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Sample records for africa monsoon wam

  1. 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.

  2. 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.

    2016-12-01

    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.

  3. 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.

  4. 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.

    2016-12-01

    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.

  5. Examining Intraseasonal Variability in the West African Monsoon Using the Superparameterized Community Climate System Model

    NASA Astrophysics Data System (ADS)

    McCrary, Rachel; Randall, David; Stan, Cristiana

    2013-04-01

    In West Africa, the ability to predict intraseasonal variations in rainfall would have important social and economic impacts for local populations. In particular, such predictions might be useful for estimating the timing of the monsoon onset and break periods in monsoon rains. Current theory suggests that on 25-90 day timescales, the West African monsoon (WAM) is influenced by intraseasonal variations in the Indo-Pacific region, namely the Madden Julian Oscillation (MJO) and the Asian summer monsoon. Unfortunately, most general circulation models (GCMs) show weak skill in simulating the seasonal variations in the WAM as well as intraseasonal variability in the Indo-Pacific. These model limitations make it difficult to study the dynamical links in variability across the tropics. Unlike traditional GCMs, models that have implemented the superparameterization (where traditional convective parameterizations are replaced by embedding a two dimensional cloud resolving model in each grid box) have been shown to be able to represent the WAM, the MJO and the Asian Summer Monsoon with reasonable fidelity. These model advances may allow us to study the teleconnections between the Indo-Pacific and West Africa in more detail. This study examines the intraseasonal variability of the WAM in the Superparameterized Community Climate System model (SP-CCSM). Results from the SP-CCSM are consistent with observations where intraseasonal variability accounts for 15-20% of the total variability in rainfall over West Africa during the monsoon season. We also show that on 25-90 day timescales, increases in precipitation over West Africa correspond with a northward shift of the African easterly jet and an increase in African easterly wave activity. Lag-composite analysis indicates that intraseasonal variations in WAM precipitation correspond with the North-South propagation of the MJO during boreal summer as well as the active and breaking phases of the Asian summer monsoon. Preliminary

  6. 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.

  7. 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.

  8. Characterizing Diurnal and Seasonal Cycles in Monsoon Systems from TRMM and CEOP Observations

    NASA Technical Reports Server (NTRS)

    Lau, William K. M.

    2007-01-01

    The CEOP Inter-Monsoon Study (CIMS) is one of the two main science drivers of CEOP that aims to (a) provide better understanding of fundamental physical processes in monsoon regions around the world, and (b) demonstrate the synergy and utility of CEOP data in providing a pathway for model physics evaluation and improvement. As the data collection phase for EOP-3 and EOP-4 is being completed, two full annual cycles (2003-2004) of research-quality data sets from satellites, reference sites, and model output location time series (MOLTS) have been processed and made available for data analyses and model validation studies. This article presents preliminary results of a CIMS study aimed at the characterization and intercomparison of all major monsoon systems. The CEOP reference site data proved its value in such exercises by being a powerful tool to cross-validate the TRMM data, and to intercompare with multi-model results in ongoing work. We use 6 years (1998-2003) of pentad CEOP/TRMM data with 2 deg x 2.5 deg. latitude-longitude grid, over the domain of interests to define the monsoon climatological diurnal and annual cycles for the East Asian Monsoon (EAM), the South Asian Monsoon (SAM), the West Africa Monsoon (WAM), the North America/Mexican Monsoon (NAM), the South American Summer Monsoon (SASM) and the Australian Monsoon (AUM). As noted, the TRMM data used in the study were cross-validated using CEOP reference site data, where applicable. Results show that the observed diurnal cycle of rain peaked around late afternoon over monsoon land, and early morning over the oceans. The diurnal cycles in models tend to peak 2-3 hours earlier than observed. The seasonal cycles of the EAM and SAM show the strongest continentality, i.e, strong control by continental processes away from the ITCZ. The WAM, and the AUM shows the less continentality, i.e, strong control by the oceanic ITCZ.

  9. Characterizing diurnal and seasonal cycles in monsoon systems from TRMM and CEOP observations

    NASA Technical Reports Server (NTRS)

    Lau, William K. M.

    2006-01-01

    The CEOP Inter-Monsoon Study (CIMS) is one of the two main science drivers of CEOP that aims to (a) provide better understanding of fundamental physical processes in monsoon regions around the world, and (b) demonstrate the synergy and utility of CEOP data in providing a pathway for model physics evaluation and improvement. As the data collection phase for EOP-3 and EOP-4 is being completed, two full annual cycles (2003-2004) of research-quality data sets from satellites, reference sites, and model output location time series (MOLTS) have been processed and made available for data analyses and model validation studies. This article presents preliminary results of a CIMS study aimed at the characterization and intercomparison of all major monsoon systems. The CEOP reference site data proved its value in such exercises by being a powerful tool to cross-validate the TRMM data, and to intercompare with multi-model results in ongoing work. We use 6 years (1998-2003) of pentad CEOP/TRMM data with 2deg x 2.5deg latitude-longitude grid, over the domain of interests to define the monsoon climatological diurnal and annual cycles for the East Asian Monsoon (EAM), the South Asian Monsoon (SAM), the West Africa Monsoon (WAM), the North America/Mexican Monsoon (NAM), the South American Summer Monsoon (SASM) and the Australian Monsoon (AUM). As noted, the TRMM data used in the study were cross-validated using CEOP reference site data, where applicable. Results show that the observed diurnal cycle of rain peaked around late afternoon over monsoon land, and early morning over the oceans. The diurnal cycles in models tend to peak 2-3 hours earlier than observed. The seasonal cycles of the EAM and SAM show the strongest continentality, i.e, strong control by continental processes away from the ITCZ. The WAM, and the AUM shows the less continentality, i.e, strong control by the oceanic ITCZ.

  10. 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.

  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. 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

  13. Uncertainties from above and below: West African monsoon patterns generated by a WRF multi-physics ensemble

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    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, the ability of a 27-member mixed-physics ensemble of the Weather Research and Forecasting model to represent the WAM is investigated in a process-based manner in order to extract transferable information on parameterization influences. The uncertainties introduced by three cumulus (CU), microphysics (MP) and planetary boundary layer (PBL) parameterizations are analyzed to explore interdependencies of processes leading to a certain WAM regime during the wet year 1999. We identify the modification 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. It is predominantly altered by the PBL schemes 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, weaker precipitation and a southward displaced African Easterly Jet and monsoon rainband. This identifies the representation of clouds as a critical "uncertainty from above" in simulating the WAM. The partitioning of sensible and latent heat fluxes is found to be another major source for the ensemble spread inducing "uncertainties from below" for the modeled monsoon regime. Finally, we show that regionally adapted simulations at convection-allowing scales with ingested dynamical land surface parameters improve the representation of convection, net radiation and surface flux partitioning.

  14. 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

  15. Transport pathways of CO in the African upper troposphere during the monsoon season: a study based upon the assimilation of spaceborne observations

    NASA Astrophysics Data System (ADS)

    Barret, B.; Ricaud, P.; Mari, C.; Attié, J.-L.; Bousserez, N.; Josse, B.; Le Flochmoën, E.; Livesey, N. J.; Massart, S.; Peuch, V.-H.; Piacentini, A.; Sauvage, B.; Thouret, V.; Cammas, J.-P.

    2008-06-01

    The transport pathways of carbon monoxide (CO) in the African Upper Troposphere (UT) during the West African Monsoon (WAM) is investigated through the assimilation of CO observations by the Aura Microwave Limb Sounder (MLS) in the MOCAGE Chemistry Transport Model (CTM). The assimilation setup, based on a 3-D First Guess at Assimilation Time (3-D-FGAT) variational method is described. Comparisons between the assimilated CO fields and in situ airborne observations from the MOZAIC program between Europe and both Southern Africa and Southeast Asia show an overall good agreement around the lowermost pressure level sampled by MLS (~215 hPa). The 4-D assimilated fields averaged over the month of July 2006 have been used to determine the main dynamical processes responsible for the transport of CO in the African UT. The studied period corresponds to the second AMMA (African Monsoon Multidisciplinary Analyses) aircraft campaign. At 220 hPa, the CO distribution is characterized by a latitudinal maximum around 5° N mostly driven by convective uplift of air masses impacted by biomass burning from Southern Africa, uplifted within the WAM region and vented predominantly southward by the upper branch of the winter hemisphere Hadley cell. Above 150 hPa, the African CO distribution is characterized by a broad maximum over northern Africa. This maximum is mostly controlled by the large scale UT circulation driven by the Asian Summer Monsoon (ASM) and characterized by the Asian Monsoon Anticyclone (AMA) centered at 30° N and the Tropical Easterly Jet (TEJ) on the southern flank of the anticyclone. Asian pollution uplifted to the UT over large region of Southeast Asia is trapped within the AMA and transported by the anticyclonic circulation over Northeast Africa. South of the AMA, the TEJ is responsible for the tranport of CO-enriched air masses from India and Southeast Asia over Africa. Using the high time resolution provided by the 4-D assimilated fields, we give evidence that the

  16. Transport pathways of CO in the African upper troposphere during the monsoon season: a study based upon the assimilation of spaceborne observations

    NASA Astrophysics Data System (ADS)

    Barret, B.; Ricaud, P.; Mari, C.; Attié, J.-L.; Bousserez, N.; Josse, B.; Le Flochmoën, E.; Livesey, N. J.; Massart, S.; Peuch, V.-H.; Piacentini, A.; Sauvage, B.; Thouret, V.; Cammas, J.-P.

    2008-02-01

    The transport pathways of carbon monoxide (CO) in the African Upper Troposphere (UT) during the West African Monsoon (WAM) is investigated through the assimilation of CO observations by the Aura Microwave Limb Sounder (MLS) in the MOCAGE Chemistry Transport Model (CTM). The assimilation setup, based on a 3-D First Guess at Assimilation Time (3-D-FGAT) variational method is described. Comparisons between the assimilated CO fields and in situ airborne observations from the MOZAIC program between Europe and both Southern Africa and Southeast Asia show an overall good agreement around the lowermost pressure level sampled by MLS (~215 hPa). The 4-D assimilated fields averaged over the month of July 2006 have been used to determine the main dynamical processes responsible for the transport of CO in the African UT. The studied period corresponds to the second AMMA (African Monsoon Multidisciplinary Analyses) aircraft campaign. At 220 hPa, the CO distribution is characterized by a latitudinal maximum around 5° N mostly driven by convective uplift of air masses impacted by biomass burning from Southern Africa, uplifted within the WAM region and vented predominantly southward by the upper branch of the winter hemisphere Hadley cell. Above 150 hPa, the African CO distribution is characterized by a broad maximum over northern Africa. This maximum is mostly controlled by the large scale UT circulation driven by the Asian Summer Monsoon (ASM) and characterized by the Asian Monsoon Anticyclone (AMA) centered at 30° N and the Tropical Easterly Jet (TEJ) on the southern flank of the anticyclone. Asian pollution uplifted to the UT over large region of Southeast Asia is trapped within the AMA and transported by the anticyclonic circulation over Northeast Africa. South of the AMA, the TEJ is responsible for the tranport of CO-enriched air masses from India and Southeast Asia over Africa. Using the high time resolution provided by the 4-D assimilated fields, we give evidence that the

  17. Analysis of intraseasonal convective variability modes over West Africa during the monsoon season

    NASA Astrophysics Data System (ADS)

    Ceratto, Jeffrey

    Intraseasonal variability of rainfall within the West African Monsoon has been shown to be an important factor in the weather of this region. Multiple factors have been found to contribute to variability at this timescale. Mounier, et al (2008) use EOF analysis to uncover and describe a quasi-stationary dipole of precipitation between the West African Monsoon system and the West Atlantic/Caribbean Sea. This mode, termed the Quasi Biweekly Zonal Dipole mode, operates on timescales of roughly 13 days. The stationary nature of this dipole is focused upon in their work, while the role of Kelvin waves in the mode are considered secondary. In this work, the role of Kelvin waves in the dipole mode is considered. Regression analyses are performed with time lags to observe how the dipole evolves with time. Kelvin waves are observed to dominate the timing and the phase of the dipole mode. Dynamical regressions indicate a possible source region for these Kelvin waves, over the South American continent, as well as the effects the Kelvin waves have on the West African Monsoon system as they enter and exit the region. Impacts on the strength of the Saharan Heat Low and on African Easterly Wave activity are observed. A case study highlighting Kelvin wave activity in relation to the QBZD is also considered. The second EOF pattern is also examined with lagged regressions; a relationship is found between it and the first EOF pattern.

  18. Chemical and aerosol characterisation of the troposphere over West Africa during the monsoon period as part of AMMA

    NASA Astrophysics Data System (ADS)

    Reeves, C. E.; Formenti, P.; Afif, C.; Ancellet, G.; Attie, J.-L.; Bechara, J.; Borbon, A.; Cairo, F.; Coe, H.; Crumeyrolle, S.; Fierli, F.; Flamant, C.; Gomes, L.; Hamburger, T.; Lambert, C.; Law, K. S.; Mari, C.; Matsuki, A.; Methven, J.; Mills, G. P.; Minikin, A.; Murphy, J. G.; Nielsen, J. K.; Oram, D. E.; Parker, D. J.; Richter, A.; Schlager, H.; Schwarzenboeck, A.; Thouret, V.

    2010-03-01

    During June, July and August 2006 five aircraft took part in a campaign over West Africa to observe the aerosol content and chemical composition of the troposphere and lower stratosphere as part of the African Monsoon Multidisciplinary Analysis (AMMA) project. These are the first such measurements in this region during the monsoon period. In addition to providing an overview of the tropospheric composition, this paper provides a description of the measurement strategy (flights performed, instrumental payloads, wing-tip to wing-tip comparisons) and points to some of the important findings discussed in more detailed in other papers in this special issue. The ozone data exhibits an "S" shaped vertical profile which appears to result from significant losses in the lower troposphere due to rapid deposition to forested areas and photochemical destruction in the moist monsoon air, and convective uplift of O3-poor air to the upper troposphere. This profile is disturbed, particularly in the south of the region, by the intrusions in the lower and middle troposphere of air from the Southern Hemisphere impacted by biomass burning. Comparisons with longer term data sets suggest the impact of these intrusions on West Africa in 2006 was greater than in other recent wet seasons. There is evidence for net photochemical production of ozone in these biomass burning plumes as well as in urban plumes, in particular that from Lagos, convective outflow in the upper troposphere and in boundary layer air affected by nitrogen oxide emissions from recently wetted soils. This latter effect, along with enhanced deposition to the forested areas, contributes to a latitudinal gradient of ozone in the lower troposphere. Biogenic volatile organic compounds are also important in defining the composition both for the boundary layer and upper tropospheric convective outflow. Mineral dust was found to be the most abundant and ubiquitous aerosol type in the atmosphere over Western Africa. Data collected

  19. Chemical and aerosol characterisation of the troposphere over West Africa during the monsoon period as part of AMMA

    NASA Astrophysics Data System (ADS)

    Reeves, C. E.; Formenti, P.; Afif, C.; Ancellet, G.; Attié, J.-L.; Bechara, J.; Borbon, A.; Cairo, F.; Coe, H.; Crumeyrolle, S.; Fierli, F.; Flamant, C.; Gomes, L.; Hamburger, T.; Jambert, C.; Law, K. S.; Mari, C.; Jones, R. L.; Matsuki, A.; Mead, M. I.; Methven, J.; Mills, G. P.; Minikin, A.; Murphy, J. G.; Nielsen, J. K.; Oram, D. E.; Parker, D. J.; Richter, A.; Schlager, H.; Schwarzenboeck, A.; Thouret, V.

    2010-08-01

    During June, July and August 2006 five aircraft took part in a campaign over West Africa to observe the aerosol content and chemical composition of the troposphere and lower stratosphere as part of the African Monsoon Multidisciplinary Analysis (AMMA) project. These are the first such measurements in this region during the monsoon period. In addition to providing an overview of the tropospheric composition, this paper provides a description of the measurement strategy (flights performed, instrumental payloads, wing-tip to wing-tip comparisons) and points to some of the important findings discussed in more detail in other papers in this special issue. The ozone data exhibits an "S" shaped vertical profile which appears to result from significant losses in the lower troposphere due to rapid deposition to forested areas and photochemical destruction in the moist monsoon air, and convective uplift of ozone-poor air to the upper troposphere. This profile is disturbed, particularly in the south of the region, by the intrusions in the lower and middle troposphere of air from the southern hemisphere impacted by biomass burning. Comparisons with longer term data sets suggest the impact of these intrusions on West Africa in 2006 was greater than in other recent wet seasons. There is evidence for net photochemical production of ozone in these biomass burning plumes as well as in urban plumes, in particular that from Lagos, convective outflow in the upper troposphere and in boundary layer air affected by nitrogen oxide emissions from recently wetted soils. This latter effect, along with enhanced deposition to the forested areas, contributes to a latitudinal gradient of ozone in the lower troposphere. Biogenic volatile organic compounds are also important in defining the composition both for the boundary layer and upper tropospheric convective outflow. Mineral dust was found to be the most abundant and ubiquitous aerosol type in the atmosphere over Western Africa. Data

  20. Midnight Temperature Maximum (MTM) in Whole Atmosphere Model (WAM) Simulations

    DTIC Science & Technology

    2016-04-14

    C. G. (1996), Simulations of the low -latitude midnight temperature maximum, J. Geophys. Res., 101, 26,863–26,874. Forbes, J. M., S. L. Bruinsma, Y...Midnight temperature maximum (MTM) in Whole Atmosphere Model (WAM) simulations R. A. Akmaev,1 F. Wu,2 T. J. Fuller-Rowell,2 and H. Wang2 Received 13...February 2009; accepted 18 March 2009; published 14 April 2009. [1] Discovered almost four decades ago, the midnight temperature maximum (MTM) with

  1. Satellite-based climatology of low-level continental clouds in southern West Africa during the summer monsoon season

    NASA Astrophysics Data System (ADS)

    Linden, Roderick; Fink, Andreas H.; Redl, Robert

    2015-02-01

    Synoptic observations and various satellite products have been utilized for computing climatologies of low-level stratus over southern West Africa for the wet monsoon seasons July-September of 2006-2011. Previous studies found inconsistencies between satellite cloud products; climate models often fail to reproduce the extensive stratus decks. Therefore, a better observational reference and an understanding of its limitations are urgently needed to better validate models. Most detailed information of the spatiotemporal characteristics of low-level clouds was obtained from two Meteosat Second Generation (MSG) satellite-based data sets. However, CALIPSO and CloudSat cross sections of cloud occurrence frequency suggest that both MSG products underestimate the low-level cloudiness over Nigeria due to shielding by abundant upper level and midlevel clouds and reveal that the stratus is lower over the continent than over the ocean. The Terra Multiangle Imaging Spectroradiometer product appears to overestimate the morning extent of low-level clouds. The climatology presented here shows that the zone of abundant low-level stratiform clouds is at its diurnal minimum south of 6-7°N around sunset (~1800 UTC). Thereafter, it starts to spread inland and reaches its maximum northward extent of 10-11°N between 0900 and 1000 UTC. The maximum affected area is approximately 800,000 km2. After about 1000 UTC, the northern boundary gets fragmented due to the breakup of stratus decks into fair-weather cumuli. The stratus is most frequent around Cape Palmas, over Ivory Coast, and at the windward sides of the Mampong Range (Ghana) and Oshogbo Hills (Nigeria).

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 3-Step dynamical downscaling with empirical correction of sea-surface conditions: application to a CORDEX Africa simulation

    NASA Astrophysics Data System (ADS)

    Hernández-Díaz, Leticia; Laprise, René; Nikiéma, Oumarou; Winger, Katja

    2016-06-01

    Dynamical downscaling of climate projections over a limited-area domain using a Regional Climate Model (RCM) requires boundary conditions (BC) from a Coupled Global Climate Model (CGCM) simulation. Biases in CGCM-generated BC can have detrimental effects in RCM simulations, so attempts to improve the BC used to drive the RCM simulations are worth exploring. It is in this context that an empirical method involving the bias correction of the sea-surface conditions (SSCs; sea-surface temperature and sea-ice concentration) simulated by a CGCM has been developed: The 3-step dynamical downscaling approach. The SSCs from a CGCM simulation are empirically corrected and used as lower BC over the ocean for an atmosphere-only global climate model (AGCM) simulation, which in turn provides the atmospheric lateral BC to drive the RCM simulation. We analyse the impact of this strategy on the simulation of the African climate, with a special attention to the West African Monsoon (WAM) precipitation, using the fifth-generation Canadian Regional Climate Model (CRCM5) over the CORDEX-Africa domain. The Earth System Model of the Max-Planck-Institut für Meteorologie (MPI-ESM-LR) is used as CGCM and a global version of CRCM5 is used as AGCM. The results indicate that the historical climate is much improved, approaching the skill of reanalysis-driven hindcast simulations. The most remarkable effect of this approach is the positive impact on the simulation of all aspects of the WAM precipitation, mainly due to the correction of SSCs. In fact, our results show that proper sea surface temperature (SST) in the Gulf of Guinea is a necessary condition for an adequate simulation of WAM precipitation, especially over the equatorial region of West Africa. It was found that the climate-change projections under RCP4.5 scenario obtained with the 3-step approach are substantially different from those obtained with usual downscaling approach in which the RCM is directly driven by the CGCM output; in

  8. 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.

  9. Africa.

    ERIC Educational Resources Information Center

    Martz, Carlton

    2001-01-01

    This publication explores issues related to Africa. It examines the U.S. response to the Barbary pirate states (Morocco, Algiers, Tunis, Tripoli) in the early 19th century; the current AIDS crisis in Africa; and 14th century Mali and other Islamic lands through the eyes of Ibn Battuta, who traveled throughout the Muslim world. Each article…

  10. Africa.

    ERIC Educational Resources Information Center

    Happel, Sue; Loeb, Joyce

    Although the activities in this unit are designed primarily for students in the intermediate grades, the document's text, illustrations, and bibliographic references are suitable for anyone interested in learning about Africa. Following a brief introduction and map work, the document is arranged into six sections. Section 1 traces Africa's history…

  11. The annual cycle of the West African Monsoon in a two-dimensional model:Mechanisms of the rainband migration

    NASA Astrophysics Data System (ADS)

    Peyrille, P.; Lafore, J. P.; Boone, A. A.

    2015-12-01

    The processes that drive the annual cycle of the West African Monsoon (WAM) are analysed using an idealized meridional-vertical numerical model that includes moist physics. Using the work by Peyrillé and Lafore (2007) as a starting point, the framework is adapted to studying the annual cycle. A suitable forcing methodology for temperature and humidity is derived allowing the 2D model to reproduce the main features of the WAM.A budget analysis of the simulated temperature and humidity variables leads to a picture of the ITCZ seasonal displacement, for which the moistening on the northern side of the ITCZ is key. It is due to the near surface moisture advection by the monsoon flow to the north of the ITCZ, in addition to the turbulent fluxes and shallow convection which transport humidity to the top of the PBL. On a larger scale, the warming of the Saharan Heat Low by turbulence and radiation and the cooling/moistening within the ITCZ by convective downdrafts reinforces the monsoon flow. The mechanism seems at play during the whole seasonal cycle, which is seen as a steady translation of these structures. Sensitivity experiments show the importance of the low level processes such as downdrafts, horizontal advection and water recycling. Although advection is the 1st order process, the water recycling appears as a key element by directly modulating the intensity of rainfall and by allowing the convective downdraft to feed back onto the WAM.

  12. 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

  13. Eocene monsoons

    NASA Astrophysics Data System (ADS)

    Huber, Matthew; Goldner, Aaron

    2012-01-01

    A prominent example of climate-tectonic coupling is the Asian monsoon and the uplift of the Tibetan Plateau. Here we review some of what is known about the history of the monsoon, within a global context and present results from fully coupled Eocene simulations in which Tibetan Plateau height is varied. Peak elevations were doubled from 2000 m to 4000 m whereas mean elevations increased from 750 to 1500 m. The fully coupled Eocene simulations show that introducing a higher Tibetan Plateau into Asian topography intensifies rainfall over southwest Asia, but induces drying over and behind the Plateau. This atmospheric response is controlled by increases in heating over the Plateau region which drives increases in moisture convergence inducing shifts in lower level atmospheric moisture flux. With Eocene boundary conditions aspects of the canonical response from prior work remain the same: cooling over the uplifted region, a large stationary wave response emanating from the plateau and extending into North America, and a large increase in precipitation in summer in the regions with strongest relief, with a rain shadow behind it. But some important local responses are different from similar studies with modern boundary conditions, such as a warming behind the uplifted mountains, and southward advection of warm, moist air from Paratethys onto the Plateau. These results demonstrate that simulations with fully interactive ocean-atmosphere coupled models with a realistic history of paleogeographic boundary conditions will increase the realism of the resulting climatic simulations and increase the body of available proxy evidence for comparison. More generally we find that a global monsoon distribution of precipitation exists in the Eocene regardless of Tibetan Plateau height. Changing Plateau height has minor global impacts, which include a slight drying of midlatitude and cooling of the North Pacific. The results are robust to changes in climate model resolution and

  14. 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.

  15. 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.

  16. TESTING THE E {sub peak}-E {sub iso} RELATION FOR GRBs DETECTED BY SWIFT AND SUZAKU-WAM

    SciTech Connect

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

    2009-10-20

    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 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 to 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 2005 July and the end of 2009 April, there were 48 GRBs that triggered both Swift/BAT and WAM, and an additional 48 bursts that 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 their 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 91 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 E {sub peak} and isotropic energy. We show through time-resolved spectroscopy that individual burst pulses are also consistent with this relationship.

  17. Where East Africa and the Levant Are Climatically Connected: An Alternative View of the Northward Shifts of Either the ITCZ and/or the Indian Summer Monsoon

    NASA Astrophysics Data System (ADS)

    Enzel, Y.; Kushnir, Y.; Quade, J.

    2014-12-01

    Lake levels in basins in areas bordering northern Arabian Sea have been used to reconstruct regional paleohydrological patterns through lake-level statuses. For the early-middle Holocene, dramatic increases in regional rainfall have been proposed. These rainfall changes are commonly thought to be associated with an intensified Indian summer monsoon (ISM) and a large northward shift in the latitude of the boreal summer ITCZ over the Indian Ocean; this shift was proposed to reach latitudes as far north as the Levant. However, the ISM currently forces total summer drought not rains, in the Levant and neighboring deserts, including Arabia. The drought is due to large-scale air subsidence forced by the ISM and dries the region except in southernmost Arabia, where topography lifts air and produces orographic rain. This Arabian summer drought is assisted by increased upwelling that limits rainfall inland. How large the actual changes in paleohydrology were in the Arabian Peninsula? If not the ISM, what are the real causes of these changes? We summarize paleohydrologic information from Arabia and revisit the paleolake status of all lacustrine-like deposits and their basins in Arabia. From reinterpretation of these data and sedimentology and fauna, we conclude that these basins were occupied by shallow marsh environments, not lakes. Consequently, the paleohydrologic changes required to support restricted wetland versus lakes were much smaller. These conclusions are supported by the temporal and spatial distribution of other paleoenvironmental indicators such as pollen and speleothems. They indicate that (a) rainfall changes were very small in the heart of and northern Arabia, and (b) that these changes were only at the elevated edges of southwestern, southern, and southeastern Arabian Peninsula, where it rains at present, mainly due to orographic effects on precipitation in the presence of increased moisture supply. We propose that (a) latitudinal and slight inland impact

  18. 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.

  19. 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

  20. Basic mechanism for abrupt monsoon transitions.

    PubMed

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

    2009-12-08

    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.

  1. 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

  2. Potential Change in the Indian Monsoon Circulation

    NASA Astrophysics Data System (ADS)

    Funk, C. C.; Williams, A. P.; Mishra, V.; Barlow, M. A.; Hoerling, M. P.; Hoell, A.

    2011-12-01

    In India and East Africa more than 350 million people face chronic undernourishment; population growth alone could bring this number to 500 million by 2030. Below normal rains have become more frequent as falling water tables, land degradation, warmer air temperatures, and rising fuel and fertilizer costs limit crop production growth. The Indian and East African boreal summer monsoons rely on large moisture transports from the southern Indian Ocean (SIO, 55-90°E, 0-15°S) and a low pressure cell over the north Indian Ocean (NIO, 55-90°E, 0-15°N). The relatively cloud free NIO warm pool receives a large excess of solar radiation, which the ocean transports south across the equator. While many factors influence this system, we present here observations and climate simulations linking preferential SIO-versus-NIO warming, evaporation and precipitation changes to weaker monsoon winds, weaker northward moisture transports, and warmer and drier weather in India and East Africa. Observations show that increasing SIO sea surface temperatures (SSTs) below rapid surface winds provide an 'evaporative window' (Fig. 1) that transfers energy and moisture to the atmosphere, increasing SIO rainfall. Climate simulations driven with i) observed SSTs and ii) mid-tropospheric SIO heating associate increased SIO rainfall with lower NIO rainfall. Given the empirical relationships between increasing SIO rainfall and reduced summer monsoon rains, continued warming in the Indian Ocean could lead to more frequent droughts in India, and perhaps, East Africa.

  3. 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.

  4. 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

  5. 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

    2017-02-01

    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

  6. 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.

  7. 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

  8. Role of sea surface temperature and Saharan dust radiative forcing on the multi-decadal variation of rainfall over West Africa and northern Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Kim, K. M.; Lau, W. K. M.; Colarco, P. R.

    2015-12-01

    Under the Second West African Monsoon Model Evaluation Experiments project (WAMME-2), we have carried out model experiments to investigate multi-decadal variation of sea surface temperature (SST), and Saharan dust radiative forcing on the West Africa Monsoon (WAM), and associated dust emission and transport of. Comparing experiments with prescribed SST during the 1980s to the 1950s, we find that SST forcing significant alter the large-scale circulation, rainfall, and the dust emissions and transport during these two decades. Colder SST over northern Atlantic Ocean in 1980s strengthened the subtropical high and expanded it southwestward, compared to the 1950's. As a result, the rain band over the tropical Atlantic Ocean and Sahel moves southward, and rainfall is reduced over the Sahel. Stronger surface winds associated with enhanced surface temperature gradients increase dust emission in the southern Saharan desert and northern Sahel. Combined with circulation changes induced by strengthening the subtropical high and reduced wet deposition, dust transport is increased in the deep tropics (10-20N), but relatively reduced in the northern path (20-30N) To examine the role of the increased dust aerosol radiative forcing, additional experiments are conducted with reduced dust shortwave absorption. With reduced atmospheric heating by dust aerosol, model still simulates aforementioned contrast between 1980s and 1950s, but the anomalies of Sahel drought and dust transports is weaker. The atmospheric heating due to shortwave absorption by dust provides additional buoyance and lifts dust particles to higher altitudes. Dust radiative forcing also increases meridional temperature gradients and strengthens the African Easterly Jet, resulting in an increased residence time of dust and farther westward transport. Increased dust loading and lifetime further enhance dryness over the Sahel, but bring more rain to the south of the dust region.

  9. Energetics and monsoon bifurcations

    NASA Astrophysics Data System (ADS)

    Seshadri, Ashwin K.

    2017-01-01

    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.

  10. Seasonal forecast quality of the West African monsoon rainfall regimes by multiple forecast systems

    NASA Astrophysics Data System (ADS)

    Rodrigues, Luis Ricardo Lage; García-Serrano, Javier; Doblas-Reyes, Francisco

    2014-07-01

    A targeted methodology to study the West African monsoon (WAM) rainfall variability is considered where monthly rainfall is averaged over 10°W-10°E to take into account the latitudinal migration and temporal distribution of the WAM summer rainfall. Two observational rainfall data sets and a large number of quasi-operational forecast systems, among them two systems from the European Seasonal to Interannual Prediction initiative and six systems from the North American Multi-model Ensemble project, are used in this research. The two leading modes of the WAM rainfall variability, namely, the Guinean and Sahelian regimes, are estimated by applying principal component analysis (PCA) on the longitudinally averaged precipitation. The PCA is performed upon the observations and each forecast system and lead time separately. A statistical model based on simple linear regression using sea surface temperature indices as predictors is considered both as a benchmark and an additional forecast system. The combination of the dynamical forecast systems and the statistical model is performed using different methods of combination. It is shown that most forecast systems capture the main features associated with the Guinean regime, that is, rainfall located mainly south of 10°N and the northward migration of rainfall over the season. On the other hand, only a fraction of the forecast systems capture the characteristics of the rainfall signal north of 10°N associated with the Sahelian regime. A simple statistical model proves to be of great value and outperforms most state-of-the-art dynamical forecast systems when predicting the principal components associated with the Guinean and Sahelian regimes. Combining all forecast systems do not lead to improved forecasts when compared to the best single forecast system, the European Centre for Medium-Range Weather Forecasts System 4 (S4). In fact, S4 is far better than any forecast system when predicting the variability of the WAM rainfall

  11. Response of water temperature to surface wave effects 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

    2016-04-01

    The effects of wind waves on the Baltic Sea water temperature has been studied by coupling the hydrodynamical model NEMO with the wave model WAM. The wave forcing terms that have been taken into consideration are: Stokes-Coriolis force, seastate dependent energy flux and sea-state dependent momentum flux. The combined role of these processes as well as their individual contributions on simulated temperature is analysed. The results indicate a pronounced effect of waves on surface temperature, on the distribution of vertical temperature and on upwellinǵs. In northern parts of the Baltic Sea a warming of the surface layer occurs in the wave included simulations. This in turn reduces the cold bias between simulated and measured data. The warming is primarily caused by sea-state dependent energy flux. Wave induced cooling is mostly observed in near coastal areas and is mainly due to Stokes-Coriolis forcing. The latter triggers effect of intensifying upwellings near the coasts, depending on the direction of the wind. The effect of sea-state dependent momentum flux is predominantly to warm the surface layer. During the summer the wave induced water temperature changes were up to 1 °C.

  12. 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.

  13. 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.

  14. Seasonal forecasts for regional onset of the West African monsoon

    NASA Astrophysics Data System (ADS)

    Vellinga, Michael; Arribas, Alberto; Graham, Richard

    2013-06-01

    The West African monsoon has over the years proven difficult to represent in global coupled models. The current operational seasonal forecasting system of the UK Met Office (GloSea4) has a good representation of monsoon rainfall over West Africa. It reproduces the various stages of the monsoon: a coastal phase in May and June, followed by onset of the Sahelian phase in July when rainfall maxima shift northward of 10N until September; and a secondary coastal rainfall maximum in October. We explore the dynamics of monsoon onset in GloSea4 and compare it to reanalyses. An important difference is the change in the Saharan heat low around the time of Sahelian onset. In Glosea4 the deepening heat low introduces moisture convergence across an east-west Sahelian band, whereas in the reanalyses such an east-west organisation of moisture does not occur and moisture is transported northwards to the Sahara. Lack of observations in the southern Sahara makes it difficult to verify this process in GloSea4 and also suggests that reanalyses may not be strongly constrained by station observations in an area key to Sahelian onset. Timing of monsoon onset has socio-economic importance for many countries in West Africa and we explore onset predictability in GloSea4. We use tercile categories to calculate probabilities for onset occurring before, near and after average in four different onset indicators. Glosea4 has modest skill at 2-3 months' lead time, with ROC scores of 0.6-0.8. Similar skill is seen in hindcasts with models from the ENSEMBLES project, even in models with large rainfall biases over the Sahel. Forecast skill derives from tropical SST in June and many models capture at least the influence of the tropical Atlantic. This suggests that long-range skill for onset could be present in other seasonal forecasting systems in spite of mean rainfall biases.

  15. Trace gas transport out of the Indian Summer Monsoon

    NASA Astrophysics Data System (ADS)

    Tomsche, Laura; Pozzer, Andrea; Zimmermann, Peter; Parchatka, Uwe; Fischer, Horst

    2016-04-01

    The trace gas transport out of the Indian summer monsoon was investigated during the aircraft campaign OMO (Oxidation Mechanism Observations) with the German research aircraft HALO (High Altitude and Long Range Research Aircraft) in July/August 2015. HALO was based at Paphos/Cyprus and also on Gan/Maledives. Flights took place over the Mediterranean Sea, the Arabian Peninsula and the Arabian Sea. In this work the focus is on the distribution of carbon monoxide (CO) and methane (CH4) in the upper troposphere. They were measured with the laser absorption spectrometer TRISTAR on board of HALO. During the Indian summer monsoon strong convection takes place over India and the Bay of Bengal. In this area the population is high accompanied by many emission sources e.g. wetlands and cultivation of rice. Consequently the boundary layer is polluted containing high concentrations of trace gases like methane and carbon monoxide. Due to vertical transport these polluted air masses are lifted to the upper troposphere. Here they circulate with the so called Asian monsoon anticyclone. In the upper troposphere polluted air masses lead to a change in the chemical composition thus influence the chemical processes. Furthermore the anticyclone spreads the polluted air masses over a larger area. Thus the outflow of the anticyclone in the upper troposphere leads to higher concentrations of trace gases over the Arabian Sea, the Arabian Peninsula and also over the eastern part of North Africa and the eastern part of the Mediterranean Sea. During OMO higher concentrations of methane and carbon monoxide were detected at altitudes between 11km and 15km. The highest measured concentrations of carbon monoxide and methane were observed over Oman. The CO concentration in the outflow of the monsoon exceeds background levels by 10-15ppb. However the enhancement in the concentration is not obviously connected to the monsoon due to the natural variability in the troposphere. The enhancement in the

  16. 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

  17. Indo-China monsoon indices.

    PubMed

    Tsai, ChinLeong; Behera, Swadhin K; Waseda, Takuji

    2015-01-29

    Myanmar and Thailand often experience severe droughts and floods that cause irreparable damage to the socio-economy condition of both countries. In this study, the Southeastern Asian Summer Monsoon variation is found to be the main element of interannual precipitation variation of the region, more than the El Niño/Southern Oscillation (ENSO). The ENSO influence is evident only during the boreal spring season. Although the monsoon is the major factor, the existing Indian Monsoon Index (IMI) and Western North Pacific Monsoon Index (WNPMI) do not correlate well with the precipitation variation in the study regions of Southern Myanmar and Thailand. Therefore, a new set of indices is developed based on the regional monsoon variations and presented here for the first time. Precipitation variations in Southern Myanmar and Thailand differ as well as the elements affecting the precipitation variations in different seasons. So, separate indices are proposed for each season for Southern Myanmar and Thailand. Four new monsoon indices based on wind anomalies are formulated and are named as the Indochina Monsoon Indices. These new indices correlate better with the precipitation variations of the study region as compared to the existing IMI and WNPMI.

  18. Indo-China Monsoon Indices

    NASA Astrophysics Data System (ADS)

    Tsai, Chinleong; Behera, Swadhin K.; Waseda, Takuji

    2015-01-01

    Myanmar and Thailand often experience severe droughts and floods that cause irreparable damage to the socio-economy condition of both countries. In this study, the Southeastern Asian Summer Monsoon variation is found to be the main element of interannual precipitation variation of the region, more than the El Niño/Southern Oscillation (ENSO). The ENSO influence is evident only during the boreal spring season. Although the monsoon is the major factor, the existing Indian Monsoon Index (IMI) and Western North Pacific Monsoon Index (WNPMI) do not correlate well with the precipitation variation in the study regions of Southern Myanmar and Thailand. Therefore, a new set of indices is developed based on the regional monsoon variations and presented here for the first time. Precipitation variations in Southern Myanmar and Thailand differ as well as the elements affecting the precipitation variations in different seasons. So, separate indices are proposed for each season for Southern Myanmar and Thailand. Four new monsoon indices based on wind anomalies are formulated and are named as the Indochina Monsoon Indices. These new indices correlate better with the precipitation variations of the study region as compared to the existing IMI and WNPMI.

  19. The West African Monsoon in the Regional Climate Model COSMO-CLM

    NASA Astrophysics Data System (ADS)

    Kothe, S.; Ahrens, B.

    2010-09-01

    The West African Monsoon is in parts of Africa the exceedingly climatic process with a high influence on flora, fauna and economy. In this study we evaluated ECHAM5 and ERA-Interim driven CCLM regional climate simulations of Africa to analyze the reproduction of characteristics of the West African Monsoon in the model. As indicators for the monsoon we looked at the total precipitation and the outgoing long-wave radiation (OLR) as a hint for convective clouds. Additionally the West African Monsoon Index (WAMI) should give a view at the dynamical component of the monsoon. Compared to the large-scale driving models, CCLM was not able to achieve more accurate results. There were regional strong under- and overestimations in precipitation but the mean values showed quite good results with a maximum difference of about 20%. For the ECHAM5 driven CCLM simulation, the strongest overestimation of precipitation at the African West coast, was combined with a strong overestimation of OLR, which indicated too much convection in this area. The model caught the WAMI very well. In a next step we want to quantify the influence of the driving model and the impact of surface features like the surface albedo on the monsoon.

  20. Atlantic effects on recent decadal trends in global monsoon

    NASA Astrophysics Data System (ADS)

    Kamae, Youichi; Li, Xichen; Xie, Shang-Ping; Ueda, Hiroaki

    2017-01-01

    Natural climate variability contributes to recent decadal climate trends. Specifically the trends during the satellite era since 1979 include Atlantic and Indian Ocean warming and Pacific cooling associated with phase shifts of the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation, and enhanced global monsoon (GM) circulation and rainfall especially in the Northern Hemisphere. Here we evaluate effects of the oceanic changes on the global and regional monsoon trends by partial ocean temperature restoring experiments in a coupled atmosphere-ocean general circulation model. Via trans-basin atmosphere-ocean teleconnections, the Atlantic warming drives a global pattern of sea surface temperature change that resembles observations, giving rise to the enhanced GM. The tropical Atlantic warming and the resultant Indian Ocean warming favor subtropical deep-tropospheric warming in both hemispheres, resulting in the enhanced monsoon circulations and precipitation over North America, South America and North Africa. The extratropical North Atlantic warming makes an additional contribution to the monsoon enhancement via Eurasian continent warming and resultant land-sea thermal gradient over Asia. The results of this study suggest that the Atlantic multidecadal variability can explain a substantial part of global climate variability including the recent decadal trends of GM.

  1. The contribution of CEOP data to the understanding and modeling of monsoon systems

    NASA Technical Reports Server (NTRS)

    Lau, William K. M.

    2005-01-01

    CEOP has contributed and will continue to provide integrated data sets from diverse platforms for better understanding of the water and energy cycles, and for validating models. In this talk, I will show examples of how CEOP has contributed to the formulation of a strategy for the study of the monsoon as a system. The CEOP data concept has led to the development of the CEOP Inter-Monsoon Studies (CIMS), which focuses on the identification of model bias, and improvement of model physics such as the diurnal and annual cycles. A multi-model validation project focusing on diurnal variability of the East Asian monsoon, and using CEOP reference site data, as well as CEOP integrated satellite data is now ongoing. Similar validation projects in other monsoon regions are being started. Preliminary studies show that climate models have difficulties in simulating the diurnal signals of total rainfall, rainfall intensity and frequency of occurrence, which have different peak hours, depending on locations. Further more model diurnal cycle of rainfall in monsoon regions tend to lead the observed by about 2-3 hours. These model bias offer insight into lack of, or poor representation of key components of the convective,and stratiform rainfall. The CEOP data also stimulated studies to compare and contrasts monsoon variability in different parts of the world. It was found that seasonal wind reversal, orographic effects, monsoon depressions, meso-scale convective complexes, SST and land surface land influences are common features in all monsoon regions. Strong intraseasonal variability is present in all monsoon regions. While there is a clear demarcation of onset, breaks and withdrawal in the Asian and Australian monsoon region associated with climatological intraseasonal variability, it is less clear in the American and Africa monsoon regions. The examination of satellite and reference site data in monsoon has led to preliminary model experiments to study the impact of aerosol on

  2. 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

  3. The Origins of ITCZs, Monsoons, and Monsoon Onset

    NASA Technical Reports Server (NTRS)

    Chao, Winston C.

    2009-01-01

    Intertropical convergence zones (ITCZs), monsoons and monsoon onset are among the most prominent of atmospheric phenomena. Understanding their origins is fundamental to a full understanding of the atmospheric general circulation and has challenged meteorologists for a very long time. There has been important progress in understanding these phenomena in recent years, and in this seminar, recent developments, to which the speaker has contributed, are reviewed. First, contrary to conventional belief, land-sea thermal contrast is not necessary for monsoons to form. Second, monsoon onset occurs when there is a sudden poleward jump of an ITCZ during its annual cycle of latitudinal movement. A monsoon, then, is an ITCZ after its poleward jump. Third, the SST latitudinal maximum is not the most significant, or even a necessary, factor in the formation of an ITCZ; there are other important, if not more important, factors. These factors are the interaction between convection and surface fluxes, the interaction between convection and radiation, and the earth's rotation. Finally, the recent understanding of how ITCZs form has led to a conceptual explanation for the origin of the double ITCZ bias in GCM simulations.

  4. The South Asian Monsoon and the Tropospheric Biennial Oscillation.

    NASA Astrophysics Data System (ADS)

    Meehl, Gerald A.

    1997-08-01

    A mechanism is described that involves the south Asian monsoon as an active part of the tropospheric biennial oscillation (TBO) described in previous studies. This mechanism depends on coupled land-atmosphere-ocean interactions in the Indian sector, large-scale atmospheric east-west circulations in the Tropics, convective heating anomalies over Africa and the Pacific, and tropical-midlatitude interactions in the Northern Hemisphere. A key element for the monsoon role in the TBO is land-sea or meridional tropospheric temperature contrast, with area-averaged surface temperature anomalies over south Asia that are able to persist on a 1-yr timescale without the heat storage characteristics that contribute to this memory mechanism in the ocean. Results from a global coupled general circulation model show that soil moisture anomalies contribute to land-surface temperature anomalies (through latent heat flux anomalies) for only one season after the summer monsoon. A global atmospheric GCM in perpetual January mode is run with observed SSTs with specified convective heating anomalies to demonstrate that convective heating anomalies elsewhere in the Tropics associated with the coupled ocean-atmosphere biennial mechanism can contribute to altering seasonal midlatitude circulation. These changes in the midlatitude longwave pattern, forced by a combination of tropical convective heating anomalies over East Africa, Southeast Asia, and the western Pacific (in association with SST anomalies), are then able to maintain temperature anomalies over south Asia via advection through winter and spring to set up the land-sea meridional tropospheric temperature contrast for the subsequent monsoon. The role of the Indian Ocean, then, is to provide a moisture source and a low-amplitude coupled response component for meridional temperature contrast to help drive the south Asian monsoon. The role of the Pacific is to produce shifts in regionally coupled convection-SST anomalies. These regions

  5. The Contribution of CEOP Data to the Understanding and Modeling of Monsoon Systems

    NASA Technical Reports Server (NTRS)

    Lau, William K. M.

    2005-01-01

    CEOP has contributed and will continue to provide integrated data sets from diverse platforms for better understanding of the water and energy cycles, and for validaintg models. In this talk, I will show examples of how CEOP has contributed to the formulation of a strategy for the study of the monsoon as a system. The CEOP data concept has led to the development of the CEOP Inter-Monsoon Studies (CIMS), which focuses on the identification of model bias, and improvement of model physics such as the diurnal and annual cycles. A multi-model validation project focusing on diurnal variability of the East Asian monsoon, and using CEOP reference site data, as well as CEOP integrated satellite data is now ongoing. Preliminary studies show that climate models have difficulties in simulating the diurnal signals of total rainfall, rainfall intensity and frequency of occurrence, which have different peak hours, depending on locations. Further more model diurnal cycle of rainfall in monsoon regions tend to lead the observed by about 2-3 hours. These model bias offer insight into lack of, or poor representation of, key components of the convective and stratiform rainfall. The CEOP data also stimulated studies to compare and contrasts monsoon variability in different parts of the world. It was found that seasonal wind reversal, orographic effects, monsoon depressions, meso-scale convective complexes, SST and land surface land influences are common features in all monsoon regions. Strong intraseasonal variability is present in all monsoon regions. While there is a clear demarcation of onset, breaks and withdrawal in the Asian and Australian monsoon region associated with climatological intraseasonal variabillity, it is less clear in the American and Africa monsoon regions. The examination of satellite and reference site data in monsoon has led to preliminary model experiments to study the impact of aerosol on monsoon variability. I will show examples of how the study of the

  6. 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

  7. 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.

  8. 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.

  9. Response of the African monsoon to orbital forcing and ocean feedbacks in the middle holocene

    SciTech Connect

    Kutzbach, J.E.; Liu, Z.

    1997-10-17

    Simulations with a climate model that asynchronously couples the atmosphere and the ocean showed that the increased amplitude of the seasonal cycle of insolation in the Northern Hemisphere 6000 years ago could have increased tropical Atlantic sea surface temperatures in late summer. The simulated increase in sea surface temperature and associated changes in atmospheric circulation enhanced the summer monsoon precipitation of northern Africa by more than 25 percent, compared with the middle Holocene simulation with prescribed modern sea surface temperatures, and provided better agreement with paleorecords of enhanced monsoons. 28 refs., 4 figs., 1 tab.

  10. Monsoon low-level jet over the gateway of Indian summer monsoon: a comparative study for two distinct monsoon years

    NASA Astrophysics Data System (ADS)

    Narayanan, Suresh; Kottayil, Ajil; Mohanakumar, K.

    2016-12-01

    High-resolution radiosonde measurements are used to study the characteristics and dynamics of monsoon low-level jet at the monsoon onset region of Cochin (10.04°N; 76.32°E) in India under two contrasting monsoon years, 2013 and 2015. The core speed and core height of the low-level jet is significantly higher during the strong monsoon year of 2013 than for the monsoon-deficient year of 2015. The average core heights for these years are seen to exist at 2.03 and 2.20 km, respectively. The low-level jet-modulated parameters such as moisture flux, momentum flux and kinetic energy flux show higher values during monsoon of 2013 as compared to 2015. Among the monsoon low-level jet parameters, the moisture flux has the strongest influence on the observed rainfall over Cochin. Also, an exponential function is seen to best explain the moisture flux-rainfall relationship. The weakening of monsoon during 2015 is attributed most likely to an eastward shift of the core convective activity from the Indian subcontinent as revealed from satellite observation of the upper tropospheric humidity. A close association is seen between the rainfall over Cochin and the convective activity over the Indian subcontinent. Observational studies such as this, which links monsoon rainfall, monsoon low-level jet parameters and convective activity, are expected to enhance the understanding of monsoon processes in general and subsequently improve the forecasting skill of models.

  11. 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

    2016-12-01

    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

  12. 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

  13. 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.

  14. 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

  15. 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.

  16. Land surface coupling in regional climate simulations of tropical monsoon systems

    NASA Astrophysics Data System (ADS)

    Steiner, A. L.; Pal, J. S.; Bell, J. L.; Diffenbaugh, N. S.; Rauscher, S. A.; Giorgi, F.; Sloan, L. C.

    2007-12-01

    Simulations with the ICTP Regional Climate Model version 3 coupled to the Common Land Model version 3 (RegCM3-CLM3) show significant improvement in the simulation of summer monsoon precipitation and temperature. A ten-year simulation (1992-2001) over Europe and northern Africa driven by reanalysis boundary conditions indicates that timing and magnitude of the African monsoon more closely match observations when a new land surface scheme is implemented. The RegCM3-CLM3 improves the timing of the monsoon advance and retreat across the Guinean Coast and reduces the precipitation bias in the Sahel and Northern Africa. As a result, simulated temperatures are higher, thereby reducing the cool temperature bias noted in northern Africa in RegCM3. The complex treatment of soil in CLM3 leads to a more accurate representation of interannual soil moisture and land surface albedo in RegCM3-CLM, which may lead to the strong land-atmosphere feedback.

  17. The global monsoon definition using the difference of local minimum and maximum pentad precipitation rates associated with cross-equatorial flow reversal

    NASA Astrophysics Data System (ADS)

    Qian, Weihong; Jiang, Ning

    2016-05-01

    Since most previous attempts to establish monsoon indices have been limited to specific regions, they have lacked the applicability to universally describe the global monsoon domain. In this paper, we first review the history of global monsoon study and then identify the climatology of global precipitation associated with major systems of the atmospheric general circulation. A new index, based on the annual and semiannual harmonic precipitation rate difference between two local calendar maximal and minimal precipitation pentads, is used to identify the global monsoon domain focusing on where experienced and what caused the climatic dry-wet alteration. The global monsoon domain is defined by the regions where two pentad-mean precipitation difference exceeds 4 mm ṡday-1, which is also influenced by the low-level prevailing wind reversal associated with the cross-equatorial flow. This definition not only confirmed previous results of the classical global monsoon domain from the tropical Africa to Asia-Australia and non-classical monsoon region in the tropical America but also solved an issue of missing local summer monsoon spots.

  18. Aerosol and monsoon climate interactions over Asia

    NASA Astrophysics Data System (ADS)

    Li, Zhanqing; Lau, W. K.-M.; Ramanathan, V.; Wu, G.; Ding, Y.; Manoj, M. G.; Liu, J.; Qian, Y.; Li, J.; Zhou, T.; Fan, J.; Rosenfeld, D.; Ming, Y.; Wang, Y.; Huang, J.; Wang, B.; Xu, X.; Lee, S.-S.; Cribb, M.; Zhang, F.; Yang, X.; Zhao, C.; Takemura, T.; Wang, K.; Xia, X.; Yin, Y.; Zhang, H.; Guo, J.; Zhai, P. M.; Sugimoto, N.; Babu, S. S.; Brasseur, G. P.

    2016-12-01

    The increasing severity of droughts/floods and worsening air quality from increasing aerosols in Asia monsoon regions are the two gravest threats facing over 60% of the world population living in Asian monsoon regions. These dual threats have fueled a large body of research in the last decade on the roles of aerosols in impacting Asian monsoon weather and climate. This paper provides a comprehensive review of studies on Asian aerosols, monsoons, and their interactions. The Asian monsoon region is a primary source of emissions of diverse species of aerosols from both anthropogenic and natural origins. The distributions of aerosol loading are strongly influenced by distinct weather and climatic regimes, which are, in turn, modulated by aerosol effects. On a continental scale, aerosols reduce surface insolation and weaken the land-ocean thermal contrast, thus inhibiting the development of monsoons. Locally, aerosol radiative effects alter the thermodynamic stability and convective potential of the lower atmosphere leading to reduced temperatures, increased atmospheric stability, and weakened wind and atmospheric circulations. The atmospheric thermodynamic state, which determines the formation of clouds, convection, and precipitation, may also be altered by aerosols serving as cloud condensation nuclei or ice nuclei. Absorbing aerosols such as black carbon and desert dust in Asian monsoon regions may also induce dynamical feedback processes, leading to a strengthening of the early monsoon and affecting the subsequent evolution of the monsoon. Many mechanisms have been put forth regarding how aerosols modulate the amplitude, frequency, intensity, and phase of different monsoon climate variables. A wide range of theoretical, observational, and modeling findings on the Asian monsoon, aerosols, and their interactions are synthesized. A new paradigm is proposed on investigating aerosol-monsoon interactions, in which natural aerosols such as desert dust, black carbon from

  19. Thermal controls on the Asian summer monsoon.

    PubMed

    Wu, Guoxiong; Liu, Yimin; He, Bian; Bao, Qing; Duan, Anmin; Jin, Fei-Fei

    2012-01-01

    The Asian summer monsoon affects more than sixty percent of the world's population; understanding its controlling factors is becoming increasingly important due to the expanding human influence on the environment and climate and the need to adapt to global climate change. Various mechanisms have been suggested; however, an overarching paradigm delineating the dominant factors for its generation and strength remains debated. Here we use observation data and numerical experiments to demonstrates that the Asian summer monsoon systems are controlled mainly by thermal forcing whereas large-scale orographically mechanical forcing is not essential: the South Asian monsoon south of 20°N by land-sea thermal contrast, its northern part by the thermal forcing of the Iranian Plateau, and the East Asian monsoon and the eastern part of the South Asian monsoon by the thermal forcing of the Tibetan Plateau.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

    Bala, G.; N, D.; Modak, A.

    2015-12-01

    In this study, we investigate the bio-geophysical effects of large-scale deforestation on monsoon regions using idealized deforestation simulations. The simulations are performed using the NCAR CAM5 atmospheric model coupled to a mixed layer ocean model. The four deforestation experiments are named Global, Boreal, Temperate and Tropical, respectively. In these deforestation experiments, trees are replaced by grasses around the globe, between 20oS and 20oN, between 20oN and 50oN and poleward of 50oN, respectively. We find that the remote forcing from large-scale deforestation in the Temperate and Boreal cases shift the Inter-tropical Convergence Zone (ITCZ) southward. This results in a significant decrease in precipitation in the Northern Hemisphere monsoon regions (East Asia, North America, North Africa, 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 depend 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 in the Global deforestation case. Our results indicate that any comprehensive assessment of afforestation/reforestation as climate change mitigation strategies should carefully evaluate the remote effects on monsoonal precipitation besides the large local impacts on temperatures and carbon sequestration benefits. Our results also demonstrate the linkages between any large scale forcing that causes large warming/cooling in the high latitudes and rainfall changes in tropical monsoonal regions via ITCZ shifts. Figure Caption: Changes in annual mean precipitation (mm/day) between the deforestation experiments and the control simulation. Hatched areas are regions where changes are statistically significant at the 95% confidence level. Shading in line plots represents the ±1 standard

  4. Role of soil moisture-atmosphere interactions in model simulation of the West African Monsoon

    NASA Astrophysics Data System (ADS)

    Berg, Alexis; Lintner, Benjamin; Giannini, Alessandra

    2015-04-01

    Land-atmosphere interactions play a major role in climate characteristics over land. One of the key features of those interactions is the feedback of soil moisture on precipitation: driven by atmosphere variability, soil moisture variations in turn modulate land-atmosphere fluxes, altering surface climate and boundary layer conditions and potentially feeding back on precipitation, both through local and large-scale processes. Prior studies have highlighted West Africa as one of the regions where such interactions play an important role in precipitation variability. Here we investigate the role of soil moisture-atmosphere interactions on the West African Monsoon in the GFDL-ESM2M model, comparing simulations from the GLACE-CMIP5 experiment with prescribed (climatological seasonal cycle) and interactive soil moisture. Results indicate that total monsoon precipitation is enhanced in the prescribed case, suggesting that overall soil moisture-atmosphere interactions act to reduce precipitation. However, contrasting effects appear between the "core" of the monsoon (in a time- latitude sense) where precipitation is reduced with interactive soil moisture, and the "margins" (in a time-latitude view) where precipitation increases. We investigate the processes responsible for these differences, from changes in the surface energy budget and Bowen Ratio to changes in large-scale circulation and monsoon dynamics. Simulations from other GLACE-CMIP5 participating models are also analyzed to assess the inter-model robustness of the results.

  5. The spectrum of Asian monsoon variability

    NASA Astrophysics Data System (ADS)

    Loope, G. R.; Overpeck, J. T.

    2014-12-01

    The Indian monsoon is the critical source of freshwater for over one billion people. Variability in monsoon precipitation occurs on all time scales and has severe consequences for the people who depend on monsoon rains. Extreme precipitation events have increased in the 20th century and are predicted to continue to become more frequent with anthropogenic global warming. The most recent models project that both monsoon precipitation and variability of precipitation will increase over the 21st century leading to increased flooding and possibly severe droughts. Although current models are able to capture the risk of relatively short droughts (1-5 years) reasonably well, they tend to underestimate the risk of longer, decadal- multidecadal droughts. I use observational records over the last 100 years in conjunction with cave, tree ring, and lake data from the NOAA paleoclimate database to reconstruct Holocene monsoon variability. I am able to show that the Asian monsoon has more low frequency variability than is projected by current climate models. The growing evidence for this discrepancy in hydroclimate variability between models and observational/paleoclimate records is of grave concern. If these models fail to capture the decadal-multidecadal droughts of the past it is likely they will underestimate the possibility of such droughts in the future.

  6. Potential Predictability of the Monsoon Subclimate Systems

    NASA Technical Reports Server (NTRS)

    Yang, Song; Lau, K.-M.; Chang, Y.; Schubert, S.

    1999-01-01

    While El Nino/Southern Oscillation (ENSO) phenomenon can be predicted with some success using coupled oceanic-atmospheric models, the skill of predicting the tropical monsoons is low regardless of the methods applied. The low skill of monsoon prediction may be either because the monsoons are not defined appropriately or because they are not influenced significantly by boundary forcing. The latter characterizes the importance of internal dynamics in monsoon variability and leads to many eminent chaotic features of the monsoons. In this study, we analyze results from nine AMIP-type ensemble experiments with the NASA/GEOS-2 general circulation model to assess the potential predictability of the tropical climate system. We will focus on the variability and predictability of tropical monsoon rainfall on seasonal-to-interannual time scales. It is known that the tropical climate is more predictable than its extratropical counterpart. However, predictability is different from one climate subsystem to another within the tropics. It is important to understand the differences among these subsystems in order to increase our skill of seasonal-to-interannual prediction. We assess potential predictability by comparing the magnitude of internal and forced variances as defined by Harzallah and Sadourny (1995). The internal variance measures the spread among the various ensemble members. The forced part of rainfall variance is determined by the magnitude of the ensemble mean rainfall anomaly and by the degree of consistency of the results from the various experiments.

  7. On the association between pre-monsoon aerosol and all-India summer monsoon rainfall

    NASA Astrophysics Data System (ADS)

    Patil, S. D.; Preethi, B.; Bansod, S. D.; Singh, H. N.; Revadekar, J. V.; Munot, A. A.

    2013-09-01

    Summer monsoon rainfall which gives 75-90% of the annual rainfall plays vital role in Indian economy as the food grain production in India is very much dependent on the summer monsoon rainfall. It has been suggested by recent studies that aerosol loading over the Indian region plays significant role in modulating the monsoon circulation and consequent rainfall distribution over the Indian sub-continent. Increased industrialization and the increasing deforestation over past few decades probably cause a gradual increase in the aerosol concentration. A significant negative relationship between pre-monsoon (March-May i.e. MAM) aerosol loading over BOB and IGP regions and the forthcoming monsoon rainfall have been observed from the thorough analysis of the fifteen years (1997-2011) monthly Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI) and All-India Summer Monsoon Rainfall (AISMR) data. Composite analysis revealed that AI anomalies during pre-monsoon season are negative for excess year and positive for deficient monsoon years over the Indian subcontinent, with strong variation over Bay of Bengal (BOB) and Indo-Gangetic Plain (IGP) regions from the month of March onwards. The correlation coefficients between AISMR and pre-monsoon AI over BOB and IGP regions are found to be negative and significant at 5% level. The study clearly brings out that the pre-monsoon aerosol loading over the BOB and IGP regions has a significant correlational link with the forthcoming monsoon intensity; however a further study of the aerosol properties and their feedback to the cloud microphysical properties is asked for establishing their causal linkage.

  8. The global monsoon division combining the k-means clustering method and low-level cross-equatorial flow

    NASA Astrophysics Data System (ADS)

    Jiang, Ning; Qian, Weihong; Leung, Jeremy Cheuk-Hin

    2016-10-01

    The global monsoon domain has been recently determined utilizing two criteria: difference of local maximum and minimum pentad-mean precipitation rates exceeding 4 mm day-1, and wind reversal of low-level cross-equatorial flow. In this paper, 22 major dry-wet alteration regions under six categories were first derived through the k-means clustering method from the climatological evolution of global precipitation. Considering the seasonal influences of the low-level cross-equatorial flow in these major dry-wet alternation regions, the global monsoon was objectively divided into 16 major regions under five climatological precipitation categories. Nine monsoon regions are distributed between Asia and Australia while four regions are from Africa to the Southwest Indian Ocean and three regions in Americas. Precipitation trends during rainy seasons of 1981-2010 were examined in the 16 monsoon regions. Four regions with decreasing trends of precipitation are located in Africa and the Southwest Indian Ocean while three regions with increasing trends are situated in Americas. Six regions of increasing precipitation trends are concentrated in Asia and the biggest increasing trend is found in south China.

  9. Aerosol and monsoon climate interactions over Asia: AEROSOL AND MONSOON CLIMATE INTERACTIONS

    SciTech Connect

    Li, Zhanqing; Lau, W. K. -M.; Ramanathan, V.; Wu, G.; Ding, Y.; Manoj, M. G.; Liu, J.; Qian, Y.; Li, J.; Zhou, T.; Fan, J.; Rosenfeld, D.; Ming, Y.; Wang, Y.; Huang, J.; Wang, B.; Xu, X.; Lee, S. -S.; Cribb, M.; Zhang, F.; Yang, X.; Zhao, C.; Takemura, T.; Wang, K.; Xia, X.; Yin, Y.; Zhang, H.; Guo, J.; Zhai, P. M.; Sugimoto, N.; Babu, S. S.; Brasseur, G. P.

    2016-11-15

    Asian monsoons and aerosols have been studied extensively which are intertwined in influencing the climate of Asia. This paper provides a comprehensive review of ample studies on Asian aerosol, monsoon and their interactions. The region is the primary source of aerosol emissions of varies species, influenced by distinct weather and climatic regimes. On continental scale, aerosols reduce surface insolation and weaken the land-ocean thermal contrast, thus inhibiting the development of monsoons. Locally, aerosol radiative effects alter the thermodynamic stability and convective potential of the lower atmosphere leading to reduced temperatures, increased atmospheric stability, and weakened wind and atmospheric circulation. The atmospheric thermodynamic state may also be altered by the aerosol serving as cloud condensation nuclei or ice nuclei. Many mechanisms have been put forth regarding how aerosols modulate the amplitude, frequency, intensity, and phase of numerous monsoon climate variables. A wide range of theoretical, observational, and modeling findings on the Asian monsoon, aerosols, and their interactions are synthesized. A new paradigm is proposed on investigating aerosol-monsoon interactions, in which natural aerosols such as desert dust, black carbon from biomass burning, and biogenic aerosols from vegetation are considered integral components of an intrinsic aerosol-monsoon climate system, subject to external forcings of global warming, anthropogenic aerosols, and land use and change. Future research on aerosol-monsoon interactions calls for an integrated approach and international collaborations based on long-term sustained observations, process measurements, and improved models, as well as using observations to constrain model simulations and projections.

  10. Quasi-biweekly oscillations of the South Asian monsoon and its co-evolution in the upper and lower troposphere

    NASA Astrophysics Data System (ADS)

    Ortega, Sebastián; Webster, Peter J.; Toma, Violeta; Chang, Hai-Ru

    2017-01-01

    The Upper Tropospheric Quasi-Biweekly Oscillation (UQBW) of the South Asian monsoon is studied using the potential vorticity field on the 370 K isentrope. The UQBW is shown to be a common occurrence in the upper troposphere during the monsoon, and its typical evolution is described. We suggest that the UQBW is a phenomenon of both the middle and tropical latitudes, owing its existence to the presence of the planetary-scale upper-tropospheric monsoon anticyclone. The UQBW is first identified as Rossby waves originating in the northern flank of the monsoon anticyclone. These Rossby waves break when reaching the Pacific Ocean, and their associated cyclonic PV anomalies move southward to the east of Asia and then westward across the Indian Ocean and Africa advected by the monsoon anticyclone. A strong correlation, or co-evolution, between the UQBW and quasi-biweekly oscillations in the lower troposphere (QBW) is also found. In particular, analysis of vertically-integrated horizontal moisture transport, 850 hPa geopotential, and outgoing long-wave radiation show that the UQBW is usually observed at the same time as, and co-evolves with, the lower tropospheric QBW over South Asia. We discuss the nature of the UQBW, and its possible physical link with the QBW.

  11. Response of the North African summer monsoon to precession and obliquity forcings in the EC-Earth GCM

    NASA Astrophysics Data System (ADS)

    Bosmans, J. H. C.; Drijfhout, S. S.; Tuenter, E.; Hilgen, F. J.; Lourens, L. J.

    2015-01-01

    We investigate, for the first time, the response of the North African summer monsoon to separate precession and obliquity forcings using a high-resolution state-of-the-art coupled general circulation model, EC-Earth. Our aim is to better understand the mechanisms underlying the astronomical forcing of this low-latitude climate system in detail. The North African monsoon is strengthened when northern hemisphere summer insolation is higher, as is the case in the minimum precession and maximum obliquity experiments. In these experiments, the low surface pressure areas over the Sahara are intensified and located farther north, and the meridional pressure gradient is further enhanced by a stronger South Atlantic high pressure area. As a result, the southwesterly monsoon winds are stronger and bring more moisture into the monsoon region from both the northern and southern tropical Atlantic. The monsoon winds, precipitation and convection also extend farther north into North Africa. The precession-induced changes are much larger than those induced by obliquity, but the latter are remarkable because obliquity-induced changes in summer insolation over the tropics are nearly zero. Our results provide a different explanation than previously proposed for mechanisms underlying the precession- and, especially, obliquity-related signals in paleoclimate proxy records of the North African monsoon. The EC-Earth experiments reveal that, instead of higher latitude mechanisms, increased moisture transport from both the northern and southern tropical Atlantic is responsible for the precession and obliquity signals in the North African monsoon. This increased moisture transport results from both increased insolation and an increased tropical insolation gradient.

  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. Southern Africa

    Atmospheric Science Data Center

    2013-04-16

    ... tip of South Africa is at the bottom of the image, and Zambia is at the top. Distinctive features about a third of the way from the ... MISR Team. Aug 25, 2000 - South Africa to Zambia including the Okavango Delta. project:  MISR ...

  14. 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).

  15. Characterization of southwest monsoon onset over Myanmar

    NASA Astrophysics Data System (ADS)

    Mie Sein, Z. M.; Islam, A. R. M. Towfiqul; Maw, K. W.; Moya, T. B.

    2015-10-01

    The aim of this paper was to characterize the southwest monsoon onset over Myanmar based on the model. The Regional Climate Model (RegCM3) was run for a period of 10 years (2000-2009) to simulate the meteorological fields which focused on April to July season. The model input data were obtained from the reanalyzed datasets of the National Center for Environmental Prediction (NCEP) and National Centre for Atmospheric Research (NCAR). Grell scheme with Arakawa closure for cumulus parameterization assumption was used for simulation with 45 km horizontal resolution. The results revealed that southwest monsoon onset was confirmed when the prevailing wind direction up to 600 hPa level had shifted from northeasterly to westerly or southwesterly. The southwest monsoon first arrived at southernmost Kawthoung station of Myanmar and progressed through the Deltaic and Central parts until it reached at northernmost Putao station. Over the simulation periods, the southwest monsoon onset progressed from the southernmost to northernmost parts of the country in 19 ± 10 days. The position of Intertropical Convergence Zone (ITCZ) appeared (23°N-28°N) over the Northern part of the country before the onset. Furthermore, 500 hPa ridge appeared consistently over the Deltaic area of Myanmar from 6 to 10 days before the monsoon onset. Its position is about 6° to the south of the ITCZ.

  16. The Role of African topography in the South Asian Monsoon

    NASA Astrophysics Data System (ADS)

    Wei, H. H.; Bordoni, S.

    2014-12-01

    The Somali cross-equatorial jet is estimated to contribute up to half of the mass flux crossing the equator during the Asian monsoon season. Previous studies have argued that the Somali jet is strengthened by the East African Highlands, which act as a wall and accelerate the flow (e.g., Krishnamurti et al. 1976, Sashegyi and Geisler 1987). Besides, observational studies have shown a positive correlation between the strength of the Somali jet and the South Asian Monsoon (SAM) precipitation (e.g., Findlater 1969, Halpern and Woiceshyn 2001). These imply that the existence of the topography would relate to a stronger SAM. However, in a more recent study, Chakraborty et al. (2002) found that if the African topography is removed in a comprehensive general circulation model (GCM), the SAM strengthens. In this study, we use the GFDL AM2.1 GCM to conduct experiments with and without topography in Africa, to further examine its influence on the cross-equatorial Somali jet and the SAM. We find that when the African topography is removed, the SAM precipitation increases, consistent with the results in Chakraborty et al. (2002). Interestingly, our results also show that the cross-equatorial Somali jet does weaken in the absence of the African topography, in agreement with previous studies. The moisture budget shows that the increase in precipitation in the no-African topography experiment is primarily due to stronger wind convergence. The dynamics of the cross-equatorial Somali jet is investigated within the framework of the Potential Vorticity (PV) budget, showing the contribution of the changes in friction and diabatic heating to the circulation as the topography is removed. A backward trajectory analysis is also conducted to further examine the influence of topography on both the material tendencies of the PV budget and trajectories of parcels reaching the Indian subcontinent.

  17. Intraseasonal Variability of the Low-Level Jet Stream of the Asian Summer Monsoon.

    NASA Astrophysics Data System (ADS)

    Joseph, P. V.; Sijikumar, S.

    2004-04-01

    The strong cross-equatorial low level jet stream (LLJ) with its core around 850 hPa of the Asian summer monsoon (June September) is found to have large intraseasonal variability. During the monsoon onset over Kerala, India, and during break monsoon periods, when the convective heating of the atmosphere is over the low latitudes of the Indian Ocean, the axis of the LLJ is oriented southeastward over the eastern Arabian Sea and it flows east between Sri Lanka and the equator and there is no LLJ through peninsular India. This affects the transport of moisture produced over the Indian Ocean to peninsular India and the Bay of Bengal. In contrast, during active monsoon periods when there is an east west band of strong convective heating in the latitudes 10° 20°N from about longitude 70° to about 120°E, the LLJ axis passes from the central Arabian Sea eastward through peninsular India and it provides moisture for the increased convection in the Bay of Bengal and for the monsoon depressions forming there. The LLJ does not show splitting into two branches over the Arabian Sea. Splitting of the jet was first suggested by Findlater and has since found wide acceptance as seen from the literature. Findlater's findings were based on analysis of monthly mean winds. Such an analysis is likely to show the LLJ of active and break monsoons as occurring simultaneously, suggesting a split.Strengths of the convective heat source (OLR) over the Bay of Bengal and the strength of the LLJ (zonal component of wind) at 850 hPa over peninsular India and also the Bay of Bengal between latitudes 10° and 20°N have the highest linear correlation coefficient at a lag of 2 3 days, with OLR leading. The LLJ crossing the equator close to the coast of East Africa will pass through India only if there is active monsoon convection in the latitude belt 10° 20°N over south Asia. The position in latitude of the LLJ axis between longitudes 70° and 100°E is decided by the south north movement of the

  18. Large volcanic aerosol load in the stratosphere linked to Asian monsoon transport.

    PubMed

    Bourassa, Adam E; Robock, Alan; Randel, William J; Deshler, Terry; Rieger, Landon A; Lloyd, Nicholas D; Llewellyn, E J Ted; Degenstein, Douglas A

    2012-07-06

    The Nabro stratovolcano in Eritrea, northeastern Africa, erupted on 13 June 2011, injecting approximately 1.3 teragrams of sulfur dioxide (SO(2)) to altitudes of 9 to 14 kilometers in the upper troposphere, which resulted in a large aerosol enhancement in the stratosphere. The SO(2) was lofted into the lower stratosphere by deep convection and the circulation associated with the Asian summer monsoon while gradually converting to sulfate aerosol. This demonstrates that to affect climate, volcanic eruptions need not be strong enough to inject sulfur directly to the stratosphere.

  19. Getting a grip on Indian Ocean monsoons

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    An improved understanding of the Indian Ocean monsoon season could help researchers to better forecast floods and the associated spread of cholera in low-lying Bangladesh.In a joint effort by the University of Colorado at Boulder, the Asian Disaster Preparedness Center, and the Bangladesh government, researchers are using a variety of monitoring and forecast modeling tools to better understand and characterize the monsoon season's active and calm periods. By studying Indian Ocean climatic conditions and probabilities that lead to regular flooding of the Bangladesh delta, researchers also can provide probabilities concerning outbreaks of cholera, an intestinal disease that infects large segments of that country's population.

  20. 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.

  1. Interannual- to multicentiennial-scale variability in the West African Monsoon during the Eemian

    NASA Astrophysics Data System (ADS)

    McKay, N. P.; Overpeck, J. T.; Shanahan, T. M.; Peck, J. A.; King, J. W.; Scholz, C. A.; Heil, C. W.

    2011-12-01

    The Eemian was the last interglacial period prior to the Holocene, lasting from 130 to 118 ka. Whereas annual insolation during the Eemian was comparable to the Holocene, the substantial differences in seasonal forcing and the reduced extent of continental ice sheets make the interval an important benchmark for understanding how altered climatic forcing drives changes in both global and regional climate. Climate variability during the period is, however, poorly understood, especially on annual to decadal timescales. Here we present the initial results of 4,000-yr-long annually-resolved varve record from the Lake Bosumtwi from the early Eemian (ca. 130 to 126 ka). Lake Bosumtwi (6.5°N, 1.4°W) is a 1.07 Ma impact crater lake in southern Ghana. The lake is hydrologically closed, and is relatively small, and consequently, is particularly sensitive to changes in effective moisture and the West African Monsoon (WAM). In 2004, an ICDP lake drilling expedition recovered the complete 291-m sediment sequence that spans the 1 Myr history of the lake. More than half of the 1 Myr sediment sequence appears to be annually laminated, including the late Holocene. This allows us the rare opportunity to compare long, annually-resolved records between interglacials. We analyzed the varve sequence for major element composition at 25-μm resolution using a high-resolution scanning X-ray fluorescence analyzer (or μXRF). The abundance of terrestrial elements (i.e., Al, Si, K, Ti) in the sediments, as inferred by XRF, has been shown to be a proxy for lake level at Lake Bosumtwi. During the Holocene, lake level in Lake Bosumtwi generally tracked summer insolation; for most of the early Holocene lake level was near the crater rim and the lake overflowed. Summer insolation was substantially higher during the early Eemian (up to 30 W m-2), however there is no evidence of comparably high lake level at Lake Bosumtwi during any part of last interglacial. In contrast, abundant evidence from the

  2. Analysis of the seasonal ozone budget and the impact of the summer monsoon on the northeastern Qinghai-Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Zhu, Bin; Hou, Xuewei; Kang, Hanqing

    2016-02-01

    Seasonal variations in ozone (O3) and the impact of the East Asian summer monsoon at Mount Waliguan (WLG) in the northeastern Qinghai-Tibetan Plateau (TP) and in the surrounding regions were analyzed for 1997-2007 using a global chemical transport model coupled with O3 tagging simulations. The model-simulated O3 and its precursors agreed well with observed values. An O3 budget analysis combined with O3 tagging results implied that photochemistry over the TP and long-range transport of O3 from East Asia, Europe, and Africa were responsible for the surface O3 summer maximum at WLG. In June, the contribution of O3 from the TP was 11.8 ppbv, and the total contribution of O3 transport from eastern China, Japan, Korean Peninsula, Europe, and Africa was 22.7 ppbv. At 400 mb, the O3 exports from the stratosphere, Europe, Africa, and the Americas seemed to be the main sources of O3 at WLG. The contributions to surface O3 from deep convection process and lightning-induced photochemistry at WLG were both low in summer and are unlikely to be the key processes or contributors for the O3 peak. At several mountain sites in southeast East Asia, the increasing summer monsoon index was related to a decreasing trend for O3 from spring onward at Mount Tai and Mount Huang. At Mount Hua and WLG, regional O3 accumulated over the monsoon's northernmost marginal zone under the influence of the East Asian summer monsoon and TP thermal circulation; this is most likely a key reason for the O3 summer maxima.

  3. High carbon dioxide uptake by subtropical forest ecosystems in the East Asian monsoon region.

    PubMed

    Yu, Guirui; Chen, Zhi; Piao, Shilong; Peng, Changhui; Ciais, Philippe; Wang, Qiufeng; Li, Xuanran; Zhu, Xianjin

    2014-04-01

    Temperate- and high-latitude forests have been shown to contribute a carbon sink in the Northern Hemisphere, but fewer studies have addressed the carbon balance of the subtropical forests. In the present study, we integrated eddy covariance observations established in the 1990s and 2000s to show that East Asian monsoon subtropical forests between 20 °N and 40 °N represent an average net ecosystem productivity (NEP) of 362 ± 39 g C m(-2) yr(-1) (mean ± 1 SE). This average forest NEP value is higher than that of Asian tropical and temperate forests and is also higher than that of forests at the same latitudes in Europe-Africa and North America. East Asian monsoon subtropical forests have comparable NEP to that of subtropical forests of the southeastern United States and intensively managed Western European forests. The total NEP of East Asian monsoon subtropical forests was estimated to be 0.72 ± 0.08 Pg C yr(-1), which accounts for 8% of the global forest NEP. This result indicates that the role of subtropical forests in the current global carbon cycle cannot be ignored and that the regional distributions of the Northern Hemisphere's terrestrial carbon sinks are needed to be reevaluated. The young stand ages and high nitrogen deposition, coupled with sufficient and synchronous water and heat availability, may be the primary reasons for the high NEP of this region, and further studies are needed to quantify the contribution of each underlying factor.

  4. High carbon dioxide uptake by subtropical forest ecosystems in the East Asian monsoon region

    PubMed Central

    Yu, Guirui; Chen, Zhi; Piao, Shilong; Peng, Changhui; Ciais, Philippe; Wang, Qiufeng; Li, Xuanran; Zhu, Xianjin

    2014-01-01

    Temperate- and high-latitude forests have been shown to contribute a carbon sink in the Northern Hemisphere, but fewer studies have addressed the carbon balance of the subtropical forests. In the present study, we integrated eddy covariance observations established in the 1990s and 2000s to show that East Asian monsoon subtropical forests between 20°N and 40°N represent an average net ecosystem productivity (NEP) of 362 ± 39 g C m−2 yr−1 (mean ± 1 SE). This average forest NEP value is higher than that of Asian tropical and temperate forests and is also higher than that of forests at the same latitudes in Europe–Africa and North America. East Asian monsoon subtropical forests have comparable NEP to that of subtropical forests of the southeastern United States and intensively managed Western European forests. The total NEP of East Asian monsoon subtropical forests was estimated to be 0.72 ± 0.08 Pg C yr−1, which accounts for 8% of the global forest NEP. This result indicates that the role of subtropical forests in the current global carbon cycle cannot be ignored and that the regional distributions of the Northern Hemisphere's terrestrial carbon sinks are needed to be reevaluated. The young stand ages and high nitrogen deposition, coupled with sufficient and synchronous water and heat availability, may be the primary reasons for the high NEP of this region, and further studies are needed to quantify the contribution of each underlying factor. PMID:24639529

  5. 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.

  6. Palaeoclimatic insights into forcing and response of monsoon rainfall.

    PubMed

    Mohtadi, Mahyar; Prange, Matthias; Steinke, Stephan

    2016-05-12

    Monsoons are the dominant seasonal mode of climate variability in the tropics and are critically important conveyors of atmospheric moisture and energy at a global scale. Predicting monsoons, which have profound impacts on regions that are collectively home to more than 70 per cent of Earth's population, is a challenge that is difficult to overcome by relying on instrumental data from only the past few decades. Palaeoclimatic evidence of monsoon rainfall dynamics across different regions and timescales could help us to understand and predict the sensitivity and response of monsoons to various forcing mechanisms. This evidence suggests that monsoon systems exhibit substantial regional character.

  7. Palaeoclimatic insights into forcing and response of monsoon rainfall

    NASA Astrophysics Data System (ADS)

    Mohtadi, Mahyar; Prange, Matthias; Steinke, Stephan

    2016-05-01

    Monsoons are the dominant seasonal mode of climate variability in the tropics and are critically important conveyors of atmospheric moisture and energy at a global scale. Predicting monsoons, which have profound impacts on regions that are collectively home to more than 70 per cent of Earth’s population, is a challenge that is difficult to overcome by relying on instrumental data from only the past few decades. Palaeoclimatic evidence of monsoon rainfall dynamics across different regions and timescales could help us to understand and predict the sensitivity and response of monsoons to various forcing mechanisms. This evidence suggests that monsoon systems exhibit substantial regional character.

  8. Bay of Bengal: coupling of pre-monsoon tropical cyclones with the monsoon onset in Myanmar

    NASA Astrophysics Data System (ADS)

    Fosu, Boniface O.; Wang, Shih-Yu Simon

    2015-08-01

    The pre-monsoon tropical cyclone (TC) activity and the monsoon evolution in the Bay of Bengal (BoB) are both influenced by the Madden-Julian Oscillation (MJO), but the two do not always occur in unison. This study examines the conditions that allow the MJO to modulate the monsoon onset in Myanmar and TC activity concurrently. Using the APHRODITE gridded precipitation and the ERA-Interim reanalysis datasets, composite evolutions of monsoon rainfall and TC genesis are constructed for the period of 1979-2010. It is found that the MJO exhibits a strong interannual variability in terms of phase and intensity, which in some years modulate the conditions for BoB TCs to shortly precede or form concurrently with the monsoon onset in Myanmar. Such a modulation is absent in years of weaker MJO events. Further understanding of the interannual variability of MJO activity could facilitate the prediction of the monsoon onset and TC formation in the BoB.

  9. 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.

  10. 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.

  11. The MONSOON Generic Pixel Server software design

    NASA Astrophysics Data System (ADS)

    Buchholz, Nick C.; Daly, Philip N.

    2004-09-01

    MONSOON is the next generation OUV-IR controller development project being conducted at NOAO. MONSOON was designed from the start as an "architecture" that provides the flexibility to handle multiple detector types, rather than as a set of specific hardware to control a particular detector. The hardware design was done with maintainability and scalability as key factors. We have, wherever possible chosen commercial off-the-shelf components rather than use in-house or proprietary systems. From first principles, the software design had to be configurable in order to handle many detector types and focal plane configurations. The MONSOON software is multi-layered with simulation of the hardware built in. By keeping the details of hardware interfaces confined to only two libraries and by strict conformance to a set of interface control documents the MONSOON software is usable with other hardware systems with minimal change. In addition, the design provides that focal plane specific details are confined to routines that are selected at load time. At the top-level, the MONSOON Supervisor Level (MSL), we use the GPX dictionary, a defined interface to the software system that instruments and high-level software can use to control and query the system. Below this are PAN-DHE pairs that interface directly with portions of the focal plane. The number of PAN-DHE pairs can be scaled up to increase channel counts and processing speed or to handle larger focal planes. The range of detector applications supported goes from single detector LAB systems, four detector IR systems like NEWFIRM, up to 500 CCD focal planes like LSST. In this paper we discuss the design of the PAN software and it's interaction with the detector head electronics.

  12. Energetic constraints on monsoonal Hadley circulations

    NASA Astrophysics Data System (ADS)

    Merlis, T. M.; Schneider, T.; Bordoni, S.; Eisenman, I.

    2011-12-01

    The strength of monsoons is believed to have varied in the past in response to changes in the seasonal shortwave radiation distribution associated with orbital precession and is expected to vary during the coming century due to increases in greenhouse gas concentrations. Here, we examine the constraint that the moist static energy budget imposes on the response to radiative perturbations of the cross-equatorial, or monsoonal, Hadley circulations. Changes in the strength of the mass transport can occur in response to radiative perturbations, which has been frequently discussed in the past. An additional factor in the energetic balance, however, is the atmosphere's energy stratification, which is commonly known as the gross moist stability in tropical meteorology. Therefore, changes in the atmosphere's gross moist stability can play a fundamental role in determining changes in the mass transport of mean circulations. Also, the influence of spatial variations in surface heat capacity on the top-of-the-atmosphere energy balance, rather than its widely discussed role in determining surface temperature, is important in determining how radiative perturbations are energetically balanced by monsoonal Hadley circulations. We examine the importance of energetic constraints on monsoonal Hadley circulations in idealized general circulation model simulations that have either an aquaplanet slab-ocean boundary condition or a zonally symmetric subtropical continent. The radiative balance in the simulations is perturbed first by insolation variations associated with orbital precession and then by increased carbon dioxide concentration. The simulation results demonstrate that summertime changes in gross moist stability are important for understanding past and future monsoon variations.

  13. 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

  14. 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

    2009-12-03

    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

  15. 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.

  16. 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

  17. 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

    2017-03-01

    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.

  18. Evolving the linkages between North American Monsoon Experiment research and services in the binational monsoon region

    NASA Astrophysics Data System (ADS)

    Ray, A. J.

    2007-05-01

    Multi-year drought, high interannual precipitation variability, and rapid population growth present major challenges to water resources and land managers in the U.S. Southwest and binational monsoon region. The NAME strategy to improve warm season precipitation forecasts is paying off in the understanding of the system and its potential predictability, illustrated by a special issue of the Journal of Climate with about 25 articles and numerous other published papers (e.g. Higgins and Gochis et al. 2006; Gutzler et al. 2004, Higgins et al. 2003). NOAA now has set a goal to NAME and other initiatives also have the potential to provide key insights, such as historic information regarding onset and overall strength of the monsoon as it affects stakeholder interests in flooding, soil moisture, vegetation health, and summer water demand. However, the usual avenues for scientific output, such as peer-reviewed publications and web sites designed for use by climate and weather experts, do not adequately support the flow of knowledge to operational decisionmakers. A recent workshop on Monsoon Region climate Applications in Guaymas, Sonora identified several areas in which monsoon science might contribute to reducing societal vulnerability, as well as some research findings that are suited to transition into model development and operations at service providers including NOAA and SMN. They recommended that products are needed that interpret climate forecasts for water resource management applications, and developing new regionally-tailored climate information products. This presentation will discuss how to enhance the flow of monsoon information and predictions to stakeholders by linking user-oriented perspectives with research results from NAME and other programs, including a new effort for a North American Monsoon Forecast Forum which plans to develop periodic consolidated North American Monsoon outlooks.

  19. South Africa

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This true-color image of South Africa was acquired on May 14, 2000, by NASA's Moderate-resolution Imaging Spectroradiometer, or MODIS. The image was produced using a combination of the sensor's 250-m and 500-m resolution visible wavelength bands. As part of the opening ceremony to begin the joint U.S.-South Africa SAFARI Field Experiment, NASA presented print copies of this image as GIFts to Dr. Ben Ngubane, Minister of Arts, Science and Technology, and Honorable Advocate Ngoaka Ramathlodi, Premier of the Northern Province, South Africa. The area shown in this image encompasses seven capital cities and a number of the region's distinctive geological features can be seen clearly. Toward the northern (top) central part of the image, the browns and tans comprise the Kalahari Desert of southern Botswana. The Tropic of Capricorn runs right through the heart of the Kalahari and the Botswanan capital city of Gaborone sits on the Limpopo River, southeast of the Kalahari. Along the western coastline of the continent is the country of Namibia, where the Namib Desert is framed against the sea by the Kaokoveld Mountains. The Namibian capital of Windhoek is obscured by clouds. Looking closely in the center of the image, the Orange River can be seen running from east to west, demarcating the boundary between Namibia and South Africa. On the southwestern corner of the continent is the hook-like Cape of Good Hope peninsula and Cape Town, the parliamentary capital of South Africa. Running west to east away from Cape Town are the Great Karroo Mountains. The shadow in this image conveys a sense of the very steep grade of the cliffs along the southern coast of South Africa. Port Elizabeth sits on the southeasternmost point of South Africa, and a large phytoplankton bloom can be seen in the water about 100 miles east of there. Moving northward along the east coast, the Drakensberg Mountains are visible. The two small nations of Lesotho and Swaziland are in this region, completely

  20. A Comparison of Pre-monsoonal and Monsoonal Radiative Forcing by Anthropogenic Aerosols over South Asia

    NASA Astrophysics Data System (ADS)

    Lee, S.; Cohen, J. B.; Wang, C.

    2012-12-01

    Radiative forcing by anthropogenic aerosols after monsoon onset is often considered unimportant compared to forcing during the pre-monsoonal period, due to precipitation scavenging. We tested this assumption for the South Asian monsoon using three model runs with forcing prescribed during the pre-monsoonal period (March-May), monsoon period (June-September) and both periods. The forcing represents the direct radiative effects of sulfate, organic carbon and black carbon. It was derived from a set of Kalman filter-optimised black carbon emissions from a modelling system based on the CAM3 GCM, a two-moment multi-scheme aerosol and radiation model, and a coupled urban scale processing package; we expect it to be reliable within its given error bounds. The monthly climatological forcing values were prescribed over South Asia every year for 100 years to CESM 1.0.4, a coupled atmosphere-ocean model. We shall compare the three resultant climatologies with climatologies from a no aerosol model and a full aerosol model.

  1. 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.

  2. 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; ...

    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

  3. 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

    2014-06-27

    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.

  4. Asian monsoon failure and megadrought during the last millennium.

    PubMed

    Cook, Edward R; Anchukaitis, Kevin J; Buckley, Brendan M; D'Arrigo, Rosanne D; Jacoby, Gordon C; Wright, William E

    2010-04-23

    The Asian monsoon system affects more than half of humanity worldwide, yet the dynamical processes that govern its complex spatiotemporal variability are not sufficiently understood to model and predict its behavior, due in part to inadequate long-term climate observations. Here we present the Monsoon Asia Drought Atlas (MADA), a seasonally resolved gridded spatial reconstruction of Asian monsoon drought and pluvials over the past millennium, derived from a network of tree-ring chronologies. MADA provides the spatiotemporal details of known historic monsoon failures and reveals the occurrence, severity, and fingerprint of previously unknown monsoon megadroughts and their close linkages to large-scale patterns of tropical Indo-Pacific sea surface temperatures. MADA thus provides a long-term context for recent monsoon variability that is critically needed for climate modeling, prediction, and attribution.

  5. Mesoscale model forecast verification during monsoon 2008

    NASA Astrophysics Data System (ADS)

    Ashrit, Raghavendra; Mohandas, Saji

    2010-08-01

    There have been very few mesoscale modelling studies of the Indian monsoon, with focus on the verification and intercomparison of the operational real time forecasts. With the exception of Das et al (2008), most of the studies in the literature are either the case studies of tropical cyclones and thunderstorms or the sensitivity studies involving physical parameterization or climate simulation studies. Almost all the studies are based on either National Center for Environmental Prediction (NCEP), USA, final analysis fields (NCEP FNL) or the reanalysis data used as initial and lateral boundary conditions for driving the mesoscale model. Here we present a mesoscale model forecast verification and intercomparison study over India involving three mesoscale models: (i) the Weather Research and Forecast (WRF) model developed at the National Center for Atmospheric Research (NCAR), USA, (ii) the MM5 model developed by NCAR, and (iii) the Eta model of the NCEP, USA. The analysis is carried out for the monsoon season, June to September 2008. This study is unique since it is based entirely on the real time global model forecasts of the National Centre for Medium Range Weather Forecasting (NCMRWF) T254 global analysis and forecast system. Based on the evaluation and intercomparison of the mesoscale model forecasts, we recommend the best model for operational real-time forecasts over the Indian region. Although the forecast mean 850 hPa circulation shows realistic monsoon flow and the monsoon trough, the systematic errors over the Arabian Sea indicate an easterly bias to the north (of mean flow) and westerly bias to the south (of mean flow). This suggests that the forecasts feature a southward shift in the monsoon current. The systematic error in the 850 hPa temperature indicates that largely the WRF model forecasts feature warm bias and the MM5 model forecasts feature cold bias. Features common to all the three models include warm bias over northwest India and cold bias over

  6. 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.

  7. Influence of Soil Moisture on the Asian and African Monsoons. Part II: Interannual Variability.

    NASA Astrophysics Data System (ADS)

    Douville, H.

    2002-04-01

    The relevance of soil moisture (SM) for simulating the interannual climate variability has not been much investigated until recently. Much more attention has been paid on SST anomalies, especially in the Tropics where the El Niño-Southern Oscillation represents the main mode of variability. In the present study, ensembles of atmospheric integrations based on the Action de Recherche Petit Echelle Grande Echelle (ARPEGE) climate model have been performed for two summer seasons: 1987 and 1988, respectively. The aim is to compare the relative impacts of using realistic boundary conditions of SST and SM on the simulated variability of the Asian and African monsoons. Besides control runs with interactive SM, sensitivity tests have been done in which SM is relaxed toward a state-of-the-art SM climatology, either globally or regionally over the monsoon domain. The simulations indicate that the variations of the Asian monsoon between 1987 and 1988 are mainly driven by SST anomalies. This result might be explained by the strong teleconnection with the ENSO and by a weak SM-precipitation feedback over south Asia (Part I of the study). The influence of SM is more obvious over Africa. The model needs both realistic SST and SM boundary conditions to simulate the observed variability of the Sahelian monsoon rainfall. The positive impact of the SM relaxation is not only due to a local mechanism whereby larger surface evaporation leads to larger precipitation. The best results are obtained when the relaxation is applied globally, suggesting that remote SM impacts also contribute to the improved simulation of the precipitation variability. A relationship between the Sahelian rainfall anomalies and the meridional wind anomalies over North Africa points out the possible influence of the Northern Hemisphere midlatitudes. The comparison of the low- and midtropospheric anomalies in the various pairs of experiments indicates that SM anomalies can trigger stationary waves over Europe, and

  8. 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.

  9. Detection of a gas flaring signature in the AERONET optical properties of aerosols at a tropical station in West Africa

    NASA Astrophysics Data System (ADS)

    Fawole, Olusegun G.; Cai, Xiaoming; Levine, James G.; Pinker, Rachel T.; MacKenzie, A. R.

    2016-12-01

    The West African region, with its peculiar climate and atmospheric dynamics, is a prominent source of aerosols. Reliable and long-term in situ measurements of aerosol properties are not readily available across the region. In this study, Version 2 Level 1.5 Aerosol Robotic Network (AERONET) data were used to study the absorption and size distribution properties of aerosols from dominant sources identified by trajectory analysis. The trajectory analysis was used to define four sources of aerosols over a 10 year period. Sorting the AERONET aerosol retrievals by these putative sources, the hypothesis that there exists an optically distinct gas flaring signal was tested. Dominance of each source cluster varies with season: desert-dust (DD) and biomass burning (BB) aerosols are dominant in months prior to the West African Monsoon (WAM); urban (UB) and gas flaring (GF) aerosol are dominant during the WAM months. BB aerosol, with single scattering albedo (SSA) at 675 nm value of 0.86 ± 0.03 and GF aerosol with SSA (675 nm) value of 0.9 ± 0.07, is the most absorbing of the aerosol categories. The range of Absorption Angstr&öm Exponent (AAE) for DD, BB, UB and GF classes are 1.99 ± 0.35, 1.45 ± 0.26, 1.21 ± 0.38 and 0.98 ± 0.25, respectively, indicating different aerosol composition for each source. The AAE (440-870 nm) and Angstr&öm Exponent (AE) (440-870 nm) relationships further show the spread and overlap of the variation of these optical and microphysical properties, presumably due in part to similarity in the sources of aerosols and in part, due to mixing of air parcels from different sources en route to the measurement site.

  10. Assessment of the 1997-1998 Asian Monsoon Anomalies

    NASA Technical Reports Server (NTRS)

    Lau, William 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 Asian monsoon anomalies in terms of three basic causal factors: basin-scale SST, regional coupling, and internal variability. Singular Value Decomposition analysis of rainfall and SST are carried out globally over the entire tropics and regionally over the Asian 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. it is noted that some subcontinental regions such as all-India, or arbitrarily chosen land regions over East Asia, while important socio-economically, are not near the centers of influence from El Nino, hence are not necessarily representative of the response of the entire monsoon region to El Nino. The observed 1997-98 Asian monsoon anomalies are found to be very complex with approximately 34% of the anomalies attributable to basin- scale SST influence associated with El Nino. Regional coupled processes contribute an additional 19%, leaving about 47% due to internal dynamics. Also noted is 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 monsoon regional coupled processes and their modulation by long-term climate change.

  11. 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

  12. Effects of mountain uplift on global monsoon precipitation

    NASA Astrophysics Data System (ADS)

    Lee, June-Yi; Wang, Bin; Seo, Kyong-Hwan; Ha, Kyung-Ja; Kitoh, Akio; Liu, Jian

    2015-08-01

    This study explores the role of the global mountain uplift (MU), which occurred during the middle and late Cenozoic, in modulating global monsoon precipitation using the Meteorological Research Institute atmosphere-ocean coupled model experiments. First, the MU causes changes in the annual mean of major monsoon precipitation. Although the annual mean precipitation over the entire globe remains about the same from the no-mountain experiment (MU0) to the realistic MU (MU1), that over the Asian-Australian monsoon region and Americas increases by about 16% and 9%, respectively. Second, the MU plays an essential role in advancing seasonal march, and summer-monsoon onset, especially in the Northern Hemisphere, by shaping pre-monsoon circulation. The rainy seasons are lengthened as a result of the earlier onset of the summer monsoon since the monsoon retreat is not sensitive to the MU. The East Asian monsoon is a unique consequence of the MU, while other monsoons are attributed primarily to land-sea distribution. Third, the strength of the global monsoon is shown to be substantially affected by the MU. In particular, the second annual cycle (AC) mode of global precipitation (the spring-autumn asymmetry mode) is more sensitive to the progressive MU than the first mode of the AC (the solstice mode), suggesting that the MU may have a greater impact during transition seasons than solstice seasons. Finally, the MU strongly modulates interannual variation in global monsoon precipitation in relation to El Niño and Southern Oscillation (ENSO). The Progressive MU changes not only the spatial distribution but also the periodicity of the first and second AC mode of global precipitation on interannual timescale.

  13. 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

  14. Multiscale Variability of the Monsoon Climate

    NASA Astrophysics Data System (ADS)

    Krishnamurthy, V.

    2005-05-01

    The reliability of weather forecasts is limited to a few days and is mainly determined by the synoptic scale features of the atmosphere. The predictability of weather models depends on the error growth determined by nonlinear terms representing advection. Smaller scale features, such as convection, may also influence the predictability of the synoptic scale forecasts. While the prediction of instantaneous states of the system may be impossible on longer time scale, there is optimism for medium-range and long-range forecasts of time-averaged features of the climate system. Such optimism is based on the observation that slowly-varying boundary forces such as sea surface temperature, soil moisture and snow influence the variability of the atmosphere on a longer time scale, especially in the tropical region. This study discusses the variability of such a tropical climate system, the monsoon, and shows that its variability consists of a combination of large-scale persistent seasonal mean component and intraseasonal variability of different time scales. The spatial variability of these components is also found to consist of different scales. By performing multi-channel singular spectrum analysis of daily rainfall, low-pressure systems, outgoing long-wave radiation and winds, two oscillatory modes with periods of about 45 and 20 days have been identified and shown to correspond to the active and break phases of the monsoon. These two intraseasonal modes, however, do not contribute much to the seasonal mean rainfall. Three other components of the MSSA are identified as the contributors to the seasonal mean rainfall, possibly arising from the influence of slowly-varying boundary forces. The prospect for making accurate long-range forecasts of the monsoon depends on the relative magnitudes of the large-scale seasonally persistent component and the intraseasonal component and on climate model experiments to establish a relation between the two components.

  15. West Africa

    NASA Technical Reports Server (NTRS)

    2002-01-01

    With its vast expanses of sand, framed by mountain ranges and exposed rock, northwestern Africa makes a pretty picture when viewed from above. This image was acquired by the Moderate-resolution Imaging Spectroradiometer (MODIS), flying aboard NASA's Terra spacecraft. The Canary Islands can be seen on the left side of the image just off Africa's Atlantic shore. The light brown expanse running through the northern two thirds of the image is the Sahara Desert. The desert runs up against the dark brown Haut Atlas mountain range of Morocco in the northwest, the Atlantic Ocean to the west and the semi-arid (light brown pixels) Sahelian region in the South. The Sahara, however, isn't staying put. Since the 1960s, the desert has been expanding into the Sahelian region at a rate of up to 6 kilometers per year. In the 1980s this desert expansion, combined with over cultivation of the Sahel, caused a major famine across west Africa. Over the summer months, strong winds pick up sands from the Sahara and blow them across the Atlantic as far west as North America, causing air pollution in Miami and damaging coral reefs in the Bahamas and the Florida Keys. The white outlines on the map represent country borders. Starting at the top-most portion of the map and working clockwise, the countries shown are Morocco, Western Sahara, Mauritania, Senegal, Mali, Burkina Fasso, Nigeria, Mali (again), and Algeria. Image by Reto Stockli, Robert Simmon, and Brian Montgomery, NASA Earth Observatory, based on data from MODIS

  16. Influence of dynamic and thermodynamic features on Indian summer monsoon

    SciTech Connect

    Babu, C.A.; Leena, P.; Priya, P.

    1996-12-31

    Indian summer monsoon plays vital role in the economy of the country. Being an agricultural country, the onset phase of monsoon is important since beginning of cultivation depends on rain-fed irrigation. Summer heating of the Asian land mass and subsequent differential heating between peninsular and north India are considered to be the principal cause for the summer monsoon. An east-west synoptic scale zonal circulation is observed over the Indian region during monsoon period which is similar to the planetary scale circulation. The ascending branch of this circulation is over northwest India and the descending branch is over the northeast India. This east-west zonal circulation is closely related to the monsoon activity. During the onset phase of monsoon spectacular changes occur in the dynamical and thermodynamic structure of the atmosphere. In this paper an attempt is made to diagnose the features of the atmosphere over the Indian region employing dynamical and thermodynamical parameters to as to bring out the relationship between structure of atmosphere and strength of monsoon. Preliminary results indicate that the strength of monsoon and its various epochs are influenced by dynamic and thermodynamic features of the atmosphere.

  17. Advanced Asian summer monsoon onset in recent decades

    NASA Astrophysics Data System (ADS)

    Kajikawa, Y.; Yasunari, T.; Yoshida, S.; Fujinami, H.

    2011-12-01

    Anthropogenic climate change in the Asian monsoon area is one of the most important issues due to the maximum population over the world. Many studies have revealed the long-term change of the Asian summer monsoon rainfall, especially over the China. It is suggested that the trend of monsoonal rainfall in China and India has been attributed to increase in the black carbon and sulphate aerosol. Most of the previous studies assessed the rainfall trend in boreal summer mean. Meanwhile, the seasonal march of the Asian summer monsoon displays a stepwise northward and northeastward migration of rainfall with abrupt onset during boreal spring and summer. Because of large seasonal variability, the long-term trend of the Asian monsoon would exhibit seasonally dependent features which we have to take a consideration of. Here, we analyze the trend of the Asian monsoon rainfall, wind circulation and water vapor flux during 1979-2008 on a monthly mean basis to clarify its seasonality. The transition phase from boreal spring to summer is specially focused. Significant increasing rainfall trend in May is remarkable over the Asian Sea, Bay of Bengal and southeastern monsoon region, which corresponds to advanced monsoon onset in recent decades. The trends are, however, nearly reversed in June over the abovementioned region. Of interest is that the Asian monsoonal rainfall in July and August does not show clear significant trend. Thus, the Asian monsoon has significant trend during the transient phase from boreal spring to summer in particular. The advanced monsoon onset and weakening of the monsoon during early summer are most likely to be attributed to the heat contrast between the Asian landmass and the tropical Indian Ocean. The heating trend over the Asian landmass contributes to the heat contrast variability, because of the persistent SST increase in the Indian Ocean throughout the season. Warming trends in the mid-upper troposphere over the landmass area in May is suggested to

  18. 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.

  19. 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.

  20. Anti-correlation of summer/winter monsoons?

    PubMed

    Zhang, De'er; Lu, Longhua

    2007-11-15

    On the basis of the anti-correlation of their palaeoclimatic proxy for the strength of the East Asian winter monsoon from Lake Huguang Maar, China, with stalagmite records of the strength of the summer monsoon, Yancheva et al. claim that the strengths of the summer and winter monsoons are anti-correlated on a decadal timescale. They argue that the summer rainfall deficit during ad 700-900 that they infer from their evidence of a stronger winter monsoon, in conjunction with a Tanros battle, led to the collapse of the Tang dynasty (ad 618-907). Using historical climate records, we show here that most cold winters during ad 700-900 were associated with relatively wet summers, indicating that the strengths of the winter and summer monsoons were not negatively correlated during this period.

  1. Dead Sea drawdown and monsoonal impacts in the Levant during the last interglacial

    NASA Astrophysics Data System (ADS)

    Torfstein, Adi; Goldstein, Steven L.; Kushnir, Yochanan; Enzel, Yehouda; Haug, Gerald; Stein, Mordechai

    2015-02-01

    Sediment cores recovered by the Dead Sea Deep Drilling Project (DSDDP) from the deepest basin of the hypersaline, terminal Dead Sea (lake floor at ∼725 m below mean sea level) reveal the detailed climate history of the lake's watershed during the last interglacial period (Marine Isotope Stage 5; MIS5). The results document both a more intense aridity during MIS5 than during the Holocene, and the moderating impacts derived from the intense MIS5e African Monsoon. Early MIS5e (∼133-128 ka) was dominated by hyperarid conditions in the Eastern Mediterranean-Levant, indicated by thick halite deposition triggered by a lake-level drop. Halite deposition was interrupted however, during the MIS5e peak (∼128-122 ka) by sequences of flood deposits, which are coeval with the timing of the intense precession-forced African monsoon that generated Mediterranean sapropel S5. A subsequent weakening of this humidity source triggered extreme aridity in the Dead Sea watershed and resulting in the biggest known lake level drawdown in its history, reflected by the deposition of thick salt layers, and a capping pebble layer corresponding to a hiatus at ∼116-110 ka. The DSDDP core provides the first evidence for a direct association of the African monsoon with mid subtropical latitude climate systems effecting the Dead Sea watershed. Combined with coeval deposition of Arabia and southern Negev speleothems, Arava travertines, and calcification of Red Sea corals, the evidence points to a climatically wet corridor that could have facilitated homo sapiens migration "out of Africa" during the MIS5e peak. The hyperaridity documented during MIS5e may provide an important analogue for future warming of arid regions of the Eastern Mediterranean-Levant.

  2. Comparison of East Asian winter monsoon indices

    NASA Astrophysics Data System (ADS)

    Hui, Gao

    2007-04-01

    Four East Asian winter monsoon (EAWM) indices are compared in this paper. In the research periods, all the indices show similar interannual and decadal-interdecadal variations, with predominant periods centering in 3-4 years, 6.5 years and 9-15 years, respectively. Besides, all the indices show remarkable weakening trends since the 1980s. The correlation coefficient of each two indices is positive with a significance level of 99%. Both the correlation analyses and the composites indicate that in stronger EAWM years, the Siberian high and the higher-level subtropical westerly jet are stronger, and the Aleutian low and the East Asia trough are deeper. This circulation pattern is favorable for much stronger northwesterly wind and lower air temperature in the subtropical regions of East Asia, while it is on the opposite in weaker EAWM years. Besides, EAWM can also exert a remarkable leading effect on the summer monsoon. After stronger (weaker) EAWM, less (more) summer precipitation is seen over the regions from the Yangtze River valley of China to southern Japan, while more (less) from South China Sea to the tropical western Pacific.

  3. 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.

  4. The Dynamics of Bursts in the Australian Monsoon

    NASA Astrophysics Data System (ADS)

    Reeder, M. J.; Berry, G.

    2015-12-01

    The wet season of the Australian monsoon is characterized by sub-seasonal periods of excessively wet or dry conditions, commonly know as monsoon bursts and breaks. This study is concerned with the synoptic evolution prior to monsoon bursts, which are defined here by abrupt transitions of the area-averaged rainfall over the tropical parts of the Australian continent. There is large variability in the number of monsoon bursts from year-to-year and in the time interval between consecutive monsoon bursts. Reanalysis data are used to construct a lag composite of the sequence of events prior to a monsoon burst. It is found that a burst in the Australian monsoon is preceded by the development of a well-defined extratropical wave packet in the Indian Ocean, which propagates toward the Australian continent in the few days leading up to the onset of heavy rainfall in the tropics. As in the case of previous studies on the monsoon onset, the extratropical disturbances propagate equatorward over the Australian continent. These extratropical systems are accompanied by lower tropospheric air mass boundaries, which also propagate into low latitudes. Ahead of these boundaries, relatively warm moist air is advected from the surrounding oceans, locally increasing the convective available potential energy. Commonly employed climate indices shows that monsoon bursts are more likely to occur when the active phase of the Madden-Julian Oscillation is in the vicinity of Australia. Neither the El-Nino Southern Oscillation nor Southern Annular Mode have a significant effect on the occurrence of monsoon bursts.

  5. Does Aerosol Weaken or Strengthen the South Asian Monsoon?

    NASA Technical Reports Server (NTRS)

    Lau, William K. M.

    2007-01-01

    Aerosols are known to have the ability to block off solar radiation reaching the earth surface, causing it to cool - the so-called solar dimming (SDM) effect. In the Asian monsoon region, the SDM effect by aerosol can produce differential cooling at the surface reducing the meridional thermal contrast between land and ocean, leading to a weakening of the monsoon (Ramanathan et al. 2005). On the other hand, absorbing aerosols such as black carbon and dust, when forced up against the steep slopes of the southern Tibetan Plateau can produce upper tropospheric heating, and induce convection-dynamic feedback leading to an advance of the rainy season over northern India and an enhancement of the South Asian monsoon through the "Elevated Heat Pump" (EHP) effect (Lau et al. 2006). In this paper, we present modeling results showing that in a coupled ocean-atmosphere-land system in which concentrations of greenhouse gases are kept constant, the response of the South Asian monsoon to dust and black carbon forcing is the net result of the two opposing effects of SDM and EHP. For the South Asian monsoon, if the increasing upper tropospheric thermal contrast between the Tibetan Plateau and region to the south spurred by the EHP overwhelms the reduction in surface temperature contrast due to SDM, the monsoon strengthens. Otherwise, the monsoon weakens. Preliminary observations are consistent with the above findings. We find that the two effects are strongly scale dependent. On interannual and shorter time scales, the EHP effect appears to dominate in the early summer season (May-June). On decadal or longer time scales, the SDM dominates for the mature monsoon (July-August). Better understanding the physical mechanisms underlying the SDM and the EHP effects, the local emission and transport of aerosols from surrounding deserts and arid-regions, and their interaction with monsoon water cycle dynamics are important in providing better prediction and assessment of climate change

  6. Does Aerosol Weaken or Strengthen the South Asian Monsoon?

    NASA Technical Reports Server (NTRS)

    Lau, William K.

    2010-01-01

    Aerosols are known to have the ability to block off solar radiation reaching the earth surface, causing it to cool - the so-called solar dimming (SDM) effect. In the Asian monsoon region, the SDM effect by aerosol can produce differential cooling at the surface reducing the meridional thermal contrast between land and ocean, leading to a weakening of the monsoon. On the other hand, absorbing aerosols such as black carbon and dust, when forced up against the steep slopes of the southern Tibetan Plateau can produce upper tropospheric heating, and induce convection-dynamic feedback leading to an advance of the rainy season over northern India and an enhancement of the South Asian monsoon through the "Elevated Heat Pump" (EHP) effect. In this paper, we present modeling results showing that in a coupled ocean-atmosphere-land system in which concentrations of greenhouse gases are kept constant, the response of the South Asian monsoon to dust and black carbon forcing is the net result of the two opposing effects of SDM and EHP. For the South Asian monsoon, if the increasing upper tropospheric thermal contrast between the Tibetan Plateau and region to the south spurred by the EHP overwhelms the reduction in surface temperature contrast due to SDM, the monsoon strengthens. Otherwise, the monsoon weakens. Preliminary observations are consistent with the above findings. We find that the two effects are strongly scale dependent. On interannual and shorter time scales, the EHP effect appears to dominate in the early summer season (May-June). On decadal or longer time scales, the SDM dominates for the mature monsoon (July-August). Better understanding the physical mechanisms underlying the SDM and the EHP effects, the local emission and transport of aerosols from surrounding deserts and arid-regions, and their interaction with monsoon water cycle dynamics are important in providing better prediction and assessment of climate change impacts on precipitation of the Asian monsoon

  7. Assessing the level of spatial homogeneity of the agronomic Indian monsoon onset

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, Rory G. J.; Parker, Douglas J.; Willetts, Peter D.

    2016-11-01

    Over monsoon regions, such as the Indian subcontinent, the local onset of persistent rainfall is a crucial event in the annual climate for agricultural planning. Recent work suggested that local onset dates are spatially coherent to a practical level over West Africa; a similar assessment is undertaken here for the Indian subcontinent. Areas of coherent onset, defined as local onset regions or LORs, exist over the studied region. These LORs are significant up to the 95% confidence interval and are primarily clustered around the Arabian Sea (adjacent to and extending over the Western Ghats), the Monsoon Trough (north central India), and the Bay of Bengal. These LORs capture regions where synoptic scale controls of onset may be present and identifiable. In other regions, the absence of LORs is indicative of regions where local and stochastic factors may dominate onset. A potential link between sea surface temperature anomalies and LOR variability is presented. Finally, Kerala, which is often used as a representative onset location, is not contained within an LOR suggesting that variability here may not be representative of wider onset variability.

  8. Orbital forcing on West African monsoon system revealed by KZai 02 pollen record spectral analysis

    NASA Astrophysics Data System (ADS)

    Dalibard, Mathieu; Popescu, Speranta-Maria; Pittet, Bernard; Fernandez, Vincent; Marsset, Tania; Droz, Laurence; Suc, Jean-Pierre

    2013-04-01

    The present-day intertropical climate is forced by yearly fluctuations of insolation reorganizing pressure cells. They control, via the wind system, the variations of the precipitation front known as the InterTropical Convergence Zone (ITCZ). Its latitudinal oscillation drives a strong seasonality of rainfalls over Africa. However, connections between African climate during Pleistocene and orbital forcing are blurred by high-latitudes and local direct influence of insolation and need further investigations. The study of KZai 02 core pollen content provides a high-resolution record of changes in West African plant ecosystems during the last 160 kyrs. Spectral analyses were performed on pollen signals to identify periodicity in vegetation dynamics related to environmental fluctuations. The large range of frequencies detected testifies for the sensibility of African biotopes to past climate fluctuations. Milankovitch parameters, especially precession, are identified within variations of the ecological groups of KZai 02 pollen record and interpreted in terms of West African monsoon system variability. Asynchrony in the different plant ecosystem fluctuations suggests the out of step influence of several climatic parameters (precipitation, CO2, temperature) involving local insolation and high-latitude influence. Spectral analysis also reveals sub-Milankovitch periods related to (1) Heinrich and Dansgaard/Oeschger glacial pulsation events and (2) East Asian monsoon oscillations controlled by ice sheet pulses testifying for the strong relationship between low- and high-latitude climate changes.

  9. 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

  10. Leaf physiognomy and climate: Are monsoon systems different?

    NASA Astrophysics Data System (ADS)

    Jacques, Frédéric M. B.; Su, Tao; Spicer, Robert A.; Xing, Yaowu; Huang, Yongjiang; Wang, Weiming; Zhou, Zhekun

    2011-03-01

    Our understanding of past climatic changes depends on our ability to obtain reliable palaeoclimate reconstructions. Climate Leaf Analysis Multivariate Program (CLAMP) uses the physiognomy of woody dicot leaf assemblages to quantitatively reconstruct terrestrial palaeoclimates. However, the present calibrations do not always allow us to reconstruct correctly the climate of some regions due to differing palaeofloristic histories. Present calibrations are also inappropriate for regions experiencing strong monsoon regimes. To help solve this problem, we have established a new calibration that can accommodate monsoonal climates in Asia. Our new calibration is based on the Physg3brcAZ dataset with 45 new Chinese sites added. These Chinese sites are taken from humid to mesic vegetations across China, and all are influenced by monsoonal conditions to some extent. They plot in a distinct part of physiognomic space, whether they are analysed as passive or active samples. The standard deviations for the new monsoonal calibration (1.25 °C for MAT and 217.7 mm for GSP) are in the same range as those observed for previous calibrations. The new monsoonal calibration was tested using a cross validation procedure. The estimates derived from the new monsoonal calibration (PhysgAsia1) for the Chinese sites are more accurate than those obtained from the Physg3brcAZ calibration, especially for the moisture related parameters. The mean absolute error for GSP of the Chinese sites is 294.6 mm in the new monsoonal calibration, whereas it was 1609.6 mm in the Physg3brcAZ calibration. Results for the three wettest months and three driest months are also more accurate and precise, which allows us to study the seasonality of the precipitation, and hence the monsoon. The new monsoonal calibration also gives accurate results for enthalpy reconstruction. Enthalpy is a parameter that is used for palaeoaltimetry, the new calibration is therefore useful for studies of land surface height changes in

  11. Northern Hemisphere summer monsoon intensified by mega-El Nino/southern oscillation and Atlantic multidecadal oscillation.

    PubMed

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

    2013-04-02

    Prediction of monsoon changes in the coming decades is important for infrastructure planning and sustainable economic development. The decadal prediction involves both natural decadal variability and anthropogenic forcing. Hitherto, the causes of the decadal variability of Northern Hemisphere summer monsoon (NHSM) are largely unknown because the monsoons over Asia, West Africa, and North America have been studied primarily on a regional basis, which is unable to identify coherent decadal changes and the overriding controls on planetary scales. Here, we show that, during the recent global warming of about 0.4 °C since the late 1970s, a coherent decadal change of precipitation and circulation emerges in the entirety of the NHSM system. Surprisingly, the NHSM as well as the Hadley and Walker circulations have all shown substantial intensification, with a striking increase of NHSM rainfall by 9.5% per degree of global warming. This is unexpected from recent theoretical prediction and model projections of the 21st century. The intensification is primarily attributed to a mega-El Niño/Southern Oscillation (a leading mode of interannual-to-interdecadal variation of global sea surface temperature) and the Atlantic Multidecadal Oscillation, and further influenced by hemispherical asymmetric global warming. These factors driving the present changes of the NHSM system are instrumental for understanding and predicting future decadal changes and determining the proportions of climate change that are attributable to anthropogenic effects and long-term internal variability in the complex climate system.

  12. What is the role of historical and future anthropogenically-induced land-cover change on the surface climate of West Africa? Results from the LUCID and LUCID-CMIP5 intercomparison project

    NASA Astrophysics Data System (ADS)

    Sy, Souleymane; de Noblet Ducoudré, Nathalie; Boisier, Juan Pablo; Sultan, benjamin; Thierno Gaye, Amadou

    2016-04-01

    West Africa has been highlighted as a hot spot of land surface-atmosphere interactions. A significant climate feature in this region is the West African monsoon (WAM), which variability dominants the climate variability. The role of historical anthropogenically induced land-cover change on the surface climate of West Africa is assessed using the outputs of the project Land-Use and Climate, IDentification of Robust Impacts (LUCID). Focusing the analysis on Sahel and Guinea, the results reveal that even though a common experimental design are used among the seven climate LUCID models, the areas of crops and pastures are specific for each Land Surface Model (LSM) due to different interpretations of land-use changes. In addition, the historical effects of land-use changes are not regionally significant among the seven climate models due to a small land-use change prescribed in these regions, the intercomparison analysis reveals a very contrasted responses between the models which transforms crops and pastures to desert fraction and others which deforest massively. Despite this various characterization within the seven LSMs, the results reveal that the change in surface albedo, leaf area index, and roughness surface is roughly proportional in Guinea to the amount of deforestation imposed on the individual models. The analysis highlights also the importance of having a realistic land-cover distribution to correctly represent the present-day surface climate in West African regions. The obtained results show that there is neither better nor worse performance among the climate models than others in these regions. Furthermore, there is no consistency among the various models regarding the response on both imposed land cover map to present day surface climate resulting in uncertainty in the representation of atmospheric processes. These climatic effects of land-use changes are relatively small compared to those resulting from the increased greenhouse gases. Therefore, for a

  13. 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.

  14. 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.

  15. Will the South Asian monsoon overturning circulation stabilize any further?

    NASA Astrophysics Data System (ADS)

    Krishnan, R.; Sabin, T. P.; Ayantika, D. C.; Kitoh, A.; Sugi, M.; Murakami, H.; Turner, A. G.; Slingo, J. M.; Rajendran, K.

    2013-01-01

    Understanding the response of the South Asian monsoon (SAM) system to global climate change is an interesting scientific problem that has enormous implications from the societal viewpoint. While the CMIP3 projections of future changes in monsoon precipitation used in the IPCC AR4 show major uncertainties, there is a growing recognition that the rapid increase of moisture in a warming climate can potentially enhance the stability of the large-scale tropical circulations. In this work, the authors have examined the stability of the SAM circulation based on diagnostic analysis of climate datasets over the past half century; and addressed the issue of likely future changes in the SAM in response to global warming using simulations from an ultra-high resolution (20 km) global climate model. Additional sensitivity experiments using a simplified atmospheric model have been presented to supplement the overall findings. The results here suggest that the intensity of the boreal summer monsoon overturning circulation and the associated southwesterly monsoon flow have significantly weakened during the past 50-years. The weakening trend of the monsoon circulation is further corroborated by a significant decrease in the frequency of moderate-to-heavy monsoon rainfall days and upward vertical velocities particularly over the narrow mountain ranges of the Western Ghats. Based on simulations from the 20-km ultra high-resolution model, it is argued that a stabilization (weakening) of the summer monsoon Hadley-type circulation in response to global warming can potentially lead to a weakened large-scale monsoon flow thereby resulting in weaker vertical velocities and reduced orographic precipitation over the narrow Western Ghat mountains by the end of the twenty-first century. Supplementary experiments using a simplified atmospheric model indicate a high sensitivity of the large-scale monsoon circulation to atmospheric stability in comparison with the effects of condensational heating.

  16. 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.

  17. Anti-phase relationship between the East Asian winter monsoon and summer monsoon during the Holocene?

    NASA Astrophysics Data System (ADS)

    Ge, Qian; Xue, Zuo; Yao, Zhigang; Zang, Zhengchen; Chu, Fengyou

    2017-04-01

    The relationship between the East Asian winter monsoon (EAWM) and East Asian summer monsoon (EASM) during the Holocene is complicated and remains controversial. In this study, analysis of grain size and benthic foraminiferal oxygen isotope, as well as accelerator mass spectrometry 14C dating was performed on a sediment core retrieved from the newly revealed muddy deposit on the northern South China Sea continental shelf. The history of the EAWM and EASM were reconstructed for the last 8200 a BP. Further analysis in conjunction with previously published paleo-climate proxies revealed that the relationship between the EAWM and EASM during the Holocene is more complex than a simple and strict anti-phase one-both negative and positive correlations were identified. The EAWM and EASM are negatively correlated around 7500, 4800, 4200, 3200, and 300 a BP (cooling periods), while positively correlated around 7100, 3700, and 2100 a BP (warm periods). In particular, both the EAWM and EASM intensified during the three positive correlation periods. However, we also found that the relationship between these two sub-monsoons is anti-phase during the final phase of particularly hot periods like Holocene Optimum and Medieval warm period. The possible impact from variations of solar irradiance on the relationship between the EAWM and EASM was also discussed.

  18. 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

  19. 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 (...

  20. 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.

  1. The effect of Eurasian snow cover on the Indian monsoon

    SciTech Connect

    Vernekar, A.D.; Zhou, J.; Shukla, J.

    1995-02-01

    More than a century ago, Blanford suggested the inverse relation between Himalayan winter and spring snow accumulation and subsequent summer monsoon rainfall over India. This relation was later substantiated with additional data by Walker. Because of an inadequate observational network to obtain the spatial variation of snow cover over the Himalayan region, little progress was made until the availability of satellite measurements. Snow cover data derived from satellite observations was used to show that the correlation between winter Eurasian snow cover south of 52{degrees}N and the following Indian summer monsoon rainfall is negative and statistically significant. This result was further supported by additional research. The relationship between snow cover and monsoon circulation is consistent with a suggestion that the Indian monsoon circulation is a dynamically stable system and its interannual variations are largely determined by slowly varying surface boundary conditions. 64 refs., 22 figs.

  2. Radiative energy budget estimates for the 1979 southwest summer monsoon

    NASA Technical Reports Server (NTRS)

    Ackerman, Steven A.; Cox, Stephen K.

    1987-01-01

    A major objective of the summer monsoon experiment (SMONEX) was the determination of the heat sources and sinks associated with the southwest summer monsoon. The radiative component is presented here. The vertically integrated tropospheric radiation energy budget is negative and varies significantly as a function of monsoon activity. The gradient in the latitudinal mean tropospheric cooling reverses between the winter periods and the late spring/early summer periods. The radiative component of the vertical profile of the diabatic heating is derived. These profiles are a strong function of the stage of the monsoon as well as the geographic region. In general, the surface experiences a net gain of radiative energy during the late spring and early summer periods. During the winter periods, areas northward of 25 N display net surface losses, while the remaining areas exhibit net gains.

  3. Effects of volcanic eruptions on China's monsoon precipitation over the past 700 years

    NASA Astrophysics Data System (ADS)

    Zhuo, Z.; Gao, C.

    2013-12-01

    Tropical volcanic eruptions were found to affect precipitation especially in Asia and Africa monsoon region. However, studies with different types of eruptions suggested different impacts as well as the spatial patterns. In this study, we combined the Monsoon Asia Drought Atlas (MADA, [Cook et al., 2010]) and the Chinese Historical Drought Disaster Index (CHDDI) compiled from the historic meteorological records to study the effect of volcanic eruptions on China's monsoon precipitation over the past 700 years. Histories of past volcanism were compiled from the IVI2[Gao et al., 2008] and Crowley2013[Crowley and Unterman, 2013] reconstructions. Volcanic events were classified into 2×Pinatubo, 1×Pinatubo , ≥5 Tg sulfate aerosols injection in the northern hemisphere (NH) stratosphere for IVI2; and NH sulfate flux more than 20/15/10/5 kg km-2 for Crowley2013. In both cases, average MADA show a drying trend over mainland China from year zero(0) to year three(+3) after the eruption; and the more sulfate aerosol injected into the NH stratosphere or the larger the sulfate flux, the more severe this drying trend seem to reveal. In comparison, a wetting trend was found in the eruption year with Southern Hemisphere (SH) only injections. Superposed epoch analysis with a 10,000 Monte Carlo resampling procedure showed that 97.9% (96.9%) of the observed MADA values are statistically significant at the 95% (99%) confidence level. The drying is probably caused by a reduction of the latent heat flux due to volcanic aerosol' cooling effect, leading to the weakening of south Asian monsoon and decrease of moisture vapor over tropical oceans, which contribute to a reduced moisture flux over china. Spatial distribution of the average MADA show a southward movement of the driest areas in eastern China from year zero to year three after the 1×Pinatubo and 2×Pinatubo eruptions, whereas part of north china experienced unusual wetting condition. This is in good agreement with CHDDI, which

  4. 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.

  5. 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

  6. The simulated Indian monsoon: A GCM sensitivity study

    NASA Technical Reports Server (NTRS)

    Fennessy, M. J.; Kinter, J. L., III; Kirtman, B.; Marx, L.; Nigam, S.; Schneider, E.; Shukla, J.; Straus, D.; Vernekar, A.; Xue, Y.

    1994-01-01

    A series of sensitivity experiments are conducted in an attempt to understand and correct deficiencies in the simulation of the seasonal mean Indian monsoon with a global atmospheric general circulation model. The seasonal mean precipitation is less than half that observed. This poor simulation in seasonal integrations is independent of the choice of initial conditions and global sea surface temperature data used. Experiments are performed to test the sensitivity of the Indian monsoon simulation to changes in orography, vegetation, soil, wetness, and cloudiness. The authors find that the deficiency of the model precipitation simulation may be attributed to the use of an enhanced orography in the integrations. Replacement of this orography with a mean orography results in a much more realistic simulation of Indian monsoon circulation and rainfall. Experiments with a linear primitive equation model on the sphere suggest that this striking improvement is due to modulations of the orographically forced waves in the lower troposphere. This improvement in the monsoon simulation is due to the kinematic and dynamical effects of changing the topography, rather than the thermal effects, which were minimal. The magnitude of the impact on the Indian monsoon of the other sensitivity experiments varied considerably, but was consistently less than the impact of using the mean orography. However, results from the soil moisture sensitivity experiments suggest a possibly important role for soil moisture in simulating tropical precipitation, including that associated with the Indian monsoon.

  7. 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

  8. Causal evidence between monsoon and evolution of rhizomyine rodents.

    PubMed

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

    2015-03-11

    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.

  9. Causal evidence between monsoon and evolution of rhizomyine rodents

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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.

  10. Effect of dust on the iNdian summer monsoon

    NASA Astrophysics Data System (ADS)

    Maharana, Pyarimohan; Priyadarshan Dimri, Ashok

    2015-04-01

    The atmospheric dust plays a major role in deciding the radiation balance over the earth. The dust scatters the light, acts as cloud condensation nuclei, and hence helps in the formation of different types of clouds. This property of the dust has a long term effect on the Indian summer monsoon and its spatial distribution. India receives around 80% of its annual rainfall during summer monsoon and around 50% of the Indian population depends upon the monsoonal rain for the agricultural activities. The rain also has an important contribution to the industry, water resource management, ground water recharge, provide relief from the heat and also play a major role in deciding the socio-economic condition of a major part of the population. Two sets of simulations (control and dust chemistry simulation) are made to analyze the effect of dust on the Indian summer monsoon. Both the simulations nicely represent the spatial structure of different meteorological parameters. The magnitude of the pressure gradient, circulation and the precipitation is more during the JJAS for the dust chemistry simulation except for the temperature climatology. The analysis of the pre-monsoon and May temperature climatology reflects that the heating of the land mass is more in the dust chemistry simulation as compared to the control simulation, which is providing the strength to the monsoon flow during JJAS. The dust simulation shows that it increases the hydrological cycle over the Indian land mass.

  11. North Africa

    SciTech Connect

    Nicod, M.A.

    1981-10-01

    The total area covered by petroleum rights in the six countries described in this paper increased by more than 17% in 1980 compared to 1979. Joint venture agreements were finalized for 19 blocks over 94,000 km/sup 2/ in the Algerian venture. Although official information is scarce for Algeria and Libya, seismic activity probably increased in 1980 compared to 1979. Exploration drilling activity increased with 121 wildcats drilled compared to 93 during the previous year. This effort led to 40 discoveries, a 34.5% success ratio. Chevron was especially successful in wildcatting, with 6 oil discoveries for 8 wells drilled in the interior basins of Sudan. One Moroccan discovery can be considered as a highlight: the BRPM Meskala 101 well in the Essaouira basin found an apparently large amount of gas in Triassic sandstones. This discovery deserves special attention, since the gas has been found in Triassic pays rather than in the usual Jurassic pays in the Essaouira basin. Oil production in North Africa decreased from about 13.5% in 1980, with about 3,405,000 barrels of oil per day compared to 3,939,500 barrels of oil per day in 1979. When oil output strongly decreased in Algeria (-16.4%) and Libya (-15.6%), Tunisian production peaked at 116,287 barrels of oil per day and Egypt production also peaked at 584,148 barrels of oil per day. Total gas production in 1980 strongly declined from 44%, mostly due to the decline of the Algerian gas production. 8 figures, 40 tables.

  12. The strong association between western Sahelian monsoon rainfall and intense atlantic hurricanes

    SciTech Connect

    Landsea, C.W.; Gray, W.M. )

    1992-05-01

    Seasonal variability of Atlantic basin tropical cyclones is examined with respect to the monsoon rainfall over West Africa. Variations of intense hurricanes are of the most interest, as they are responsible for over three-quarters of United States tropical cyclone spawned destruction, though they account for only one-fifth of all landfalling cyclones. Intense hurricanes have also shown a strong downward trend during the last few decades. It is these storms that show the largest concurrent association with Africa's western Sahelian June-September rainfall for the years 1949-90. Though the Sahel is currently experiencing a multidecadal drought, the relationship between Atlantic tropical cyclones and western Sahelian rainfall is not dependent on the similar downward trends in both datasets. A detrended analysis confirms that a strong association still exists, though reduced somewhat in variance explained. Additionally, independent data from the years 1899 to 1948 substantiate the existence of the tropical cyclone-western Sahelian rainfall association. The fact that the Sahel periodically experiences multidecadal wet and dry regimes suggests that the current Sahelian drought, which began in the late 1960s, could be a temporary condition that may end in the near future. When this occurs, the Atlantic hurricane basin-especially the Caribbean islands and the United States East Coast-will likely see a large increase in intense hurricane activity associated with abundant Sahelian rainfall similar to the period of the late 1940s through the 1960s.

  13. 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.

  14. Gaseous and particulate pollutants in the upper troposphere and lower stratosphere (UTLS) of the Asian Monsoon region simulated by the CCM EMAC

    NASA Astrophysics Data System (ADS)

    Brühl, Christoph; Tost, Holger; Höpfner, Michael

    2016-04-01

    Results of a transient simulation for 2002 to 2011 using the chemistry climate model EMAC with interactive tropospheric and stratospheric aerosol processes are presented. The simulation includes anthropogenic gaseous emissions based on EDGAR but also more than 100 volcanic SO2 injections into the UTLS using estimates from satellite data. The lower boundary conditions for the different aerosol types are based on AEROCOM. We demonstrate that in the Asian monsoon region CO and organic and black carbon are strongly enhanced in the UTLS. We also show that the monsoon circulation transports anthropogenic SO2, originating in China, to the lower stratosphere, as well as volcanic SO2 injected into the upper troposphere in East Africa and Indonesia. The results are compared with MIPAS/ENVISAT observations.

  15. Africa: Prosperous times

    SciTech Connect

    1996-08-01

    Political instability and corruption is the rule, rather than the exception, in Africa`s main producing regions, but exploration and production prospects there are bright and attractive to foreign operators. The paper discusses exploration, drilling, resource development, and production in Nigeria, Libya, Algeria, Egypt, Angola, Congo, Gabon, and Tunisia. The other countries of Africa are briefly mentioned, i.e., Cameroon, Cote D`Ivoire, South Africa, Sudan, Namibia, Equatorial Guinea, Eritrea, Zaire, Mozambique, Ghana, Niger, and Seychelles.

  16. Sustainability Within the Great Monsoon River Basins

    NASA Astrophysics Data System (ADS)

    Webster, P. J.

    2014-12-01

    For over five millenia, the great monsoon river basins of the Ganges, Brahmaputra and Indus have provided for great and flourishing agrarian civilizations. However, rapid population growth and urbanization have placed stress on the rural sector causing the use of land that is more prone for flood and drought. In addition, increased population and farming have stressed the availability of fresh water both from rivers and aquifers. Additionally, rapid urbanization has severely reduced water quality within the great rivers. Added to these problems is delta subsidence from water withdrawal that, at the moment far surpasses sea level rise from both natural and anthropogenic effects. Finally, there appear to be great plans for river diversion that may reduce fresh water inflow into the Brahmaputra delta. All of these factors fall against a background of climate change, both anthropogenic and natural, of which there is great uncertainty. We an attempt a frank assessment assessment of the sustainability of society in the great basins and make some suggestions of factors that require attention in the short term.

  17. Climatology of monsoon rains of Myanmar (Burma)

    NASA Astrophysics Data System (ADS)

    Roy, N. Sen; Kaur, Surinder

    2000-06-01

    Based on 33 years' rainfall data of Myanmar for the summer monsoon months (June-September), the detailed rainfall climatology of the country has been studied. Seasonal rainfall series are found to approximate to a Gaussian distribution. By using the rainfall distribution and coefficient of variation, it has been possible to divide the country into five homogeneous rainfall regions. Different statistical characteristics of the seasonal, monthly and zonal rainfall, as well as the whole country's rainfall, have been determined. Analysis of interannual and intraseasonal variability highlights the fact that the correlation between the rainfall of different months and zones is rather weak. Trend and periodicity of the rainfall series have been examined by different statistical techniques, indicating little evidence of a trend. The power spectrum of the rainfall series appears to show only marginal significance at the 95% level for an 11 year cycle. The rainfall series of Myanmar shows little correspondence with neighbouring Bangladesh and Northeast India, even though all of them are influenced by similar weather systems.

  18. Monsoon failure enhances drought in southwestern North America

    NASA Astrophysics Data System (ADS)

    Griffin, D.; Woodhouse, C. A.; Meko, D. M.; Stahle, D. W.

    2012-12-01

    The North American monsoon has emerged as a research frontier for paleoclimatology. Precisely dated tree-ring latewood (summer growth) offers unparalleled promise for studying interannual- to decadal-scale monsoon variability over past centuries. From the new network of latewood chronologies in the southwestern U.S., we present a high-quality, 470-year long reconstruction of June-August (monsoon) precipitation for the Arizona-Sonora sub-region of the North American monsoon. For comparison, we developed a companion reconstruction of October-April (cool-season) precipitation from chronologies of earlywood (spring growth). Foremost, these reconstructions demonstrate that many of the well-known southwestern droughts were not just cool-season events, but were also characterized by concurrent failure of the summer monsoon. The early 21st century drought, the late 19th century drought, the 17th century Puebloan drought, and even the 16th century megadrought each contain notable runs of consecutive years with below average monsoon rainfall. The reconstructions also reveal that the interannual relationship between winter and summer precipitation has been unstable through time and that the tendency for dry (wet) winters to be followed by wet [dry] summers was anomalously high during the mid-late 20th century. Cool-season and monsoon moisture variability in this region can be linked to patterns of ocean-atmosphere circulation. However, our understanding of the climate dynamics that would facilitate persistence of dual-season drought and transience in the winter-summer precipitation relationship is far from complete.

  19. 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

  20. 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

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. Intraseasonal oscillations in East Asian and South Asian monsoons

    NASA Astrophysics Data System (ADS)

    Krishnamurthy, V.

    2016-11-01

    This study has investigated the relation between the East Asian monsoon and the South Asian monsoon at intraseasonal time scale during the boreal summer. Applying a data adaptive method on daily anomalies of precipitation, two leading intraseasonal oscillations (ISOs) were extracted separately in the regions of South Asia, tropical East Asia and subtropical East Asia. The first ISO has a period of about 45 days and propagates northward and eastward over the South Asian and tropical East Asian regions. The second ISO, with a period of about 26 days, propagates northeastward over South Asia and northwestward over tropical East Asia. Although both the ISOs are also present over the subtropical East Asia, the variance is low while no propagation is evident. The circulation patterns associated with the ISOs were found to be consistent with the corresponding precipitation patterns of the ISOs. The two ISOs also reveal consistency with the space-time evolution of diabatic heating, convection, vertical motion, upper-level divergence and moisture transport. The zonal and meridional propagation of the ISOs provide a strong link between the South Asian monsoon and East Asian monsoon regions. The subtropical East Asian region seems to have a weaker link with the other monsoon regions.

  7. 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

  8. 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.

  9. 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.

  10. 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

    2015-06-18

    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.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Carbon dioxide emissions from Indian monsoonal estuaries

    NASA Astrophysics Data System (ADS)

    Sarma Vedula, VSS

    2012-07-01

    The oceans act as a net sink for atmospheric CO2, however, the role of coastal bodies on global CO2 fluxes remains unclear due to lack of data. The estimated absorption of CO2 from the continental shelves, with limited data, is 0.22 to 1.0 PgC/y, and of CO2 emission by estuaries to the atmosphere is 0.27 PgC/y. The estimates from the estuaries suffer from large uncertainties due to large variability and lack of systematic data collection. It is especially true for Southeast Asian estuaries as the biogeochemical cycling of material are different due to high atmospheric temperature, seasonality driven by monsoons, seasonal discharge etc. In order to quantify CO2 emissions from the Indian estuaries, samples were collected at 27 estuaries all along the Indian coast during discharge wet and dry periods. The emissions of CO2 to the atmosphere from Indian estuaries were 4-5 times higher during wet than dry period. The pCO2 ranged between ~300 and 18492 microatm which were within the range of world estuaries. The mean pCO2 and particulate organic carbon (POC) showed positive relation with rate of discharge suggesting availability of high quantities of organic matter that led to enhanced microbial decomposition. The annual CO2 fluxes from the Indian estuaries, together with dry period data available in the literature, amounts to 1.92 TgC which is >10 times less than that from the European estuaries. The low CO2 fluxes from the Indian estuaries are attributed to low flushing rates and less human settlements along the banks of the Indian estuaries.

  20. Reduction of monsoon rainfall in response to past and future land use and land cover changes

    NASA Astrophysics Data System (ADS)

    Quesada, Benjamin; Devaraju, Narayanappa; Noblet-Ducoudré, Nathalie; Arneth, Almut

    2017-01-01

    Land use and land cover changes (LULCC) can have significant biophysical impacts on regional precipitation, including monsoon rainfall. Using global simulations with and without LULCC from five general circulation models, under the Representative Concentration Pathway 8.5 scenario, we find that future LULCC significantly reduce monsoon precipitation in at least four (out of eight) monsoon regions. While monsoon rainfalls are likely to intensify under future global warming, we estimate that biophysical effects of LULCC substantially weaken future projections of monsoons' rainfall by 9% (Indian region), 12% (East Asian), 32% (South African), and 41% (North African), with an average of 30% for projections across the global monsoon region. A similar strong contribution is found for biophysical effects of past LULCC to monsoon rainfall changes since the preindustrial period. Rather than remote effects, local land-atmosphere interactions, implying a decrease in evapotranspiration, soil moisture, and clouds along with more anticyclonic conditions, could explain this reduction in monsoon rainfall.

  1. Environmental status of groundwater affected by chromite ore processing residue (COPR) dumpsites during pre-monsoon and monsoon seasons.

    PubMed

    Matern, Katrin; Weigand, Harald; Singh, Abhas; Mansfeldt, Tim

    2017-02-01

    Chromite ore processing residue (COPR) is generated by the roasting of chromite ores for the extraction of chromium. Leaching of carcinogenic hexavalent chromium (Cr(VI)) from COPR dumpsites and contamination of groundwater is a key environmental risk. The objective of the study was to evaluate Cr(VI) contamination in groundwater in the vicinity of three COPR disposal sites in Uttar Pradesh, India, in the pre-monsoon and monsoon seasons. Groundwater samples (n = 57 pre-monsoon, n = 70 monsoon) were taken in 2014 and analyzed for Cr(VI) and relevant hydrochemical parameters. The site-specific ranges of Cr(VI) concentrations in groundwater were <0.005 to 34.8 mg L(-1) (Rania), <0.005 to 115 mg L(-1) (Chhiwali), and <0.005 to 2.0 mg L(-1) (Godhrauli). Maximum levels of Cr(VI) were found close to the COPR dumpsites and significantly exceeded safe drinking water limits (0.05 mg L(-1)). No significant dependence of Cr(VI) concentration on monsoons was observed.

  2. Is the Indian summer monsoon stable against global change?

    NASA Astrophysics Data System (ADS)

    Zickfeld, K.; Knopf, B.; Petoukhov, V.; Schellnhuber, H. J.

    2005-08-01

    The stability of the Indian summer monsoon is investigated by means of a box model of the tropical atmosphere. At the heart of this model is the moisture-advection feedback which allows for the existence of two stable regimes: besides the ``wet'' summer monsoon, a stable state exists which is characterized by low precipitation. The model is employed for the identification of changes in the qualitative systems behavior in response to changes in boundary conditions. The most notable result is the occurrence of saddle-node bifurcations against changes in those quantities which govern the heat balance of the system, i.e., the planetary albedo, the insolation, and the CO2 concentration. These findings are remarkable insofar as they indicate that anthropogenic perturbations of the planetary albedo, such as sulphur emissions and/or land-use changes, or natural variations in insolation and CO2 concentration could trigger abrupt transitions between different monsoon regimes.

  3. Observational relationships between aerosol and Asian monsoon rainfall, and circulation

    NASA Astrophysics Data System (ADS)

    Lau, K.-M.; Kim, K.-M.

    2006-11-01

    Preliminary observational evidences are presented showing that the Indian subcontinent and surrounding regions are subject to heavy loading of absorbing aerosols, i.e., dust and black carbon, which possess spatial and temporal variability that are closely linked to those of the Asian monsoon water cycle. Consistent with the Elevated Heat Pump hypothesis, we find that increased loading of absorbing aerosols over the Indo-Gangetic Plain in the pre-monsoon season is associated with a) increased heating of the upper troposphere, with the formation of a warm-core upper level anticyclone over the Tibetan Plateau in April-May, b) an advance of the monsoon rainy season in northern India in May, and c) subsequent increased rainfall over the Indian subcontinent, and decreased rainfall over East Asia in June-July.

  4. Ice-sheet influences on global Monsoon systems (Invited)

    NASA Astrophysics Data System (ADS)

    Timmermann, A.; Elison Timm, O.; Friedrich, T.; Abe-Ouchi, A.; Menviel, L.; Tigchelaar, M.

    2013-12-01

    The waxing and waning of the northern Hemisphere ice-sheets on orbital and millennial timescales and corresponding changes in atmospheric and oceanic circulation played an essential role in modulating monsoon systems globally. Here we review the mechanisms by which changes in ice-sheet orography, global sea-level and freshwater input into the North Atlantic can influence global wind patterns and tropical moisture convergence. Our analysis is based on a series of transient model simulations conducted with the newly developed 3-dimensional coupled ice-sheet-climate model iLOVE. Forced by orbital and greenhouse gas concentrations over the past 80 ka, this model realistically simulates the evolution of Northern Hemisphere ice volume. It is demonstrated that orbital-scale changes in ice-sheet orography influence the South American and African Monsoons, but leave Asian Monsoon systems relatively unaltered. On millennial timescales the situation is very different. Freshwater forcing from calving ice-sheets causes variations of the thermohaline circulation, North Atlantic sea surface temperatures and global wind patterns. Using an earth system model hindcast for the period 30-50 ka in combination with high-resolution hydroclimate proxies, we demonstrate that this mechanism can explain for the bulk of MIS3 global Monsoon variability on millennial-timescales. In addition to these remote influences, rainfall intensity in the dominant Monsoon regions is also modulated by precessional forcing and corresponding shifts of the meridional surface temperature gradients. This presentation will conclude with a brief discussion of gaps in our understanding of how orbital forcing affected Monsoons and Intertropical Convergence Zones during the Pleistocene.

  5. The relationship between Arabian Sea upwelling and Indian Monsoon revisited

    NASA Astrophysics Data System (ADS)

    Yi, Xing; Zorita, Eduardo; Hünicke, Birgit

    2015-04-01

    Coastal upwelling is important to marine ecosystems and human activities. It transports nutrient-rich deep water mass that supports marine biological productivity. In this study, we aim to characterize the large-scale climate forcings that drive upwelling along the western Arabian Sea coast. Studies based on ocean sediments suggest that there is a link between this coastal upwelling system and the Indian summer monsoon. However, a more direct method is needed to examine the influence of various forcings on upwelling. For this purpose, we analyse a high-resolution (about 10 km) global ocean simulation (denoted STORM), which is based on the MPI-OM model developed by the Max-Planck-Institute for Meteorology in Hamburg driven by the global meteorological reanalysis NCEP over the period 1950-2010. This very high spatial resolution allows us to identify characteristics of the coastal upwelling system. We compare the simulated upwelling velocity of STORM with two traditional upwelling indices: along-shore wind speed and sea surface temperature. The analysis reveals good consistency between these variables, with high correlations between coastal upwelling and along-shore wind speed (r=0.85) as well as coastal sea surface temperature (r=-0.77). To study the impact of the monsoon on the upwelling we analyse both temporal and spatial co-variability between upwelling velocity and the Indian summer monsoon index. The spatial analysis shows that the impact of the monsoon on the upwelling is concentrated along the coast, as expected. However, somewhat unexpectedly, the temporal correlation between the coastal upwelling and the monsoon index is rather weak (r=0.26). Also, the spatial structure of upwelling in the Arabian Sea as revealed by a Principal Component Analysis is rather rich, indicating that factors other than the Monsoon are also important drivers of upwelling. In addition, no detectable trend in our coastal upwelling is found in the simulation that would match the

  6. South Asian summer monsoon variability in a model with doubled atmospheric carbon dioxide concentration

    SciTech Connect

    Meehl, G.A.; Washington, W.M. )

    1993-05-21

    Doubled atmospheric carbon dioxide concentration in a global coupled ocean-atmosphere climate model produced increased surface temperatures and evaporation and greater mean precipitation in the south Asian summer monsoon region. As a partial consequence, interannual variability of area-averaged monsoon rainfall was enhanced. Consistent with the climate sensitivity results from the model, observations showed a trend of increased interannual variability of Indian monsoon precipitation associated with warmer land and ocean temperatures in the monsoon region. 26 refs., 3 figs., 1 tab.

  7. Numerical prediction of the monsoon depression of 5-7 July 1979. [Monsoon Experiment (MONEX)

    NASA Technical Reports Server (NTRS)

    Shukla, J.; Atlas, R.; Baker, W. E.

    1981-01-01

    A well defined monsoon depression was used for two assimilation and forecast experiments: (1) using conventional surface and upper air data, (2) using these data plus Monex data. The data sets were assimilated and used with a general circulation model to make numerical predictions. The model, the analysis and assimilation procedure, the differences in the analyses due to different data inputs, and the differences in the numerical predictions are described. The MONEX data have a positive impact, although the differences after 24 hr are not significant. The MONEX assimilation does not agree with manual analysis location of depression center. The 2.5 x 3 deg horizontal resolution of the prediction model is too coarse. The assimilation of geopotential height data derived from satellite soundings generated gravity waves with amplitudes similar to the meteorologically significant features investigated.

  8. Nonstationary phase of the plio-pleistocene Asian monsoon

    SciTech Connect

    Clemens, S.C.; Murray, D.W.; Prell, W.L.

    1996-11-08

    Paleoclimate records indicate that the strength of the Asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods (41,000 and 23,000 years, respectively) and the extent of Northern Hemisphere glaciation. Over the past 2.6 million years, the timing (phase) of strong monsoons has changed by {approximately}83 degrees in the precession and {approximately}124 degrees in the obliquity bands relative to the phase of maximum global ice volume (inferred from the marine oxygen isotope record). These results suggest that one or both of these systems is nonstationary relative to orbital forcing. 1 ref., 4 figs.

  9. Monsoon circulations and tropical heterogeneous chlorine chemistry in the stratosphere

    NASA Astrophysics Data System (ADS)

    Solomon, Susan; Kinnison, Doug; Garcia, Rolando R.; Bandoro, Justin; Mills, Michael; Wilka, Catherine; Neely, Ryan R.; Schmidt, Anja; Barnes, John E.; Vernier, Jean-Paul; Höpfner, Michael

    2016-12-01

    Model simulations presented in this paper suggest that transport processes associated with the summer monsoons bring increased abundances of hydrochloric acid into contact with liquid sulfate aerosols in the cold tropical lowermost stratosphere, leading to heterogeneous chemical activation of chlorine species. The calculations indicate that the spatial and seasonal distributions of chlorine monoxide and chlorine nitrate near the monsoon regions of the northern hemisphere tropical and subtropical lowermost stratosphere could provide indicators of heterogeneous chlorine processing. In the model, these processes impact the local ozone budget and decrease ozone abundances, implying a chemical contribution to longer-term northern tropical ozone profile changes at 16-19 km.

  10. A Holistic View of the Coupled Monsoon System

    NASA Astrophysics Data System (ADS)

    Webster, P. J.

    2008-12-01

    The basic dynamical constraint on both the atmospheric and oceanic components of the monsoon is the strong cross-equatorial pressure gradient (CEPG). The CEPG is positive and strongest in the lower troposphere during the boreal summer and weakest and negative in the boreal winter. Counter gradients exist at higher elevations. The CEPG is a slowly varying field set up by land-sea differences, convective heating and the seasonal cycle of sea-surface temperature. The dynamic response to this evolving CEPG creates the seasonal structure of the ocean and the atmosphere and determines how the monsoon system will respond to forcing from outside the system. It determines the mode of interannual variability of the system. The CEPG drives a cross-equatorial flow that gains moisture through evaporation. Strong latent heat release occurs in littoral seas and land areas during the summer and to the south of the equator during winter creating net cross-equatorial heat fluxes from the winter to summer hemispheres. However, the cross- equatorial wind fields, so generated, cause an Ekman heat transport from the winter to the summer hemisphere. The net flux is large with a seasonal amplitude of about 2 PW. This almost matches the net atmospheric heat transport, but with reversed sign. For example, the oceanic heat flux is sufficient to reduce the north Indian Ocean upper temperature by 1-2C during summer and warm it by a comparable amount during winter. The net effect is to reduce the vigor of the atmospheric monsoon. To a large degree, the couple ocean-atmosphere system is self-regulated and closed system. Occasional outside influences (ENSO, anomalous springtime snow cover etc.) influence the monsoon. For example there is evidence that El Nino (La Nina) is associated with a weak (strong) monsoon. But a strong (weak) monsoon creates a stronger (weaker) cross-equatorial flow and an enhanced (reduced) oceanic heat flux to the winter hemisphere. In this manner, the system returns to

  11. The Origin of Monsoons: The Role of Continental-Scale Landmass

    NASA Technical Reports Server (NTRS)

    Chao, Winston

    2010-01-01

    In a challenge to the traditional explanation for the cause of monsoons Chao and Chen (JAS 2001) argued that land-sea thermal contrast is not necessary for the existence of monsoons. However, the question of whether land-sea thermal contrast plays any modifying role still exists. This study tries to answer that question. The result is a more complete theory of the origin of monsoons than that proposed by Chao and Chen. Two criticisms of the traditional explanation for the cause of monsoons do not apply to this theory. They are: 1) no explanation for monsoon onset and retreat, let alone the fact that monsoon onset is much faster than monsoon retreat, and 2) for the South Asian monsoon, land-sea thermal contrast is greatest just prior to monsoon onset, not at the height of the monsoon season. Land-sea thermal contrast acts as a facilitator for monsoon onset. If it does not exist, monsoon onset can still occur but at a later time. Our results are supported by GCM experiments.

  12. Out of Africa: the importance of rivers as human migration corridors

    NASA Astrophysics Data System (ADS)

    Ramirez, J. A.; Coulthard, T. J.; Rogerson, M.; Barton, N.; Bruecher, T.

    2013-12-01

    The route and timing of Homo sapiens exiting Africa remains uncertain. Corridors leading out of Africa through the Sahara, the Nile Valley, and the Red Sea coast have been proposed as migration routes for anatomically modern humans 80,000-130,000 years ago. During this time climate conditions in the Sahara were wetter than present day, and monsoon rainfall fed rivers that flowed across the desert landscape. The location and timing of these rivers may have supported human migration northward from central Africa to the Mediterranean coast, and onwards to Europe or Asia. Here, we use palaeoclimate rainfall and a hydrological model to spatially simulate and quantitatively test the existence of three major rivers crossing the Sahara from south to north during the time of human migration. We provide evidence that, given realistic underlying climatology, the well-known Sahabi and Kufrah rivers very likely flowed across modern day Libya and reached the coast. More unexpectedly an additional river crossed the core of the Sahara through Algeria (Irharhar river) and flowed into the Chotts basin. The Irharhar river is unique, because it links locations in central Africa experiencing monsoon climates with temperate coastal Mediterranean environments where food and resources were likely abundant. From an ecological perspective, this little-known corridor may prove to be the most parsimonious migration route. Support for the Irharar as a viable migration corridor is provided by its geographic proximity to middle Stone Age archaeological artefacts found in North Africa. Our new, highly novel approach provides the first quantitative analysis of the likelihood that rivers occurred during the critical period of human migration out of Africa. Simulated probability of surface water in North Africa during the last interglacial and the location of tools and ornaments from the Middle Stone Age.

  13. The turbulence underside of the West African Monsoon

    NASA Astrophysics Data System (ADS)

    Lothon, M.; Lohou, F.; Saïd, F.; Campistron, B.; Canut, G.; Couvreux, F.; Durand, P.; Kalapureddy, M. C.; Lee, Y.; Madougou, S.; Serça, D.

    2009-09-01

    We present an experimental analysis of the sahelian Planetary Boundary Layer (PBL) processes in the context of the AMMA (African Monsoon Multidisciplinary Analysis) program and its extensive observational deployment in 2006. From May to October, two opposite flows are interacting in the first 5 thousands m over surface in Sahel: the moist southerly monsoon flow and the overlying northeasterly Saharan Air Layer (SAL) in which the African Easterly Jet (AEJ) is developing, generated by the contrast of surface moisture and temperature between Sahara and the Gulf of Guinea. Until the monsoon onset in mid-July, the low troposphere is slowly moistening through advection from the Guinea Gulf by the monsoon flow, especially during the night. During the day, the dry convection occurring within the PBL vertically redistributes part of the water vapour. After the onset, deep convection occurs much more frequently and the role played by the PBL completely changes. The relative position of the interface between monsoon and SAL and the PBL top inversion is crucial for the nature of the interaction and its impact on scalars, especially water vapour. We consider the role of the PBL processes in this context, and focus on four main aspects: (1) the diurnal cycle of the low troposphere, (2) the interaction between the PBL and the AEJ, (3) the entrainment at the PBL top (4) the impact of the PBL processes at surface. We base our analysis on long term profilers, radiosondes, and surface flux data, short term aircraft turbulence measurements made during the Special Observing Periods and Large Eddy Simulation. The network of wind profilers enables us to study the large scale circulation and highlight the consistence and extent of the nocturnal jet, and the importance of the diurnal cycle of the low troposphere for the West African Monsoon. During daytime, both the wind within the monsoon flow and the AEJ windspeed in the overlying SAL decrease, due to turbulent mixing within the PBL and

  14. Large-scale response of the Eastern Mediterranean thermohaline circulation to African monsoon intensification during sapropel S1 formation

    NASA Astrophysics Data System (ADS)

    Tesi, T.; Asioli, A.; Minisini, D.; Maselli, V.; Dalla Valle, G.; Gamberi, F.; Langone, L.; Cattaneo, A.; Montagna, P.; Trincardi, F.

    2017-03-01

    The formation of Eastern Mediterranean sapropels has periodically occurred during intensification of northern hemisphere monsoon precipitation over North Africa. However, the large-scale response of the Eastern Mediterranean thermohaline circulation during these monsoon-fuelled freshening episodes is poorly constrained. Here, we investigate the formation of the youngest sapropel (S1) along an across-slope transect in the Adriatic Sea. Foraminifera-based oxygen index, redox-sensitive elements and biogeochemical parameters reveal - for the first time - that the Adriatic S1 was synchronous with the deposition of south-eastern Mediterranean S1 beds. Proxies of paleo thermohaline currents indicate that the bottom-hugging North Adriatic Dense Water (NAdDW) suddenly decreased at the sapropel onset simultaneously with the maximum freshening of the Levantine Sea during the African Humid Period. We conclude that the lack of the "salty" Levantine Intermediate Water hampered the preconditioning of the northern Adriatic waters necessary for the NAdDW formation prior to the winter cooling. Consequently, a weak NAdDW limited in turn the Eastern Mediterranean Deep Water (EMDWAdriatic) formation with important consequences for the ventilation of the Ionian basin as well. Our results highlight the importance of the Adriatic for the deep water ventilation and the interdependence among the major eastern Mediterranean water masses whose destabilization exerted first-order control on S1 deposition.

  15. Mean state and kinematic properties of mesoscale convective systems over West Africa

    NASA Astrophysics Data System (ADS)

    Ogungbenro, Stephen B.; Ajayi, V. O.; Adefolalu, D. O.

    2016-04-01

    A 17-year (1984 to 2000) dataset of brightness temperature (T b) was employed to study the spatial and temporal scales of mesoscale convective systems (MCS) over West Africa. The kinematic properties of MCS were tested using wind products. A threshold brightness temperature (T b) of ≤213 K and spatial coverage specifications of more than 5000 km2 were used as two set criteria for initiating MCS tracking. MCS occurrences vary in seasons and locations over West Africa, and their activities vary with different weather zones. They can appear at any time of the day, but this study revealed a significant preference for early morning hours and night hours over continental West Africa. The well-organized systems occur between July and September in the Sahel, and between May and September in the Savanna band. MCS activities in the Gulf of Guinea peak between March and April, while the Savanna and Sahel zones peak between June and August. The produced annual atlas gives a spatial account of areas of MCS dominance in West Africa. The presence of African Easterly Jet (AEJ) and Tropical Easterly Jet (TEJ), and deep monsoon depth all characterize an environment where MCS thrive. Kinematic study of a typical MCS reveals that the monsoon depth increases at the passage of MCS, with cyclonic vorticity dominating from the surface to 300 hpa while anticyclonic vorticity was observed around 200 hpa, and this confirms the importance of low level convergence and upper level divergence as the major requirements for storm mobilization and maintenance.

  16. Asynchronous Little Ice Age Megadroughts in Sub-Saharan Africa

    NASA Astrophysics Data System (ADS)

    Overpeck, J.; Wheeler, W.; Beck, W.; Cole, J.; Scholz, C.; Arko, J.; Sharp, E.

    2002-12-01

    Lake Bosumtwi is a small (8 km-dia.), deep (78 m), hydrologically-closed lake located in the lowland forest zone of southern Ghana, West Africa. The steep-walled meteorite crater basin (10.5 km-dia.) is particularly sensitive to subtle changes in the regional precipitation-evaporation balance, and thus has long been cited as a benchmark paleoenvironmental site for West Africa. In an effort to enhance the value of the Bosumtwi sediments in reconstructing decade to century-scale monsoon variability, we collected a new suite of freeze-cores, and subsequently determined (e.g., with two independent radiometric systems) that the finely laminated sediments represented annual varves (Wheeler et al., AGU Fall Meeting 2002). In light of previous studies, we hypothesized that the ratio of carbon to nitrogen in the lake sediments provides a proxy for changing lake area, and hence regional hydrologic balance and monsoon strength. We confirmed the reliability of this proxy by comparing the sediment based ratio of carbon to nitrogen (C:N) against the age of well-dated dead trees submerged in water depths of 10 to 20m, and then created the first near-annually dated record of West African rainfall extending back eight centuries. The 20th century has been the wettest of the last eight centuries, with the 19th century close behind. Prior to ca. 1800, the Lake Bosumtwi region was generally characterized by drought, with the periods prior to 1300, and 1640 to 1720 AD the driest. This contrasts with comparable records from East Africa, and indicates that much of the Little Ice Age, including some hypothesized periods of reduced solar output, did not result in synchronous enhanced precipitation across North Africa. Instead, it appears that the solar Maunder Minimum resulted in a megadrought in subtropical West Africa coincident with increased rainfall in the Sahel. Thus, the out-of-phase relationship that characterizes interannual variability may extend to longer time scales of variation

  17. 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.

  18. Agriculture in West Africa in the Twenty-First Century: Climate Change and Impacts Scenarios, and Potential for Adaptation.

    PubMed

    Sultan, Benjamin; Gaetani, Marco

    2016-01-01

    West Africa is known to be particularly vulnerable to climate change due to high climate variability, high reliance on rain-fed agriculture, and limited economic and institutional capacity to respond to climate variability and change. In this context, better knowledge of how climate will change in West Africa and how such changes will impact crop productivity is crucial to inform policies that may counteract the adverse effects. This review paper provides a comprehensive overview of climate change impacts on agriculture in West Africa based on the recent scientific literature. West Africa is nowadays experiencing a rapid climate change, characterized by a widespread warming, a recovery of the monsoonal precipitation, and an increase in the occurrence of climate extremes. The observed climate tendencies are also projected to continue in the twenty-first century under moderate and high emission scenarios, although large uncertainties still affect simulations of the future West African climate, especially regarding the summer precipitation. However, despite diverging future projections of the monsoonal rainfall, which is essential for rain-fed agriculture, a robust evidence of yield loss in West Africa emerges. This yield loss is mainly driven by increased mean temperature while potential wetter or drier conditions as well as elevated CO2 concentrations can modulate this effect. Potential for adaptation is illustrated for major crops in West Africa through a selection of studies based on process-based crop models to adjust cropping systems (change in varieties, sowing dates and density, irrigation, fertilizer management) to future climate. Results of the cited studies are crop and region specific and no clear conclusions can be made regarding the most effective adaptation options. Further efforts are needed to improve modeling of the monsoon system and to better quantify the uncertainty in its changes under a warmer climate, in the response of the crops to such

  19. Agriculture in West Africa in the Twenty-First Century: Climate Change and Impacts Scenarios, and Potential for Adaptation

    PubMed Central

    Sultan, Benjamin; Gaetani, Marco

    2016-01-01

    West Africa is known to be particularly vulnerable to climate change due to high climate variability, high reliance on rain-fed agriculture, and limited economic and institutional capacity to respond to climate variability and change. In this context, better knowledge of how climate will change in West Africa and how such changes will impact crop productivity is crucial to inform policies that may counteract the adverse effects. This review paper provides a comprehensive overview of climate change impacts on agriculture in West Africa based on the recent scientific literature. West Africa is nowadays experiencing a rapid climate change, characterized by a widespread warming, a recovery of the monsoonal precipitation, and an increase in the occurrence of climate extremes. The observed climate tendencies are also projected to continue in the twenty-first century under moderate and high emission scenarios, although large uncertainties still affect simulations of the future West African climate, especially regarding the summer precipitation. However, despite diverging future projections of the monsoonal rainfall, which is essential for rain-fed agriculture, a robust evidence of yield loss in West Africa emerges. This yield loss is mainly driven by increased mean temperature while potential wetter or drier conditions as well as elevated CO2 concentrations can modulate this effect. Potential for adaptation is illustrated for major crops in West Africa through a selection of studies based on process-based crop models to adjust cropping systems (change in varieties, sowing dates and density, irrigation, fertilizer management) to future climate. Results of the cited studies are crop and region specific and no clear conclusions can be made regarding the most effective adaptation options. Further efforts are needed to improve modeling of the monsoon system and to better quantify the uncertainty in its changes under a warmer climate, in the response of the crops to such

  20. Sub-seasonal Modulation of Indian Summer Monsoon Seasonal Predictability

    NASA Astrophysics Data System (ADS)

    Robertson, A. W.; Moron, V.; Pai, D. S.

    2015-12-01

    Recent studies have demonstrated that the Indian Summer Monsoon is more predictable during the early and late stages of the season, with a drop in rainfall predictability during the core monsoon months of July and August. Various theories have been advanced for this sub-seasonal evolution, but its origins are still poorly understood. We use a new 0.25-degree 1901-2014 daily rainfall dataset from the Indian Meteorological Department (IMD) to investigate this phenomenon at near-local scale, using more than a century of data. The analysis is based on daily rainfall characteristics, including the spatial coherence of sub-seasonal rainfall anomalies, and on relating these to large-scale moisture variables computed from reanalysis data. Indian summer monsoon rainfall is partitioned into three sub-seasonal phases, with a steep ramp-up (June), persistent core (July-August), and a slower decay phase (Sept-Oct). Spatial coherence of sub-seasonal rainfall anomalies is shown to be highest during the onset and decay phases with a marked mark drop during the core phase. Systematic shifts in seasonal timing are found to typify rainfall anomalies during the onset and decay phases, with ENSO preferentially impacting the latter. We identify a large-scale low-level moisture threshold as a necessary condition for local daily rainfall occuring at >5% of spatial locations across monsoonal India. Sub-seasonal rainfall variability during the onset and decay phases is argued to be controlled largely by the crossing of this threshold. However, this necessary condition is generally easily met during the core season, at which time interannual variability in low-level moisture and interannual correlation between rainfall and large-scale ascent both decrease. This decrease in large-scale control and the loss of spatial coherence imply that sub-seasonal to seasonal rainfall variations at local scales during the core of the monsoon are largely a result of local-scale processes, and are thus

  1. 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

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. Sea surface temperature associations with the Indian summer monsoon

    NASA Astrophysics Data System (ADS)

    Terray, P.; Delecluse, P.; Labattu, S.; Terray, L.

    2003-04-01

    This paper uses recent gridded data and Atmospheric General Circulation Model (AGCM) simulations in order to assess the relationships between interannual variability of the Indian Summer Monsoon (ISM) and Sea Surface Temperature (SST) anomaly patterns over the Indian and Pacific oceans. Interannual variability of ISM rainfall and dynamical indices for the traditional summer monsoon season (June-September) are strongly influenced by rainfall and circulation anomalies observed during August and September, or the Late Indian Summer Monsoon (LISM). Southern Indian Ocean SST acts as a major boundary forcing for the LISM system. Strong (weak) LISMs are preceded by significant positive (negative) SST anomalies in the southeastern subtropical Indian Ocean, off Australia. These SST anomalies are highly persistent and affect the northwestward translation of the Mascarene high from austral to boreal summer. The southeastward (northwestward) shift of this subtropical high associated with cold (warm) SST anomalies off Australia causes a weakening (strengthening) of the whole monsoon circulation through a modulation of the local Hadley cell during the LISM. Furthermore, it is suggested that the Mascarene high interacts with the underlying SST anomalies through a positive dynamical feedback mechanism, maintaining its anomalous position during the LISM. Southeastern Indian Ocean SST anomalies during boreal winter are mainly linked to subtropical Indian Ocean dipole events, studied by Behera and Yamagata (2001), and to the El Niño-Southern Oscillation phenomenon. An El Niño event and the associated warm SST anomalies over the southeastern Indian Ocean during boreal winter may play a key role in the development of a strong ISM by strengthening the local Hadley circulation during the LISM. On the other hand, a developing La Niña event in boreal summer may also enhance the east-west Walker circulation and the monsoon.

  7. 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.

  8. 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.

  9. Generation 2030/Africa

    ERIC Educational Resources Information Center

    You, Danzhen; Hug, Lucia; Anthony, David

    2014-01-01

    Until relatively recently, much of Africa has been among the economically least developed and least densely populated places on earth, replete with villages and rural communities. Africa is changing rapidly, in its economy, trade and investment; in climate change; in conflict and stability; in urbanization, migration patterns, and most of all in…

  10. Islam in Africa

    DTIC Science & Technology

    2008-05-09

    orders as well as followers in West Africa and Sudan, and, like other orders, strives to know God through meditation and emotion. Sufis may be Sunni or...Shi’ite, and their ceremonies may involve chanting, music, dancing, and meditation . West Africa and Sudan have various Sufi orders regarded

  11. Language in South Africa.

    ERIC Educational Resources Information Center

    Mesthrie, Rajend, Ed.

    This collection of 24 papers focuses on language and society in South Africa. Part 1, "The Main Language Groupings," includes (1) "South Africa: A Sociolinguistic Overview" (R. Mesthrie); (2) "The Khoesan Languages" (A. Traill); (3) "The Bantu Languages: Sociohistorical Perspectives" (Robert K. Herbert and…

  12. Teaching about Francophone Africa.

    ERIC Educational Resources Information Center

    Merryfield, Mary; Timbo, Adama

    Lessons and resources for Social Studies and French courses are included in this document. The major goals of these materials are to help students (1) explore the history and geography of Francophone Africa, (2) examine French influences in contemporary Africa, (3) recognize and appreciate cultural differences and similarities in values and…

  13. Potential modulations of pre-monsoon aerosols during El Niño: impact on Indian summer monsoon

    NASA Astrophysics Data System (ADS)

    Fadnavis, S.; Roy, Chaitri; Sabin, T. P.; Ayantika, D. C.; Ashok, K.

    2016-11-01

    The potential role of aerosol loading on the Indian summer monsoon rainfall during the El Niño years are examined using satellite-derived observations and a state of the art fully interactive aerosol-chemistry-climate model. The Aerosol Index (AI) from TOMS (1978-2005) and Aerosol Optical Depth (AOD) from MISR spectroradiometer (2000-2010) indicate a higher-than-normal aerosol loading over the Indo-Gangetic plain (IGP) during the pre-monsoon season with a concurrent El Niño. Sensitivity experiments using ECHAM5-HAMMOZ climate model suggests that this enhanced loading of pre-monsoon absorbing aerosols over the Indo-Gangetic plain can reduce the drought during El Niño years by invoking the `Elevated-Heat-Pump' mechanism through an anomalous aerosol-induced warm core in the atmospheric column. This anomalous heating upshot the relative strengthening of the cross-equatorial moisture inflow associated with the monsoon and eventually reduces the severity of drought during El Niño years. The findings are subject to the usual limitations such as the uncertainties in observations, and limited number of El Niño years (during the study period).

  14. 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.

    2016-10-01

    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.

  15. Role of regional thermal contrast over West Asia in interannual variation in atmospheric moisture transportation over the Indian Ocean and neighboring areas at summer monsoon onset

    NASA Astrophysics Data System (ADS)

    Watanabe, Takeshi

    2015-12-01

    The low-level temperature contrast over West Asia influences the interannual variation in water vapor transportation over the northern and equatorial Indian Ocean and neighboring monsoon area. A composite analysis that takes into account the thermal contrast over West Asia during the monsoon seasonal transition is performed based on the reanalysis and merged observational precipitation data sets. The positive (negative) low-level thermal contrast anomaly over the Iranian Plateau (IP) strengthens (weakens) the thermal contrast over the Arabian Sea. The low-level westerly anomaly develops earlier in the positive IP thermal contrast years than in the negative years. As a result, water vapor transport varies. This variation in water vapor transport in turn has an influence on the abrupt increase in precipitation over South Asia and the Arabian Sea and the decrease over equatorial East Africa. The variation in low-level temperature over the IP precedes the variation of precipitation over these regions by a few pentads. A numerical experiment using the Lagrangian particle dispersion model agrees with the results of the composite analysis. Particles are emitted from the western tropical Indian Ocean region from the preonset to onset period. Results of numerical experiments concerning positive IP thermal contrast years show that particles can be transported into South Asia and the Arabian Sea before the climatological Asian summer monsoon onset pentad. However, small amounts of particles arrive in South Asia and the Arabian Sea at the onset period in negative IP years. The transport into equatorial East Africa becomes weak earlier in positive IP years.

  16. Summer monsoon onset-induced changes of autotrophic pico- and nanoplankton in the largest monsoonal estuary along the west coast of India.

    PubMed

    Mohan, Arya P; Jyothibabu, R; Jagadeesan, L; Lallu, K R; Karnan, C

    2016-02-01

    This study presents the response of autotrophic pico- and nanoplankton to southwest monsoon-associated hydrographical transformations in the Cochin backwaters (CBW), the largest monsoonal estuary along the west coast of India. By the onset of the southwest monsoon, the euhaline/mesohaline conditions in the downstream/upstream of CBW usually transform into oligohaline/limnohaline. The flow cytometer analysis revealed the dominance of picoeukaryotes > Synechococcus > nanoautotrophs, with Prochlorococcus either very low or entirely absent. Synechococcus abundance was high during the pre-southwest monsoon (10(6) L(-1)), which dwindled with heavy fresh water influx during the southwest monsoon (10(5) L(-1)). The drastic drop in salinity and faster flushing of the CBW during the southwest monsoon replaced the euhaline/mesohaline strain of Synechococcus with an oligohaline/limnohaline strain. Epifluorescence microscopy analyses showed that, among the two strains of Synechococcus, the phycoerythrin-rich (PE-rich) one was dominant in the mesohaline/euhaline conditions, whereas the phycocyanin-rich (PC-rich) strain dominated in oligohaline/limnohaline conditions. Although Synechococcus abundance diminished during the southwest monsoon, the total abundance of picoplankton community remained virtually unchanged in the upstream due to an increase in the abundance of picoeukaryotes. On the other hand, the autotrophic nanoplankton abundance increased from pre-monsoon levels of av. 3.8 × 10(6)-av. 9.5 × 10(6) L(-1) at the onset of the southwest monsoon. Utilizing suitable multivariate analyses, the study illustrated the differential response and niche preference of various smaller communities of autotrophs to the southwest monsoon-associated hydrographical ramifications in a large monsoonal estuary, which may be applicable to similar such estuaries situated along the Indian coastline.

  17. Sea Surface Temperature Forcing of the Late Indian Summer Monsoon

    NASA Astrophysics Data System (ADS)

    Terray, P.; Delecluse, P.; Labattu, S.; Terray, L.; Cassou, C.

    2002-12-01

    This paper uses recent historical data and Atmospheric General Circulation Model (AGCM) simulations in order to assess the relationships between interannual variability of the Indian Summer Monsoon (ISM) and Sea Surface Temperature (SST) anomaly patterns over the Indian and Pacific oceans. The focus is on the predictability of ISM rainfall and circulation, and its links to local (Indian Ocean) and remote (Pacific Ocean) SST forcing. Interannual variability of ISM rainfall and dynamical indices for the traditional summer monsoon season (June-September) are strongly influenced by rainfall and circulation anomalies observed during August and September, or the Late Indian Summer Monsoon (LISM). Anomalous monsoons are linked to well-defined LISM rainfall and large-scale circulation anomalies. The whole three-dimensional monsoon circulation, i.e., the east-west Walker and local Hadley circulations, fluctuates during the LISM of anomalous ISM years. LISM circulation is weakened and shifted eastward during weak ISM years. Therefore, we focus on the predictability of the LISM in this study. It is found that southern Indian Ocean SST acts as a major boundary forcing for the LISM system. Strong (weak) LISMs are preceded by significant positive (negative) SST anomalies in the southeastern subtropical Indian Ocean, off Australia. These SST anomalies are highly persistent and affect the northwestward translation of the Mascarene high from austral to boreal summer. The southeastward (northwestward) shift of this subtropical high associated with cold (warm) SST anomalies off Australia causes a weakening (strengthening) of the whole monsoon circulation through a modulation of the local Hadley cell during the LISM. Furthermore, it is suggested that the Mascarene high interacts with the underlying SST anomalies through a positive dynamical feedback mechanism, maintaining its anomalous position during the LISM. Southeastern Indian Ocean SST anomalies during boreal winter are mainly

  18. 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.

  19. Poverty reduction in Africa

    PubMed Central

    Collier, Paul

    2007-01-01

    Poverty in Africa has been rising for the last quarter-century, while it has been falling in the rest of the developing world. Africa's distinctive problem is that its economies have not been growing. This article attempts to synthesize a range of recent research to account for this failure of the growth process. I argue that the reasons lie not in African peculiarities but rather in geographic features that globally cause problems but that are disproportionately pronounced in Africa. These features interact to create three distinct challenges that are likely to require international interventions beyond the conventional reliance on aid. PMID:17942702

  20. Poverty reduction in Africa.

    PubMed

    Collier, Paul

    2007-10-23

    Poverty in Africa has been rising for the last quarter-century, while it has been falling in the rest of the developing world. Africa's distinctive problem is that its economies have not been growing. This article attempts to synthesize a range of recent research to account for this failure of the growth process. I argue that the reasons lie not in African peculiarities but rather in geographic features that globally cause problems but that are disproportionately pronounced in Africa. These features interact to create three distinct challenges that are likely to require international interventions beyond the conventional reliance on aid.

  1. 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.

  2. 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.

  3. Asian monsoon transport of pollution to the stratosphere.

    PubMed

    Randel, William J; Park, Mijeong; Emmons, Louisa; Kinnison, Doug; Bernath, Peter; Walker, Kaley A; Boone, Chris; Pumphrey, Hugh

    2010-04-30

    Transport of air from the troposphere to the stratosphere occurs primarily in the tropics, associated with the ascending branch of the Brewer-Dobson circulation. Here, we identify the transport of air masses from the surface, through the Asian monsoon, and deep into the stratosphere, using satellite observations of hydrogen cyanide (HCN), a tropospheric pollutant produced in biomass burning. A key factor in this identification is that HCN has a strong sink from contact with the ocean; much of the air in the tropical upper troposphere is relatively depleted in HCN, and hence, broad tropical upwelling cannot be the main source for the stratosphere. The monsoon circulation provides an effective pathway for pollution from Asia, India, and Indonesia to enter the global stratosphere.

  4. 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.

  5. Empirical prediction of the summer monsoon rainfall over India

    NASA Technical Reports Server (NTRS)

    Shukla, J.; Mooley, D. A.

    1987-01-01

    Forty-six years (1939-1984) of observed data were examined to study synoptic and statistical relationships between the summer monsoon rainfall over India, the Southern Oscillation, and the midtropospheric circulation over India. The change in Darwin pressure from January to April and the latitudinal position of the April 500-mb ridge along 75 deg E are taken as two quasi-independent predictor parameters to develop a regression equation to predict the summer monsoon rainfall. Verification of predictions on independent data shows that the root-mean-square error for predicted rainfall is 36 mm, which is less than half of the standard deviation and only about 4 percent of the mean rainfall (857 mm).

  6. Spatiotemporal patterns and trends of Indian monsoonal rainfall extremes

    PubMed Central

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

    2016-01-01

    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 towards 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. PMID:27909349

  7. 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.

  8. Stable isotopic signature of Australian monsoon controlled by regional convection

    NASA Astrophysics Data System (ADS)

    Zwart, C.; Munksgaard, N. C.; Kurita, N.; Bird, M. I.

    2016-11-01

    The aim of this study was to identify the main meteorological drivers of rainfall isotopic variation in north Australia in order to improve the interpretation of isotopic proxy records in this region. An intense monitoring program was conducted during two monsoonal events that showed significant and systematic isotopic change over time. The results showed a close link between isotopic variation in precipitation and variability in monsoon conditions, associated with the presence of large convective envelopes propagating through the study site. The largest negative amplitudes in the isotopic signal were observed when eastward and westward moving precipitation systems within the convective envelope merged over the measurement site. This suggests that the amplitude of the isotopic signal is related to the size and activity of the convective envelope. The strong correlation between rainfall isotopic variation, regional outgoing longwave radiation and regional rainfall amount supports this conclusion. This is further strengthened by the strong relationship between isotopic variation and the integrated rainfall history of air masses prior to arriving at the measurement locations. A local amount effect was not significant and these findings support the interpretation of δ18O as proxy for regional climatic conditions rather than local rainfall amount. Meteorological parameters that characterize intra-seasonal variability of monsoon conditions were also found to be strongly linked to inter-seasonal variability of the monthly based δ18O values in the Global Network of Isotopes in Precipitation (GNIP) database. This leads to the conclusion that information about the Australian monsoon variability can likely be inferred from the isotopic proxy record in North Australia on short (intra seasonal) and long (inter seasonal or longer) timescales.

  9. Radiative Energy Budget Estimates for the 1979 Southwest Summer Monsoon.

    NASA Astrophysics Data System (ADS)

    Ackerman, Steven A.; Cox, Stephen K.

    1987-10-01

    Obsemations of temperature moisture, cloud amount, cloud height and soil-derived aerosols are incorporated into radiative transfer models to yield estimates of the tropospheric and surface radiative energy budgets for the summer Monsoon of 1979. Results are presented for six phases of the monsoon for the region 30°S to 40°N latitude and 30°E to 100°E longitude. The derived radiative fields are significantly different from climatological estimates. The evolution of the radiative energy budgets are discussed in relation to monsoon activity. Total tropospheric convergence (TTC) for the January and February phases exhibits a minimum cooling over the southern Indian Ocean and a maximum tropospheric radiative energy loss over the Arabian Sea and Bay of Bengal. The early May, pre-onset, onset and post-onset periods exhibit cellular patterns in TTC, with maximum cooling over the cloud-free oceanic regions, and minimum cooling associated with continental regions and areas with large amounts of cloud. This cellular structure is still evident when TTC is averaged over 10° regions. Large seasonal variations in TTC are observed over the deserts, due to the presence of dust in the summer. Regions with large seasonal variations in cloud cover (e.g., the Arabian Sea) also display large variations in TTC. Regionally averaged radiative heating profiles also change significantly with period. These variations result primarily from changes in the cloud distribution associated with the evolution of the monsoon.The net surface radiative flux varies markedly from period to period, and within the same period. As expected, all six periods have a maximum surface radiative energy gain for the cloud-free oceanic regions, while cloudy and continental regions tend to have relative minimae. Large spatial and temporal variations exist in the net surface flux.

  10. 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

  11. 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.

  12. Contemporary Problems in Africa.

    ERIC Educational Resources Information Center

    O'Meara, Patrick; Winchester, N. Brian

    1987-01-01

    Provides a brief overview of political and economic developments of the past 25 years in Africa. Maintains this was a period of experimentation with vast differences in the ways in which governments dealt with human and natural problems. (JDH)

  13. Child Labour in Africa.

    ERIC Educational Resources Information Center

    Bonnet, Michel

    1993-01-01

    The question of child labor in Africa is complicated by the failures of the educational system, family relations, traditional forms of apprenticeship, proliferation of the informal economic sector, and continuing existence of a rural economy. Hazardous working conditions prevail. (SK)

  14. Tropospheric ozone pool over Arabian sea during pre-monsoon

    NASA Astrophysics Data System (ADS)

    Jia, Jia; Ladstätter-Weißenmayer, Annette; Hou, Xuewei; Rozanov, Alexei; Burrows, John

    2016-04-01

    This study focuses on the remarkable and stable phenomenon-enhancement of the tropospheric ozone over Arabian Sea (AS) during the pre-monsoon season. Satellite data (SCIAMACHY LNM, OMI/MLS and TES) showed a strong and clear ozone seasonality over AS with ~42 DU maxima in pre-monsoon season. With the help of MACC reanalysis data, our results showed that 3/4 of the enhanced ozone during this season is contributed at 0-8 km height. The main source of the ozone enhancement is believed to be a long range transport, together with a suitable meteorological condition for pollution accumulation. Local chemistry plays different roles over different altitudes. However we believe the contribution to the tropospheric ozone enhancement from the chemistry is low. The contribution of the STE is unclear. In addition, the interannual variation of the pre-monsoon tropospheric ozone enhancement over AS is discussed. The anomalies in 2005 and 2010 could be due to the dynamical variation of ozone caused by the El Niño events.

  15. Shift in Indian summer monsoon onset during 1976/1977

    NASA Astrophysics Data System (ADS)

    Sahana, A. S.; Ghosh, Subimal; Ganguly, Auroop; Murtugudde, Raghu

    2015-05-01

    The Indian summer monsoon rainfall (ISMR) contributes nearly 80% of the annual rainfall over India and has a significant influence on the country’s gross domestic product through the agricultural sector. Onset of the ISMR displays substantial interannual variability and controls the crop calendar and hence the agricultural output. This variability is traditionally linked to sea surface temperature (SST) anomalies over the tropical Pacific Ocean. The tropical Pacific SST underwent a regime shift during 1976/77. We report a prominent delay in the Indian summer monsoon (ISM) onset following the regime shift. The onset dates are computed with the Hydrologic Onset and Withdrawal Index, based on vertically integrated moisture transport over the Arabian Sea (AS). The shift in onset is found to be due to the change in moisture availability over the AS. A delay in the development of easterly vertical shear reduces northward-propagating intraseasonal variability during May-June, limiting the moisture supply from the equatorial Indian Ocean (IO) to the AS. This, along with enhanced precipitation over the IO during the pre-monsoon, drives a reduction in moisture availability over the AS region from pre- to post-1976/77, delaying the ISM onset in recent decades. Our findings highlight the need for the re-assessment of the crop calendar in India, which is now based on the mean onset date computed from long-term data, without considering the regime shift or trends in onset.

  16. Regional Climate Model Projection Credibility for the North American Monsoon

    NASA Astrophysics Data System (ADS)

    Bukovsky, M. S.; Carrillo, C. M.; Gochis, D. J.; Mearns, L. O.

    2014-12-01

    Climate change projections from the North American Regional Climate Change Assessment Program (NARCCAP) suite of regional climate model (RCM) simulations for the North American monsoon system are assessed herein. We focus on changes in precipitation and the many factors effecting the projections. The end goal of our in-depth, process-based assessment is to establish the differential credibility of the ensemble members. In the end, there is a deceptively strong full-ensemble agreement for a decrease in precipitation during the monsoon season. Bias is considerably affecting many of the model projections, and we find that the simulations that are the most biased, in varying ways, in the baseline/current climate, produce the greatest decreases. Problems in the baseline simulations and projections include those related to: atmospheric moisture content, the monsoon high, the Gulf of California low-level jet, tropical easterly waves, the El Niño Southern Oscillation, precipitation intensity, and other features/phenomena. This presentation will provide a summary of our findings.

  17. The role of peninsular India in the South Asian monsoon

    NASA Astrophysics Data System (ADS)

    Turner, A. G.; Martin, G.

    2012-04-01

    Several studies have examined the role of the Tibetan Plateau and Himalayas in the initiation and maintenance of the South Asian summer monsoon, but few have looked at the impact of the Indian peninsula itself. In this study we describe the results of a series of novel experiments with the Met Office Unified Model HadGEM3 run in atmosphere-only configuration, in which the role of the Indian peninsula is assessed. The contributions of the topography, orography and land surface properties to the monsoon circulation and distribution of precipitation in the tropical Indo-Pacific region are examined. While the model usually features a wet bias over the Western Ghats and Himalaya and a dry bias over the northern part of the peninsula, initial results in experiments removing the Indian peninsula and replacing it with sea surface boundary conditions suggest a large re-distribution of precipitation in the northern Indian Ocean: the region at Indian longitudes featuring enhanced precipitation. This may relate simply to the availability of moisture at the surface, however the diurnal cycle of sensible heating will also be reduced in the absence of the land surface. In a further experiment, the land surface characteristics of the peninsula are altered such that, while the land is present, there are no limitations to the supply of moisture to the monsoon. We speculate that this will help isolate the impact of the moisture constraint from that of the diurnal cycle of sensible heating.

  18. Atmospheric water budget over the South Asian summer monsoon region

    NASA Astrophysics Data System (ADS)

    Unnikrishnan, C. K.; Rajeevan, M.

    2017-02-01

    High resolution hybrid atmospheric water budget over the South Asian monsoon region is examined. The regional characteristics, variability, regional controlling factors and the interrelations of the atmospheric water budget components are investigated. The surface evapotranspiration was created using the High Resolution Land Data Assimilation System (HRLDAS) with the satellite-observed rainfall and vegetation fraction. HRLDAS evapotranspiration shows significant similarity with in situ observations and MODIS satellite-observed evapotranspiration. Result highlights the fundamental importance of evapotranspiration over northwest and southeast India on atmospheric water balance. The investigation shows that the surface net radiation controls the annual evapotranspiration over those regions, where the surface evapotranspiration is lower than 550 mm. The rainfall and evapotranspiration show a linear relation over the low-rainfall regions (<500 mm/year). Similar result is observed in in NASA GLDAS data (1980-2014). The atmospheric water budget shows annual, seasonal, and intra-seasonal variations. Evapotranspiration does not show a high intra-seasonal variability as compared to other water budget components. The coupling among the water budget anomalies is investigated. The results show that regional inter-annual evapotranspiration anomalies are not exactly in phase with rainfall anomalies; it is strongly influenced by the surface conditions and other atmospheric forcing (like surface net radiation). The lead and lag correlation of water budget components show that the water budget anomalies are interrelated in the monsoon season even up to 4 months lead. These results show the important regional interrelation of water budget anomalies on south Asian monsoon.

  19. 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.

  20. 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.

  1. Role of inertial instability in the West African monsoon jump

    NASA Astrophysics Data System (ADS)

    Cook, Kerry H.

    2015-04-01

    The West African monsoon jump is a sudden shift in the latitude of the West African precipitation maximum from the Guinean coast near 4°N into Sahel near 12°N in late June or early July. An examination of reanalyses and observations indicates that the Sahel rainy season develops smoothly and the monsoon jump occurs because of an abrupt decrease in Guinean coast rainfall. We show that this abrupt end of the coastal rainy season occurs when inertial instability develops over the region, 1 month later than it develops in the vicinity of the marine Atlantic Intertropical Convergence Zone. The reason for this delay is the presence of the African easterly jet, which places strong negative meridional zonal wind gradients over the coast to preserve the inertially stable environment. When the African easterly jet moves farther north due to the seasonal solar forcing, these gradients weaken and then reverse to satisfy the threshold condition for inertial instability; the rapid end of the Guinean coast rainy season follows. The northward movement and intensity of the African easterly jet are controlled by the seasonal development of strong meridional land surface temperature gradients and are independent of the formation of the Atlantic cold tongue. This explanation for the West African monsoon jump relates the phenomenon to the shape and location of the African continent, including the low-latitude position of the Guinean coast and the large expanse of the continent to the north.

  2. Astronomy Landscape in Africa

    NASA Astrophysics Data System (ADS)

    Nemaungani, Takalani

    2015-01-01

    The vision for astronomy in Africa is embedded in the African Space Policy of the African Union in early 2014. The vision is about positioning Africa as an emerging hub for astronomy sciences and facilities. Africa recognized the need to take advantage of its natural resource, the geographical advantage of the clear southern skies and pristine sites for astronomy. The Pan African University (PAU) initiative also presents an opportunity as a post-graduate training and research network of university nodes in five regions of Africa and supported by the African Union. The Southern African node based in South Africa concentrates on space sciences which also includes astronomy. The PAU aims to provide the opportunity for advanced graduate training and postgraduate research to high-performing African students. Objectives also include promoting mobility of students and teachers and harmonizing programs and degrees.A number of astronomy initiatives have burgeoned in the Southern African region and these include the Southern Africa Largest Optical Telescope (SALT), HESS (High Energy Stereoscopic System), the SKA (Square Kilometre Array) and the AVN (African Very Long Baseline Interferometer Network). There is a growing appetite for astronomy sciences in Africa. In East Africa, the astronomy community is well organized and is growing - the East African Astronomical society (EAAS) held its successful fourth annual conference since 2010 on 30 June to 04 July 2014 at the University of Rwanda. Centred around the 'Role of Astronomy in Socio-Economic Transformation,' this conference aimed at strengthening capacity building in Astronomy, Astrophysics and Space Science in general, while providing a forum for astronomers from the region to train young and upcoming scientists.

  3. AIDS in Africa

    DTIC Science & Technology

    2006-03-09

    have recommended that Africans infected with HIV be treated with an antibiotic/ sulfa drug combination known as cotrimoxazole in order to prevent...response is the subject of much debate. An estimated 500,000 Africa AIDS patients were being treated with antiretroviral drugs in mid-2005, up from 150,000...whether drugs can be made widely accessible without costly health infrastructure improvements. U.S. concern over AIDS in Africa grew in the 1980s, as the

  4. Profile of South Africa

    SciTech Connect

    Fox, G.J.; Tonneson, L.C.

    1996-08-01

    A broad overview of the Republic of South Africa`s nuclear energy program is presented. Economic aspects are the main focus of the article, and numerical data is provided for electricity generation and use and uranium production. The role of the molecular laser isotope process for enrichment is discussed. The research reactor program, waste disposal and decommissioning, mining history, uranium production, and nonproliferation policy are other highlighted topics.

  5. Decolonizing Bioethics in Africa

    PubMed Central

    Macaulay-Adeyelure, O.C.

    2017-01-01

    The global spread of bioethics from its North-American and European provenance to non-Western societies is currently raising some concerns. Part of the concern has to do with whether or not the exportation of bioethics in its full Western sense to developing non-Western states is an instance of ethical imperialism or bioethical neocolonialism. This paper attempts an exploration of this debate in the context of bioethics in sub-Saharan Africa. Rather than conceding that bioethics has a colonial agenda in Africa, this paper defends the position that the current bioethics trend in sub-Saharan Africa is an unintended imperialistic project. It argues that its colonizing character is not entirely a product of the Western programmed goals of training and institution building; rather, it is a structural consequence of many receptive African minds and institutions. Though bioethics in Africa is turning out as a colonizing project, one serious implication of such trend, if unchecked urgently, is that bioethics’ invaluable relevance to Africa is being incapacitated. This paper, therefore, attempts a decolonizing trajectory of bioethics in Africa. Contrary to the pretense of ‘African bioethics,’ which some African scholars are now defending, this paper through the logic of decolonization makes case for ‘bioethics in Africa’. In such logic, the principle of existential needs is prioritized over the principle of identity and authenticity that define African voice in bioethics. PMID:28344985

  6. Secondary Organic Aerosol from Biogenic VOCs over West Africa during AMMA

    NASA Astrophysics Data System (ADS)

    Capes, G. L.; Murphy, J. G.; Reeves, C. E.; McQuaid, J. B.; Hamilton, J. F.; Hopkins, J. R.; Coe, H.

    2008-12-01

    As part of the international AMMA (African Monsoon Multidisciplinary Analyses) project a large field experiment took place in West Africa during July and August 2006. This involved a number of ground-based facilities and 5 aircraft, including the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe-146, which was based in Niamey, Niger and made 21 flights. The 146 was equipped with instruments measuring parameters relevant to dynamics, gas phase composition, radiation, aerosols and clouds. The flights made were designed to examine a range of multidisciplinary scientific questions. This paper presents measurements of organic aerosol above subtropical West Africa during the monsoon season using data from the FAAM aircraft. Measurements of biogenic volatile organic compounds (BVOC) at low altitudes over these subtropical forests were made during July and August 2006 mainly above Benin, Nigeria and Niger. In air masses characterised by high BVOC concentrations, data from an Aerodyne Quadrupole Aerosol Mass Spectrometer show an organic aerosol loading of 0.58 μgm-3 over tropical West Africa. In contrast, organic aerosol mass (OM) concentrations were negligible when BVOC concentrations were low. This represents the first regionally averaged assessment of OM in this region during the wet season. This is in good agreement with predictions based on aerosol yields from isoprene and monoterpenes during chamber studies and model predictions based on partitioning schemes, contrasting markedly with the large under representations of OM in similar models when compared with data from mid latitudes.

  7. Increase in the Asian southwest monsoon during the past four centuries.

    PubMed

    Anderson, David M; Overpeck, Jonathan T; Gupta, Anil K

    2002-07-26

    Climate reconstructions reveal unprecedented warming in the past century; however, little is known about trends in aspects such as the monsoon. We reconstructed the monsoon winds for the past 1000 years using fossil Globigerina bulloides abundance in box cores from the Arabian Sea and found that monsoon wind strength increased during the past four centuries as the Northern Hemisphere warmed. We infer that the observed link between Eurasian snow cover and the southwest monsoon persists on a centennial scale. Alternatively, the forcing implicated in the warming trend (volcanic aerosols, solar output, and greenhouse gases) may directly affect the monsoon. Either interpretation is consistent with the hypothesis that the southwest monsoon strength will increase during the coming century as greenhouse gas concentrations continue to rise and northern latitudes continue to warm.

  8. Sensitivity of the South Asian monsoon to elevated and non-elevated heating.

    PubMed

    Boos, William R; Kuang, Zhiming

    2013-01-01

    Elevated heating by the Tibetan Plateau was long thought to drive the South Asian summer monsoon, but recent work showed this monsoon was largely unaffected by removal of the plateau in a climate model, provided the narrow orography of adjacent mountain ranges was preserved. There is debate about whether those mountain ranges generate a strong monsoon by insulating the thermal maximum from cold and dry extratropical air or by providing a source of elevated heating. Here we show that the strength of the monsoon in a climate model is more sensitive to changes in surface heat fluxes from non-elevated parts of India than it is to changes in heat fluxes from adjacent elevated terrain. This result is consistent with the hypothesis that orography creates a strong monsoon by serving as a thermal insulator, and suggests that monsoons respond most strongly to heat sources coincident with the thermal maximum.

  9. CLIVAR Asian-Australian Monsoon Panel Report to Scientific Steering Group-18

    SciTech Connect

    Sperber, Ken R.; Hendon, Harry H.

    2011-05-04

    These are a set of slides on CLIVAR Asian-Australian Monsoon Panel Report to Scientific Steering Group-18. These are the major topics covered within: major activities over the past year, AAMP Monsoon Diagnostics/Metrics Task Team, Boreal Summer Asian Monsoon, Workshop on Modelling Monsoon Intraseasonal Variability, Workshop on Interdecadal Variability and Predictability of the Asian-Australian Monsoon, Evidence of Interdecadal Variability of the Asian-Australian Monsoon, Development of MJO metrics/process-oriented diagnostics/model evaluation/prediction with MJOTF and GCSS, YOTC MJOTF, GEWEX GCSS, AAMP MJO Diabatic Heating Experiment, Hindcast Experiment for Intraseasonal Prediction, Support and Coordination for CINDY2011/DYNAMO, Outreach to CORDEX, Interaction with FOCRAII, WWRP/WCRP Multi-Week Prediction Project, Major Future Plans/Activities, Revised AAMP Terms of Reference, Issues and Challenges.

  10. Effect of Temporally and Spatially Variable Meteorological Forcing on the Stratification Dynamics of Lake Victoria, East Africa

    NASA Astrophysics Data System (ADS)

    MacIntyre, S.; Romero, J. R.

    2011-12-01

    The annual cycle of stratification of tropical lakes is driven by seasonal changes in cloud cover as it affects solar radiation and net long wave radiation and seasonal changes in wind speed and relative humidity as they affect latent heat fluxes. For large tropical lakes, latent heat fluxes and net long wave radiation vary across the lake due to lake effects but remain largely unquantified, as are the resulting spatial differences in temperature. Here we present meteorological data and surface energy budgets for six stations around Lake Victoria, East Africa, and time series temperature profiles and transect data taken during different times of day and different seasons. Seasonality is determined by the northeast and southeast monsoons and intervening rainy seasons. Winds were higher in the afternoon to the north in the northeast monsoon and higher at night and in the morning to the south during the southeast monsoon. Cloud cover was least during the monsoons. Lakewide, latent heat fluxes range from 150W m-2 to 250 W m-2 in the afternoon with larger values to the north during the northeast monsoon. Values during the morning range from 100 W m-2 to 150 W m-2 but increase to 200 W m-2 - 300 W m-2 to the south and west during the southeast monsoon. The seasonal thermocline is generated during the northeast monsoon due to the higher afternoon winds which mix heat downwards and overall net heating. Holomixis, but with warmer temperatures to the north, occurs during the southeast monsoon due to the accentuated night time cooling and net heat loss. Wind speeds are lower and the diel range of air temperature and relative humidity is higher inshore than off. Consequently, computed monthly heat losses were at least 30% higher offshore and water temperatures are cooler offshore. Scaling analyses indicate that the stratification induced by inflows of cool water to the north at the end of the southeast monsoon are wind driven and that despite the warmer waters inshore which

  11. 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.

  12. 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

  13. SST Control by Subsurface Mixing during Indian Ocean Monsoons: 1-yr Pilot Project

    DTIC Science & Technology

    2013-09-30

    public release; distribution is unlimited. SST Control by Subsurface Mixing during Indian Ocean Monsoons : 1-yr Pilot Project Emily Shroyer and James...observational basis and physical interpretation for new mixing parameterizations that will contribute to improved monsoon predictions in this sensitive...4. TITLE AND SUBTITLE SST Control by Subsurface Mixing during Indian Ocean Monsoons : 1-yr Pilot Project 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c

  14. Teleconnections between Eurasian snow cover and the Maldives monsoon rainfall

    NASA Astrophysics Data System (ADS)

    Zahid, Zahid; Sturman, Andrew; Hart, Deirdre; Zawar-Reza, Peyman

    2010-05-01

    Anomalous snow cover over Eurasia can influence monsoon circulation through changes in surface energy balance. Much of the research on the snow-monsoon relationship has focused on the Indian or Chinese monsoon, without examining possible links between the snow-monsoon relationship and summer rainfall over other parts of Asia. Although the Maldives lies in the Indian Ocean (southwest of India), the Asian monsoon flow influences the circulation patterns over the Maldives. However, no previous studies have directly examined possible relationships between Eurasian snow and Maldives monsoon rainfall (MMR: June-September). This paper describes a first attempt to explore the possible relationships between Eurasian snow cover (ESC) and the MMR. The possible relationships between Eurasian snow and the rainfall over the Maldives has been investigated using composite and correlation analyses. The relationship between ESC and monsoon rainfall was also examined using lag-lead correlations. Anomalies of an area-weighted MMR index have been correlated with anomalies of ESC for October-December of the previous year and January-May of the current year. Correlations have also been carried out between MMR and snow cover anomalies for winter (December-January), spring (March-May) and with snowmelt (snow cover difference between February and May). The time series were de-trended to minimize the influence of trends on the strength and significance of the correlations between variables. Relatively very weak correlations were found between the MMR and ESC anomalies for January-May of the current year and October-December of the previous year. The highest correlation between MMR and ESC (r = -0.15, insignificant at 5% level) was found for the month of February. Significant positive correlations were found between ESC in subsequent months, with the highest correlation (r = 0.80) between April and May, significant at the 1% level. Correlations between MMR and snow cover anomaly for winter

  15. Dynamics of the Asian Summer Monsoon Onset and the Tibetan Plateau Impacts

    NASA Astrophysics Data System (ADS)

    Yimin, Liu; Guoxiong, Wu; Boqi, Liu; Suling, Ren; Yue, Guan

    2015-04-01

    The formation and development of the South Asian High (SAH) in early spring over South China Sea (SCS) provides upper tropospheric pumping over the Southeast Bay of Bengal (BOB) and leads to the BOB monsoon onset. The strong latent heat release of the BOB monsoon results in the northeastward unstable development of the SAH which contributes to the SCS monsoon onset. The zonal asymmetric unstable development of the SAH after the SCS monsoon onset leads to the Indian summer monsoon onset. In spring over South BOB, usually there is vortex development preceding the Asian summer monsoon onset. The rapid development of the BOB monsoon onset vortex is due to the local strong air-sea interaction, which is modulated by the Tibetan Plateau (TP) forcing and the land-sea thermal contrast across South Asia. Strong heating from BOB monsoon generates stationary Rossby-wave in lower troposphere, producing weak cold advection and convection over North SCS. Development of surface BOB cyclone provides Northeastward water vapor transport towards North SCS where convection develops. Before the Indian Summer Monsoon (ISM) onset, the North- South land- sea thermal contrast increases eastward remarkably on the southeast of Arabian Sea. Air traveling eastward along the near- surface tropical westerly jet gets northward accelerated, forcing a lower tropospheric convergence near and to the north of the jet stream. Such a forced convection development occurs intensively over the southeastern Arabian Sea and southwestern India, contributing to the ISM onset.

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

    PubMed

    Boos, William R; Storelvmo, Trude

    2016-02-09

    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.

  17. Downscaling Reanalysis over Continental Africa with a Regional Model: NCEP Versus ERA Interim Forcing

    NASA Technical Reports Server (NTRS)

    Druyan, Leonard M.; Fulakeza, Matthew B.

    2013-01-01

    Five annual climate cycles (1998-2002) are simulated for continental Africa and adjacent oceans by a regional atmospheric model (RM3). RM3 horizontal grid spacing is 0.44deg at 28 vertical levels. Each of 2 simulation ensembles is driven by lateral boundary conditions from each of 2 alternative reanalysis data sets. One simulation downs cales National Center for Environmental Prediction reanalysis 2 (NCPR2) and the other the European Centre for Medium Range Weather Forecasts Interim reanalysis (ERA-I). NCPR2 data are archived at 2.5deg grid spacing, while a recent version of ERA-I provides data at 0.75deg spacing. ERA-I-forced simulations are recomrp. ended by the Coordinated Regional Downscaling Experiment (CORDEX). Comparisons of the 2 sets of simulations with each other and with observational evidence assess the relative performance of each downscaling system. A third simulation also uses ERA-I forcing, but degraded to the same horizontal resolution as NCPR2. RM3-simulated pentad and monthly mean precipitation data are compared to Tropical Rainfall Measuring Mission (TRMM) data, gridded at 0.5deg, and RM3-simulated circulation is compared to both reanalyses. Results suggest that each downscaling system provides advantages and disadvantages relative to the other. The RM3/NCPR2 achieves a more realistic northward advance of summer monsoon rains over West Africa, but RM3/ERA-I creates the more realistic monsoon circulation. Both systems recreate some features of JulySeptember 1999 minus 2002 precipitation differences. Degrading the resolution of ERA-I driving data unrealistically slows the monsoon circulation and considerably diminishes summer rainfall rates over West Africa. The high resolution of ERA-I data, therefore, contributes to the quality of the downscaling, but NCPR2laterai boundary conditions nevertheless produce better simulations of some features.

  18. Subseasonal teleconnections South America - South Africa

    NASA Astrophysics Data System (ADS)

    Grimm, Alice; Reason, Chris

    2016-04-01

    There is marked subseasonal variability over South America and southern Africa. Based on previous work showing that a teleconnection exists between the South American monsoon system and interannual summer rainfall variability over southern Africa, this study shows teleconnections between subseasonal variability over these landmasses. Observed daily gauge precipitation data for 1970-1999 are gridded to 1° resolution for South America and 2.5° for South Africa. At each grid point, anomalies of daily precipitation are calculated and submitted to a bandpass Lanczos filter to isolate subseasonal oscillations in the 20-90 day band. For each season, the filtered precipitation anomalies for the South African grid boxes are correlated with filtered precipitation anomalies in the grid boxes over South America. Lags from 0 up to 12 days are applied to the South African data, in order to investigate convection anomalies over South America that could produce atmospheric perturbations associated with South African precipitation anomalies. The significance of correlation between the filtered data takes autocorrelation into account and uses effective sample sizes. The results shown represent the best correlations for different climatic regimes such as the winter-rainfall dominated southwestern Cape, the all season rainfall South Coast and the summer-rainfall dominated Limpopo region. NCEP re-analyses are used to composite subseasonal anomalies in OLR, 200 hPa streamfunction, and vertically integrated moisture flux associated with precipitation anomaly above one standard deviation in the filtered series (positive phases) of the South African selected regions. The possible origin of the atmospheric circulation anomalies associated with those positive phases is determined using influence functions (IFs) of a vorticity equation model with a divergence source. The model is linearized about a realistic basic state and includes the divergence of the basic state and the advection of

  19. Climatology and dynamics of nocturnal low-level stratus over the southern West African monsoon region

    NASA Astrophysics Data System (ADS)

    Fink, A. H.; Schuster, R.; Knippertz, P.; van der Linden, R.

    2013-12-01

    The southern parts of West Africa, from the coast to about 10°N, are frequently covered by an extensive deck of shallow, low (200 - 400 m above ground) stratus or stratocumulus clouds during the summer monsoon season. These clouds usually form at night in association with a nocturnal low-level jet (NLLJ) and can persist into the early afternoon hours until they are dissipated or replaced by fair-weather cumuli. Recent work suggests that the stratus deck and its effect on the surface radiation balance are unsatisfactorily represented in standard satellite retrievals and simulations by state-of-the-art climate models. We will present the first ever climatology of the diurnal cycle of the low cloud deck based on surface observations and satellite products. In addition, we use high-resolution regional simulations with the Weather Research and Forecast (WRF) model and observations from the African Monsoon Multidisciplinary Analysis (AMMA) 2006 campaign to investigate (a) the spatiotemporal distribution, (b) the influence on the radiation balance, and (c) the detailed formation and maintenance mechanisms of the stratiform clouds as simulated by the model. The model configuration used for this study has been determined following an extensive sensitivity study, which has shown that at least some configurations of WRF satisfactorily reproduce the diurnal cycle of the low cloud evolution. The main conclusions are: (a) The observed stratus deck forms after sunset along the coast, spreads inland in the course of the night, reaches maximum poleward extent at about 10°N around 09-10 local time and dissipates in the early afternoon. (b) The average surface net radiation balance in stratus-dominated regions is 35 W m-2 lower than in those with less clouds. (c) The cloud formation is related to a subtle balance between 'stratogenic' upward (downward) fluxes of latent (sensible) heat caused by shear-driven turbulence below the NLLJ, cold advection from the ocean, forced lifting at

  20. Spatio-temporal variation in physicochemical properties of coastal waters off Kalpakkam, southeast coast of India, during summer, pre-monsoon and post-monsoon period.

    PubMed

    Satpathy, Kamala Kanta; Mohanty, Ajit Kumar; Sahu, Gouri; Sarguru, S; Sarkar, Santosh Kumar; Natesan, Usha

    2011-09-01

    Seasonal observations on water-quality parameters and chlorophyll-a in the coastal waters off Kalpakkam, southeast coast of India, was carried out covering an area of about 30 km(2) to find out the variations in physicochemical properties during a monsoonal cycle of the year. Most of the parameters exhibited a significant spatial and seasonal variation. It revealed that the coastal water was significantly influenced by freshwater input from the nearby backwaters during North-east monsoon and post-monsoon periods. A marginal increase in pH from coast towards offshore was noticed during the observation. Relatively low salinity values were observed during pre and post monsoon when compared to summer. Bottom water was found to be highly turbid during summer and pre-monsoon conditions when compared to surface. This could be attributed to the strong northerly wind and northward current prior to the onset of southwest monsoon. N, P and Si based nutrients are relatively high in their concentration in the bottom water. Nitrate was significantly high during post-monsoon and contributed greatly towards total nitrogen as evident from the statistical correlation. Ammonia concentration was relatively high in the bottom samples during all the seasons except on a few occasions during post-monsoon. In general, phosphate and total phosphorous values remained low and particularly so in the surface water. Higher silicate concentration was observed in the bottom water, and there was a reducing trend towards offshore. High chlorophyll-a values were observed during summer and surface water was found to have higher pigment concentrations as compared to the bottom. Results show that phosphate acts as the limiting factor for phytoplankton production particularly during post-monsoon period whereas; none of the nutrients were found to be limiting the phytoplankton growth during other seasons.

  1. 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

  2. Hantaviruses in Africa.

    PubMed

    Witkowski, Peter T; Klempa, Boris; Ithete, Ndapewa L; Auste, Brita; Mfune, John K E; Hoveka, Julia; Matthee, Sonja; Preiser, Wolfgang; Kruger, Detlev H

    2014-07-17

    This paper summarizes the progress in the search for hantaviruses and hantavirus infections in Africa. After having collected molecular evidence of an indigenous African hantavirus in 2006, an intensive investigation for new hantaviruses has been started in small mammals. Various novel hantaviruses have been molecularly identified not only in rodents but also in shrews and bats. In addition, the first African hantavirus, Sangassou virus, has been isolated and functionally characterized in cell culture. Less is known about the ability of these hantaviruses to infect humans and to cause diseases. To date, no hantavirus genetic material could be amplified from patients' specimens collected in Africa. Serological studies in West Africa, based on a battery of screening and confirmatory assays, led to the detection of hantavirus antibodies in the human population and in patients with putative hantavirus disease. In addition to this overview, we present original data from seroepidemiological and field studies conducted in the Southern part of Africa. A human seroprevalence rate of 1.0% (n=1442) was detected in the South African Cape Region whereas no molecular evidence for the presence of hantavirus was found in 2500 small animals trapped in South Africa and Namibia.

  3. Neogene desertification of Africa

    NASA Astrophysics Data System (ADS)

    Senut, Brigitte; Pickford, Martin; Ségalen, Loïc

    2009-08-01

    Throughout the Neogene, the faunas and floras in Africa recorded global climatic changes. We present an overview of Neogene desertification in Africa by tracing stable isotopes in eggshells and mammalian enamel, by faunal (changes in hypsodonty, etc.) and floral changes in sequences at the latitudinal extremities of the continent and the equator. This work reveals that desertification started in the southwest ca 17-16 Ma, much earlier than the region of the present-day Sahara (ca 8-7 Ma) and long before the deserts in East Africa (Plio-Pleistocene). A consequence of this history is that animals and plants inhabiting the South of the continent had a long period of time in which to adapt to arid, unstable climatic conditions. When parts of East Africa became arid during the Late Miocene and Plio-Pleistocene, several of these lineages expanded northwards and occupied developing arid niches before local lineages could adapt. Several of the latter became extinct, while others withdrew westwards as the tropical forest diminished in extent. It is proposed that the history of desertification in Africa was related to that of the polar ice caps (Antarctic, Arctic).

  4. Examining Impact of Global warming on the summer monsoon system using regional Climate Model (PRECIS)

    NASA Astrophysics Data System (ADS)

    Patwardhan, S. K.; Kundeti, K.; Krishna Kumar, K.

    2011-12-01

    Every year, southwest monsoon arrives over Indian region with remarkable regularity. It hits the southern state of Kerala first by the end of May or the early June. More than 70% of the annual precipitation is received during the four monsoon months viz. June to September. This monsoon rainfall is vital for the agriculture as well as for the yearly needs of Indian population. The performance of the monsoon depends on the timely onset over southern tip of India and its progress along the entire country. This northward progression of monsoon to cover the entire Indian landmass, many times, is associated with the formation of synoptic scale system in the Bay of Bengal region and their movement along the monsoon trough region. The analysis of the observed cyclonic disturbances show that their frequency has reduced in recent decades. It is, therefore, necessary to assess the effect of global warming on the monsoon climate of India. A state-of-art regional climate modelling system, known as PRECIS (Providing REgional Climates for Impacts Studies) developed by the Hadley Centre for Climate Prediction and Research, U.K. is applied over the South Asian domain to investigate the impact of global warming on the cyclonic disturbances. The PRECIS simulations at 50 km x 50 km horizontal resolution are made for two time slices, present (1961-1990) and the future (2071-2100), for two socio-economic scenarios A2 and B2. The model skills are evaluated using observed precipitation and surface air temperature. The model has shown reasonably good skill in simulating seasonal monsoon rainfall, whereas cold bias is seen in surface air temperature especially in post-monsoon months. The typical monsoon features like monsoon trough, precipitation maxima over west coast and northeast India are well simulated by the model. The model simulations under the scenarios of increasing greenhouse gas concentrations and sulphate aerosols are analysed to study the likely changes in the quasi

  5. Vegetation and soil feedbacks on the response of the African monsoon to orbital forcing in the early to middle Holocene

    NASA Astrophysics Data System (ADS)

    Kutzbach, J.; Bonan, G.; Foley, J.; Harrison, S. P.

    1996-12-01

    FOSSIL pollen, ancient lake sediments and archaeological evidence from Africa indicate that the Sahel and Sahara regions were considerably wetter than today during the early to middle Holocene period, about 12,000 to 5,000 years ago1-4. Vegetation associated with the modern Sahara/Sahel boundary was about 5° farther north, and there were more and larger lakes between 15 and 30° N. Simulations with climate models have shown that these wetter conditions were probably caused by changes in Earth's orbital parameters that increased the amplitude of the seasonal cycle of solar radiation in the Northern Hemisphere, enhanced the land-ocean temperature contrast, and thereby strengthened the African summer monsoon5-7. However, these simulations underestimated the consequent monsoon enhancement as inferred from palaeorecords4. Here we use a climate model to show that changes in vegetation and soil may have increased the climate response to orbital forcing. We find that replacing today's orbital forcing with that of the mid-Holocene increases summer precipitation by 12% between 15 and 22° N. Replacing desert with grassland, and desert soil with more loamy soil, further enhances the summer precipitation (by 6 and 10% respectively), giving a total precipitation increase of 28%. When the simulated climate changes are applied to a biome model, vegetation becomes established north of the current Sahara/Sahel boundary, thereby shrinking the area of the Sahara by 11% owing to orbital forcing alone, and by 20% owing to the combined influence of orbital forcing and the prescribed vegetation and soil changes. The inclusion of the vegetation and soil feedbacks thus brings the model simulations and palaeovegetation observations into closer agreement.

  6. Signature of a southern hemisphere extratropical influence on the summer monsoon over India

    NASA Astrophysics Data System (ADS)

    Viswambharan, Nithin; Mohanakumar, K.

    2013-07-01

    The weakening relationship of El Nino with Indian summer monsoon reported in recent years is a major issue to be addressed. The altered relationships of Indian monsoon with various parameters excite to search for other dominant modes of variability that can influence the precipitation pattern. Since the Indian summer monsoon circulation originates in the oceanic region of the southern hemisphere, the present study investigates the association of southern extratropical influence on Indian summer monsoon using rainfall and reanalysis parameters. The effect of Southern Annular Mode (SAM) index during the month of June associated with the onset phase of Indian summer monsoon and that during July-August linked with the active phase of the monsoon were analysed separately for a period from 1951 to 2008. The extra-tropical influence over the monsoon is illustrated by using rainfall, specific humidity, vertical velocity, circulation and moisture transport. The June high SAM index enhances the lower level wind flow during the onset phase of monsoon over Indian sub-continent. The area of significant positive correlation between precipitation and SAM in June also shows enhancement in both ascending motion and specific humidity during the strong phase of June SAM. On the other hand, the June high SAM index adversely affects July-August monsoon over Indian subcontinent. The lower level wind flow weakens due to the high SAM. Enhancement of divergence and reduction in moisture transport results in the Indian monsoon region due to the activity of this high southern annular mode. The effect is more pronounced over the southwest region where the precipitation spell has high activity during the period. Significant correlation exists between SAM and ISMR, even after removing the effect of El Nino. It indicates that the signals of Indian summer monsoon characteristics can be envisaged to a certain extend using the June SAM index.

  7. Propagation and effects of monsoonal seasonally intense rainfall signal in river strata

    NASA Astrophysics Data System (ADS)

    Plink-Bjorklund, P.

    2014-12-01

    Climatic forcing signals in river systems tend to be modified on different temporal and spatial scales due to inherent signal buffering, re-routing, and a complex mixing of multiple autogenic and allogenic signals. Thus climate forcing response is generally assumed inherently non-linear with significant hysteresis effects. This paper explores propagation and effects of monsoonal, seasonally intense rainfall signal in river strata in the monsoonal and bordering subtropical domains. Some such rivers occur completely within the monsoon climate zone. Others have parts of their drainages in temperate climate zones, or on high elevations and receive some of their water discharge from other sources. Yet others, have their upstream drainages in the tropical monsoon climates, but flow through bordering subtropical drylands. Yet, all these rivers characteristically experience seasonal high magnitude floods as the effect of intense monsoon precipitation. Many rivers in the bordering subtropical zone receive monsoon rain and transmit discharge only during abnormal or strengthened monsoon seasons and associated cyclonic flow. Field datasets, comparison to modern river deposits and a literature review of monsoonal and bordering subtropical domain rivers reveal that the effects of the intense seasonal monsoon rain and the resultant flooding are readily recognizable in modern and ancient fluvial strata. This paper argues that this distinct and dominant climate signal propagation occurs because it is the monsoon discharge that is commonly responsible for up to 100% of sediment erosion, transport and deposition, creating a system wide flushing or splash effect on a single season to multi-million year time scale. The distinct monsoon flood deposits are interbedded with other types of fluvial strata in systems where significant deposition also occurs from low-magnitude flood or non-flood discharges.

  8. Non-stationary analysis of dry spells in monsoon season of Senegal River Basin using data from Regional Climate Models (RCMs)

    NASA Astrophysics Data System (ADS)

    Giraldo Osorio, J. D.; García Galiano, S. G.

    2012-07-01

    SummaryThe Senegal River Basin, located in West Africa, has been affected by several droughts since the end of the 1960s. In its valley, which is densely populated and highly vulnerable to climate variability and water availability, agricultural activities provide the livelihood for thousands of people. Increasing the knowledge about plausible trends of drought events will allow to improve the adaptation and mitigation measures in order to build "adaptive capacity" to climate change in West Africa. An innovative methodology for the non-stationary analysis of droughts events, which allows the prediction of regional trends associated to several return periods, is presented. The analyses were based on Regional Climate Models (RCMs) provided by the European ENSEMBLES project for West Africa, together with observed data. A non-stationary behaviour of the annual series of maximum length of dry spells (AMDSL) in the monsoon season is reflected in temporal changes in mean and variance. The non-stationary nature of hydrometeorological series, due to climate change and anthropogenic activities, is the main criticism to traditional frequency analysis. Therefore, in this paper, the modelling tool GAMLSS (Generalized Additive Models for Location, Scale and Shape), is applied to develop regional probability density functions (pdfs) fitted to AMDSL series for the monsoon season in the Senegal River Basin. The skills of RCMs in the representation of maximum length of dry spells observed for the period 1970-1990, are evaluated considering observed data. Based on the results obtained, a first selection of the RCMs with which to apply GAMLSS to the AMDSL series identified, for the time period 1970-2050, is made. The results of GAMLSS analysis exhibit divergent trends, with different value ranges for parameters of probability distributions being detected. Therefore, in the second stage of the paper, regional pdfs are constructed using bootstrapping distributions based on probabilistic

  9. Intense convection over West Africa during AMMA SOP3 experiment

    NASA Astrophysics Data System (ADS)

    Lenouo, André; Sall, Saïdou Moustapha; Badiane, Daouda; Gaye, Amadou Thierno; Kamga Mkankam, F.

    2016-11-01

    ERA-Interim product from the European Center for Medium-Range Weather Forecast (ECMWF) assimilation of African Monsoon Multidisciplinary Analysis (AMMA) resources, Meteosat satellite images, and synoptic observations were used to study local- and regional-scale environments associated with intense convective systems during the AMMA-SOP3 experiment over West Africa in the Northern Hemisphere of summer 2006. The convective system, from the 21st to 23rd of August 2006, was more active at 0000 and 1800 UTC showing diurnal cycle of deep convection over West Africa where the African easterly waves (AEWs) are developed downstream. Downstream barotropic and baroclinic energy conversions associated with strong AEWs are important for the maintenance of AEW activity in West Africa. Barotropic energy conversions dominate south of the African easterly jet (AEJ), while baroclinic energy conversions are most important north of the AEJ. From a dynamical viewpoint, the low-level vorticity presents strong positive values over the sea and Sahara zone, indicating that exists on the cyclonic shear side of the African easterly jet, which is consistent with baroclinic growth. The 925-hPa equivalent potential temperature structure show a maximum over the Sahara which corresponds to the depression observed in this region. A mosaic of three hourly infrared (IR) satellite images, depicts a very distinct signal from an initial region of convection, developing through several stages and moving off the African coast. These observations, along with those available from the World Weather Watch, provide an opportunity to carry out numerical weather prediction (NWP) studies over West Africa utilizing high resolution limited area models.

  10. Potential Climate Effects of Dust Aerosols' over West Africa

    NASA Astrophysics Data System (ADS)

    JI, Z.; Wang, G.; Pal, J. S.; Yu, M.

    2014-12-01

    Climate in West Africa is under the influence of the West African monsoon circulation and mineral dust emitted from the Sahara desert (which is the world's largest source of mineral dust emission). Dust aerosols alter the atmospheric radiative fluxes and act as cloud condensation nuclei in the process of emission, transportation and deposition. However, our understanding regarding how dust aerosols influence the present-day and future climate of West Africa is very limited. In this study, a regional climate model RegCM4.3.4-CLM4.5 is used to investigate the potential climatic effects of dust aerosols both in present (1981-2000) and future (2081-2100) periods over WA. First, the model performance and dust climatic effects are evaluated. The contribution of dust climatic effects under RCP8.5 scenario and their confounding effects with land use change are assessed. Our results indicate that the model can reproduce with reasonable accuracy the spatial and temporal distribution of climatology, aerosol optical depth and surface concentration over WA. The shortwave radiative forcing of dust is negative in the surface and positive in the atmosphere, with greater changes in JJA and MAM compared to those in SON and DJF. Over most of West Africa, cooling is the dominant effect on temperature. Their impact on precipitation features a dipole pattern, with decrease in the north and increase in the south of West Africa. Despite the dust-induced decrease of precipitation amount, dusts cause extreme precipitation to increase. To evaluate the uncertainties surrounding our modeling results, sensitivity experiments driven by ICBC from MIROC-ESM and CESM and their dynamic downscaling results are used for comparisons. Results from these sensitivity experiments indicate that the impact of dust aerosols on present and future climate is robust.

  11. Regional and Global Aspects of Aerosols in Western Africa: From Air Quality to Climate

    NASA Technical Reports Server (NTRS)

    Chin, Mian; Diehl, Thomas; Kucsera, Tom; Spinhime, Jim; Palm, Stephen; Holben, Brent; Ginoux, Paul

    2006-01-01

    Western Africa is one of the most important aerosol source regions in the world. Major aerosol sources include dust from the world's largest desert Sahara, biomass burning from the Sahel, pollution aerosols from local sources and long-range transport from Europe, and biogenic sources from vegetation. Because these sources have large seasonal variations, the aerosol composition over the western Africa changes significantly with time. These aerosols exert large influences on local air quality and regional climate. In this study, we use the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model to analyze satellite lidar data from the GLAS instrument on the ICESat and the sunphotometer data from the ground-based network AERONET taken in both the wet (September - October 2003) and dry (February - March 2004) seasons over western Africa. We will quantify the seasonal variations of aerosol sources and compositions and aerosol spatial (horizontal and vertical) distributions over western Africa. We will also assess the climate impact of western African aerosols. Such studies will be applied to support the international project, Africa Monsoon Multidisciplinary Analysis (AMMA) and to analyze the AMMA data.

  12. 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

  13. 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.

  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. Centennial-scale teleconnection between North Atlantic sea surface temperatures and the Indian summer monsoon during the Holocene

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaojian; Jin, Liya; Jia, Wanna

    2016-05-01

    Proxy records have shown that abrupt changes in the Indian summer monsoon (ISM) are closely linked to cold events in the North Atlantic at centennial timescales during the Holocene. However, mechanisms for these co-occurring phenomena are not fully understood. This study uses simulation results from a coupled atmosphere-ocean-sea-ice general circulation model forced by astronomical variations to investigate how summer (June, July, August and September) North Atlantic sea surface temperatures (SSTs) may have influenced the ISM at centennial timescales during the Holocene (9.5-0 ka BP). Our analyses identified an intimate relationship between the North Atlantic tripole SST (NATS) mode and the ISM. The NATS mode can affect the ISM in several ways. First, air-sea interactions over the tropical Atlantic can induce negative tropospheric temperature (TT) anomalies over the Indian Ocean, resulting in a strengthened meridional TT gradient favorable to a prolonged monsoonal rainy season. Second, a positive NATS mode tends to induce closed zonal vertical circulation over the tropical Atlantic, North Africa and the tropical Indian Ocean, creating anomalous convergence over India, and hence an enhanced ISM. Third, westerly surface wind anomalies, related to the NATS mode and coursing over the Arabian Sea, can increase moisture delivery to the monsoon region, causing enhanced rainfall in India. This mechanism resembles a decadal-scale mechanism that operates in the present-day climate. We also compared the Atlantic multidecadal oscillation (AMO), an alternative North Atlantic SST mode, with the NATS mode to determine their relationships to the ISM. A Holocene transient simulation indicates that the AMO's trend has diverged from that of the ISM since 5.5 ka BP, due to inverse SST trends over the tropical and extratropical North Atlantic. This latter trend leads to a much weaker relationship between the AMO and the ISM, relative to that observed between the NATS mode and the ISM

  16. Multi-Scale Predictions of the Asian Monsoons in the NCEP Climate Forecast System

    NASA Astrophysics Data System (ADS)

    Yang, S.

    2013-12-01

    A comprehensive analysis of the major features of the Asian monsoon system in the NCEP Climate Forecast System version 2 (CFSv2) and predictions of the monsoon by the model has been conducted. The intraseasonal-to-interannual variations of both summer monsoon and winter monsoon, as well as the annual cycles of monsoon climate, are focused. Features of regional monsoons including the monsoon phenomena over South Asia, East Asia, and Southeast Asia are discussed. The quasi-biweekly oscillation over tropical Asia and the Mei-yu climate over East Asia are also investigated. Several aspects of monsoon features including the relationships between monsoon and ENSO (including different types of ENSO: eastern Pacific warming and central Pacific warming), extratropical effects, dependence on time leads (initial conditions), regional monsoon features, and comparison between CFSv2 and CFS version 1 (CFSv1) are particularly emphasized. Large-scale characteristics of the Asian summer monsoon including several major dynamical monsoon indices and their associated precipitation patterns can be predicted several months in advance. The skill of predictions of the monsoon originates mostly from the impact of ENSO. It is found that large predictability errors occur in first three lead months and they only change slightly as lead time increases. The large errors in the first three lead months are associated with the large errors in surface thermal condition and atmospheric circulation in the central and eastern Pacific and the African continent. In addition, the response of the summer monsoon to ENSO becomes stronger with increase in lead time. The CFSv2 successfully simulates several major features of the East Asian winter monsoon and its relationships with the Arctic Oscillation, the East Asian subtropical jet, the East Asian trough, the Siberian high, and the lower-tropospheric winds. Surprisingly, the upper-tropospheric winds over the middle-high latitudes can be better simulated

  17. 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

  18. 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

  19. 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

  20. Ozone and carbon monoxide over India during the summer monsoon: regional emissions and transport

    NASA Astrophysics Data System (ADS)

    Ojha, Narendra; Pozzer, Andrea; Rauthe-Schöch, Armin; Baker, Angela K.; Yoon, Jongmin; Brenninkmeijer, Carl A. M.; Lelieveld, Jos

    2016-03-01

    We compare in situ measurements of ozone (O3) and carbon monoxide (CO) profiles from the CARIBIC program with the results from the regional chemistry transport model (WRF-Chem) to investigate the role of local and regional emissions and long-range transport over southern India during the summer monsoon of 2008. WRF-Chem successfully reproduces the general features of O3 and CO distributions over the South Asian region. However, absolute CO concentrations in the lower troposphere are typically underestimated. Here we investigate the influence of local relative to remote emissions through sensitivity simulations. The influence of 50 % increased CO emissions over South Asia leads to a significant enhancement (upto 20 % in July) in upper tropospheric CO in the northern and central Indian regions. Over Chennai in southern India, this causes a 33 % increase in surface CO during June. However, the influence of enhanced local and regional emissions is found to be smaller (5 %) in the free troposphere over Chennai, except during September. Local to regional emissions are therefore suggested to play a minor role in the underestimation of CO by WRF-Chem during June-August. In the lower troposphere, a high pollution (O3: 146.4 ± 12.8, CO: 136.4 ± 12.2 nmol mol-1) event (15 July 2008), not reproduced by the model, is shown to be due to transport of photochemically processed air masses from the boundary layer in southern India. A sensitivity simulation combined with backward trajectories indicates that long-range transport of CO to southern India is significantly underestimated, particularly in air masses from the west, i.e., from Central Africa. This study highlights the need for more aircraft-based measurements over India and adjacent regions and the improvement of global emission inventories.

  1. 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

  2. Country Energy Profile, South Africa

    SciTech Connect

    1995-08-01

    This country energy profile provides energy and economic information about South Africa. Areas covered include: Economics, demographics, and environment; Energy situation; Energy structure; Energy investment opportunities; Department of Energy (DOE) programs in South Africa; and a listing of International aid to South Africa.

  3. Family Planning Programmes in Africa.

    ERIC Educational Resources Information Center

    Pradervand, Pierre

    The countries discussed in this paper are the francophone countries of West Africa and the Republic of Congo, with comparative references made to North Africa (mainly Morocco, Algeria, and Tunisia). Obstacles to the adoption of family planning in the countries of tropical Africa are a very high mortality rate among children; a socioeconomic…

  4. Emergency nursing in South Africa.

    PubMed

    Brysiewicz, Petra; Bruce, Judy

    2008-04-01

    The role of the emergency nurse in South Africa is a challenging one due to a variety of reasons. This article describes the healthcare system of South Africa with particular attention to the emergency medical system as well as the reason why most emergency clients present to the emergency departments. The actual experience of working as an emergency nurse in South Africa is highlighted.

  5. 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

  6. 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.

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

    PubMed

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

    2016-09-26

    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.

  8. Multi-decadal Variation of the Indian Monsoon Rainfall: Implications of ENSO

    NASA Astrophysics Data System (ADS)

    Pothuri, D.; Nuernberg, D.; Mohtadi, M.

    2014-12-01

    Scientific consensus exists on the inverse relationship between the El Nino Southern Oscillation (ENSO) and the Indian Monsoon Rainfall. Conversely, recent historical records of 140 years revealed that the relationship between Indian Monsoon and ENSO has broken down (Kumar et al., 1999). Indian Monsoon rainfall variability on decadal time scale was reconstructed by using seawater oxygen isotopes (d18Ow) estimated from oxygen isotopes and Mg/Ca ratios of Globigerinoides ruber from a sediment core in the Bay of Bengal. A comparison of Indian Monsoon rainfall variability on decadal time scale with the number of ENSO events over last 2000 years reveals an inverse relationship between the monsoon rainfall in the Indian Subcontinent and ENSO Events. Furthermore, d18Ow variations reveal increased monsoon rainfall during Roman Warm Period (RWP) and Medieval Warm Period (MWP) and larger monsoon rainfall fluctuations during the Little Ice Age (LIA). Therefore, our study suggests that on decadal time scale ENSO affects the Indian Monsoon Rainfall through the stronger Walker Circulation and associated tropical convection process.

  9. 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

  10. 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).

  11. Recent and future changes in the Asian monsoon-ENSO relationship: Natural or forced?

    NASA Astrophysics Data System (ADS)

    Li, Xiaoqiong; Ting, Mingfang

    2015-05-01

    The Asian monsoon-ENSO (El Niño-Southern Oscillation) relationship in the 20th and 21st centuries is examined using observations and Coupled Model Intercomparison Project Phase 5 (CMIP5) model simulations. CMIP5 models can simulate the ENSO-monsoon spatial structure reasonably well when using the multimodel mean. Running correlations show prominent decadal variability of the ENSO-monsoon relationship in observations. The modeled ENSO-monsoon relation shows large intermodel spread, indicating large variations across the model ensemble. The anthropogenically forced component of ENSO-monsoon relationship is separated from the naturally varying component based on a signal-to-noise maximizing empirical orthogonal function analysis using global sea surface temperature (SST). Results show that natural variability plays a dominant role in the varied ENSO-monsoon relationship during the 20th century. In the 21st century, the forced component is dominated by enhanced monsoon rainfall associated with SST warming, which may contribute to a slightly weakened ENSO-monsoon relation in the future.

  12. Continental drift and plateau uplift control origination and evolution of Asian and Australian monsoons.

    PubMed

    Liu, Xiaodong; Dong, Buwen; Yin, Zhi-Yong; Smith, Robin S; Guo, Qingchun

    2017-01-13

    Evolutions of Asian and Australian monsoons have important significance for understanding the past global change but are still a controversial subject. Here, we explore systematically the effects of plate movement and plateau uplift on the formation and evolution of the Asian and Australian monsoons by numerical simulations based on land-sea distributions and topographic conditions for five typical geological periods during the Cenozoic. Our results suggest that the timings and causes of formation of the monsoons in South Asia, East Asia and northern Australia are different. The Indian Subcontinent, which was located in the tropical Southern Hemisphere in the Paleocene, was influenced by the austral monsoon system simulated at that time. Once it moved to the tropical Northern Hemisphere in the Eocene, the South Asian monsoon established and remained persistently thereafter. However, the monsoons of East Asia and northern Australia did not appear until the Miocene. The establishment of the simulated low-latitude South Asian (northern Australian) monsoon appeared to have strongly depended on the location of mainland India (Australia), associated with northward plate motion, without much relation to the plateau uplift. On the contrary, the establishment of the mid-latitude East Asian monsoon was mainly controlled by the uplift of Tibetan plateau.

  13. Continental drift and plateau uplift control origination and evolution of Asian and Australian monsoons

    NASA Astrophysics Data System (ADS)

    Liu, Xiaodong; Dong, Buwen; Yin, Zhi-Yong; Smith, Robin S.; Guo, Qingchun

    2017-01-01

    Evolutions of Asian and Australian monsoons have important significance for understanding the past global change but are still a controversial subject. Here, we explore systematically the effects of plate movement and plateau uplift on the formation and evolution of the Asian and Australian monsoons by numerical simulations based on land-sea distributions and topographic conditions for five typical geological periods during the Cenozoic. Our results suggest that the timings and causes of formation of the monsoons in South Asia, East Asia and northern Australia are different. The Indian Subcontinent, which was located in the tropical Southern Hemisphere in the Paleocene, was influenced by the austral monsoon system simulated at that time. Once it moved to the tropical Northern Hemisphere in the Eocene, the South Asian monsoon established and remained persistently thereafter. However, the monsoons of East Asia and northern Australia did not appear until the Miocene. The establishment of the simulated low-latitude South Asian (northern Australian) monsoon appeared to have strongly depended on the location of mainland India (Australia), associated with northward plate motion, without much relation to the plateau uplift. On the contrary, the establishment of the mid-latitude East Asian monsoon was mainly controlled by the uplift of Tibetan plateau.

  14. 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.

  15. Continental drift and plateau uplift control origination and evolution of Asian and Australian monsoons

    PubMed Central

    Liu, Xiaodong; Dong, Buwen; Yin, Zhi-Yong; Smith, Robin S.; Guo, Qingchun

    2017-01-01

    Evolutions of Asian and Australian monsoons have important significance for understanding the past global change but are still a controversial subject. Here, we explore systematically the effects of plate movement and plateau uplift on the formation and evolution of the Asian and Australian monsoons by numerical simulations based on land-sea distributions and topographic conditions for five typical geological periods during the Cenozoic. Our results suggest that the timings and causes of formation of the monsoons in South Asia, East Asia and northern Australia are different. The Indian Subcontinent, which was located in the tropical Southern Hemisphere in the Paleocene, was influenced by the austral monsoon system simulated at that time. Once it moved to the tropical Northern Hemisphere in the Eocene, the South Asian monsoon established and remained persistently thereafter. However, the monsoons of East Asia and northern Australia did not appear until the Miocene. The establishment of the simulated low-latitude South Asian (northern Australian) monsoon appeared to have strongly depended on the location of mainland India (Australia), associated with northward plate motion, without much relation to the plateau uplift. On the contrary, the establishment of the mid-latitude East Asian monsoon was mainly controlled by the uplift of Tibetan plateau. PMID:28084310

  16. Spectral width of premonsoon and monsoon clouds over Indo-Gangetic valley

    NASA Astrophysics Data System (ADS)

    Prabha, Thara V.; Patade, S.; Pandithurai, G.; Khain, A.; Axisa, D.; Pradeep-Kumar, P.; Maheshkumar, R. S.; Kulkarni, J. R.; Goswami, B. N.

    2012-10-01

    The combined effect of humidity and aerosol on cloud droplet spectral width (σ) in continental monsoon clouds is a topic of significant relevance for precipitation and radiation budgets over monsoon regions. The droplet spectral width in polluted, dry premonsoon conditions and moist monsoon conditions observed near the Himalayan Foothills region during Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) is the focus of this study. Here σis small in premonsoon clouds developing from dry boundary layers. This is attributed to numerous aerosol particles and the absence/suppression of collision-coalescence during premonsoon. For polluted and dry premonsoon clouds,σ is constant with height. In contrast to premonsoon clouds, σ in monsoon clouds increases with height irrespective of whether they are polluted or clean. The mean radius of polluted monsoon clouds is half that of clean monsoon clouds. In monsoon clouds, both mean radius and σ decreased with total cloud droplet number concentration (CDNC). The spectral widths of premonsoon clouds were independent of total droplet number concentrations, but both σ and mean radius decreased with small droplet (diameter < 20 μm) number concentrations in the diluted part of the cloud. Observational evidence is provided for the formation of large droplets in the adiabatic regions of monsoon clouds. The number concentration of small droplets is found to decrease in the diluted cloud volumes that may be characterized by various spectral widths or mean droplet radii.

  17. Impacts of the East Asian Monsoon on springtime dust concentrations over China: IMPACTS OF MONSOON ON DUST

    SciTech Connect

    Lou, Sijia; Russell, Lynn M.; Yang, Yang; Xu, Li; Lamjiri, Maryam A.; DeFlorio, Michael J.; Miller, Arthur J.; Ghan, Steven J.; Liu, Ying; Singh, Balwinder

    2016-07-12

    We use 150 year preindustrial simulations of the Community Earth System Model to quantify the impacts of the East Asian Monsoon strength on interannual variations of springtime dust concentrations over China. The simulated interannual variations in March-April-May (MAM) dust column concentrations range between 20–40% and 10–60% over eastern and western China, respectively. The dust concentrations over eastern China correlate negatively with the East Asian Monsoon (EAM) index, which represents the strength of monsoon, with a regionally averaged correlation coefficient of 0.64. Relative to the strongest EAM years, MAMdust concentrations in the weakest EAM years are higher over China, with regional relative differences of 55.6%, 29.6%, and 13.9% in the run with emissions calculated interactively and of 33.8%, 10.3%, and 8.2% over eastern, central, and western China, respectively, in the run with prescribed emissions. Both interactive run and prescribed emission run show the similar pattern of climate change between the weakest and strongest EAM years. Strong anomalous northwesterly and westerly winds over the Gobi and Taklamakan deserts during the weakest EAM years result in larger transport fluxes, and thereby increase the dust concentrations over China. These differences in dust concentrations between the weakest and strongest EAM years (weakest-strongest) lead to the change in the net radiative forcing by up to 8 and 3Wm2 at the surface, compared to 2.4 and +1.2Wm2 at the top of the atmosphere over eastern and western China, respectively.

  18. Simulated climate and biomes of Africa during the late quaternary: comparison with pollen and lake status data

    NASA Astrophysics Data System (ADS)

    Jolly, D.; Harrison, S. P.; Damnati, B.; Bonnefille, R.

    New compilations of African pollen and lake data are compared with climate (CCM1, NCAR, Boulder) and vegetation (BIOME 1.2, GSG, Lund) simulations for the last glacial maximum (LGM) and early to mid-Holocene (EMH). The simulated LGM climate was ca 4°C colder and drier than present, with maximum reduction in precipitation in semi-arid regions. Biome simulations show lowering of montane vegetation belts and expansion of southern xerophytic associations, but no change in the distribution of deserts and tropical rain forests. The lakes show LGM conditions similar or drier than present throughout northern and tropical Africa. Pollen data indicate lowering of montane vegetation belts, the stability of the Sahara, and a reduction of rain forest. The paleoenvironmental data are consistent with the simulated changes in temperature and moisture budgets, although they suggest the climate model underestimates equatorial aridity. EMH simulations show temperatures slightly less than present and increased monsoonal precipitation in the eastern Sahara and East Africa. Biome simulations show an upward shift of montane vegetation belts, fragmentation of xerophytic vegetation in southern Africa, and a major northward shift of the southern margin of the eastern Sahara. The lakes indicate conditions wetter than present across northern Africa. Pollen data show an upward shift of the montane forests, the northward shift of the southern margin of the Sahara, and a major extension of tropical rain forest. The lake and pollen data confirm monsoon expansion in eastern Africa, but the climate model fails to simulate the wet conditions in western Africa.

  19. Trends and oscillations in the Indian summer monsoon rainfall over the last two millennia.

    PubMed

    Sinha, Ashish; Kathayat, Gayatri; Cheng, Hai; Breitenbach, Sebastian F M; Berkelhammer, Max; Mudelsee, Manfred; Biswas, Jayant; Edwards, R L

    2015-02-17

    Observations show that summer rainfall over large parts of South Asia has declined over the past five to six decades. It remains unclear, however, whether this trend is due to natural variability or increased anthropogenic aerosol loading over South Asia. Here we use stable oxygen isotopes in speleothems from northern India to reconstruct variations in Indian monsoon rainfall over the last two millennia. We find that within the long-term context of our record, the current drying trend is not outside the envelope of monsoon's oscillatory variability, albeit at the lower edge of this variance. Furthermore, the magnitude of multi-decadal oscillatory variability in monsoon rainfall inferred from our proxy record is comparable to model estimates of anthropogenic-forced trends of mean monsoon rainfall in the 21st century under various emission scenarios. Our results suggest that anthropogenic-forced changes in monsoon rainfall will remain difficult to detect against a backdrop of large natural variability.

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

    PubMed

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

    2014-11-06

    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. 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.

  2. Intraseasonal Variability of the South Asian Summer Monsoon: Present-day Simulations with the Regional Atmospheric Model HIRHAM5

    NASA Astrophysics Data System (ADS)

    Hanf, F. S.; Rinke, A.; Dethloff, K.

    2014-12-01

    Since 1950, observations show a robust negative trend of the seasonal rainfall associated with the South Asian summer monsoon over India coinciding with a continuous decrease in surface solar radiation ("dimming") over South Asia due to an increase of local aerosol emissions. On the intraseasonal timescale the summer monsoon fluctuates between periods of enhanced and reduced rainfall. The frequency of occurrence of these active and breaks monsoon phases affects directly the seasonal monsoon rainfall. This study investigates the regional pattern and changes of the South Asian monsoon for the period 1979-2012 using the regional atmospheric model HIRHAM5 with a horizontal resolution of 0.25° forced at the lateral and lower boundaries with ERA-Interim reanalysis data. Despite the dry bias in the mean summer monsoon rainfall over the Indian landmass, the simulated temperature and atmospheric circulation patterns are in agreement with the ERA-Interim reanalysis indicating a realistic representation of important dynamical summer monsoon features. In addition, mechanisms which controls active and break phases within the summer monsoon season are analyzed using daily outgoing longwave radiation model data as an identification tool of monsoon breaks as proposed by Krishnan et al. (2000). Model results reveal an increasing trend of the cumulative monsoon break days of around 1.4 days per year during the last 30 years. The possible link between this increasing of cumulative monsoon break days and the observed decrease of seasonal South Asian monsoon rainfall will be the scope of further investigations.

  3. Out of Africa

    ERIC Educational Resources Information Center

    Wilbert, Nancy Corrigan

    2009-01-01

    Karen Blixen (Isak Dinesen), author of "Out of Africa," said, "God made the world round so people would never be able to see too far down the road." The author embraced this wonderful thought by venturing on a three-week journey to Kenya and Tanzania in search of grand adventure. In this article, the author shares her adventure…

  4. Anglicising Postapartheid South Africa

    ERIC Educational Resources Information Center

    Louw, P. Eric

    2004-01-01

    The apartheid state deliberately encouraged linguistic diversity and actively built cultural infrastructures which impeded Anglicisation. With the end of apartheid has come "de facto" Anglicisation. So although South Africa has, since 1994, had 11 official languages, in reality, English is swamping the other 10 languages. Afrikaans has,…

  5. Who Speaks for Africa?

    ERIC Educational Resources Information Center

    Nealy, Michelle

    2005-01-01

    Judging by the press coverage, it would seem that Europeans are the only ones concerned about conditions in Africa, but perhaps the media is not telling the whole story. According to Mark P. Fancher, chair of the National Conference of Black Lawyers' Section on International Affairs & World Peace and the author of "The Splintering of…

  6. South Africa's Constitutional Change.

    ERIC Educational Resources Information Center

    Getman, Thomas

    1987-01-01

    Describes the striking dichotomy of South Africa's beauty and the squalor resulting from the apartheid policies of the government. Reviews reactions of black South Africans to recent constitutional changes and details efforts to secure more sweeping reform. Includes stories of several individuals who have taken actions which oppose the system of…

  7. West and Central Africa.

    PubMed

    Lydie, N; Robinson, N J

    1998-01-01

    This article reviews scientific and other literature during the 1990s that links migration and mobility with the spread of sexually transmitted diseases (STDs), including HIV/AIDS. The focus is on key population groups linked to the spread of HIV and STDs in West and Central Africa: migrant laborers, truck drivers, itinerant traders, commercial sex workers (CSWs), and refugees. Countries with high emigration and immigration tend to have high levels of HIV infection, with the exception of Senegal. The main destination of immigrants are Senegal, Nigeria, and Cote d'Ivoire in West Africa and Cameroon, Congo, Gabon, and Congo in Central Africa. The risk of infection and the spread of HIV is variable among migrants. There is little in the literature that substantiates hypotheses about the strong association between migration and HIV-positive status. Information is needed on the duration, frequency of return visits, living conditions, sexual activities with multiple partners, and information before departure, along the routes, at final destination, and at the time of returns. Action-based research in five West African countries (Burkina Faso, Cote d'Ivoire, Mali, Niger, and Senegal) should produce results in late 1998. Comparable studies in Central Africa are unknown. Regional studies should be complemented by local studies. Prevention would benefit from studies on the relative size of these five population groups by geographic location.

  8. AED in Africa

    ERIC Educational Resources Information Center

    Academy for Educational Development, 2004

    2004-01-01

    Founded in 1961, the Academy for Educational Development (AED) is an independent, nonprofit, charitable organization that operates development programs in the United States and throughout the world. This directory presents an overview of the AED programs in Africa since 1975. Current AED Programs include: (1) HIV/AIDS Prevention and Impact…

  9. AED in Africa.

    ERIC Educational Resources Information Center

    Academy for Educational Development, Washington, DC.

    For 30 years, the Academy for Educational Development (AED) has worked to support African development. In Uganda, Tanzania, and Botswana AED promoted some of Africa's first AIDS prevention programs. AED is funding research in Ethiopia, Tanzania, and perhaps Zambia that will target stigma and its role in AIDS prevention. Working with governments…

  10. Africa: Myth and Reality.

    ERIC Educational Resources Information Center

    Brown, Barbara B.

    1994-01-01

    Reports on the Third International Social Studies Conference held in Nairobi, Kenya, in 1994. Discusses democracy, educational reform efforts, and the importance of tourism to the Kenyan economy. Asserts that U.S. teachers must use accurate and nonstereotypical instructional materials in teaching about Africa. (CFR)

  11. Topical Research: Africa.

    ERIC Educational Resources Information Center

    Lynn, Karen

    This lesson plan can be used in social studies, language arts, or library research. The instructional objective is for students to select a topic of study relating to Africa, write a thesis statement, collect information from media sources, and develop a conclusion. The teacher may assign the lesson for written or oral evaluation. The teacher…

  12. Africa and Applied Linguistics.

    ERIC Educational Resources Information Center

    Makoni, Sinfree, Ed.; Meinhof, Ulrike H., Ed.

    2003-01-01

    This collection of articles includes: "Introducing Applied Linguistics in Africa" (Sinfree Makoni and Ulrike H. Meinhof); "Language Ideology and Politics: A Critical Appraisal of French as Second Official Language in Nigeria" (Tope Omoniyi); "The Democratisation of Indigenous Languages: The Case of Malawi" (Themba…

  13. Trends Abroad: South Africa

    ERIC Educational Resources Information Center

    Varley, Douglas H.

    1970-01-01

    In South Africa today there is a complex structure of laws and regulations which impose a variety of restrictions on individual liberties including the freedom to publish and read literary material. The successive steps by which this state of affairs has been reached are briefly described. (NH)

  14. Anatomy: Spotlight on Africa

    ERIC Educational Resources Information Center

    Kramer, Beverley; Pather, Nalini; Ihunwo, Amadi O.

    2008-01-01

    Anatomy departments across Africa were surveyed regarding the type of curriculum and method of delivery of their medical courses. While the response rate was low, African anatomy departments appear to be in line with the rest of the world in that many have introduced problem based learning, have hours that are within the range of western medical…

  15. What aspects of future rainfall changes matter for crop yields in West Africa?

    NASA Astrophysics Data System (ADS)

    Guan, Kaiyu; Sultan, Benjamin; Biasutti, Michela; Baron, Christian; Lobell, David B.

    2015-10-01

    How rainfall arrives, in terms of its frequency, intensity, the timing and duration of rainy season, may have a large influence on rainfed agriculture. However, a thorough assessment of these effects is largely missing. This study combines a new synthetic rainfall model and two independently validated crop models (APSIM and SARRA-H) to assess sorghum yield response to possible shifts in seasonal rainfall characteristics in West Africa. We find that shifts in total rainfall amount primarily drive the rainfall-related crop yield change, with less relevance to intraseasonal rainfall features. However, dry regions (total annual rainfall below 500 mm/yr) have a high sensitivity to rainfall frequency and intensity, and more intense rainfall events have greater benefits for crop yield than more frequent rainfall. Delayed monsoon onset may negatively impact yields. Our study implies that future changes in seasonal rainfall characteristics should be considered in designing specific crop adaptations in West Africa.

  16. Secondary Organic Aerosol from biogenic VOCs over West Africa during AMMA

    NASA Astrophysics Data System (ADS)

    Capes, G.; Murphy, J. G.; Reeves, C. E.; McQuaid, J. B.; Hamilton, J. F.; Hopkins, J. R.; Crosier, J.; Williams, P. I.; Coe, H.

    2009-01-01

    This paper presents measurements of organic aerosols above subtropical West Africa during the wet season using data from the UK Facility for Airborne Atmospheric Measurements (FAAM) aircraft. Measurements of biogenic volatile organic compounds (BVOC) at low altitudes over these subtropical forests were made during the African Monsoon Multidisciplinary Analysis (AMMA) field experiment during July and August 2006 mainly above Benin, Nigeria and Niger. Data from an Aerodyne Quadrupole Aerosol Mass Spectrometer show a median organic aerosol loading of 1.08 μg m-3 over tropical West Africa, which represents the first regionally averaged assessment of organic aerosol mass (OM) in this region during the wet season. This is in good agreement with predictions based on aerosol yields from isoprene and monoterpenes during chamber studies and model predictions based on partitioning schemes, contrasting markedly with the large under representations of OM in similar models when compared with data from mid latitudes.

  17. Were rivers flowing across the Sahara during the last interglacial? Implications for human migration through Africa.

    PubMed

    Coulthard, Tom J; Ramirez, Jorge A; Barton, Nick; Rogerson, Mike; Brücher, Tim

    2013-01-01

    Human migration north through Africa is contentious. This paper uses a novel palaeohydrological and hydraulic modelling approach to test the hypothesis that under wetter climates c.100,000 years ago major river systems ran north across the Sahara to the Mediterranean, creating viable migration routes. We confirm that three of these now buried palaeo river systems could have been active at the key time of human migration across the Sahara. Unexpectedly, it is the most western of these three rivers, the Irharhar river, that represents the most likely route for human migration. The Irharhar river flows directly south to north, uniquely linking the mountain areas experiencing monsoon climates at these times to temperate Mediterranean environments where food and resources would have been abundant. The findings have major implications for our understanding of how humans migrated north through Africa, for the first time providing a quantitative perspective on the probabilities that these routes were viable for human habitation at these times.

  18. The possible role of local air pollution in climate change in West Africa

    NASA Astrophysics Data System (ADS)

    Knippertz, Peter; Evans, Mat J.; Field, Paul R.; Fink, Andreas H.; Liousse, Catherine; Marsham, John H.

    2015-09-01

    The climate of West Africa is characterized by a sensitive monsoon system that is associated with marked natural precipitation variability. This region has been and is projected to be subject to substantial global and regional-scale changes including greenhouse-gas-induced warming and sea-level rise, land-use and land-cover change, and substantial biomass burning. We argue that more attention should be paid to rapidly increasing air pollution over the explosively growing cities of West Africa, as experiences from other regions suggest that this can alter regional climate through the influences of aerosols on clouds and radiation, and will also affect human health and food security. We need better observations and models to quantify the magnitude and characteristics of these impacts.

  19. Were Rivers Flowing across the Sahara During the Last Interglacial? Implications for Human Migration through Africa

    PubMed Central

    Coulthard, Tom J.; Ramirez, Jorge A.; Barton, Nick; Rogerson, Mike; Brücher, Tim

    2013-01-01

    Human migration north through Africa is contentious. This paper uses a novel palaeohydrological and hydraulic modelling approach to test the hypothesis that under wetter climates c.100,000 years ago major river systems ran north across the Sahara to the Mediterranean, creating viable migration routes. We confirm that three of these now buried palaeo river systems could have been active at the key time of human migration across the Sahara. Unexpectedly, it is the most western of these three rivers, the Irharhar river, that represents the most likely route for human migration. The Irharhar river flows directly south to north, uniquely linking the mountain areas experiencing monsoon climates at these times to temperate Mediterranean environments where food and resources would have been abundant. The findings have major implications for our understanding of how humans migrated north through Africa, for the first time providing a quantitative perspective on the probabilities that these routes were viable for human habitation at these times. PMID:24040347

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Transport of sulfonamide antibiotics in crop fields during monsoon season.

    PubMed

    Park, Jong Yol; Ruidisch, Marianne; Huwe, Bernd

    2016-11-01

    Previous studies have documented the occurrence of veterinary sulfonamide antibiotics in groundwater and rivers located far from pollution sources, although their transport and fate is relatively unknown. In mountainous agricultural fields, the transport behaviour can be influenced by climate, slope and physico-chemical properties of the sulfonamides. The objective of this research is to describe the transport behaviour of three sulfonamide antibiotics (sulfamethoxazole, sulfadimethoxine and sulfamethazine) in sloped agricultural fields located in the Haean catchment, South Korea. During dry and monsoon seasons, a solute transport experiment was conducted in two typical sandy loam agricultural fields after application of antibiotics and potassium bromide as conservative tracers. Field measurement and modelling revealed that frequency and amount of runoff generation indicate a relation between slope and rain intensity during monsoon season. Since the steepness of slope influenced partitioning of precipitation between runoff and subsurface flow, higher loss of sulfonamide antibiotics and bromide by runoff was observed at the steeper sloped field. Bromide on topsoil rapidly infiltrated at high infiltration rates. On the contrary, the sulfonamides were relatively retarded in the upper soil layer due to adsorption onto soil particles. Presence of furrows and ridges affected the distribution of sulfonamide antibiotics in the subsurface due to gradient from wetter furrows to drier ridges induced by topography. Modelling results with HydroGeoSphere 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 generation by storm events.

  6. 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.

  7. 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.

  8. Impulsive alluviation during early Holocene strengthened monsoons, central Nepal Himalaya

    NASA Astrophysics Data System (ADS)

    Pratt, Beth; Burbank, Douglas W.; Heimsath, Arjun; Ojha, Tank

    2002-10-01

    The steep-walled bedrock gorges of the Greater Himalayan rivers currently lack significant stored sediment, suggesting that fluvial erosion and transport capacity outpace the supply of sediment from adjacent hillsides. Despite this appearance of sustained downcutting, such rivers can become choked with sediments and aggrade during intervals of higher precipitation. Cosmogenic dating (10Be and 26Al) of fluvially carved bedrock surfaces indicates that sediment at least 80 m thick filled the Marsyandi River valley in central Nepal during a time of strengthened early Holocene monsoons. Despite threefold differences in height (43 124 m) above the modern river, these fluvial surfaces display strikingly similar cosmogenic exposure ages clustering around 7 ± 1 ka. We speculate that enhanced monsoonal precipitation increased pore pressure and the frequency of landsliding, thereby generating a pulse of hillslope-derived sediment that temporarily overwhelmed this alpine fluvial system's transport capacity. After the easily liberated material was exhausted ca. 7 ka, the hillslope flux dropped, and the river incised through the aggraded alluvium. It concurrently eroded adjacent rock walls, thereby removing previously accumulated 10Be and 26Al and resetting the cosmogenic clock in the bedrock. Unlike previous studies, these exposure ages cannot be used to derive river-incision rates; instead they record a coupled fluvial-hillslope response to climate change.

  9. 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.

  10. Predictability of Java Monsoon Rainfall Anomalies: A Case Study.

    NASA Astrophysics Data System (ADS)

    Hastenrath, Stefan

    1987-01-01

    A substantial portion of the interannual variability of rainfall at Jakarta, Java, can be predicted from antecedent pressure anomalies at Darwin, northern Australia; the pressure persistence, the concurrent correlation of pressure and rainfall, and the predictability of rainfall from antecedent pressure are all largest during the `east' monsoon (June-November). Because of the relatively simple large-scale circulation setting, warranting a single predictor (Darwin pressure), this region is chosen for a series of experiments aimed at exploring the seasonality and secular variations of predictability, optimal length of dependent record, and updating of the regression base period used for predictions on the independent data set.The major features of pressure-rainfall relationships are common through much of the 1911-83 record, namely sign and general magnitude of correlations and the closer relationships during the east, as compared to the west monsoon. Considerable differences are, however, apparent between decades. Them may stem from both sampling deficiencies (noise) and real long-term changes of the pressure-rainfall couplings due to secular alterations in the large-scale circulation setting. The competition between these two factors is relevant concerning the optimal length of the dependent record used for predictions into the independent data set, as well as the updating of the regression base period.

  11. Weather and Climate Prediction for the North American Monsoon

    NASA Astrophysics Data System (ADS)

    Krishnamurti, T. N.; Chakraborty, A.

    2005-05-01

    Some of the major elements of the North American monsoon include the onset and seasonal behavior of precipitation, the moisture sources, orographic responses, effects of sea surface temperature (SST) anomalies over the Gulf of Mexico, Pacific and Atlantic Oceans, and the teleconnection with the intertropical convergence zone (ITCZ). This study addresses these issues on the medium range (a week) to seasonal (3 month) time scales. Our approach is one of constructing ensemble forecasts that include 11 weather models for the medium range and 13 coupled atmosphere-ocean models for seasonal time scales. The metrics for forecasts evaluation include deterministic measures such as RMS error and anomaly correlation, and probabilistic measures such as the equitable threat scores and Briar skill scores. The ensemble forecast approach includes a conventional FSU superensemble for weather and a variant called the synthetic superensemble for the seasonal climate. These superensemble strings covering a 13-year period show that it is possible to predict some of the important features of the North American monsoon at a higher skill with the superensemble compared to the participating member models.

  12. 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.

  13. The Role of Continental-scale Landmass in Monsoonal and Global Precipitation Distribution

    NASA Technical Reports Server (NTRS)

    Chao, Winston C.

    2008-01-01

    It was argued by Chao and Chen (20011) 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. in this article the roles of land-sea thermal contrast 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. 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 1TCZ 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 other band, in winter the landmass does not present a competition for rainfall and thus allow middle latitude storm tracks to expand over the ocean.

  14. Western North Pacific monsoon depressions: Transitions to pre-tropical cyclone seedlings

    NASA Astrophysics Data System (ADS)

    Beattie, Jodi C.; Elsberry, Russell L.

    2016-11-01

    The objective of this study is to describe how a monsoon depression in the western North Pacific, which typically has a diameter of 1000 km, may be transitioned into a tropical cyclone with an inner core of strong winds and deep convection on the order of 100 km. Our previous case study of the pre-Typhoon Man-Yi monsoon depression formation is extended to show that the same cross-equatorial airstream continued and led to enhanced equatorial westerlies on the equatorward side of the pre-Man-Yi circulation, and a surge in the trade easterlies was also present on the poleward side. As these surges in the near-equatorial flow are inertially unstable, inward-directed wave-activity fluxes then led to flux convergence over the eastern vorticity maximum of the monsoon depression, which resulted in a scale contraction to that of a pretropical cyclone seedling. Eight case studies of the transitions of monsoon depressions during 2009 are presented that document persistent inward-directed wave-activity fluxes over a vorticity maximum within the monsoon depression is a key feature of each transition. In some transitions, the same cross-equatorial airstream as led to the monsoon depression formation continues as the primary airstream, and in other transitions another airstream to the west or enhanced tropical easterlies become the primary airstream. Analysis of 10 non-transitioning monsoon depressions during 2009 indicated the airstream wave-activity flux did not persist after the formation of the monsoon depression. In another 11 non-transitioning monsoon depressions, the inward-directed wave-activity flux was small and no region of wave-activity flux convergence was associated with the vorticity maximum in the monsoon depression.

  15. 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

  16. Cholera outbreaks in Africa.

    PubMed

    Mengel, Martin A; Delrieu, Isabelle; Heyerdahl, Leonard; Gessner, Bradford D

    2014-01-01

    During the current seventh cholera pandemic, Africa bore the major brunt of global disease burden. More than 40 years after its resurgence in Africa in 1970, cholera remains a grave public health problem, characterized by large disease burden, frequent outbreaks, persistent endemicity, and high CFRs, particularly in the region of the central African Great Lakes which might act as reservoirs for cholera. There, cases occur year round with a rise in incidence during the rainy season. Elsewhere in sub-Saharan Africa, cholera occurs mostly in outbreaks of varying size with a constant threat of widespread epidemics. Between 1970 and 2011, African countries reported 3,221,050 suspected cholera cases to the World Health Organization, representing 46 % of all cases reported globally. Excluding the Haitian epidemic, sub-Saharan Africa accounted for 86 % of reported cases and 99 % of deaths worldwide in 2011. The number of cholera cases is possibly much higher than what is reported to the WHO due to the variation in modalities, completeness, and case definition of national cholera data. One source on country specific incidence rates for Africa, adjusting for underreporting, estimates 1,341,080 cases and 160,930 deaths (52.6 % of 2,548,227 estimated cases and 79.6 % of 209,216 estimated deaths worldwide). Another estimates 1,411,453 cases and 53,632 deaths per year, respectively (50 % of 2,836,669 estimated cases and 58.6 % of 91,490 estimated deaths worldwide). Within Africa, half of all cases between 1970 and 2011 were notified from only seven countries: Angola, Democratic Republic of the Congo, Mozambique, Nigeria, Somalia, Tanzania, and South Africa. In contrast to a global trend of decreasing case fatality ratios (CFRs), CFRs have remained stable in Africa at approximately 2 %. Early propagation of cholera outbreaks depends largely on the extent of individual bacterial shedding, host and organism characteristics, the likelihood of people coming into contact with

  17. A return to wet conditions over Africa: 1995-2010

    NASA Astrophysics Data System (ADS)

    Jury, Mark R.

    2013-02-01

    Climatic trends over sub-Saharan Africa are described using major river flows, European Community Medium-Range Weather Forecasts, Coupled Forecast System, global land surface data assimilation and National Center for Environmental Prediction reanalysis, Global Precipitation Climate Center gauge data, and satellite observations in the period 1995-2010. The Niger and Zambezi rivers reached flow levels last seen in the 1950s (2,000 and 5,000 m3 s-1, respectively), and rainfall across the Congo Basin increased steadily ~+0.16 mm day-1 year-1. Weather events that contributed to flooding are studied and include the Zambezi tropical trough of 4 January 2008 and the Sahelian easterly wave of 19 July 2010. Diurnal summer rainfall increased threefold over the 1995-2010 period in conjunction with a strengthened land-sea temperature contrast, onshore flow, and afternoon uplift. 700 mb zonal winds over East Africa became easterly after 2001, so clean Indian Ocean air was entrained to the Congo, improving convective efficiency. Relationships between the African monsoon circulation and global teleconnections are explored. Zonal wind convergence around the Congo appears related with the tropical multi-decadal oscillation and signals in the Atlantic during the study period.

  18. Robust features of future climate change impacts on sorghum yields in West Africa

    NASA Astrophysics Data System (ADS)

    Sultan, B.; Guan, K.; Kouressy, M.; Biasutti, M.; Piani, C.; Hammer, G. L.; McLean, G.; Lobell, D. B.

    2014-10-01

    West Africa is highly vulnerable to climate hazards and better quantification and understanding of the impact of climate change on crop yields are urgently needed. Here we provide an assessment of near-term climate change impacts on sorghum yields in West Africa and account for uncertainties both in future climate scenarios and in crop models. Towards this goal, we use simulations of nine bias-corrected CMIP5 climate models and two crop models (SARRA-H and APSIM) to evaluate the robustness of projected crop yield impacts in this area. In broad agreement with the full CMIP5 ensemble, our subset of bias-corrected climate models projects a mean warming of +2.8 °C in the decades of 2031-2060 compared to a baseline of 1961-1990 and a robust change in rainfall in West Africa with less rain in the Western part of the Sahel (Senegal, South-West Mali) and more rain in Central Sahel (Burkina Faso, South-West Niger). Projected rainfall deficits are concentrated in early monsoon season in the Western part of the Sahel while positive rainfall changes are found in late monsoon season all over the Sahel, suggesting a shift in the seasonality of the monsoon. In response to such climate change, but without accounting for direct crop responses to CO2, mean crop yield decreases by about 16-20% and year-to-year variability increases in the Western part of the Sahel, while the eastern domain sees much milder impacts. Such differences in climate and impacts projections between the Western and Eastern parts of the Sahel are highly consistent across the climate and crop models used in this study. We investigate the robustness of impacts for different choices of cultivars, nutrient treatments, and crop responses to CO2. Adverse impacts on mean yield and yield variability are lowest for modern cultivars, as their short and nearly fixed growth cycle appears to be more resilient to the seasonality shift of the monsoon, thus suggesting shorter season varieties could be considered a potential

  19. Characteristics of Extreme Summer Convection over equatorial America and Africa

    NASA Astrophysics Data System (ADS)

    Zuluaga, M. D.; Houze, R.

    2013-12-01

    Fourteen years of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) version 7 data for June-August show the temporal and spatial characteristics of extreme convection over equatorial regions of the American and African continents. We identify three types of extreme systems: storms with deep convective cores (contiguous convective 40 dBZ echoes extending ≥10 km in height), storms with wide convective cores (contiguous convective 40 dBZ echoes with areas >1,000 km2) and storms with broad stratiform regions (stratiform echo >50,000 km2). European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis is used to describe the environmental conditions around these forms of extreme convection. Storms with deep convective cores occur mainly over land: in the equatorial Americas, maximum occurrence is in western Mexico, Northern Colombia and Venezuela; in Africa, the region of maximum occurrence is a broad zone enclosing the central and west Sudanian Savanna, south of the Sahel region. Storms with wide convective radar echoes occur in these same general locations. In the American sector, storms with broad stratiform precipitation regions (typifying robust mesoscale convective systems) occur mainly over the eastern tropical Pacific Ocean and the Colombia-Panama bight. In the African sector, storms with broad stratiform precipitation areas occur primarily over the eastern tropical Atlantic Ocean near the coast of West Africa. ECMWF reanalyses show how the regions of extreme deep convection associated with both continents are located mainly in regions affected by diurnal heating and influenced by atmospheric jets in regions with strong humidity gradients. Composite analysis of the synoptic conditions leading to the three forms of extreme convection provides insights into the forcing mechanisms in which these systems occur. These analyses show how the monsoonal flow directed towards the Andes slopes is mainly what concentrates the occurrence of extreme

  20. Nocturnal low-level clouds over southern West Africa analysed using high-resolution simulations

    NASA Astrophysics Data System (ADS)

    Adler, Bianca; Kalthoff, Norbert; Gantner, Leonhard

    2017-01-01

    We performed a high-resolution numerical simulation to study the development of extensive low-level clouds that frequently form over southern West Africa during the monsoon season. This study was made in preparation for a field campaign in 2016 within the Dynamics-aerosol-chemistry-cloud interactions in West Africa (DACCIWA) project and focuses on an area around the city of Savè in southern Benin. Nocturnal low-level clouds evolve a few hundred metres above the ground around the same level as a distinct low-level jet. Several processes are found to determine the spatio-temporal evolution of these clouds including (i) significant cooling of the nocturnal atmosphere caused by horizontal advection with the south-westerly monsoon flow during the first half of the night, (ii) vertical cold air advection due to gravity waves leading to clouds in the wave crests and (iii) enhanced convergence and upward motion upstream of existing clouds that trigger new clouds. The latter is caused by an upward shift of the low-level jet in cloudy areas leading to horizontal convergence in the lower part and to horizontal divergence in the upper part of the cloud layer. Although this single case study hardly allows for a generalisation of the processes found, the results added to the optimisation of the measurements strategy for the field campaign and the observations will be used to test the hypotheses for cloud formation resulting from this study.

  1. Holocene monsoon variability inferred from palaeolake sediments in NW India.

    NASA Astrophysics Data System (ADS)

    Dixit, Y.; Hodell, D. A.; Petrie, C. A.

    2012-04-01

    The plains of NW India encompasses arid, semi-arid to sub-humid zones and are characterized by numerous palaeolakes and playas. The sedimentary records from these water bodies provide a rich source of paleoclimatic information. We present a high-resolution, Holocene monsoon-variation record inferred from three palaeolakes lying across the precipitation gradient in NW India; palaeolake Karsandi in arid Rajasthan and palaeolake Riwasa, palaeolake Kotla Dahar in semi-arid and sub-humid regions, respectively, in Haryana plains. Laminated and massive gypsum deposits characterize Palaeolake Karsandi in the arid region. Oxygen isotopes are being measured on the gastropod shells and gypsum hydration of water (Hodell et al 2011) for a continuous isotopic record from Rajasthan. The oxygen isotope record from palaeolake Riwasa in the semi-arid region indicates the inception of a wet period at 9700-9500 cal yr (BP) with the establishment of a deep, permanent lake coinciding with the early Holocene maximum in the Indian monsoon. The deep, permanent-lake phase ended with a desiccation event at approximately 8200 BP coinciding with the '8.2kyr' weakening of the monsoon. In contrast, palaeolake Kotla Dahar, lying further east of Riwasa in the sub-humid region, receives 500-700mm annual rainfall. At Kotla Dahar, bulk CaCO3 (%), gastropod abundance and isotope data indicate that the deep lacustrine sequence ends at c.185 cm. Extrapolating from the AMS radio-carbon dated sediments at 135cm (4870-4650 BP) and 230cm (2000-1870 BP), places the 185 cm horizon at c.3970-3720 BP. Our results so far indicate that the Riwasa paleolake lying west of Kotla Dahar dries earlier than Kotla Dahar during the mid-Holocene. The precise date of the transition from a deep-lake water phase to an ephemeral lake in Kotla Dahar is pending, but the projected date suggests that the event coincides with the decline of the urban phase of the Indus Civilization at c. 3900 BP. These three lakes lying across

  2. An Analysis of the Environments of Intense Convective Systems in West Africa in 2003

    NASA Technical Reports Server (NTRS)

    Nicholls, Stephen D.; Mohr, Karen I.

    2010-01-01

    We investigated the local- and regional-scale thermodynamical and dynamical environments associated with intense convective systems in West Africa during 2003. We identified convective system cases from TRMM microwave imagery, classifying each case by the system minimum 85-GHz brightness temperature and by the estimated elapsed time of propagation from high terrain. The speed of the mid-level jet, the magnitude of the low-level shear, and the surface equivalent potential temperature (theta(sub e)) were greater for the intense cases compared to the non-intense cases, although the differences between the means tended to be small, less than 3K for surface theta(sub e). Hypothesis testing of a series of commonly used intensity prediction metrics resulted in significant results only for low-level metrics such as convective available potential energy and not for any of the mid- or upper-level metrics such as 700-hPa theta(sub e). None of the environmental variables or intensity metrics by themselves or in combination appeared to be reliable direct predictors of intensity. In the regional scale analysis, the majority of intense convective systems occurred in the surface baroclinic zone where surface theta(sub e) exceeded 344 K and the 700-hPa zonal wind speeds were less than -6/ms. Fewer intense cases compared to non-intense cases were associated with African easterly wave troughs. Fewer than 25% of our cases occurred in environments with detectable Saharan dust loads, and the results for intense and non-intense cases were similar. Our results for the regional analysis were consistent with the seasonal movement of the WAM and the intertropical front, regional differences in topography, and AEW energetics.

  3. Variations in phytoplankton community in a monsoon-influenced tropical estuary.

    PubMed

    Patil, Jagadish S; Anil, Arga Chandrashekar

    2011-11-01

    In a monsoon-affected tropical estuary, oscillations in freshwater discharge during monsoon shifted the phytoplankton blooms from those adapted to low salinities to high salinities and vice versa. Salinity stratification during monsoon (onset and restart after an intermittent break) favored diatom (Skeletonema) bloom in low-saline surface waters. In high-saline, nutrient-rich bottom waters, Fragilariopsis (diatom) bloom was observed during onset of monsoon and persisted till the end of monsoon. The break period in monsoon altered the phytoplankton community leading to mixed species bloom of large-sized diatoms and harmful dinoflagellates (Gymnodinium catenatum and Cochlodinium polykrikoides) under high-saline, nutrient-poor, non-stratified, and transparent water column. Such variations in community should be considered for better understanding the biogeochemistry of monsoon-influenced tropical estuaries. The dominance of Skeletonema is determined positively by the extent of low-saline stratified condition whereas most of the observed taxa were favored by high-saline, nutrient-poor, and transparent waters.

  4. On the anomalous precipitation enhancement over the Himalayan foothills during monsoon breaks

    NASA Astrophysics Data System (ADS)

    Vellore, Ramesh K.; Krishnan, R.; Pendharkar, Jayant; Choudhury, Ayantika Dey; Sabin, T. P.

    2014-10-01

    An intriguing feature associated with `breaks' in the Indian summer monsoon is the occurrence of intense/flood-producing precipitation confined to central-eastern parts of the Himalayan (CEH) foothills and north-eastern parts of India. Past studies have documented various large-scale circulation aspects associated with monsoon-breaks, however the dynamical mechanisms responsible for anomalous precipitation enhancement over CEH foothills remain unclear. This problem is investigated using diagnostic analyses of observed and reanalysis products and high-resolution model simulations. The present findings show that the anomalous precipitation enhancement over the CEH foothills during monsoon-breaks emerges as a consequence of interactions between southward intruding mid-latitude westerly troughs and the South Asian monsoon circulation in its weak phase. These interactions facilitate intensification of mid-tropospheric cyclonic vorticity and strong ascending motion over the CEH foothills, so as to promote deep convection and concentrated rainfall activity over the region during monsoon-breaks. Mesoscale orographic effects additionally tend to amplify the vertical motions and precipitation over the CEH foothills as evidenced from the high-resolution model simulations. It is further noted from the model simulations that the coupling between precipitation and circulation during monsoon-breaks can produce nearly a threefold increase of total precipitation over the CEH foothills and neighborhood as opposed to active-monsoon conditions.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    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.

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

    PubMed

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

    2016-02-09

    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.

  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. Elucidation of the tidal influence on bacterial populations in a monsoon influenced estuary through simultaneous observations.

    PubMed

    Khandeparker, Lidita; Eswaran, Ranjith; Gardade, Laxman; Kuchi, Nishanth; Mapari, Kaushal; Naik, Sneha D; Anil, Arga Chandrashekar

    2017-01-01

    The influence of tides on bacterial populations in a monsoon influenced tropical estuary was assessed through fine resolution sampling (1 to 3 h) during spring and neap tides from mouth to the freshwater end at four stations during pre-monsoon, monsoon and post-monsoon seasons. Higher abundance of total bacterial count (TBC) in surface water near the river mouth, compared to the upstream, during pre-monsoon was followed by an opposite scenario during the monsoon When seasonally compared, it was during the post-monsoon season when TBC in surface water was highest, with simultaneous decrease in their count in the river sediment. The total viable bacterial count (TVC) was influenced by the depth-wise stratification of salinity, which varied with tidal fluctuation, usually high and low during the neap and spring tides respectively. The abundance of both the autochthonous Vibrio spp. and allochthonous coliform bacteria was influenced by the concentrations of dissolved nutrients and suspended particulate matter (SPM). It is concluded that depending on the interplay of riverine discharge and tidal amplitude, sediment re-suspension mediated increase in SPM significantly regulates bacteria populations in the estuarine water, urging the need of systematic regular monitoring for better prediction of related hazards, including those associated with the rise in pathogenic Vibrio spp. in the changing climatic scenarios.

  10. 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

  11. Global warming and South Indian monsoon rainfall-lessons from the Mid-Miocene.

    PubMed

    Reuter, Markus; Kern, Andrea K; Harzhauser, Mathias; Kroh, Andreas; Piller, Werner E

    2013-04-01

    Precipitation over India is driven by the Indian monsoon. Although changes in this atmospheric circulation are caused by the differential seasonal diabatic heating of Asia and the Indo-Pacific Ocean, it is so far unknown how global warming influences the monsoon rainfalls regionally. Herein, we present a Miocene pollen flora as the first direct proxy for monsoon over southern India during the Middle Miocene Climate Optimum. To identify climatic key parameters, such as mean annual temperature, warmest month temperature, coldest month temperature, mean annual precipitation, mean precipitation during the driest month, mean precipitation during the wettest month and mean precipitation during the warmest month the Coexistence Approach is applied. Irrespective of a ~ 3-4 °C higher global temperature during the Middle Miocene Climate Optimum, the results indicate a modern-like monsoonal precipitation pattern contrasting marine proxies which point to a strong decline of Indian monsoon in the Himalaya at this time. Therefore, the strength of monsoon rainfall in tropical India appears neither to be related to global warming nor to be linked with the atmospheric conditions over the Tibetan Plateau. For the future it implies that increased global warming does not necessarily entail changes in the South Indian monsoon rainfall.

  12. Global warming and South Indian monsoon rainfall—lessons from the Mid-Miocene

    PubMed Central

    Reuter, Markus; Kern, Andrea K.; Harzhauser, Mathias; Kroh, Andreas; Piller, Werner E.

    2013-01-01

    Precipitation over India is driven by the Indian monsoon. Although changes in this atmospheric circulation are caused by the differential seasonal diabatic heating of Asia and the Indo-Pacific Ocean, it is so far unknown how global warming influences the monsoon rainfalls regionally. Herein, we present a Miocene pollen flora as the first direct proxy for monsoon over southern India during the Middle Miocene Climate Optimum. To identify climatic key parameters, such as mean annual temperature, warmest month temperature, coldest month temperature, mean annual precipitation, mean precipitation during the driest month, mean precipitation during the wettest month and mean precipitation during the warmest month the Coexistence Approach is applied. Irrespective of a ~ 3–4 °C higher global temperature during the Middle Miocene Climate Optimum, the results indicate a modern-like monsoonal precipitation pattern contrasting marine proxies which point to a strong decline of Indian monsoon in the Himalaya at this time. Therefore, the strength of monsoon rainfall in tropical India appears neither to be related to global warming nor to be linked with the atmospheric conditions over the Tibetan Plateau. For the future it implies that increased global warming does not necessarily entail changes in the South Indian monsoon rainfall. PMID:27087778

  13. 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

    2017-03-01

    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.

  14. Attribution of aerosol radiative forcing over India during the winter monsoon to emissions from source categories and geographical regions

    NASA Astrophysics Data System (ADS)

    Verma, S.; Venkataraman, C.; Boucher, O.

    2011-08-01

    We examine the aerosol radiative effects due to aerosols emitted from different emission sectors (anthropogenic and natural) and originating from different geographical regions within and outside India during the northeast (NE) Indian winter monsoon (January-March). These studies are carried out through aerosol transport simulations in the general circulation (GCM) model of the Laboratoire de Météorologie Dynamique (LMD). The model estimates of aerosol single scattering albedo (SSA) show lower values (0.86-0.92) over the region north to 10°N comprising of the Indian subcontinent, Bay of Bengal, and parts of the Arabian Sea compared to the region south to 10°N where the estimated SSA values lie in the range 0.94-0.98. The model estimated SSA is consistent with the SSA values inferred through measurements on various platforms. Aerosols of anthropogenic origin reduce the incoming solar radiation at the surface by a factor of 10-20 times the reduction due to natural aerosols. At the top-of-atmosphere (TOA), aerosols from biofuel use cause positive forcing compared to the negative forcing from fossil fuel and natural sources in correspondence with the distribution of SSA which is estimated to be the lowest (0.7-0.78) from biofuel combustion emissions. Aerosols originating from India and Africa-west Asia lead to the reduction in surface radiation (-3 to -8 W m -2) by 40-60% of the total reduction in surface radiation due to all aerosols over the Indian subcontinent and adjoining ocean. Aerosols originating from India and Africa-west Asia also lead to positive radiative effects at TOA over the Arabian Sea, central India (CNI), with the highest positive radiative effects over the Bay of Bengal and cause either negative or positive effects over the Indo-Gangetic plain (IGP).

  15. Internet Performance to Africa

    SciTech Connect

    Cottrell, L

    2003-10-01

    We report the first results ever for real-time Internet performance to Africa using the PingER methodology. Multiple monitoring hosts were used to enable comparisons with performance from different parts of the world. From these preliminary measurements, we have found that Internet packet losses to some African sites in recent months range from very poor to bad (> 12%), some getting better, others are holding steady or getting worse. This, together with the average monthly Round Trip Times, imply end-to-end maximum TCP throughputs that are order of magnitudes different between countries in the region. Africa is shown to be far from the Internet performance in industrialized nations due to the poor infrastructure in place today. These monitoring efforts can provide valuable information to analyze the relative rates of future improvement and today they help us to quantify the digital divide and can provide quantitative information to policy makers.

  16. Tuberculosis in tropical Africa

    PubMed Central

    Roelsgaard, E.; Iversen, E.; Bløcher, C.

    1964-01-01

    Up to the end of the nineteenth century the tubercle bacillus apparently had little opportunity of disseminating among the rather isolated tribes of tropical Africa. With the creation of large centres of trade and industry in the wake of European colonization, tuberculosis seems to have spread rapidly over the continent and is today found everywhere. In a number of tuberculosis prevalence surveys conducted by WHO during 1955-60, randomly selected population groups were tuberculin tested, X-rayed and had sputa examined by direct microscopy. The three methods of examination were applied independently of one another. Data collected during the surveys have been analysed with a view to discovering common epidemiological features of tuberculosis in tropical Africa, assessing the reliability of the diagnostic methods employed and discussing their usefulness in future tuberculosis control programmes. PMID:14178027

  17. 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.

  18. 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

  19. Dominating Controls for Wetter South Asian Summer Monsoon in the Twenty-First Century

    DOE PAGES

    Mei, Rui; Ashfaq, Moetasim; Rastogi, Deeksha; ...

    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

  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. Simulation of the northern summer monsoon in the ECMWF model: Sensitivity to horizontal resolution

    SciTech Connect

    Sperber, K.R.; Potter, G.L.; Boyle, J.S.; Hameed, S.

    1994-11-01

    The ability of the ECMWF model (cycle 33) to simulate the Indian and East Asian summer monsoons is evaluated at four different horizontal resolutions: T21, T42, T63, and T106. Generally, with respect to the large-scale features of the circulation, the largest differences among the simulations occur at T42 relative to T21. However, on regional scales, important differences among the high-frequency temporal variability serve as a further critical test of the model`s ability to simulate the monsoon. T106 best captures both the spatial and temporal characteristics of the Indian and East Asian monsoons, whereas T42 fails to correctly simulate the sequence and development of synoptic-scale milestones that characterize the monsoon flow. In particular, T106 is superior at simulating the development and migration of the monsoon trough over the Bay of Bengal. In the T42 simulation, the development of the monsoon occurs one month earlier than typically observed. At this time the trough is incorrectly located adjacent to the east coast of India, which results in an underestimate of precipitation over the Burma-Thailand region. This early establishment of the monsoon trough affects the evolution of the East Asian monsoon and yields excessive preseason rainfall over the Mei-yu-region. EOF analysis of precipitation over China indicates that T106 best simulates the Mei-yu mode of variability, which is associated with an oscillation of the rainband that gives rise to periods of Mei-yu mode of variability, which is associated with an oscillation of the rainband that gives rise to periods of enhanced rainfall over the Yangtze River valley. The coarse resolution of T21 precludes simulation of the aforementioned regional-scale monsoon flows. 43 refs., 14 figs.

  2. 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.

  3. 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).

  4. 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.

  5. 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.

  6. 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.

  7. The effects of monsoons and climate teleconnections on the Niangziguan Karst Spring discharge in North China

    NASA Astrophysics Data System (ADS)

    Zhang, Juan; Hao, Yonghong; Hu, Bill X.; Huo, Xueli; Hao, Pengmei; Liu, Zhongfang

    2017-01-01

    Karst aquifers supply drinking water for 25 % of the world's population, and they are, however, vulnerable to climate change. This study is aimed to investigate the effects of various monsoons and teleconnection patterns on Niangziguan Karst Spring (NKS) discharge in North China for sustainable exploration of the karst groundwater resources. The monsoons studied include the Indian Summer Monsoon, the West North Pacific Monsoon and the East Asian Summer Monsoon. The climate teleconnection patterns explored include the Indian Ocean Dipole, E1 Niño Southern Oscillation, and the Pacific Decadal Oscillation. The wavelet transform and wavelet coherence methods are used to analyze the karst hydrological processes in the NKS Basin, and reveal the relations between the climate indices with precipitation and the spring discharge. The study results indicate that both the monsoons and the climate teleconnections significantly affect precipitation in the NKS Basin. The time scales that the monsoons resonate with precipitation are strongly concentrated on the time scales of 0.5-, 1-, 2.5- and 3.5-year, and that climate teleconnections resonate with precipitation are relatively weak and diverged from 0.5-, 1-, 2-, 2.5-, to 8-year time scales, respectively. Because the climate signals have to overcome the resistance of heterogeneous aquifers before reaching spring discharge, with high energy, the strong climate signals (e.g. monsoons) are able to penetrate through aquifers and act on spring discharge. So the spring discharge is more strongly affected by monsoons than the climate teleconnections. During the groundwater flow process, the precipitation signals will be attenuated, delayed, merged, and changed by karst aquifers. Therefore, the coherence coefficients between the spring discharge and climate indices are smaller than those between precipitation and climate indices. Further, the fluctuation of the spring discharge is not coincident with that of precipitation in most

  8. Terrorism in South Africa.

    PubMed

    MacFarlane, Campbell

    2003-01-01

    The Republic of South Africa lies at the southern tip of the African continent. The population encompasses a variety of races, ethnic groups, religions, and cultural identities. The country has had a turbulent history from early tribal conflicts, colonialisation, the apartheid period, and post-apartheid readjustment. Modern terrorism developed mainly during the apartheid period, both by activities of the state and by the liberation movements that continued to the time of the first democratic elections in 1994, which saw South Africa evolve into a fully representative democratic state with equal rights for all. Since 1994, terrorist acts have been criminal-based, evolving in the Cape Town area to political acts, largely laid at the feet of a predominantly Muslim organisation, People against Gangsterism and Drugs, a vigilant organisation allegedly infiltrated by Muslim fundamentalists. Along with this, has been terrorist activities, mainly bombings by disaffected members of white, right-wing groups. In the apartheid era, a Draconian series of laws was enacted to suppress liberation activities. After 1994, most of these were repealed and new legislation was enacted, particularly after the events of 11 September 2001; this legislation allows the government to act against terrorism within the constraints of a democratic system. Disaster management in South Africa has been largely local authority-based, with input from provincial authorities and Civil Defence. After 1994, attempts were made to improve this situation, and national direction was provided. After 11 September 2001, activity was increased and the Disaster Management Act 2002 was brought into effect. This standardized disaster management system at national, provincial, and local levels, also facilites risk assessment and limitation as well as disaster mitigation. The potential still exists for terrorism, mainly from right-wing and Muslim fundamentalist groups, but the new legislation should stimulate disaster

  9. Mozambique Coast, Africa

    NASA Technical Reports Server (NTRS)

    1983-01-01

    The serene coastline of Mozambique (17.0S, 39.5E) Africa and the Indian Ocean offer some of the best beaches and recreational diving water in the world. Offshore reefs provide interesting coral formations that host a wide variety of marine life. Inland, the coastal savannas of this tropical nation are filled with a wide range of wildlife in some of the last animal refuges on the African continent.

  10. The Dragon Enters Africa

    DTIC Science & Technology

    2011-05-04

    1950s. China’s establishment of modern relations with Africa started with the 1955 Bandung Conference where 29 developing nations, including China and a...few Af1ican nations, met to show solidarity by denouncing neocolonialism and pledging to stand up to the western powers. 2 The Bandung Conference ...problems; The report caused western banks and loan agencies to bail on a donor’s conference scheduled for July of 2002. The collapse of the donor’s

  11. Islamic Militancy in Africa

    DTIC Science & Technology

    2012-11-01

    has also actively resisted Western influences—seen as negatively affecting Muslims ’ religiosity .3 Both al Shabaab and Boko Haram have their roots in...focused on local concerns. u Islamic militant organizations in Africa generally only command the support of small minorities within Muslim communities...educated activist, inspired by the Islamist Muslim Students’ Society of Nigeria1 (MSSN), formed in 1954, and in particular Ibrahim al Zakzaki, as

  12. Lake Chad, Chad, Africa

    NASA Technical Reports Server (NTRS)

    1988-01-01

    The fluctuating water levels of Lake Chad, (13.0N, 15.0E) at the intersection of the borders of Chad, Niger and Cameroon in the Sahara Desert, is an index of the drought in Africa. The lake level continues to decrease as indicated by the growing number and extent of emerging islands as previously submerged ancient sand dunes become visible. The water impounded between the dunes is probably because of local rainfall rather than a reversal of desertification.

  13. France in Black Africa,

    DTIC Science & Technology

    1989-01-01

    disease and the lack of support from the metropole (mother 4 France Acquires and Adninisters an Empire country), French rule over the small...as socially 9 France in Black Africa undesirable in an officer corps still dominated by the aristocracy; they were apt to be republicans, anticler- ics ...the interior. Endemic tropical diseases like yellow fever and malaria claimed a high proportion of Europeans who attempted to live in this region up to

  14. Epilepsy: Asia versus Africa.

    PubMed

    Bhalla, Devender; Tchalla, Achille Edem; Marin, Benoît; Ngoungou, Edgard Brice; Tan, Chong Tin; Preux, Pierre-Marie

    2014-09-01

    Is epilepsy truly an "African ailment"? We aimed to determine this, since international health agencies often refer to epilepsy as an African disease and the scientific literature has spoken the same tone. Various published materials, mainly reports, articles, were used to gather Asian and African evidence on various aspects of epilepsy and many of its risk and associated factors. Our results suggest that in no way can epilepsy be considered as an African ailment and such characterization is most likely based on popular beliefs rather than scientific evidence. In comparison to Africa, Asia has a 5.0% greater burden from all diseases, and is 17.0% more affected from neuropsychiatric disorders (that include epilepsy). Given that more countries in Asia are transitioning, there may be large demographic and lifestyle changes in the near future. However these changes are nowhere close to those expected in Africa. Moreover, 23 million Asians have epilepsy in comparison to 3.3 million Africans and 1.2 million sub-Saharan Africans. In comparison to Africa, Asia has more untreated patients, 55.0% more additional epilepsy cases every year, because of its larger population, with greater treatment cost and possibly higher premature mortality. Of several associated factors discussed herein, many have more importance for Asia than Africa. The current state of epilepsy in Asia is far less than ideal and there is an urgent need to recognize and accept the importance of epilepsy in Asia. In no way can epilepsy be considered as an African ailment. This is most likely based on popular beliefs rather than scientific evidence. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.

  15. Astrophysics in Southern Africa

    NASA Astrophysics Data System (ADS)

    Whitelock, Patricia

    2008-03-01

    The government of South Africa has identified astronomy as a field in which their country has a strategic advantage and is consequently investing very significantly in astronomical infrastructure. South Africa now operates a 10-m class optical telescope, the Southern African Large Telescope (SALT), and is one of two countries short listed to host the Square Kilometre Array (SKA), an ambitious international project to construct a radio telescope with a sensitivity one hundred times that of any existing telescope. The challenge now is to produce an indigenous community of users for these facilities, particularly from among the black population which was severely disadvantaged under the apartheid regime. In this paper I briefly describe the observing facilities in Southern Africa before going on to discuss the various collaborations that are allowing us to use astronomy as a tool for development, and at the same time to train a new generation of astronomers who will be well grounded in the science and linked to their colleagues internationally.

  16. Astronomy Across Africa

    NASA Astrophysics Data System (ADS)

    Williams, Ted

    2014-01-01

    African astronomy is growing rapidly. The Southern African Large Telescope is the largest optical telescope in the southern hemisphere, MeerKat and the Square Kilometer Array will revolutionize radio astronomy in the coming decade, and Namibia hosts HESS II, the world’s largest gamma-ray telescope. A growing community of observational and theoretical astronomers utilizes these multi-wavelength observational facilities. The largest concentrations of researchers are in southern Africa, but the community is now expanding across the continent. Substantial resources are being invested in developing the next generation of African astronomers. The African Astronomical Society was formed in 2011 to foster and coordinate the growth of the science in Africa. The IAU has located its global Office of Astronomy for Development in South Africa, with the mandate to find innovative ways of using astronomy to promote social and educational development around the world. African astronomy offers abundant opportunities for collaborative research with colleagues from across the globe. This special session will introduce many of the aspects of African astronomy to the US community, with the aim of engendering new partnerships and strengthening existing ones.

  17. Dermatophytosis in northern Africa.

    PubMed

    Nweze, E I; Eke, I

    2016-03-01

    Infections caused by dermatophytes are a global problem and a major public health burden in the world today. In Africa, especially in the northern geographical zone, dermatophytic infections are being reported at an alarming rate. This is mostly because of some local but unique cultural practices, socioeconomic and environmental conditions, lack of reliable diagnostic personnel and facilities and ineffective treatment. Interestingly, the pathogen spectrum and the clinical manifestation are most times different from what is seen in other continents. Several epidemiological studies have been performed on the incidence and aetiology of dermatophytoses in northern Africa. However, there is currently no review article with up-to-date information on the relevant findings reported so far in this region. This information is necessary for clinicians who treat dermatophytic infections all over the world since agents of dermatophytes are no longer restricted because of the rapid mobility of humans from one part of the world to another. Moreover, the epidemiology of dermatophytoses is known to change over time, thus requiring the update of information from time to time. A review of relevant studies published on dermatophytoses in northern Africa is presented. This covers all of old Sudan, Algeria, Egypt, Libya, Tunisia and Morocco.

  18. [Epidemic typhus in Africa].

    PubMed

    Ndihokubwayo, J B; Raoult, D

    1999-01-01

    Epidemic typhus is caused by a small strictly intracellular virus named Rickettsia prowazekii, a member of the Rickettsial family. It is transmitted to man by the body louse, Pediculus humanus. Although now rare in Western countries, exanthematic typhus remains common in the Southern hemisphere due to poverty, inadequate clothing hygiene, and poor socioeconomic conditions. In Africa, outbreaks have historically occurred in Burundi, Rwanda, southwest Ouganda, and Ethiopia. The largest outbreak of epidemic typhus since the World War II was reported in Burundi where ongoing civil war since October 1993 has forced 10 p. 100 of the population of Burundi to live in cold, promiscuity, and malnutrition of makeshift refugee camps. The purpose of this report based on our two-year experience working with this unfortunate population is to describe the characteristics of this disease in Africa where the epidemic form had become rare until recently. Indeed political unrest as well as numerous civil wars are now epidmiological factors favorizing outbreaks of epidemic typhus at any time. This overview also provides an opportunity to recall epidemiological, bacteriological, and clinical aspects of typhus as well as diagnosis and treatment of the disease in the context of Africa.

  19. Drought in West Africa

    NASA Technical Reports Server (NTRS)

    2007-01-01

    Drought settled over West Africa's Ivory Coast region when wet season rains came late in 2007. Instead of beginning in February, the rainy season didn't start until March, and steady rains didn't start until late March, said the Famine Early Warning System Network. Though the rain had started to alleviate the drought, vegetation was still depressed in parts of Cote d'Ivoire (Ivory Coast) between March 22 and April 6, 2007, when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured the data used to make this image. The image shows current vegetation conditions compared to average conditions recorded since 2000. Areas where plants are growing more slowly or more sparsely than average are brown, while areas where vegetation is denser than average are green. The brown tint that dominates the image indicates that plants through most of the country are more sparse than normal. Among the crops affected by the lack of rain was West Africa's cocoa crop. About 70 percent of the world's cocoa comes from West Africa, and Cote d'Ivoire is a top grower, said Reuters. Cocoa prices climbed as the crop fell short. Farmers called the drought the worst in living memory, Reuters said. The delay in rainfall also led to water shortages in parts of Cote d'Ivoire, according to the United Nations Office for the Coordination of Humanitarian Affairs.

  20. 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.

  1. 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.

  2. 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

  3. An Indian Ocean precursor for Indian summer monsoon rainfall variability

    NASA Astrophysics Data System (ADS)

    Sreejith, O. P.; Panickal, S.; Pai, S.; Rajeevan, M.

    2015-11-01

    The Indian summer monsoon rainfall (ISMR) depicts large interannual variability strongly linked with El Niño-Southern Oscillation (ENSO). However, many of the El Niño years were not accompanied by deficient ISMR. The results from the study reveal the significant role of coupled air-sea interaction over the tropical Indian Ocean (IO) in modifying the ENSO-ISMR association. The IO warm water volume (WWV), a measure of heat content variations in the equatorial IO has strong influence on ISMR. A deepening (shoaling) of thermocline in the eastern equatorial IO (EEIO) during late boreal spring (April-May) accompanied by increase (decrease) in WWV anomalies weaken (enhance) the ISMR by enhancing (suppressing) the convection over EEIO resulting in the below (above) normal ISMR. Thus, the changes in the WWV anomalies in the EEIO along with ENSO conditions during boreal spring can be considered as a precursor for the performance of subsequent ISMR.

  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. 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.

  7. 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.

  8. Urbanization causes nonstationarity in Indian Summer Monsoon Rainfall extremes

    NASA Astrophysics Data System (ADS)

    Singh, Jitendra; Vittal, H.; Karmakar, Subhankar; Ghosh, Subimal; Niyogi, Dev

    2016-11-01

    Global and local environmental changes are likely to introduce nonstationarity in the characteristics of Indian Summer Monsoon Rainfall (ISMR) extremes. Here we perform a nonstationary frequency analysis on ISMR extremes in a Generalized Additive Model for Location, Scale and Shape framework with a cluster of 74 models, considering nonstationarity in different possible combinations. Interestingly, we observe significant nonstationarity in ISMR extremes in urbanizing/developing-urban areas (transitioning from rural to urban), compared to completely urbanized or rural areas. This presents a postulation that the extent of urbanization plays a significant role in introducing nonstationarity in ISMR extremes. We emphasize the effect of urbanization in changing the character of ISMR extremes, which further needs a scientific re-evaluation by implementing physics-based modeling. The impact of these observational studies will be critical in correcting the bias of model projections of ISMR.

  9. Late Holocene climate reorganisation and the North American Monsoon

    NASA Astrophysics Data System (ADS)

    Jones, Matthew D.; Metcalfe, Sarah E.; Davies, Sarah J.; Noren, Anders

    2015-09-01

    The North American Monsoon (NAM) provides the majority of rainfall for central and northern Mexico as well as parts of the south west USA. The controls over the strength of the NAM in a given year are complex, and include both Pacific and Atlantic systems. We present here an annually resolved proxy reconstruction of NAM rainfall variability over the last ˜6 ka, from an inwash record from the Laguna de Juanacatlán, Mexico. This high resolution, exceptionally well dated record allows changes in the NAM through the latter half of the Holocene to be investigated in both time and space domains, improving our understanding of the controls on the system. Our analysis shows a shift in conditions between c. 4 and 3 ka BP, after which clear ENSO/PDO type forcing patterns are evident.

  10. 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

  11. Impacts of enhanced CCN on the organization of convection and recent reduced counts of monsoon depressions

    NASA Astrophysics Data System (ADS)

    Krishnamurti, T. N.; Martin, Andrew; Krishnamurti, Ruby; Simon, Anu; Thomas, Aype; Kumar, Vinay

    2012-11-01

    Monsoon depressions, that form during the Indian summer monsoon season (June to September) are known to be baroclinic disturbances (horizontal scale 2000 to 3000 km) and are driven by deep convection that carries a very large vertical slope towards cold air aloft in the upper troposphere. Deep convection is nearly always organized around the scale of these depressions. In the maintenance of the monsoon depression the generation of eddy kinetic energy on the scale of the monsoon depression is largely governed by the "in scale" covariance of heating and temperature and of vertical velocity and temperature over the region of the monsoon depression. There are normally about 6 to 8 monsoon depressions during a summer monsoon season. Recent years 2009, 2010 and 2011 saw very few (around 1, 0 and 1 per season respectively). The best numerical models such as those from ECMWF and US (GFS) carried many false alarms in their 3 to 5 day forecasts, more like 6 to 8 disturbances. Even in recent years with fewer observed monsoon depressions a much larger number of depressions is noted in ECMWF forecasts. These are fairly comprehensive models that carry vast data sets (surface and satellite based), detailed data assimilation, and are run at very high resolutions. The monsoon depression is well resolved by these respective horizontal resolutions in these models (at 15 and 35km). These models carry complete and detailed physical parameterizations. The false alarms in their forecasts leads us to suggest that some additional important ingredient may be missing in these current best state of the art models. This paper addresses the effects of pollution for the enhancement of cloud condensation nuclei and the resulting disruption of the organization of convection in monsoon depressions. Our specific studies make use of a high resolution mesoscale model (WRF/CHEM) to explore the impacts of the first and second aerosol indirect effects proposed by Twomey and Albrecht. We have conducted

  12. Impacts of enhanced CCN on the organization of convection and recent reduced counts of monsoon depressions

    NASA Astrophysics Data System (ADS)

    Krishnamurti, T. N.; Martin, Andrew; Krishnamurti, Ruby; Simon, Anu; Thomas, Aype; Kumar, Vinay

    2013-07-01

    Monsoon depressions, that form during the Indian summer monsoon season (June to September) are known to be baroclinic disturbances (horizontal scale 2,000-3,000 km) and are driven by deep convection that carries a very large vertical slope towards cold air aloft in the upper troposphere. Deep convection is nearly always organized around the scale of these depressions. In the maintenance of the monsoon depression the generation of eddy kinetic energy on the scale of the monsoon depression is largely governed by the "in scale" covariance of heating and temperature and of vertical velocity and temperature over the region of the monsoon depression. There are normally about 6-8 monsoon depressions during a summer monsoon season. Recent years 2009, 2010 and 2011 saw very few (around 1, 0 and 1 per season respectively). The best numerical models such as those from ECMWF and US (GFS) carried many false alarms in their 3-5 day forecasts, more like 6-8 disturbances. Even in recent years with fewer observed monsoon depressions a much larger number of depressions is noted in ECMWF forecasts. These are fairly comprehensive models that carry vast data sets (surface and satellite based), detailed data assimilation, and are run at very high resolutions. The monsoon depression is well resolved by these respective horizontal resolutions in these models (at 15 and 35 km). These models carry complete and detailed physical parameterizations. The false alarms in their forecasts leads us to suggest that some additional important ingredient may be missing in these current best state of the art models. This paper addresses the effects of pollution for the enhancement of cloud condensation nuclei and the resulting disruption of the organization of convection in monsoon depressions. Our specific studies make use of a high resolution mesoscale model (WRF/CHEM) to explore the impacts of the first and second aerosol indirect effects proposed by Twomey and Albrecht. We have conducted preliminary

  13. 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.

  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. Black carbon in cloud-water and rain water during monsoon season at a high altitude station in India

    NASA Astrophysics Data System (ADS)

    Budhavant, K. B.; Rao, P. S. P.; Safai, P. D.; Leck, C.; Rodhe, H.

    2016-03-01

    We present results of measurements of black carbon (BC) from ground-based wet-only rainwater (RW) and cloud-water (CW) sampling at a mountain field station, Sinhagad, situated in south western India during the period from June 2008 to October 2010. The amount of BC in the sample was determined by photometry at a wavelength of 528 nm after a procedure including the filtration through a 0.4 μm polycarbonate membrane filter. Water soluble concentrations of major anions in RW and CW were also determined. The average concentration of BC in RW (16 μmol dm-3) is higher by at least a factor 2 than that found in similar studies reported from other parts of the world. On the other hand, the average concentration of BC in CW (47 μmol dm-3) is lower by about a factor of 2 than that found at other sites. The ratio between the average concentrations in CW and RW varies from 2 (K+) to 7 (SO42-). The ratio for BC was about 3. No significant difference was observed for pH. Analysis of air mass back trajectories and of correlations between the various components indicates that long range transport of pollutants and dust from East Africa and Southern part of the Arabian peninsula might contribute to the high concentrations of BC and some of the ionic constituents at Sinhagad during the monsoon season.

  16. Downscaling GISS ModelE boreal summer climate over Africa

    NASA Astrophysics Data System (ADS)

    Druyan, Leonard M.; Fulakeza, Matthew

    2016-12-01

    The study examines the perceived added value of downscaling atmosphere-ocean global climate model simulations over Africa and adjacent oceans by a nested regional climate model. NASA/Goddard Institute for Space Studies (GISS) coupled ModelE simulations for June-September 1998-2002 are used to form lateral boundary conditions for synchronous simulations by the GISS RM3 regional climate model. The ModelE computational grid spacing is 2° latitude by 2.5° longitude and the RM3 grid spacing is 0.44°. ModelE precipitation climatology for June-September 1998-2002 is shown to be a good proxy for 30-year means so results based on the 5-year sample are presumed to be generally representative. Comparison with observational evidence shows several discrepancies in ModelE configuration of the boreal summer inter-tropical convergence zone (ITCZ). One glaring shortcoming is that ModelE simulations do not advance the West African rain band northward during the summer to represent monsoon precipitation onset over the Sahel. Results for 1998-2002 show that onset simulation is an important added value produced by downscaling with RM3. ModelE Eastern South Atlantic Ocean computed sea-surface temperatures (SST) are some 4 K warmer than reanalysis, contributing to large positive biases in overlying surface air temperatures (Tsfc). ModelE Tsfc are also too warm over most of Africa. RM3 downscaling somewhat mitigates the magnitude of Tsfc biases over the African continent, it eliminates the ModelE double ITCZ over the Atlantic and it produces more realistic orographic precipitation maxima. Parallel ModelE and RM3 simulations with observed SST forcing (in place of the predicted ocean) lower Tsfc errors but have mixed impacts on circulation and precipitation biases. Downscaling improvements of the meridional movement of the rain band over West Africa and the configuration of orographic precipitation maxima are realized irrespective of the SST biases.

  17. Downscaling GISS ModelE Boreal Summer Climate over Africa

    NASA Technical Reports Server (NTRS)

    Druyan, Leonard M.; Fulakeza, Matthew

    2015-01-01

    The study examines the perceived added value of downscaling atmosphere-ocean global climate model simulations over Africa and adjacent oceans by a nested regional climate model. NASA/Goddard Institute for Space Studies (GISS) coupled ModelE simulations for June- September 1998-2002 are used to form lateral boundary conditions for synchronous simulations by the GISS RM3 regional climate model. The ModelE computational grid spacing is 2deg latitude by 2.5deg longitude and the RM3 grid spacing is 0.44deg. ModelE precipitation climatology for June-September 1998-2002 is shown to be a good proxy for 30-year means so results based on the 5-year sample are presumed to be generally representative. Comparison with observational evidence shows several discrepancies in ModelE configuration of the boreal summer inter-tropical convergence zone (ITCZ). One glaring shortcoming is that ModelE simulations do not advance the West African rain band northward during the summer to represent monsoon precipitation onset over the Sahel. Results for 1998-2002 show that onset simulation is an important added value produced by downscaling with RM3. ModelE Eastern South Atlantic Ocean computed sea-surface temperatures (SST) are some 4 K warmer than reanalysis, contributing to large positive biases in overlying surface air temperatures (Tsfc). ModelE Tsfc are also too warm over most of Africa. RM3 downscaling somewhat mitigates the magnitude of Tsfc biases over the African continent, it eliminates the ModelE double ITCZ over the Atlantic and it produces more realistic orographic precipitation maxima. Parallel ModelE and RM3 simulations with observed SST forcing (in place of the predicted ocean) lower Tsfc errors but have mixed impacts on circulation and precipitation biases. Downscaling improvements of the meridional movement of the rain band over West Africa and the configuration of orographic precipitation maxima are realized irrespective of the SST biases.

  18. 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.

  19. 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.

  20. 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.

  1. Response of the Water Cycle of West Africa and Atlantic to Radiative Forcing by Saharan Dust

    NASA Technical Reports Server (NTRS)

    Lau, K. M.; Kim, Kyu-Myong; Sud, Yogesh C.; Walker, Gregory L.

    2010-01-01

    The responses of the atmospheric water cycle and climate of West Africa and the Atlantic to radiative forcing of Saharan dust are studied using the NASA finite volume general circulation model (fvGCM), coupled to a mixed layer ocean. We find evidence in support of the "elevated heat pump" (EHP) mechanism that underlines the responses of the atmospheric water cycle to dust forcing as follow. During the boreal summer, as a result of large-scale atmospheric feed back triggered by absorbing dust aerosols, rainfall and cloudiness are enhanced over the West Africa/Easter Atlantic ITCZ, and suppressed over the West Atlantic and Caribbean. region. Shortwave radiation absorption by dust warms the atmosphere and cools the surface, while long wave has the opposite response. The elevated dust layer warms the air over Nest Africa and the eastern Atlantic. The condensation heating associated with the induced deep convection drives and maintains an anomalous large-scale east-west overturning circulation with rising motion over West Africa/eastern Atlantic, and sinking motion over the Caribbean region. The response also includes a strengthening of the West African monsoon, manifested in northward shift of the West Africa precipitation over land, increased low-level westerlies flow over West Africa at the southern edge of the dust layer, and a near surface energy fluxes, resulting in cooling of the Nest African land and the eastern Atlantic, and a warming in the West Atlantic and Caribbean. The EHP effect is most effective for moderate to highly absorbing dusts, and becomes minimized for reflecting dust with single scattering albedo at 0.95 or higher.

  2. Teleconnections between the subtropical monsoons and high-latitude climates during the last deglaciation

    SciTech Connect

    Sirocko, F.; Schonberg, D.G.; McIntyre A.

    1996-04-26

    The major deglacial intensification of the southwest monsoon occurred at 11,450 {+-} 150 calendar years before present, synchronous with a major climate transition as recorded in Greenland ice. An earlier event of monsoon intensification at 16,000 {+-} 150 calendar years before present occurred at the end of Heinrich layer 1 in the Atlantic and parallels the initial rise in global atmospheric methane concentrations and the first abrupt climate changes in the Antarctic; thus, the evolution of the monsoonal and high-latitude climates show teleconnections but hemispheric asymmetries. Superimposed on abrupt events, the monsoonal climate shows high-frequency variability of 1785-, 1450-, and 1150-year oscillations, and abrupt climate change seems to occur when at least two of these oscillations are in phase. 40 refs., 5 figs.

  3. 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.

  4. 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.

  5. 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).

  6. Massive Open Online Courses for Africa by Africa

    ERIC Educational Resources Information Center

    Oyo, Benedict; Kalema, Billy Mathias

    2014-01-01

    Africa is known for inadequate access to all sorts of human needs including health, education, food, shelter, transport, security, and energy. Before the emergence of massive open online courses (MOOCs), open access to higher education (HE) was exclusive of Africa. However, as a generally affordable method of post-secondary education delivery,…

  7. 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

  8. Mid-Late Holocene Asian monsoon variations recorded in the Lake Rara sediment, western Nepal

    NASA Astrophysics Data System (ADS)

    Nakamura, A.; Yokoyama, Y.; Maemoku, H.; Yagi, H.; Okamura, M.; Matsuoka, H.; Miyake, N.; Adhikari, D.; Dangol, V.; Miyairi, Y.; Obrochta, S.; Matsuzaki, H.; Ikehara, M.

    2011-12-01

    The Asian monsoon is an important component of the Earth's climate system to understand regional and global climate dynamics. While geological reconstructions indicate that the Asian summer monsoon intensity gradually decreased through the Holocene, a clear and coherent picture of millennial and centennial scale variability has yet to emerge (e.g., Overpeck and Cole, 2007). The Himalayas are a key location for understanding centennial to millennial scale variations in the Asian monsoon, yet few studies of the Holocene have been conducted in this sensitive area. Direct evidence for shifts in monsoonal wind strength is often limited to marine proxy records, while terrestrial reconstructions (e.g., lake levels and spleothems) focus on precipitation. Here, we present the first evidence of terrestrial summer monsoon wind strength changes from Lake Rara, western Nepal. The lake is located at 3,000m above sea level and has a maximum water depth of 168m. Lake Rara Mn/Ti data, a proxy for lake stratification, provide the first direct comparison of the Indian summer monsoon wind intensity between the terrestrial Himalayan region and the marine Arabian sea region (Gupta et al., 2003) during mid-late Holocene. Centennial to millennial scale variability found in those records are synchronous, with the weak wind intervals corresponding to drier periods of East Asian. Strong similarities between the Lake Rara monsoon record and the Dongge cave speleothems precipitation record (Wang et al., 2005) suggest that the influence of Indian summer monsoon penetrates into southeastern China, which should be taken into account when interpreting paleomonsoon reconstructions. Overpeck JT, Cole JE. 2007. Climate change - Lessons from a distant monsoon. Nature 445: 270-271. Gupta AK, Anderson DM, Overpeck JT. 2003. Abrupt changes in the Asian southwest monsoon during the Holocene and their links to the North Atlantic Ocean. Nature 421: 354-357. Wang YJ, Cheng H, Edwards RL, He YQ, Kong XG, An

  9. Mixing to Monsoons: Air-Sea Interactions in the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Lucas, A. J.; Shroyer, E. L.; Wijesekera, H. W.; Fernando, H. J. S.; D'Asaro, E.; Ravichandran, M.; Jinadasa, S. U. P.; MacKinnon, J. A.; Nash, J. D.; Sharma, R.; Centurioni, L.; Farrar, J. T.; Weller, R.; Pinkel, R.; Mahadevan, A.; Sengupta, D.; Tandon, A.

    2014-07-01

    More than 1 billion people depend on rainfall from the South Asian monsoon for their livelihoods. Summertime monsoonal precipitation is highly variable on intraseasonal time scales, with alternating "active" and "break" periods. These intraseasonal oscillations in large-scale atmospheric convection and winds are closely tied to 1°C-2°C variations of sea surface temperature in the Bay of Bengal.

  10. 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).

  11. GMMIP (v1.0) contribution to CMIP6: Global Monsoons Model Inter-comparison Project

    SciTech Connect

    Zhou, Tianjun; Turner, Andrew G.; Kinter, James L.; Wang, Bin; Qian, Yun; Chen, Xiaolong; Wu, Bo; Wang, Bin; Liu, Bo; Zou, Liwei; He, Bian

    2016-10-10

    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.

  12. Climate variability in a coupled GCM. Part II: The Indian Ocean and monsoon

    SciTech Connect

    Latif, M.; Sterl, A.; Assenbaum, M.; Junge, M.M.; Maier-Reimer, E.

    1994-10-01

    We have investigated the seasonal cycle and the interannual variability of the tropical Indian Ocean circulation and the Indian summer monsoon simulated by a coupled ocean-atmosphere general circulation model in a 26-year integration. Although the model exhibits significant climate drift, overall, the coupled GCM simulates realistically the seasonal changes in the tropical Indian Ocean and the onset and evolution of the Indian summer monsoon. The amplitudes of the seasonal changes, however, are underestimated. The coupled GCM also simulates considerable interannual variability in the tropical Indian Ocean circulation, which is partly related to the El Nino/Southern Oscillation phenomenon and the associated changes in the Walker circulation. Changes in the surface wind stress appear to be crucial in forcing interannual variations in the Indian Ocean SST. As in the Pacific Ocean, the net surface heat flux acts as a negative feedback on the SST anomalies. The interannual variability in monsoon rainfall, simulated by the coupled GCM, is only about half as strong as observed. The reason for this is that the simulated interannual variability in the Indian monsoon appears to be related to internal processes within the atmosphere only. In contrast, an investigation based on observations shows a clear lead-lag relationship between interannual variations in the monsoon rainfall and tropical Pacific SST anomalies. Furthermore, the atmospheric GCM also fails to reproduce this lead-lag relationship between monsoon rainfall and tropical Pacific SST when run in a stand-alone integration with observed SSTs prescribed during the period 1970-1988. These results indicate that important physical processes relating tropical Pacific SST to Indian monsoon rainfall are not adequately modeled in our atmospheric GCM. Monsoon rainfall predictions appear therefore premature. 24 refs., 13 figs, 2 tabs.

  13. 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.

  14. Hydrologic Processes Associated with the First Transition of the Asian Summer Monsoon: A TRMM Pilot Study

    NASA Technical Reports Server (NTRS)

    Lau, William K. M.

    1998-01-01

    We present results of a pilot study of the evolution of large scale hydrologic processes associated with the first transition of the Asian summer monsoon in conjunction with the launching of the South China Sea Monsoon Experiment (SCSMEX) in May, 1998. Using a combination of satellite-estimated rainfall, moisture, surface wind and sea surface temperature, we present some interesting and hitherto unknown features in large scale atmospheric and oceanic hydrologic processes associated with the fluctuation of the SCS monsoon. Results show that, climatologically, the SCS monsoon occurs during mid-May when major convection zone shifts from the eastern Indian Ocean/southern Indochina to the SCS. Simultaneously with the SCS monsoon onset is the development of a moist tongue and frontal rainband emanating from northern SCS, across southern China and the East China Sea to southern Japan as well as the enhancement of equatorial convection in the western Pacific ITCZ. Analysis of the satellite-derived moisture and rainfall show that the onset of the SCS monsoon during 1997 was preceded by the development of eastward propagating supercloud clusters over the Indian Ocean. The satellite data also reveal a strong onset vortex over the SCS and large scale cooling and warming patterns over the Indian Ocean and western Pacific. These features signal a major shift of the large-scale hydrologic cycle in the ocean-atmosphere system, which underpins the SCS monsoon onset. The paper concludes with a brief discussion of the observational platform of SCSMEX and a call for the utility of satellite data, field observations and models for comprehensive studies of the Asian monsoon.

  15. 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.

  16. 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

  17. AIDS in South Africa.

    PubMed

    Ijsselmuiden, C; Evian, C; Matjilla, J; Steinberg, M; Schneider, H

    1993-01-01

    The National AIDS Convention in South Africa (NACOSA) in October 1992 was the first real attempt to address HIV/AIDS. In Soweto, government, the African National Congress, nongovernmental organizations, and organized industry and labor representatives worked for 2 days to develop a national plan of action, but it did not result in a united effort to fight AIDS. The highest HIV infection rates in South Africa are among the KwaZulu in Natal, yet the Inkatha Freedom Party did not attend NACOSA. This episode exemplifies the key obstacles for South Africa to prevent and control AIDS. Inequality of access to health care may explain why health workers did not diagnose the first AIDS case in blacks until 1985. Migrant labor, Bantu education, and uprooted communities affect the epidemiology of HIV infection. Further, political and social polarization between blacks and whites contributes to a mindset that AIDS is limited to the other race which only diminishes the personal and collective sense of susceptibility and the volition and aptitude to act. The Department of National Health and Population Development's voluntary register of anonymously reported cases of AIDS specifies 1517 cumulative AIDS cases (October 1992), but this number is low. Seroprevalence studies show between 400,000-450,000 HIV positive cases. Public hospitals cannot give AIDS patients AZT and DDI. Few communities provided community-based care. Not all hospitals honor confidentiality and patients' need for autonomy. Even though HIV testing is not mandatory, it is required sometimes, e.g., HIV testing of immigrants. AIDS Training, Information and Counselling Centers are in urban areas, but not in poor areas where the need is most acute. The government just recently developed in AIDS education package for schools, but too many people consider it improper, so it is not being used. The poor quality education provided blacks would make it useless anyhow. Lifting of the academic boycott will allow South African

  18. Regions. [Africa, Middle East].

    PubMed

    1985-03-01

    This discussion of population focuses on the regions of Africa and the Middle East. In South Africa more white women are working but fewer black women work. The overall result is that the percentage of women who work is declining. Marita de Beer, research liaison executive at the South African Advertising Research Foundation, reports that the female population grew by 31% in the past 10 years while the number of working women has grown by only 11%. Among blacks the female population rose by 36%, but the number of workers among them declined by about 1%. Married women are among the fastest growing groups of working women in South Africa. The most recent estimate of the population of Nigeria is 92 million. According to Professor Vremudia Diejomaoh, Nigeria's population will probably reach 155 million by 2000 with 33% living in urban areas. In Saudi Arabia the Pan Arab Research Center recently completed a census of retail outlets in 3 metropolitan areas: Jeddah, Riyadh, and Dammam. The types of outlets surveyed include large supermarkets, small supermarkets, groceries with and without deep freeze, tobacco shops, meat shop/delis, small cafeterias, large restaurants/hotels, cosmetics shops or perfumeries, camera stores, toy shops, pharmacies, watch and gift shop, newsstands, department store, and appliance outlets. Using the Census of Retail Outlets as a base, Pan Arab Research Center also has a new distribution audit system that will cover 500 outlets. By plotting Arab countries according to their population policies and their current growth rates, it is possible to project where the middle class will grow fastest in the Arab world. The countries that have declining growth rates and strong population programs designed to encourage lower fertility rates among women are Egypt, Tunisia, Morocco, Algeria, and Lebanon. The countries most likely to have a better per capita distribution of resources within this decade are those where governments encourage reductions in

  19. Nutrition in Africa.

    PubMed

    Murray-lee, M

    1989-07-01

    Village women have adopted techniques set down by UNICEF in achieving higher food production and, ultimately, self sufficiency. Women's cooperatives integrate kitchen gardening and irrigated agriculture in an effort to combat the complex nutritional problems in Africa. Projects also offered training in a variety of areas including management of plots, labor-saving technology--diesel-driven grinding mills, rice husking, machines, wells with hand pumps, motor pumps for irrigation, all geared towards women benefitting themselves by growing their own food and furthering their children's health and development. Projects such as the one in Senegal were undertaken in other regions of Africa, like the Sahel and the Wadis--low-lying areas. From these projects, aid agencies and governments have suggested a number of recommendations in seeking a solution to Africa's nutritional problems. 1st, a balance between production of cash crops and food for consumption is called for. 2nd, research is necessary to improve the quality of locally grown food as much as livestock. 3rd, governments should extend surface area cultivation, 4th, more research on the advantage of indigenous food plants, 5th, women should be in on all levels of decision making in food production, 6th, governments should increase women farmer's efficiency, and further women's access to land and credit and 7th, women should be provided with increased educational opportunities. Nutrition in developing countries cannot be viewed as an isolated phenomenon--solutions to nutritional development should include all aspects of the problem including health and nutrition education, growth monitoring, water supply, literacy, technological know-how, and agricultural and plant and soil conservation.

  20. Zika virus outside Africa.

    PubMed

    Hayes, Edward B

    2009-09-01

    Zika virus (ZIKV) is a flavivirus related to yellow fever, dengue, West Nile, and Japanese encephalitis viruses. In 2007 ZIKV caused an outbreak of relatively mild disease characterized by rash, arthralgia, and conjunctivitis on Yap Island in the southwestern Pacific Ocean. This was the first time that ZIKV was detected outside of Africa and Asia. The history, transmission dynamics, virology, and clinical manifestations of ZIKV disease are discussed, along with the possibility for diagnostic confusion between ZIKV illness and dengue.The emergence of ZIKV outside of its previously known geographic range should prompt awareness of the potential for ZIKV to spread to other Pacific islands and the Americas.

  1. Fires in Central Africa

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Hundreds of fires are set every year during the dry season in Central Africa. This true color image from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) shows dozens of smoke plumes in the Democratic Republic of the Congo on June 29, 2000. Residents burn away scrub and brush annually in the woody savanna to clear land for farming and grazing. For more information, visit the SeaWiFS Home Page, Global Fire Monitoring Fact Sheet, and 4km2 Fire Data Image Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

  2. Anvil Clouds of Tropical Mesoscale Convective Systems in Monsoon Regions

    NASA Technical Reports Server (NTRS)

    Cetrone, J.; Houze, R. A., Jr.

    2009-01-01

    The anvil clouds of tropical mesoscale convective systems (MCSs) in West Africa, the Maritime Continent and the Bay of Bengal have been examined with TRMM and CloudSat satellite data and ARM ground-based radar observations. The anvils spreading out from the precipitating cores of MCSs are subdivided into thick, medium and thin portions. The thick portions of anvils show distinct differences from one climatological regime to another. In their upper portions, the thick anvils of West Africa MCSs have a broad, flat histogram of reflectivity, and a maximum of reflectivity in their lower portions. The reflectivity histogram of the Bay of Bengal thick anvils has a sharply peaked distribution of reflectivity at all altitudes with modal values that increase monotonically downward. The reflectivity histogram of the Maritime Continent thick anvils is intermediate between that of the West Africa and Bay of Bengal anvils, consistent with the fact this region comprises a mix of land and ocean influences. It is suggested that the difference between the statistics of the continental and oceanic anvils is related to some combination of two factors: (1) the West African anvils tend to be closely tied to the convective regions of MCSs while the oceanic anvils are more likely to be extending outward from large stratiform precipitation areas of MCSs, and (2) the West African MCSs result from greater buoyancy, so that the convective cells are more likely to produce graupel particles and detrain them into anvils

  3. 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.

  4. 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.

  5. 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.

  6. Evolution of the Asian monsoon from the Cretaceous to the modern - a modelling study.

    NASA Astrophysics Data System (ADS)

    Lunt, Dan; Farnsworth, Alex; Loptson, Claire; Markwick, Paul

    2014-05-01

    It has long been suggested that palaeogeography could have an important role in the modulation of the Asian monsoon. In particular, orogenesis associated with the Himalayas and Tibetan Plateau has been associated with the intensification of the Asian monsoon through the Neogene, a paradigm which has some support from both data and modelling studies. Here we go further by considering the evolution of the Asian monsoon over a much longer time period than ususally considered, namely, the early Cretaceous right through to the modern day. Through a series of more than 30 climate model simulations spanning 150 million years, we investigate how changing palaeogeography (continental distribution, mountain height, and bathymetry) has affected monsoon evolution. The palaeogeographies are provided by Getech Plc, and we use the HadCM3L climate model, developed by the UK Met Office. All simulations are run for more than 500 years from an identical initial state. We show that a monsoon system has existed in the western Pacific and Indian Ocean since the early Cretaceous, but that intense precipitation only began to penetrate onto the east Asian continent in the late Paleogene and early Eocene. As well as focussing on the Asian (or proto-Asian for the earliest Cretaceous) monsoon, we present the results in a global context.

  7. A tree-ring reconstruction of monsoon precipitation for the southwestern United States

    NASA Astrophysics Data System (ADS)

    Griffin, D.; Woodhouse, C. A.; Meko, D. M.; Touchan, R.; Leavitt, S. W.; Castro, C. L.

    2010-12-01

    The southwestern United States (SWUS) receives up to sixty percent of its annual precipitation from July-September in association with the North American monsoon system. However, because the SWUS is largely on the fringe of monsoon influence, warm-season precipitation across the region is highly variable on annual to decadal time scales. Although tree rings have revealed much about long-term moisture variability in this region’s westerly-driven winter climate regime, no dendroclimatic studies have systematically targeted the monsoon across the SWUS. Toward this end, the region’s first network of monsoon-sensitive chronologies is currently being developed, drawing on variability in the latewood (summer growth) of precisely dated tree rings. This study presents the first tree-ring reconstruction of monsoon (July-August) precipitation for southeastern Arizona and southwestern New Mexico, where the monsoon’s influence is most substantial in the SWUS. The long-term history of monsoon drought is characterized and contrasted with a reconstruction of winter (November-April) precipitation for the region. The widely discussed phase relationship between cool- and warm-season precipitation is examined and the reconstructions are analyzed in the frequency domain for evidence of amplified variance at wavelengths corresponding to the large-scale modes of climate thought to influence the region’s seasonal precipitation regimes.