can develop; above R c, two stable regimes exist. We identify a nondimensional parameter l that defines the threshold and makes monsoon systems comparable with respect to the character of their abrupt transition. This dynamic similitude may be helpful in understanding past and future variations in monsoon circulation. Within the restrictions of the model, we compute R c for current monsoon systems in India, China, the Bay of Bengal, West Africa, North America, and Australia, where moisture advection is the main driver of the circulation.

  15. Asian Black Carbon Influence on East Asian Summer Monsoons

    NASA Astrophysics Data System (ADS)

    Mahmood, R.; Li, S.

    2011-12-01

    Since the black carbon (BC) emission in East and South Asia has increased significantly during the last decades of the 20th century, there is an ever growing concern about its impact on Asian monsoon. In this study we provide an in-depth analysis of the influence by performing several ensemble sensitive experiments with or without historical BC concentrations over East Asia, South Asia, and the combined East and South Asia in an atmospheric general circulation model, GFDL AM2.1. The results show that: (a) The East Asian summer climate is sensitive to the East Asian BC (EABC) concentrations in a sense that EABC contributes significantly to the frequently occurring north-drought and south-flood patterns in Eastern China. In detail, the large scale precipitation anomalies induced by EABC characterize more rainfalls over central/south China, East China Sea and southern Japan and less rainfall over northern China and the west Pacific region between 10N to 20N. These anomalous precipitation patterns are mainly attributed to the EABC induced large scale circulation changes including the weakened Western Pacific Subtropical High (WPSH), anomalous ascent motions over central-southern China (centering over the Yangtze River valley (YRV)) and the subsequent descent motions over northern China and the South China Sea. These modeled results suggest that the EABC experiment reproduces the climate shift event of eastern China during the late 1970s, including intensified rainfall in the YRV and the weakened summer monsoonal circulation. (b) The anomalous results of South Asian BC (SABC) experiment signify a tri-polar precipitation response over East Asia, with a reduction from the YRV to East China Sea and southern Japan sandwiched with increases over a northern domain from northern China/ Korea to northern Japan and over southern China. As for southern China, particularly the YRV, the impact of SABC is to offset a fraction of intensified rainfall induced by local BC of East Asia

  16. African Easterly Jet: Barotropic Instability, Waves, and Cyclogenesis

    NASA Technical Reports Server (NTRS)

    Wu, Man-Li C; Reale, Oreste; Schubert, Siegfried D.; Suarez, Max J.; Thorncroft, Chris D.

    2012-01-01

    This study investigates the structure of the African easterly jet, focusing on instability processes on a seasonal and subseasonal scale, with the goal of identifying features that could provide increased predictability of Atlantic tropical cyclogenesis. The Modern-Era Retrospective Analysis for Research and Applications (MERRA) is used as the main investigating tool. MERRA is compared with other reanalyses datasets from major operational centers around the world and was found to describe very effectively the circulation over the African monsoon region. In particular, a comparison with precipitation datasets from the Global Precipitation Climatology Project shows that MERRA realistically reproduces seasonal precipitation over that region. The verification of the generalized Kuo barotropic instability condition computed from seasonal means is found to have the interesting property of defining well the location where observed tropical storms are detected. This property does not appear to be an artifact of MERRA and is present also in the other adopted reanalysis datasets. Therefore, the fact that the areas where the mean flow is unstable seems to provide a more favorable environment for wave intensification, could be another factor to include-in addition to sea surface temperature, vertical shear, precipitation, the role of Saharan air, and others-among large-scale forcings affecting development and tropical cyclone frequency. In addition, two prominent modes of variability are found based on a spectral analysis that uses the Hilbert-Huang transform: a 2.5-6-day mode that corresponds well to the African easterly waves and also a 6-9-day mode that seems to be associated with tropical- extratropical interaction.

  17. Improving GEFS Weather Forecasts for Indian Monsoon with Statistical Downscaling

    NASA Astrophysics Data System (ADS)

    Agrawal, Ankita; Salvi, Kaustubh; Ghosh, Subimal

    2014-05-01

    Weather forecast has always been a challenging research problem, yet of a paramount importance as it serves the role of 'key input' in formulating modus operandi for immediate future. Short range rainfall forecasts influence a wide range of entities, right from agricultural industry to a common man. Accurate forecasts actually help in minimizing the possible damage by implementing pre-decided plan of action and hence it is necessary to gauge the quality of forecasts which might vary with the complexity of weather state and regional parameters. Indian Summer Monsoon Rainfall (ISMR) is one such perfect arena to check the quality of weather forecast not only because of the level of intricacy in spatial and temporal patterns associated with it, but also the amount of damage it can cause (because of poor forecasts) to the Indian economy by affecting agriculture Industry. The present study is undertaken with the rationales of assessing, the ability of Global Ensemble Forecast System (GEFS) in predicting ISMR over central India and the skill of statistical downscaling technique in adding value to the predictions by taking them closer to evidentiary target dataset. GEFS is a global numerical weather prediction system providing the forecast results of different climate variables at a fine resolution (0.5 degree and 1 degree). GEFS shows good skills in predicting different climatic variables but fails miserably over rainfall predictions for Indian summer monsoon rainfall, which is evident from a very low to negative correlation values between predicted and observed rainfall. Towards the fulfilment of second rationale, the statistical relationship is established between the reasonably well predicted climate variables (GEFS) and observed rainfall. The GEFS predictors are treated with multicollinearity and dimensionality reduction techniques, such as principal component analysis (PCA) and least absolute shrinkage and selection operator (LASSO). Statistical relationship is

  18. Cloud radar deployment for Indian Monsoon observations: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Chakravarty, K.; Kalapureddy, M.; Pa, M.; Deshpandy, S.; Das, S.; Pandithurai, G.; Prabhakaran, T.; Chandrasekar, C. V.; Goswami, B.

    2013-12-01

    Indian Institute of Tropical Meteorology (IITM)'s acquired Ka-band radar for the Study of the interaction between Cloud and Environment for formation of Precipitation. Main objective of it is to make simultaneous high resolution measurements on dynamical, cloud microphysical and precipitation parameters pertain to monsoon system probably at diverse locations. The goal is to understand the interplay between cloud processes and environment that not only allow understanding the fundamental cloud-environment interactions but also precipitation formation mechanisms and further to estimate cloud contribution to the re-distribution of energy and water in climate system. For this, Polarimetric weather Doppler Radar at higher frequencies (9.5 and 35 GHz) can be a potential tool to gain knowledge on this scientific as well as societal application oriented programme. IITM's Polarimetric scanning Ka-band (cloud) radar operations started recently during May 2013. Mobile Ka-band Scanning Polarimetric Doppler Radar (KaSPR) is a cloud radar operating at wavelength of 8.5 mm with average powers of 110 W. KaSPR incorporates a conduction cooled Extended Interaction Klystron Amplifier. It is having four foot diameter Ka-band cassegrain antenna. Liquid cooled air-sealed RF unit provides excellent temperature stability. Antenna on the top of RF unit is mounted on the Elevation over azimuth pedestal which is designed to rotate continuously in the azimuth axis and a full 180 degrees in the elevation axis (horizon to horizon) with a maximum velocity of 200/sec and maximum acceleration of 120/s2. KaSPR uses dual channel 16-bit digital receiver having dynamic range of more than 80 dB with bandwidths 10 MHz. Arbitrary waveform generator capable of generating any user-defined waveform of up to 16K samples in length. It is having sensitivity of the order -45 dBZ at 5 km. KaSPR has been providing high sensitivity versatile measurements of cloud and precipitation at tropical site (Manderdev, 18

  19. Understanding traditional African healing

    PubMed Central

    MOKGOBI, M.G.

    2015-01-01

    Traditional African healing has been in existence for many centuries yet many people still seem not to understand how it relates to God and religion/spirituality. Some people seem to believe that traditional healers worship the ancestors and not God. It is therefore the aim of this paper to clarify this relationship by discussing a chain of communication between the worshipers and the Almighty God. Other aspects of traditional healing namely types of traditional healers, training of traditional healers as well as the role of traditional healers in their communities are discussed. In conclusion, the services of traditional healers go far beyond the uses of herbs for physical illnesses. Traditional healers serve many roles which include but not limited to custodians of the traditional African religion and customs, educators about culture, counselors, social workers and psychologists. PMID:26594664

  20. Human African trypanosomiasis.

    PubMed

    Lejon, Veerle; Bentivoglio, Marina; Franco, José Ramon

    2013-01-01

    Human African trypanosomiasis or sleeping sickness is a neglected tropical disease that affects populations in sub-Saharan Africa. The disease is caused by infection with the gambiense and rhodesiense subspecies of the extracellular parasite Trypanosoma brucei, and is transmitted to humans by bites of infected tsetse flies. The disease evolves in two stages, the hemolymphatic and meningoencephalitic stages, the latter being defined by central nervous system infection after trypanosomal traversal of the blood-brain barrier. African trypanosomiasis, which leads to severe neuroinflammation, is fatal without treatment, but the available drugs are toxic and complicated to administer. The choice of medication is determined by the infecting parasite subspecies and disease stage. Clinical features include a constellation of nonspecific symptoms and signs with evolving neurological and psychiatric alterations and characteristic sleep-wake disturbances. Because of the clinical profile variability and insidiously progressive central nervous system involvement, disease staging is currently based on cerebrospinal fluid examination, which is usually performed after the finding of trypanosomes in blood or other body fluids. No vaccine being available, control of human African trypanosomiasis relies on diagnosis and treatment of infected patients, assisted by vector control. Better diagnostic tools and safer, easy to use drugs are needed to facilitate elimination of the disease.

  1. Diversity among African Pygmies

    PubMed Central

    Ramírez Rozzi, Fernando V.; Sardi, Marina L.

    2010-01-01

    Although dissimilarities in cranial and post-cranial morphology among African pygmies groups have been recognized, comparative studies on skull morphology usually pull all pygmies together assuming that morphological characters are similar among them and different with respect to other populations. The main aim of this study is to compare cranial morphology between African pygmies and non-pygmies populations from Equatorial Africa derived from both the Eastern and the Western regions in order to test if the greatest morphological difference is obtained in the comparison between pygmies and non-pygmies. Thirty three-dimensional (3D) landmarks registered with Microscribe in four cranial samples (Western and Eastern pygmies and non-pygmies) were obtained. Multivariate analysis (generalized Procrustes analysis, Mahalanobis distances, multivariate regression) and complementary dimensions of size were evaluated with ANOVA and post hoc LSD. Results suggest that important cranial shape differentiation does occur between pygmies and non-pygmies but also between Eastern and Western populations and that size changes and allometries do not affect similarly Eastern and Western pygmies. Therefore, our findings raise serious doubt about the fact to consider African pygmies as a homogenous group in studies on skull morphology. Differences in cranial morphology among pygmies would suggest differentiation after divergence. Although not directly related to skull differentiation, the diversity among pygmies would probably suggest that the process responsible for reduced stature occurred after the split of the ancestors of modern Eastern and Western pygmies. PMID:21049030

  2. African horse sickness.

    PubMed

    Zientara, S; Weyer, C T; Lecollinet, S

    2015-08-01

    African horse sickness (AHS) is a devastating disease of equids caused by an arthropod-borne virus belonging to the Reoviridae family, genus Orbivirus. It is considered a major health threat for horses in endemic areas in sub-Saharan Africa. African horse sickness virus (AHSV) repeatedly caused large epizootics in the Mediterranean region (North Africa and southern Europe in particular) as a result of trade in infected equids. The unexpected emergence of a closely related virus, the bluetongue virus, in northern Europe in 2006 has raised fears about AHSV introduction into Europe, and more specifically into AHSV-free regions that have reported the presence of AHSV vectors, e.g. Culicoides midges. North African and European countries should be prepared to face AHSV incursions in the future, especially since two AHSV serotypes (serotypes 2 and 7) have recently spread northwards to western (e.g. Senegal, Nigeria, Gambia) and eastern Africa (Ethiopia), where historically only serotype 9 had been isolated. The authors review key elements of AHS epidemiology, surveillance and prophylaxis. PMID:26601437

  3. East African Rift Valley, Kenya

    NASA Technical Reports Server (NTRS)

    1990-01-01

    This rare, cloud free view of the East African Rift Valley, Kenya (1.5N, 35.5E) shows a clear view of the Turkwell River Valley, an offshoot of the African REift System. The East African Rift is part of a vast plate fracture which extends from southern Turkey, through the Red Sea, East Africa and into Mozambique. Dark green patches of forests are seen along the rift margin and tea plantations occupy the cooler higher ground.

  4. Study on the association of green house gas (CO2) with monsoon rainfall using AIRS and TRMM satellite observations

    NASA Astrophysics Data System (ADS)

    Singh, R. B.; Janmaijaya, M.; Dhaka, S. K.; Kumar, V.

    Monsoon water cycle is the lifeline to over 60 per cent of the world's population. Throughout history, the monsoon-related calamities of droughts and floods have determined the life pattern of people. The association of Green House Gases (GHGs) particularly Carbon dioxide (CO2) with monsoon has been greatly debated amongst the scientific community in the past. The effect of CO2 on the monsoon rainfall over the Indian-Indonesian region (8-30°N, 65°-100°E) is being investigated using satellite data. The correlation coefficient (Rxy) between CO2 and monsoon is analysed. The Rxy is not significantly positive over a greater part of the study region, except a few regions. The inter-annual anomalies of CO2 is identified for playing a secondary role to influencing monsoon while other phenomenon like ENSO might be exerting a much greater influence.

  5. Regionalization of Tibetan Plateau precipitation and its relation to the Asian Monsoon

    NASA Astrophysics Data System (ADS)

    Conroy, J. L.; Overpeck, J. T.

    2008-12-01

    Many paleoclimate records from the Tibetan Plateau link past changes in local precipitation to Southwest (SW, or Indian) and East (E) Asian Monsoon variability. However, few of these records are correlated with instrumental records of local or regional monsoon variability. And, although the majority of Tibetan precipitation occurs in the summer months, a dearth of station data limits the connection of instrumental precipitation variability across Tibet to the Asian Monsoon regimes. To properly interpret proxy climate records, a quantitative understanding of Asian Monsoon influences on the Tibetan Plateau is required. With this goal in mind, we investigated precipitation variability across the Tibetan Plateau using monthly gridded merged precipitation (CMAP) and outgoing longwave radiation (OLR) datasets to quantify the relationship between summer precipitation on the Tibetan Plateau and the SW and E Asian Monsoons. Average summer OLR and precipitation are significantly correlated at the 95% confidence level between southwest, northwest, southeast Tibet and the central Himalayas, but average summer OLR and precipitation in northeast Tibet is only significantly correlated with OLR and precipitation in southeastern Tibet. OLR over the central Himalayas, southwest Tibet, and northwest Tibet correlates at the 95% confidence level with the Indian Monsoon Index, and precipitation in the central Himalayas correlates at the 95% confidence level with the Webster-Yang Index of SW Monsoon variability. OLR and precipitation over the central Himalayas, southwest Tibet, and northwest Tibet also significantly correlate with OLR and precipitation over India, as well as surface wind speed, 850 mb zonal, and 850 mb meridional wind speeds over the southwest Arabian Sea. These significant correlations indicate precipitation variability over western Tibet and the central Himalayas is related to SW Asian Monsoon variability. Correlations between southeastern and northeastern Tibet OLR

  6. The impact of North Indian Ocean sea surface temperatures on the Indian summer monsoon

    NASA Astrophysics Data System (ADS)

    Levine, Richard; Turner, Andrew

    2010-05-01

    The relationship between sea surface temperature (SST) in the North Indian Ocean and Indian monsoon rainfall is investigated in both observational/re-analyses and climate model simulations. We focus on the partially land-enclosed Arabian Sea and Bay of Bengal, where SSTs are found to have significant correlations with All Indian Rainfall (AIR). This part of the Indian Ocean is therefore important for monsoon predictions, while this area tends to provide significant problems in coupled atmosphere-ocean model simulations. The observational variability of the SST-rainfall relationship is investigated on seasonal to decadal time-scales. This highlights a predominantly negative correlation over the monsoon trough area in North East India and a positive correlation over the rest of India, while these relationships are found to be weakened by the ENSO-monsoon teleconnection. Mechanisms are further investigated by performing a series of atmosphere-only model simulations using the Met Office Unified Model (MetUM). In these experiments we determine the response of the atmosphere to forced cold SST anomalies over isolated areas, which we also extend out into the equatorial Indian Ocean. The cold SSTs in the Arabian Sea and Bay of Bengal lead to a dramatic reduction in Indian rainfall, while cold biases in the equatorial Indian Ocean have the opposite effect, highlighting the competition between oceanic and continental Tropical Convergence Zones (TCZ). However, the impacts for the Arabian Sea and Bay of Bengal experiments are found to change between the pre-monsoon and post-monsoon onset periods.The impact on monsoon rainfall for cold SST biases in these regions is found to be the result of a balance between changes in regional low-level temperature gradients and the availability of moisture over the oceans, which determine the pathway of the monsoon jet and the moisture transport towards India. These experiments suggest that the intra-seasonal variability of the relationship

  7. The vertical structure of cloud radiative heating over the Indian subcontinent during summer monsoon

    NASA Astrophysics Data System (ADS)

    Johansson, E.; Devasthale, A.; L'Ecuyer, T.; Ekman, A. M. L.; Tjernström, M.

    2015-02-01

    Every year the monsoonal circulation over the Indian subcontinent gives rise to a variety of cloud types that differ considerably in their ability to heat or cool the atmosphere. These clouds in turn affect monsoon dynamics via their radiative impacts, both at the surface and in the atmosphere. New generation of satellites carrying active radar and lidar sensors are allowing realistic quantification of cloud radiative heating (CRH) by resolving the vertical structure of the atmosphere in an unprecedented detail. Obtaining this information is a first step in closing the knowledge gap in our understanding of the role that different clouds play as regulators of the monsoon and vice versa. Here, we use collocated CloudSat-CALIPSO data sets to understand following aspects of cloud-radiation interactions associated with Indian monsoon circulation. (1) How does the vertical distribution of CRH evolve over the Indian continent throughout monsoon season? (2) What is the absolute contribution of different clouds types to the total CRH? (3) How do active and break periods of monsoon affect the distribution of CRH? And finally, (4) what are the net radiative effects of different cloud types on surface heating? In general, the vertical structure of CRH follows the northward migration and the retreat of monsoon from May to October. It is found that the alto- and nimbostratus clouds intensely warm the middle troposphere and equally strongly cool the upper troposphere. Their warming/cooling consistently exceeds ±0.2 K day-1 (after weighing by vertical cloud fraction) in monthly mean composites throughout the middle and upper troposphere respectively, with largest impact observed in June, July and August. Deep convective towers cause considerable warming in the middle and upper troposphere, but strongly cool the base and inside of the tropical tropopause layer (TTL). Such cooling is stronger during active (-1.23 K day-1) monsoon conditions compared to break periods (-0.36 K day-1

  8. The Role of Continental-scale Landmass in Monsoons-A GCM Investigation

    NASA Technical Reports Server (NTRS)

    Chao, Winston

    2008-01-01

    It was argued by Chao and Chen (2001) that land-sea thermal contrast on the continental scale is not a necessary condition for monsoons and that a monsoon is an ITCZ that have moved into the subtropics in its annual cycle of latitudinal movement. Chao and Chen supported their contention by GCM experiments in which they replaced landmass by ocean and were able to generate monsoons. However, land-sea thermal contrast does exist and must play a role in monsoonal rainfall distribution. Land-sea thermal contrast is one facet of continental-scale landmass. The other important characteristic of landmass is its topography. In this article the roles of landmass in monsoonal rainfall distribution and in middle latitude storm tracks are examined through GCM experiments. Comparison of a set of two GCM experiments in which the sea surface temperature (SST) from observations is prescribed from observations with and without a six-month delay reveals the role of Land-sea thermal contrast. Another set of experiments, which repeats the first set but with topography of all landmass reduced to zero, reveals the role of topography of landmass. These experiments confirm that land-sea thermal contrast is not a necessary condition for monsoons and that a monsoon should be viewed as an ITCZ displaced into the subtropics, instead of a continent-sized giant sea breeze. However, land-sea thermal contrast does have influence on the distribution of monsoonal rainfall. The temperature rise over south Asia as the season moves into summer helps the Asian monsoon to start early. However, this role is not the same as that of the land-sea thermal contrast as in the conventional explanation for the cause of monsoon. The heated landmass in summer contributes to the displacement of ITCZ into the subtropics. Also, the heated landmass in summer, by drawing moisture toward itself, limits the range of the summer storm tracks in the middle latitude oceans. On the ether hand, in winter the landmass does not

  9. Mountain Heavy Rainfall Measurement Experiments in a Subtropical Monsoon Environment

    NASA Astrophysics Data System (ADS)

    Jong-Dao Jou, Ben; Chi-June Jung, Ultimate; Lai, Hsiao-Wei; Feng, Lei

    2014-05-01

    Quantitative rainfall measurement experiments have been conducted in Taiwan area for the past 5 years (since 2008), especially over the complex terrain region. In this paper, results from these experiments will be analyzed and discussed, especially those associated with heavy rain events in the summer monsoon season. Observations from s-band polarimetric radar (SPOL of NCAR) and also x-band vertically-pointing radar are analyzed to reveal the high resolution temporal and spatial variation of precipitation structure. May and June, the Meiyu season in the area, are months with subtropical frontal rainfall events. Mesoscale convective systems, i.e., pre-frontal squall lines and frontal convective rainbands, are very active and frequently produce heavy rain events over mountain areas. Accurate quantitative precipitation measurements are needed in order to meet the requirement for landslide and flood early warning purpose. Using ground-based disdrometers and vertically-pointing radar, we have been trying to modify the quantitative precipitation estimation in the mountain region by using coastal operational radar. In this paper, the methodology applied will be presented and the potential of its application will be discussed. *corresponding author: Ben Jong-Dao Jou, jouben43@gmail.com

  10. Holocene Climatic Variability in the Indian Monsoon Domain

    NASA Astrophysics Data System (ADS)

    Mishra, Praveen Kumar; Anoop, Ambili; Menzel, Philip; Gaye, Birgit; Basavaiah, Nathani; Jehangir, Arshid; Prasad, Sushma

    2013-04-01

    The available data on Holocene climate variability from Asia indicates spatio-temporal changes in the precipitation over this vast region. Detailed information on the timing, duration, regionality, and causes of these fluctuations is not well understood, especially over the Indian subcontinent. My work focuses on long core sediments from lake Tso Moriri (78°14'-78°25'N and 32°40'-33°02'E; altitude: 4500 m) situated in climatically sensitive zone of NW Himalayas affected by both mid-latitude westerlies and Indian summer monsoon. Two cores ca.7 m were retrieved from the lake at different water depths (ca. 40m and 105m) in July 2011. Investigations reveal marked changes in grain size, lamination quality, mineralogy, organic and carbonate content suggesting changes in lake level, direction of inflow, and biological productivity that in turn are influenced by regional climate. As the lake lies in a tectonically active region, I have also undertaken detailed geomorphometric (knick-point, Hack index), and drainage pattern analysis of the major inflowing streams to decipher the active tectonics in the region. Sharp changes in river course and slope gradient indicates the presence of an active N-S trending fault in western flank of the lake. The data from lake Tso Moriri will be compared with other high-resolution records from lake Lonar and stalagmites in NE India to reconstruct the forcing mechanism of Holocene climatic variability.

  11. The abrupt onset of the modern South Asian Monsoon winds

    NASA Astrophysics Data System (ADS)

    Betzler, Christian; Eberli, Gregor P.; Kroon, Dick; Wright, James D.; Swart, Peter K.; Nath, Bejugam Nagender; Alvarez-Zarikian, Carlos A.; Alonso-García, Montserrat; Bialik, Or M.; Blättler, Clara L.; Guo, Junhua Adam; Haffen, Sébastien; Horozal, Senay; Inoue, Mayuri; Jovane, Luigi; Lanci, Luca; Laya, Juan Carlos; Mee, Anna Ling Hui; Lüdmann, Thomas; Nakakuni, Masatoshi; Niino, Kaoru; Petruny, Loren M.; Pratiwi, Santi D.; Reijmer, John J. G.; Reolid, Jesús; Slagle, Angela L.; Sloss, Craig R.; Su, Xiang; Yao, Zhengquan; Young, Jeremy R.

    2016-07-01

    The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment’s content of particulate organic matter. A weaker ‘proto-monsoon’ existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system.

  12. Summer climate of Madagascar and monsoon pulsing of its vortex

    NASA Astrophysics Data System (ADS)

    Jury, Mark R.

    2016-02-01

    This study analyzes the climate of Madagascar (12°-26°S, 43°-50°E) and its relation to the Indian Ocean during austral summer (Dec-Mar). Moisture converges onto a standing easterly wave and floods are prevalent in late summer. All-island daytime land temperatures exceed 38 °C in October and are ~4 °C above sea temperatures during summer. Analysis of thermally induced diurnal convection and circulation revealed inflow during the afternoon recirculated from the southeastern mountains and the warm Mozambique Channel. Summer rainfall follows latent and sensible heat flux during the first half of the day, and gains a surplus by evening via thunderstorms over the western plains. At the inter-annual time-scale, 2.3 years oscillations in all-island rainfall appear linked with the stratospheric quasi-biennial oscillation and corresponding 80 Dobson Unit ozone fluctuations during flood events. Wet spells at frequencies from 11-27 days derive from locally-formed tropical cyclones and NW-cloud bands. Flood case studies exhibit moisture recycling in the confluence zone between the sub-tropical anticyclone and the lee-side vortex. Hovmoller analysis of daily rainfall reinforces the concept of local generation and pulsing by cross-equatorial (Indian winter) monsoon flow rather than zonal atmospheric waves. Since the surface water budget is critical to agriculture in Madagascar, this study represents a further step to understand its meso-scale summer climate.

  13. The abrupt onset of the modern South Asian Monsoon winds

    PubMed Central

    Betzler, Christian; Eberli, Gregor P.; Kroon, Dick; Wright, James D.; Swart, Peter K.; Nath, Bejugam Nagender; Alvarez-Zarikian, Carlos A.; Alonso-García, Montserrat; Bialik, Or M.; Blättler, Clara L.; Guo, Junhua Adam; Haffen, Sébastien; Horozal, Senay; Inoue, Mayuri; Jovane, Luigi; Lanci, Luca; Laya, Juan Carlos; Mee, Anna Ling Hui; Lüdmann, Thomas; Nakakuni, Masatoshi; Niino, Kaoru; Petruny, Loren M.; Pratiwi, Santi D.; Reijmer, John J. G.; Reolid, Jesús; Slagle, Angela L.; Sloss, Craig R.; Su, Xiang; Yao, Zhengquan; Young, Jeremy R.

    2016-01-01

    The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment’s content of particulate organic matter. A weaker ‘proto-monsoon’ existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system. PMID:27436574

  14. First observations of Gigantic Jets from Monsoon Thunderstorms over India

    NASA Astrophysics Data System (ADS)

    Singh, Rajesh; Maurya, Ajeet; Chanrion, Olivier; Neubert, Torsten; Cummer, Steven; Mlynarczyk, Janusz; Bór, József; Siingh, Devendraa; Cohen, Morris; Kumar, Sushil

    2016-04-01

    Gigantic Jets are electric discharges from thunderstorm cloud tops to the bottom of the ionosphere at ~80 km altitude. After their first discovery in 2001, relatively few observations have been reported. Most of these are from satellites at large distances and a few tens from the ground at higher spatial resolution. Here we report the first Gigantic Jets observed in India from two thunderstorm systems that developed over the land surface from monsoon activity, each storm producing two Gigantic Jets. The jets were recorded by a video camera system at standard video rate (20 ms exposure) at a few hundred km distance. ELF measurements suggest that the jets are of the usual negative polarity and that they develop in less than 40 ms, which is faster than most jets reported in the past. The jets originate from the leading edge of a slowly drifting convective cloud complex close to the highest regions of the clouds and carry ~25 Coulomb of charge to the ionosphere. One jet has a markedly horizontal displacement that we suggest is caused by a combination of close-range cloud electric fields at inception, and longer-range cloud fields at larger distances during full development. The Gigantic Jets are amongst the few that have been observed over land.

  15. Intrinsic Coupled Ocean-Atmosphere Modes of the Asian Summer Monsoon: A Re-assessment of Monsoon-ENSO Relationships

    NASA Technical Reports Server (NTRS)

    Lau, K.-M.; Wu, H. T.

    2000-01-01

    Using global rainfall and sea surface temperature (SST) data for the past two decades (1979-1998), we have investigated the intrinsic modes of Asian summer monsoon (ASM) and ENSO co-variability. Three recurring ASM rainfall-SST coupled modes were identified. The first is a basin scale mode that features SST and rainfall variability over the entire tropics (including the ASM region), identifiable with those occurring during El Nino or La Nina. This mode is further characterized by a pronounced biennial variation in ASM rainfall and SST associated with fluctuations of the anomalous Walker circulation that occur during El Nino/La Nina transitions. The second mode comprises mixed regional and basin-scale rainfall and SST signals, with pronounced intraseasonal and interannual variabilities. This mode features a SST pattern associated with a developing La Nina, with a pronounced low level anticyclone in the subtropics of the western Pacific off the coast of East Asia. The third mode depicts an east-west rainfall and SST dipole across the southern equatorial Indian Ocean, most likely stemming from coupled ocean-atmosphere processes within the ASM region. This mode also possesses a decadal time scale and a linear trend, which are not associated with El Nino/La Nina variability. Possible causes of year-to-year rainfall variability over the ASM and sub-regions have been evaluated from a reconstruction of the observed rainfall from singular eigenvectors of the coupled modes. It is found that while basin-scale SST can account for portions of ASM rainfall variability during ENSO events (up to 60% in 1998), regional processes can accounts up to 20-25% of the rainfall variability in typical non-ENSO years. Stronger monsoon-ENSO relationship tends to occur in the boreal summer immediately preceding a pronounced La Nina, i.e., 1998, 1988 and 1983. Based on these results, we discuss the possible impacts of the ASM on ENSO variability via the west Pacific anticyclone and articulate a

  16. Late Holocene primary productivity and sea surface temperature variations in the northeastern Arabian Sea: Implications for winter monsoon variability

    NASA Astrophysics Data System (ADS)

    Böll, Anna; Lückge, Andreas; Munz, Philipp; Forke, Sven; Schulz, Hartmut; Ramaswamy, V.; Rixen, Tim; Gaye, Birgit; Emeis, Kay-Christian

    2014-08-01

    Variability in the oceanic environment of the Arabian Sea region is strongly influenced by the seasonal monsoon cycle of alternating wind directions. Prominent and well studied is the summer monsoon, but much less is known about late Holocene changes in winter monsoon strength with winds from the northeast that drive convective mixing and high surface ocean productivity in the northeastern Arabian Sea. To establish a high-resolution record of winter monsoon variability for the late Holocene, we analyzed alkenone-derived sea surface temperature (SST) variations and proxies of primary productivity (organic carbon and δ15N) in a well-laminated sediment core from the Pakistan continental margin. Weak winter monsoon intensities off Pakistan are indicated from 400 B.C. to 250 A.D. by reduced productivity and relatively high SST. At about 250 A.D., the intensity of the winter monsoon increased off Pakistan as indicated by a trend to lower SST. We infer that monsoon conditions were relatively unstable from ~500 to 1300 A.D., because primary production and SST were highly variable. Declining SST and elevated biological production from 1400 to 1900 A.D. suggest invigorated convective winter mixing by strengthening winter monsoon circulation, most likely a regional expression of colder climate conditions during the Little Ice Age on the Northern Hemisphere. The comparison of winter monsoon intensity with records of summer monsoon intensity suggests that an inverse relationship between summer and winter monsoon strength exists in the Asian monsoon system during the late Holocene, effected by shifts in the Intertropical Convergence Zone.

  17. Orbital pacing and ocean circulation-induced collapses of the Mesoamerican monsoon over the past 22,000 y

    PubMed Central

    Lachniet, Matthew S.; Asmerom, Yemane; Bernal, Juan Pablo; Polyak, Victor J.; Vazquez-Selem, Lorenzo

    2013-01-01

    The dominant controls on global paleomonsoon strength include summer insolation driven by precession cycles, ocean circulation through its influence on atmospheric circulation, and sea-surface temperatures. However, few records from the summer North American Monsoon system are available to test for a synchronous response with other global monsoons to shared forcings. In particular, the monsoon response to widespread atmospheric reorganizations associated with disruptions of the Atlantic Meridional Overturning Circulation (AMOC) during the deglacial period remains unconstrained. Here, we present a high-resolution and radiometrically dated monsoon rainfall reconstruction over the past 22,000 y from speleothems of tropical southwestern Mexico. The data document an active Last Glacial Maximum (18–24 cal ka B.P.) monsoon with similar δ18O values to the modern, and that the monsoon collapsed during periods of weakened AMOC during Heinrich stadial 1 (ca. 17 ka) and the Younger Dryas (12.9–11.5 ka). The Holocene was marked by a trend to a weaker monsoon that was paced by orbital insolation. We conclude that the Mesoamerican monsoon responded in concert with other global monsoon regions, and that monsoon strength was driven by variations in the strength and latitudinal position of the Intertropical Convergence Zone, which was forced by AMOC variations in the North Atlantic Ocean. The surprising observation of an active Last Glacial Maximum monsoon is attributed to an active but shallow AMOC and proximity to the Intertropical Convergence Zone. The emergence of agriculture in southwestern Mexico was likely only possible after monsoon strengthening in the Early Holocene at ca. 11 ka. PMID:23690596

  18. Future projection of mean and variability of the Asian Summer Monsoon and Indian Ocean Climate systems

    SciTech Connect

    Annamalai, H.

    2014-09-15

    The overall goal of this project is to assess the ability of the CMIP3/5 models to simulate the Indian-Ocean monsoon systems. The PI along with post-docs investigated research issues ranging from synoptic systems to long-term trends over the Asian monsoon region. The PI applied diagnostic tools such as moist static energy (MSE) to isolate: the moist and radiative processes responsible for extended monsoon breaks over South Asia, precursors in the ENSO-monsoon association, reasons for the drying tendency over South Asia and the possible effect on tropical Indian Ocean climate anomalies influencing certain aspects of ENSO characteristics. By diagnosing various observations and coupled model simulations, we developed working hypothesis and tested them by carrying out sensitivity experiments with both linear and nonlinear models. Possible physical and dynamical reasons for model sensitivities were deduced. On the teleconnection front, the ability of CMIP5 models in representing the monsoon-desert mechanism was examined recently. Further more, we have applied a suite of diagnostics and have performed an in depth analysis on CMIP5 integrations to isolate the possible reasons for the ENSO-monsoon linkage or lack thereof. The PI has collaborated with Dr. K.R. Sperber of PCMDI and other CLIVAR Asian-Australian monsoon panel members in understanding the ability of CMIP3/5 models in capturing monsoon and its spectrum of variability. The objective and process-based diagnostics aided in selecting models that best represent the present-day monsoon and its variability that are then employed for future projections. Two major highlights were an invitation to write a review on present understanding monsoons in a changing climate in Nature Climate Change, and identification of an east-west shift in observed monsoon rainfall (more rainfall over tropical western Pacific and drying tendency over South Asia) in the last six decades and attributing that shift to SST rise over the tropical

  19. Assessing the strength of the monsoon during the late Pleistocene in southwestern United States

    NASA Astrophysics Data System (ADS)

    Cisneros-Dozal, Luz M.; Huang, Yongsong; Heikoop, Jeffrey M.; Fawcett, Peter J.; Fessenden, Julianna; Anderson, R. Scott; Meyers, Philip A.; Larson, Toti; Perkins, George; Toney, Jaime; Werne, Josef P.; Goff, Fraser; WoldeGabriel, Giday; Allen, Craig D.; Berke, Melissa A.

    2014-11-01

    Improved predictions of drought require an understanding of natural and human-induced climate variability. Long-term records across glacial-interglacial cycles provide the natural component of variability, however few such records exist for the southwestern United States (US) and quantitative or semi-quantitative records of precipitation are absent. Here we use the hydrogen isotope (δD) value of C28n-alkanoic acid in lacustrine sediments of Pleistocene age to reconstruct δD values of precipitation in northern New Mexico over two glacial-interglacial cycles (˜550,000-360,000 years before present) and obtain a record of monsoon strength. Overall, reconstructed δD values range from -53.8‰ to -94.4‰, with a mean value of -77.5 ± 8‰. Remarkably, this variation falls within the measured present-day summer monsoonal and winter weighted means (-50.3 ± 3‰ and -106.4 ± 20‰ respectively), suggesting that processes similar to those of present time also controlled precipitation during Marine Isotope Stage (MIS) 13 to 10. Using the δD summer monsoonal and winter mean values as end-members, we interpret our reconstructed δD record of precipitation as a direct, and semi-quantitative, indicator of monsoon strength during MIS 13 to 10. Interglacial periods were characterized by greater monsoon strength but also greater variability compared to glacial periods. Pronounced cycles in the strength of the monsoon occurred during interglacial periods and in general were positively correlated with maximum mean annual temperatures. Our estimates of monsoon strength are supported by independent proxies of ecosystem productivity, namely, TOC, δ13C of TOC and Si/Ti ratio and warm pollen taxa Juniperus and Quercus. Interglacial variability in the strength of the monsoon resembles a response to the land-sea surface temperature contrast (LSTC) except for the early part of MIS 11. During this period, LSTC would have remained relatively strong while monsoonal strength decreased

  20. Classification of typical summer rainfall patterns in the East China monsoon region and their association with the East Asian summer monsoon

    NASA Astrophysics Data System (ADS)

    Yang, Liu; Zhao, Junhu; Feng, Guolin

    2016-06-01

    In this study, the summer rainfall patterns in the East China monsoon region during 1951-2015 were objectively classified into four typical categories: the northern China rainfall pattern (NCP), the intermediate rainfall pattern (IRP), the Yangtze River rainfall pattern (YRP), and the South China rainfall pattern (SCP). The periods of the four patterns show significant decadal characteristics. The NCP occurred mainly between the late 1950s and the early 1980s, and the IRP in the late 1950s to the early 1970s and the 2000s. The YRP occurred mainly between the 1980s and the 1990s, and the SCP between the mid-1990s and the early 21st century. The relationship between the East Asian summer monsoon index (EASM I WF) and the four rainfall patterns was comparatively analyzed. The results confirmed that the four rainfall patterns have obvious differences in the EASM. In the NCP, IRP, or SCP years, the EASM I WF primarily showed a positive phase and a strong summer monsoon; in the YRP years, the EASM I WF primarily showed a negative phase and a weak summer monsoon.

  1. Was the Asian monsoon climate stable or not during the last interglacial?

    NASA Astrophysics Data System (ADS)

    Cai, Y.; An, Z.; Qin, S.; Cheng, H.; Edwards, R.; Zhang, H.

    2012-12-01

    The climate during the last interglacial was stable or not is still an open question. Here, we present an absolute-dated δ18O record during the Marin Isotope Stage 5e (Emian in Europe) from Xiaotian Cave, southeast of Chinese Loess Plateau, a region sensitive to the East Asia monsoon changes. This speleothem calcite δ18O record shows substantial centennial time-scales changes with large amplitude of ~3‰ during the last interglacial. These changes are similar to the variations found in the δ18O record from Tianmen Cave, south central Tibetan, another region sensitive to the Indian summer monsoon changes. This similarity indicates that there were significant changes occurred in the Asian summer monsoon circulations and confirms the instability of Asian summer monsoon climate during the last interglacial. Our record also indicates that the speleothem calcite δ18O values increased abruptly around 122ka BP, which is consistent with the previously reported δ18O records from Dongge, Sanbao and Tianmen caves within the quoted dating errors, demonstrating the abrupt weakening of Asian summer monsoon at the transition from MIS 5e to MIS 5d. This abrupt change of Asian summer monsoon could correlate with the temperature records from North Atlantic region. It is most likely that the decreased thermohaline circulation resulted in the cooling of the high north latitude regions and then weakened the Asian summer monsoon. In addition, the general trend of the speleothem calcite δ18O records during the last interglacial was not following the insolation changes, which is different from the scenery during the Holocene. This discrepancy may be caused by the different seasonality of insolation in the northern hemisphere and also the different lower boundary conditions, such as the ice sheet size and distribution and ocean circulations etc.

  2. The Evolution of Tropospheric Temperature Field and its Relationship With The Onset of Asian Summer Monsoon

    NASA Technical Reports Server (NTRS)

    He, H.; Sui, C-H.; Jian, M.; Wen, Z.

    2000-01-01

    The mean state and year-to-year variations of the tropospheric temperature fields and their relationship with the establishment of the summertime East Asian monsoon (EAM) and the Indian monsoon (INM) are studied using the NCEP reanalysis data of 15 years (1982-1996). The results show that the seasonal shift of the South Asian High in the upper troposphere and the establishment of the EAM and the INM are closely related to the seasonal warming which causes a reversal of the meridional gradient of upper tropospheric mean temperature over the monsoon regions. On the average of 15 years, the reversal time of the temperature gradient in the EAM region (INM region) is concurrent with (one pentad earlier than) the onset time of the summer monsoon. In most years of the 15-year period, the reversal of temperature gradient coincides or precedes the onset time of the summer monsoon in both the EAM region and the INM region. The results suggest an important role of thermal processes on the establishment of the Asian monsoon. The contributors to the upper tropospheric warming over the EAM region are the strong horizontal warm advection and the diabetic heating against the adiabatic cooling due to upward motion. In the INM region, strong adiabatic heating by subsidence and the diabetic heating are major warming processes against the strong horizontal cold advection related to the persistent northwestlies to the southwestern periphery of the Tibetan Plateau. It appears that the early or late establishment of the Asian summer monsoon is not directly related to the differential warming near the surface.

  3. Relationship between tropospheric temperature and Indian summer monsoon rainfall as simulated by RegCM3

    NASA Astrophysics Data System (ADS)

    Pattnayak, K. C.; Panda, S. K.; Saraswat, Vaishali; Dash, S. K.

    2016-05-01

    Relationship between rainfall and tropospheric temperature (TT) has been examined over the Indian subcontinent during four seasons of the year using Regional Climate Model Version 3.0 (RegCM3). The model has been integrated at 55 km horizontal resolution over India during the years 1980-2000 with prescribed lateral boundary forcing from the 40 years re-analysis (ERA40) of the European Centre for Medium-range Weather Forecasts. Results of this study show that RegCM3 in general is able to capture the spatial distributions of rainfall in all the seasons as compared to the corresponding IMD0.5 gridded rainfall. The model has simulated warmer TT over the Himalayan region in all the seasons as compared to ERA40. However, it is well captured over the peninsular India and the oceanic regions. In the model, larger warming by about 0.5 °C over the northwest and Central India in the summer monsoon months might have lead to lower surface pressure there. Also, the vertical extent of the monsoon trough is found to be up to 500 hPa in the model as compared to that in NCEP/NCAR reanalysis. As a consequence, the simulated monsoon circulation and rainfall are stronger than those observed. The two most important rainfall seasons, the summer monsoon and winter are reasonably well simulated with correlation coefficients (CC) of 0.60 and 0.59 respectively significant at 99 % confidence level with the corresponding observed values of IMD0.5. Further, Indian summer monsoon rainfall (ISMR) and TT during the contrasting monsoon years are also close to their respective observed values. Temporal CCs between the TT over Tibet, Pakistan and Central India during the summer monsoon season and gridded ISMR values reveals that the TT over Pakistan has been better correlated with the ISMR than those over Tibet and Central India. This relationship has been well supported by the model simulations.

  4. Seasonal response of zooplankton to monsoonal reversals in the Arabian Sea

    NASA Astrophysics Data System (ADS)

    Smith, Sharon; Roman, Michael; Prusova, Irina; Wishner, Karen; Gowing, Marcia; Codispoti, L. A.; Barber, Richard; Marra, John; Flagg, Charles

    The US JGOFS Arabian Sea Process Study was designed to provide a seasonally and spatially resolved carbon budget for a basin exhibiting some of the highest and lowest concentrations of plant biomass in the world's ocean. During the US JGOFS Process Study in the Arabian Sea (September 1994-January 1996), the absolute maximum in biomass of epipelagic zooplankton in the entire study was observed during the Southwest Monsoon season inshore of the Findlater Jet in the area of upwelling. The greatest contrast between high and low biomass in the study area also was observed during the Southwest Monsoon, as was the strongest onshore-offshore gradient in biomass. Lowest biomass throughout the study was observed at the most offshore station (S15), outside the direct influence of the monsoon forcing. The greatest day/night contrasts in biomass were observed nearshore in all seasons, with nighttime biomass exceeding daytime in the Northeast Monsoon season, but daytime exceeding nighttime in the Southwest Monsoon season. The diel vertical migration patterns in general reversed between the monsoons at all stations in the southern part of the study area. Virtually, no diel vertical migration of zooplankton took place in any season at the station with strong, persistent subsurface suboxic conditions (N7), suggesting that these conditions suppress migration. Based on the distribution of biomass, we hypothesize that inshore of the Findlater Jet, zooplankton grazing on phytoplankton is the dominant pathway of carbon transformation during both monsoon seasons, whereas offshore the zooplankton feed primarily on microplankton or are carnivorous, conditions that result in reduction of the carbon flux mediated by the zooplankton. Predation by mesopelagic fish, primarily myctophids, may equal daily growth of zooplankton inshore of the Findlater Jet during all seasons. This suggests that the food web inshore of the Findlater Jet is well integrated, may have evolved during past periods of

  5. Monsoon control on faunal composition of planktic foraminifera in the Arabian Sea

    NASA Astrophysics Data System (ADS)

    Munz, P.; Siccha, M.; Kucera, M.; Schulz, H.

    2013-12-01

    Being among the most productive open ocean basins, sea surface properties in the Arabian Sea are highly influenced by the seasonal reversal of the monsoonal wind system. During boreal summer wind direction from the southwest induces strong upwelling along the coast off Somalia and Oman. Vertical transport of cold and nutrient-rich deep-water masses by Ekman pumping reduces sea surface temperature and triggers primary productivity. Reversed cold and dry winds during boreal winter lead to cooling of the surface- and subsurface-waters and hereby to deep convective mixing, bringing nutrients into the photic zone and enhancing primary productivity especially in the northern part of the Arabian Sea. Here, we study the influence of the different seasonal monsoon systems on the faunal composition of planktic foraminifera, in order to improve our understanding how the faunal community record is influenced by the respective monsoon systems and to provide baseline information for the reconstruction of ancient monsoon conditions. We used published core-top foraminiferal databases, significantly increased in spatial coverage by new contributions. The resulting combined database consists of 413 core-top samples spanning the Arabian Sea and the Northern Indian Ocean to 10° S. The seasonal sea surface properties at these stations could be binned into categories of different monsoon influence, based on satellite-derived chlorophyll-a concentrations. Interpretation of species response to environmental control is based on multivariate statistical analyses of each of the categorical bins. First results show that samples influenced only by winter- and summer monsoon conditions, respectively, feature specifiable faunal composition. Globigerina bulloides is mostly associated with summer upwelling conditions, whereas Globigerina falconensis and Pulleniatina obliquiloculata are typical species of winter conditions. Redundancy analysis reveals preferences of species populations with

  6. Extreme monsoon precipitation events over South Asia in a warming world

    NASA Astrophysics Data System (ADS)

    Raghavan, K.; Sabin, T. P.; Mujumdar, M.; Priya, P.

    2012-04-01

    The recent series of flood events over Pakistan and Northwest India during the monsoon seasons of 2010 and 2011 are examples of extreme phenomena during the last century that have evoked considerable interest among various scientific communities. One of the causes for the 2010 intense precipitation over Pakistan has been attributed to the interaction between the tropical monsoon surge and southward intruding extra-tropical circulation anomalies (Hong et al. 2011). On the other hand, it has been hypothesized by Mujumdar et al. (2012) that the westward shift of the West Pacific Subtropical High (WPSH) in response to the strong La Nina conditions during 2010 was instrumental in altering the convection and circulation over the Bay of Bengal and the monsoon trough region, which in turn sustained the moist convective activities over Indo-Pak through transport of moisture from the Arabian Sea. However several aspects of the dynamics of these intense monsoon precipitation events are not adequately understood especially when atmospheric convective instabilities are expected to amplify in the backdrop of the ongoing global warming. Here, we have carried out a set of ensemble simulation experiments using a high-resolution global climate model to understand the evolution of intense monsoon precipitation events over Pakistan and Northwest India as in 2010. The results based on the model simulations indicate that while interactions among the WPSH, the South Asian monsoon trough and sub-tropical westerlies are conducive for development of convective instabilities over the Indo-Pak region, the local convective activities are found to significantly amplify in response to the large build up of moisture associated with global warming. The present results have implications in understanding how extreme monsoon precipitation events in the Indo-Pak region might have responded to past climatic variations.

  7. Understanding land surface response to changing South Asian monsoon in a warming climate

    NASA Astrophysics Data System (ADS)

    Ramarao, M. V. S.; Krishnan, R.; Sanjay, J.; Sabin, T. P.

    2015-09-01

    Recent studies have drawn attention to a significant weakening trend of the South Asian monsoon circulation and an associated decrease in regional rainfall during the last few decades. While surface temperatures over the region have steadily risen during this period, most of the CMIP (Coupled Model Intercomparison Project) global climate models have difficulties in capturing the observed decrease of monsoon precipitation, thus limiting our understanding of the regional land surface response to monsoonal changes. This problem is investigated by performing two long-term simulation experiments, with and without anthropogenic forcing, using a variable resolution global climate model having high-resolution zooming over the South Asian region. The present results indicate that anthropogenic effects have considerably influenced the recent weakening of the monsoon circulation and decline of precipitation. It is seen that the simulated increase of surface temperature over the Indian region during the post-1950s is accompanied by a significant decrease of monsoon precipitation and soil moisture. Our analysis further reveals that the land surface response to decrease of soil moisture is associated with significant reduction in evapotranspiration over the Indian land region. A future projection, based on the representative concentration pathway 4.5 (RCP4.5) scenario of the Intergovernmental Panel on Climate Change (IPCC), using the same high-resolution model indicates the possibility for detecting the summer-time soil drying signal over the Indian region during the 21st century in response to climate change. Given that these monsoon hydrological changes have profound socio-economic implications the present findings provide deeper insights and enhance our understanding of the regional land surface response to the changing South Asian monsoon. While this study is based on a single model realization, it is highly desirable to have multiple realizations to establish the robustness

  8. Adaptability of Irrigation to a Changing Monsoon in India: How far can we go?

    NASA Astrophysics Data System (ADS)

    Zaveri, E.; Grogan, D. S.; Fisher-Vanden, K.; Frolking, S. E.; Wrenn, D. H.; Nicholas, R.

    2014-12-01

    Agriculture and the monsoon are inextricably linked in India. A large part of the steady rise in agricultural production since the onset of the Green Revolution in the 1960's has been attributed to irrigation. Irrigation is used to supplement and buffer crops against precipitation shocks, but water availability for such use is itself sensitive to the erratic, se