Astronomical and Hydrological Perspective of Mountain Impacts on the Asian Summer Monsoon.

PubMed

He, Bian; Wu, Guoxiong; Liu, Yimin; Bao, Qing

2015-12-01

The Asian summer monsoon has great socioeconomic impacts. Understanding how the huge Tibetan and Iranian Plateaus affect the Asian summer monsoon is of great scientific value and has far-reaching significance for sustainable global development. One hypothesis considers the plateaus to be a shield for monsoon development in India by blocking cold-dry northerly intrusion into the tropics. Based on astronomical radiation analysis and numerical modeling, here we show that in winter the plateaus cannot block such a northerly intrusion; while in summer the daily solar radiation at the top of the atmosphere and at the surface, and the surface potential temperature to the north of the Tibetan Plateau, are higher than their counterparts to its south, and such plateau shielding is not needed. By virtue of hydrological analysis, we show that the high energy near the surface required for continental monsoon development is maintained mainly by high water vapor content. Results based on potential vorticity-potential temperature diagnosis further demonstrate that it is the pumping of water vapor from sea to land due to the thermal effects of the plateaus that breeds the Asian continental monsoon.

Summer Monsoon, Kalahari Desert, Africa

NASA Image and Video Library

1992-11-01

STS052-152-047 (22 Oct- 1 Nov 1992) --- The Kalahari Desert had not seen any significant rainfall for months before the launch of STS-52. Here, Shuttle astronauts have captured the onset of the (Southern Hemisphere) summer monsoon over the Kalahari Desert, as illustrated by the large thunderstorm towers poking up through the sun's terminator. The summer monsoon, with its associated thunderstorms, generally lasts from November through March. Scientist observers of this area report that the summer monsoon contributes most of the annual rainfall to this environmentally sensitive area. Shuttle nadir position: 28.0 degrees south, 25.1 degrees east. The center of the scene is 22.0 degrees south, 25.0 degrees east, 16:20:04 GMT.

The Holocene Indian Summer Monsoon Variability Recorded in a Stalagmite From NE India.

NASA Astrophysics Data System (ADS)

Breitenbach, S.; Plessen, B.; Oberhänsli, H.; Marwan, N.; Lund, D.; Adkins, J.; Günther, D.; Fricker, M.; Haug, G.

2007-12-01

South Asian economies depend on the timely onset of the Indian Summer Monsoon (ISM), but understanding of the ISM variability is incomplete, due to lack of information on past ISM. Our stalagmite is the first well-dated climate record from the heart of the ISM region spanning the past 11,000 years. The speleothem was collected from Krem Umsynrang Cave, located 825 m above sea level in NE India. This region is influenced by the ISM, with more than 75% of annual rainfall falling during the monsoon season. The chronology of the stalagmite is based on 36 U/Th multi-collector ICP MS dates. Our data reveal profound changes in ISM rainfall and moisture balance. A strong increase of the ISM between 11.4 and 9.3 kyr BP is followed by a gradual decline over the course of the Holocene. This may be best explained by a strong coupling between ISM and the Intertropical Convergence Zone (ITCZ), with a stronger ISM during a more northerly position of the ITCZ. This long-term trend is punctuated by centennial to multi- to sub-decadal events of a weaker ISM. The most pronounced events occurred at 10.7, 8.5-8.1, 7.4, 4.4-4.0, 3.5, 1.4, 0.3 kyr BP. The δ13C record is interpreted to reflect centennial to decadal changes in the drip rate of the stalagmite. δ13C fractionation during periods of higher drip rates (i.e. times of longer residence time of percolating water) correspond with periods of a weaker ISM as inferred from our δ18O record. Our record shows in great detail periods of weaker ISM. They provide new insights on the sensitivity of terrestrial climate archives on the Indian subcontinent. Drought events recorded in our stalagmite correspond well with intervals of severe aridity known from other regions of the Asian monsoon. Moreover, our 11,000 year climate record shows that NE India experienced its driest conditions during the last three millennia.

Meta-heuristic ant colony optimization technique to forecast the amount of summer monsoon rainfall: skill comparison with Markov chain model

NASA Astrophysics Data System (ADS)

Chaudhuri, Sutapa; Goswami, Sayantika; Das, Debanjana; Middey, Anirban

2014-05-01

Forecasting summer monsoon rainfall with precision becomes crucial for the farmers to plan for harvesting in a country like India where the national economy is mostly based on regional agriculture. The forecast of monsoon rainfall based on artificial neural network is a well-researched problem. In the present study, the meta-heuristic ant colony optimization (ACO) technique is implemented to forecast the amount of summer monsoon rainfall for the next day over Kolkata (22.6°N, 88.4°E), India. The ACO technique belongs to swarm intelligence and simulates the decision-making processes of ant colony similar to other adaptive learning techniques. ACO technique takes inspiration from the foraging behaviour of some ant species. The ants deposit pheromone on the ground in order to mark a favourable path that should be followed by other members of the colony. A range of rainfall amount replicating the pheromone concentration is evaluated during the summer monsoon season. The maximum amount of rainfall during summer monsoon season (June—September) is observed to be within the range of 7.5-35 mm during the period from 1998 to 2007, which is in the range 4 category set by the India Meteorological Department (IMD). The result reveals that the accuracy in forecasting the amount of rainfall for the next day during the summer monsoon season using ACO technique is 95 % where as the forecast accuracy is 83 % with Markov chain model (MCM). The forecast through ACO and MCM are compared with other existing models and validated with IMD observations from 2008 to 2012.

Source of moist air for the Asian summer monsoon lower stratosphere

NASA Astrophysics Data System (ADS)

Zhang, K.; Fu, R.; Wang, T.

2015-12-01

The Asian monsoon region is the most prominent moist center of lower stratospheric (LS) water vapor during boreal summer. However, the origin of such moist air is still unclear. Using Aura Microwave Limb Sounder (MLS) satellite observations and a domain-filling forward trajectory model, we show that moist air originates mostly from the western Asian Monsoon region where dehydration temperatures are warmer than those on the eastside of the Asian monsoon region. On seasonal scale, a shift of convective and dehydration center from the eastern to western monsoon region from early to late summer may contribute to the increase of LS water vapor over the Asian monsoon region. An increasing convection over the west side of the monsoon region can significantly moisten the LS. Air detrained from convection ascends with enhanced large-scale rising motion and dehydrate mostly within this region under warmer temperature, thus anomalously higher water vapor concentration. After final dehydration, water vapor anomalies show an upper-eastward propagation across the Asian monsoon region. This is primarily due to that air parcels tend to arise across the tropopause layer over the western region (eastern Iranian Plateau and northwestern India) after final dehydration as simulated by the trajectory model. This work highlights the importance of transport pathway shift, induced by the convective regime shift, on both seasonal and intraseasonal variations of water vapor in the Asian monsoon LS.

Multi-model projections of Indian summer monsoon climate changes under A1B scenario

NASA Astrophysics Data System (ADS)

Niu, X.; Wang, S.; Tang, J.

2016-12-01

As part of the Regional Climate Model Intercomparison Project for Asia, the projections of Indian summer monsoon climate changes are constructed using three global climate models (GCMs) and seven regional climate models (RCMs) during 2041-2060 based on the Intergovernmental Panel on Climate Change A1B emission scenario. For the control climate of 1981-2000, most nested RCMs show advantage over the driving GCM of European Centre/Hamburg Fifth Generation (ECHAM5) in the temporal-spatial distributions of temperature and precipitation over Indian Peninsula. Following the driving GCM of ECHAM5, most nested RCMs produce advanced monsoon onset in the control climate. For future climate widespread summer warming is projected over Indian Peninsula by all climate models, with the Multi-RCMs ensemble mean (MME) temperature increasing of 1°C to 2.5°C and the maximum warming center located in northern Indian Peninsula. While for the precipitation, a large inter-model spread is projected by RCMs, with wetter condition in MME projections and significant increase over southern India. Driven by the same GCM, most RCMs project advanced monsoon onset while delayed onset is found in two Regional Climate Model (RegCM3) projections, indicating uncertainty can be expected in the Indian Summer Monsoon onset. All climate models except Conformal-Cubic Atmospheric Model with equal resolution (referred as CCAMP) and two RegCM3 models project stronger summer monsoon during 2041-2060. The disagreement in precipitation projections by RCMs indicates that the surface climate change on regional scale is not only dominated by the large-scale forcing which is provided by driving GCM but also sensitive to RCM' internal physics.

Documentary reconstruction of monsoon rainfall variability over western India, 1781-1860

NASA Astrophysics Data System (ADS)

Adamson, George C. D.; Nash, David J.

2014-02-01

Investigations into the climatic forcings that affect the long-term variability of the Indian summer monsoon are constrained by a lack of reliable rainfall data prior to the late nineteenth century. Extensive qualitative and quantitative meteorological information for the pre-instrumental period exists within historical documents, although these materials have been largely unexplored. This paper presents the first reconstruction of monsoon variability using documentary sources, focussing on western India for the period 1781-1860. Three separate reconstructions are generated, for (1) Mumbai, (2) Pune and (3) the area of Gujarat bordering the Gulf of Khambat. A composite chronology is then produced from the three reconstructions, termed the Western India Monsoon Rainfall reconstruction (WIMR). The WIMR exhibits four periods of generally deficient monsoon rainfall (1780-1785, 1799-1806, 1830-1838 and 1845-1857) and three of above-normal rainfall (1788-1794, 1813-1828 and 1839-1844). The WIMR shows good correspondence with a dendroclimatic drought reconstruction for Kerala, although agreement with the western Indian portion of the tree-ring derived Monsoon Asia Drought Atlas is less strong. The reconstruction is used to examine the long-term relationship between the El Nino-Southern Oscillation (ENSO) and monsoon rainfall over western India. This exhibits peaks and troughs in correlation over time, suggesting a regular long-term fluctuation. This may be an internal oscillation in the ENSO-monsoon system or may be related to volcanic aerosol forcings. Further reconstructions of monsoon rainfall are necessary to validate this. The study highlights uncertainties in existing published rainfall records for 1817-1846 for western India.

Role of aerosols on the Indian Summer Monsoon variability, as simulated by state-of-the-art global climate models

NASA Astrophysics Data System (ADS)

Cagnazzo, Chiara; Biondi, Riccardo; D'Errico, Miriam; Cherchi, Annalisa; Fierli, Federico; Lau, William K. M.

2016-04-01

Recent observational and modeling analyses have explored the interaction between aerosols and the Indian summer monsoon precipitation on seasonal-to-interannual time scales. By using global scale climate model simulations, we 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 (EHP) mechanism. The increase in rainfall during the early monsoon season has a cooling effect on the land surface that may also be amplified through solar dimming (SD) by more cloudiness and aerosol loading with subsequent reduction in monsoon rainfall over India. We extend this analyses to a subset of CMIP5 climate model simulations. Our results suggest that 1) absorbing aerosols, by influencing the seasonal variability of the Indian summer monsoon with the discussed time-lag, may act as a source of predictability for the Indian Summer Monsoon and 2) if the EHP and SD effects are operating also in a number of state-of-the-art climate models, their inclusion could potentially improve seasonal forecasts.

Interannual variability of Indian monsoon rainfall

NASA Technical Reports Server (NTRS)

Paolino, D. A.; Shukla, J.

1984-01-01

The interannual variability of the Indian summer monsoon and its relationships with other atmospheric fluctuations were studied in hopes of gaining some insight into the predicability of the rainfall. Rainfall data for 31 meteorological subdivisions over India were provided by the India Meteorological Department (IMD). Fifty-three years of seasonal mean anomaly sea-level pressure (SLP) fields were used to determine if any relationships could be detected between fluctuations in Northern Hemisphere surface pressure and Indian monsoon rainfall. Three month running mean sea-level pressure anomalies at Darwin (close to one of the centers of the Southern Oscillation) were compiled for months preceding and following extreme years for rainfall averaged over all of India. Anomalies are small before the monsoon, but are quite large in months following the summer season. However, there is a large decrease in Darwin pressure for months preceding a heavy monsoon, while a deficient monsoon is preceded by a sharp increase in Darwin pressure. If a time series is constructed of the tendency of Darwin SLP between the Northern Hemisphere winter (DJF) and spring (MAM) and a correlation coefficient is computed between it and 81 years of rainfall average over all of India, one gets a C. C. of -.46, which is higher than any other previously computed predictor of the monsoon rainfall. This relationship can also be used to make a qualitative forecast for rainfall over the whole of India by considering the sign of the tendency in extreme monsoon years.

Relative roles of aerosols, SST, and snow impurity on snowmelt over the Tibetan Plateau and its their impacts on South Asian summer monsoon

NASA Astrophysics Data System (ADS)

Kim, K. M.; Tsay, S. C.; Lau, W. K. M.; Yasunari, T. J.; Mahanama, S. P. P.; Koster, R. D.; daSilva, A.

2017-12-01

We examine the relative roles of atmospheric aerosol radiative forcing, year-to-year SST (sea surface temperature) variability, and surface radiative forcing by snow impurity on snowmelt over the Tibetan Plateau and their impacts on rainfall and circulation of South Asian summer monsoon. Five-member ensemble experiments are conducted with NASA's GEOS-5 (Goddard Earth Observing System model version 5), equipped with a snow darkening module - GOSWIM (GOddard SnoW Impurity Module), on the Water-Year 2008 (October 2007 to September 2008). Asian summer monsoon in 2008 was near normal in terms of monsoon rainfall over India subcontinent. However, rainfall was excessive in the North while the southern India suffered from the rainfall deficit. The 2008 summer monsoon was accompanied with high loading of aerosols in the Arabian Sea and La Niña condition in the tropical Pacific. To examine the roles high aerosol loading and La Niña condition on the north-south dipole in Indian monsoon rainfall, two sets of experiments, in addition to control runs (CNTRL), are conducted without SST anomalies (CSST) and aerosol radiative feedback (NRF), respectively. Results show that increased aerosol loading in early summer is associated with the increased dust transport during La Niña years. Increased aerosols over the northern India induces EHP-like (elevated heat pump) circulation and increases rainfall over the India subcontinent. Aerosol radiative forcing feedback (CNTRL-NRF) strengthens the EHP-like monsoon circulation even more. Results indicate that anomalous circulation associated with La Niña condition increases aerosol loading by enhancing dust transport as well as by increasing aerosol lifetime. Increased aerosols induces EHP-like feedback processes and increases rainfall over the India subcontinent.

Assessment of two versions of regional climate model in simulating the Indian Summer Monsoon over South Asia CORDEX domain

NASA Astrophysics Data System (ADS)

Pattnayak, K. C.; Panda, S. K.; Saraswat, Vaishali; Dash, S. K.

2018-04-01

This study assess the performance of two versions of Regional Climate Model (RegCM) in simulating the Indian summer monsoon over South Asia for the period 1998 to 2003 with an aim of conducting future climate change simulations. Two sets of experiments were carried out with two different versions of RegCM (viz. RegCM4.2 and RegCM4.3) with the lateral boundary forcings provided from European Center for Medium Range Weather Forecast Reanalysis (ERA-interim) at 50 km horizontal resolution. The major updates in RegCM4.3 in comparison to the older version RegCM4.2 are the inclusion of measured solar irradiance in place of hardcoded solar constant and additional layers in the stratosphere. The analysis shows that the Indian summer monsoon rainfall, moisture flux and surface net downward shortwave flux are better represented in RegCM4.3 than that in the RegCM4.2 simulations. Excessive moisture flux in the RegCM4.2 simulation over the northern Arabian Sea and Peninsular India resulted in an overestimation of rainfall over the Western Ghats, Peninsular region as a result of which the all India rainfall has been overestimated. RegCM4.3 has performed well over India as a whole as well as its four rainfall homogenous zones in reproducing the mean monsoon rainfall and inter-annual variation of rainfall. Further, the monsoon onset, low-level Somali Jet and the upper level tropical easterly jet are better represented in the RegCM4.3 than RegCM4.2. Thus, RegCM4.3 has performed better in simulating the mean summer monsoon circulation over the South Asia. Hence, RegCM4.3 may be used to study the future climate change over the South Asia.

Influence of preonset land atmospheric conditions on the Indian summer monsoon rainfall variability

NASA Astrophysics Data System (ADS)

Rai, Archana; Saha, Subodh K.; Pokhrel, Samir; Sujith, K.; Halder, Subhadeep

2015-05-01

A possible link between preonset land atmospheric conditions and the Indian summer monsoon rainfall (ISMR) is explored. It is shown that, the preonset positive (negative) rainfall anomaly over northwest India, Pakistan, Afghanistan, and Iran is associated with decrease (increase) in ISMR, primarily in the months of June and July, which in turn affects the seasonal mean. ISMR in the months of June and July is also strongly linked with the preonset 2 m air temperature over the same regions. The preonset rainfall/2 m air temperature variability is linked with stationary Rossby wave response, which is clearly evident in the wave activity flux diagnostics. As the predictability of Indian summer monsoon relies mainly on the El Niño-Southern Oscillation (ENSO), the found link may further enhance our ability to predict the monsoon, particularly during a non-ENSO year.

Long-range forecast of all India summer monsoon rainfall using adaptive neuro-fuzzy inference system: skill comparison with CFSv2 model simulation and real-time forecast for the year 2015

NASA Astrophysics Data System (ADS)

Chaudhuri, S.; Das, D.; Goswami, S.; Das, S. K.

2016-11-01

All India summer monsoon rainfall (AISMR) characteristics play a vital role for the policy planning and national economy of the country. In view of the significant impact of monsoon system on regional as well as global climate systems, accurate prediction of summer monsoon rainfall has become a challenge. The objective of this study is to develop an adaptive neuro-fuzzy inference system (ANFIS) for long range forecast of AISMR. The NCEP/NCAR reanalysis data of temperature, zonal and meridional wind at different pressure levels have been taken to construct the input matrix of ANFIS. The membership of the input parameters for AISMR as high, medium or low is estimated with trapezoidal membership function. The fuzzified standardized input parameters and the de-fuzzified target output are trained with artificial neural network models. The forecast of AISMR with ANFIS is compared with non-hybrid multi-layer perceptron model (MLP), radial basis functions network (RBFN) and multiple linear regression (MLR) models. The forecast error analyses of the models reveal that ANFIS provides the best forecast of AISMR with minimum prediction error of 0.076, whereas the errors with MLP, RBFN and MLR models are 0.22, 0.18 and 0.73 respectively. During validation with observations, ANFIS shows its potency over the said comparative models. Performance of the ANFIS model is verified through different statistical skill scores, which also confirms the aptitude of ANFIS in forecasting AISMR. The forecast skill of ANFIS is also observed to be better than Climate Forecast System version 2. The real-time forecast with ANFIS shows possibility of deficit (65-75 cm) AISMR in the year 2015.

Relative role of pre-monsoon conditions and intraseasonal oscillations in determining early-vs-late indian monsoon intensity in a GCM

NASA Astrophysics Data System (ADS)

Ghosh, Rohit; Chakraborty, Arindam; Nanjundiah, Ravi S.

2018-01-01

The aim of this paper is to identify relative roles of different land-atmospheric conditions, apart from sea surface temperature (SST), in determining early vs. late summer monsoon intensity over India in a high resolution general circulation model (GCM). We find that in its early phase (June-July; JJ), pre-monsoon land-atmospheric processes play major role to modulate the precipitation over Indian region. These effects of pre-monsoon conditions decrease substantially during its later phase (August-September; AS) for which the interannual variation is mainly governed by the low frequency northward propagating intraseasonal oscillations. This intraseasonal variability which is related to mean vertical wind shear has a significant role during the early phase of monsoon as well. Further, using multiple linear regression, we show that interannual variation of early and late monsoon rainfall over India is best explained when all these land-atmospheric parameters are taken together. Our study delineates the relative role of different processes affecting early versus later summer monsoon rainfall over India that can be used for determining its subseasonal predictability.

South Asian summer monsoon breaks: Process-based diagnostics in HIRHAM5

NASA Astrophysics Data System (ADS)

Hanf, Franziska S.; Annamalai, H.; Rinke, Annette; Dethloff, Klaus

2017-05-01

This study assesses the ability of a high-resolution downscaling simulation with the regional climate model (RCM) HIRHAM5 in capturing the monsoon basic state and boreal summer intraseasonal variability (BSISV) over South Asia with focus on moist and radiative processes during 1979-2012. A process-based vertically integrated moist static energy (MSE) budget is performed to understand the model's fidelity in representing leading processes that govern the monsoon breaks over continental India. In the climatology (June-September) HIRHAM5 simulates a dry bias over central India in association with descent throughout the free troposphere. Sources of dry bias are interpreted as (i) near-equatorial Rossby wave response forced by excess rainfall over the southern Bay of Bengal promotes anomalous descent to its northwest and (ii) excessive rainfall over near-equatorial Arabian Sea and Bay of Bengal anchor a "local Hadley-type" circulation with descent anomalies over continental India. Compared with observations HIRHAM5 captures the leading processes that account for breaks, although with generally reduced amplitudes over central India. In the model too, anomalous dry advection and net radiative cooling are responsible for the initiation and maintenance of breaks, respectively. However, weaker contributions of all adiabatic MSE budget terms, and an inconsistent relationship between negative rainfall anomalies and radiative cooling reveals shortcomings in HIRHAM5's moisture-radiation interaction. Our study directly implies that process-based budget diagnostics are necessary, apart from just checking the northward propagation feature to examine RCM's fidelity to simulate BSISV.

Predicting onset and withdrawal of Indian Summer Monsoon in 2016: results of Tipping elements approach

NASA Astrophysics Data System (ADS)

Surovyatkina, Elena; Stolbova, Veronika; Kurths, Jurgen

2017-04-01

The monsoon is the season of rain caused by a global seasonal reverse in winds direction and a change in pressure distribution. The Southwest winds bring summer monsoon to India. The economy of India is able to maintain its GDP in the wake of a good monsoon. However, if monsoon gets delayed by even two weeks, it can spell disaster because the high population depending on agriculture - 70% of its people directly related to farming. Agriculture, in turn, is dependent on the monsoon. Although the rainy season happens annually between June and September, the time of monsoon season's onset and withdrawal varies within a month from year to year. The important feature of the monsoon is that it starts and ends suddenly. Hence, despite enormous progress having been made in predicting monsoon since 1886, it remains a significant scientific challenge. To make predictions of monsoon timing in 2016, we applied our recently developed method [1]. Our approach is based on a teleconnection between the Eastern Ghats (EG) and North Pakistan (NP) - Tipping Elements of Indian Summer Monsoon. Both our predictions - for monsoon onset and withdrawal - were made for the Eastern Ghats region (EG-20N,80E) in the central part of India, while the Indian Meteorological Department forecasts monsoon over Kerala - a state at the southern tip of the Indian subcontinent. Our prediction for monsoon onset was published on May 6-th, 2016 [2]. We predicted the monsoon arrival to the EG on the 13th of June with a deviation of +/-4 days. In fact, monsoon onset was on June 17-th, that was confirmed by information from meteorological stations located around the EG-region. Hence, our prediction of monsoon onset (made 40 days in advance) was correct. We delivered the prediction of monsoon withdrawal on July 27, 2016 [3], announcing the monsoon withdrawal from the EG on October 5-th with a deviation of +/-5 days. The actual monsoon withdrawal started on October 10-th when the relative humidity in the region

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

Long-term variability in the date of monsoon onset over western India

NASA Astrophysics Data System (ADS)

Adamson, George C. D.; Nash, David J.

2013-06-01

The date of onset of the southwest monsoon in western India is critical for farmers as it influences the timing of crop plantation and the duration of the summer rainy season. Identifying long-term variability in the date of monsoon onset is difficult, however, as onset dates derived from the reanalysis of instrumental rainfall data are only available for the region from 1879. This study uses documentary evidence and newly uncovered instrumental data to reconstruct annual monsoon onset dates for western India for the period 1781-1878, extending the existing record by 97 years. The mean date of monsoon onset over the Mumbai (Bombay) area during the reconstruction period was 10 June with a standard deviation of 6.9 days. This is similar to the mean and standard deviation of the date of monsoon onset derived from instrumental data for the twentieth century. The earliest identified onset date was 23 May (in 1802 and 1839) and the latest 22 June (in 1825). The longer-term perspective provided by this study suggests that the climatic regime that governs monsoon advance over western India did not change substantially from 1781 to 1955. Monsoon onset over Mumbai has occurred at a generally later date since this time. Our results indicate that this change is unprecedented during the last 230 years. Following a discussion of the results, the nature of the relationship between the date of monsoon onset and the El Niño-Southern Oscillation is discussed. This relationship is shown to have been stable since 1781.

The link between Tibetan Plateau monsoon and Indian summer precipitation: a linear diagnostic perspective

NASA Astrophysics Data System (ADS)

Ge, Fei; Sielmann, Frank; Zhu, Xiuhua; Fraedrich, Klaus; Zhi, Xiefei; Peng, Ting; Wang, Lei

2017-12-01

The thermal forcing of the Tibetan Plateau (TP) is analyzed to investigate the formation and variability of Tibetan Plateau Summer Monsoon (TPSM), which affects the climates of the surrounding regions, in particular the Indian summer monsoon precipitation. Dynamic composites and statistical analyses indicate that the Indian summer monsoon precipitation is less/greater than normal during the strong/weak TPSM. Strong (weak) TPSM is associated with an anomalous near surface cyclone (anticyclone) over the western part of the Tibetan Plateau, enhancing (reducing) the westerly flow along its southern flank, suppressing (favoring) the meridional flow of warm and moist air from the Indian ocean and thus cutting (providing) moisture supply for the northern part of India and its monsoonal rainfall. These results are complemented by a dynamic and thermodynamic analysis: (i) A linear thermal vorticity forcing primarily describes the influence of the asymmetric heating of TP generating an anomalous stationary wave flux. Composite analysis of anomalous stationary wave flux activity (after Plumb in J Atmos Sci 42:217-229, 1985) strongly indicate that non-orographic effects (diabatic heating and/or interaction with transient eddies) of the Tibetan Plateau contribute to the generation of an anomalous cyclone (anti-cyclone) over the western TP. (ii) Anomalous TPSM generation shows that strong TPSM years are related to the positive surface sensible heating anomalies over the eastern TP favoring the strong diabatic heating in summer. While negative TPSM years are associated with the atmospheric circulation anomalies during the preceding spring, enhancing northerly dry-cold air intrusions into TP, which may weaken the condensational heat release in the middle and upper troposphere, leading to a weaker than normal summer monsoon over the TP in summer.

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

The decadal-scale variation of the South Asian summer monsoon onset and its connection with the PDO

NASA Astrophysics Data System (ADS)

Watanabe, T.; Yamazaki, K.

2013-12-01

The summer Asian monsoon shows the abrupt increase of precipitation on the onset phase. It is an interesting and important problem when the summer monsoon onset occurs because natural resources, such as water and renewable energy agricultural product, are influenced by the variation of the summer Asian monsoon. Some researchers suggested the advance of the Asian summer monsoon onset in recent decades. We investigated the variation of the Asian monsoon onset using the long-term onset data over Kerala, a state in the southwest region of India, for 1948-2011. We discuss three main questions: 1) how is the variation of the monsoon onset date in the long-term period, 2) how the variation of the onset date is related to variations of atmospheric circulation and SST, and 3) what is the mechanism of such variation. Our main method is composite analysis using monthly-mean data. Though the onset date over Kerala shows the trend toward the early onset in recent three decades, such a trend is not observed in the whole period. It is noteworthy that the onset over Kerala shows the interannual variation on a multi-decadal scale. As regards the early onset years of Kerala, the summer monsoon onset is early over the following regions: the region from the southern Arabian Sea to southwestern India, the region from the southern Bay of Bengal to the Indochina Peninsula and the western North Pacific Ocean. On the other hand, the onset is late over southern China, Taiwan and the northern Philippine Sea. In early onset years of Kerala, the sea surface temperature over the northern Pacific Ocean is very similar to the negative PDO. The stationary wave train related with the negative PDO reaches into the Central Asia region, generates warm anomaly there and hence intensifies the land-sea thermal contrast there, which promotes the summer monsoon onset over South and Southeast Asia. Though the correlation between the onset over Kerala and the PDO is weak before 1976, it becomes high after

Indian Monsoon Depression: Climatology and Variability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoon, Jin-Ho; Huang, Wan-Ru

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 andmore » 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.« less

Highly Improved Predictability in the Forecasting of the East Asian Summer Monsoon

NASA Astrophysics Data System (ADS)

Lee, E.; Chase, T. N.; Rajagopalan, B.

2007-12-01

The East Asian summer monsoon greatly influences the lives and property of about a quarter of all the people in the world. However, the predictability of the monsoon is very low in comparison with that of Indian summer monsoon because of the complexity of the system which involves both tropical and sub-tropical climates. Previous monsoon prediction models emphasized ocean factors as the primary monsoon forcing. Here we show that pre-season land surface cover is at least as important as ocean indices. A new statistical forecast model of the East Asian summer monsoon using land cover conditions in addition to ocean heat sources doubles the predictability relative to a model using ocean factors alone. This work highlights the, as yet, undocumented importance of seasonal land cover in monsoon prediction and the role of the biosphere in the climate system as a whole. We also detail the physical mechanisms involved in these land surface forcings.

Multiscale characterization and prediction of monsoon rainfall in India using Hilbert-Huang transform and time-dependent intrinsic correlation analysis

NASA Astrophysics Data System (ADS)

Adarsh, S.; Reddy, M. Janga

2017-07-01

In this paper, the Hilbert-Huang transform (HHT) approach is used for the multiscale characterization of All India Summer Monsoon Rainfall (AISMR) time series and monsoon rainfall time series from five homogeneous regions in India. The study employs the Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) for multiscale decomposition of monsoon rainfall in India and uses the Normalized Hilbert Transform and Direct Quadrature (NHT-DQ) scheme for the time-frequency characterization. The cross-correlation analysis between orthogonal modes of All India monthly monsoon rainfall time series and that of five climate indices such as Quasi Biennial Oscillation (QBO), El Niño Southern Oscillation (ENSO), Sunspot Number (SN), Atlantic Multi Decadal Oscillation (AMO), and Equatorial Indian Ocean Oscillation (EQUINOO) in the time domain showed that the links of different climate indices with monsoon rainfall are expressed well only for few low-frequency modes and for the trend component. Furthermore, this paper investigated the hydro-climatic teleconnection of ISMR in multiple time scales using the HHT-based running correlation analysis technique called time-dependent intrinsic correlation (TDIC). The results showed that both the strength and nature of association between different climate indices and ISMR vary with time scale. Stemming from this finding, a methodology employing Multivariate extension of EMD and Stepwise Linear Regression (MEMD-SLR) is proposed for prediction of monsoon rainfall in India. The proposed MEMD-SLR method clearly exhibited superior performance over the IMD operational forecast, M5 Model Tree (MT), and multiple linear regression methods in ISMR predictions and displayed excellent predictive skill during 1989-2012 including the four extreme events that have occurred during this period.

Coupling of Community Land Model with RegCM4 for Indian Summer Monsoon Simulation

NASA Astrophysics Data System (ADS)

Maurya, R. K. S.; Sinha, P.; Mohanty, M. R.; Mohanty, U. C.

2017-11-01

Three land surface schemes available in the regional climate model RegCM4 have been examined to understand the coupling between land and atmosphere for simulation of the Indian summer monsoon rainfall. The RegCM4 is coupled with biosphere-atmosphere transfer scheme (BATS) and the National Center for Atmospheric Research (NCAR) Community Land Model versions 3.5, and 4.5 (CLM3.5 and CLM4.5, respectively) and model performance is evaluated for recent drought (2009) and normal (2011) monsoon years. The CLM4.5 has a more distinct category of surface and it is capable of representing better the land surface characteristics. National Centers for Environmental Prediction (NCEP) and Department of Energy (DOE) reanalysis version 2 (NNRP2) datasets are considered as driving force to conduct the experiments for the Indian monsoon region (30°E-120°E; 30°S-50°N). The NNRP2 and India Meteorological Department (IMD) gridded precipitation data are used for verification analysis. The results indicate that RegCM4 simulations with CLM4.5 (RegCM4-CLM4.5) and CLM3.5 (RegCM4-CLM3.5) surface temperature (at 2 ms) have very low warm biases ( 1 °C), while with BATS (RegCM4-BATS) has a cold bias of about 1-3 °C in peninsular India and some parts of central India. Warm bias in the RegCM4-BATS is observed over the Indo-Gangetic plain and northwest India and the bias is more for the deficit year as compared to the normal year. However, the warm (cold) bias is less in RegCM4-CLM4.5 than other schemes for both the deficit and normal years. The model-simulated maximum (minimum) surface temperature and sensible heat flux at the surface are positively (negatively) biased in all the schemes; however, the bias is higher in RegCM4-BATS and lower in RegCM4-CLM4.5 over India. All the land surface schemes overestimated the precipitation in peninsular India and underestimated in central parts of India for both the years; however, the biases are less in RegCM4-CLM4.5 and more in RegCM4-CLM3.5 and Reg

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.

Indian Summer Monsoon Rainfall: Implications of Contrasting Trends in the Spatial Variability of Means and Extremes.

PubMed

Ghosh, Subimal; Vittal, H; Sharma, Tarul; Karmakar, Subhankar; Kasiviswanathan, K S; Dhanesh, Y; Sudheer, K P; Gunthe, S S

2016-01-01

India's agricultural output, economy, and societal well-being are strappingly dependent on the stability of summer monsoon rainfall, its variability and extremes. Spatial aggregate of intensity and frequency of extreme rainfall events over Central India are significantly increasing, while at local scale they are spatially non-uniform with increasing spatial variability. The reasons behind such increase in spatial variability of extremes are poorly understood and the trends in mean monsoon rainfall have been greatly overlooked. Here, by using multi-decadal gridded daily rainfall data over entire India, we show that the trend in spatial variability of mean monsoon rainfall is decreasing as exactly opposite to that of extremes. The spatial variability of extremes is attributed to the spatial variability of the convective rainfall component. Contrarily, the decrease in spatial variability of the mean rainfall over India poses a pertinent research question on the applicability of large scale inter-basin water transfer by river inter-linking to address the spatial variability of available water in India. We found a significant decrease in the monsoon rainfall over major water surplus river basins in India. Hydrological simulations using a Variable Infiltration Capacity (VIC) model also revealed that the water yield in surplus river basins is decreasing but it is increasing in deficit basins. These findings contradict the traditional notion of dry areas becoming drier and wet areas becoming wetter in response to climate change in India. This result also calls for a re-evaluation of planning for river inter-linking to supply water from surplus to deficit river basins.

Characteristics of occurrence of heavy rainfall events over Odisha during summer monsoon season

NASA Astrophysics Data System (ADS)

Swain, Madhusmita; Pattanayak, Sujata; Mohanty, U. C.

2018-06-01

During summer monsoon season heavy to very heavy rainfall events have been occurring over most part of India, routinely result in flooding over Indian Monsoon Region (IMR). It is worthwhile to mention that as per Geological Survey of India, Odisha is one of the most flood prone regions of India. The present study analyses the occurrence of very light (0-2.4 mm/day), light (2.5 - 15.5 mm/day), moderate (15.6 - 64.4 mm/day), heavy (64.5 - 115.4 mm/day), very heavy (115.5 - 204.4 mm/day) and extreme (≥ 204.5 mm/day) rainy days over Odisha during summer monsoon season for a period of 113 years (1901 - 2013) and a detailed study has been done for heavy-to-extreme rainy days. For this purpose, India Meteorological Department (IMD) gridded (0.25° × 0.25° lat/lon) rainfall data and the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) (0.125° × 0.125° lat/lon) datasets are used. The analysis reveals that the frequency of very light, light and moderate rainy days persists with almost constant trend, but the heavy, very heavy and extreme rainy days exhibit an increasing trend during the study period. It may be noted that more than 60% of heavy-to-extreme rainy days are observed in the month of July and August. Furthermore, during the recent period (1980-2013), there are a total of 150 extreme rainy days are observed over Odisha, out of which 47% are associated with monsoon depressions (MDs) and cyclonic storms, 41% are with lows, 2% are due to the presence of middle and upper tropospheric cyclonic circulations, 1% is due to monsoon trough and other 9% of extreme rainy days does not follow any of these synoptic conditions. Since a large (nearly half) percentage of extreme rainy days over Odisha is due to the presence of MDs, a detailed examination of MDs is illustrated in this study. Analysis reveals that there are a total of 91 MDs formed over the Bay of Bengal (BoB) during 1980 - 2013, and out of which 56 (61.5% of total MD) MDs

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.

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

Indian Summer Monsoon Rainfall: Implications of Contrasting Trends in the Spatial Variability of Means and Extremes

PubMed Central

Ghosh, Subimal; Vittal, H.; Sharma, Tarul; Karmakar, Subhankar; Kasiviswanathan, K. S.; Dhanesh, Y.; Sudheer, K. P.; Gunthe, S. S.

2016-01-01

India’s agricultural output, economy, and societal well-being are strappingly dependent on the stability of summer monsoon rainfall, its variability and extremes. Spatial aggregate of intensity and frequency of extreme rainfall events over Central India are significantly increasing, while at local scale they are spatially non-uniform with increasing spatial variability. The reasons behind such increase in spatial variability of extremes are poorly understood and the trends in mean monsoon rainfall have been greatly overlooked. Here, by using multi-decadal gridded daily rainfall data over entire India, we show that the trend in spatial variability of mean monsoon rainfall is decreasing as exactly opposite to that of extremes. The spatial variability of extremes is attributed to the spatial variability of the convective rainfall component. Contrarily, the decrease in spatial variability of the mean rainfall over India poses a pertinent research question on the applicability of large scale inter-basin water transfer by river inter-linking to address the spatial variability of available water in India. We found a significant decrease in the monsoon rainfall over major water surplus river basins in India. Hydrological simulations using a Variable Infiltration Capacity (VIC) model also revealed that the water yield in surplus river basins is decreasing but it is increasing in deficit basins. These findings contradict the traditional notion of dry areas becoming drier and wet areas becoming wetter in response to climate change in India. This result also calls for a re-evaluation of planning for river inter-linking to supply water from surplus to deficit river basins. PMID:27463092

New spatial and temporal indices of Indian summer monsoon rainfall

NASA Astrophysics Data System (ADS)

Dwivedi, Sanjeev; Uma, R.; Lakshmi Kumar, T. V.; Narayanan, M. S.; Pokhrel, Samir; Kripalani, R. H.

2018-02-01

The overall yearly seasonal performance of Indian southwest monsoon rainfall (ISMR) for the whole Indian land mass is presently expressed by the India Meteorological Department (IMD) by a single number, the total quantum of rainfall. Any particular year is declared as excess/deficit or normal monsoon rainfall year on the basis of this single number. It is well known that monsoon rainfall also has high interannual variability in spatial and temporal scales. To account for these aspects in ISMR, we propose two new spatial and temporal indices. These indices have been calculated using the 115 years of IMD daily 0.25° × 0.25° gridded rainfall data. Both indices seem to go in tandem with the in vogue seasonal quantum index. The anomaly analysis indicates that the indices during excess monsoon years behave randomly, while for deficit monsoon years the phase of all the three indices is the same. Evaluation of these indices is also studied with respect to the existing dynamical indices based on large-scale circulation. It is found that the new temporal indices have better link with circulation indices as compared to the new spatial indices. El Nino and Southern Oscillation (ENSO) especially over the equatorial Pacific Ocean still have the largest influence in both the new indices. However, temporal indices have much better remote influence as compared to that of spatial indices. Linkages over the Indian Ocean regions are very different in both the spatial and temporal indices. Continuous wavelet transform (CWT) analysis indicates that the complete spectrum of oscillation of the QI is shared in the lower oscillation band by the spatial index and in the higher oscillation band by the temporal index. These new indices may give some extra dimension to study Indian summer monsoon variability.

Southern Indian Ocean SST as a modulator for the progression of Indian summer monsoon

NASA Astrophysics Data System (ADS)

Shahi, Namendra Kumar; Rai, Shailendra; Mishra, Nishant

2018-01-01

This study explores the possibility of southern Indian Ocean (SIO) sea surface temperature (SST) as a modulator for the early phase of Indian summer monsoon and its possible physical mechanism. A dipole-like structure is obtained from the empirical orthogonal function (EOF) analysis which is similar to an Indian Ocean subtropical dipole (IOSD) found earlier. A subtropical dipole index (SDI) is defined based on the SST anomaly over the positive and negative poles. The regression map of rainfall over India in the month of June corresponding to the SDI during 1983-2013 shows negative patterns along the Western Ghats and Central India. However, the regression pattern is insignificant during 1952-1982. The multiple linear regression models and partial correlation analysis also indicate that the SDI acts as a dominant factor to influence the rainfall over India in the month of June during 1983-2013. The similar result is also obtained with the help of composite rainfall over the land points of India in the month of June for positive (negative) SDI events. It is also observed that the positive (negative) SDI delays (early) the onset dates of Indian monsoon over Kerala during the time domain of our study. The study is further extended to identify the physical mechanism of this impact, and it is found that the heating (cooling) in the region covering SDI changes the circulation pattern in the SIO and hence impacts the progression of monsoon in India.

The impact of monsoon intraseasonal variability on renewable power generation in India

NASA Astrophysics Data System (ADS)

Dunning, C. M.; Turner, A. G.; Brayshaw, D. J.

2015-06-01

India is increasingly investing in renewable technology to meet rising energy demands, with hydropower and other renewables comprising one-third of current installed capacity. Installed wind-power is projected to increase 5-fold by 2035 (to nearly 100GW) under the International Energy Agency's New Policies scenario. However, renewable electricity generation is dependent upon the prevailing meteorology, which is strongly influenced by monsoon variability. Prosperity and widespread electrification are increasing the demand for air conditioning, especially during the warm summer. This study uses multi-decadal observations and meteorological reanalysis data to assess the impact of intraseasonal monsoon variability on the balance of electricity supply from wind-power and temperature-related demand in India. Active monsoon phases are characterized by vigorous convection and heavy rainfall over central India. This results in lower temperatures giving lower cooling energy demand, while strong westerly winds yield high wind-power output. In contrast, monsoon breaks are characterized by suppressed precipitation, with higher temperatures and hence greater demand for cooling, and lower wind-power output across much of India. The opposing relationship between wind-power supply and cooling demand during active phases (low demand, high supply) and breaks (high demand, low supply) suggests that monsoon variability will tend to exacerbate fluctuations in the so-called demand-net-wind (i.e., electrical demand that must be supplied from non-wind sources). This study may have important implications for the design of power systems and for investment decisions in conventional schedulable generation facilities (such as coal and gas) that are used to maintain the supply/demand balance. In particular, if it is assumed (as is common) that the generated wind-power operates as a price-taker (i.e., wind farm operators always wish to sell their power, irrespective of price) then investors in

Prediction model for peninsular Indian summer monsoon rainfall using data mining and statistical approaches

NASA Astrophysics Data System (ADS)

Vathsala, H.; Koolagudi, Shashidhar G.

2017-01-01

In this paper we discuss a data mining application for predicting peninsular Indian summer monsoon rainfall, and propose an algorithm that combine data mining and statistical techniques. We select likely predictors based on association rules that have the highest confidence levels. We then cluster the selected predictors to reduce their dimensions and use cluster membership values for classification. We derive the predictors from local conditions in southern India, including mean sea level pressure, wind speed, and maximum and minimum temperatures. The global condition variables include southern oscillation and Indian Ocean dipole conditions. The algorithm predicts rainfall in five categories: Flood, Excess, Normal, Deficit and Drought. We use closed itemset mining, cluster membership calculations and a multilayer perceptron function in the algorithm to predict monsoon rainfall in peninsular India. Using Indian Institute of Tropical Meteorology data, we found the prediction accuracy of our proposed approach to be exceptionally good.

Sensitivity of convective precipitation to soil moisture and vegetation during break spell of Indian summer monsoon

NASA Astrophysics Data System (ADS)

Kutty, Govindan; Sandeep, S.; Vinodkumar; Nhaloor, Sreejith

2017-07-01

Indian summer monsoon rainfall is characterized by large intra-seasonal fluctuations in the form of active and break spells in rainfall. This study investigates the role of soil moisture and vegetation on 30-h precipitation forecasts during the break monsoon period using Weather Research and Forecast (WRF) model. The working hypothesis is that reduced rainfall, clear skies, and wet soil condition during the break monsoon period enhance land-atmosphere coupling over central India. Sensitivity experiments are conducted with modified initial soil moisture and vegetation. The results suggest that an increase in antecedent soil moisture would lead to an increase in precipitation, in general. The precipitation over the core monsoon region has increased by enhancing forest cover in the model simulations. Parameters such as Lifting Condensation Level, Level of Free Convection, and Convective Available Potential Energy indicate favorable atmospheric conditions for convection over forests, when wet soil conditions prevail. On spatial scales, the precipitation is more sensitive to soil moisture conditions over northeastern parts of India. Strong horizontal gradient in soil moisture and orographic uplift along the upslopes of Himalaya enhanced rainfall over the east of Indian subcontinent.

Future projections of active-break spells of Indian summer monsoon in a climate change perspective

NASA Astrophysics Data System (ADS)

Sudeepkumar, B. L.; Babu, C. A.; Varikoden, Hamza

2018-02-01

The effect of global climate change on Indian summer monsoon has been analysed with special emphasis on active-break cycle. The changes in intensity and duration of active and break monsoon conditions towards the end of the century are studied by using 850 hPa zonal circulations. The analysis is carried out using twenty year climatology of historical period (1986-2005) and future projections (2080-2099) simulated as part of Coupled Model Intercomparison Project phase 5 (CMIP5). Models are compared with NCEP/NCAR reanalysis data. The models that effectively capture the circulation pattern of monsoon (JJAS) are considered for assessing the future climate in RCP 4.5 scenario. They are CanESM2, CNRM-CM5, GFDL-ESM2M, MIROC5 and MPI-ESM-LR. During the southwest monsoon period, the ensemble mean of models projects a strengthening of the wind speed towards north (north of 15°N) and weakening to the southern region (especially south of 12°N) which facilitates wetting of northern Indian regions and drying of southern peninsular regions. In the case of active-break conditions, the active spells are found to be strengthening over northern India and weakening over the peninsular India, the break spells intensify over southern tip of peninsular India indicating intense breaks. Increased propensity of short intense active days and decreased propensity of long active days are also projected by the models. The number of break spells does not show any significant changes.

Asian Summer Monsoon Anomalies Induced by Aerosol Direct Forcing: The Role of the Tibetan Plateau

NASA Technical Reports Server (NTRS)

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

2006-01-01

In this paper we present results of a numerical study using the NASA finite-volume GCM to elucidate a plausible mechanism for aerosol impact on the Asian summer monsoon involving interaction with physical processes over the Tibetan Plateau (TP). During the premonsoon season of March April, dusts from the deserts of western China, Afghanistan/Pakistan, and the Middle East are transported into and stacked up against the northern and southern slopes of the TP. The absorption of solar radiation by dust heats up the elevated surface air over the slopes. On the southern slopes, the atmospheric heating is reinforced by black carbon from local emission. The heated air rises via dry convection, creating a positive temperature anomaly in the mid-to-upper troposphere over the TP relative to the region to the south. In May through early June in a manner akin to an elevated heat pump , the rising hot air forced by the increasing heating in the upper troposphere, draws in warm and moist air over the Indian subcontinent, setting the stage for the onset of the South Asia summer monsoon. Our results suggest that increased dust loading coupled with black carbon emission from local sources in northern India during late spring may lead to an advance of the rainy periods and subsequently an intensification of the Indian summer monsoon. The enhanced rainfall over India is associated with the development of an aerosol-induced large-scale sea level pressure anomaly pattern, which causes the East Asia (Mei-yu) rain belt to shift northwestward, suppressing rainfall over East Asia and the adjacent oceanic regions.

Tropical cyclone influence on the long-term variability of Philippine summer monsoon onset

NASA Astrophysics Data System (ADS)

Kubota, Hisayuki; Shirooka, Ryuichi; Matsumoto, Jun; Cayanan, Esperanza O.; Hilario, Flaviana D.

2017-12-01

The long-term variability of Philippine summer monsoon onset from 1903 to 2013 was investigated. The onset date is defined by daily rainfall data at eight stations in the northwestern Philippines. Summer monsoons tended to start earlier in May after the mid-1990s. Other early onset periods were found during the 1900s, 1920s, and 1930s, and an interdecadal variability of summer monsoon onset was identified. Independent surface wind data observed by ships in the South China Sea (SCS) revealed prevailing westerly wind in May during the early monsoon onset period. To identify atmospheric structures that trigger Philippine summer monsoon onset, we focused on the year 2013, conducting intensive upper-air observations. Tropical cyclone (TC) Yagi traveled northward in the Philippine Sea (PS) in 2013 and triggered the Philippine monsoon onset by intensifying moist low-level southwesterly wind in the southwestern Philippines and intensifying low-level southerly wind after the monsoon onset in the northwestern Philippines. The influence of TC was analyzed by the probability of the existence of TC in the PS and the SCS since 1951, which was found to be significantly correlated with the Philippine summer monsoon onset date. After the mid-1990s, early monsoon onset was influenced by active TC formation in the PS and the SCS. However, the role of TC activity decreased during the late summer monsoon periods. In general, it was found that TC activity in the PS and the SCS plays a key role in initiating Philippine summer monsoon onset. [Figure not available: see fulltext.

Early forecasting of Indian Summer Monsoon: case study 2016

NASA Astrophysics Data System (ADS)

Surovyatkina, Elena; Stolbova, Veronika; Kurths, Jurgen

2017-04-01

The prior knowledge of dates of onset and withdrawal of monsoon is of vital importance for the population of the Indian subcontinent. In May 2016 before monsoon season, India recorded its highest-ever temperature of 51C. Hot waves have decimated crops, killed livestock and left 330 million people without enough water. At the end of monsoon season the floods in Indian this year have also broken previous records. Severe and devastating rainfall poured down, triggering dams spilling and floods. Such extreme conditions pose the vital questions such as: When will the monsoon come? When will the monsoon withdraw? More lead time in monsoon forecast warning is crucial for taking appropriate decisions at various levels - from the farmer's field (e.g. plowing day, seeding) to the central government (e.g. managing water and energy resources, food procurement policies). The Indian Meteorological Department issues forecasts of onset of monsoon for Kerala state in South India on May 15-th. It does not give such predictions for the other 28 states of the country. Our study concerns the central part of India. We made the monsoon forecast using our recently developed method which focuses on Tipping elements of the Indian monsoon [1]. Our prediction relies on observations of near-surface air temperature and relative humidity from both the ERA-40 and NCEP/NCAR reanalyses. We performed both of our forecasts for the onset and withdrawal of monsoon for the central part of India, the Eastern Ghats (20N,80E). We predicted the monsoon arrival to the Eastern Ghats (20N,80E) on the 13th of June with a deviation of +/-4 days. The prediction was made on May 6-th, 2016 [2], that is 40 days in advance of the date of the forecast. The actual monsoon arrival was June 17-th. In this day near-surface air temperature and relative humidity overcame the critical values and the monsoon season started, that was confirmed by observations of meteorological stations located around the EG-region. We

Late Holocene anti-phase change in the East Asian summer and winter monsoons

NASA Astrophysics Data System (ADS)

Kang, Shugang; Wang, Xulong; Roberts, Helen M.; Duller, Geoff A. T.; Cheng, Peng; Lu, Yanchou; An, Zhisheng

2018-05-01

Changes in East Asian summer and winter monsoon intensity have played a pivotal role in the prosperity and decline of society in the past, and will be important for future climate scenarios. However, the phasing of changes in the intensity of East Asian summer and winter monsoons on millennial and centennial timescales during the Holocene is unclear, limiting our ability to understand the factors driving past and future changes in the monsoon system. Here, we present a high resolution (up to multidecadal) loess record for the last 3.3 ka from the southern Chinese Loess Plateau that clearly demonstrates the relationship between changes in the intensity of the East Asian summer and winter monsoons, particularly at multicentennial scales. At multimillennial scales, the East Asian summer monsoon shows a steady weakening, while the East Asian winter monsoon intensifies continuously. At multicentennial scales, a prominent ∼700-800 yr cycle in the East Asian summer and winter monsoon intensity is observed, and here too the two monsoons are anti-phase. We conclude that multimillennial changes are driven by Northern Hemisphere summer insolation, while multicentennial changes can be correlated with solar activity and changing strength of the Atlantic meridional overturning circulation.

Estimating sowing and harvest dates based on the Asian summer monsoon

NASA Astrophysics Data System (ADS)

Mathison, Camilla; Deva, Chetan; Falloon, Pete; Challinor, Andrew J.

2018-05-01

Sowing and harvest dates are a significant source of uncertainty within crop models, especially for regions where high-resolution data are unavailable or, as is the case in future climate runs, where no data are available at all. Global datasets are not always able to distinguish when wheat is grown in tropical and subtropical regions, and they are also often coarse in resolution. South Asia is one such region where large spatial variation means higher-resolution datasets are needed, together with greater clarity for the timing of the main wheat growing season. Agriculture in South Asia is closely associated with the dominating climatological phenomenon, the Asian summer monsoon (ASM). Rice and wheat are two highly important crops for the region, with rice being mainly cultivated in the wet season during the summer monsoon months and wheat during the dry winter. We present a method for estimating the crop sowing and harvest dates for rice and wheat using the ASM onset and retreat. The aim of this method is to provide a more accurate alternative to the global datasets of cropping calendars than is currently available and generate more representative inputs for climate impact assessments. We first demonstrate that there is skill in the model prediction of monsoon onset and retreat for two downscaled general circulation models (GCMs) by comparing modelled precipitation with observations. We then calculate and apply sowing and harvest rules for rice and wheat for each simulation to climatological estimates of the monsoon onset and retreat for a present day period. We show that this method reproduces the present day sowing and harvest dates for most parts of India. The application of the method to two future simulations demonstrates that the estimated sowing and harvest dates are successfully modified to ensure that the growing season remains consistent with the internal model climate. The study therefore provides a useful way of modelling potential growing season

Vertical structure of atmospheric boundary layer over Ranchi during the summer monsoon season

NASA Astrophysics Data System (ADS)

Chandra, Sagarika; Srivastava, Nishi; Kumar, Manoj

2018-04-01

Thermodynamic structure and variability in the atmospheric boundary layer have been investigated with the help of balloon-borne GPS radiosonde over a monsoon trough station Ranchi (Lat. 23°45'N, Long. 85°43'E, India) during the summer monsoon season (June-September) for a period of 2011-2013. Virtual potential temperature gradient method is used for the determination of mixed layer height (MLH). The MLH has been found to vary in the range of 1000-1300 m during the onset, 600-900 m during the active and 1400-1750 m during the break phase of monsoon over this region. Inter-annual variations noticed in MLH could be associated with inter-annual variability in convection and rainfall prevailing over the region. Along with the MLH, the cloud layer heights are also derived from the thermodynamic profiles for the onset, active and break phases of monsoon. Cloud layer height varied a lot during different phases of the monsoon. For the determination of boundary-layer convection, thermodynamic parameter difference (δθ = θ es- θ e) between saturated equivalent potential temperature (θ es ) and equivalent potential temperature (θ e) is used. It is a good indicator of convection and indicates the intense and suppressed convection during different phases of monsoon.

A hemispheric climatology of monsoon depressions

NASA Astrophysics Data System (ADS)

Hurley, J. V.; Boos, W.

2012-12-01

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

Impact of East Asian Summer Monsoon on the Air Quality over China: View from space

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Chun; Wang, Yuhang; Yang, Qing

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 disappearmore » 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.« less

Impact of atmospheric circulation types on southwest Asian dust and Indian summer monsoon rainfall

NASA Astrophysics Data System (ADS)

Kaskaoutis, D. G.; Houssos, E. E.; Solmon, F.; Legrand, M.; Rashki, A.; Dumka, U. C.; Francois, P.; Gautam, R.; Singh, R. P.

2018-03-01

This study examines the meteorological feedback on dust aerosols and rainfall over the Arabian Sea and India during the summer monsoon using satellite data, re-analysis and a regional climate model. Based on days with excess aerosol loading over the central Ganges basin during May - September, two distinct atmospheric circulation types (weather clusters) are identified, which are associated with different dust-aerosol and rainfall distributions over south Asia, highlighting the role of meteorology on dust emissions and monsoon rainfall. Each cluster is characterized by different patterns of mean sea level pressure (MSLP), geopotential height at 700 hPa (Z700) and wind fields at 1000 hPa and at 700 hPa, thus modulating changes in dust-aerosol loading over the Arabian Sea. One cluster is associated with deepening of the Indian/Pakistan thermal low leading to (i) increased cyclonicity and thermal convection over northwestern India and Arabian Peninsula, (ii) intensification of the southwest monsoon off the Horn of Africa, iii) increase in dust emissions from Rub-Al-Khali and Somalian deserts, (iv) excess dust accumulation over the Arabian Sea and, (v) strengthening of the convergence of humid air masses and larger precipitation over Indian landmass compared to the other cluster. The RegCM4.4 model simulations for dust-aerosol and precipitation distributions support the meteorological fields and satellite observations, while the precipitation over India is positively correlated with the aerosol loading over the Arabian Sea on daily basis for both weather clusters. This study highlights the key role of meteorology and atmospheric dynamics on dust life cycle and rainfall over the monsoon-influenced south Asia.

Identification of tipping elements of the Indian Summer Monsoon using climate network approach

NASA Astrophysics Data System (ADS)

Stolbova, Veronika; Surovyatkina, Elena; Kurths, Jurgen

2015-04-01

Spatial and temporal variability of the rainfall is a vital question for more than one billion of people inhabiting the Indian subcontinent. Indian Summer Monsoon (ISM) rainfall is crucial for India's economy, social welfare, and environment and large efforts are being put into predicting the Indian Summer Monsoon. For predictability of the ISM, it is crucial to identify tipping elements - regions over the Indian subcontinent which play a key role in the spatial organization of the Indian monsoon system. Here, we use climate network approach for identification of such tipping elements of the ISM. First, we build climate networks of the extreme rainfall, surface air temperature and pressure over the Indian subcontinent for pre-monsoon, monsoon and post-monsoon seasons. We construct network of extreme rainfall event using observational satellite data from 1998 to 2012 from the Tropical Rainfall Measuring Mission (TRMM 3B42V7) and reanalysis gridded daily rainfall data for a time period of 57 years (1951-2007) (Asian Precipitation Highly Resolved Observational Data Integration Towards the Evaluation of Water Resources, APHRODITE). For the network of surface air temperature and pressure fields, we use re-analysis data provided by the National Center for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR). Second, we filter out data by coarse-graining the network through network measures, and identify tipping regions of the ISM. Finally, we compare obtained results of the network analysis with surface wind fields and show that occurrence of the tipping elements is mostly caused by monsoonal wind circulation, migration of the Intertropical Convergence Zone (ITCZ) and Westerlies. We conclude that climate network approach enables to select the most informative regions for the ISM, providing realistic description of the ISM dynamics with fewer data, and also help to identify tipping regions of the ISM. Obtained tipping elements deserve a

Influences of spring-to-summer sea surface temperatures over different Indian Ocean domains on the Asian summer monsoon

NASA Astrophysics Data System (ADS)

Li, Zhenning; Yang, Song

2017-11-01

The influences of spring-to-summer sea surface temperature (SST) anomalies in different domains of the Indian Ocean (IO) on the Asian summer monsoon are investigated by conducting a series of numerical experiments using the NCAR CAM4 model. It is found that, to a certain extent, the springtime IO SST anomalies can persist to the summer season. The spring-to-summer IO SST anomalies associated with the IO basin warming mode are strongly linked to the summer climate over Asia, especially the South Asian monsoon (SAM) and the East Asian monsoon. Among this connection, the warming of tropical IO plays the most critical role, and the warming of southern IO is important for monsoon variation and prediction prior to the full development of the monsoon. The atmospheric response to IO basin wide warming is similar with that to tropical IO warming. The influence of northern IO warming on the SAM, however, is opposite to the effect of southern IO warming. Meanwhile, the discrepancies between the results from idealized SST forcing simulations and observations, especially for the southern IO, reveal that the dominant role of air-sea interaction in the monsoon-IO coupled system cannot be ignored. Moreover, the springtime northern IO warming seems to favor an early onset or a stronger persistence of the SAM.

On Winning the Race for Predicting the Indian Summer Monsoon Rainfall

NASA Astrophysics Data System (ADS)

Goswami, Bhupendra

2013-03-01

Skillful prediction of Indian summer monsoon rainfall (ISMR) one season in advance remains a ``grand challenge'' for the climate science community even though such forecasts have tremendous socio-economic implications over the region. Continued poor skill of the ocean-atmosphere coupled models in predicting ISMR is an enigma in the backdrop when these models have high skill in predicting seasonal mean rainfall over the rest of the Tropics. Here, I provide an overview of the fundamental processes responsible for limited skill of climate models and outline a framework for achieving the limit on potential predictability within a reasonable time frame. I also show that monsoon intra-seasonal oscillations (MISO) act as building blocks of the Asian monsoon and provide a bridge between the two problems, the potential predictability limit and the simulation of seasonal mean climate. The correlation between observed ISMR and ensemble mean of predicted ISMR (R) can still be used as a metric for forecast verification. Estimate of potential limit of predictability of Asian monsoon indicates that the highest achievable R is about 0.75. Improvements in climate models and data assimilation over the past one decade has slowly improved R from near zero a decade ago to about 0.4 currently. The race for achieving useful prediction can be won, if we can push this skill up to about 0.7. It requires focused research in improving simulations of MISO, monsoon seasonal cycle and ENSO-monsoon relationship by the climate models. In order to achieve this goal by 2015-16 timeframe, IITM is leading a Program called Monsoon Mission supported by the Ministry of Earth Sciences, Govt. of India (MoES). As improvement in skill of forecasts can come only if R & D is carried out on an operational modeling system, the Climate Forecast System of National Centre for Environmental Prediction (NCEP) of NOAA, U.S.A has been selected as our base system. The Mission envisages building partnership between

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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mei, Rui; Ashfaq, Moetasim; Rastogi, Deeksha

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

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

Confronting the “Indian summer monsoon response to black carbon aerosol” with the uncertainty in its radiative forcing and beyond

DOE PAGES

Kovilakam, Mahesh; Mahajan, Salil

2016-06-28

While black carbon aerosols (BC) are believed to modulate the Indian monsoons, the radiative forcing estimate of BC suffers from large uncertainties globally. In this paper, we analyze a suite of idealized experiments forced with a range of BC concentrations that span a large swath of the latest estimates of its global radiative forcing. Within those bounds of uncertainty, summer precipitation over the Indian region increases nearly linearly with the increase in BC burden. The linearity holds even as the BC concentration is increased to levels resembling those hypothesized in nuclear winter scenarios, despite large surface cooling over India andmore » adjoining regions. The enhanced monsoonal circulation is associated with a linear increase in the large-scale meridional tropospheric temperature gradient. The precipitable water over the region also increases linearly with an increase in BC burden, due to increased moisture transport from the Arabian sea to the land areas. The wide range of Indian monsoon response elicited in these experiments emphasizes the need to reduce the uncertainty in BC estimates to accurately quantify their role in modulating the Indian monsoons. Finally, the increase in monsoonal circulation in response to large BC concentrations contrasts earlier findings that the Indian summer monsoon may break down following a nuclear war.« less

Confronting the “Indian summer monsoon response to black carbon aerosol” with the uncertainty in its radiative forcing and beyond

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kovilakam, Mahesh; Mahajan, Salil

While black carbon aerosols (BC) are believed to modulate the Indian monsoons, the radiative forcing estimate of BC suffers from large uncertainties globally. In this paper, we analyze a suite of idealized experiments forced with a range of BC concentrations that span a large swath of the latest estimates of its global radiative forcing. Within those bounds of uncertainty, summer precipitation over the Indian region increases nearly linearly with the increase in BC burden. The linearity holds even as the BC concentration is increased to levels resembling those hypothesized in nuclear winter scenarios, despite large surface cooling over India andmore » adjoining regions. The enhanced monsoonal circulation is associated with a linear increase in the large-scale meridional tropospheric temperature gradient. The precipitable water over the region also increases linearly with an increase in BC burden, due to increased moisture transport from the Arabian sea to the land areas. The wide range of Indian monsoon response elicited in these experiments emphasizes the need to reduce the uncertainty in BC estimates to accurately quantify their role in modulating the Indian monsoons. Finally, the increase in monsoonal circulation in response to large BC concentrations contrasts earlier findings that the Indian summer monsoon may break down following a nuclear war.« less

Did Aboriginal vegetation burning affect the Australian summer monsoon?

NASA Astrophysics Data System (ADS)

Balcerak, Ernie

2011-08-01

For thousands of years, Aboriginal Australians burned forests, creating grasslands. Some studies have suggested that in addition to changing the landscape, these burning practices also affected the timing and intensity of the Australian summer monsoon. Different vegetation types can alter evaporation, roughness, and surface reflectivity, leading to changes in the weather and climate. On the basis of an ensemble of experiments with a global climate model, Notaro et al. conducted a comprehensive evaluation of the effects of decreased vegetation cover on the summer monsoon in northern Australia. They found that although decreased vegetation cover would have had only minor effects during the height of the monsoon season, during the premonsoon season, burning-induced vegetation loss would have caused significant decreases in precipitation and increases in temperature. Thus, by burning forests, Aboriginals altered the local climate, effectively extending the dry season and delaying the start of the monsoon season. (Geophysical Research Letters, doi:10.1029/2011GL047774, 2011)

Holocene Summer Monsoon Variability- Evidence from Marine Sediment of western Continental Shelf of Sri Lanka

NASA Astrophysics Data System (ADS)

Ranasinghage, P. N.; Ratnayake, K. M.; Dassanayake, D. M. K. K.; Mohtadi, M.; Hewawasam, T.; Jinadasa, S. U. P.; Jayawardena, S.; Siriwardana, S.

2016-12-01

Understanding long term variability of Indian monsoon system is essential for better climate forecasting which is a prerequisite for agricultural development and disaster management. Yet, it has been a least attended scientific question in Sri Lanka Therefore, this study was carried out to understand the monsoonal variability during the Holocene using multiple proxies on a sediment core, representing unmixed summer monsoonal record. A 390 cm long piston core was obtained from the continental shelf off Negombo by National Aquatic Resources Research and Development Agency , was used for this study. This site mainly receives sediment from rivers fed by summer monsoon. Colour reflectance and chemical composition of the sediments, and δ18O and δ13C of Globigerinoides ruber foraminifera, extracted from the sediments were measured at 0.1-2.0 cm resolutions. Principal component analysis of chemical compositional data and colour reflectance data was performed to extract important components that represent climate variability. Benthic and planktonic foraminifera species that indicate upwelling were counted at 2 cm resolution. Radiocarbon dating was carried out using intact micro-shells. Results indicate that upwelling proxies (δ13C, foraminiferal proxies, and colour reflectance-Chlorophyll) and δ18O, which indicates evaporation-precipitation (E-P), increased during 8000-10000 cal yrs BP, 2000-4000 cal yrs BP and again after 1000 cal yrs BP. This increase in upwelling and E-P indicates strengthening of summer monsoon during these periods. However, terrestrial proxies, (XRF-PC1-Terrestrial, Ti, and DSR-PC3-iron oxides)indicate decrease in terrestrial influx which represents rainfall, from 6000-1000 cal yrs BP followed by an increase after 1000 cal yrs BP. Gradual decrease in precipitation has been observed locally as well as regionally after around 6000 cal yrs BP followed by an increase after 1000 cal yrs BP. The contrast behavior of strengthening monsoonal winds and

Upper tropospheric CH4 and CO affected by the Indian summer monsoon during OMO

NASA Astrophysics Data System (ADS)

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

2017-04-01

The trace gas transport through the Indian summer monsoon convection was investigated as part of the aircraft campaign OMO (Oxidation Mechanism Observations) using the German research aircraft HALO (High Altitude and Long Range Research Aircraft) in July/August 2015. HALO was operated alternatively from Cyprus and the Maldives. Flights took place over the Mediterranean Sea, the Arabian Peninsula and the Arabian Sea. Here we investigate the distribution of carbon monoxide (CO) and methane (CH4) in the upper troposphere, measured in-situ with the IR-laser absorption spectrometer TRISTAR. During OMO enhanced concentrations of CH4 and CO were detected in the Asian Summer monsoon anticyclone at altitudes between 11 km and 15 km. Mixing ratios exceeded background levels for CO and CH4 by 10-15 ppb and 30-40 ppb, respectively. The enhancement in the CO concentration appears to be within the range of tropospheric variability, while the methane enhancement is much higher than its natural variability. Therefore CH4 is found to be a very good tracer for air masses influenced by the monsoon. This is confirmed by back trajectory calculations with FLEXPART, indicating convective transport from India approximately 10 days before the observations. A comparison of observations with EMAC atmospheric chemistry - climate model simulations generally agree within ± 10% and ± 0.5% for CO and CH4, respectively.

South Asian Summer Monsoon Rainfall Variability and Trend: Its Links to Indo-Pacific SST Anomalies and Moist Processes

NASA Astrophysics Data System (ADS)

Prasanna, V.

2016-06-01

The warm (cold) phase of El Niño (La Niña) and its impact on all Indian Summer Monsoon rainfall (AISMR) relationship is explored for the past 100 years. The 103-year (1901-2003) data from the twentieth century reanalysis datasets (20CR) and other major reanalysis datasets for southwest monsoon season (JJAS) is utilized to find out the simultaneous influence of the El Niño Southern Oscillation (ENSO)-AISMR relationship. Two cases such as wet, dry monsoon years associated with ENSO(+) (El Niño), ENSO(-) (La Niña) and Non-ENSO (neutral) events have been discussed in detail using observed rainfall and three-dimensional 20CR dataset. The dry and wet years associated with ENSO and Non-ENSO periods show significant differences in the spatial pattern of rainfall associated with three-dimensional atmospheric composite, the 20CR dataset has captured the anomalies quite well. During wet (dry) years, the rainfall is high (low), i.e. 10 % above (below) average from the long-term mean and this wet or dry condition occur both during ENSO and Non-ENSO phases. The Non-ENSO year dry or wet composites are also focused in detail to understand, where do the anomalous winds come from unlike in the ENSO case. The moisture transport is coherent with the changes in the spatial pattern of AISMR and large-scale feature in the 20CR dataset. Recent 50-year trend (1951-2000) is also analyzed from various available observational and reanalysis datasets to see the influence of Indo-Pacific SST and moist processes on the South Asian summer monsoon rainfall trend. Apart from the Indo-Pacific sea surface temperatures (SST), the moisture convergence and moisture transport among India (IND), Equatorial Indian Ocean (IOC) and tropical western pacific (WNP) is also important in modifying the wet or dry cycles over India. The mutual interaction among IOC, WNP and IND in seasonal timescales is significant in modifying wet and dry cycles over the Indian region and the seasonal anomalies.

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.

Reforecasting the 1972-73 ENSO Event and the Monsoon Drought Over India

NASA Astrophysics Data System (ADS)

Shukla, J.; Huang, B.; Shin, C. S.

2016-12-01

This paper presents the results of reforcasting the 1972-73 ENSO event and the Indian summer monsoon drought using the National Centers for Environmental Prediction (NCEP) Climate Forecast System, version 2 (CFSv2), initialized with the Eu­ropean Centre for Medium-Range Weather Forecasts (ECMWF) global ocean reanalysis version 4, and observation-based land and atmosphere reanalyses. The results of this paper demonstrate that if the modern day climate models were available during the 1970's, even with the limited observations at that time, it should have been possible to predict the 1972-73 ENSO event and the associated monsoon drought. These results further suggest the necessity of continuing to develop realistic models of the climate system for accurate and reliable seasonal predictions. This paper also presents a comparison of the 1972-73 El Niño reforecast with the 1997-98 case. As the strongest event during 1958-78, the 1972-73 El Niño is distinguished from the 1997-98 one by its early termination. Initialized in the spring season, the forecast system predicted the onset and development of both events reasonably well, although the reforecasts underestimate the ENSO peaking magnitudes. On the other hand, the reforecasts initialized in spring and fall of 1972 persistently predicted lingering wind and SST anomalies in the eastern equatorial Pacific during the spring of 1973. Initialized in fall of 1997, the reforecast also grossly overestimates the peaking westerly wind and warm SST anomalies in the 1997-98 El Niño.In 1972-73, both the Eastern Pacific SST anomalies (for example Nino 3 Index) and the summer monsoon drought over India and the adjoining areas were predicted remarkably well. In contrast, the Eastern Pacific SST anomalies for the 1997-98 event were predicted well, but the normal summer monsoon rainfall over India of 1997 was not predicted by the model. This case study of the 1972-73 event is part of a larger, comprehensive reforecast project

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.

Mediterranean summer climate and the monsoon regimes

NASA Astrophysics Data System (ADS)

Baldi, M.; Crisci, A.; Dalu, G. A.; Maracchi, G.; Meneguzzo, F.; Pasqui, M.

2003-04-01

The Authors examine the general features of climate of the Mediterranean Region, i.e. its variability and trends in the last 40 years, and the teleconnections between Mediterranean climate and the global climate, using zonal and global indices. In particular they focus the attention on the analysis of the summer Mediterranean climate, and its variability and connection with the summer monsoon regimes. Several subregions can be distinguished in the Mediterranean for each season, and the occurrence of Mediterranean Oscillation is evident between West and East sub-basins. Precipitation and SLP fields in the Eastern basin are shown to be correlated with Mediterranean Oscillation. A total decrease of precipitation has been detected in last few years, although there are some very intense. During winter a fundamental role is played by NAO index, which, influencing the storm tracks coming from the Atlantic and passing over the Mediterranean and North Europe, it has a major role in the precipitation patterns over the Region. Moreover, temperature analysis over the last 40 years in the Mediterranean shows a distinct warming, in agreement with the pattern over North Emisphere and NAO index fluctuations. During summer the Hadley cell extend further northwards, influencing the Mediterranean climate, and there is evidence of a possible teleconnection with the Asian Monsoon, and the Sahel precipitation (and related Hadley cell): the SLP field in the Eastern Mediterranean is inversely correlated with those two precipitation indices, while it is positively correlated with the pressure in the Western Mediterranean. Leading mechanisms of interaction between Mediterranean summer rainfall and SLP patterns and precipitation indices associated with monsoon regimes are stressed out and investigated, as well as the influence of the position and strength of the Hadley cell, by means of both statistical and dynamical analytical arguments. A modeling study has been carried out in order to

An 8,600 year lacustrine record of summer monsoon variability from Yunnan, China

NASA Astrophysics Data System (ADS)

Hillman, Aubrey L.; Abbott, Mark B.; Finkenbinder, Matthew S.; Yu, JunQing

2017-10-01

Interactions between the Indian Summer Monsoon (ISM) and East Asian Summer Monsoon (EASM) are complex, yet needed to provide a long-term perspective of precipitation patterns in southeast Asia. Here we present an 8600-year sediment record from Xingyun Lake in Yunnan, China, a transitional zone that receives inputs of precipitation from both the ISM and EASM. Analysis of stable oxygen isotopes (δ18O) from authigenic calcite yields a semi-quantitative estimate of the timing and magnitude of lake level change that reflects changes in effective moisture from monsoon variability. Between 8600 and 6900 years BP, δ18O values are stable and low, indicating high lake levels and overflowing conditions resulting from a strong ISM. After 6900 years BP, δ18O values shift to higher values, which we suggest reflects a weakening of the ISM caused by declining summer insolation. The most substantial positive shift in isotopes occurs from 5000 to 4300 years BP and is coincident with aridity in India and the Tibetan Plateau. Other proxy records indicate increased ENSO variability and a southward shift in the ITCZ, which has an effect on the strength and onset of the ISM and may account for this change in hydrologic balance. After 4300 years BP, δ18O values continue to increase reflecting a gradual drying trend, but increases are smaller than prior periods, in part due to lake bathymetry that limits the potential for isotopic enrichment driven by evaporation. The relative influence of the ISM and EASM in the Yunnan Province of China during the Holocene remains a topic for future study, but our results suggest the predominance of the ISM and a possible connection to ENSO patterns on centennial to millennial timescales.

Indian summer monsoon rainfall variability during 2014 and 2015 and associated Indo-Pacific upper ocean temperature patterns

NASA Astrophysics Data System (ADS)

Kakatkar, Rashmi; Gnanaseelan, C.; Chowdary, J. S.; Parekh, Anant; Deepa, J. S.

2018-02-01

In this study, factors responsible for the deficit Indian Summer Monsoon (ISM) rainfall in 2014 and 2015 and the ability of Indian Institute of Tropical Meteorology-Global Ocean Data Assimilation System (IITM-GODAS) in representing the oceanic features are examined. IITM-GODAS has been used to provide initial conditions for seasonal forecast in India during 2014 and 2015. The years 2014 and 2015 witnessed deficit ISM rainfall but were evolved from two entirely different preconditions over Pacific. This raises concern over the present understanding of the role of Pacific Ocean on ISM variability. Analysis reveals that the mechanisms associated with the rainfall deficit over the Indian Subcontinent are different in the two years. It is found that remote forcing in summer of 2015 due to El Niño is mostly responsible for the deficit monsoon rainfall through changes in Walker circulation and large-scale subsidence. In the case of the summer of 2014, both local circulation with anomalous anticyclone over central India and intrusion of mid-latitude dry winds from north have contributed for the deficit rainfall. In addition to the above, Tropical Indian Ocean (TIO) sea surface temperature (SST) and remote forcing from Pacific Ocean also modulated the ISM rainfall. It is observed that Pacific SST warming has extended westward in 2014, making it a basin scale warming unlike the strong El Niño year 2015. The eastern equatorial Indian Ocean is anomalously warmer than west in summer of 2014, and vice versa in 2015. These differences in SST in both tropical Pacific and TIO have considerable impact on ISM rainfall in 2014 and 2015. The study reveals that initializing coupled forecast models with proper upper ocean temperature over the Indo-Pacific is therefore essential for improved model forecast. It is important to note that the IITM-GODAS which assimilates only array for real-time geostrophic oceanography (ARGO) temperature and salinity profiles could capture most of the

Regional Climate Model Performance in Simulating Intra-seasonal and Interannual Variability of Indian Summer Monsoon

NASA Astrophysics Data System (ADS)

Bhatla, R.; Ghosh, Soumik; Mall, R. K.; Sinha, P.; Sarkar, Abhijit

2018-05-01

Establishment of Indian summer monsoon (ISM) rainfall passes through the different phases and is not uniformly distributed over the Indian subcontinent. This enhancement and reduction in daily rainfall anomaly over the Indian core monsoon region during peak monsoon season (i.e., July and August) are commonly termed as `active' and `break' phases of monsoon. The purpose of this study is to analyze REGional Climate Model (RegCM) results obtained using the most suitable convective parameterization scheme (CPS) to determine active/break phases of ISM. The model-simulated daily outgoing longwave radiation (OLR), mean sea level pressure (MSLP), and the wind at 850 hPa of spatial resolution of 0.5°× 0.5° are compared with NOAA, NCEP, and EIN15 data, respectively over the South-Asia Co-Ordinated Regional Climate Downscaling EXperiment (CORDEX) region. 25 years (1986-2010) composites of OLR, MSLP, and the wind at 850 hPa are considered from start to the dates of active/break phase and up to the end dates of active/break spell of monsoon. A negative/positive anomaly of OLR with active/break phase is found in simulations with CPSs Emanuel and Mix99 (Grell over land; Emanuel over ocean) over the core monsoon region as well as over Monsoon Convergence Zone (MCZ) of India. The appearance of monsoon trough during active phase over the core monsoon zone and its shifting towards the Himalayan foothills during break phase are also depicted well. Because of multi-cloud function over oceanic region and single cloud function over the land mass, the Mix99 CPSs perform well in simulating the synoptic features during the phases of monsoon.

Influence of Latent Heating over the Asian and Western Pacific Monsoon Region on Sahel Summer Rainfall.

PubMed

He, Shan; Yang, Song; Li, Zhenning

2017-08-09

There has been an interdecadal shift towards a less humid state in Sahel summer rainfall since the 1960s. The decreased Sahel summer rainfall was associated with enhanced summer latent heating over the South Asian and western Pacific summer monsoon region and anomalous zonal-vertical cell of the Asian summer monsoon circulation, indicating that the latent heating plays a significant role in the change in Sahel rainfall. The effects of the latent heating over different monsoon domains on the Sahel rainfall are investigated through several model experiments. Results show that the remote monsoon heating mainly affects Sahel rainfall by generating changes in the zonal-vertical atmospheric circulation.

Summer monsoon response of the Northern Somali Current, 1995

NASA Astrophysics Data System (ADS)

Schott, Friedrich; Fischer, Jürgen; Garternicht, Ulf; Quadfasel, Detlef

Preliminary results on the development of the northern Somali Current regime and Great Whirl during the summer monsoon of 1995 are reported. They are based on the water mass and current profiling observations from three shipboard surveys of R/V Meteor and on the time series from a moored current-meter and ADCP array. The monsoon response of the GW was deep-reaching, to more than 1000m. involving large deep transports. The northern Somali Current was found to be disconnected from the interior Arabian Sea in latitude range 4°N-12°N in both, water mass properties and current fields. Instead, communication dominantly occurs through the passages between Socotra and the African continent. From moored stations in the main passage a northward throughflow from the Somali Current to the Gulf of Aden of about 5 Sv was determined for the summer monsoon of 1995.

Early-Holocene decoupled summer temperature and monsoon precipitation in southwest China

NASA Astrophysics Data System (ADS)

Wu, D.; Chen, F.; Chen, X.; Lv, F.; Zhou, A.; Chen, J.; Abbott, M. B.; Yu, J.

2017-12-01

Proxy based reconstructions of Holocene temperature have shown that both the timing and magnitude of the thermal maximum vary substantially between different regions; the simulations results from climate models also show that summers were substantially cooler over regions directly influenced by the presence of the Laurentide ice sheet during the early Holocene, whereas other regions of the Northern Hemisphere were dominated by orbital forcing. However, for lack of summer temperature reconstruction in the low latitude regions like southwestern China dominated by the Indian summer monsoon, the Holocene summer temperature variations and it underlying forcing mechanism are ambiguous. Here we present a well-dated record of pollen-based quantitative summer temperature (mean July; MJT) over the last 14000 years from Xingyun Lake, Yunnan Province, southwest China. It was found that MJT decreased during the YD event, then increased slowly until 7400 yr BP, and decreased thereafter. The MJT shows a pattern with middle Holocene maximum of MJT, indicating a different changing pattern with the carbonate oxygen isotope record (d18O) from the same core during the early Holocene (11500-7400 yr BP), which has the similar variation with speleothem d18O record from Dongge cave, both indicate the variation of monsoon precipitation with the highest precipitation occurred during the early Holocene. Therefore, we propose that the variation of summer temperature and precipitation in southwest China was decoupled during the early Holocene. However, both MJT and monsoon precipitation decreased after the middle Holocene following the boreal summer insolation. We suggest that the high precipitation with strong summer monsoon and hence higher cloud cover may depress the temperature increasing forced by increasing summer insolation during the early Holocene; while melting ice-sheet in the high latitude regions had strongly influenced the summer temperature increase during the deglacial period

Stratospheric Influence on Summer Monsoon and Associated Planetary Wave Breaking and Mixing in the Subtropical Tropopause Region

NASA Astrophysics Data System (ADS)

Lubis, S. W.; Nakamura, N.

2017-12-01

Previous studies have shown that the monsoonal circulation plays an important role in planetary wave breaking (PWB). The highest frequency of breaking events occurs just downstream (east) of the monsoon region in summer. PWB induces mixing of potential vorticity (PV) and hence, alter the horizontal mixing in the atmosphere. Here, the authors hypothesize that the stratospheric easterlies in the boreal summer also play a significant role in the PWB and mixing associated with the summer monsoon. If the stratospheric winds were westerly in boreal summer, the frequency of PWB would be decreased due to more waves penetrating in the stratosphere, resulting in less horizontal PWB and thus reduced mixing in the subtropical tropopause region. The hypothesis is examined by using a set of idealized moist GFDL simulations. The monsoon circulation is produced by adding a land-sea contrast with a Gaussian-shaped mountains positioned in the midlatitudes. Other key ingredients for the monsoon, including albedo, oceanic warm pool, and Q-flux, were also ideally imposed in all simulations. Our control simulation produces a summer monsoon-like circulation similar to the observation. In particular, the thermally forced monsoonal circulation forms a prominent closed upper-level anticyclone that dominates the summertime upper-level flow. Associated with this circulation is an upward-bulging tropopause that forms a large reservoir of anomalously low PV. Consistent with previous studies, the well-defined tropospheric jet lies just poleward of the upper-level anticyclone, and acts as a dynamical barrier between the low-PV reservoir over the monsoonal region and the high-PV reservoir in the extratropics. This barrier disappears just northeast of the monsoon area in the jet exit region, allowing more quasi-planetary waves to break in this region. Repetitive wave breaking further weakens the PV gradient, leading to the formation of the surf zone and stronger mixing in this region. To quantify

Regional changes in extreme monsoon rainfall deficit and excess in India

NASA Astrophysics Data System (ADS)

Pal, Indrani; Al-Tabbaa, Abir

2010-04-01

With increasing concerns about climate change, the need to understand the nature and variability of monsoon climatic conditions and to evaluate possible future changes becomes increasingly important. This paper deals with the changes in frequency and magnitudes of extreme monsoon rainfall deficiency and excess in India from 1871 to 2005. Five regions across India comprising variable climates were selected for the study. Apart from changes in individual regions, changing tendencies in extreme monsoon rainfall deficit and excess were also determined for the Indian region as a whole. The trends and their significance were assessed using non-parametric Mann-Kendall technique. The results show that intra-region variability for extreme monsoon seasonal precipitation is large and mostly exhibited a negative tendency leading to increasing frequency and magnitude of monsoon rainfall deficit and decreasing frequency and magnitude of monsoon rainfall excess.

Initial results from the StratoClim aircraft campaign in the Asian Monsoon in summer 2017

NASA Astrophysics Data System (ADS)

Rex, M.

2017-12-01

The Asian Monsoon System is one of the Earth's largest and most energetic weather systems. Monsoon rainfall is critical to feeding over a billion people in Asia and the monsoon circulation affects weather patterns over the entire northern hemisphere. The Monsoon also acts like an enormous elevator, pumping vast amounts of air and pollutants from the surface up to the tropopause region at levels above 16km altitude, from where air can ascend into the stratosphere, where it spreads globally. Thus the monsoon affects the chemical composition of the global tropopause region and the stratosphere, and hence plays a key role for the composition of the UTS. Dynamically the monsoon circulation leads to the formation of a large anticyclone at tropopause levels above South Asia - the Asian Monsoon Anticyclone (AMA). Satellite images show a large cloud of aerosols directly above the monsoon, the Asian Tropopause Aerosol Layer (ATAL). In July to August 2017 the international research project StratoClim carried out the first in-situ aircraft measurements in the AMA and the ATAL with the high altitude research aircraft M55-Geophysica. Around 8 scientific flights took place in the airspaces of Nepal, India and Bangladesh and have horizontally and vertically probed the AMA and have well characterized the ATAL along flight patterns that have been carefully designed by a theory, modelling and satellite data analysing team in the field. The aircraft campaign has been complemented by launches of research balloons from ground stations in Nepal, Bangladesh, China and Palau. The presentation will give an overview of the StratoClim project, the aircraft and balloon activities and initial results from the StratoClim Asian Monsoon campaign in summer 2017.

On the shortening of Indian summer monsoon season in a warming scenario

NASA Astrophysics Data System (ADS)

Sabeerali, C. T.; Ajayamohan, R. S.

2018-03-01

Assessing the future projections of the length of rainy season (LRS) has paramount societal impact considering its potential to alter the seasonal mean rainfall over the Indian subcontinent. Here, we explored the projections of LRS using both historical and Representative Concentration Pathways 8.5 (RCP8.5) simulations of the Coupled Model Intercomparison Project Phase5 (CMIP5). RCP8.5 simulations project shortening of the LRS of Indian summer monsoon by altering the timing of onset and withdrawal dates. Most CMIP5 RCP8.5 model simulations indicate a faster warming rate over the western tropical Indian Ocean compared to other regions of the Indian Ocean. It is found that the pronounced western Indian Ocean warming and associated increase in convection results in warmer upper troposphere over the Indian Ocean compared to the Indian subcontinent, reducing the meridional gradient in upper tropospheric temperature (UTT) over the Asian summer monsoon (ASM) domain. The weakening of the meridional gradient in UTT induces weakening of easterly vertical wind shear over the ASM domain during first and last phase of monsoon, facilitate delayed (advanced) monsoon onset (withdrawal) dates, ensues the shortening of LRS of the Indian summer monsoon in a warming scenario.

Role of Oceanic and Terrestrial Atmospheric Moisture Sources in Intraseasonal Variability of Indian Summer Monsoon Rainfall.

PubMed

Pathak, Amey; Ghosh, Subimal; Kumar, Praveen; Murtugudde, Raghu

2017-10-06

Summer Monsoon Rainfall over the Indian subcontinent displays a prominent variability at intraseasonal timescales with 10-60 day periods of high and low rainfall, known as active and break periods, respectively. Here, we study moisture transport from the oceanic and terrestrial sources to the Indian landmass at intraseasonal timescales using a dynamic recycling model, based on a Lagrangian trajectory approach applied to the ECMWF-ERA-interim reanalysis data. Intraseasonal variation of monsoon rainfall is associated with both a north-south pattern from the Indian landmass to the Indian Ocean and an east-west pattern from the Core Monsoon Zone (CMZ) to eastern India. We find that the oceanic sources of moisture, namely western and central Indian Oceans (WIO and CIO) contribute to the former, while the major terrestrial source, Ganga basin (GB) contributes to the latter. The formation of the monsoon trough over Indo-Gangetic plain during the active periods results in a high moisture transport from the Bay of Bengal and GB into the CMZ in addition to the existing southwesterly jet from WIO and CIO. Our results indicate the need for the correct representation of both oceanic and terrestrial sources of moisture in models for simulating the intraseasonal variability of the monsoon.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mei, Rui; Ashfaq, Moetasim; Rastogi, Deeksha

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. Ourmore » 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.« less

South Asian Summer Monsoon and Its Relationship with ENSO in the IPCC AR4 Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Annamalai, H; Hamilton, K; Sperber, K R

In this paper we use the extensive integrations produced for the IPCC Fourth Assessment Report (AR4) to examine the relationship between ENSO and the monsoon at interannual and decadal timescales. We begin with an analysis of the monsoon simulation in the 20th century integrations. Six of the 18 models were found to have a reasonably realistic representation of monsoon precipitation climatology. For each of these six models SST and anomalous precipitation evolution along the equatorial Pacific during El Nino events display considerable differences when compared to observations. Out of these six models only four (GFDL{_}CM{_}2.0, GFDL{_}CM{_}2.1, MRI, and MPI{_}ECHAM5) exhibitmore » a robust ENSO-monsoon contemporaneous teleconnection, including the known inverse relationship between ENSO and rainfall variations over India. Lagged correlations between the all-India rainfall (AIR) index and Nino3.4 SST reveal that three models represent the timing of the teleconnection, including the spring predictability barrier which is manifested as the transition from positive to negative correlations prior to the monsoon onset. Furthermore, only one of these three models (GFDL{_}CM{_}2.1) captures the observed phase lag with the strongest anticorrelation of SST peaking 2-3 months after the summer monsoon, which is partially attributable to the intensity of simulated El Nino itself. We find that the models that best capture the ENSO-monsoon teleconnection are those that correctly simulate the timing and location of SST and diabatic heating anomalies in the equatorial Pacific, and the associated changes to the equatorial Walker Circulation during El Nino events. The strength of the AIR-Nino3.4 SST correlation in the model runs waxes and wanes to some degree on decadal timescales. The overall magnitude and timescale for this decadal modulation in most of the models is similar to that seen in observations. However, there is little consistency in the phase among the realizations

Estimates of methane emissions from India using CH4-CO-C2H6 relationships from CARIBIC observations in monsoon convective outflow

NASA Astrophysics Data System (ADS)

Baker, A. K.; Rauthe-Schöch, A.; Schuck, T. J.; van Velthoven, P. F.; Slemr, F.; Brenninkmeijer, C. A.

2010-12-01

A large fraction of methane sources are anthropogenic, and include fossil fuel use, biomass/biofuel burning, agriculture and waste treatment. Recently, much attention regarding emissions of greenhouse gases has focused on large, developing nations, as their emissions are expected to rise rapidly over the coming decades. As the second most populous country in the world, and one of the fastest growing economies, India has been of particular interest. Arguably the most important feature of meteorology in India is the Asian summer monsoon. During the monsoon period there exists persistent deep convection over Southern Asia, and the composition of convected air masses is strongly influenced by emissions from India. This ultimately results in a well-mixed air parcel containing air from India being transported to the upper troposphere. Over the course of the 2008 monsoon period the CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) passenger aircraft conducted monthly measurement flights which probed this outflow. Data collected during these flights provides a unique opportunity to examine sources of atmospheric species in India. Here we use measurements of methane (CH4), carbon monoxide (CO) and ethane (C2H6) from whole air samples collected during CARIBIC flights to estimate emissions of methane and to quantify those emissions related to flooding during the monsoon. Methane data from the monsoon period show enhancements inside the monsoon plume, which increase as the monsoon progresses. Using emission data for CO and ΔCH4/ΔCO derived from CARIBIC measurements, we estimate total methane emissions to be ~40 Tg yr-1. Relationships of methane to ethane, which shares the bulk of its sources with methane but lacks a biological component, are further used to estimate the fraction of “extra” emissions from biological activity related to increased monsoon rains. This additional methane is a considerable fraction of

Indian Ocean and Indian summer monsoon: relationships without ENSO in ocean-atmosphere coupled simulations

NASA Astrophysics Data System (ADS)

Crétat, Julien; Terray, Pascal; Masson, Sébastien; Sooraj, K. P.; Roxy, Mathew Koll

2017-08-01

The relationship between the Indian Ocean and the Indian summer monsoon (ISM) and their respective influence over the Indo-Western North Pacific (WNP) region are examined in the absence of El Niño Southern Oscillation (ENSO) in two partially decoupled global experiments. ENSO is removed by nudging the tropical Pacific simulated sea surface temperature (SST) toward SST climatology from either observations or a fully coupled control run. The control reasonably captures the observed relationships between ENSO, ISM and the Indian Ocean Dipole (IOD). Despite weaker amplitude, IODs do exist in the absence of ENSO and are triggered by a boreal spring ocean-atmosphere coupled mode over the South-East Indian Ocean similar to that found in the presence of ENSO. These pure IODs significantly affect the tropical Indian Ocean throughout boreal summer, inducing a significant modulation of both the local Walker and Hadley cells. This meridional circulation is masked in the presence of ENSO. However, these pure IODs do not significantly influence the Indian subcontinent rainfall despite overestimated SST variability in the eastern equatorial Indian Ocean compared to observations. On the other hand, they promote a late summer cross-equatorial quadrupole rainfall pattern linking the tropical Indian Ocean with the WNP, inducing important zonal shifts of the Walker circulation despite the absence of ENSO. Surprisingly, the interannual ISM rainfall variability is barely modified and the Indian Ocean does not force the monsoon circulation when ENSO is removed. On the contrary, the monsoon circulation significantly forces the Arabian Sea and Bay of Bengal SSTs, while its connection with the western tropical Indian Ocean is clearly driven by ENSO in our numerical framework. Convection and diabatic heating associated with above-normal ISM induce a strong response over the WNP, even in the absence of ENSO, favoring moisture convergence over India.

Seasonal Transitions and the Westerly Jet in the Holocene East Asian Summer Monsoon

NASA Astrophysics Data System (ADS)

Chiang, J. C. H.; Kong, W.; Swenson, L. M.

2016-12-01

The Holocene East Asian Summer Monsoon (EASM) evolution was previously characterized as a trend towards weaker monsoon intensity paced by orbital insolation. We argue that this evolution is more accurately characterized as changes in the transition timing and duration of the EASM seasonal stages (Spring, pre Mei-Yu, Mei-Yu, Midsummer), and tied to the north-south displacement of the westerlies relative to Tibet. To this end, we employ atmospheric general circulation model time-slice simulations across the Holocene, and objectively identify the transition timing and duration of the EASM seasonal stages. Compared to the late Holocene, we find an earlier onset of Mei-Yu and an earlier transition from Mei-Yu to Summer in the early-mid Holocene, resulting in a shortened Mei-Yu and prolonged Summer stage. These changes are accompanied by an earlier northward positioning of the westerlies relative to Tibet. Our hypothesis provides a more satisfactory explanation for two key observations of Holocene East Asian climate: the `asynchronous Holocene optimum', and changes to East Asian dustiness. Our results highlight a key difference in the way that the East Asian monsoon dynamically responds to precessional insolation changes compared to the other monsoons. For other monsoon systems, changes to the land-ocean contrast drive changes to monsoon intensity. While this also occurs for the East Asian monsoon, more importantly changes to the meridional position of the westerlies relative to the Tibetan Plateau determine the timing of seasonal transitions; a northward shift triggers earlier seasonal rainfall transitions and in particular a shorter Mei-Yu and longer Midsummer stage. By similar reasoning, changes to obliquity also strongly affect East Asian summer monsoon seasonality, with a larger tilt resulting in earlier northward shift of the westerlies.

Simulation of South-Asian Summer Monsoon in a GCM

NASA Astrophysics Data System (ADS)

Ajayamohan, R. S.

2007-10-01

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

Future projection of Indian summer monsoon variability under climate change scenario: An assessment from CMIP5 climate models

NASA Astrophysics Data System (ADS)

Sharmila, S.; Joseph, S.; Sahai, A. K.; Abhilash, S.; Chattopadhyay, R.

2015-01-01

In this study, the impact of enhanced anthropogenic greenhouse gas emissions on the possible future changes in different aspects of daily-to-interannual variability of Indian summer monsoon (ISM) is systematically assessed using 20 coupled models participated in the Coupled Model Inter-comparison Project Phase 5. The historical (1951-1999) and future (2051-2099) simulations under the strongest Representative Concentration Pathway have been analyzed for this purpose. A few reliable models are selected based on their competence in simulating the basic features of present-climate ISM variability. The robust and consistent projections across the selected models suggest substantial changes in the ISM variability by the end of 21st century indicating strong sensitivity of ISM to global warming. On the seasonal scale, the all-India summer monsoon mean rainfall is likely to increase moderately in future, primarily governed by enhanced thermodynamic conditions due to atmospheric warming, but slightly offset by weakened large scale monsoon circulation. It is projected that the rainfall magnitude will increase over core monsoon zone in future climate, along with lengthening of the season due to late withdrawal. On interannual timescales, it is speculated that severity and frequency of both strong monsoon (SM) and weak monsoon (WM) might increase noticeably in future climate. Substantial changes in the daily variability of ISM are also projected, which are largely associated with the increase in heavy rainfall events and decrease in both low rain-rate and number of wet days during future monsoon. On the subseasonal scale, the model projections depict considerable amplification of higher frequency (below 30 day mode) components; although the dominant northward propagating 30-70 day mode of monsoon intraseasonal oscillations may not change appreciably in a warmer climate. It is speculated that the enhanced high frequency mode of monsoon ISOs due to increased GHG induced warming

Can the Southern annular mode influence the Korean summer monsoon rainfall?

NASA Astrophysics Data System (ADS)

Prabhu, Amita; Kripalani, Ramesh; Oh, Jaiho; Preethi, Bhaskar

2017-05-01

We demonstrate that a large-scale longitudinally symmetric global phenomenon in the Southern Hemisphere sub-polar region can transmit its influence over a remote local region of the Northern Hemisphere traveling more than 100° of latitudes (from 70°S to 40°N). This is illustrated by examining the relationship between the Southern Annular Mode (SAM) and the Korean Monsoon Rainfall (KMR) based on the data period 1983-2013. Results reveal that the May-June SAM (MJSAM) has a significant in-phase relationship with the subsequent KMR. A positive MJSAM is favorable for the summer monsoon rainfall over the Korean peninsula. The impact is relayed through the central Pacific Ocean. When a negative phase of MJSAM occurs, it gives rise to an anomalous meridional circulation in a longitudinally locked air-sea coupled system over the central Pacific that propagates from sub-polar to equatorial latitudes and is associated with the central Pacific warming. The ascending motion over the central Pacific descends over the Korean peninsula during peak-boreal summer resulting in weakening of monsoon rainfall. The opposite features prevail during a positive phase of SAM. Thus, the extreme modes of MJSAM could possibly serve as a predictor for ensuing Korean summer monsoon rainfall.

Impact of the springtime Himalayan-Tibetan Plateau on the onset on the Indian summer monsoon in coupled forecasts

NASA Astrophysics Data System (ADS)

Orsolini, Yvan; Senan, Retish; Weisheimer, Antje; Vitart, Frederic; Balsamo, Gianpaolo; Doblas-Reyes, Francisco; Stockdale, Timothy; Dutra, Emanuel

2016-04-01

The springtime snowpack over the Himalayan-Tibetan Plateau (HTP) region has long been suggested to be an influential factor on the onset of the Indian summer monsoon. In the frame of the SPECS project, we have assessed the impact of realistic snow initialization in springtime over HTP on the onset of the Indian summer monsoon. We examine a suite of coupled ocean-atmosphere 4-month ensemble reforecasts made at the European Centre for Medium-Range Weather Forecasts (ECMWF), using the Seasonal Forecasting System 4. The reforecasts were initialized on 1 April every year for the period 1981-2010. In these seasonal reforecasts, the snow is initialized "realistically" with ERA-Interim/Land Reanalysis. In addition, we carried out an additional set of forecasts, identical in all aspects except that initial conditions for snow-related land surface variables over the HTP region are randomized. We show that high snow depth over HTP influences the meridional tropospheric temperature gradient reversal that marks the monsoon onset. Composite difference based on a normalized HTP snow index reveal that, in high snow years, (i) the onset is delayed by about 8 days, and (ii) negative precipitation anomalies and warm surface conditions prevail over India. We show that about half of this delay can be attributed to the realistic initialization of snow over the HTP region. We further demonstrate that high April snow depths over HTP are not uniquely influenced by either the El Nino-Southern Oscillation, the Indian Ocean Dipole or the North Atlantic Oscillation.

Soil moisture variations in remotely sensed and reanalysis datasets during weak monsoon conditions over central India and central Myanmar

NASA Astrophysics Data System (ADS)

Shrivastava, Sourabh; Kar, Sarat C.; Sharma, Anu Rani

2017-07-01

Variation of soil moisture during active and weak phases of summer monsoon JJAS (June, July, August, and September) is very important for sustenance of the crop and subsequent crop yield. As in situ observations of soil moisture are few or not available, researchers use data derived from remote sensing satellites or global reanalysis. This study documents the intercomparison of soil moisture from remotely sensed and reanalyses during dry spells within monsoon seasons in central India and central Myanmar. Soil moisture data from the European Space Agency (ESA)—Climate Change Initiative (CCI) has been treated as observed data and was compared against soil moisture data from the ECMWF reanalysis-Interim (ERA-I) and the climate forecast system reanalysis (CFSR) for the period of 2002-2011. The ESA soil moisture correlates rather well with observed gridded rainfall. The ESA data indicates that soil moisture increases over India from west to east and from north to south during monsoon season. The ERA-I overestimates the soil moisture over India, while the CFSR soil moisture agrees well with the remotely sensed observation (ESA). Over Myanmar, both the reanalysis overestimate soil moisture values and the ERA-I soil moisture does not show much variability from year to year. Day-to-day variations of soil moisture in central India and central Myanmar during weak monsoon conditions indicate that, because of the rainfall deficiency, the observed (ESA) and the CFSR soil moisture values are reduced up to 0.1 m3/m3 compared to climatological values of more than 0.35 m3/m3. This reduction is not seen in the ERA-I data. Therefore, soil moisture from the CFSR is closer to the ESA observed soil moisture than that from the ERA-I during weak phases of monsoon in the study region.

Intensified summer monsoon and the urbanization of Indus Civilization in northwest India.

PubMed

Dixit, Yama; Hodell, David A; Giesche, Alena; Tandon, Sampat K; Gázquez, Fernando; Saini, Hari S; Skinner, Luke C; Mujtaba, Syed A I; Pawar, Vikas; Singh, Ravindra N; Petrie, Cameron A

2018-03-09

Today the desert margins of northwest India are dry and unable to support large populations, but were densely occupied by the populations of the Indus Civilization during the middle to late Holocene. The hydroclimatic conditions under which Indus urbanization took place, which was marked by a period of expanded settlement into the Thar Desert margins, remains poorly understood. We measured the isotopic values (δ 18 O and δD) of gypsum hydration water in paleolake Karsandi sediments in northern Rajasthan to infer past changes in lake hydrology, which is sensitive to changing amounts of precipitation and evaporation. Our record reveals that relatively wet conditions prevailed at the northern edge of Rajasthan from ~5.1 ± 0.2 ka BP, during the beginning of the agricultural-based Early Harappan phase of the Indus Civilization. Monsoon rainfall intensified further between 5.0 and 4.4 ka BP, during the period when Indus urban centres developed in the western Thar Desert margin and on the plains of Haryana to its north. Drier conditions set in sometime after 4.4 ka BP, and by ~3.9 ka BP an eastward shift of populations had occurred. Our findings provide evidence that climate change was associated with both the expansion and contraction of Indus urbanism along the desert margin in northwest India.

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

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.

Is the negative IOD during 2016 the reason for monsoon failure over southwest peninsular India?

NASA Astrophysics Data System (ADS)

Sreelekha, P. N.; Babu, C. A.

2018-01-01

The study investigates the mechanism responsible for the deficit rainfall over southwest peninsular India during the 2016 monsoon season. Analysis shows that the large-scale variation in circulation pattern due to the strong, negative Indian Ocean Dipole phenomenon was the reason for the deficit rainfall. Significant reduction in the number of northward-propagating monsoon-organized convections together with fast propagation over the southwest peninsular India resulted in reduction in rainfall. On the other hand, their persistence for longer time over the central part of India resulted in normal rainfall. It was found that the strong convection over the eastern equatorial Indian Ocean creates strong convergence over that region. The combined effect of the sinking due to the well-developed Walker circulation originated over the eastern equatorial Indian Ocean and the descending limb of the monsoon Hadley cell caused strong subsidence over the western equatorial Indian Ocean. The tail of this large-scale sinking extended up to the southern parts of India. This hinders formation of monsoon-organized convections leading to a large deficiency of rainfall during monsoon 2016 over the southwest peninsular India.

Influence of large-scale climate modes on dynamical complexity patterns of Indian Summer Monsoon rainfall

NASA Astrophysics Data System (ADS)

Papadimitriou, Constantinos; Donner, Reik V.; Stolbova, Veronika; Balasis, Georgios; Kurths, Jürgen

2015-04-01

Indian Summer monsoon is one of the most anticipated and important weather events with vast environmental, economical and social effects. Predictability of the Indian Summer Monsoon strength is crucial question for life and prosperity of the Indian population. In this study, we are attempting to uncover the relationship between the spatial complexity of Indian Summer Monsoon rainfall patterns, and the monsoon strength, in an effort to qualitatively determine how spatial organization of the rainfall patterns differs between strong and weak instances of the Indian Summer Monsoon. Here, we use observational satellite data from 1998 to 2012 from the Tropical Rainfall Measuring Mission (TRMM 3B42V7) and reanalysis gridded daily rainfall data for a time period of 57 years (1951-2007) (Asian Precipitation Highly Resolved Observational Data Integration Towards the Evaluation of Water Resources, APHRODITE). In order to capture different aspects of the system's dynamics, first, we convert rainfall time series to binary symbolic sequences, exploring various thresholding criteria. Second, we apply the Shannon entropy formulation (in a block-entropy sense) using different measures of normalization of the resulting entropy values. Finally, we examine the effect of various large-scale climate modes such as El-Niño-Southern Oscillation, North Atlantic Oscillation, and Indian Ocean Dipole, on the emerging complexity patterns, and discuss the possibility for the utilization of such pattern maps in the forecasting of the spatial variability and strength of the Indian Summer Monsoon.

Rainfall trends in the South Asian summer monsoon and its related large-scale dynamics with focus over Pakistan

NASA Astrophysics Data System (ADS)

Latif, M.; Syed, F. S.; Hannachi, A.

2017-06-01

The study of regional rainfall trends over South Asia is critically important for food security and economy, as both these factors largely depend on the availability of water. In this study, South Asian summer monsoon rainfall trends on seasonal and monthly (June-September) time scales have been investigated using three observational data sets. Our analysis identify a dipole-type structure in rainfall trends over the region north of the Indo-Pak subcontinent, with significant increasing trends over the core monsoon region of Pakistan and significant decreasing trends over the central-north India and adjacent areas. The dipole is also evident in monthly rainfall trend analyses, which is more prominent in July and August. We show, in particular, that the strengthening of northward moisture transport over the Arabian Sea is a likely reason for the significant positive trend of rainfall in the core monsoon region of Pakistan. In contrast, over the central-north India region, the rainfall trends are significantly decreasing due to the weakening of northward moisture transport over the Bay of Bengal. The leading empirical orthogonal functions clearly show the strengthening (weakening) patterns of vertically integrated moisture transport over the Arabian Sea (Bay of Bengal) in seasonal and monthly interannual time scales. The regression analysis between the principal components and rainfall confirm the dipole pattern over the region. Our results also suggest that the extra-tropical phenomena could influence the mean monsoon rainfall trends over Pakistan by enhancing the cross-equatorial flow of moisture into the Arabian Sea.

Anomalies of the Asian Monsoon Induced by Aerosol Forcings

NASA Technical Reports Server (NTRS)

Lau, William K. M.; Kim, M. K.

2004-01-01

Impacts of aerosols on the Asian summer monsoon are studied using the NASA finite volume General Circulation Model (fvGCM), with radiative forcing derived from three-dimensional distributions of five aerosol species i.e., black carbon, organic carbon, soil dust, and sea salt from the Goddard Chemistry Aerosol Radiation and Transport Model (GOCART). Results show that absorbing aerosols, i.e., black carbon and dust, induce large-scale upper-level heating anomaly over the Tibetan Plateau in April and May, ushering in & early onset of the Indian summer monsoon. Absorbing aerosols also I i enhance lower-level heating and anomalous ascent over northern India, intensifying the Indian monsoon. Overall, the aerosol-induced large-scale surface' temperature cooling leads to a reduction of monsoon rainfall over the East Asia continent, and adjacent oceanic regions.

Deep learning for predicting the monsoon over the homogeneous regions of India

NASA Astrophysics Data System (ADS)

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

2017-06-01

Indian monsoon varies in its nature over the geographical regions. Predicting the rainfall not just at the national level, but at the regional level is an important task. In this article, we used a deep neural network, namely, the stacked autoencoder to automatically identify climatic factors that are capable of predicting the rainfall over the homogeneous regions of India. An ensemble regression tree model is used for monsoon prediction using the identified climatic predictors. The proposed model provides forecast of the monsoon at a long lead time which supports the government to implement appropriate policies for the economic growth of the country. The monsoon of the central, north-east, north-west, and south-peninsular India regions are predicted with errors of 4.1%, 5.1%, 5.5%, and 6.4%, respectively. The identified predictors show high skill in predicting the regional monsoon having high variability. The proposed model is observed to be competitive with the state-of-the-art prediction models.

Response of the Asian summer monsoons to idealized precession and obliquity forcing in a set of GCMs

NASA Astrophysics Data System (ADS)

Bosmans, J. H. C.; Erb, M. P.; Dolan, A. M.; Drijfhout, S. S.; Tuenter, E.; Hilgen, F. J.; Edge, D.; Pope, J. O.; Lourens, L. J.

2018-05-01

We examine the response of the Indian and East Asian summer monsoons to separate precession and obliquity forcing, using a set of fully coupled high-resolution models for the first time: EC-Earth, GFDL CM2.1, CESM and HadCM3. We focus on the effect of insolation changes on monsoon precipitation and underlying circulation changes, and find strong model agreement despite a range of model physics, parameterization, and resolution. Our results show increased summer monsoon precipitation at times of increased summer insolation, i.e. minimum precession and maximum obliquity, accompanied by a redistribution of precipitation and convection from ocean to land. Southerly monsoon winds over East Asia are strengthened as a consequence of an intensified land-sea pressure gradient. The response of the Indian summer monsoon is less straightforward. Over south-east Asia low surface pressure is less pronounced and winds over the northern Indian Ocean are directed more westward. An Indian Ocean Dipole pattern emerges, with increased precipitation and convection over the western Indian Ocean. Increased temperatures occur during minimum precession over the Indian Ocean, but not during maximum obliquity when insolation is reduced over the tropics and southern hemisphere during northern hemisphere summer. Evaporation is reduced over the northern Indian Ocean, which together with increased precipitation over the western Indian Ocean dampens the increase of monsoonal precipitation over the continent. The southern tropical Indian Ocean as well as the western tropical Pacific (for precession) act as a moisture source for enhanced monsoonal precipitation. The models are in closest agreement for precession-induced changes, with more model spread for obliquity-induced changes, possibly related to a smaller insolation forcing. Our results indicate that a direct response of the Indian and East Asian summer monsoons to insolation forcing is possible, in line with speleothem records but in

Interannual Variability, Global Teleconnection, and Potential Predictability Associated with the Asian Summer Monsoon

NASA Technical Reports Server (NTRS)

Lau, K. M.; Kim, K. M.; Li, J. Y.

2001-01-01

In this Chapter, aspects of global teleconnections associated with the interannual variability of the Asian summer monsoon (ASM) are discussed. The basic differences in the basic dynamics of the South Asian Monsoon and the East Asian monsoon, and their implications on global linkages are discussed. Two teleconnection modes linking ASM variability to summertime precipitation over the continental North America were identified. These modes link regional circulation and precipitation anomalies over East Asia and continental North America, via coupled atmosphere-ocean variations over the North Pacific. The first mode has a large zonally symmetrical component and appears to be associated with subtropical jetstream variability and the second mode with Rossby wave dispersion. Both modes possess strong sea surface temperature (SST) expressions in the North Pacific. Results show that the two teleconnection modes may have its origin in intrinsic modes of sea surface temperature variability in the extratropical oceans, which are forced in part by atmospheric variability and in part by air-sea interaction. The potential predictability of the ASM associated with SST variability in different ocean basins is explored using a new canonical ensemble correlation prediction scheme. It is found that SST anomalies in tropical Pacific, i.e., El Nino, is the most dominant forcing for the ASM, especially over the maritime continent and eastern Australia. SST anomalies in the India Ocean may trump the influence from El Nino in western Australia and western maritime continent. Both El Nino, and North Pacific SSTs contribute to monsoon precipitation anomalies over Japan, southern Korea, northern and central China. By optimizing SST variability signals from the world ocean basins using CEC, the overall predictability of ASM can be substantially improved.

Dominant Drivers of GCMs Errors in the Simulation of South Asian Summer Monsoon

NASA Astrophysics Data System (ADS)

Ashfaq, Moetasim

2017-04-01

Accurate simulation of the South Asian summer monsoon (SAM) is a longstanding unresolved problem in climate modeling science. There has not been a benchmark effort to decipher the origin of undesired yet virtually invariable unsuccessfulness of general circulation models (GCMs) over this region. This study analyzes a large ensemble of CMIP5 GCMs to demonstrate that most of the simulation errors in the summer season and their driving mechanisms are systematic and of similar nature across the GCMs, with biases in meridional differential heating playing a critical role in determining the timing of monsoon onset over land, the magnitude of seasonal precipitation distribution and the trajectories of monsoon depressions. Errors in the pre-monsoon heat low over the lower latitudes and atmospheric latent heating over the slopes of Himalayas and Karakoram Range induce significant errors in the atmospheric circulations and meridional differential heating. Lack of timely precipitation over land further exacerbates such errors by limiting local moisture recycling and latent heating aloft from convection. Most of the summer monsoon errors and their sources are reproducible in the land-atmosphere configuration of a GCM when it is configured at horizontal grid spacing comparable to the CMIP5 GCMs. While an increase in resolution overcomes many modeling challenges, coarse resolution is not necessarily the primary driver in the exhibition of errors over South Asia. These results highlight the importance of previously less well known pre-monsoon mechanisms that critically influence the strength of SAM in the GCMs and highlight the importance of land-atmosphere interactions in the development and maintenance of SAM.

Oblique propagation of monsoon gravity waves during the northern hemisphere 2007 summer

NASA Astrophysics Data System (ADS)

Thurairajah, Brentha; Siskind, David E.; Bailey, Scott M.; Carstens, Justin N.; Russell, James M.; Mlynczak, Martin G.

2017-05-01

We present a combination of satellite observation and high-resolution model output to understand monsoon convection as a source of high-latitude mesospheric gravity waves (GWs). The GWs generated over the Northern Hemisphere (NH) monsoon region during the 2007 summer and the role of the winds in focusing these GWs toward the high-latitude middle atmosphere are analyzed using the Sounding of the Atmosphere using Broadband Emission Radiometry/Thermosphere Ionosphere Mesosphere Energetics and Dynamics (SABER/TIMED) satellite temperature data and the high-resolution Navy Operational Global Atmospheric Prediction System-Advanced Level Physics High Altitude (NOGAPS/ALPHA) model results. In the NH, above the stratosphere, the monsoon GW Momentum Flux (GWMF) exhibits a poleward tilt that follows the slanted structure of the easterly jet. The correlation coefficients (>0.5) between the time series of NH tropical stratospheric GWMF and the global winds also have a slanted structure that coincide with the easterly jet, confirming the modeling theory that stratospheric monsoon GWs are refracted into the summer easterly jet and can reach the high-latitude mesosphere. Since Polar Mesospheric Clouds (PMCs) are sensitive indicators of changes in the polar summer mesosphere, we compared the time series of tropical stratospheric GWMF to the PMC occurrence frequency (OF) obtained from the Cloud Imaging and Particle Size/Aeronomy of Ice in the Mesosphere satellite data to assess the influence of this wave focusing in the mesosphere. There is a significant positive correlation between the high-latitude PMC OF and the tropical stratospheric GWMF suggesting a definite influence of monsoon GWs on the high-latitude mesosphere. The disagreement in correlation at the end of the PMC season is attributed to the enhancement of the quasi 5 day planetary wave dominating over the influence of monsoon GWs on PMCs.

The impacts of summer monsoons on the ozone budget of the atmospheric boundary layer of the Asia-Pacific region.

PubMed

Hou, Xuewei; Zhu, Bin; Fei, Dongdong; Wang, Dongdong

2015-01-01

The seasonal and inter-annual variations of ozone (O3) in the atmospheric boundary layer of the Asia-Pacific Ocean were investigated using model simulations (2001-2007) from the Model of Ozone and Related chemical Tracers, version 4 (MOZART-4). The simulated O3 and diagnostic precipitation are in good agreement with the observations. Model results suggest that the Asia-Pacific monsoon significantly influences the seasonal and inter-annual variations of ozone. The differences of anthropogenic emissions and zonal winds in meridional directions cause a pollutants' transition zone at approximately 20°-30°N. The onset of summer monsoons with a northward migration of the rain belt leads the transition zone to drift north, eventually causing a summer minimum of ozone to the north of 30°N. In years with an early onset of summer monsoons, strong inflows of clean oceanic air lead to low ozone at polluted oceanic sites near the continent, while strong outflows from the continent exist, resulting in high levels of O3 over remote portions of the Asia-Pacific Ocean. The reverse is true in years when the summer monsoon onset is late. Copyright © 2014 Elsevier B.V. All rights reserved.

Assessment of Land Surface Models in a High-Resolution Atmospheric Model during Indian Summer Monsoon

NASA Astrophysics Data System (ADS)

Attada, Raju; Kumar, Prashant; Dasari, Hari Prasad

2018-04-01

Assessment of the land surface models (LSMs) on monsoon studies over the Indian summer monsoon (ISM) region is essential. In this study, we evaluate the skill of LSMs at 10 km spatial resolution in simulating the 2010 monsoon season. The thermal diffusion scheme (TDS), rapid update cycle (RUC), and Noah and Noah with multi-parameterization (Noah-MP) LSMs are chosen based on nature of complexity, that is, from simple slab model to multi-parameterization options coupled with the Weather Research and Forecasting (WRF) model. Model results are compared with the available in situ observations and reanalysis fields. The sensitivity of monsoon elements, surface characteristics, and vertical structures to different LSMs is discussed. Our results reveal that the monsoon features are reproduced by WRF model with all LSMs, but with some regional discrepancies. The model simulations with selected LSMs are able to reproduce the broad rainfall patterns, orography-induced rainfall over the Himalayan region, and dry zone over the southern tip of India. The unrealistic precipitation pattern over the equatorial western Indian Ocean is simulated by WRF-LSM-based experiments. The spatial and temporal distributions of top 2-m soil characteristics (soil temperature and soil moisture) are well represented in RUC and Noah-MP LSM-based experiments during the ISM. Results show that the WRF simulations with RUC, Noah, and Noah-MP LSM-based experiments significantly improved the skill of 2-m temperature and moisture compared to TDS (chosen as a base) LSM-based experiments. Furthermore, the simulations with Noah, RUC, and Noah-MP LSMs exhibit minimum error in thermodynamics fields. In case of surface wind speed, TDS LSM performed better compared to other LSM experiments. A significant improvement is noticeable in simulating rainfall by WRF model with Noah, RUC, and Noah-MP LSMs over TDS LSM. Thus, this study emphasis the importance of choosing/improving LSMs for simulating the ISM phenomena in

Equatorially/globally conditioned meteorological analysis of heaviest monsoon rains over India during 23-28 July 2005

NASA Astrophysics Data System (ADS)

Ranade, Ashwini; Singh, Nityanand

2018-06-01

The heaviest monsoon rainstorm of the period 1951-2007 over India occurred during 23-28 July 2005, mostly the peninsula received rainfall, and each day the rainwater over the country was 40.0 bcm (billion cubic meter) or more, highest 98.4 bcm fell on 25 July 2005. Present premise of monsoon genesis is that it evolves in association with spreading and intensification of equatorial atmospheric condition over Afro-Eurasian landmass and adjoining Indian and Pacific Oceans during boreal summer. Robust natural criteria have been applied to demarcate monsoon and other global weather regimes (GWRs) at standard levels (1000‒100 hPa). Global atmospheric (1000‒100 hPa) thermal condition and monsoon and general circulations during 23-28 July 2005 have been compared with normal features of respective parameters. Over tropics-subtropics (45°S-45°N), troposphere (1000‒250 hPa) was warmer-thicker and pressure lower than normal and mixed conditions of positive/negative departures in temperature, height/thickness and pressure over northern and southern mid-high latitudes. Noticeable changes in 3D monsoon structure were: horizontally spread and eastward-southward shifted over western North Pacific and stretched further southeastward across equatorial Pacific; intense warm-low lower tropospheric confluence-convergence across Asia-Pacific with vertical depth extending beyond 400 hPa; and intense warm-high upper tropospheric anticyclonic circulation zonally stretched and divided into three interconnected cells. Outflows from anticyclonic cells over Tibetan plateau and western North Pacific were mostly directed westward/southwestward/southward. Troposphere was warmer-thicker and pressure higher over eastern part of both subpolars-polars and cooler-thinner and pressure lower over western part. During the period, a deep cyclonic circulation moved from Bay of Bengal through central India while near-stationary atmospheric condition prevailed across the globe.

Clay mineralogical and geochemical proxies of the East Asian summer monsoon evolution in the South China Sea during Late Quaternary.

PubMed

Chen, Quan; Liu, Zhifei; Kissel, Catherine

2017-02-08

The East Asian summer monsoon controls the climatic regime of an extended region through temperature and precipitation changes. As the East Asian summer monsoon is primarily driven by the northern hemisphere summer insolation, such meteorological variables are expected to significantly change on the orbital timescale, influencing the composition of terrestrial sediments in terms of both mineralogy and geochemistry. Here we present clay mineralogy and major element composition of Core MD12-3432 retrieved from the northern South China Sea, and we investigate their relationship with the East Asian summer monsoon evolution over the last 400 ka. The variability of smectite/(illite + chlorite) ratio presents a predominant precession periodicity, synchronous with the northern hemisphere summer insolation changes and therefore with that of the East Asian summer monsoon. Variations in K 2 O/Al 2 O 3 are characterized by eccentricity cycles, increasing during interglacials when the East Asian summer monsoon is enhanced. Based on the knowledge of sediment provenances, we suggest that these two proxies in the South China Sea are linked to the East Asian summer monsoon evolution with different mechanisms, which are (1) contemporaneous chemical weathering intensity in Luzon for smectite/(illite + chlorite) ratio and (2) river denudation intensity for K 2 O/Al 2 O 3 ratio of bulk sediment.

South China Sea summer monsoon onset in relation to the off-equatorial ITCZ

NASA Astrophysics Data System (ADS)

Zhou, Wen; Chan, Johnny Chung-Leung; Li, Chongyin

2005-09-01

Observations of the South China Sea summer monsoon (SCSSM) demonstrate the different features between the early and late onsets of the monsoon. The determining factor related to the onset and the resultant monsoon rainfall might be the off-equatorial ITCZ besides the land-sea thermal contrast. The northward-propagating cumulus convection over the northern Indian Ocean could enhance the monsoon trough so that the effect of the horizontal advection of moisture and heat is substantially increased, thus westerlies can eventually penetrate and prevail over the South China Sea (SCS) region.

Local and remote impacts of aerosol species on Indian summer monsoon rainfall in a GCM

NASA Astrophysics Data System (ADS)

Guo, Liang; Turner, Andrew; Highwood, Eleanor

2016-04-01

The HadGEM2 AGCM is used to determine the most important anthropogenic aerosols in the Indian monsoon using experiments in which observed trends in individual aerosol species are imposed. Sulphur dioxide (SD) emissions are shown to impact rainfall more strongly than black carbon (BC) aerosols, causing reduced rainfall especially over northern India. Significant perturbations due to BC are not noted until its emissions are scaled up in a sensitivity test, in which rainfall increases over northern India as a result of the Elevated Heat Pump mechanism, enhancing convection during the pre-monsoon and bringing forward the monsoon onset. Secondly, the impact of anthropogenic aerosols is compared to that of increasing greenhouse-gas concentrations and observed sea-surface temperature (SST) warming. The tropospheric temperature gradient driving the monsoon shows weakening when forced by either SD or imposed SST trends. However the observed SST trend is dominated by warming in the deep tropics; when the component of SST trend related to aerosol emissions is removed, further warming is found in the extratropical northern hemisphere that tends to offset monsoon weakening. This suggests caution is needed when using SST forcing as a proxy for greenhouse warming. Finally, aerosol emissions are decomposed into those from the Indian region and those elsewhere, in pairs of experiments with SD and BC. Both local and remote aerosol emissions are found to lead to rainfall changes over India; for SD, remote aerosols contribute around 75% of the rainfall decrease over India, while for BC the remote forcing is even more dominant.

Weakening of Indian Summer Monsoon Rainfall due to Changes in Land Use Land Cover

PubMed Central

Paul, Supantha; Ghosh, Subimal; Oglesby, Robert; Pathak, Amey; Chandrasekharan, Anita; Ramsankaran, RAAJ

2016-01-01

Weakening of Indian summer monsoon rainfall (ISMR) is traditionally linked with large-scale perturbations and circulations. However, the impacts of local changes in land use and land cover (LULC) on ISMR have yet to be explored. Here, we analyzed this topic using the regional Weather Research and Forecasting model with European Center for Medium range Weather Forecast (ECMWF) reanalysis data for the years 2000–2010 as a boundary condition and with LULC data from 1987 and 2005. The differences in LULC between 1987 and 2005 showed deforestation with conversion of forest land to crop land, though the magnitude of such conversion is uncertain because of the coarse resolution of satellite images and use of differential sources and methods for data extraction. We performed a sensitivity analysis to understand the impacts of large-scale deforestation in India on monsoon precipitation and found such impacts are similar to the observed changes in terms of spatial patterns and magnitude. We found that deforestation results in weakening of the ISMR because of the decrease in evapotranspiration and subsequent decrease in the recycled component of precipitation. PMID:27553384

Monsoon source shifts during the drying mid-Holocene: Biomarker isotope based evidence from the core 'monsoon zone' (CMZ) of India

NASA Astrophysics Data System (ADS)

Sarkar, Saswati; Prasad, Sushma; Wilkes, Heinz; Riedel, Nils; Stebich, Martina; Basavaiah, Nathani; Sachse, Dirk

2015-09-01

C4 grasses. In agreement with other proxy data, such as deposition of evaporite minerals, we interpret this period to reflect the driest conditions in the region during the last 10.1 ka. This transition led to protracted late Holocene arid conditions after 4 ka with the presence of a permanent saline lake, supported by the sustained presence of tetrahymanol and more positive average δDwax values (-122‰ to -141‰). A late Holocene peak of cyanobacterial biomarker input at 1.3 cal ka BP might represent an event of lake eutrophication, possibly due to human impact and the onset of cattle/livestock farming in the catchment. A unique feature of our record is the presence of a distinct transitional period between 4.8 and 4 cal ka BP, which was characterized by some of the most negative δDwax values during the Holocene (up to -180‰), when all other proxy data indicate the driest conditions during the Holocene. These negative δDwax values can as such most reasonably be explained by a shift in moisture source area and/or pathways or rainfall seasonality during this transitional period. We hypothesize that orbital induced weakening of the summer solar insolation and associated reorganization of the general atmospheric circulation, as a possible southward displacement of the tropical rainbelt, led to an unstable hydroclimate in central India between 4.8 and 4 ka. Our findings shed light onto the sequence of changes during mean state changes of the monsoonal system, once an insolation driven threshold has been passed, and show that small changes in solar insolation can be associated with major hydroclimate changes on the continents, a scenario that may be relevant with respect to future changes in the ISM system.

Clay mineralogical and geochemical proxies of the East Asian summer monsoon evolution in the South China Sea during Late Quaternary

PubMed Central

Chen, Quan; Liu, Zhifei; Kissel, Catherine

2017-01-01

The East Asian summer monsoon controls the climatic regime of an extended region through temperature and precipitation changes. As the East Asian summer monsoon is primarily driven by the northern hemisphere summer insolation, such meteorological variables are expected to significantly change on the orbital timescale, influencing the composition of terrestrial sediments in terms of both mineralogy and geochemistry. Here we present clay mineralogy and major element composition of Core MD12-3432 retrieved from the northern South China Sea, and we investigate their relationship with the East Asian summer monsoon evolution over the last 400 ka. The variability of smectite/(illite + chlorite) ratio presents a predominant precession periodicity, synchronous with the northern hemisphere summer insolation changes and therefore with that of the East Asian summer monsoon. Variations in K2O/Al2O3 are characterized by eccentricity cycles, increasing during interglacials when the East Asian summer monsoon is enhanced. Based on the knowledge of sediment provenances, we suggest that these two proxies in the South China Sea are linked to the East Asian summer monsoon evolution with different mechanisms, which are (1) contemporaneous chemical weathering intensity in Luzon for smectite/(illite + chlorite) ratio and (2) river denudation intensity for K2O/Al2O3 ratio of bulk sediment. PMID:28176842

Pollen evidence for a mid-Holocene East Asian summer monsoon maximum in northern China

NASA Astrophysics Data System (ADS)

Wen, Ruilin; Xiao, Jule; Fan, Jiawei; Zhang, Shengrui; Yamagata, Hideki

2017-11-01

There is a controversy regarding whether the high precipitation delivered by an intensified East Asian summer monsoon occurred during the early Holocene, or during the middle Holocene, especially in the context of the monsoonal margin region. The conflicting views on the subject may be caused by chronological uncertainties and ambiguities in the interpretation of different climate proxies measured in different sedimentary sequences. Here, we present a detailed record of the Holocene evolution of vegetation in northern China based on a high-resolution pollen record from Dali Lake, located near the modern summer monsoon limit. From 12,000-8300 cal BP, the sandy land landscape changed from desert to open elm forest and shrubland, while dry steppe dominated the hilly lands and patches of birch forest developed in the mountains. Between 8300 and 6000 cal BP, elm forest was extensively distributed in the sandy lands, while typical steppe covered the hilly lands and mixed coniferous-broadleaved forests expanded in the mountains. Our pollen evidence contradicts the view that the monsoonal rainfall increased during the early Holocene; rather, it indicates that the East Asian summer monsoon did not become intensified until ∼8000 cal BP in northern China. The low precipitation during the early Holocene can be attributed to the boundary conditions, i.e., to the remnant high-latitude Northern Hemisphere ice sheets and the relatively low global sea level.

Decreasing Indian summer monsoon on the northern Indian sub-continent during the last 180 years: evidence from five tree-ring cellulose oxygen isotope chronologies

NASA Astrophysics Data System (ADS)

Xu, Chenxi; Sano, Masaki; Priyadarshan Dimri, Ashok; Ramesh, Rengaswamy; Nakatsuka, Takeshi; Shi, Feng; Guo, Zhengtang

2018-05-01

We have constructed a regional tree-ring cellulose oxygen isotope (δ18O) record for the northern Indian sub-continent based on two new records from northern India and central Nepal and three published records from northwestern India, western Nepal and Bhutan. The record spans the common interval from 1743 to 2008 CE. Correlation analysis reveals that the record is significantly and negatively correlated with the three regional climatic indices: all India rainfall (AIR; r = -0.5, p < 0.001, n = 138), Indian monsoon index (IMI; r = -0.45, p < 0.001, n = 51) and the intensity of monsoonal circulation (r = -0.42, p < 0.001, n = 51). The close relationship between tree-ring cellulose δ18O and the Indian summer monsoon (ISM) can be explained by oxygen isotope fractionation mechanisms. Our results indicate that the regional tree-ring cellulose δ18O record is suitable for reconstructing high-resolution changes in the ISM. The record exhibits significant interannual and long-term variations. Interannual changes are closely related to the El Niño-Southern Oscillation (ENSO), which indicates that the ISM was affected by ENSO in the past. However, the ISM-ENSO relationship was not consistent over time, and it may be partly modulated by Indian Ocean sea surface temperature (SST). Long-term changes in the regional tree-ring δ18O record indicate a possible trend of weakened ISM intensity since 1820. Decreasing ISM activity is also observed in various high-resolution ISM records from southwest China and Southeast Asia, and may be the result of reduced land-ocean thermal contrasts since 1820 CE.

Increases in aerosol concentrations over eastern China due to the decadal-scale weakening of the East Asian summer monsoon

NASA Astrophysics Data System (ADS)

Zhu, Jianlei; Liao, Hong; Li, Jianping

2012-05-01

China has been experiencing increased concentrations of aerosols, commonly attributed to the large increases in emissions associated with the rapid economic development. We show by using a chemical transport model driven by the assimilated meteorological fields that the observed decadal-scale weakening of the East Asian summer monsoon also contributed to the increases in aerosols in China. We find that the simulated aerosol concentrations have strong negative correlations with the strength of the East Asian Summer monsoon. Accounting for sulfate, nitrate, ammonium, black carbon, and organic carbon aerosols, the summer surface-layer PM2.5 concentration averaged over eastern China (110°-125°E, 20°-45°N) can be 17.7% higher in the weakest monsoon years than in the strongest monsoon years. The weakening of the East Asian Summer monsoon increases aerosol concentrations mainly by the changes in atmospheric circulation (the convergence of air pollutants) in eastern China.

Features of clouds and convection during the pre- and post-onset periods of the Asian summer monsoon

NASA Astrophysics Data System (ADS)

Wang, Yi; Wang, Chenghai

2016-02-01

The statistical characteristics of the vertical structure of clouds in the Asian summer monsoon region are investigated using two CloudSat standard products (Geometrical Profiling Product (GEOPROF) and GEOPROF-lidar) during the pre- and post-onset periods of the Asian summer monsoon, from April to August in 2007-2010. The characteristics of the vertical structure of clouds are analyzed and compared for different underlying surfaces in four subregions during this period. Also analyzed are the evolution of precipitation and hydrometeors with the northward advance of the Asian summer monsoon, and different hydrometeor characteristics attributed to the underlying surface features. The results indicate that the vertical cloud amounts increase significantly after the summer monsoon onset; this increase occurs first in the upper troposphere and then at lower altitudes over tropical regions (South Asian and tropical Northwest Pacific regions). The heights of the cloud top ascend, and the vertical height between the top and the base of the whole cloud increases. Single-layer (SL) and double-layer (DL) hydrometeors contribute over half and one third of the cloudiness in these 5 months (April to August), respectively. The multilayer frequencies increase in four different regions, and cloud layer depths (CLD) increase after the summer monsoon onset. These changes are stronger in tropical regions than in subtropical regions, while the vertical distance between cloud layers (VDCL) deceases in tropical regions and increases in subtropical regions.

Relative influence of precession and obliquity in the early Holocene: Topographic modulation of subtropical seasonality during the Asian summer monsoon

NASA Astrophysics Data System (ADS)

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

2018-07-01

On orbital timescales, higher summer insolation is thought to strengthen the continental monsoon while weakening the maritime monsoon in the Northern hemisphere. Through simulations using the Community Earth System Model, we evaluated the relative influence of perihelion precession and high obliquity in the early Holocene during the Asian summer monsoon. The major finding was that precession dominates the atmospheric heating change over the Tibetan Plateau-Himalayas and Maritime Continent, whereas obliquity is responsible for the heating change over the equatorial Indian Ocean. Thus, precession and obliquity can play contrasting roles in driving the monsoons on orbital timescales. In late spring-early summer, interior Asian continental heating drives the South and East Asian monsoons. The broad-scale monsoonal circulation further expands zonally in July-August, corresponding to the development of summer monsoons in West Africa and the subtropical Western North Pacific (WNP) as well as a sizable increase in convection over the equatorial Indian Ocean. Tropical and oceanic heating becomes crucial in late summer. Over South Asia-Indian Ocean (50°E-110°E), the precession maximum intensifies the monsoonal Hadley cell (heating with an inland/highland origin), which is opposite to the meridional circulation change induced by high obliquity (heating with a tropical origin). The existence of the Tibetan Plateau-Himalayas intensifies the precessional impact. During the late-summer phase of the monsoon season, the effect of obliquity on tropical heating can be substantial. In addition to competing with Asian continental heating, obliquity-enhanced heating over the equatorial Indian Ocean also has a Walker-type circulation impact, resulting in suppression of precession-enhanced heating over the Maritime Continent.

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.

Dynamics and Composition of the Asian Summer Monsoon Anticyclone

NASA Astrophysics Data System (ADS)

Gottschaldt, K. D.; Schlager, H.; Baumann, R.; Bozem, H.; Cai, D. S.; Eyring, V.; Hoor, P. M.; Graf, P.; Joeckel, P.; Jurkat, T.; Voigt, C.; Grewe, V.; Zahn, A.; Ziereis, H.

2017-12-01

This study places trace gas observations in the upper-tropospheric Asian summer monsoon anticyclone (ASMA) obtained with the HALO research aircraft during the ESMVal campaign into the context of regional, intra-annual variability by hindcasts with the EMAC model. The simulations demonstrate that tropospheric trace gas profiles in the monsoon season are distinct from the rest of the year. Air uplifted from the lower troposphere to the tropopause layer dominates the eastern part of the ASMA's interior, while the western part is characterized by subsidence down to the mid-troposphere. Soluble compounds are being washed out when uplifted by convection in the eastern part, where lightning simultaneously replenishes reactive nitrogen in the upper troposphere. Net photochemical ozone production is significantly enhanced in the ASMA, contrasted by an ozone depleting regime in the mid-troposphere and more neutral conditions in autumn and winter. An analysis of multiple monsoon seasons in the simulation shows that stratospherically influenced tropopause layer air is regularly entrained at the eastern ASMA flank, and then transported in the southern fringe around the interior region. Observed and simulated tracer-tracer relations reflect photochemical O3 production, as well as in-mixing from the lower troposphere and the tropopause layer. The simulation additionally shows entrainment of clean air from the equatorial region by northerly winds at the western ASMA flank. Although the in situ measurements were performed towards the end of summer, the main ingredients needed for their interpretation are present throughout the monsoon season.Subseasonal dynamical instabilities of the ASMA effectively overcome horizontal transport barriers, occur quite frequently, and are of paramount importance for the trace gas composition of the ASMA and its outflow into regions around the world.

Subseasonal forecast skills and biases of global summer monsoons in the NCEP Climate Forecast System version 2

NASA Astrophysics Data System (ADS)

Liu, Xiangwen; Yang, Song; Li, Qiaoping; Kumar, Arun; Weaver, Scott; Liu, Shi

2014-03-01

Subseasonal forecast skills and biases of global summer monsoons are diagnosed using daily data from the hindcasts of 45-day integrations by the NCEP Climate Forecast System version 2. Predictions for subseasonal variability of zonal wind and precipitation are generally more skillful over the Asian and Australian monsoon regions than other monsoon regions. Climatologically, forecasts for the variations of dynamical monsoon indices have high skills at leads of about 2 weeks. However, apparent interannual differences exist, with high skills up to 5 weeks in exceptional cases. Comparisons for the relationships of monsoon indices with atmospheric circulation and precipitation patterns between skillful and unskillful forecasts indicate that skills for subseasonal variability of a monsoon index depend partially on the degree to which the observed variability of the index attributes to the variation of large-scale circulation. Thus, predictions are often more skillful when the index is closely linked to atmospheric circulation over a broad region than over a regional and narrow range. It is also revealed that, the subseasonal variations of biases of winds, precipitation, and surface temperature over various monsoon regions are captured by a first mode with seasonally independent biases and a second mode with apparent phase transition of biases during summer. The first mode indicates the dominance of overall weaker-than-observed summer monsoons over major monsoon regions. However, at certain stages of monsoon evolution, these underestimations are regionally offset or intensified by the time evolving biases portrayed by the second mode. This feature may be partially related to factors such as the shifts of subtropical highs and intertropical convergence zones, the reversal of biases of surface temperature over some monsoon regions, and the transition of regional circulation system. The significant geographical differences in bias growth with increasing lead time reflect the

Ocean heat budget analysis on sea surface temperature anomaly in western Indian Ocean during strong-weak Asian summer monsoon

NASA Astrophysics Data System (ADS)

Fathrio, Ibnu; Manda, Atsuyoshi; Iizuka, Satoshi; Kodama, Yasu-Masa; Ishida, Sachinobu

2018-05-01

This study presents ocean heat budget analysis on seas surface temperature (SST) anomalies during strong-weak Asian summer monsoon (southwest monsoon). As discussed by previous studies, there was close relationship between variations of Asian summer monsoon and SST anomaly in western Indian Ocean. In this study we utilized ocean heat budget analysis to elucidate the dominant mechanism that is responsible for generating SST anomaly during weak-strong boreal summer monsoon. Our results showed ocean advection plays more important role to initate SST anomaly than the atmospheric prcess (surface heat flux). Scatterplot analysis showed that vertical advection initiated SST anomaly in western Arabian Sea and southwestern Indian Ocean, while zonal advection initiated SST anomaly in western equatorial Indian Ocean.

Prediction of Indian Summer-Monsoon Onset Variability: A Season in Advance.

PubMed

Pradhan, Maheswar; Rao, A Suryachandra; Srivastava, Ankur; Dakate, Ashish; Salunke, Kiran; Shameera, K S

2017-10-27

Monsoon onset is an inherent transient phenomenon of Indian Summer Monsoon and it was never envisaged that this transience can be predicted at long lead times. Though onset is precipitous, its variability exhibits strong teleconnections with large scale forcing such as ENSO and IOD and hence may be predictable. Despite of the tremendous skill achieved by the state-of-the-art models in predicting such large scale processes, the prediction of monsoon onset variability by the models is still limited to just 2-3 weeks in advance. Using an objective definition of onset in a global coupled ocean-atmosphere model, it is shown that the skillful prediction of onset variability is feasible under seasonal prediction framework. The better representations/simulations of not only the large scale processes but also the synoptic and intraseasonal features during the evolution of monsoon onset are the comprehensions behind skillful simulation of monsoon onset variability. The changes observed in convection, tropospheric circulation and moisture availability prior to and after the onset are evidenced in model simulations, which resulted in high hit rate of early/delay in monsoon onset in the high resolution model.

Large-scale control of the Arabian Sea monsoon inversion in August

NASA Astrophysics Data System (ADS)

Wu, Chi-Hua; Wang, S.-Y. Simon; Hsu, Huang-Hsiung

2017-12-01

The summer monsoon inversion in the Arabian Sea is characterized by a large amount of low clouds and August as the peak season. Atmospheric stratification associated with the monsoon inversion has been considered a local system influenced by the advancement of the India-Pakistan monsoon. Empirical and numerical evidence from this study suggests that the Arabian Sea monsoon inversion is linked to a broader-scale monsoon evolution across the African Sahel, South Asia, and East Asia-Western North Pacific (WNP), rather than being a mere byproduct of the India-Pakistan monsoon progression. In August, the upper-tropospheric anticyclone in South Asia extends sideways corresponding with the enhanced precipitation in the subtropical WNP, equatorial Indian Ocean, and African Sahel while the middle part of this anticyclone weakens over the Arabian Sea. The increased heating in the adjacent monsoon systems creates a suppression effect on the Arabian Sea, suggesting an apparent competition among the Africa-Asia-WNP monsoon subsystems. The peak Sahel rainfall in August, together with enhanced heating in the equatorial Indian Ocean, produces a critical effect on strengthening the Arabian Sea thermal inversion. By contrast, the WNP monsoon onset which signifies the eastward expansion of the subtropical Asian monsoon heating might play a secondary or opposite role in the Arabian Sea monsoon inversion.

Delivery of halogenated very short-lived substances from the west Indian Ocean to the stratosphere during the Asian summer monsoon

NASA Astrophysics Data System (ADS)

Fiehn, Alina; Quack, Birgit; Hepach, Helmke; Fuhlbrügge, Steffen; Tegtmeier, Susann; Toohey, Matthew; Atlas, Elliot; Krüger, Kirstin

2017-06-01

Halogenated very short-lived substances (VSLSs) are naturally produced in the ocean and emitted to the atmosphere. When transported to the stratosphere, these compounds can have a significant influence on the ozone layer and climate. During a research cruise on RV Sonne in the subtropical and tropical west Indian Ocean in July and August 2014, we measured the VSLSs, methyl iodide (CH3I) and for the first time bromoform (CHBr3) and dibromomethane (CH2Br2), in surface seawater and the marine atmosphere to derive their emission strengths. Using the Lagrangian particle dispersion model FLEXPART with ERA-Interim meteorological fields, we calculated the direct contribution of observed VSLS emissions to the stratospheric halogen burden during the Asian summer monsoon. Furthermore, we compare the in situ calculations with the interannual variability of transport from a larger area of the west Indian Ocean surface to the stratosphere for July 2000-2015. We found that the west Indian Ocean is a strong source for CHBr3 (910 pmol m-2 h-1), very strong source for CH2Br2 (930 pmol m-2 h-1), and an average source for CH3I (460 pmol m-2 h-1). The atmospheric transport from the tropical west Indian Ocean surface to the stratosphere experiences two main pathways. On very short timescales, especially relevant for the shortest-lived compound CH3I (3.5 days lifetime), convection above the Indian Ocean lifts oceanic air masses and VSLSs towards the tropopause. On a longer timescale, the Asian summer monsoon circulation transports oceanic VSLSs towards India and the Bay of Bengal, where they are lifted with the monsoon convection and reach stratospheric levels in the southeastern part of the Asian monsoon anticyclone. This transport pathway is more important for the longer-lived brominated compounds (17 and 150 days lifetime for CHBr3 and CH2Br2). The entrainment of CHBr3 and CH3I from the west Indian Ocean to the stratosphere during the Asian summer monsoon is lower than from previous

Solar forcing of the Indian summer monsoon variability during the Ållerød period.

PubMed

Gupta, Anil K; Mohan, Kuppusamy; Das, Moumita; Singh, Raj K

2013-09-25

Rapid climatic shifts across the last glacial to Holocene transition are pervasive feature of the North Atlantic as well as low latitude proxy archives. Our decadal to centennial scale record of summer monsoon proxy Globigerina bulloides from rapidly accumulating sediments from Hole 723A, Arabian Sea shows two distinct intervals of weak summer monsoon wind coinciding with cold periods within Ållerød inerstadial of the North Atlantic named here as IACP-A1 and IACP-A2 and dated (within dating uncertainties) at 13.5 and 13.3 calibrated kilo years before the present (cal kyr BP), respectively. Spectral analysis of the Globigerina bulloides time series for the segment 13.6-13.1 kyr (Ållerød period) reveals a strong solar 208-year cycle also known as de Vries or Suess cycle, suggesting that the centennial scale variability in Indian summer monsoon winds during the Ållerød inerstadial was driven by changes in the solar irradiance through stratospheric-tropospheric interactions.

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.

2017-10-01

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).

Influence of Madden-Julian Oscillation on water budget transported by the Somali low-level jet and the associated Indian summer monsoon rainfall

NASA Astrophysics Data System (ADS)

Ordonez, Paulina; Ribera, Pedro; Gallego, David; Pena-Ortiz, Cristina

2013-10-01

Recent studies suggest that there is a strong linkage between the moisture uptake over the equatorial area of the Somali low level jet (SLLJ) and the rainfall variability over most of continental India. Additionally, the Madden-Julian Oscillation (MJO) strongly modulates the intraseasonal variability of the Indian summer monsoon rainfall, since the northward propagation of the boreal summer MJO is closely associated with the active and break phases of monsoon rainfall. But a question remains open: is there a relationship between the moisture transported by the SLLJ and the MJO evolution? In this paper, a Lagrangian approach is used to track the evaporation minus precipitation (E - P) evolution along trajectories of particles initially situated over the equatorial region of SLLJ. The impact of the MJO on the water budget transport of the SLLJ is examined by making composites of the obtained (E-P) fields for the different MJO phases. The spatial structures of the boreal summer intraseasonal oscillation are revealed in our results, which strongly suggest that the main responsible for the rainfall variability associated to the MJO in these regions are the changes in the moisture advected by the SLLJ. In order to assess the MJO-SLLJ interaction, an analysis of the total-column mass and the total-column specific humidity transported by the SLLJ during the MJO life cycle is performed. While a systematic difference between air mass advected to India during active and break phases of MJO is not detected, changes in the moisture of particles are found, with wet (dry) anomalies over enhanced (suppressed) convection region. This result implicitly leads to assume air-sea interaction processes.

Impacts of snow darkening by absorbing aerosols on South Asian monsoon

NASA Astrophysics Data System (ADS)

Kim, K. M.; Lau, W. K. M.; Kim, M. K.; Sang, J.; Yasunari, T. J.; Koster, R. D.

2016-12-01

Seasonal heating over the Tibetan Plateau is a main driver of the onset of the South Asian Monsoon. Aerosols can play an important role in pre- and early monsoon seasonal heating process over the Tibetan Plateau by increasing atmospheric heating in the northern India, and by heating of the surface of the Tibetan Plateau and Himalayan slopes, via reduction of albedo of the snow surface through surface deposition - the so call snow-darkening effect (SDE). To examine the impact of SDE on weather and climate during late spring and early summer, two sets of NASA/GEOS-5 model simulations with and without SDE are conducted. Results show that SDE-induced surface heating accelerates snow melts and increases surface temperature over 4K in the entire Tibetan Plateau regions during boreal summer. Warmer Tibetan Plateau further accelerates seasonal warming in the upper troposphere and increases the north-south temperature gradient between the Tibetan Plateau and the equatorial Indian Ocean. This reversal of the north-south temperature gradient is a primary cause of the onset of the South Asian monsoon. SDE-induced increase of the meridional temperature gradient drives meridional circulation and enhanced upper tropospheric easterlies and lower tropospheric westerlies, and intensifies monsoon circulation and rainfall. This pattern enhances the EHP-like circulation anomalies induced by atmospheric heating of absorbing aerosols over the northern India. SDE-induced change in the India subcontinent differs that in Eurasia. SDE-induced land-atmospheric interactions in two regions will be also compared.

The Evolution of Tropospheric Temperature Field and its Relationship With The Onset of Asian Summer Monsoon

NASA Technical Reports Server (NTRS)

He, H.; Sui, C-H.; Jian, M.; Wen, Z.

2000-01-01

The mean state and year-to-year variations of the tropospheric temperature fields and their relationship with the establishment of the summertime East Asian monsoon (EAM) and the Indian monsoon (INM) are studied using the NCEP reanalysis data of 15 years (1982-1996). The results show that the seasonal shift of the South Asian High in the upper troposphere and the establishment of the EAM and the INM are closely related to the seasonal warming which causes a reversal of the meridional gradient of upper tropospheric mean temperature over the monsoon regions. On the average of 15 years, the reversal time of the temperature gradient in the EAM region (INM region) is concurrent with (one pentad earlier than) the onset time of the summer monsoon. In most years of the 15-year period, the reversal of temperature gradient coincides or precedes the onset time of the summer monsoon in both the EAM region and the INM region. The results suggest an important role of thermal processes on the establishment of the Asian monsoon. The contributors to the upper tropospheric warming over the EAM region are the strong horizontal warm advection and the diabetic heating against the adiabatic cooling due to upward motion. In the INM region, strong adiabatic heating by subsidence and the diabetic heating are major warming processes against the strong horizontal cold advection related to the persistent northwestlies to the southwestern periphery of the Tibetan Plateau. It appears that the early or late establishment of the Asian summer monsoon is not directly related to the differential warming near the surface.

Local and remote impacts of aerosol species on Indian summer monsoon rainfall in a GCM

NASA Astrophysics Data System (ADS)

Turner, A. G.; Guo, L.; Highwood, E.

2016-12-01

The HadGEM2 AGCM is used to determine the most important anthropogenic aerosols in the Indian monsoon using experiments in which observed trends in individual aerosol species are imposed. Sulphur dioxide (SD) emissions are shown to impact rainfall more strongly than black carbon (BC) aerosols, causing reduced rainfall especially over northern India. Significant perturbations due to BC are not noted until its emissions are scaled up in a sensitivity test, resulting in rainfall increases over northern India due to the Elevated Heat Pump mechanism, enhancing convection during the premonsoon and bringing forward the monsoon onset. Secondly, the impact of anthropogenic aerosols is compared to that of increasing greenhouse-gas concentrations and observed sea-surface temperature (SST) warming. The tropospheric temperature gradient driving the monsoon shows weakening when forced by either SD or imposed SST trends. However the observed SST trend is dominated by warming in the deep tropics; when the component of SST trend related to aerosol emissions is removed, further warming is found in the extratropical northern hemisphere that tends to offset monsoon weakening. This suggests caution is needed when using SST forcing as a proxy for greenhouse warming. Finally, aerosol emissions are decomposed into those from the Indian region and those elsewhere, in pairs of experiments with SD and BC. Both local and remote aerosol emissions are found to lead to rainfall changes over India; for SD, remote aerosols contribute around 75% of the rainfall decrease over India, while for BC the remote forcing is even more dominant.

Re-assessment of feedbacks from biosphere to Indian Monsoon: RegCMv4.4.5.10 simulations

NASA Astrophysics Data System (ADS)

Lodh, A.

2016-12-01

Biosphere feedback plays an important role in the progression of moisture laden Indian summer monsoon winds over the land regions of India, towards the north-western regions of India, during the Indian summer monsoon regime. Hence, for understanding the biosphere-feedback to Indian monsoon numerical experiments for "control" and "design" cases are performed using ICTP RegCMv4.4.5.10 climate model forced with National Center for Atmospheric Research - II reanalysed fields. The RegCMv4.4.5.10 simulations are performed from 00GMT 1st November 1999 to 24 GMT 1st January 2011, with combination of mixed convective parameterization (viz. Emanuel and Grell) schemes over land and ocean, combined with "University of Washington- Planetary boundary layer" (UW-PBL) and Holtslag PBL scheme. Validation studies are then performed for correct representation of Indian summer monsoon features particularly precipitation and soil moisture. Then, four numerical experiments with LULCC change in the climate model are carried out (for the same initial, boundary forcings and time-period as in control experiment) for determining possible influence of vegetation cover (viz. extended desertification, deforestation and increase in afforestation, irrigated land) on Indian monsoon meteorology. Results from the extended desert and deforestation experiment, informs us that the moisture laden easterlies from Bay of Bengal are not able to move towards the land region owing to formation of anomalous anti-cyclone circulations, resulting in decrease in precipitation over India. From irrigation and afforestation experiment, it is found that there is increase in precipitation, precipitable water, recycling ratio, precipitation efficiency and development of anomalous cyclonic circulations over Central and North-west India. More details about the results from the numerical experiments performed will be explained.

Organized convection over southwest peninsular India during the pre-monsoon season

NASA Astrophysics Data System (ADS)

Sreelekha, P. N.; Babu, C. A.

2018-03-01

The paper addresses observational aspects of widespread rain associated with the organized convection that forms over the southwest peninsular India during the pre-monsoon season. The evolution of the cloud band over the equatorial region, its northward propagation, development of cross equatorial flow near the Somalia coast, and appearance of equatorial westerly wind resemble closely to that of the monsoon organized convection. Low-level convergence, cyclonic vorticity, and ascending motion are other major characteristics of the cloud bands associated with the pre-monsoon organized convection which exhibits similarity with that of monsoon. The ascending motion plays vital role on the formation of cloud band that produces widespread rainfall persisting for more than a week. The vertical shear of meridional winds is found to co-exist with precipitation over the Arabian Sea off the southwest peninsular India. The velocity potential values derived from the winds at 850 and 200 hPa levels confirm the rising motion on the basis of low-level convergence and upper level divergence. Also, shifting of ascending limb of the local Hadley circulation to the north of the equator is observed during the days of the presence of organized convection over the southwest peninsular region. Noticeable shift in the Walker circulation rising limb is also identified during the same time.

Multidecadal Weakening of Indian Summer Monsoon Circulation Induces an Increasing Northern Indian Ocean Sea Level

NASA Astrophysics Data System (ADS)

Swapna, P.; Jyoti, J.; Krishnan, R.; Sandeep, N.; Griffies, S. M.

2017-10-01

North Indian Ocean sea level has shown significant increase during last three to four decades. Analyses of long-term climate data sets and ocean model sensitivity experiments identify a mechanism for multidecadal sea level variability relative to global mean. Our results indicate that North Indian Ocean sea level rise is accompanied by a weakening summer monsoon circulation. Given that Indian Ocean meridional heat transport is primarily regulated by the annual cycle of monsoon winds, weakening of summer monsoon circulation has resulted in reduced upwelling off Arabia and Somalia and decreased southward heat transport, and corresponding increase of heat storage in the North Indian Ocean. These changes in turn lead to increased retention of heat and increased thermosteric sea level rise in the North Indian Ocean, especially in the Arabian Sea. These findings imply that rising North Indian Ocean sea level due to weakening of monsoon circulation demands adaptive strategies to enable a resilient South Asian population.

Impact of high resolution land surface initialization in Indian summer monsoon simulation using a regional climate model

NASA Astrophysics Data System (ADS)

Unnikrishnan, C. K.; Rajeevan, M.; Rao, S. Vijaya Bhaskara

2016-06-01

The direct impact of high resolution land surface initialization on the forecast bias in a regional climate model in recent years over Indian summer monsoon region is investigated. Two sets of regional climate model simulations are performed, one with a coarse resolution land surface initial conditions and second one used a high resolution land surface data for initial condition. The results show that all monsoon years respond differently to the high resolution land surface initialization. The drought monsoon year 2009 and extended break periods were more sensitive to the high resolution land surface initialization. These results suggest that the drought monsoon year predictions can be improved with high resolution land surface initialization. Result also shows that there are differences in the response to the land surface initialization within the monsoon season. Case studies of heat wave and a monsoon depression simulation show that, the model biases were also improved with high resolution land surface initialization. These results show the need for a better land surface initialization strategy in high resolution regional models for monsoon forecasting.

Seasonal modulation of the Asian summer monsoon between the Medieval Warm Period and Little Ice Age: a multi model study

NASA Astrophysics Data System (ADS)

Kamae, Youichi; Kawana, Toshi; Oshiro, Megumi; Ueda, Hiroaki

2017-12-01

Instrumental and proxy records indicate remarkable global climate variability over the last millennium, influenced by solar irradiance, Earth's orbital parameters, volcanic eruptions and human activities. Numerical model simulations and proxy data suggest an enhanced Asian summer monsoon during the Medieval Warm Period (MWP) compared to the Little Ice Age (LIA). Using multiple climate model simulations, we show that anomalous seasonal insolation over the Northern Hemisphere due to a long cycle of orbital parameters results in a modulation of the Asian summer monsoon transition between the MWP and LIA. Ten climate model simulations prescribing historical radiative forcing that includes orbital parameters consistently reproduce an enhanced MWP Asian monsoon in late summer and a weakened monsoon in early summer. Weakened, then enhanced Northern Hemisphere insolation before and after June leads to a seasonally asymmetric temperature response over the Eurasian continent, resulting in a seasonal reversal of the signs of MWP-LIA anomalies in land-sea thermal contrast, atmospheric circulation, and rainfall from early to late summer. This seasonal asymmetry in monsoon response is consistently found among the different climate models and is reproduced by an idealized model simulation forced solely by orbital parameters. The results of this study indicate that slow variation in the Earth's orbital parameters contributes to centennial variability in the Asian monsoon transition.[Figure not available: see fulltext.

On the relationship between the Indian summer monsoon rainfall and the EQUINOO in the CFSv2

NASA Astrophysics Data System (ADS)

Vishnu, S.; Francis, P. A.; Ramakrishna, S. S. V. S.; Shenoi, S. S. C.

2018-03-01

Several recent studies have shown that positive (negative) phase of Equatorial Indian Ocean Oscillation (EQUINOO) is favourable (unfavourable) to the Indian summer monsoon. However, many ocean-atmosphere global coupled models, including the state-of-the-art Climate Forecast System (CFS) version 2 have difficulty in reproducing this link realistically. In this study, we analyze the retrospective forecasts by the CFS model for the period 1982-2010 with an objective to identify the reasons behind the failure of the model to simulate the observed links between Indian summer monsoon and EQUINOO. It is found that, in the model hindcasts, the rainfall in the core monsoon region was mainly due to westward propagating synoptic scale systems, that originated from the vicinity of the tropical convergence zone (TCZ). Our analysis shows that unlike in observations, in the CFS, majority of positive (negative) EQUINOO events are associated with El Niño (La Niña) events in the Pacific. In addition to this, there is a strong link between EQUINOO and Indian Ocean Dipole (IOD) in the model. We show that, during the negative phase of EQUINOO/IOD, northward propagating TCZs remained stationary over the Bay of Bengal for longer period compared to the positive phase of EQUINOO/IOD. As a result, compared to the positive phase of EQUINOO/IOD, during a negative phase of EQUINOO/IOD, more westward propagating synoptic scale systems originated from the vicinity of TCZ and moved on to the core monsoon region, which resulted in higher rainfall over this region in the CFS. We further show that frequent, though short-lived, westward propagating systems, generated near the vicinity of TCZ over the Bay moved onto the mainland were responsible for less number of break monsoon spells during the negative phase of EQUINOO/IOD in the model hindcasts. This study underlines the necessity for improving the skill of the coupled models, particularly CFS model, to simulate the links between EQUINOO/IOD and

Interaction of Convective Organization and Monsoon Precipitation, Atmosphere, Surface and Sea (INCOMPASS)

NASA Astrophysics Data System (ADS)

Turner, Andrew; Bhat, Gs; Evans, Jonathan; Marsham, John; Martin, Gill; Parker, Douglas; Taylor, Chris; Bhattacharya, Bimal; Madan, Ranju; Mitra, Ashis; Mrudula, Gm; Muddu, Sekhar; Pattnaik, Sandeep; Rajagopal, En; Tripathi, Sachida

2015-04-01

The monsoon supplies the majority of water in South Asia, making understanding and predicting its rainfall vital for the growing population and economy. However, modelling and forecasting the monsoon from days to the season ahead is limited by large model errors that develop quickly, with significant inter-model differences pointing to errors in physical parametrizations such as convection, the boundary layer and land surface. These errors persist into climate projections and many of these errors persist even when increasing resolution. At the same time, a lack of detailed observations is preventing a more thorough understanding of monsoon circulation and its interaction with the land surface: a process governed by the boundary layer and convective cloud dynamics. The INCOMPASS project will support and develop modelling capability in Indo-UK monsoon research, including test development of a new Met Office Unified Model 100m-resolution domain over India. The first UK detachment of the FAAM research aircraft to India, in combination with an intensive ground-based observation campaign, will gather new observations of the surface, boundary layer structure and atmospheric profiles to go with detailed information on the timing of monsoon rainfall. Observations will be focused on transects in the northern plains of India (covering a range of surface types from irrigated to rain-fed agriculture, and wet to dry climatic zones) and across the Western Ghats and rain shadow in southern India (including transitions from land to ocean and across orography). A pilot observational campaign is planned for summer 2015, with the main field campaign to take place during spring/summer 2016. This project will advance our ability to forecast the monsoon, through a programme of measurements and modelling that aims to capture the key surface-atmosphere feedback processes in models. The observational analysis will allow a unique and unprecedented characterization of monsoon processes that

Boreal summer sub-seasonal variability of the South Asian monsoon in the Met Office GloSea5 initialized coupled model

NASA Astrophysics Data System (ADS)

Jayakumar, A.; Turner, A. G.; Johnson, S. J.; Rajagopal, E. N.; Mohandas, Saji; Mitra, A. K.

2017-09-01

Boreal summer sub-seasonal variability in the Asian monsoon, otherwise known as the monsoon intra-seasonal oscillation (MISO), is one of the dominant modes of intraseasonal variability in the tropics, with large impacts on total monsoon rainfall and India's agricultural production. However, our understanding of the mechanisms involved in MISO is incomplete and its simulation in various numerical models is often flawed. In this study, we focus on the objective evaluation of the fidelity of MISO simulation in the Met Office Global Seasonal forecast system version 5 (GloSea5), an initialized coupled model. We analyze a series of nine-member hindcasts from GloSea5 over 1996-2009 during the peak monsoon period (July-August) over the South-Asian monsoon domain focusing on aspects of the time-mean background state and air-sea interaction processes pertinent to MISO. Dominant modes during this period are evident in power spectrum analysis, but propagation and evolution characteristics of the MISO are not realistic. We find that simulated air-sea interactions in the central Indian Ocean are not supportive of MISO initiation in that region, likely a result of the low surface wind variance there. As a consequence, the expected near-quadrature phase relationship between SST and convection is not represented properly over the central equatorial Indian Ocean, and northward propagation from the equator is poorly simulated. This may reinforce the equatorial rainfall mean state bias in GloSea5.

SMMR-SSM/I derived Greenland Sea ice variability: links with Indian and Korean Monsoons

NASA Astrophysics Data System (ADS)

Prabhu, Amita; Oh, Jaiho; Kim, In-won; Kripalani, R. H.; Pandithurai, G.

2018-02-01

Greenland Sea ice area (GRESIA) in boreal autumn and its association with the subsequent summer monsoon rainfall over India and South Korea is assessed for the period 1983-2013. It is found that GRESIA in the month of October has a significant positive relation (correlation coefficient (cc) = 0.45) with the subsequent Indian monsoon rainfall (IMR) while having a significant negative relation (cc = -0.40) with the ensuing Korean monsoon rainfall (KMR). GRESIA episodes in the preceding autumn impact the ensuing summer monsoon rainfall over India (South Korea) adversely (favourably). While central Pacific sea surface temperatures (SSTs) play a mediating role in transmitting the GRESIA signal towards the Indian subcontinent, snow over eastern Eurasia, just north of the Korea-Japan peninsula, plays a mediating role in transmitting the GRESIA signal towards the Korean peninsula. Although, the anomalies of equatorial central Pacific SSTs and eastern Eurasian snow play a crucial role in modulating IMR and KMR respectively, the GRESIA variability also plays a dominant role in modulating the monsoon variability over both the regions. Thus, a combination of autumn GRESIA along with SSTs over the central Pacific and snow over the eastern Eurasia, may possibly serve as a unique precursor to presage Asia's two diverse regional subsystems.

Aerosols cause intraseasonal short-term suppression of Indian monsoon rainfall.

PubMed

Dave, Prashant; Bhushan, Mani; Venkataraman, Chandra

2017-12-11

Aerosol abundance over South Asia during the summer monsoon season, includes dust and sea-salt, as well as, anthropogenic pollution particles. Using observations during 2000-2009, here we uncover repeated short-term rainfall suppression caused by coincident aerosols, acting through atmospheric stabilization, reduction in convection and increased moisture divergence, leading to the aggravation of monsoon break conditions. In high aerosol-low rainfall regions extending across India, both in deficient and normal monsoon years, enhancements in aerosols levels, estimated as aerosol optical depth and absorbing aerosol index, acted to suppress daily rainfall anomaly, several times in a season, with lags of a few days. A higher frequency of prolonged rainfall breaks, longer than seven days, occurred in these regions. Previous studies point to monsoon rainfall weakening linked to an asymmetric inter-hemispheric energy balance change attributed to aerosols, and short-term rainfall enhancement from radiative effects of aerosols. In contrast, this study uncovers intraseasonal short-term rainfall suppression, from coincident aerosol forcing over the monsoon region, leading to aggravation of monsoon break spells. Prolonged and intense breaks in the monsoon in India are associated with rainfall deficits, which have been linked to reduced food grain production in the latter half of the twentieth century.

Adaptation for Planting and Irrigation Decisions to Changing Monsoon Regime in Northeast India: Risk-based Hydro-economic Optimization

NASA Astrophysics Data System (ADS)

Zhu, T.; Cai, X.

2013-12-01

Delay in onset of Indian summer monsoon becomes increasingly frequent. Delayed monsoon and occasional monsoon failures seriously affect agricultural production in the northeast as well as other parts of India. In the Vaishali district of the Bihar State, Monsoon rainfall is very skewed and erratic, often concentrating in shorter durations. Farmers in Vaishali reported that delayed Monsoon affected paddy planting and, consequently delayed cropping cycle, putting crops under the risks of 'terminal heat.' Canal system in the district does not function due to lack of maintenance; irrigation relies almost entirely on groundwater. Many small farmers choose not to irrigate when monsoon onset is delayed due to high diesel price, leading to reduced production or even crop failure. Some farmers adapt to delayed onset of Monsoon by planting short-duration rice, which gives the flexibility for planting the next season crops. Other sporadic autonomous adaptation activities were observed as well, with various levels of success. Adaptation recommendations and effective policy interventions are much needed. To explore robust options to adapt to the changing Monsoon regime, we build a stochastic programming model to optimize revenues of farmer groups categorized by landholding size, subject to stochastic Monsoon onset and rainfall amount. Imperfect probabilistic long-range forecast is used to inform the model onset and rainfall amount probabilities; the 'skill' of the forecasting is measured using probabilities of correctly predicting events in the past derived through hindcasting. Crop production functions are determined using self-calibrating Positive Mathematical Programming approach. The stochastic programming model aims to emulate decision-making behaviors of representative farmer agents through making choices in adaptation, including crop mix, planting dates, irrigation, and use of weather information. A set of technological and policy intervention scenarios are tested

Dynamics and composition of the Asian summer monsoon anticyclone

NASA Astrophysics Data System (ADS)

Gottschaldt, Klaus-Dirk; Schlager, Hans; Baumann, Robert; Sinh Cai, Duy; Eyring, Veronika; Graf, Phoebe; Grewe, Volker; Jöckel, Patrick; Jurkat-Witschas, Tina; Voigt, Christiane; Zahn, Andreas; Ziereis, Helmut

2018-04-01

This study places HALO research aircraft observations in the upper-tropospheric Asian summer monsoon anticyclone (ASMA) into the context of regional, intra-annual variability by hindcasts with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. The observations were obtained during the Earth System Model Validation (ESMVal) campaign in September 2012. Observed and simulated tracer-tracer relations reflect photochemical O3 production as well as in-mixing from the lower troposphere and the tropopause layer. The simulations demonstrate that tropospheric trace gas profiles in the monsoon season are distinct from those in the rest of the year, and the measurements reflect the main processes acting throughout the monsoon season. Net photochemical O3 production is significantly enhanced in the ASMA, where uplifted precursors meet increased NOx, mainly produced by lightning. An analysis of multiple monsoon seasons in the simulation shows that stratospherically influenced tropopause layer air is regularly entrained at the eastern ASMA flank and then transported in the southern fringe around the interior region. Radial transport barriers of the circulation are effectively overcome by subseasonal dynamical instabilities of the anticyclone, which occur quite frequently and are of paramount importance for the trace gas composition of the ASMA. Both the isentropic entrainment of O3-rich air and the photochemical conversion of uplifted O3-poor air tend to increase O3 in the ASMA outflow.

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.

South American Summer Monsoon of 1997/1998 and 1998/1999

NASA Technical Reports Server (NTRS)

Lau, William K.-M.; Zhou, Jiayu

2000-01-01

It is well known that during El Nino years severe drought occurs in the area of Amazon and northeastern Brazil. According to the linear model result the reduced latent heating over the Amazon may lead to a weaker than normal upper tropospheric Bolivian high. As a result, some studies have suggested a weaker South American summer monsoon (SASM) during El Nino years. Using re-analysis. Zhou and Lau data found a statistically significant positive correlation between the tropical eastern Pacific sea surface temperature (SST) and the strength of low-level jet (LLJ) along the eastern foothills of the tropical-subtropical Andes. Douglas also showed a strong LLJ at Santa Cruz, Bolivia during a special pilot balloon observation period in 1997/98 El Nino austral summer. Since this LLJ is an integral part of the monsoon system in the summertime, these results indicated that SASM could be stronger than normal in El Nino years. To clarify this issue, we conducted an investigation on SASM anomaly in the recent ENSO event of 1997/98 El Nino and 1998/99 La Nina In the following we first give a brief review on SASM and the interannual variability of summer rainfall over South America. Then, the impact of 1997-99 ENSO on the South American regional thermal structure and its dynamical consequences to SASM will be discussed.

What controls the atmospheric methane seasonal variability over India?

NASA Astrophysics Data System (ADS)

Guha, Tania; Tiwari, Yogesh K.; Valsala, Vinu; Lin, Xin; Ramonet, Michel; Mahajan, Anoop; Datye, Amey; Kumar, K. Ravi

2018-02-01

Atmospheric CH4 observations from two ground-based stations within Indian subcontinent, namely, Sinhagad (SNG) and Cape Rama station (CRI) showed a strong seasonality with a minima (∼1800 ± 20 ppb) during southwest monsoon (SWM; i.e. June-September, JJAS) and a maxima (2000 ± 30 ppb) during northeast monsoon (NEM i.e. December-February, DJF) with a peak-to-peak seasonality close to 200 ppb. The Indian summer (winter) monsoon is characterized with strong southwesterly (northeasterly) winds of oceanic (land) origin at the surface level and strong easterly (westerly) jet streams aloft. The monsoon dynamics has pronounced impact on CH4 variability over India and is analyzed with winds, Lagrangian trajectories, and 3-dimentional distributions of CH4 simulated by a general circulation model. The model simulations suggest a consistent annual vertical structure (mean and sub-seasonal uncertainty) of CH4 over India with a stark contrast in concentration from summer to winter at surface levels (below 750 mb) in confirmation with what is identified by the ground-based observations. During SWM (NEM) the air with comparatively lower (higher) CH4 concentrations from southern (northern) hemisphere reduces the CH4 over India by 1814 ± 26 ppb (enhances by 1950 ± 51 ppb). The contribution of local fluxes to this seasonality appears to be albeit weak as the synthesized CH4 fluxes (from EDGAR dataset) of the Indian peninsula itself show a peak in summer and a dip in winter. Similar property of CH4 is also common to nearby oceanic region (i.e. over Arabian Sea, 1765 ± 10 ppb during summer) suggesting the role of monsoon dynamics as the controlling factor. Further the mixing and convection carries the CH4 to the upper atmosphere and advect inward or outward aloft according the seasonal monsoon dynamics.

Investigating the impact of land-use land-cover change on Indian summer monsoon daily rainfall and temperature during 1951–2005 using a regional climate model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halder, Subhadeep; Saha, Subodh K.; Dirmeyer, Paul A.

Daily moderate rainfall events, which constitute a major portion of seasonal summer monsoon rainfall over central India, have decreased significantly during the period 1951 through 2005. On the other hand, mean and extreme near-surface daily temperature during the monsoon season have increased by a maximum of 1–1.5 °C. Using simulations made with a high-resolution regional climate model (RegCM4) and prescribed land cover of years 1950 and 2005, it is demonstrated that part of the changes in moderate rainfall events and temperature have been caused by land-use/land-cover change (LULCC), which is mostly anthropogenic. Model simulations show that the increase in seasonal mean and extreme temperature over centralmore » India coincides with the region of decrease in forest and increase in crop cover. Our results also show that LULCC alone causes warming in the extremes of daily mean and maximum temperatures by a maximum of 1–1.2 °C, which is comparable with the observed increasing trend in the extremes. Decrease in forest cover and simultaneous increase in crops not only reduces the evapotranspiration over land and large-scale convective instability, but also contributes toward decrease in moisture convergence through reduced surface roughness. These factors act together in reducing significantly the moderate rainfall events and the amount of rainfall in that category over central India. Additionally, the model simulations are repeated by removing the warming trend in sea surface temperatures over the Indian Ocean. As a result, enhanced warming at the surface and greater decrease in moderate rainfall events over central India compared to the earlier set of simulations are noticed. Results from these additional experiments corroborate our initial findings and confirm the contribution of LULCC in the decrease in moderate rainfall events and increase in daily mean and extreme temperature over India. Therefore, this study demonstrates the important

Investigating the impact of land-use land-cover change on Indian summer monsoon daily rainfall and temperature during 1951–2005 using a regional climate model

DOE PAGES

Halder, Subhadeep; Saha, Subodh K.; Dirmeyer, Paul A.; ...

2016-05-10

Daily moderate rainfall events, which constitute a major portion of seasonal summer monsoon rainfall over central India, have decreased significantly during the period 1951 through 2005. On the other hand, mean and extreme near-surface daily temperature during the monsoon season have increased by a maximum of 1–1.5 °C. Using simulations made with a high-resolution regional climate model (RegCM4) and prescribed land cover of years 1950 and 2005, it is demonstrated that part of the changes in moderate rainfall events and temperature have been caused by land-use/land-cover change (LULCC), which is mostly anthropogenic. Model simulations show that the increase in seasonal mean and extreme temperature over centralmore » India coincides with the region of decrease in forest and increase in crop cover. Our results also show that LULCC alone causes warming in the extremes of daily mean and maximum temperatures by a maximum of 1–1.2 °C, which is comparable with the observed increasing trend in the extremes. Decrease in forest cover and simultaneous increase in crops not only reduces the evapotranspiration over land and large-scale convective instability, but also contributes toward decrease in moisture convergence through reduced surface roughness. These factors act together in reducing significantly the moderate rainfall events and the amount of rainfall in that category over central India. Additionally, the model simulations are repeated by removing the warming trend in sea surface temperatures over the Indian Ocean. As a result, enhanced warming at the surface and greater decrease in moderate rainfall events over central India compared to the earlier set of simulations are noticed. Results from these additional experiments corroborate our initial findings and confirm the contribution of LULCC in the decrease in moderate rainfall events and increase in daily mean and extreme temperature over India. Therefore, this study demonstrates the important

Impact of East Asian Summer Monsoon on Surface Ozone Pattern in China

NASA Astrophysics Data System (ADS)

Li, Shu; Wang, Tijian; Huang, Xing; Pu, Xi; Li, Mengmeng; Chen, Pulong; Yang, Xiu-Qun; Wang, Minghuai

2018-01-01

Tropospheric ozone plays a key role in regional and global atmospheric and climate systems. In East Asia, ozone can be affected both in concentration level and spatial pattern by typical monsoon climate. This paper uses three different indices to identify the strength of East Asian summer monsoon (EASM) and explores the possible impact of EASM intensity on the ozone pattern through synthetic and process analysis. The difference in ozone between three strong and three weak monsoon years was analyzed using the simulations from regional climate model RegCM4-Chem. It was found that EASM intensity can significantly influence the spatial distribution of ozone in the lower troposphere. When EASM is strong, ozone in the eastern part of China (28°N - 42° N) is reduced, but the inverse is detected in the north and south. The surface ozone difference ranges from -7 to 7 ppbv during the 3 months (June to August) of the EASM, with the most obvious difference in August. Difference of the 3 months' average ozone ranges from -3.5 to 4 ppbv. Process analysis shows that the uppermost factor controlling ozone level during summer monsoon seasons is the chemistry process. Interannual variability of EASM can impact the spatial distribution of ozone through wind in the lower troposphere, cloud cover, and downward shortwave radiation, which affect the transport and chemical formation of ozone. The phenomenon should be addressed when considering the interaction between ozone and the climate in East Asia region.

The effect of El-Niño on South Asian Monsoon and agricultural production

NASA Astrophysics Data System (ADS)

Mukherjee, A.

2015-12-01

Mukherjee A, Wang S.Y.Abstract:The South Asian Monsoon has a prominent and significant impact on South Asian countries like India, Bangladesh, Nepal, Pakistan, Sri Lanka and it is one of the most studied phenomena in the world. The monsoon is historically known to be influenced by El Niño-Southern Oscillation (ENSO). The inter-annual and inter-decadal variability of seasonal precipitation over India strongly depends upon the ENSO phasing. The average southwest monsoon rainfall received during the years with El Niño was found to be less compared to normal years and the average rainfall during the northeast monsoon is higher in coastal Andhra Pradesh. ENSO is anti-correlated with Indian summer monsoon (ISM). The last prominent effect of ENSO on India's monsoon occurred in 2009 with 23% reduction in annual rainfall, reducing summer sown crops such as rice, sugar cane etc. and pushing up food prices. Climatic resources endowment plays a major role in planning agricultural production in tropical and sub-tropical environment especially under rain-fed agriculture, and so contingent crop planning drawn on this relationship would help to mitigate the effects of ENSO episodes in the region. The unexplored area in this domain of research is the changes in the frequency and intensity of ENSO due to global warming and its impact on ENSO prediction and agricultural management practices. We analyze the last 30 years datasets of Pacific SST, and precipitation and air temperature over Southeast Asia to examine the evolution of ENSO teleconnections with ISM, as well as making estimates of drought indices such as Palmer Drought Severity Index. This research can lead toward better crop management strategies in the South Asian monsoon region.

On the dynamical basis for the Asian summer monsoon rainfall-El Nino relationship

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nigam, S.

The dynamical basis for the Asian summer monsoon rainfall-El Nino linkage is explored through diagnostic calculations with a linear steady-state multilayer primitive equation model. The contrasting monsoon circulation during recent El Nino (1987) and La Nina (1988) years is first simulated using orography and the residually diagnosed heating (from the thermodynamic equation and the uninitialized, but mass-balanced, ECMWF analysis) as forcings, and then analyzed to provide insight into the importance of various regional forcings, such as the El Nino-related heating anomalies over the tropical Indian and Pacific Oceans. The striking simulation of the June-August (1987-1988) near-surface and upper-air tropical circulationmore » anomalies indicates that tropical anomaly dynamics during northern summer is essentially linear even at the 150-mb level. The vertical structure of the residually diagnosed heating anomaly that contributes to this striking simulation differs significantly from the specified canonical vertical structure (used in generating 3D heating from OLR/precipitation distributions) near the tropical tropopause. The dynamical diagnostic analysis of the anomalous circulation during 1987 and 1988 March-May and June-August periods shows the orographically forced circulation anomaly (due to changes in the zonally averaged basic-state flow) to be quite dominant in modulating the low-level moisture-flux convergence and hence monsoon rainfall over Indochina. The El Nino-related persistent (spring-to-summer) heating anomalies over the tropical Pacific and Indian Ocean basins, on the other hand, mostly regulate the low-level westerly monsoon flow intensity over equatorial Africa and the northern Indian Ocean and, thereby, the large-scale moisture flux into Sahel and Indochina. 38 refs., 12 figs.« less

Urban heat mitigation by roof surface materials during the East Asian summer monsoon

NASA Astrophysics Data System (ADS)

Lee, Seungjoon; Ryu, Youngryel; Jiang, Chongya

2017-04-01

Roof surface materials, such as green and white roofs, have attracted attention in their role in urban heat mitigation, and various studies have assessed the cooling performance of roof surface materials during hot and sunny summer seasons. However, summers in the East Asian monsoon climate region are characterized by significant fluctuations in weather events, such as dry periods, heatwaves, and rainy and cloudy days. This study investigated the efficacy of different roof surface materials for heat mitigation, considering the temperatures both at and beneath the surface of the roof covering materials during a summer monsoon in Seoul, Korea. We performed continuous observations of temperature at and beneath the surface of the roof covering materials, and manual observation of albedo and the normalized difference vegetation index (NDVI) for a white roof, two green roofs (grass [Poa pratensis] and sedum [Sedum sarmentosum]), and a reference surface. Overall, the surface temperature of the white roof was significantly lower than that of the grass and sedum roofs (1.1 and 1.3°C), whereas the temperature beneath the surface of the white roof did not differ significantly from that of the grass and sedum roofs during the summer. The degree of cloudiness significantly modified the surface temperature of the white roof compared with that of the grass and sedum roofs, which depended on plant metabolisms. It was difficult for the grass to maintain its cooling ability without adequate watering management. After considering the cooling performance and maintenance efforts for different environmental conditions, we concluded that white roof performed better in urban heat mitigation than grass and sedum during the East Asian summer monsoon. Our findings will be useful in urban heat mitigation in the region.

Monotonic trends in spatio-temporal distribution and concentration of monsoon precipitation (1901-2002), West Bengal, India

NASA Astrophysics Data System (ADS)

Chatterjee, Soumendu; Khan, Ansar; Akbari, Hashem; Wang, Yupeng

2016-12-01

This paper intended to investigate spatio-temporal monotonic trend and shift in concentration of monsoon precipitation across West Bengal, India, by analysing the time series of monthly precipitation from 18 weather stations during the period from 1901 to 2002. In dealing with, the inhomogeneity in the precipitation series, RHtestsV4 software package is used to detect, and adjust for, multiple change points (shifts) that could exist in data series. Finally, the cumulative deviation test was applied at 5% significant level to check the homogeneity (presence of historic changes by cumulative deviations test). Afterward, non-parametric Mann-Kendall (MK) test and Theil-Sen estimator (TSE) was applied to detect of nature and slope of trends; and, Sequential Mann Kendall (SQMK) test was applied for detection of turning point and magnitude of change in trends. Prior to the application of statistical tests, the pre-whitening technique was used to eliminate the effect of autocorrelation in precipitation data series. Four indices- precipitation concentration index (PCI), precipitation concentration degree (PCD), precipitation concentration period (PCP) and fulcrum (centre of gravity) were used to detect precipitation concentration and the spatial pattern in it. The application of the above-mentioned procedures has shown very notable statewide monotonic trend for monsoon precipitation time series. Regional cluster analysis by SQMK found increasing precipitation in mountain and coastal regions in general, except during the non- monsoon seasons. The results show that higher PCI values were mainly observed in South Bengal, whereas lower PCI values were mostly detected in North Bengal. The PCI values are noticeably larger in places where both monsoon total precipitation and span of rainy season are lower. The results of PCP reveal that precipitation in Gangetic Bengal mostly occurs in summer (monsoon season), and the rainy season arrives earlier in North Bengal than South Bengal

Interdecadal variability of the Afro-Asian summer monsoon system

NASA Astrophysics Data System (ADS)

Li, Yi; Ding, Yihui; Li, Weijing

2017-07-01

The Afro-Asian summer monsoon is a zonally planetary-scale system, with a large-scale rainbelt covering Africa, South Asia and East Asia on interdecadal timescales both in the past century (1901-2014) and during the last three decades (1979-2014). A recent abrupt change of precipitation occurred in the late 1990s. Since then, the entire rainbelt of the Afro-Asia monsoon system has advanced northwards in a coordinated way. Consistent increases in precipitation over the Huanghe-Huaihe River valley and the Sahel are associated with the teleconnection pattern excited by the warm phase of the Atlantic Multidecadal Oscillation (AMO). A teleconnection wave train, with alternating cyclones/anticyclones, is detected in the upper troposphere. Along the teleconnection path, the configuration of circulation anomalies in North Africa is characterized by coupling of the upper-level anticyclone (divergence) with low-level thermal low pressure (convergence), facilitating the initiation and development of ascending motions in the Sahel. Similarly, in East Asia, a coupled circulation pattern also excites ascending motion in the Huanghe-Huaihe River valley. The synchronous increase in precipitation over the Sahel and Huanghe-Huaihe River valley can be attributed to the co-occurrences and in-phase changes of ascending motion. On the other hand, the warm phase of the AMO results in significant warming in the upper troposphere in North Africa and the northern part of East Asia. Such warming contributes to intensification of the tropical easterly jet through increasing the meridional pressure gradient both at the entrance region (East Asia) and the exit region (Africa). Accordingly, precipitation over the Sahel and Huanghe-Huaihe River valley intensifies, owing to ageostrophic secondary cells. The results of this study provide evidence for a consistent and holistic interdecadal change in the Afro-Asian summer monsoon.

Possible impacts of the Arctic oscillation on the interdecadal variation of summer monsoon rainfall in East Asia

NASA Astrophysics Data System (ADS)

Jianhua, Ju; Junmei, Lü; Jie, Cao; Juzhang, Ren

2005-01-01

The influences of the wintertime AO (Arctic Oscillation) on the interdecadal variation of summer monsoon rainfall in East Asia were examined. An interdecadal abrupt change was found by the end of the 1970s in the variation of the AO index and the leading principal component time series of the summer rainfall in East Asia. The rainfall anomaly changed from below normal to above normal in central China, the southern part of northeastern China and the Korean peninsula around 1978. However, the opposite interdecadal variation was found in the rainfall anomaly in North China and South China. The interdecadal variation of summer rainfall is associated with the weakening of the East Asia summer monsoon circulation. It is indicated that the interdecadal variation of the AO exerts an influence on the weakening of the monsoon circulation. The recent trend in the AO toward its high-index polarity during the past two decades plays important roles in the land-sea contrast anomalies and wintertime precipitation anomaly. The mid- and high-latitude regions of the Asian continent are warming, while the low-latitude regions are cooling in winter and spring along with the AO entering its high-index polarity after the late 1970s. In the meantime, the precipitation over the Tibetan Plateau and South China is excessive, implying an increase of soil moisture. The cooling tendency of the land in the southern part of Asia will persist until summer because of the memory of soil moisture. So the warming of the Asian continent is relatively slow in summer. Moreover, the Indian Ocean and Pacific Ocean, which are located southward and eastward of the Asian land, are warming from winter to summer. This suggests that the contrast between the land and sea is decreased in summer. The interdecadal decrease of the land-sea heat contrast finally leads to the weakening of the East Asia summer monsoon circulation.

Holocene East Asian summer monsoon records in northern China and their inconsistency with Chinese stalagmite δ18O records

NASA Astrophysics Data System (ADS)

Liu, Jianbao; Chen, Jianhui; Zhang, Xiaojian; Chen, Fahu

2016-04-01

Monsoon precipitation over China exhibits large spatial differences. It has been found that a significantly enhanced East Asian summer monsoon (EASM) is characterized by increased rainfall in northern China and by reduced rainfall in southern China, and this relationship occurs on different time scales during the Holocene. This study presents results from a diverse range of proxy paleoclimatic records from northern China where precipitation variability is traditionally considered as an EASM proxy. Our aim is to evaluate the evolution of the EASM during the Holocene and to compare it with all of the published stalagmite δ18O records from the Asian Monsoon region in order to explore the potential mechanism(s) controlling the Chinese stalagmite δ18O. We found that the intensity of the EASM during the Holocene recorded by the traditional EASM proxy of moisture (or precipitation) records from northern China are significantly different from the Chinese stalagmite δ18O records. The EASM maximum occurred during the mid-Holocene, challenging the prevailing view of an early Holocene EASM maximum mainly inferred from stalagmite δ18O records in eastern China. In addition, all of the well-dated Holocene stalagmite δ18O records, covering a broad geographical region, exhibit a remarkably similar trend of variation and are statistically well-correlated on different time scales, thus indicating a common signal. However, in contrast with the clear consistency in the δ18O values in all of the cave records, both instrumental and paleoclimatic records exhibit significant spatial variations in rainfall on decadal-to- centennial time scales over eastern China. In addition, both paleoclimatic records and modeling results suggest that Holocene East Asian summer monsoon precipitation reached a maximum at different periods in different regions of China. Thus the stalagmite δ18O records from the EASM region should not be regarded as a reliable indicator of the strength of the East

Intraseasonal variability of the West African monsoon and African easterly waves during boreal summer

NASA Astrophysics Data System (ADS)

Alaka, Ghassan J., Jr.

Substantial subseasonal variability in African easterly wave (AEW) activity and cyclogenesis frequency occurs in the main hurricane development region of the Atlantic during boreal summer. A complete understanding of intraseasonal variability in the Atlantic and west Africa during boreal summer requires analysis of how the Madden-Julian Oscillation (MJO) modulates the west African monsoon and consequently AEWs. Because the MJO is predictable a few weeks in advance, understanding how and why the MJO impacts the west African monsoon may have a profound influence on Atlantic tropical cyclone prediction. This study documents the MJO influence on the west African monsoon system during boreal summer using a variety of reanalysis and satellite datasets. This study aims to identify and explain the MJO teleconnection to the west African monsoon, and the processes that induce precipitation and AEW variability in this region. Intraseasonal west African and Atlantic convective anomalies on 30-90 day timescales are likely induced by equatorial Kelvin and Rossby waves generated in the Indian Ocean and west Pacific by the MJO. Previous studies have hypothesized that an area including the Darfur mountains and the Ethiopian highlands is an initiation region for AEWs. It is shown here that the initial MJO influence on precipitation and AEW activity in the African monsoon appears to occur in these regions, where eddy kinetic energy (EKE) anomalies first appear in advance of MJO-induced periods of enhanced and suppressed AEW activity. In the initiation region, upper tropospheric temperature anomalies are reduced, the atmosphere moistens by horizontal advection, and an eastward extension of the African easterly jet occurs in advance of the MJO wet phase of the African monsoon, when AEW activity is also enhanced. These factors all support strong precursor disturbances in the initiation region that seed the African easterly jet and contribute to downstream development of AEWs. Opposite

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

Detailed Analysis of Indian Summer Monsoon Rainfall Processes with Modern/High-Quality Satellite Observations

NASA Technical Reports Server (NTRS)

Smith, Eric A.; Kuo, Kwo-Sen; Mehta, Amita V.; Yang, Song

2007-01-01

We examine, in detail, Indian Summer Monsoon rainfall processes using modernhigh quality satellite precipitation measurements. The focus here is on measurements derived from three NASA cloud and precipitation satellite missionslinstruments (TRMM/PR&TMI, AQUNAMSRE, and CLOUDSATICPR), and a fourth TRMM Project-generated multi-satellite precipitation measurement dataset (viz., TRMM standard algorithm 3b42) -- all from a period beginning in 1998 up to the present. It is emphasized that the 3b42 algorithm blends passive microwave (PMW) radiometer-based precipitation estimates from LEO satellites with infi-ared (IR) precipitation estimates from a world network of CEO satellites (representing -15% of the complete space-time coverage) All of these observations are first cross-calibrated to precipitation estimates taken from standard TRMM combined PR-TMI algorithm 2b31, and second adjusted at the large scale based on monthly-averaged rain-gage measurements. The blended approach takes advantage of direct estimates of precipitation from the PMW radiometerequipped LEO satellites -- but which suffer fi-om sampling limitations -- in combination with less accurate IR estimates from the optical-infrared imaging cameras on GEO satellites -- but which provide continuous diurnal sampling. The advantages of the current technologies are evident in the continuity and coverage properties inherent to the resultant precipitation datasets that have been an outgrowth of these stable measuring and retrieval technologies. There is a wealth of information contained in the current satellite measurements of precipitation regarding the salient precipitation properties of the Indian Summer Monsoon. Using different datasets obtained from the measuring systems noted above, we have analyzed the observations cast in the form of: (1) spatially distributed means and variances over the hierarchy of relevant time scales (hourly I diurnally, daily, monthly, seasonally I intra-seasonally, and inter

The Red Sea outflow regulated by the Indian monsoon

NASA Astrophysics Data System (ADS)

Aiki, Hidenori; Takahashi, Keiko; Yamagata, Toshio

2006-08-01

To investigate why the Red Sea water overflows less in summer and more in winter, we have developed a locally high-resolution global OGCM with transposed poles in the Arabian peninsula and India. Based on a series of sensitivity experiments with different sets of idealized atmospheric forcing, the present study shows that the summer cessation of the strait outflow is remotely induced by the monsoonal wind over the Indian Ocean, in particular that over the western Arabian Sea. During the southwest monsoon (May-September), thermocline in the Gulf of Aden shoals as a result of coastal Ekman upwelling induced by the predominantly northeastward wind in the Gulf of Aden and the Arabian Sea. Because this shoaling is maximum during the southwest summer monsoon, the Red Sea water is blocked at the Bab el Mandeb Strait by upwelling of the intermediate water of the Gulf of Aden in late summer. The simulation also shows the three-dimensional evolution of the Red Sea water tongue at the mid-depths in the Gulf of Aden. While the tongue meanders, the discharged Red Sea outflow water (RSOW) (incoming Indian Ocean intermediate water (IOIW)) is always characterized by anticyclonic (cyclonic) vorticity, as suggested from the potential vorticity difference.

Observational Analysis of Two Contrasting Monsoon Years

NASA Astrophysics Data System (ADS)

Karri, S.; Ahmad, R.; Sujata, P.; Jose, S.; Sreenivas, G.; Maurya, D. K.

2014-11-01

The Indian summer monsoon rainfall contributes about 75 % of the total annual rainfall and exhibits considerable interannual variations. The agricultural economy of the country depends mainly on the monsoon rainfall. The long-range forecast of the monsoon rainfall is, therefore of significant importance in agricultural planning and other economic activities of the country. There are various parameters which influence the amount of rainfall received during the monsoon. Some of the important parameters considered by the Indian Meteorological Department (IMD) for the study of monsoon are Outgoing Longwave Radiation (OLR), moisture content of the atmosphere, zonal wind speed, low level vorticity, pressure gradient etc. Compared to the Long Period Average (LPA) value of rain fall, the country as a whole received higher amount of rainfall in June, 2013 (34 % more than LPA). The same month showed considerable decrease next year as the amount of rainfall received was around 43 % less compared to LPA. This drastic difference of monsoon prompted to study the behaviour of some of the monsoon relevant parameters. In this study we have considered five atmospheric parameters as the indicators of monsoon behaviour namely vertical relative humidity, OLR, aerosol optical depth (AOD), wind at 850 hPa and mean sea level pressure (MSLP). In the initial analysis of weekly OLR difference for year 2013 and 2014 shows positive values in the month of May over north-western parts of India (region of heat low). This should result in a weaker monsoon in 2014. This is substantiated by the rainfall data received for various stations over India. Inference made based on the analysis of RH profiles coupled with AOD values is in agreement with the rainfall over the corresponding stations.

Indian summer monsoon variability forecasts in the North American multimodel ensemble

NASA Astrophysics Data System (ADS)

Singh, Bohar; Cash, Ben; Kinter, James L., III

2018-04-01

The representation of the seasonal mean and interannual variability of the Indian summer monsoon rainfall (ISMR) in nine global ocean-atmosphere coupled models that participated in the North American Multimodal Ensemble (NMME) phase 1 (NMME:1), and in nine global ocean-atmosphere coupled models participating in the NMME phase 2 (NMME:2) from 1982-2009, is evaluated over the Indo-Pacific domain with May initial conditions. The multi-model ensemble (MME) represents the Indian monsoon rainfall with modest skill and systematic biases. There is no significant improvement in the seasonal forecast skill or interannual variability of ISMR in NMME:2 as compared to NMME:1. The NMME skillfully predicts seasonal mean sea surface temperature (SST) and some of the teleconnections with seasonal mean rainfall. However, the SST-rainfall teleconnections are stronger in the NMME than observed. The NMME is not able to capture the extremes of seasonal mean rainfall and the simulated Indian Ocean-monsoon teleconnections are opposite to what are observed.

Sensitivity of Asian Summer Monsoon precipitation to tropical sea surface temperature anomalies

NASA Astrophysics Data System (ADS)

Fan, Lei; Shin, Sang-Ik; Liu, Zhengyu; Liu, Qinyu

2016-10-01

Sensitivity of Asian Summer Monsoon (ASM) precipitation to tropical sea surface temperature (SST) anomalies was estimated from ensemble simulations of two atmospheric general circulation models (GCMs) with an array of idealized SST anomaly patch prescriptions. Consistent sensitivity patterns were obtained in both models. Sensitivity of Indian Summer Monsoon (ISM) precipitation to cooling in the East Pacific was much weaker than to that of the same magnitude in the local Indian-western Pacific, over which a meridional pattern of warm north and cold south was most instrumental in increasing ISM precipitation. This indicates that the strength of the ENSO-ISM relationship is due to the large-amplitude East Pacific SST anomaly rather than its sensitivity value. Sensitivity of the East Asian Summer Monsoon (EASM), represented by the Yangtze-Huai River Valley (YHRV, also known as the meiyu-baiu front) precipitation, is non-uniform across the Indian Ocean basin. YHRV precipitation was most sensitive to warm SST anomalies over the northern Indian Ocean and the South China Sea, whereas the southern Indian Ocean had the opposite effect. This implies that the strengthened EASM in the post-Niño year is attributable mainly to warming of the northern Indian Ocean. The corresponding physical links between these SST anomaly patterns and ASM precipitation were also discussed. The relevance of sensitivity maps was justified by the high correlation between sensitivity-map-based reconstructed time series using observed SST anomaly patterns and actual precipitation series derived from ensemble-mean atmospheric GCM runs with time-varying global SST prescriptions during the same period. The correlation results indicated that sensitivity maps derived from patch experiments were far superior to those based on regression methods.

Ice versus liquid water saturation in simulations of the indian summer monsoon

NASA Astrophysics Data System (ADS)

Glazer, Russell H.; Misra, Vasubandhu

2018-02-01

At the same temperature, below 0 °C, the saturation vapor pressure (SVP) over ice is slightly less than the SVP over liquid water. Numerical models use the Clausius-Clapeyron relation to calculate the SVP and relative humidity, but there is not a consistent method for the treatment of saturation above the freezing level where ice and mixed-phase clouds may be present. In the context of current challenges presented by cloud microphysics in climate models, we argue that a better understanding of the impact that this treatment has on saturation-related processes like cloud formation and precipitation, is needed. This study explores the importance of the SVP calculation through model simulations of the Indian summer monsoon (ISM) using the regional spectral model (RSM) at 15 km grid spacing. A combination of seasonal and multiyear simulations is conducted with two saturation parameterizations. In one, the SVP over liquid water is prescribed through the entire atmospheric column (woIce), and in another the SVP over ice is used above the freezing level (wIce). When SVP over ice is prescribed, a thermodynamic drying of the middle and upper troposphere above the freezing level occurs due to increased condensation. In the wIce runs, the model responds to the slight decrease in the saturation condition by increasing, relative to the SVP over liquid water only run, grid-scale condensation of water. Increased grid-scale mean seasonal precipitation is noted across the ISM region in the simulation with SVP over ice prescribed. Modification of the middle and upper troposphere moisture results in a decrease in mean seasonal mid-level cloud amount and an increase in high cloud amount when SVP over ice is prescribed. Multiyear simulations strongly corroborate the qualitative results found in the seasonal simulations regarding the impact of ice versus liquid water SVP on the ISM's mean precipitation and moisture field. The mean seasonal rainfall difference over All India between w

Simulation skill of APCC set of global climate models for Asian summer monsoon rainfall variability

NASA Astrophysics Data System (ADS)

Singh, U. K.; Singh, G. P.; Singh, Vikas

2015-04-01

The performance of 11 Asia-Pacific Economic Cooperation Climate Center (APCC) global climate models (coupled and uncoupled both) in simulating the seasonal summer (June-August) monsoon rainfall variability over Asia (especially over India and East Asia) has been evaluated in detail using hind-cast data (3 months advance) generated from APCC which provides the regional climate information product services based on multi-model ensemble dynamical seasonal prediction systems. The skill of each global climate model over Asia was tested separately in detail for the period of 21 years (1983-2003), and simulated Asian summer monsoon rainfall (ASMR) has been verified using various statistical measures for Indian and East Asian land masses separately. The analysis found a large variation in spatial ASMR simulated with uncoupled model compared to coupled models (like Predictive Ocean Atmosphere Model for Australia, National Centers for Environmental Prediction and Japan Meteorological Agency). The simulated ASMR in coupled model was closer to Climate Prediction Centre Merged Analysis of Precipitation (CMAP) compared to uncoupled models although the amount of ASMR was underestimated in both models. Analysis also found a high spread in simulated ASMR among the ensemble members (suggesting that the model's performance is highly dependent on its initial conditions). The correlation analysis between sea surface temperature (SST) and ASMR shows that that the coupled models are strongly associated with ASMR compared to the uncoupled models (suggesting that air-sea interaction is well cared in coupled models). The analysis of rainfall using various statistical measures suggests that the multi-model ensemble (MME) performed better compared to individual model and also separate study indicate that Indian and East Asian land masses are more useful compared to Asia monsoon rainfall as a whole. The results of various statistical measures like skill of multi-model ensemble, large spread

Indian summer monsoon rainfall variability in response to differences in the decay phase of El Niño

NASA Astrophysics Data System (ADS)

Chowdary, Jasti S.; Harsha, H. S.; Gnanaseelan, C.; Srinivas, G.; Parekh, Anant; Pillai, Prasanth; Naidu, C. V.

2017-04-01

In general the Indian summer monsoon (ISM) rainfall is near normal or excess during the El Niño decay phase. Nevertheless the impact of large variations in decaying El Niño on the ISM rainfall and circulation is not systematically examined. Based on the timing of El Niño decay with respect to boreal summer season, El Niño decay phases are classified into three types in this study using 142 years of sea surface temperature (SST) data, which are as follows: (1) early-decay (ED; decay during spring), (2) mid-summer decay (MD; decay by mid-summer) and (3) no-decay (ND; no decay in summer). It is observed that ISM rainfall is above normal/excess during ED years, normal during MD years and below normal/deficit in ND years, suggesting that the differences in El Niño decay phase display profound impact on the ISM rainfall. Tropical Indian Ocean (TIO) SST warming, induced by El Niño, decays rapidly before the second half of the monsoon season (August and September) in ED years, but persists up to the end of the season in MD years, whereas TIO warming maintained up to winter in ND case. Analysis reveals the existence of strong sub-seasonal ISM rainfall variations in the summer following El Niño years. During ED years, strong negative SST anomalies develop over the equatorial central-eastern Pacific by June and are apparent throughout the summer season accompanied by anomalous moisture divergence and high sea level pressure (SLP). The associated moisture convergence and low SLP over ISM region favour excess rainfall (mainly from July onwards). This circulation and rainfall anomalies are highly influenced by warm TIO SST and Pacific La Niña conditions in ED years. Convergence of southwesterlies from Arabian Sea and northeasterlies from Bay of Bengal leads to positive rainfall over most part of the Indian subcontinent from August onwards in MD years. ND years are characterized by negative rainfall anomaly spatial pattern and weaker circulation over India throughout the

Summer monsoon circulation and precipitation over the tropical Indian Ocean during ENSO in the NCEP climate forecast system

NASA Astrophysics Data System (ADS)

Chowdary, J. S.; Chaudhari, H. S.; Gnanaseelan, C.; Parekh, Anant; Suryachandra Rao, A.; Sreenivas, P.; Pokhrel, S.; Singh, P.

2014-04-01

season after summer). This study strongly supports the need of simulating the correct onset and decay phases of El Niño/La Niña for capturing the realistic ENSO teleconnections. These results have strong implications for the forecasting of Indian summer monsoon as this model is currently being adopted as an operational model in India.

Maintenance of Summer Monsoon Circulations: A Planetary-Scale Perspective.

NASA Astrophysics Data System (ADS)

Chen, Tsing-Chang

2003-06-01

The monsoon circulation, which is generally considered to be driven by the landmass-ocean thermal contrast, like a gigantic land-sea breeze circulation, exhibits a phase reversal in its vertical structure; a monsoon high aloft over a continental thermal low is juxtaposed with a midoceanic trough underlaid by an oceanic anticyclone. This classic monsoon circulation model is well matched by the monsoon circulation depicted with the observational data prior to the First Global Atmospheric Research Program (GARP) Global Experiment (FGGE). However, synthesizing findings of the global circulation portrayed with the post-FGGE data, it was found that some basic features of major monsoon circulations in Asia, North America, South America, and Australia differ from those of the classic monsoon circulation model. Therefore, a revision of the classic monsoon theory is suggested. With four different wave regimes selected to fit the horizontal dimensions of these monsoon circulations, basic features common to all four major monsoons are illustrated in terms of diagnostic analyses of the velocity potential maintenance equation (which relates diabatic heating and velocity potential) and the streamfunction budget (which links velocity potential and streamfunction) in these wave regimes. It is shown that a monsoon circulation is actually driven by the east-west differential heating and maintained dynamically by a balance between a vorticity source and advection. This dynamic balance is reflected by a spatial quadrature relationship between the monsoon divergent circulation and the monsoon high (low) at upper (lower) levels.

Strengthened African summer monsoon in the mid-Piacenzian

NASA Astrophysics Data System (ADS)

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

2016-09-01

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

Variations of the Indian summer monsoon over the Mio-Pliocene recorded in the Bengal Fan (IODP Exp354): implications for the evolution of the terrestrial biosphere.

NASA Astrophysics Data System (ADS)

Galy, Valier; Feakins, Sarah; Karkabi, Elias; Ponton, Camilo; Galy, Albert; France-Lanord, Christian

2017-04-01

A pressing challenge in climate research is understanding the temporal evolution of the Indian monsoon system; its response to global and regional climatic controls (including warming); as well as implications in terms of vegetation (C4 expansion), erosion of the Himalaya and carbon sequestration in the Bengal Fan. Studies on climate dynamics have recently offered new insights into the mechanistic controls on the monsoon: the tectonic boundary of the Himalaya is implicated as the major control on Indian summer monsoon dynamics today. Since this region has been uplifted since at least the late Oligocene, it is possible to test the response of monsoon precipitation to global and regional climate change, and also understand feedbacks on the climate system via carbon sequestration in the Bengal Fan. The evidence for monsoon intensity changes across the Miocene and Pliocene is currently incomplete given temporal uncertainty and diagenesis in terrestrial records; biases in the records reconstructed from the distal fan; and conflicting evidence from wind speed and aridity metrics for a stronger or weaker monsoon. Our alternative approach is therefore to study the basin-wide hydrological changes recorded in a multi-proxy, multi-site study of the marine sediments of the Bengal Fan recovered during IODP expedition 354. In turbiditic sediments of Himalayan origin, the late Miocene C4 expansion was found in all three long records recovered during expedition 354 (i.e. at sites U1451, U1450 and U1455, from East to West) based on stable carbon isotope composition of terrestrial leaf-wax compounds. Cores from sites U1455 (a reoccupation of DSDP Leg 22 Site 218) provide the highest resolution record of the C4 transition, which appears to occur abruptly within a relatively continuous series of turbiditic sequences. Bio- and magneto-stratigraphic dating of these records by members of Expedition 354 science party is underway and will provide the best stratigraphic constraint of the C4

A potential vorticity-based determination of the transport barrier in the Asian summer monsoon anticyclone

NASA Astrophysics Data System (ADS)

Ploeger, F.; Gottschling, C.; Griessbach, S.; Grooß, J.-U.; Guenther, G.; Konopka, P.; Müller, R.; Riese, M.; Stroh, F.; Tao, M.; Ungermann, J.; Vogel, B.; von Hobe, M.

2015-11-01

The Asian summer monsoon provides an important pathway of tropospheric source gases and pollution into the lower stratosphere. This transport is characterized by deep convection and steady upwelling, combined with confinement inside a large-scale anticyclonic circulation in the upper troposphere and lower stratosphere (UTLS). In this paper, we show that a barrier to horizontal transport along the 380 K isentrope in the monsoon anticyclone can be determined from a local maximum in the gradient of potential vorticity (PV), following methods developed for the polar vortex (e.g., Nash et al., 1996). The monsoon anticyclone is dynamically highly variable and the maximum in the PV gradient is weak, such that additional constraints are needed (e.g., time averaging). Nevertheless, PV contours in the monsoon anticyclone agree well with contours of trace gas mixing ratios (CO, O3) and mean age from model simulations with a Lagrangian chemistry transport model (CLaMS) and satellite observations from the Microwave Limb Sounder (MLS) instrument. Hence, the PV-based transport barrier reflects the separation between air inside the core of the anticyclone and the background atmosphere well. For the summer season 2011 we find an average PV value of 3.6 PVU for the transport barrier in the anticyclone on the 380 K isentrope.

Response of the Asian summer monsoon to changes in El Niño properties

NASA Astrophysics Data System (ADS)

Annamalai, H.; Liu, P.

2005-04-01

Diagnostics from observed precipitation and National Centers for Environmental Prediction-National Center for Atmospheric Research re-analysis products reveal that after the 1976-77 climate shift in the Pacific there was a dramatic change in the response of the Indian summer monsoon (ISM) to El Niño, particularly during the months of July and August. Based on 1950-75 (PRE76) and 1977-2001 (POST76) El Niño composites: the western North Pacific monsoon (WNPM) was stronger than normal in both periods; the ISM was weaker than normal during the entire monsoon season in PRE76, but in POST76 was weaker only during the onset and withdrawal phases. In terms of observed sea surface temperature (SST) during July-August, the major differences between the two periods are the presence of cold SST anomalies over the Indo-Pacific warm pool and the intensity of warm SST anomalies in the central Pacific in POST76. The effect of these differences on the ISM is investigated in a suite of experiments with an Atmospheric General Circulation Model (AGCM) that has a realistic monsoon precipitation climatology.Separate ten-member ensemble simulations with the AGCM were conducted for PRE76 and POST76 El Niño events with SST anomalies inserted as follows: (i) tropical Indo-Pacific (TIP), (ii) tropical Pacific only (TPO), and (iii) tropical Indian Ocean only (TIO). Qualitatively, TPO solutions reproduce the observed differences in the monsoon response in both periods. Specifically, during July-August of POST76 the cold SST anomalies in conjunction with remote subsidence suppress precipitation (3-5 mm day-1) over the maritime continent and equatorial central Indian Ocean. Inclusion of Indian Ocean SST anomalies in the TIP runs further suppresses precipitation over the entire equatorial Indian Ocean. The low-level anticyclonic circulation anomalies that develop as a Rossby-wave response to these convective anomalies increase the south-westerlies over the northern Indian Ocean, and favour a

Attributing the Human Influence on Precipitation Changes over India

NASA Astrophysics Data System (ADS)

R, D.; Achutarao, K. M.; Thanigachalam, A.

2017-12-01

Variations in rainfall over India -much of which is received during the summer monsoon season (June-September) - influences the economy of the country as nearly 50% of the population is engaged in the agricultural sector which constitutes 17.4% of the GDP of India. The agriculture and economy of India is highly vulnerable to any changes in the monsoon rainfall is well recognised. Recent decades have seen decreasing monsoon rainfall in various parts of India. Whether these are a consequence of natural monsoon variations or are caused by specific anthropogenic factors is an important question to answer in formulating the right policy response to these changes. Understanding the physical changes is also a first step towards being able to attribute downstream impacts due to rainfall changes. We have carried out an optimal fingerprint based Detection & Attribution analysis to study the changing rainfall patterns. We make use of outputs from 7 models in the Coupled Model Intercomparison Project Phase-5 (CMIP5) database that carried out single forcing experiments with, Natural, GHG, Anthropogenic Aerosols, and historical (All) forcings. We use multiple observational datasets of rainfall (CRU 3.22 and IMD gridded) to account for observational uncertainty to analyse seasonal (JJA and DJF) and annual mean rainfall over the 1906-2005 period. Our analysis shows the dominant role of GHG and Anthropogenic Aerosol forcings on the observed rainfall changes.

Revisiting the Observed Correlation Between Weekly Averaged Indian Monsoon Precipitation and Arabian Sea Aerosol Optical Depth

NASA Astrophysics Data System (ADS)

Sharma, D.; Miller, R. L.

2017-12-01

Dust influences the Indian summer monsoon on seasonal timescales by perturbing atmospheric radiation. On weekly time scales, aerosol optical depth retrieved by satellite over the Arabian Sea is correlated with Indian monsoon precipitation. This has been interpreted to show the effect of dust radiative heating on Indian rainfall on synoptic (few-day) time scales. However, this correlation is reproduced by Earth System Model simulations, where dust is present but its radiative effect is omitted. Analysis of daily variability suggests that the correlation results from the effect of precipitation on dust through the associated cyclonic circulation. Boundary layer winds that deliver moisture to India are responsible for dust outbreaks in source regions far upwind, including the Arabian Peninsula. This suggests that synoptic variations in monsoon precipitation over India enhance dust emission and transport to the Arabian Sea. The effect of dust radiative heating upon synoptic monsoon variations remains to be determined.

Revisiting the observed correlation between weekly averaged Indian monsoon precipitation and Arabian Sea aerosol optical depth

NASA Astrophysics Data System (ADS)

Sharma, Disha; Miller, Ron L.

2017-10-01

Dust influences the Indian summer monsoon on seasonal time scales by perturbing atmospheric radiation. On weekly time scales, aerosol optical depth retrieved by satellite over the Arabian Sea is correlated with Indian monsoon precipitation. This has been interpreted to show the effect of dust radiative heating on Indian rainfall on synoptic (few-day) time scales. However, this correlation is reproduced by Earth System Model simulations, where dust is present but its radiative effect is omitted. Analysis of daily variability suggests that the correlation results from the effect of precipitation on dust through the associated cyclonic circulation. Boundary layer winds that deliver moisture to India are responsible for dust outbreaks in source regions far upwind, including the Arabian Peninsula. This suggests that synoptic variations in monsoon precipitation over India enhance dust emission and transport to the Arabian Sea. The effect of dust radiative heating upon synoptic monsoon variations remains to be determined.

A six-stalagmite composite record of East Asian Summer Monsoon in northern China since 11.5 thousand years ago

NASA Astrophysics Data System (ADS)

Shen, C. C.; Dong, J.; Kong, X.; WU, C. C.; Ren, H. A.; Wang, Y.

2017-12-01

Here we present replicated carbonate δ18O records of six stalagmites with sub-decadal to multi-decadal resolutions from Lianhua Cave (38º10'N, 113º43'E), Shanxi Province, to reveal a detailed evolution of the East Asian Summer Monsoon (EASM) intensity in northern China since 11.5 thousand years ago (ka BP, before 1950 AD). This composite record shows that solar forcing dominated hydroclimatic changes, including an intensified monsoon at the Holocene Optimum from the termination of Younger Dryas to 6.5 ka BP, and a subsequent multi-millennial weakening of monsoon intensity, that agree with cave records in central and southern China. However, the EASM has retreated southwards more rapidly than the Indian summer monsoon after 6.5 ka BP, resulting in aridity conditions occurring at 4.0 ka BP in northern China, which is almost 2000-year earlier than in central and southern China. This asynchroneity may be related to the different regional responses among the coupling of the EASM, Indian summer monsoon, the solar forcing, and the differences in thermal forcing due to complex geographical configurations. In addition, a relative enrichment of 1‰ in 18O data of Lianhua record from 9.5 to 8.1 ka BP shows that the Holocene Optimum was punctuated by a millennial-long weak monsoon interval, which is not registered among previous cave records in central and southern China. The fresh water-induced cold climate conditions in the North Atlantic region could create stronger East Asian winter monsoon and induce a weakened EASM and a southward shift of rain belt in northern China. Therefore, it shall not be surprised that there are strong heterogeneities among regional hydroclimatic conditions across monsoonal China in the Holocene.

Factors Affecting the Inter-annual to Centennial Time Scale Variability of All Indian Summer Monsoon Rainfall

NASA Astrophysics Data System (ADS)

Malik, Abdul; Brönnimann, Stefan

2016-04-01

The All Indian Summer Monsoon Rainfall (AISMR) is highly important for the livelihood of more than 1 billion people living in the Indian sub-continent. The agriculture of this region is heavily dependent on seasonal (JJAS) monsoon rainfall. An early start or a slight delay of monsoon, or an early withdrawal or prolonged monsoon season may upset the farmer's agricultural plans, can cause significant reduction in crop yield, and hence economic loss. Understanding of AISMR is also vital because it is a part of global atmospheric circulation system. Several studies show that AISMR is influenced by internal climate forcings (ICFs) viz. ENSO, AMO, PDO etc. as well as external climate forcings (ECFs) viz. Greenhouse Gases, volcanic eruptions, and Total Solar Irradiance (TSI). We investigate the influence of ICFs and ECFs on AISMR using recently developed statistical technique called De-trended Partial-Cross-Correlation Analysis (DPCCA). DPCCA can analyse a complex system of several interlinked variables. Often, climatic variables, being cross correlated, are simultaneously tele-connected with several other variables and it is not easy to isolate their intrinsic relationship. In the presence of non-stationarities and background signals the calculated correlation coefficients can be overestimated and erroneous. DPCCA method removes the non-stationarities and partials out the influence of background signals from the variables being cross correlated and thus give a robust estimate of correlation. We have performed the analysis using NOAA Reconstructed SSTs and homogenised instrumental AISMR data set from 1854-1999. By employing the DPCCA method we find that there is a statistically insignificant negative intrinsic relation (by excluding the influence of ICFs, and ECFs except TSI) between AISMR and TSI on decadal to centennial time scale. The ICFs considerably modulate the relation between AISMR and solar activity between 50-80 year time scales and transform this relationship

Assessment of South Asian Summer Monsoon Simulation in CMIP5-Coupled Climate Models During the Historical Period (1850-2005)

NASA Astrophysics Data System (ADS)

Prasanna, Venkatraman

2016-04-01

This paper evaluates the performance of 29 state-of-art CMIP5-coupled atmosphere-ocean general circulation models (AOGCM) in their representation of regional characteristics of monsoon simulation over South Asia. The AOGCMs, despite their relatively coarse resolution, have shown some reasonable skill in simulating the mean monsoon and precipitation variability over the South Asian monsoon region. However, considerable biases do exist with reference to the observed precipitation and also inter-model differences. The monsoon rainfall and surface flux bias with respect to the observations from the historical run for the period nominally from 1850 to 2005 are discussed in detail. Our results show that the coupled model simulations over South Asia exhibit large uncertainties from one model to the other. The analysis clearly brings out the presence of large systematic biases in coupled simulation of boreal summer precipitation, evaporation, and sea surface temperature (SST) in the Indian Ocean, often exceeding 50 % of the climatological values. Many of the biases are common to many models. Overall, the coupled models need further improvement in realistically portraying boreal summer monsoon over the South Asian monsoon region.

Simulation of boreal Summer Monsoon Rainfall using CFSV2_SSiB model: sensitivity to Land Use Land Cover (LULC)

NASA Astrophysics Data System (ADS)

Chilukoti, N.; Xue, Y.

2016-12-01

The land surface play a vital role in determining the surface energy budget, accurate representation of land use and land cover (LULC) is necessary to improve forecast. In this study, we have investigated the influence of surface vegetation maps with different LULC on simulating the boreal summer monsoon rainfall. Using a National Centres for Environmental Prediction (NCEP) Coupled Forecast System version 2(CFSv2) model coupled with Simplified Simple Biosphere (SSiB) model, two experiments were conducted: one with old vegetation map and one with new vegetation map. The significant differences between new and old vegetation map were in semi-arid and arid areas. For example, in old map Tibetan plateau classified as desert, which is not appropriate, while in new map it was classified as grasslands or shrubs with bare soil. Old map classified the Sahara desert as a bare soil and shrubs with bare soil, whereas in new map it was classified as bare ground. In addition to central Asia and the Sahara desert, in new vegetation map, Europe had more cropped area and India's vegetation cover was changed from crops and forests to wooded grassland and small areas of grassland and shrubs. The simulated surface air temperature with new map shows a significant improvement over Asia, South Africa, and northern America by some 1 to 2ºC and 2 to 3ºC over north east China and these are consistent with the reduced rainfall biases over Africa, near Somali coast, north east India, Bangladesh, east China sea, eastern Pacific and northern USA. Over Indian continent and bay of Bengal dry rainfall anomalies that is the only area showing large dry rainfall bias, however, they were unchanged with new map simulation. Overall the CFSv2(coupled with SSiB) model with new vegetation map show a promising result in improving the monsoon forecast by improving the Land -Atmosphere interactions. To compare with the LULC forcing, experiment was conducted using the Global Forecast System (GFS) simulations

Month-to-month variability of Indian summer monsoon rainfall in 2016: role of the Indo-Pacific climatic conditions

NASA Astrophysics Data System (ADS)

Chowdary, Jasti S.; Srinivas, G.; Du, Yan; Gopinath, K.; Gnanaseelan, C.; Parekh, Anant; Singh, Prem

2018-03-01

Indian summer monsoon (ISM) rainfall during 2016 exhibited a prominent month-to-month fluctuations over India, with below normal rainfall in June and August and above normal rainfall in July. The factors determining the month-to-month fluctuations in ISM rainfall during 2016 are investigated with main focus on the Indo-Pacific climatic anomalies. Warm sea surface temperature (SST) anomalies associated with super El Niño 2015 disappeared by early summer 2016 over the central and eastern Pacific. On the other hand, negative Indian Ocean dipole (IOD) like SST anomaly pattern over the equatorial Indian Ocean and anomalous anticyclonic circulation over the western North Pacific (WNP) are reported in summer 2016 concurrently with decaying El Niño/developing La Niña phase. Observations revealed that the low rainfall over central north India in June is due to moisture divergence caused by the westward extension of ridge corresponding to WNP anticyclone and subsidence induced by local Hadley cell partly related to negative IOD. Low level convergence of southeasterly wind from Bay of Bengal associated with weak WNP anticyclone and northwesterly wind corresponding to anticyclonic circulation over the northwest India remarkably contributed to positive rainfall in July over most of the Indian subcontinent. While reduced rainfall over the Indian subcontinent in August 2016 is associated with the anomalous moisture transport from ISM region to WNP region, in contrast to July, due to local cyclogenesis corroborated by number of tropical cyclones in the WNP. In addition to this, subsidence related to strong convection supported by cyclonic circulation over the WNP also resulted in low rainfall over the ISM region. Coupled General Circulation model sensitivity experiments confirmed that strong convective activities associated with cyclonic circulation over the WNP is primarily responsible for the observed negative ISM rainfall anomalies in August 2016. It is noted that the Indo

Summer precipitation anomalies in Asia and North America induced by Eurasian non-monsoon land heating versus ENSO.

PubMed

Zhao, Ping; Wang, Bin; Liu, Jiping; Zhou, Xiuji; Chen, Junming; Nan, Sulan; Liu, Ge; Xiao, Dong

2016-02-26

When floods ravage Asian monsoon regions in summer, megadroughts often attack extratropical North America, which feature an intercontinental contrasting precipitation anomaly between Asia and North America. However, the characteristics of the contrasting Asian-North American (CANA) precipitation anomalies and associated mechanisms have not been investigated specifically. In this article, we firmly establish this summer CANA pattern, providing evidence for a significant effect of the land surface thermal forcing over Eurasian non-monsoon regions on the CANA precipitation anomalies by observations and numerical experiments. We show that the origin of the CANA precipitation anomalies and associated anomalous anticyclones over the subtropical North Pacific and Atlantic has a deeper root in Eurasian non-monsoon land surface heating than in North American land surface heating. The ocean forcing from the ENSO is secondary and tends to be confined in the tropics. Our results have strong implications to interpretation of the feedback of global warming on hydrological cycle over Asia and North America. Under the projected global warming due to the anthropogenic forcing, the prominent surface warming over Eurasian non-monsoon regions is a robust feature which, through the mechanism discussed here, would favor a precipitation increase over Asian monsoon regions and a precipitation decrease over extratropical North America.

Seismological evidence for monsoon induced micro to moderate earthquake sequence beneath the 2011 Talala, Saurashtra earthquake, Gujarat, India

NASA Astrophysics Data System (ADS)

Singh, A. P.; Mishra, O. P.

2015-10-01

In order to understand the processes involved in the genesis of monsoon induced micro to moderate earthquakes after heavy rainfall during the Indian summer monsoon period beneath the 2011 Talala, Saurashtra earthquake (Mw 5.1) source zone, we assimilated 3-D microstructures of the sub-surface rock materials using a data set recorded by the Seismic Network of Gujarat (SeisNetG), India. Crack attributes in terms of crack density (ε), the saturation rate (ξ) and porosity parameter (ψ) were determined from the estimated 3-D sub-surface velocities (Vp, Vs) and Poisson's ratio (σ) structures of the area at varying depths. We distinctly imaged high-ε, high-ξ and low-ψ anomalies at shallow depths, extending up to 9-15 km. We infer that the existence of sub-surface fractured rock matrix connected to the surface from the source zone may have contributed to the changes in differential strain deep down to the crust due to the infiltration of rainwater, which in turn induced micro to moderate earthquake sequence beneath Talala source zone. Infiltration of rainwater during the Indian summer monsoon might have hastened the failure of the rock by perturbing the crustal volume strain of the causative source rock matrix associated with the changes in the seismic moment release beneath the surface. Analyses of crack attributes suggest that the fractured volume of the rock matrix with high porosity and lowered seismic strength beneath the source zone might have considerable influence on the style of fault displacements due to seismo-hydraulic fluid flows. Localized zone of micro-cracks diagnosed within the causative rock matrix connected to the water table and their association with shallow crustal faults might have acted as a conduit for infiltrating the precipitation down to the shallow crustal layers following the fault suction mechanism of pore pressure diffusion, triggering the monsoon induced earthquake sequence beneath the source zone.

Sources of errors in the simulation of south Asian summer monsoon in the CMIP5 GCMs

DOE PAGES

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

2016-09-19

Accurate simulation of the South Asian summer monsoon (SAM) is still an unresolved challenge. There has not been a benchmark effort to decipher the origin of undesired yet virtually invariable unsuccessfulness of general circulation models (GCMs) over this region. This study analyzes a large ensemble of CMIP5 GCMs to show that most of the simulation errors in the precipitation distribution and their driving mechanisms are systematic and of similar nature across the GCMs, with biases in meridional differential heating playing a critical role in determining the timing of monsoon onset over land, the magnitude of seasonal precipitation distribution and themore » trajectories of monsoon depressions. Errors in the pre-monsoon heat low over the lower latitudes and atmospheric latent heating over the slopes of Himalayas and Karakoram Range induce significant errors in the atmospheric circulations and meridional differential heating. Lack of timely precipitation further exacerbates such errors by limiting local moisture recycling and latent heating aloft from convection. Most of the summer monsoon errors and their sources are reproducible in the land–atmosphere configuration of a GCM when it is configured at horizontal grid spacing comparable to the CMIP5 GCMs. While an increase in resolution overcomes many modeling challenges, coarse resolution is not necessarily the primary driver in the exhibition of errors over South Asia. Ultimately, these results highlight the importance of previously less well known pre-monsoon mechanisms that critically influence the strength of SAM in the GCMs and highlight the importance of land–atmosphere interactions in the development and maintenance of SAM.« less

Sources of errors in the simulation of south Asian summer monsoon in the CMIP5 GCMs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ashfaq, Moetasim; Rastogi, Deeksha; Mei, Rui

2016-09-19

Accurate simulation of the South Asian summer monsoon (SAM) is still an unresolved challenge. There has not been a benchmark effort to decipher the origin of undesired yet virtually invariable unsuccessfulness of general circulation models (GCMs) over this region. This study analyzes a large ensemble of CMIP5 GCMs to show that most of the simulation errors in the precipitation distribution and their driving mechanisms are systematic and of similar nature across the GCMs, with biases in meridional differential heating playing a critical role in determining the timing of monsoon onset over land, the magnitude of seasonal precipitation distribution and themore » trajectories of monsoon depressions. Errors in the pre-monsoon heat low over the lower latitudes and atmospheric latent heating over the slopes of Himalayas and Karakoram Range induce significant errors in the atmospheric circulations and meridional differential heating. Lack of timely precipitation further exacerbates such errors by limiting local moisture recycling and latent heating aloft from convection. Most of the summer monsoon errors and their sources are reproducible in the land–atmosphere configuration of a GCM when it is configured at horizontal grid spacing comparable to the CMIP5 GCMs. While an increase in resolution overcomes many modeling challenges, coarse resolution is not necessarily the primary driver in the exhibition of errors over South Asia. These results highlight the importance of previously less well known pre-monsoon mechanisms that critically influence the strength of SAM in the GCMs and highlight the importance of land–atmosphere interactions in the development and maintenance of SAM.« less

Sources of errors in the simulation of south Asian summer monsoon in the CMIP5 GCMs

NASA Astrophysics Data System (ADS)

Ashfaq, Moetasim; Rastogi, Deeksha; Mei, Rui; Touma, Danielle; Ruby Leung, L.

2017-07-01

Accurate simulation of the South Asian summer monsoon (SAM) is still an unresolved challenge. There has not been a benchmark effort to decipher the origin of undesired yet virtually invariable unsuccessfulness of general circulation models (GCMs) over this region. This study analyzes a large ensemble of CMIP5 GCMs to show that most of the simulation errors in the precipitation distribution and their driving mechanisms are systematic and of similar nature across the GCMs, with biases in meridional differential heating playing a critical role in determining the timing of monsoon onset over land, the magnitude of seasonal precipitation distribution and the trajectories of monsoon depressions. Errors in the pre-monsoon heat low over the lower latitudes and atmospheric latent heating over the slopes of Himalayas and Karakoram Range induce significant errors in the atmospheric circulations and meridional differential heating. Lack of timely precipitation further exacerbates such errors by limiting local moisture recycling and latent heating aloft from convection. Most of the summer monsoon errors and their sources are reproducible in the land-atmosphere configuration of a GCM when it is configured at horizontal grid spacing comparable to the CMIP5 GCMs. While an increase in resolution overcomes many modeling challenges, coarse resolution is not necessarily the primary driver in the exhibition of errors over South Asia. These results highlight the importance of previously less well known pre-monsoon mechanisms that critically influence the strength of SAM in the GCMs and highlight the importance of land-atmosphere interactions in the development and maintenance of SAM.

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.

Tropospheric biennial oscillation and south Asian summer monsoon rainfall in a coupled model

NASA Astrophysics Data System (ADS)

Konda, Gopinadh; Chowdary, J. S.; Srinivas, G.; Gnanaseelan, C.; Parekh, Anant; Attada, Raju; Rama Krishna, S. S. V. S.

2018-06-01

In this study Tropospheric Biennial Oscillation (TBO) and south Asian summer monsoon rainfall are examined in the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFSv2) hindcast. High correlation between the observations and model TBO index suggests that the model is able to capture most of the TBO years. Spatial patterns of rainfall anomalies associated with positive TBO over the south Asian region are better represented in the model as in the observations. However, the model predicted rainfall anomaly patterns associated with negative TBO years are improper and magnitudes are underestimated compared to the observations. It is noted that positive (negative) TBO is associated with La Niña (El Niño) like Sea surface temperature (SST) anomalies in the model. This leads to the fact that model TBO is El Niño-Southern Oscillation (ENSO) driven, while in the observations Indian Ocean Dipole (IOD) also plays a role in the negative TBO phase. Detailed analysis suggests that the negative TBO rainfall anomaly pattern in the model is highly influenced by improper teleconnections allied to IOD. Unlike in the observations, rainfall anomalies over the south Asian region are anti-correlated with IOD index in CFSv2. Further, summer monsoon rainfall over south Asian region is highly correlated with IOD western pole than eastern pole in CFSv2 in contrast to the observations. Altogether, the present study highlights the importance of improving Indian Ocean SST teleconnections to south Asian summer rainfall in the model by enhancing the predictability of TBO. This in turn would improve monsoon rainfall prediction skill of the model.

Modeling and forecasting rainfall patterns of southwest monsoons in North-East India as a SARIMA process

NASA Astrophysics Data System (ADS)

Narasimha Murthy, K. V.; Saravana, R.; Vijaya Kumar, K.

2018-02-01

Weather forecasting is an important issue in the field of meteorology all over the world. The pattern and amount of rainfall are the essential factors that affect agricultural systems. India experiences the precious Southwest monsoon season for four months from June to September. The present paper describes an empirical study for modeling and forecasting the time series of Southwest monsoon rainfall patterns in the North-East India. The Box-Jenkins Seasonal Autoregressive Integrated Moving Average (SARIMA) methodology has been adopted for model identification, diagnostic checking and forecasting for this region. The study has shown that the SARIMA (0, 1, 1) (1, 0, 1)4 model is appropriate for analyzing and forecasting the future rainfall patterns. The Analysis of Means (ANOM) is a useful alternative to the analysis of variance (ANOVA) for comparing the group of treatments to study the variations and critical comparisons of rainfall patterns in different months of the season.

Adaptability of Irrigation to a Changing Monsoon in India: How far can we go?

NASA Astrophysics Data System (ADS)

Zaveri, E.; Grogan, D. S.; Fisher-Vanden, K.; Frolking, S. E.; Wrenn, D. H.; Nicholas, R.

2014-12-01

Agriculture and the monsoon are inextricably linked in India. A large part of the steady rise in agricultural production since the onset of the Green Revolution in the 1960's has been attributed to irrigation. Irrigation is used to supplement and buffer crops against precipitation shocks, but water availability for such use is itself sensitive to the erratic, seasonal and spatially heterogeneous nature of the monsoon. We provide new evidence on the relationship between monsoon changes, irrigation variability and water availability by linking a process based hydrology model with an econometric model for one of the world's most water stressed countries. India uses more groundwater for irrigation than any other country, and there is substantial evidence that this has led to depletion of groundwater aquifers. First, we build an econometric model of historical irrigation decisions using detailed agriculture and weather data spanning 35 years. Multivariate regression models reveal that for crops grown in the wet season, irrigation is sensitive to distribution and total monsoon rainfall but not to ground or surface water availability. For crops grown in the dry season, total monsoon rainfall matters most, and its effect is sensitive to groundwater availability. The historical estimates from the econometric model are used to calculate future irrigated areas under three different climate model predictions of monsoon climate for the years 2010 - 2050. These projections are then used as input to a physical hydrology model, which quantifies supply of irrigation water from sustainable sources such as rechargeable shallow groundwater, rivers and reservoirs, to unsustainable sources such as non- rechargeable groundwater. We find that the significant variation in monsoon projections lead to very different results. Crops grown in the dry season show particularly divergent trends between model projections, leading to very different groundwater resource requirements.

Influence of the Summer NAO on the Spring-NAO-Based Predictability of the East Asian Summer Monsoon

NASA Astrophysics Data System (ADS)

Zheng, Fei

2017-04-01

The dominant mode of atmospheric circulation over the North Atlantic region is the North Atlantic Oscillation (NAO). The boreal spring NAO may imprint its signal on contemporaneous sea surface temperature (SST), leading to a North Atlantic SST tripolar pattern (NAST). This pattern persists into the following summer and modulates the East Asian summer monsoon (EASM). Previous studies have shown that the summer NAST is caused mainly by the preceding spring NAO, whereas the contemporaneous summer NAO plays a secondary role. The results of this study illustrate that, even if the summer NAO plays a secondary role, it may also perturb summer SST anomalies caused by the spring NAO. There are two types of perturbation caused by the summer NAO. If the spring and summer NAO patterns have the same (opposite) polarities, the summer NAST tends to be enhanced (reduced) by the summer NAO, and the correlation between the spring NAO and EASM is usually stronger (weaker). In the former (latter) case, the spring-NAO-based prediction of the EASM tends to have better (limited) skill. These results indicate that it is important to consider the evolution of the NAO when forecasting the EASM, particular when there is a clear reversal in the polarity of the NAO, because it may impair the spring-NAO-based EASM prediction.

Simulation of the Indian Summer Monsoon Using Comprehensive Atmosphere-land Interactions, in the Absence of Two-way Air-sea Interactions

NASA Technical Reports Server (NTRS)

Lim, Young-Kwon; Shin, D. W.; Cocke, Steven; Kang, Sung-Dae; Kim, Hae-Dong

2011-01-01

Community Land Model version 2 (CLM2) as a comprehensive land surface model and a simple land surface model (SLM) were coupled to an atmospheric climate model to investigate the role of land surface processes in the development and the persistence of the South Asian summer monsoon. Two-way air-sea interactions were not considered in order to identify the reproducibility of the monsoon evolution by the comprehensive land model, which includes more realistic vertical soil moisture structures, vegetation and 2-way atmosphere-land interactions at hourly intervals. In the monsoon development phase (May and June). comprehensive land-surface treatment improves the representation of atmospheric circulations and the resulting convergence/divergence through the improvements in differential heating patterns and surface energy fluxes. Coupling with CLM2 also improves the timing and spatial distribution of rainfall maxima, reducing the seasonal rainfall overestimation by approx.60 % (1.8 mm/d for SLM, 0.7 mm/dI for CLM2). As for the interannual variation of the simulated rainfall, correlation coefficients of the Indian seasonal rainfall with observation increased from 0.21 (SLM) to 0.45 (CLM2). However, in the mature monsoon phase (July to September), coupling with the CLM2 does not exhibit a clear improvement. In contrast to the development phase, latent heat flux is underestimated and sensible heat flux and surface temperature over India are markedly overestimated. In addition, the moisture fluxes do not correlate well with lower-level atmospheric convergence, yielding correlation coefficients and root mean square errors worse than those produced by coupling with the SLM. A more realistic representation of the surface temperature and energy fluxes is needed to achieve an improved simulation for the mature monsoon period.

Asian summer monsoon seasonal prediction skill in the Met Office GloSea5 model and its dependence on mean state biases

NASA Astrophysics Data System (ADS)

Bush, Stephanie; Turner, Andrew; Martin, Gill; Woolnough, Steve

2015-04-01

Predicting the circulation and precipitation features of the Asian monsoon on time scales of weeks to the season ahead remains a challenge for prediction centres. Current state-of-the-art models retain large biases, particularly dryness over India, which evolve rapidly from initialization and persist into centennial length climate integrations, illustrating the seamless nature of the monsoon problem. We present initial results from our Ministry of Earth Sciences Indian Monsoon Mission collaboration project to assess and improve weekly-to-seasonal forecasts in the Met Office Unified Model (MetUM) coupled initialized Global Seasonal Prediction System (GloSea5). Using a 14-year hindcast ensemble of integrations in which atmosphere, ocean and sea-ice components are initialized from May start dates, we assess the monsoon seasonal prediction skill and global mean state biases of GloSea5. Initial May and June biases include a lack of precipitation over the Indian peninsula, and a weakened monsoon flow, and these give way to a more robust pattern of excess precipitation in the western north Pacific, lack of precipitation over the Maritime Continent, excess westerlies across the Indian peninsula and Indochina, and cool SSTs in the eastern equatorial Indian Ocean and western north Pacific in July and August. Despite these mean state biases, the interannual correlation of predicted JJA all India rainfall from 1998 to 2009 with TRMM is fairly high at 0.68. Future work will focus on the prospects for further improving this skill with bias correction techniques.

Atmospheric circulation feedback on west Asian dust and Indian monsoon rainfall

NASA Astrophysics Data System (ADS)

Kaskaoutis, Dimitris; Houssos, Elias; Gautam, Ritesh; Singh, Ramesh; Rashki, Alireza; Dumka, Umesh

2016-04-01

Classification of the atmospheric circulation patterns associated with high aerosol loading events over the Ganges valley, via the synergy of Factor and Cluster analysis techniques, has indicated six different synoptic weather patterns, two of which mostly occur during late pre-monsoon and monsoon seasons (May to September). The current study focuses on examining these two specific clusters that are associated with different mean sea level pressure (MSLP), geopotential height at 700 hPa (Z700) and wind fields that seem to affect the aerosol (mostly dust) emissions and precipitation distribution over the Indian sub-continent. Furthermore, the study reveals that enhanced aerosol presence over the Arabian Sea is positively associated with increased rainfall over the Indian landmass. The increased dust over the Arabian Sea and rainfall over India are associated with deepening of the northwestern Indian and Arabian lows that increase thermal convection and convergence of humid air masses into Indian landmass, resulting in larger monsoon precipitation. For this cluster, negative MSLP and Z700 anomalies are observed over the Arabian Peninsula that enhance the dust outflow from Arabia and, concurrently, the southwesterly air flow resulting in increase in monsoon precipitation over India. The daily precipitation over India is found to be positively correlated with the aerosol loading over the Arabian Sea for both weather clusters, thus verifying recent results from satellite observations and model simulations concerning the modulation of the Indian summer monsoon rainfall by the Arabian dust. The present work reveals that in addition to the radiative impacts of dust on modulating the monsoon rainfall, differing weather patterns favor changes in dust emissions, accumulation as well as rainfall distribution over south Asia.

Role of Atmospheric Circulation and Westerly Jet Changes in the mid-Holocene East Asian Summer Monsoon

NASA Astrophysics Data System (ADS)

Kong, W.; Chiang, J. C. H.

2014-12-01

The East Asian Summer Monsoon (EASM) varies on inter-decadal to interglacial-glacial timescales. The EASM is stronger in the mid-Holocene than today, and these changes can be readily explained by orbitally-driven insolation increase during the boreal summer. However, a detailed understanding of the altered seasonal evolution of the EASM during this time is still lacking. In particular, previous work has suggested a close link between seasonal migration of the EASM and that of the mid-latitude westerlies impinging on the Tibetan Plateau. In this study, we explore, this problem in PMIP3 climate model simulations of the mid-Holocene, focusing on the role of atmospheric circulation and in particular how the westerly jet modulates the East Asia summer climate on paleoclimate timescales. Analysis of the model simulations suggests that, compared to the preindustrial simulations, the transition from Mei-Yu to deep summer rainfall occurs earlier in the mid-Holocene. This is accompanied by an earlier weakening and northward shift of westerly jet away from the Tibetan Plateau. The variation in the strength and the 3-D structure of the westerly jet in the mid-Holocene is summarized. We find that changes to the monsoonal rainfall, westerly jet and meridional circulation covary on paleoclimate timescales. Meridional wind changes in particular are tied to an altered stationary wave pattern, resembling today's the so-called 'Silk Road' teleconnection pattern, riding along the westerly jet. Diagnostic analysis also reveals changes in moist static energy and eddy energy fluxes associated with the earlier seasonal transition of the EASM. Our analyses suggest that the westerly jet is critical to the altered dynamics of the East Asian summer monsoon during the mid-Holocene.

Wetting and greening Tibetan Plateau in early summer since the late 1970s due to advanced Asian summer monsoon onset

NASA Astrophysics Data System (ADS)

Zhang, Wenxia; Zhou, Tianjun; Zhang, Lixia

2016-04-01

Known as the "the world water tower", the Tibetan Plateau (TP) is the origin of the ten largest rivers in Asia, breeding more than 1.4 billion people, and exerts substantial influences on water resources, agriculture, and ecosystems in downstream countries. This region is one of the most susceptible areas around the world to changing climate due to the high elevation. Observed evidence have shown significant climate changes over the TP, including surface air warming and moistening, glaciers shrinking, winds stilling, solar dimming, and atmospheric heat source weakening. However, as an essential part of the hydrological cycle, precipitation changes on the TP remain an ambiguous picture. Changes in precipitation vary largely with different seasons, time periods and climate zones considered. This study shows a robust increase in precipitation amount over the TP in May, when the rainy season starts, over the period 1979-2014 (31% relative to the climatology). The wetting trend is spatially consistent over the south-eastern TP, to which both precipitation frequency and intensity contribute. Circulation trends show that the wetting TP in May is resulted from the advanced onset of Asian summer monsoon, which onsets 1~2 pentads earlier since 1979. It intensified water vapor transport from the Bay of Bengal (BOB) to south of the TP in May and local anomalous convection. This relationship is further validated by the significant correlation coefficient (0.47) between the onset dates of Asian summer monsoon (particularly the BOB summer monsoon, 0.68) and precipitation over the south-eastern TP in May. The wetting TP in May has further exerted profound impacts on the hydrological cycle and ecosystem, such as moistening the soil and animating vegetation activities throughout early summer. Both decadal variations of soil moisture (from May to June) and Normalized Difference Vegetation Index (NDVI) (from May to July) coincide well with that of precipitation over the south

Indian summer monsoon rainfall: Dancing with the tunes of the sun

NASA Astrophysics Data System (ADS)

Hiremath, K. M.; Manjunath, Hegde; Soon, Willie

2015-02-01

There is strong statistical evidence that solar activity influences the Indian summer monsoon rainfall. To search for a physical link between the two, we consider the coupled cloud hydrodynamic equations, and derive an equation for the rate of precipitation that is similar to the equation of a forced harmonic oscillator, with cloud and rain water mixing ratios as forcing variables. Those internal forcing variables are parameterized in terms of the combined effect of external forcing as measured by sunspot and coronal hole activities with several well known solar periods (9, 13 and 27 days; 1.3, 5, 11 and 22 years). The equation is then numerically solved and the results show that the variability of the simulated rate of precipitation captures very well the actual variability of the Indian monsoon rainfall, yielding vital clues for a physical understanding that has so far eluded analyses based on statistical correlations alone. We also solved the precipitation equation by allowing for the effects of long-term variation of aerosols. We tentatively conclude that the net effects of aerosols variation are small, when compared to the solar factors, in terms of explaining the observed rainfall variability covering the full Indian monsoonal geographical domains.

Change in the relationship between the Australian summer monsoon circulation and boreal summer precipitation over Central China in the late 1990s

NASA Astrophysics Data System (ADS)

Yang, Ruowen; Wang, Jian; Zhang, Tianyu; He, Shengping

2017-09-01

Recent study revealed a close connection between the Australian summer monsoon (ASM) and boreal summer precipitation over Central China (SPCC). This study further revealed a strengthening of the ASM-SPCC relationship around the late 1990s. It is found that the relationship between the ASM and the SPCC during 1979-1997 (1998-2014) relationship is statistically insignificant (significant). Further analysis indicated that during 1998-2014, the weakened ASM is concurrent with significant positive sea surface temperature (SST) in the Indian Ocean and South China Sea, which could persist into the following boreal summer and further lead to intensified East Asian summer monsoon, strengthened western North Pacific subtropical high, and anomalous ascending motion over Central China. Consequently, more moisture is transported from the western Pacific northward to Central China where significant anomalous convergence appears. Therefore, the ASM could potentially influence the SPCC during 1998-2014. By contrast, the ASM-related SST and atmospheric circulation anomalies in boreal winter are statistically insignificant during 1979-1997. Such an interdecadal change might be attributed to the interdecadal warming that occurred in the Indian Ocean and South China Sea around the late 1990s. This study might be useful for the prediction of the SPCC.

Difference in the influence of Indo-Pacific Ocean heat content on South Asian Summer Monsoon intensity before and after 1976/1977

NASA Astrophysics Data System (ADS)

Dong, Yujie; Feng, Junqiao; Hu, Dunxin

2016-05-01

Monthly ocean temperature from ORAS4 datasets and atmospheric data from NCEP/NCAR Reanalysis I/II were used to analyze the relationship between the intensity of the South Asian summer monsoon (SASM) and upper ocean heat content (HC) in the tropical Indo-Pacific Ocean. The monsoon was differentiated into a Southwest Asian Summer Monsoon (SWASM) (2.5°-20°N, 35°-70°E) and Southeast Asian Summer Monsoon (SEASM) (2.5°-20°N, 70°-110°E). Results show that before the 1976/77 climate shift, the SWASM was strongly related to HC in the southern Indian Ocean and tropical Pacific Ocean. The southern Indian Ocean affected SWASM by altering the pressure gradient between southern Africa and the northern Indian Ocean and by enhancing the Somali cross-equatorial flow. The tropical Pacific impacted the SWASM through the remote forcing of ENSO. After the 1976/77 shift, there was a close relationship between equatorial central Pacific HC and the SEASM. However, before that shift, their relationship was weak.

Predicting Indian Summer Monsoon onset through variations of surface air temperature and relative humidity

NASA Astrophysics Data System (ADS)

Stolbova, Veronika; Surovyatkina, Elena; Kurths, Jurgen

2015-04-01

Indian Summer Monsoon (ISM) rainfall has an enormous effect on Indian agriculture, economy, and, as a consequence, life and prosperity of more than one billion people. Variability of the monsoonal rainfall and its onset have a huge influence on food production, agricultural planning and GDP of the country, which on 22% is determined by agriculture. Consequently, successful forecasting of the ISM onset is a big challenge and large efforts are being put into it. Here, we propose a novel approach for predictability of the ISM onset, based on critical transition theory. The ISM onset is defined as an abrupt transition from sporadious rainfall to spatially organized and temporally sustained rainfall. Taking this into account, we consider the ISM onset as is a critical transition from pre-monsoon to monsoon, which take place in time and also in space. It allows us to suggest that before the onset of ISM on the Indian subcontinent should be areas of critical behavior where indicators of the critical transitions can be detected through an analysis of observational data. First, we identify areas with such critical behavior. Second, we use detected areas as reference points for observation locations for the ISM onset prediction. Third, we derive a precursor for the ISM onset based on the analysis of surface air temperature and relative humidity variations in these reference points. Finally, we demonstrate the performance of this precursor on two observational data sets. The proposed approach allows to determine ISM onset in advance in 67% of all considered years. Our proposed approach is less effective during the anomalous years, which are associated with weak/strong monsoons, e.g. El-Nino, La-Nina or positive Indian Ocean Dipole events. The ISM onset is predicted for 23 out of 27 normal monsoon years (85%) during the past 6 decades. In the anomalous years, we show that time series analysis in both areas during the pre-monsoon period reveals indicators whether the

Response of rainy season duration over Asian monsoon region to astronomical forcing under glacial and interglacial conditions

NASA Astrophysics Data System (ADS)

Shi, Z.

2017-12-01

The responses of Asian summer monsoon and associated precipitation to astronomical forcing have beenintensively explored during the past decades, but debate still exists regarding whether or not the Asianmonsoon is controlled by northern or southern summer insolation. Various modeling studies have been conducted that support the potential roles played by the insolation in bothhemispheres. Among these previous studies, however, the main emphasis has been on the Asianmonsoon intensity, with the response of monsoon duration having received little consideration. In thepresent study, the response of the rainy season duration over different monsoon areas to astronomical forcingand its contribution to total annual precipitation are evaluated using an atmospheric general circulationmodel. The results show that the durations of the rainy seasons, especially their withdrawal, in northernEast Asia and the India-Bay of Bengal region, are sensitive to precession change under interglacial-likeconditions. Compared to those during stronger boreal summer insolation, the Asian monsoon associatedrainy seasons at weaker insolation last longer, although the peak intensity is smaller. Thislonger duration of rainfall, which results from the change in land-ocean thermal contrast associated withatmospheric diabatic heating, can counterbalance the weakened intensity in certain places and induce anopposite response of total annual precipitation. However, the duration effect of Asian monsoon is limitedunder glacial-like conditions. Nevertheless, monsoon duration is a factor that can dominate the astronomical-scalevariability of Asian monsoon, alongside the intensity, and it should therefore receive greaterattention when attempting to explain astronomical-scale monsoon change.

East Asian Summer Monsoon Rainfall: A Historical Perspective of the 1998 Flood over Yangtze River

NASA Technical Reports Server (NTRS)

Weng, H.-Y.; Lau, K.-M.

1999-01-01

One of the main factors that might have caused the disastrous flood in China during 1998 summer is long-term variations that include a trend indicating increasing monsoon rainfall over the Yangtze River Valley. China's 160-station monthly rainfall anomaly for the summers of 1955-98 is analyzed for exploring such long-term variations. Singular value decomposition (SVD) between the summer rainfall and the global sea surface temperature (SST) anomalies reveals that the rainfall over Yangtze River Valley is closely related to global and regional SST variabilities at both interannual and interdecadal timescales. SVD1 mode links the above normal rainfall condition in central China to an El Nino-like SSTA distribution, varying on interannual timescale modified by a trend during the period. SVD3 mode links positive rainfall anomaly in Yangtze River Valley to the warm SST anomaly in the subtropical western Pacific, varying on interannual timescales modified by interdecadal timescales. This link tends to be stronger when the Nino3 area becomes colder and the western subtropical Pacific becomes warmer. The 1998 summer is a transition season when the 1997/98 El Nino event was in its decaying phase, and the SST in the Nino3 area emerged below normal anomaly while the subtropical western Pacific SST above normal. Thus, the first and third SVD modes become dominant in 1998 summer, favoring more Asian summer monsoon rainfall over the Yangtze River Valley.

Long-term changes in the South China Sea summer monsoon revealed by station observations of the Xisha Islands

NASA Astrophysics Data System (ADS)

Liang, Jianyin; Yang, Song; Li, Cunhui; Li, Xia

2007-05-01

The authors depict the long-term changes in the South China Sea (SCS) summer monsoon using observational data of the Xisha Islands. The SCS monsoon is an important component of the Asian monsoon system, and its long-term changes have seldom been explored because of the unavailability of reliable data. The daily Xisha station observations provide an important source of information for understanding the changes in the monsoon. The intensity of the SCS summer monsoon measured by kinetic energy decreased significantly from 1958-1977 to 1978-2004. This change in monsoon was mainly caused by the weakening of the meridional component of lower tropospheric winds, and the weakening in the mean flow was signaled by decreased frequency of strong southerlies (6 m s-1 and above) of the daily winds. The weakening of the monsoon was also associated with increases in sea surface temperature and surface and lower tropospheric air temperatures over SCS, which occurred more frequently when daily surface temperature reaches 29°C and higher. The long-term warming of the lower troposphere was accompanied by cooling at the upper troposphere, destabilizing the local atmosphere. However, from 1958-1977 to 1978-2004, the long-term change in Xisha precipitation tended to decrease; furthermore, in fact, the station precipitation became less variable. Thus besides local air-sea interaction, large-scale atmospheric forcing also plays an important role in causing the long-term change of the Xisha precipitation. Indeed, the warming of Xisha was linked to large-scale warming in the tropics including SCS and was associated with smaller thermal contrast between the Asian continent and the surrounding oceans, which weakened monsoon circulation.

Amplification of the solar signal in the summer monsoon rainband in China by synergistic actions of different dynamical responses

NASA Astrophysics Data System (ADS)

Zhao, Liang; Wang, Jingsong; Liu, Haiwen; Xiao, Ziniu

2017-02-01

A rainband meridional shift index (RMSI) is defined and used to statistically prove that the East Asian summer monsoon rainband is usually significantly more northward in the early summer of solar maximum years than that of solar minimum years. By applying continuous wavelet transform, cross wavelet transform, and wavelet coherence, it is found that throughout most of the 20th century, the significant decadal oscillations of sunspot number (SSN) and the RMSI are phase-locked and since the 1960s, the SSN has led the RMSI slightly by approximately 1.4 yr. Wind and Eliassen-Palm (EP) flux analysis shows that the decadal meridional oscillation of the June rainband likely results from both a stronger or earlier onset of the tropical monsoon and poleward shift of the subtropical westerly jet in high-solar months of May and June. The dynamical responses of the lower tropical monsoon and the upper subtropical westerly jet to the 11-yr solar cycle transmit bottom-up and top-down solar signals, respectively, and the synergistic actions between the monsoon and the jet likely amplify the solar signal at the northern boundary of the monsoon to some extent.

Influence of Decadal Variability of Global Oceans on South Asian Monsoon and ENSO-Monsoon Relation

NASA Astrophysics Data System (ADS)

Krishnamurthy, Lakshmi

correlation with the IMR. The AMO influences the Indian monsoon through atmospheric winds related to high summer North Atlantic Oscillation (NAO) mode leading to enhanced moisture flow over the Indian subcontinent. The Atlantic tripole mode affects the rainfall over India by enhancing the moisture flow through the equatorial westerly winds associated with the NAO. The model also simulates the positive and negative relation of AMO and tripole, respectively, with the monsoon rainfall. The model also indicates the enhanced moisture flow over India related to the positive phase of AMO through the equatorial westerly flow. But, for the tripole mode, the model indicates flow of moisture through the Bay of Bengal in contrast to observations where it is through the Arabian Sea. The reason for the absence of decadal mode in IMR inherent to the Indian Ocean is also explored. The SSA on dipole mode index (DMI) index reveals three modes. The first two modes are related to the biennial and canonical ENSO at interannual timescale while the third mode varies on decadal timescale and is related to PDO. The wind regression pattern associated with the PDO-IOD mode shows northeasterly winds enhancing the southeasterly flow from the southeastern Indian Ocean related to the Indian Ocean dipole (IOD) mode. The model also shows the influence of canonical ENSO and PDO influence on IOD, although the variance explained by PDO mode is lower in the model relative to observations.

Responses of East Asian Summer Monsoon to Natural and Anthropogenic Forcings in the 17 Latest CMIP5 Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Fengfei; Zhou, Tianjun; Qian, Yun

2014-01-31

In this study, we examined the responses of East Asian Summer Monsoon (EASM) to natural (solar variability and volcanic aerosols) and anthropogenic (greenhouse gasses and aerosols) forcings simulated in the 17 latest Coupled Model Intercomparison Program phase 5 (CMIP5) models with 105 realizations. The observed weakening trend of low-level EASM circulation during 1958-2001 is partly reproduced under all-forcing runs. A comparison of separate forcing experiments reveals that the aerosol-forcing plays a primary role in driving the weakened low-level monsoon circulation. The preferential cooling over continental East Asia caused by aerosol affects the monsoon circulation through reducing the land-sea thermal contrastmore » and results in higher sea level pressure over northern China. In the upper-level, both natural-forcing and aerosol-forcing contribute to the observed southward shift of East Asian subtropical jet through changing the meridional temperature gradient.« less

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

Assessment of regional downscaling simulations for long term mean, excess and deficit Indian Summer Monsoons

NASA Astrophysics Data System (ADS)

Varikoden, Hamza; Mujumdar, M.; Revadekar, J. V.; Sooraj, K. P.; Ramarao, M. V. S.; Sanjay, J.; Krishnan, R.

2018-03-01

This study undertakes a comprehensive assessment of dynamical downscaling of summer monsoon (June-September; JJAS) rainfall over heterogeneous regions namely the Western Ghats (WG), Central India (CI) and North-Eastern Region (NER) for long term mean, excess and deficit episodes for the historical period from 1951 to 2005. This downscaling assessment is based on six Coordinated Regional Climate Downscaling Experiments (CORDEX) for South Asia (SAS) region, their five driving Global Climate Models (GCM) simulations along with observations from India Meteorological Department (IMD) and Asian Precipitation Highly Resolved Observational Integrated Towards Evaluation for Water Resources (APHRODITE). The analysis reveals an overall reduction of dry bias in rainfall across the regions of Indian sub-continent in most of the downscaled CORDEX-SAS models and in their ensemble mean as compared to that of driving GCMs. The interannual variabilities during historical period are reasonably captured by the ensemble means of CORDEX-SAS simulations with an underestimation of 0.43%, 38% and 52% for the WG, CI and NER, respectively. Upon careful examination of the CORDEX-SAS models and their driving GCMs revealed considerable improvement in the regionally downscaled rainfall. The value addition of dynamical downscaling is apparent over the WG in Regional Climate Model (RCM) simulations with an improvement of more than 30% for the long term mean, excess and deficit episodes from their driving GCMs. In the case of NER, the improvement in the downscaled rainfall product is more than 10% for all the episodes. However, the value addition in the CORDEX-SAS simulations for CI region, dominantly influenced by synoptic scale processes, is not clear. Nevertheless, the reduction of dry bias in the complex topographical regions is remarkable. The relative performance of dynamical downscaling of rainfall over complex topography in response to local forcing and orographic lifting depict the value

Late Holocene SST and primary productivity variations in the northeastern Arabian Sea as a recorder for winter monsoon variability

NASA Astrophysics Data System (ADS)

Böll, Anna; Gaye, Birgit; Lückge, Andreas

2014-05-01

Variability in the oceanic environment of the Arabian Sea region is strongly influenced by the seasonal monsoon cycle of alternating wind directions. Strong south-westerly winds during the summer monsoon induce upwelling of nutrient rich waters along the coast off Somalia, Oman and southwest India, which result in high rates of primary production. In the northeastern Arabian Sea off Pakistan on the other hand, primary production and sea surface temperatures are linked to northeast monsoonal winds that cool the sea surface and drive convective mixing and high surface ocean productivity during the winter season. In this study, we analyzed alkenone-derived sea surface temperature (SST) variations and proxies of primary productivity (organic carbon and δ15N) in a well-laminated sediment core from the Pakistan continental margin to establish the first high-resolution record of winter monsoon variability for the late Holocene. Over the last 2400 years reconstructed SST in the northeastern Arabian Sea decreased whereas productivity increased, imaging a long-term trend of northeast monsoon strengthening in response to insolation-induced southward migration of the Intertropical Convergence Zone. The comparison of our winter monsoon record with records of summer monsoon intensity suggests that summer and winter monsoon strength was essentially anti-correlated over the late Holocene throughout the Asian monsoon system. In addition, SST variations recorded off Pakistan match very well with Northern Hemisphere temperature records supporting the growing body of evidence that Asian climate is linked to Northern Hemisphere climate change. It reveals a consistent pattern of increased summer monsoon activity in the northeastern Arabian Sea during northern hemispheric warm periods (Medieval Warm Period, Roman Warm Period) and strengthened winter monsoon activity during hemispheric colder periods (Little Ice Age).

Multiproxy Reduced-Dimension Reconstruction of Holocene Tropical Pacific SST Fields and Indian Monsoon Variability

NASA Astrophysics Data System (ADS)

Gill, E.; Rajagopalan, B.; Molnar, P. H.; Marchitto, T. M., Jr.; Kushnir, Y.

2016-12-01

We develop a multiproxy reduced-dimension methodology that blends magnesium calcium (Mg/Ca) and alkenone (UK'37) paleo sea surface temperature (SST) records from the eastern and western equatorial Pacific to recreate snapshots of full field SSTs and zonal wind anomalies from 10 to 2 ka BP in 2000-year increments. In the reconstruction, the zonal SST difference (average west Pacific SST minus average east Pacific SST) is largest at 10 ka (0.26°C), with coldest SST anomalies of -0.9°C in the eastern equatorial Pacific and concurrent easterly maximum zonal wind anomalies of 7 m s-1 throughout the central Pacific. From 10 to 2 ka, the entire equatorial Pacific warms, but at a faster rate in the east than in the west. These patterns are broadly consistent with previous inferences of reduced El Niño-Southern Oscillation variability associated with a cooler and/or "La Niña-like" state during the early to middle Holocene. At present there is a strong negative correlation between tropical pacific SSTs and Indian summer monsoon strength. Assuming ENSO-monsoon teleconnections were the same during early Holocene, we would expect a cooler tropical Pacific to enhance the summer Indian monsoon. To test this idea, we used the same tropical Pacific SST proxy records and a similar reduced-dimension technique to reconstruct fields of Arabian Sea wind-stress curl and Indian summer monsoon precipitation. Reconstructions for 10 ka reveal wind-stress curl anomalies of 30% greater than present day off the coastlines of Oman and Yemen, which suggest greater coastal upwelling and an enhanced monsoon jet during this time. Spatial rainfall reconstructions reveal the greatest difference in precipitation at 10 ka over the core monsoon region ( 20-60% greater than present day). Specifically, reconstructions from 10 ka reveal 40-60% greater rainfall over North West India, a region home to abundant paleo-lake records spanning the Holocene but is at present remarkably dry ( 200-450 mm of annual

Atmospheric water budget over the South Asian summer monsoon region

NASA Astrophysics Data System (ADS)

Unnikrishnan, C. K.; Rajeevan, M.

2018-04-01

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.

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

Heat wave over India during summer 2015: an assessment of real time extended range forecast

NASA Astrophysics Data System (ADS)

Pattanaik, D. R.; Mohapatra, M.; Srivastava, A. K.; Kumar, Arun

2017-08-01

Hot winds are the marked feature of summer season in India during late spring preceding the climatological onset of the monsoon season in June. Some years the conditions becomes very vulnerable with the maximum temperature ( T max) exceeding 45 °C for many days over parts of north-western, eastern coastal states of India and Indo-Gangetic plain. During summer of 2015 (late May to early June) eastern coastal states, central and northwestern parts of India experienced severe heat wave conditions leading to loss of thousands of human life in extreme high temperature conditions. It is not only the loss of human life but also the animals and birds were very vulnerable to this extreme heat wave conditions. In this study, an attempt is made to assess the performance of real time extended range forecast (forecast up to 3 weeks) of this scorching T max based on the NCEP's Climate Forecast System (CFS) latest version coupled model (CFSv2). The heat wave condition was very severe during the week from 22 to 28 May with subsequent week from 29 May to 4 June also witnessed high T max over many parts of central India including eastern coastal states of India. The 8 ensemble members of operational CFSv2 model are used once in a week to prepare the weekly bias corrected deterministic (ensemble mean) T max forecast for 3 weeks valid from Friday to Thursday coinciding with the heat wave periods of 2015. Using the 8 ensemble members separately and the CFSv2 corresponding hindcast climatology the probability of above and below normal T max is also prepared for the same 3 weeks. The real time deterministic and probabilistic forecasts did indicate impending heat wave over many parts of India during late May and early June of 2015 associated with strong northwesterly wind over main land mass of India, delaying the sea breeze, leading to heat waves over eastern coastal regions of India. Thus, the capability of coupled model in providing early warning of such killer heat wave can be very

Multifaceted intra-seasonal modes over the East Asia-western North Pacific summer monsoon region

NASA Astrophysics Data System (ADS)

Ha, K. J.; Oh, H.

2017-12-01

Intra-seasonal monsoon prediction is the most imperative task due to high impact on 2/3 of world populations' daily life, but there remains an enduring challenge in climate science. The present study aims to provide a physical understanding of the sources for prediction of dominant intra-seasonal modes in the East Asian-western North Pacific summer monsoon (EA-WNPSM): preMeiyu&Baiu, Changma&Meiyu, WNPSM, and monsoon gyre modes classified by the self-organizing map analysis. The preMeiyu-Baiu mode is strongly linked to both the anomalous low-level convergence and vertical wind shear through baroclinic instability, and the Changma&Meiyu mode has a strengthened tropic-subtropics connection along the western north Pacific subtropical high, which induces vertical destabilization and strong convective instability. The WNPSM and monsoon gyre modes are characterized by anomalous southeasterly flow of warm and moist air from western north Pacific monsoon, and low-level easterly flow, respectively. Prominent difference in response to the ENSO leads to different effects of the Indian Ocean and western Pacific thermal state, and consequently, the distinct moisture supply and instability variations for the EASM intra-seasonal modes. We attempt to determine the predictability sources for the four modes in the EA-WNPSM using physical-empirical model. The selected predictors are based on the persistent and tendency signals of the SST/2m air temperature and sea level pressure fields, which reflect the asymmetric response to the ENSO and the ocean and land surface anomalous conditions. For the preMeiyu&Baiu mode, the SST cooling tendency over the WNP, which persists into summer, is the distinguishing contributor which is causative of north-south thermal contrast. Since the Changma&Meiyu mode is strongly related to the WNP subtropical high, a major precursor is the persistent SST difference between the Indian Ocean and the western Pacific. The WNPSM mode is mostly affected by the

Changes in Water-Food-Energy Nexus in India and its consistency with changes in Monsoon

NASA Astrophysics Data System (ADS)

Barik, B.; Ghosh, S.; Pathak, A.

2017-12-01

Meeting the growing demand for food, water, and energy for a densely populated country like India is a major challenge. Green Revolution helped to maintain the food security, with Government policies such as distribution of electricity at a subsidised rate, resulting in an unregulated withdrawal of groundwater. Thus, the depleting groundwater went unnoticed as the high agricultural productivity overshadowed it. Here we present a comprehensive analysis which assess the present status of the water-food-energy nexus in India. We find that with the growth of population and consequent increase in the food demands, the food production has also increased, and this has been made possible with the intensification of irrigation. However, during the recent decade (after 1996), the increase in food production has not been sufficient to meet its growing demands, precipitating a decline in the per-capita food availability. Also, there has been a decline in the groundwater storage in India during the last decade, as derived from the Gravity Recovery and Climate Experiment (GRACE) data. Regional studies reveal contrasting trends, where North-western India and the middle Ganga basin show a decrease in the groundwater storage as opposed to an increasing storage over western-central India. We also find that, after a drought, the groundwater storage drops but is unable to recover to its original condition even after good monsoon years. The groundwater storage reveals a very strong negative correlation with the electricity consumption for agricultural usage, which may also be considered as a proxy for groundwater pumped for irrigation in a region. The electricity usage for agricultural purposes has an increasing trend and, interestingly, it does not have any correlation with the monsoon rainfall. This reveals an important finding that the irrigation has been intensified irrespective of rainfall. This also resulted in a decreasing correlation between the food production and monsoon

Parametric Sensitivity Analysis for the Asian Summer Monsoon Precipitation Simulation in the Beijing Climate Center AGCM Version 2.1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Ben; Zhang, Yaocun; Qian, Yun

In this study, we apply an efficient sampling approach and conduct a large number of simulations to explore the sensitivity of the simulated Asian summer monsoon (ASM) precipitation, including the climatological state and interannual variability, to eight parameters related to the cloud and precipitation processes in the Beijing Climate Center AGCM version 2.1 (BCC_AGCM2.1). Our results show that BCC_AGCM2.1 has large biases in simulating the ASM precipitation. The precipitation efficiency and evaporation coefficient for deep convection are the most sensitive parameters in simulating the ASM precipitation. With optimal parameter values, the simulated precipitation climatology could be remarkably improved, e.g. increasedmore » precipitation over the equator Indian Ocean, suppressed precipitation over the Philippine Sea, and more realistic Meiyu distribution over Eastern China. The ASM precipitation interannual variability is further analyzed, with a focus on the ENSO impacts. It shows the simulations with better ASM precipitation climatology can also produce more realistic precipitation anomalies during El Niño decaying summer. In the low-skill experiments for precipitation climatology, the ENSO-induced precipitation anomalies are most significant over continents (vs. over ocean in observation) in the South Asian monsoon region. More realistic results are derived from the higher-skill experiments with stronger anomalies over the Indian Ocean and weaker anomalies over India and the western Pacific, favoring more evident easterly anomalies forced by the tropical Indian Ocean warming and stronger Indian Ocean-western Pacific tele-connection as observed. Our model results reveal a strong connection between the simulated ASM precipitation climatological state and interannual variability in BCC_AGCM2.1 when key parameters are perturbed.« less

Changes in the Asian monsoon climate during 1700-1850 induced by preindustrial cultivation.

PubMed

Takata, Kumiko; Saito, Kazuyuki; Yasunari, Tetsuzo

2009-06-16

Preindustrial changes in the Asian summer monsoon climate from the 1700s to the 1850s were estimated with an atmospheric general circulation model (AGCM) using historical global land cover/use change data reconstructed for the last 300 years. Extended cultivation resulted in a decrease in monsoon rainfall over the Indian subcontinent and southeastern China and an associated weakening of the Asian summer monsoon circulation. The precipitation decrease in India was marked and was consistent with the observational changes derived from examining the Himalayan ice cores for the concurrent period. Between the 1700s and the 1850s, the anthropogenic increases in greenhouse gases and aerosols were still minor; also, no long-term trends in natural climate variations, such as those caused by the ocean, solar activity, or volcanoes, were reported. Thus, we propose that the land cover/use change was the major source of disturbances to the climate during that period. This report will set forward quantitative examination of the actual impacts of land cover/use changes on Asian monsoons, relative to the impact of greenhouse gases and aerosols, viewed in the context of global warming on the interannual, decadal, and centennial time scales.

Performance of Regional Climate Model in Simulating Monsoon Onset Over Indian Subcontinent

NASA Astrophysics Data System (ADS)

Bhatla, R.; Mandal, B.; Verma, Shruti; Ghosh, Soumik; Mall, R. K.

2018-06-01

The performance of various Convective Parameterization Schemes (CPSs) of Regional Climate Model version 4.3 (RegCM-4.3) for simulation of onset phase of Indian summer monsoon (ISM) over Kerala was studied for the period of 2001-2010. The onset date and its associated spatial variation were simulated using RegCM-4.3 four core CPS, namely Kuo, Tiedtke, Emanuel and Grell; and with two mixed convection schemes Mix98 (Emanuel over land and Grell over ocean) and Mix99 (Grell over land and Emanuel over ocean) on the basis of criteria given by the India Meteorological Department (IMD) (Pai and Rajeevan in Indian summer monsoon onset: variability and prediction. National Climate Centre, India Meteorological Department, 2007). It has been found that out of six CPS, two schemes, namely Tiedtke and Mix99 simulated the onset date properly. The onset phase is characterized with several transition phases of atmosphere. Therefore, to study the thermal response or the effect of different sea surface temperature (SST), namely ERA interim (ERSST) and weekly optimal interpolation (OI_WK SST) on Indian summer monsoon, the role of two different types of SST has been used to investigate the simulated onset date. In addition, spatial atmospheric circulation pattern during onset phase were analyzed using reanalyze dataset of ERA Interim (EIN15) and National Oceanic and Atmospheric Administration (NOAA), respectively, for wind and outgoing long-wave radiation (OLR) pattern. Among the six convective schemes of RegCM-4.3 model, Tiedtke is in good agreement with actual onset dates and OI_WK SST forcing is better for simulating onset of ISM over Kerala.

Millennial-scale Asian summer monsoon variations in South China since the last deglaciation

NASA Astrophysics Data System (ADS)

Wang, Xisheng; Chu, Guoqiang; Sheng, Mei; Zhang, Shuqin; Li, Jinhua; Chen, Yun; Tang, Ling; Su, Youliang; Pei, Junling; Yang, Zhenyu

2016-10-01

Characterizing spatiotemporal variability of the Asian summer monsoon (ASM) is critical for full understanding of its behavior, dynamics, and future impacts. The present knowledge about ASM variations since the last glaciation in South China largely relies on several precisely-dated speleothem stable oxygen isotope (δ18 O) records. Although these speleothem δ18 O signals provide useful evidence for regional past environmental changes, their validity for denoting ASM intensity remains a great controversy. The Huguangyan Maar Lake (HML) provides one of the most complete archives of environmental and climatic changes in the tropical-subtropical South and East Asia since the last glaciation. Here we document a continuous centennial- to millennial-scale ASM record over the past 16 ky BP from the high-sedimentation-rate HML sediments. In contrast with the low-amplitude variations of Chinese speleothem-derived δ18 O signals and the Chinese loess-based monsoon precipitation proxy indexes, our multi-proxy records reveal a pattern of high-amplitude regional climatic fluctuations, including fine-scale oscillations during the Bølling-Allerød warming, the 8.2 ka cooling event, and an abrupt climate shift from 6.5-5.9 ka. The existence of Bond-like cold/dry events indicates a distinct influence of the North Atlantic circulation on low-latitude monsoon changes. The broad comparability between the HML paleo-proxies, Chinese speleothem δ18 O records, and the northern hemisphere summer insolation throughout the Holocene, suggests that solar insolation exerts a profound influence on ASM changes. These findings reinforce a model of combined insolation and glacial forcing of the ASM.

Interference of the East Asian winter monsoon in the impact of ENSO on the East Asian summer monsoon in decaying phases

NASA Astrophysics Data System (ADS)

Feng, Juan; Chen, Wen

2014-03-01

The variability of the East Asian winter monsoon (EAWM) can be divided into an ENSO-related part (EAWMEN) and an ENSO-unrelated part (EAWMres). The influence of EAWMres on the ENSO-East Asian summer monsoon (EASM) relationship in the decaying stages of ENSO is investigated in the present study. To achieve this, ENSO is divided into four groups based on the EAWMres: (1) weak EAWMres-El Niño (WEAWMres-EN); (2) strong EAWMres-El Niño (SEAWMres- EN); (3) weak EAWMres-La Niña (WEAWMres-LN); (4) strong EAWMres-La Niña (SEAWMres-LN). Composite results demonstrate that the EAWMres may enhance the atmospheric responses over East Asia to ENSO for WEAWMres-EN and SEAWMres-LN. The corresponding low-level anticyclonic (cyclonic) anomalies over the western North Pacific (WNP) associated with El Niño (La Niña) tend to be strong. Importantly, this feature may persist into the following summer, causing abundant rainfall in northern China for WEAWMres-EN cases and in southwestern China for SEAWMres-LN cases. In contrast, for the SEAWMres-EN and WEAWMres-LN groups, the EAWMres tends to weaken the atmospheric circulation anomalies associated with El Niño or La Niña. In these cases, the anomalous WNP anticyclone or cyclone tend to be reduced and confined to lower latitudes, which results in deficient summer rainfall in northern China for SEAWMres-EN and in southwestern China for WEAWMres-LN. Further study suggests that anomalous EAWMres may have an effect on the extra-tropical sea surface temperature anomaly, which persists into the ensuing summer and may interfere with the influences of ENSO.

Indian Monsoon Low-Pressure Systems Feed Up-and-Over Moisture Transport to the Southwestern Tibetan Plateau

NASA Astrophysics Data System (ADS)

Dong, Wenhao; Lin, Yanluan; Wright, Jonathon S.; Xie, Yuanyu; Xu, Fanghua; Xu, Wenqing; Wang, Yan

2017-11-01

As an integral part of the South Asian summer monsoon system, monsoon low-pressure systems (LPSs) bring large amounts of precipitation to agrarian north and central India during their passage across the subcontinent. In this study, we investigate the role of LPSs in supplying moisture from north and central India to the southwestern Tibetan Plateau (SWTP) and quantify the contribution of these systems to summer rainfall over the SWTP. The results show that more than 60% of total summer rainfall over the SWTP is related to LPS occurrence. LPSs are associated with a 15% rise in average daily rainfall and a 10% rise in rainy days over the SWTP. This relationship is maintained primarily through up-and-over transport, in which convectively lifted moisture over the Indian subcontinent is swept over the SWTP by southwesterly winds in the middle troposphere. LPSs play two roles in supplying up-and-over moisture transport. First, these systems elevate large amounts of water vapor and condensed water to the midtroposphere. Second, the circulations associated with LPSs interact with the background westerlies to induce southwesterly flow in the midtroposphere, transporting elevated moisture and condensate over the Himalayan Mountains. Our findings indicate that LPSs are influential in extending the northern boundary of the South Asian monsoon system across the Himalayas into the interior of the SWTP. The strength of this connection depends on both LPS characteristics and the configuration of the midtropospheric circulation, particularly the prevailing westerlies upstream of the SWTP.

Measuring Holocene Indian Summer Monsoon Precipitation through Lake Sedimentary Proxies, Eastern Tibet

NASA Astrophysics Data System (ADS)

Perello, M. M.; Bird, B. W.; Lei, Y.; Polissar, P. J.; Thompson, L. G.; Yao, T.

2017-12-01

The Tibetan Plateau is the headwaters of several major river systems in South Asia, which serve as essential water resources for more than 40% of the world's population. The majority of regional precipitation that sustains these water resources is from the Indian summer monsoon (ISM), which can experience considerably variability in response to local and remote forcings and teleconnections. Despite the ISM's importance, its sensitivity to long term and abrupt changes in climatic boundary conditions is not well established with the modern instrumental record or the available body of paleoclimate data. Here, we present results from an ongoing study that utilizes lake sediment records to provide a longer record of relative levels of precipitation and lake level during the monsoon season. The sediments cores used in this study were collected from five lakes along an east-west transect in the Eastern Tibetan Plateau (87-95°E). Using these records, we assess temporal and spatial variability in the intensity of the ISM throughout the Holocene on decadal frequencies. Multiple proxies, including sedimentology, grain size, geochemistry, terrestrial and aquatic leaf wax isotopes, and diatom community assemblages, are used to assess paleo-precipitation and lake level. Preliminary records from our lakes indicate regional trends in monsoon strength, with higher lake levels in the Early Holocene, but with greater variability in the Late Holocene than in other regional paleoclimate records. We have also observed weak responses in our lakes to the Late Holocene events, the Medieval Climate Anomaly and the Little Ice Age. These paleoclimate reconstructions furthers our understanding of strong versus weak monsoon intensities and can be incorporated in climate models for predicting future monsoon conditions.

Differences in CAPE between wet and dry spells of the monsoon over the southeastern peninsular India

NASA Astrophysics Data System (ADS)

Mohan, T. S.; Rao, T. N.; Rajeevan, M.

2018-03-01

In the present research we explored the variability of convective available potential energy (CAPE) during wet and dry spells over southeast India. Comparison between India Meteorological Department (IMD) observations and reanalysis products (NCEP, ERA-interim, and MERRA) reconfirms that gridded data sets can be utilized to fill the void of observations. Later, GPS radiosonde measurements made at Gadanki (13.5 N, 79.2 E) Andre analysis output are utilized to address key scientific issues related to CAPE over the southeastern peninsular region. They are: (1) How does CAPE vary between different spells of the Indian summer monsoon (i.e., from wet to dry spell)? (2) Does differences in CAPE and in the vertical structure of buoyancy between spells are localized features over Gadanki or observed all over southeastern peninsular region? (3) What physical/dynamical processes are responsible for the differences in CAPE between spells and how do they affect the convection growth in dry spell? Interestingly, CAPE is higher in wet spell than in dry spell, in contrast to the observations made elsewhere over land and warm oceans. Similar feature (high CAPE in wet spell) is observed at all grid points in the southeastern peninsular India. Furthermore, vertical buoyancy profiles show only one peak in the middle-upper troposphere in wet spell, while two peaks are observed in most of the profiles (66%) in dry spell over the entire study region in all the reanalysis products. Plausible mechanisms are discussed for the observed CAPE differences. They are, among others, timing of sounding with reference to rain occurrence, rapid buildup of surface instabilities, moistening of lower troposphere by evaporation of the surface moisture in wet spell, enhanced low-level moisture convergence, evaporation of rain in relatively warm and dry atmosphere, and reduction of positive buoyancy in dry spell. The omnipresence of stable layers and strong and deep shear in the presence of weak updrafts

Possible connection between the East Asian summer monsoon and a swing of the haze-fog-prone area in eastern China

NASA Astrophysics Data System (ADS)

Liu, Qian; Cao, Ziqi; Sheng, Lifang; Diao, Yina; Wang, Wencai; Zhou, Yang; Qiu, Jingyi

2018-05-01

The summer monsoon has recently been hypothesized to influence haze-fog events over China, but the detailed processes involved have yet to be determined. In the present study, we found that the haze-fog-prone area swings over eastern China during boreal summer (May to September), coinciding with the movement of the subtropical monsoon convergence belt (hereinafter referred to simply as the "convergence belt"). Further investigation showed that the convergence belt modulates the spatial distribution of the haze-fog-prone area by altering the regional atmospheric conditions. When the warm and wet summer monsoon air mass pushes northwards and meets with cold air, a frontal zone (namely, the convergence belt) forms. The ascent of warm and wet air along the front strengthens the atmospheric stability ahead of the frontal zone, while the descent of cold and dry air weakens the vertical diffusion at the same place. These processes result in an asymmetric distribution of haze-fog along the convergence belt. Based on the criterion of absolute stability and downdraft, these atmospheric conditions favorable for haze-fog are able to identify 57-79% of haze-fog-prone stations, and the anticipation accuracy is 61-71%. After considering the influence of air pollutants on haze-fog occurrence, the anticipation accuracy rises to 78-79%. Our study reveals a connection between local haze-fog weather phenomena and regional atmospheric conditions and large-scale circulation, and demonstrates one possible mechanism for how the summer monsoon influences the distribution of haze-fog in eastern China.

Projected change in East Asian summer monsoon by dynamic downscaling: Moisture budget analysis

NASA Astrophysics Data System (ADS)

Jung, Chun-Yong; Shin, Ho-Jeong; Jang, Chan Joo; Kim, Hyung-Jin

2015-02-01

The summer monsoon considerably affects water resource and natural hazards including flood and drought in East Asia, one of the world's most densely populated area. In this study, we investigate future changes in summer precipitation over East Asia induced by global warming through dynamical downscaling with the Weather Research and Forecast model. We have selected a global model from the Coupled Model Intercomparison Project Phase 5 based on an objective evaluation for East Asian summer monsoon and applied its climate change under Representative Concentration Pathway 4.5 scenario to a pseudo global warming method. Unlike the previous studies that focused on a qualitative description of projected precipitation changes over East Asia, this study tried to identify the physical causes of the precipitation changes by analyzing a local moisture budget. Projected changes in precipitation over the eastern foothills area of Tibetan Plateau including Sichuan Basin and Yangtze River displayed a contrasting pattern: a decrease in its northern area and an increase in its southern area. A local moisture budget analysis indicated the precipitation increase over the southern area can be mainly attributed to an increase in horizontal wind convergence and surface evaporation. On the other hand, the precipitation decrease over the northern area can be largely explained by horizontal advection of dry air from the northern continent and by divergent wind flow. Regional changes in future precipitation in East Asia are likely to be attributed to different mechanisms which can be better resolved by regional dynamical downscaling.

Diagnosing GCM errors over West Africa using relaxation experiments. Part I: summer monsoon climatology and interannual variability

NASA Astrophysics Data System (ADS)

Pohl, Benjamin; Douville, Hervé

2011-10-01

The CNRM atmospheric general circulation model Arpege-Climat is relaxed towards atmospheric reanalyses outside the 10°S-32°N 30°W-50°E domain in order to disentangle the regional versus large-scale sources of climatological biases and interannual variability of the West African monsoon (WAM). On the one hand, the main climatological features of the monsoon, including the spatial distribution of summer precipitation, are only weakly improved by the nudging, thereby suggesting the regional origin of the Arpege-Climat biases. On the other hand, the nudging technique is relatively efficient to control the interannual variability of the WAM dynamics, though the impact on rainfall variability is less clear. Additional sensitivity experiments focusing on the strong 1994 summer monsoon suggest that the weak sensitivity of the model biases is not an artifact of the nudging design, but the evidence that regional physical processes are the main limiting factors for a realistic simulation of monsoon circulation and precipitation in the Arpege-Climat model. Sensitivity experiments to soil moisture boundary conditions are also conducted and highlight the relevance of land-atmosphere coupling for the amplification of precipitation biases. Nevertheless, the land surface hydrology is not the main explanation for the model errors that are rather due to deficiencies in the atmospheric physics. The intraseasonal timescale and the model internal variability are discussed in a companion paper.

Changes in the influence of the western Pacific subtropical high on Asian summer monsoon rainfall in the late 1990s

NASA Astrophysics Data System (ADS)

Huang, Yanyan; Wang, Bin; Li, Xiaofan; Wang, Huijun

2017-10-01

The Year-to-year variability of the western Pacific subtropical high (WPSH) is primarily controlled by atmosphere-ocean interaction (AOI) between the WPSH and the Indo-Pacific warm pool dipole SST anomalies (AOI mode) and the anomalous SST forcing from the equatorial central Pacific (the CP forcing mode). In this study, we show that the impacts of the WPSH variability on Asian summer monsoon rainfall have changed after the late 1990s. Before the late 1990s (the PRE epoch), the WPSH primarily affects East Asian summer monsoon (EASM) and had little influence on Indian summer monsoon (ISM), whereas after the late 1990s (the POST epoch), the WPSH has strengthened its linkage to the ISM while weakened its relationship with the EASM. This epochal change is associated with a change in the leading circulation mode in the Asia-WP region. During the PRE (POST) epoch the WPSH variation is mainly controlled by the AOI (CP forcing) that mainly affects EASM (ISM). The epochal change of the leading mode may be attributed to the change of the ENSO properties in late 1990s: the CP types of El Nino become a leading ENSO mode in the POST epoch. This work provides a new perspective for understanding decadal changes of the ENSO-monsoon relationship through subtropical dynamics.

South American Monsoon precipitation trends from 1948-2006

NASA Astrophysics Data System (ADS)

Araujo, L. R.; De Mattos, J. Z.; Goncalves, L.

2013-05-01

In South America the monsoon system affects the Amazon region extending to the center of the South American continent to the northeast and southeast coastal strip. The characteristic South America Monsoon System (SAMS) is not classical, as in East Asia and India. The SAMS do not show a typical seasonal reversal in wind circulation regime, however indicates aspect of monsoon climate, as well as the seasonal cycle of rainfall over much of the continent, this is, a period of intense rain in summer and winter extremely dry. Despite the precipitation rate in the region of the SAMS being lower than other monsoon areas of the globe, it has a great influency in the major human and economical activities in that continent what motivetis the goal of this work which is to study the trend of rainfall over South America during the monsoon season in South America. For this study Climate Research Unit (CRU) precipitation data was used for the period between 1948 and 2006 during the months from November to March. The spatial resolution of the data is 1 degree and 3 hours temporal resolution. Preliminary results show that there was a pattern of positive trend in precipitation for the months of January, February, March, months in the seasonal cycle of precipitation SAMS.

Indian Summer Monsoon Drought 2009: Role of Aerosol and Cloud Microphysics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hazra, Anupam; Taraphdar, Sourav; Halder, Madhuparna

2013-07-01

Cloud dynamics played a fundamental role in defining Indian summer monsoon (ISM) rainfall during drought in 2009. The anomalously negative precipitation was consistent with cloud properties. Although, aerosols inhibited the growth of cloud effective radius in the background of sparse water vapor, their role is secondary. The primary role, however, is played by the interactive feedback between cloud microphysics and dynamics owing to reduced efficient cloud droplet growth, lesser latent heating release and shortage of water content. Cloud microphysical processes were instrumental for the occurrence of ISM drought 2009.

Connection between ENSO and Asian Summer Monsoon Precipitation Oxygen Isotope

NASA Astrophysics Data System (ADS)

Cai, Z.; Tian, L.

2016-12-01

In an effort to understand the connection between El Niño Southern Oscillation (ENSO) and Asian Summer Monsoon (ASM) precipitation oxygen isotope, this study investigates the spatial and interannual patterns in summer (JJAS) monsoon precipitation δ18O and satellite water vapor isotope retrievals, especially those patterns associated with convection and vapor transport. Both precipitation and vapor isotope values exhibit a "V" shaped longitudinal pattern in their spatial variations, reflecting the gradual rainout and increase in convective intensity along vapor transport routes. In order to understand interannual variations, an ASM precipitation δ18O index (ASMOI) is introduced to measure the temporal variations in regional precipitation δ18O; and these variations are consistent with central Indo-Pacific convection and cloud-top height. The counter variations in the ASMOI in El Niño and La Niña years confirm the existence of a positive isotope- ENSO response (e.g., high values corresponding to warm phases) over the eastern Indian Ocean and southeastern Asia (80°E-120°E/10°S-30°N) as a response to changes in convection. However, JJAS vapor δD over the western Pacific (roughly east of 120oE) varies in opposition, due to the influence of water vapor transport. This opposite variation does not support the interpretation of precipitation isotope-ENSO relationship as changing proportion of vapor transported from different regions, but rather condensation processes associated with convection. These findings are important for studying past ASM and ENSO activity from various isotopic archives and have implications for the study of the atmospheric water cycle.

The Influence of Air-Sea Fluxes on Atmospheric Aerosols During the Summer Monsoon Over the Tropical Indian Ocean

NASA Astrophysics Data System (ADS)

Zavarsky, Alex; Booge, Dennis; Fiehn, Alina; Krüger, Kirstin; Atlas, Elliot; Marandino, Christa

2018-01-01

During the summer monsoon, the western tropical Indian Ocean is predicted to be a hot spot for dimethylsulfide emissions, the major marine sulfur source to the atmosphere, and an important aerosol precursor. Other aerosol relevant fluxes, such as isoprene and sea spray, should also be enhanced, due to the steady strong winds during the monsoon. Marine air masses dominate the area during the summer monsoon, excluding the influence of continentally derived pollutants. During the SO234-2/235 cruise in the western tropical Indian Ocean from July to August 2014, directly measured eddy covariance DMS fluxes confirm that the area is a large source of sulfur to the atmosphere (cruise average 9.1 μmol m-2 d-1). The directly measured fluxes, as well as computed isoprene and sea spray fluxes, were combined with FLEXPART backward and forward trajectories to track the emissions in space and time. The fluxes show a significant positive correlation with aerosol data from the Terra and Suomi-NPP satellites, indicating a local influence of marine emissions on atmospheric aerosol numbers.

Contrasting effects of winter and summer climate on alpine timberline evolution in monsoon-dominated East Asia

NASA Astrophysics Data System (ADS)

Cheng, Ying; Liu, Hongyan; Wang, Hongya; Piao, Shilong; Yin, Yi; Ciais, Philippe; Wu, Xiuchen; Luo, Yao; Zhang, Caina; Song, Yaqiong; Gao, Yishen; Qiu, Anan

2017-08-01

Alpine timberline is particularly sensitive to global climate change, with the danger of losing essential ecosystem services in high elevational regions. Its evolution is generally linked to annual average thermal regimes, and is regarded as an indicator of climate warming. However, the effect of uneven seasonal climate change stressed by the Hijioka et al. (2014) on alpine timberline dynamics in terms of both position migration and species composition remains unclear. Here, we documented approximately 6000 years of postglacial alpine timberline evolution on Mt. Tabai in the monsoon-dominated East Asian subtropical-temperate transition. We analyzed three high-resolution lacustrine sediment sequences located below, within, and above the current alpine timberline, an ecotone between the forest line and treeline, respectively. The timberline position appears to have varied coincidently with the temperature effect of cold East Asian Winter Monsoon (EAWM), implying that enhanced EAWM shortened the duration of the growing season and reduced forest survival at the alpine timberline. Unlike position migration, however, timberline species composition depends on summer precipitation. We found that drought-tolerant herb and shrub species were much more sensitive to variations in the water-bearing East Asian Summer Monsoon (EASM) than mesophytic trees at the alpine timberline. Our results suggest that prediction of future timberline dynamics should consider uneven seasonal climate changes.

Coherent response of the Indo-African boreal summer monsoon to Pacific SST captured in Ethiopian rain δ18O

NASA Astrophysics Data System (ADS)

Madhavan, M.; Palliyil, L. R.; Ramesh, R.

2017-12-01

Pacific Sea Surface Temperature (SST) plays an important role in the inter-annual to inter-decadal variability of boreal monsoons. We identified a common mode of inter annual variability in the Indian and African boreal summer monsoon (June to September) rainfalls, which is linked to Pacific SSTs, using Empirical Orthogonal Function (EOF) analysis. Temporal coefficients (Principle component: PC1) of the leading mode of variability (EOF-1) is well correlated with the Indian summer monsoon rainfall and Sahel rainfall. About forty year long monthly observations of δ18O (and δD) at Addis Ababa, Ethiopia show a strong association with PC1 (r=0.69 for δ18O and r=0.75 for δD). Analysis of SST, sea level pressure and lower tropospheric winds suggest that 18O depletion in Ethiopian rainfall (and wet phases of PC1) is associated with cooler eastern tropical Pacific and warmer western Pacific and strengthening of Pacific subtropical high in both the hemispheres. Associated changes in the trade winds cause enhanced westerly moisture transport into the Indian subcontinent and northern Africa and cause enhanced rainfall. The intrusion of Atlantic westerly component of moisture transport at Addis Ababa during wet phases of PC1 is clearly recorded in δ18O of rain. We also observe the same common mode of variability (EOF1) of Indo-African boreal summer monsoon rain on decadal time scales. A 100 year long δ18O record of actively growing speleothem from the Mechara cave, Ethiopia, matches very well with the PC1 on the decadal time scale. This highlights the potential of speleothem δ18O and leaf wax δD from Ethiopia to investigate the natural variability and teleconnections of Indo-African boreal monsoon.

Indian Summer Monsoon dynamics during Termination II and MIS 5e

NASA Astrophysics Data System (ADS)

Magiera, Matthias; Erhardt, Andrea M.; Hartland, Adam; Kwiecien, Ola; Cheng, Hai; Immenhauser, Adrian; Turchyn, Alexandra; Breitenbach, Sebastian F. M.

2017-04-01

The interpretation of speleothem oxygen isotope ratios (δ18O) as proxy for Indian Summer Monsoon (ISM) dynamics is ambiguous, due to multiple influencing factors. Here we combine δ18O and calcium isotope δ44Ca analyses with elemental data to delineate regional shifts in moisture source, local rainfall amount, and changes in ISM intensity and length during Termination II and MIS 5e. Oxygen isotope ratios reflect a mixed signal of moisture source dynamics and rainfall amount; δ44Ca and Mg/Ca ratios are interpreted as proxies for local effective moisture and prior calcite precipitation (PCP) in the epikarst. The age of stalagmite MAW-3 from Mawmluh Cave, NE India, is constraint by six U-series dates. 108 samples, obtained at 0.4 mm resolution from the 70 mm long speleothem sample, have been analysed for δ18O, δ44Ca and Mg/Ca. Oxygen isotope ratios were measured on a ThermoFisher Scientific MAT 253 at Ruhr-University Bochum. Elemental ratios were measured on a quadrupole ICP-MS at Waikato University. Calcium isotope ratios were analyzed on a ThermoFisher Scientific Triton at University of Cambridge. MAW-3 grew from 136 kyrs BP to 96 kyrs BP, covering Termination II and MIS 5e. Oxygen isotope values are high (ca. +0.91 ‰) during Termination II, reach a minimum during MIS 5e (-3.5 ‰), and rise again to -0.2 ‰ at the end of MIS 5e. Calcium isotope ratios range from -0.32 ‰ to -0.70 ‰ and show a positive correlation (R2= 0.7) with δ18O. High δ18O values during Termination II reflect reduced atmospheric circulation and/or a proximal moisture source (Bay of Bengal), implying lowered ISM intensity. A positive correlation of δ18O with δ44Ca suggests concurrent changes of moisture source location and local rainfall amount, with a proximal moisture source and reduced effective rainfall during periods of weak ISM. Elevated Mg/Ca ratios at such intervals corroborate PCP occurrence, which reflects dry conditions. The beginning of MIS 5e (ca. 132 kyrs BP) is

Enhanced future variability during India's rainy season

NASA Astrophysics Data System (ADS)

Menon, Arathy; Levermann, Anders; Schewe, Jacob

2013-04-01

The Indian summer monsoon shapes the livelihood of a large share of the world's population. About 80% of annual precipitation over India occurs during the monsoon season from June through September. Next to its seasonal mean rainfall the day-to-day variability is crucial for the risk of flooding, national water supply and agricultural productivity. Here we show that the latest ensemble of climate model simulations, prepared for the IPCC's AR-5, consistently projects significant increases in day-to-day rainfall variability under unmitigated climate change. While all models show an increase in day-to-day variability, some models are more realistic in capturing the observed seasonal mean rainfall over India than others. While no model's monsoon rainfall exceeds the observed value by more than two standard deviations, half of the models simulate a significantly weaker monsoon than observed. The relative increase in day-to-day variability by the year 2100 ranges from 15% to 48% under the strongest scenario (RCP-8.5), in the ten models which capture seasonal mean rainfall closest to observations. The variability increase per degree of global warming is independent of the scenario in most models, and is 8% +/- 4% per K on average. This consistent projection across 20 comprehensive climate models provides confidence in the results and suggests the necessity of profound adaptation measures in the case of unmitigated climate change.

A composite study of onset of the Australian summer monsoon

NASA Technical Reports Server (NTRS)

Hendon, Harry H.; Liebmann, Brant

1990-01-01

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

A distinction between summer rainy season and summer monsoon season over the Central Highlands of Vietnam

NASA Astrophysics Data System (ADS)

Ngo-Thanh, Huong; Ngo-Duc, Thanh; Nguyen-Hong, Hanh; Baker, Peter; Phan-Van, Tan

2018-05-01

The daily rainfall data at 13 stations over the Central Highlands (CH) Vietnam were collected for the period 1981-2014. Two different sets of criteria using daily observed rainfall and 850 hPa daily reanalysis wind data were applied to determine the onset (retreat) dates of the summer rainy season (RS) and summer monsoon (SM) season, respectively. Over the study period, the mean RS and SM onset dates were April 20 and May 13 with standard deviations of 17.4 and 17.8 days, respectively. The mean RS and SM retreat dates were November 1 and September 30 with standard deviations of 17.9 and 10.2 days, respectively . The year-to-year variations of the onset dates and the rainfall amount within the RS and SM season were closely linked with the preceding winter and spring sea surface temperature in the central-eastern and western Pacific. It was also found that the onset dates were significantly correlated with the RS and SM rainfall amount.

Assessing the role of local air-sea interaction over the South Asia region in simulating the Indian Summer Monsoon (ISM) using the new earth system model RegCM-ES

NASA Astrophysics Data System (ADS)

Di Sante, Fabio; Coppola, Erika; Farneti, Riccardo; Giorgi, Filippo

2017-04-01

The South Asia climate is dominated by the monsoon precipitation that divides the climate in two different seasons, the wet and dry seasons, and it influences the lives of billions of peoples. The Indian Summer Monsoon (ISM) has different temporal and spatial scales of variability and it is mainly driven by strong air sea interactions. The monsoon interannual variability (IAV) and the intraseasonal variability (ISV) of daily rainfall are the two most important scale of analysis of this phenomenon. In this work, the Regional Earth System Model (RegCM-ES) (Sitz et al, 2016) is used to simulate the South Asia climate. Several model settings are experimented to assess the sensitivity of the monsoon system like for example two different cumulous convection schemes (Tidtke, 1989 and Emanuel, 1991), two different lateral boundary conditions in the regional ocean model (NOAA/Geophysical 5 Fluid Dynamics Laboratory MOM run, Danabasoglu et al 2014; and ORAP reanalysis, Zuo et Al 2015) and two different hydrological models (Cetemps Hydrological Model, Coppola et al, 2007; Max-Planck's HD model, Hagemann and Dümenil, 1998) for a total of 5 coupled and uncoupled simulations all covering the period from 1979 to 2008. One of the main results of the analysis of the mini RegCM-ES ensemble shows that a better representation of the IAV and of the ENSO-monsoon relationship is present in the coupled simulations. Moreover a source of monsoon predictability has been found in the one-year-lag correlation between JJAS India precipitation and ENSO, this is only evident in the coupled system where the one-year-lagged correlation coefficient between the Niño-3.4 and the ISM rainfall is much higher respect to the uncoupled one and similar to values observed between the observations and the Niño-3.4. For the subseasonal time scale, RegCM-ES shows better performance compared to the standalone version of RegCM4 (Giorgi et al 2012), in reproducing "active" and "break" spells that characterize

Time-slice analysis of the Australian summer monsoon during the late Quaternary using the Fast Ocean Atmosphere Model

NASA Astrophysics Data System (ADS)

Marshall, A. G.; Lynch, A. H.

2006-10-01

We use the Fast Ocean Atmosphere Model (FOAM) to investigate the variation in the Australian summer monsoon over the last 55 000 years. A synthesis of palaeoenvironmental observations is used to constrain the model for six time slices: 55, 35, 21, 11, 6 and 0 ka. Both inter-hemispheric forcing and the seasonal timing of local insolation changes play key, and interacting, roles on the evolution and intensity of the monsoon.During the onset to the monsoon, a heat low develops to the west of Australia over the Indian Ocean in all time slices, but with varying strengths. Divergent outflow from Asia converges with the cyclonic flow to bring increased rainfall to northern Australia and the maritime continent. The relative importance of a low pressure pull and the high pressure push varies according to the strength of the pressure anomalies. Only in the middle Holocene is the low pressure pull the dominant forcing mechanism. At 21 ka, the climate shift to colder mean temperatures determines the large-scale dynamics of the monsoon.The general picture that emerges from these results is consistent with available palaeodata but highlights the importance of a broad regional perspective to ascribe the driving mechanisms at different times. Copyright

Competing influences of greenhouse warming and aerosols on Asian summer monsoon circulation and rainfall

NASA Astrophysics Data System (ADS)

Lau, William Ka-Ming; Kim, Kyu-Myong

2017-05-01

In this paper, we have compared and contrasted competing influences of greenhouse gases (GHG) warming and aerosol forcing on Asian summer monsoon circulation and rainfall based on CMIP5 historical simulations. Under GHG-only forcing, the land warms much faster than the ocean, magnifying the pre-industrial climatological land-ocean thermal contrast and hemispheric asymmetry, i.e., warmer northern than southern hemisphere. A steady increasing warm-ocean-warmer-land (WOWL) trend has been in effect since the 1950's substantially increasing moisture transport from adjacent oceans, and enhancing rainfall over the Asian monsoon regions. However, under GHG warming, increased atmospheric stability due to strong reduction in mid-tropospheric and near surface relative humidity coupled to an expanding subsidence areas, associated with the Deep Tropical Squeeze (DTS, Lau and Kim, 2015b) strongly suppress monsoon convection and rainfall over subtropical and extratropical land, leading to a weakening of the Asian monsoon meridional circulation. Increased anthropogenic aerosol emission strongly masks WOWL, by over 60% over the northern hemisphere, negating to a large extent the rainfall increase due to GHG warming, and leading to a further weakening of the monsoon circulation, through increasing atmospheric stability, most likely associated with aerosol solar dimming and semi-direct effects. Overall, we find that GHG exerts stronger positive rainfall sensitivity, but less negative circulation sensitivity in SASM compared to EASM. In contrast, aerosols exert stronger negative impacts on rainfall, but less negative impacts on circulation in EASM compared to SASM.

Change in the tropical cyclone activity around Korea by the East Asian summer monsoon

NASA Astrophysics Data System (ADS)

Choi, Jae-Won; Cha, Yumi; Kim, Jeoung-Yun

2017-12-01

Correlation between the frequency of summer tropical cyclones (TCs) affecting Korea and the East Asian summer monsoon index (EASMI) was analyzed over the last 37 years. A clear positive correlation existed between the two variables, and this high positive correlation remained unchanged even when excluding El Niño-Southern Oscillation (ENSO) years. To investigate the causes of the positive correlation between the two variables in non-ENSO years, after the 8 years with the highest EASMI (high EASMI years) and the 8 years with the lowest EASMI (low EASMI years) were selected, and the average difference between the two phases was analyzed. In high EASMI years, in the difference between the two phases regarding 850 and 500 hPa streamline, anomalous cyclones were reinforced in the tropical and subtropical western North Pacific, while anomalous anticyclones were reinforced in mid-latitude East Asian areas. Due to these two anomalous pressure systems, anomalous southeasterlies developed near Korea, with these anomalous southeasterlies playing the role of anomalous steering flows making the TCs head toward areas near Korea. In addition, a monsoon trough strengthened more eastward, and TCs in high EASMI years occurred more in east ward over the western North Pacific.

The Indian Summer Monsoon onset revisited: new approach based on the analysis of historical wind observations

NASA Astrophysics Data System (ADS)

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

2016-04-01

The Indian Summer Monsoon onset is one of the meteorological events most anticipated in the world. Due to its relevance for the population, the India Meteorological Department has dated the onset over the southern tip of the Indian Peninsula (Kerala) since 1901. The traditional method to date the onset was based in the judgment of skilled meteorologist and because of this, the method was considered subjective and not adequate for the study of long-term changes in the onset. A new method for determining the monsoon onset based solely on objective criteria has been in use since 2006. Unfortunately, the new method relies -among other variables- on OLR measurements. This requirement impedes the construction of an objective onset series before the satellite era. An alternative approach to establish the onset by objective methods is the use of the wind field. During the last decade, some works have demonstrated that the changes in the wind direction in some areas of the Indian Ocean can be used to determine the monsoon onset rather precisely. However, this method requires precise wind observations over a large oceanic area which has limited the periods covered for such kind of indices to those of the reanalysis products. In this work we present a new approach to track the Indian monsoon onset based solely on historical wind direction measurements taken onboard ships. Our new series provides an objective record of the onset since the last decade of the 19th century and perhaps more importantly, it can incorporate any new historical wind record not yet known in order to extend the series length. The new series captures quite precisely the rapid precipitation increase associated to the monsoon onset, correlates well with previous approaches and it is robust against anomalous (bogus) onsets. Although no significant trends in the onset date were detected, a tendency to later than average onsets during the 1900-1925 and 1970-1990 periods and earlier than average onsets between

Decline and poleward shift in Indian summer monsoon synoptic activity in a warming climate

PubMed Central

Boos, William R.; Sabin, T. P.; Praveen, V.

2018-01-01

Cyclonic atmospheric vortices of varying intensity, collectively known as low-pressure systems (LPS), travel northwest across central India and produce more than half of the precipitation received by that fertile region and its ∼600 million inhabitants. Yet, future changes in LPS activity are poorly understood, due in part to inadequate representation of these storms in current climate models. Using a high-resolution atmospheric general circulation model that realistically simulates the genesis distribution of LPS, here we show that Indian monsoon LPS activity declines about 45% by the late 21st century in simulations of a business-as-usual emission scenario. The distribution of LPS genesis shifts poleward as it weakens, with oceanic genesis decreasing by ∼60% and continental genesis increasing by ∼10%; over land the increase in storm counts is accompanied by a shift toward lower storm wind speeds. The weakening and poleward shift of the genesis distribution in a warmer climate are confirmed and attributed, via a statistical model, to the reduction and poleward shift of low-level absolute vorticity over the monsoon region, which in turn are robust features of most coupled model projections. The poleward shift in LPS activity results in an increased frequency of extreme precipitation events over northern India. PMID:29483270

Decline and poleward shift in Indian summer monsoon synoptic activity in a warming climate

NASA Astrophysics Data System (ADS)

Sandeep, S.; Ajayamohan, R. S.; Boos, William R.; Sabin, T. P.; Praveen, V.

2018-03-01

Cyclonic atmospheric vortices of varying intensity, collectively known as low-pressure systems (LPS), travel northwest across central India and produce more than half of the precipitation received by that fertile region and its ˜600 million inhabitants. Yet, future changes in LPS activity are poorly understood, due in part to inadequate representation of these storms in current climate models. Using a high-resolution atmospheric general circulation model that realistically simulates the genesis distribution of LPS, here we show that Indian monsoon LPS activity declines about 45% by the late 21st century in simulations of a business-as-usual emission scenario. The distribution of LPS genesis shifts poleward as it weakens, with oceanic genesis decreasing by ˜60% and continental genesis increasing by ˜10%; over land the increase in storm counts is accompanied by a shift toward lower storm wind speeds. The weakening and poleward shift of the genesis distribution in a warmer climate are confirmed and attributed, via a statistical model, to the reduction and poleward shift of low-level absolute vorticity over the monsoon region, which in turn are robust features of most coupled model projections. The poleward shift in LPS activity results in an increased frequency of extreme precipitation events over northern India.

Regime shift of Indian summer monsoon rainfall to a persistent arid state: external forcing versus internal variability

NASA Astrophysics Data System (ADS)

Srivastava, Ankur; Pradhan, Maheswar; Goswami, B. N.; Rao, Suryachandra A.

2017-11-01

The high propensity of deficient monsoon rainfall over the Indian sub-continent in the recent 3 decades (seven deficient monsoons against 3 excess monsoon years) compared to the prior 3 decades has serious implications on the food and water resources in the country. Motivated by the need to understand the high occurrence of deficient monsoon during this period, we examine the change in predictability of the Indian summer monsoon (ISM) and its teleconnections with Indo-Pacific sea surface temperatures between the two periods. The shift in the tropical climate in the late 1970s appears to be one of the major reasons behind this. We find an increased predictability of the ISM in the recent 3 decades owing to reduced `internal' interannual variability (IAV) due to the high-frequency modes, while the `external' IAV arising from the low-frequency modes has remained largely the same. The Indian Ocean Dipole-ISM teleconnection has become positive during the monsoon season in the recent period thereby compensating for the weakened ENSO-ISM teleconnection. The central Pacific El-Niño and the Indian Ocean (IO) warming during the recent 3 decades are working together to realise enhanced ascending motion in the equatorial IO between 70°E and 100°E, preconditioning the Indian monsoon system prone to a deficient state.

Increased chemical weathering during the deglacial to mid-Holocene summer monsoon intensification

PubMed Central

Miriyala, Pavan; Sukumaran, N. P.; Nath, B. Nagender; Ramamurty, P. B.; Sijinkumar, A. V.; Vijayagopal, B.; Ramaswamy, V.; Sebastian, Tyson

2017-01-01

Chemical weathering and the ensuing atmospheric carbon dioxide consumption has long been considered to work on geological time periods until recently when some modelling and natural records have shown that the weathering-related CO2 consumption can change at century to glacial-interglacial time scale. Last glacial to interglacial transition period is a best test case to understand the interplay between Pco2-temperature-chemical weathering when a pulse of rapid chemical weathering was initiated. Here we show, from a high resolution 54 ka record from the Andaman Sea in the northern Indian Ocean, that the chemical weathering responds to deglacial to mid-Holocene summer monsoon intensification in the Myanmar watersheds. The multi-proxy data (Al/K, CIA, Rb/Sr, 87Sr/86Sr for degree of weathering and 143Nd/144Nd for provenance) reveal an increase in silicate weathering with initiation of interglacial warm climate at ~17.7 ka followed by a major change at 15.5 ka. Inferred changes in chemical weathering have varied in tandem with the regional monsoonal proxies (δ18Osw-salinity changes of Northern Indian Ocean, effective Asian moisture content and δ18O records of Chinese caves) and are synchronous with changes in summer insolation at 30°N and δ18O of GISP2 implying that chemical weathering was not a later amplifier but worked in tandem with global climate change. PMID:28303943

Increased chemical weathering during the deglacial to mid-Holocene summer monsoon intensification

NASA Astrophysics Data System (ADS)

Miriyala, Pavan; Sukumaran, N. P.; Nath, B. Nagender; Ramamurty, P. B.; Sijinkumar, A. V.; Vijayagopal, B.; Ramaswamy, V.; Sebastian, Tyson

2017-03-01

Chemical weathering and the ensuing atmospheric carbon dioxide consumption has long been considered to work on geological time periods until recently when some modelling and natural records have shown that the weathering-related CO2 consumption can change at century to glacial-interglacial time scale. Last glacial to interglacial transition period is a best test case to understand the interplay between Pco2-temperature-chemical weathering when a pulse of rapid chemical weathering was initiated. Here we show, from a high resolution 54 ka record from the Andaman Sea in the northern Indian Ocean, that the chemical weathering responds to deglacial to mid-Holocene summer monsoon intensification in the Myanmar watersheds. The multi-proxy data (Al/K, CIA, Rb/Sr, 87Sr/86Sr for degree of weathering and 143Nd/144Nd for provenance) reveal an increase in silicate weathering with initiation of interglacial warm climate at ~17.7 ka followed by a major change at 15.5 ka. Inferred changes in chemical weathering have varied in tandem with the regional monsoonal proxies (δ18Osw-salinity changes of Northern Indian Ocean, effective Asian moisture content and δ18O records of Chinese caves) and are synchronous with changes in summer insolation at 30°N and δ18O of GISP2 implying that chemical weathering was not a later amplifier but worked in tandem with global climate change.

A high-resolved record of the Asian Summer Monsoon from Dongge Cave, China for the past 1200 years

NASA Astrophysics Data System (ADS)

Zhao, Kan; Wang, Yongjin; Edwards, R. Lawrence; Cheng, Hai; Liu, Dianbing; Kong, Xinggong

2015-08-01

Two annually-laminated and 230Th-dated stalagmite oxygen isotope (δ18O) records from Dongge Cave, China, provided a high-resolution Asian Summer Monsoon (ASM) history for the past 1200 years. A close similarity between annual band thickness and stable isotope analyses (δ13C and δ18O) suggests the calcite δ18O is most likely a proxy associated with ASM precipitation. The two duplicated stalagmite δ18O records show that the ASM varies at a periodicity of ∼220 years, concordant with a dominant cycle of solar activity. A period of strong ASM activity occurred during the Spörer Minimum (1450-1550 A.D.), followed by a striking drop circa 1580 A.D., potentially consistent with the social unrest in the final decades of China's Ming Dynasty (1368-1644 A.D.). Centennial-scale changes in ASM precipitation over the last millennium match well with changes in tropical Atlantic sea surface temperatures (SSTs) and South American summer monsoon precipitation. Our findings suggest that variations in low-latitude monsoon precipitation are probably driven by shifts in the mean position of the intertropical convergence zone (ITCZ), which is further mediated by solar activity and tropical SSTs.

The role of potential vorticity anomalies in the Somali Jet on Indian Summer Monsoon Intraseasonal Variability

NASA Astrophysics Data System (ADS)

Rai, P.; Joshi, M.; Dimri, A. P.; Turner, A. G.

2018-06-01

The climate of the Indian subcontinent is dominated by rainfall arising from the Indian summer monsoon (ISM) during June to September. Intraseasonal variability during the monsoon is characterized by periods of heavy rainfall interspersed by drier periods, known as active and break events respectively. Understanding and predicting such events is of vital importance for forecasting human impacts such as water resources. The Somali Jet is a key regional feature of the monsoon circulation. In the present study, we find that the spatial structure of Somali Jet potential vorticity (PV) anomalies varies considerably during active and break periods. Analysis of these anomalies shows a mechanism whereby sea surface temperature (SST) anomalies propagate north/northwestwards through the Arabian Sea, caused by a positive feedback loop joining anomalies in SST, convection, modification of PV by diabatic heating and mixing in the atmospheric boundary layer, wind-stress curl, and ocean upwelling processes. The feedback mechanism is consistent with observed variability in the coupled ocean-atmosphere system on timescales of approximately 20 days. This research suggests that better understanding and prediction of monsoon intraseasonal variability in the South Asian monsoon may be gained by analysis of the day-to-day dynamical evolution of PV in the Somali Jet.

The role of potential vorticity anomalies in the Somali Jet on Indian Summer Monsoon Intraseasonal Variability

NASA Astrophysics Data System (ADS)

Rai, P.; Joshi, M.; Dimri, A. P.; Turner, A. G.

2017-08-01

The climate of the Indian subcontinent is dominated by rainfall arising from the Indian summer monsoon (ISM) during June to September. Intraseasonal variability during the monsoon is characterized by periods of heavy rainfall interspersed by drier periods, known as active and break events respectively. Understanding and predicting such events is of vital importance for forecasting human impacts such as water resources. The Somali Jet is a key regional feature of the monsoon circulation. In the present study, we find that the spatial structure of Somali Jet potential vorticity (PV) anomalies varies considerably during active and break periods. Analysis of these anomalies shows a mechanism whereby sea surface temperature (SST) anomalies propagate north/northwestwards through the Arabian Sea, caused by a positive feedback loop joining anomalies in SST, convection, modification of PV by diabatic heating and mixing in the atmospheric boundary layer, wind-stress curl, and ocean upwelling processes. The feedback mechanism is consistent with observed variability in the coupled ocean-atmosphere system on timescales of approximately 20 days. This research suggests that better understanding and prediction of monsoon intraseasonal variability in the South Asian monsoon may be gained by analysis of the day-to-day dynamical evolution of PV in the Somali Jet.

Wet scavenging of organic and elemental carbon during summer monsoon and winter monsoon seasons

NASA Astrophysics Data System (ADS)

Sonwani, S.; Kulshrestha, U. C.

2017-12-01

In the era of rapid industrialization and urbanization, atmospheric abundance of carbonaceous aerosols is increasing due to more and more fossil fuel consumption. Increasing levels of carbonaceous content have significant adverse effects on air quality, human health and climate. The present study was carried out at Delhi covering summer monsoon (July -Sept) and winter monsoon (Dec-Jan) seasons as wind and other meteorological factors affect chemical composition of precipitation in different manner. During the study, the rainwater and PM10 aerosols were collected in order to understand the scavenging process of elemental and organic carbon. The Rain water samples were collected on event basis. PM10 samples were collected before rain (PR), during rain (DR) and after rain (AR) during 2016-2017. The collected samples were analysed by the thermal-optical reflectance method using IMPROVE-A protocol. In PM10, the levels of organic carbon (OC) and its fractions (OC1, OC2, OC3 and OC4) were found significantly lower in the AR samples as compared to PR and DR samples. A significant positive correlation was noticed between scavenging ratios of organic carbon and rain intensity indicating an efficient wet removal of OC. In contrast to OCs, the levels of elemental carbon and its fractions (EC1, EC2, and EC3) in AR were not distinct during PR and DR. The elemental carbon showed very week correlation with rain intensity in Delhi region which could be explained on the basis of hydrophobic nature of freshly emitted carbon soot. The detailed results will be discussed during the conference.

Asian Summer Monsoon Rainfall associated with ENSO and its Predictability

NASA Astrophysics Data System (ADS)

Shin, C. S.; Huang, B.; Zhu, J.; Marx, L.; Kinter, J. L.; Shukla, J.

2015-12-01

The leading modes of the Asian summer monsoon (ASM) rainfall variability and their seasonal predictability are investigated using the CFSv2 hindcasts initialized from multiple ocean analyses over the period of 1979-2008 and observation-based analyses. It is shown that the two leading empirical orthogonal function (EOF) modes of the observed ASM rainfall anomalies, which together account for about 34% of total variance, largely correspond to the ASM responses to the ENSO influences during the summers of the developing and decaying years of a Pacific anomalous event, respectively. These two ASM modes are then designated as the contemporary and delayed ENSO responses, respectively. It is demonstrated that the CFSv2 is capable of predicting these two dominant ASM modes up to the lead of 5 months. More importantly, the predictability of the ASM rainfall are much higher with respect to the delayed ENSO mode than the contemporary one, with the predicted principal component time series of the former maintaining high correlation skill and small ensemble spread with all lead months whereas the latter shows significant degradation in both measures with lead-time. A composite analysis for the ASM rainfall anomalies of all warm ENSO events in this period substantiates the finding that the ASM is more predictable following an ENSO event. The enhanced predictability mainly comes from the evolution of the warm SST anomalies over the Indian Ocean in the spring of the ENSO maturing phases and the persistence of the anomalous high sea surface pressure over the western Pacific in the subsequent summer, which the hindcasts are able to capture reasonably well. The results also show that the ensemble initialization with multiple ocean analyses improves the CFSv2's prediction skill of both ENSO and ASM rainfall. In fact, the skills of the ensemble mean hindcasts initialized from the four different ocean analyses are always equivalent to the best ones initialized from any individual ocean

Relationships between interannual and intraseasonal variations of the Asian-western Pacific summer monsoon hindcasted by BCC_CSM1.1(m)

NASA Astrophysics Data System (ADS)

Liu, Xiangwen; Wu, Tongwen; Yang, Song; Li, Qiaoping; Cheng, Yanjie; Liang, Xiaoyun; Fang, Yongjie; Jie, Weihua; Nie, Suping

2014-09-01

Using hindcasts of the Beijing Climate Center Climate System Model, the relationships between interannual variability (IAV) and intraseasonal variability (ISV) of the Asian-western Pacific summer monsoon are diagnosed. Predictions show reasonable skill with respect to some basic characteristics of the ISV and IAV of the western North Pacific summer monsoon (WNPSM) and the Indian summer monsoon (ISM). However, the links between the seasonally averaged ISV (SAISV) and seasonal mean of ISM are overestimated by the model. This deficiency may be partially attributable to the overestimated frequency of long breaks and underestimated frequency of long active spells of ISV in normal ISM years, although the model is capable of capturing the impact of ISV on the seasonal mean by its shift in the probability of phases. Furthermore, the interannual relationships of seasonal mean, SAISV, and seasonally averaged long-wave variability (SALWV; i.e., the part with periods longer than the intraseasonal scale) of the WNPSM and ISM with SST and low-level circulation are examined. The observed seasonal mean, SAISV, and SALWV show similar correlation patterns with SST and atmospheric circulation, but with different details. However, the model presents these correlation distributions with unrealistically small differences among different scales, and it somewhat overestimates the teleconnection between monsoon and tropical central-eastern Pacific SST for the ISM, but underestimates it for the WNPSM, the latter of which is partially related to the too-rapid decrease in the impact of El Niño-Southern Oscillation with forecast time in the model.

Changes in the Indian summer monsoon intensity in Sri Lanka during the last 30 ky - A multiproxy record from a marine sediment core.

NASA Astrophysics Data System (ADS)

Ranasinghage, P. N.; Nanayakkara, N. U.; Kodithuwakku, S.; Siriwardana, S.; Luo, C.; Fenghua, Z.

2016-12-01

Indian monsoon plays a vital role in determining climate events happening in the Asian region. There is no sufficient work in Sri Lanka to fully understand how the summer monsoonal variability affected Sri Lanka during the quaternary. Sri Lanka is situated at an ideal location with a unique geography to isolate Indian summer monsoon record from iris counterpart, Indian winter monsoon. Therefore, this study was carried out to investigate its variability and understand the forcing factors. For this purpose a 1.82 m long gravity core, extracted from western continental shelf off Colombo, Sri Lanka by Shiyan 1 research vessel, was used. Particle size, chemical composition and colour reflectance were measured using laser particle size analyzer at 2 cm resolution, X-Ray Fluorescence spectrometer (XRF) at 2 cm resolution, and color spectrophotometer at 1 cm resolution respectively. Radio carbon dating of foraminifera tests by gas bench technique yielded the sediment age. Finally, principal component analysis (PCA) of XRF and color reflectance (DSR) data was performed to identify groups of correlating elements and mineralogical composition of sediments. Particle size results indicate that Increasing temperature and strengthening monsoonal rainfall after around 18000 yrs BP, at the end of last glacial period, enhanced chemical weathering over physical weathering. Proxies for terrestrial influx (XRF PC1, DSR PC1) and upwelling and nutrient supply driven marine productivity (XRF PC3 and DSR PC2) indicate that strengthening of summer monsoon started around 15000 yrs BP and maximized around 8000-10000 yrs BP after a short period of weakening during Younger Dryas (around 11000 yrs BP). The 8.2 cold event was recorded as a period of low terrestrial influx indicating weakening of rainfall. After that terrestrial input was low till around 2000 yrs BP indicating decrease in rainfall. However, marine productivity remained increasing throughout the Holocene indicating an increase in

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

Origin, Maintenance and Variability of the Asian Tropopause Aerosol Layer (ATAL): The Roles of Monsoon Dynamics

NASA Astrophysics Data System (ADS)

Lau, W. K. M.; Yuan, C.; Li, Z.

2017-12-01

Using NASA MERRA2 daily reanalysis data, we have investigated the origin, maintenance and variability of the Asian Tropopause Aerosol Layer (ATAL) in relation to intrinsic variations of the Asia Monsoon Anticyclone (AMA) during the summer of 2008. Results show that during the pre- and early monsoon period (May to June) abundant quantities of carbon monoxide (CO), carbonaceous aerosols (CA) and dust are found from the earth surface to the upper troposphere (up to 10-12 km) in monsoon and adjacent desert regions, arising from enhanced emissions from the heated desert surface, increased biomass burning over monsoon regions and strong vertical transport by dry convection. During the peak monsoon period (July-August) strong westerlies transport large quantities of dusts from the deserts in the Middle East, North Africa, and West Asia into the Asian monsoon regions. Despite strong precipitation washout, ambient CO, CA and dust are transported by orography-forced deep convection into the UTLS ( 12-16 km) via two key pathways over the heavily polluted regions of a) the Himalayas-Gangetic Plain in northern India, and b) the Sichuan Basin of southwestern China. Upon entering the UTLS via these two pathways, the pollutants are capped by a stable layer near the tropopause, advected, and dispersed by the anticyclonic circulation of AMA, establishing the ATAL in the shape of a "double-stem chimney cloud". The development and variability of the ATAL are strongly linked to the seasonal march, and dominant monsoon intraseasonal (20-30 days) oscillations of the Asian summer monsoon.

The evolution of sub-monsoon systems in the Afro-Asian monsoon region during the Holocene - comparison of different transient climate model simulations

NASA Astrophysics Data System (ADS)

Dallmeyer, A.; Claussen, M.; Fischer, N.; Haberkorn, K.; Wagner, S.; Pfeiffer, M.; Jin, L.; Khon, V.; Wang, Y.; Herzschuh, U.

2014-05-01

The recently proposed global monsoon hypothesis interprets monsoon systems as part of one global-scale atmospheric overturning circulation, implying a connection between the regional monsoon systems and an in-phase behaviour of all northern hemispheric monsoons on annual timescales (Trenberth et al., 2000). Whether this concept can be applied to past climates and variability on longer timescales is still under debate, because the monsoon systems exhibit different regional characteristics such as different seasonality (i.e. onset, peak, and withdrawal). To investigate the interconnection of different monsoon systems during the pre-industrial Holocene, five transient global climate model simulations have been analysed with respect to the rainfall trend and variability in different sub-domains of the Afro-Asian monsoon region. Our analysis suggests that on millennial timescales with varying orbital forcing, the monsoons do not behave as a tightly connected global system. According to the models, the Indian and North African monsoons are coupled, showing similar rainfall trend and moderate correlation in rainfall variability in all models. The East Asian monsoon changes independently during the Holocene. The dissimilarities in the seasonality of the monsoon sub-systems lead to a stronger response of the North African and Indian monsoon systems to the Holocene insolation forcing than of the East Asian monsoon and affect the seasonal distribution of Holocene rainfall variations. Within the Indian and North African monsoon domain, precipitation solely changes during the summer months, showing a decreasing Holocene precipitation trend. In the East Asian monsoon region, the precipitation signal is determined by an increasing precipitation trend during spring and a decreasing precipitation change during summer, partly balancing each other. A synthesis of reconstructions and the model results do not reveal an impact of the different seasonality on the timing of the Holocene

The evolution of sub-monsoon systems in the Afro-Asian monsoon region during the Holocene- comparison of different transient climate model simulations

NASA Astrophysics Data System (ADS)

Dallmeyer, A.; Claussen, M.; Fischer, N.; Haberkorn, K.; Wagner, S.; Pfeiffer, M.; Jin, L.; Khon, V.; Wang, Y.; Herzschuh, U.

2015-02-01

The recently proposed global monsoon hypothesis interprets monsoon systems as part of one global-scale atmospheric overturning circulation, implying a connection between the regional monsoon systems and an in-phase behaviour of all northern hemispheric monsoons on annual timescales (Trenberth et al., 2000). Whether this concept can be applied to past climates and variability on longer timescales is still under debate, because the monsoon systems exhibit different regional characteristics such as different seasonality (i.e. onset, peak and withdrawal). To investigate the interconnection of different monsoon systems during the pre-industrial Holocene, five transient global climate model simulations have been analysed with respect to the rainfall trend and variability in different sub-domains of the Afro-Asian monsoon region. Our analysis suggests that on millennial timescales with varying orbital forcing, the monsoons do not behave as a tightly connected global system. According to the models, the Indian and North African monsoons are coupled, showing similar rainfall trend and moderate correlation in centennial rainfall variability in all models. The East Asian monsoon changes independently during the Holocene. The dissimilarities in the seasonality of the monsoon sub-systems lead to a stronger response of the North African and Indian monsoon systems to the Holocene insolation forcing than of the East Asian monsoon and affect the seasonal distribution of Holocene rainfall variations. Within the Indian and North African monsoon domain, precipitation solely changes during the summer months, showing a decreasing Holocene precipitation trend. In the East Asian monsoon region, the precipitation signal is determined by an increasing precipitation trend during spring and a decreasing precipitation change during summer, partly balancing each other. A synthesis of reconstructions and the model results do not reveal an impact of the different seasonality on the timing of the

Relative Contribution of Monsoon Precipitation and Pumping to Changes in Groundwater Storage in India

NASA Technical Reports Server (NTRS)

Asoka, Akarsh; Gleeson, Tom; Wada, Yoshihide; Mishra, Vimal

2017-01-01

The depletion of groundwater resources threatens food and water security in India. However, the relative influence of groundwater pumping and climate variability on groundwater availability and storage remains unclear. Here we show from analyses of satellite and local well data spanning the past decade that long-term changes in monsoon precipitation are driving groundwater storage variability in most parts of India either directly by changing recharge or indirectly by changing abstraction. We find that groundwater storage has declined in northern India at the rate of 2 cm/yr and increased by 1 to 2 cm/yr in southern India between 2002 and 2013. We find that a large fraction of the total variability in groundwater storage in north-central and southern India can be explained by changes in precipitation. Groundwater storage variability in northwestern India can be explained predominantly by variability in abstraction for irrigation, which is in turn influenced by changes in precipitation. Declining precipitation in northern India is linked to Indian Ocean warming, suggesting a previously unrecognized teleconnection between ocean temperatures and groundwater storage.

Asian Summer Monsoon Pollutes the Northern Hemispheric Stratosphere

NASA Astrophysics Data System (ADS)

Yu, P.; Gao, R. S.; Rosenlof, K. H.; Telg, H.; Liu, S.; Zhixuan, B.; Bian, J.

2016-12-01

An enhanced aerosol layer near the tropopause over Asia during the period of the Asian summer monsoon (ASM) was recently identified by satellites. Previous modeling studies suggest the layer is largely composed of organics and sulfate. However its source, detailed distribution, and climate implications are presently not well understood. To address this issue, in-situ measurements of aerosol size distribution during the 2015 ASM were made from Kunming, China. These showed a robust aerosol enhancement up to 2 km above the tropopause. We use a global climate model coupled with the Community Aerosol and Radiation Model for Atmospheres (CARMA) to show that these aerosol particles are transported to the entire 10°N - 50°N latitude band in the lower stratosphere. These transported particles, originally formed in the region of the ASM anticyclone, account for a significant fraction of total aerosol mass in the 10°N - 50°N latitude band between 16 to 20 km.

Impact of anthropogenic aerosols from global, East Asian, and non-East Asian sources on East Asian summer monsoon system

NASA Astrophysics Data System (ADS)

Wang, Qiuyan; Wang, Zhili; Zhang, Hua

2017-01-01

The impact of the total effects due to anthropogenic aerosols from global, East Asian, and non-East Asian sources on East Asian summer monsoon (EASM) system is studied using an aerosol-climate online model BCC_AGCM2.0.1_CUACE/Aero. The results show that the summer mean net all-sky shortwave fluxes averaged over East Asian monsoon region (EAMR) at the top of the atmosphere (TOA) and surface reduce by 4.8 and 5.0 W m- 2, respectively, due to the increases of global aerosol emissions in 2000 relative to 1850. Changes in radiations and their resulting changes in heat and water transport and cloud fraction contribute together to the surface cooling over EAMR in summer. The increases in global anthropogenic aerosols lead to a decrease of 2.1 K in summer mean surface temperature and an increase of 0.4 hPa in summer mean surface pressure averaged over EAMR, respectively. It is shown that the changes in surface temperature and pressure are significantly larger over land than ocean, thus decreasing the contrast of land-sea surface temperature and pressure. This results in the marked anomalies of north and northeast winds over eastern and southern China and the surrounding oceans in summer, thereby weakening the EASM. The summer mean precipitation averaged over the EAMR reduces by 12%. The changes in non-East Asian aerosol emissions play a more important role in inducing the changes of local temperature and pressure, and thus significantly exacerbate the weakness of the EASM circulation due to local aerosol changes. The weakening of circulation due to both is comparable, and even the effect of non-local aerosols is larger in individual regions. The changes of local and non-local aerosols contribute comparably to the reductions in precipitation over oceans, whereas cause opposite changes over eastern China. Our results highlight the importance of aerosol changes outside East Asia in the impact of the changes of anthropogenic aerosols on EASM.

Projected changes in rainfall and temperature over homogeneous regions of India

NASA Astrophysics Data System (ADS)

Patwardhan, Savita; Kulkarni, Ashwini; Rao, K. Koteswara

2018-01-01

The impact of climate change on the characteristics of seasonal maximum and minimum temperature and seasonal summer monsoon rainfall is assessed over five homogeneous regions of India using a high-resolution regional climate model. Providing REgional Climate for Climate Studies (PRECIS) is developed at Hadley Centre for Climate Prediction and Research, UK. The model simulations are carried out over South Asian domain for the continuous period of 1961-2098 at 50-km horizontal resolution. Here, three simulations from a 17-member perturbed physics ensemble (PPE) produced using HadCM3 under the Quantifying Model Uncertainties in Model Predictions (QUMP) project of Hadley Centre, Met. Office, UK, have been used as lateral boundary conditions (LBCs) for the 138-year simulations of the regional climate model under Intergovernmental Panel on Climate Change (IPCC) A1B scenario. The projections indicate the increase in the summer monsoon (June through September) rainfall over all the homogeneous regions (15 to 19%) except peninsular India (around 5%). There may be marginal change in the frequency of medium and heavy rainfall events (>20 mm) towards the end of the present century. The analysis over five homogeneous regions indicates that the mean maximum surface air temperatures for the pre-monsoon season (March-April-May) as well as the mean minimum surface air temperature for winter season (January-February) may be warmer by around 4 °C towards the end of the twenty-first century.

Sub-seasonal precipitation during the South Asian summer monsoon onset period

NASA Astrophysics Data System (ADS)

Takaya, Y.; Yamaguchi, M.

2017-12-01

The South Asian summer monsoon (SASM) has a great impact on human activities (e.g., agriculture and health), thus skillful prediction of the SASM is highly anticipated. In particular, precipitation amount and timing of a rainy season onset are of great importance for crop planning. This study examines the performance of precipitation prediction during the onset period of the SASM using the WWRP/WCRP sub-seasonal to seasonal prediction project (S2S) dataset. Preliminary verification of ECMWF model reforecasts against the GSMaP precipitation analysis produced by Japan Aerospace Exploration Agency (JAXA) shows that a predictive skill of precipitation is reasonably high in a sub-seasonal time-range. It is also found that the predictive skill of precipitation in the South Asia is relatively higher around the onset period, consistent with our previous finding using the latest JMA seasonal prediction system (JMA/MRI-CPS2). The results suggest that state-of-the-art operational models have the capability to provide useful SASM onset predictions at a sub-seasonal time scale. In the presentation, we will also discuss the inherent potential predictability, feasibility of prediction of the monsoon onset and relevant processes.

Systematic errors in the simulation of the Asian summer monsoon: the role of rainfall variability on a range of time and space scales

NASA Astrophysics Data System (ADS)

Martin, Gill; Levine, Richard; Klingaman, Nicholas; Bush, Stephanie; Turner, Andrew; Woolnough, Steven

2015-04-01

Despite considerable efforts worldwide to improve model simulations of the Asian summer monsoon, significant biases still remain in climatological seasonal mean rainfall distribution, timing of the onset, and northward and eastward extent of the monsoon domain (Sperber et al., 2013). Many modelling studies have shown sensitivity to convection and boundary layer parameterization, cloud microphysics and land surface properties, as well as model resolution. Here we examine the problems in representing short-timescale rainfall variability (related to convection parameterization), problems in representing synoptic-scale systems such as monsoon depressions (related to model resolution), and the relationship of each of these with longer-term systematic biases. Analysis of the spatial distribution of rainfall intensity on a range of timescales ranging from ~30 minutes to daily, in the MetUM and in observations (where available), highlights how rainfall biases in the South Asian monsoon region on different timescales in different regions can be achieved in models through a combination of the incorrect frequency and/or intensity of rainfall. Over the Indian land area, the typical dry bias is related to sub-daily rainfall events being too infrequent, despite being too intense when they occur. In contrast, the wet bias regions over the equatorial Indian Ocean are mainly related to too frequent occurrence of lower-than-observed 3-hourly rainfall accumulations which result in too frequent occurrence of higher-than-observed daily rainfall accumulations. This analysis sheds light on the model deficiencies behind the climatological seasonal mean rainfall biases that many models exhibit in this region. Changing physical parameterizations alters this behaviour, with associated adjustments in the climatological rainfall distribution, although the latter is not always improved (Bush et al., 2014). This suggests a more complex interaction between the diabatic heating and the large

An overview of dry-wet climate variability among monsoon-westerly regions and the monsoon northernmost marginal active zone in China

NASA Astrophysics Data System (ADS)

Qian, Weihong; Ding, Ting; Hu, Haoran; Lin, Xiang; Qin, Aimin

2009-07-01

Climate in mainland China can be divided into the monsoon region in the southeast and the westerly region in the northwest as well as the intercross zone, i.e., the monsoon northernmost marginal active zone that is oriented from Southwest China to the upper Yellow River, North China, and Northeast China. In the three regions, dry-wet climate changes are directly linked to the interaction of the southerly monsoon flow on the east side of the Tibetan Plateau and the westerly flow on the north side of the Plateau from the inter-annual to inter-decadal timescales. Some basic features of climate variability in the three regions for the last half century and the historical hundreds of years are reviewed in this paper. In the last half century, an increasing trend of summer precipitation associated with the enhancing westerly flow is found in the westerly region from Xinjiang to northern parts of North China and Northeast China. On the other hand, an increasing trend of summer precipitation along the Yangtze River and a decreasing trend of summer precipitation along the monsoon northernmost marginal active zone are associated with the weakening monsoon flow in East Asia. Historical documents are widely distributed in the monsoon region for hundreds of years and natural climate proxies are constructed in the non-monsoon region, while two types of climate proxies can be commonly found over the monsoon northernmost marginal active zone. In the monsoon region, dry-wet variation centers are altered among North China, the lower Yangtze River, and South China from one century to another. Dry or wet anomalies are firstly observed along the monsoon northernmost marginal active zone and shifted southward or southeastward to the Yangtze River valley and South China in about a 70-year timescale. Severe drought events are experienced along the monsoon northernmost marginal active zone during the last 5 centuries. Inter-decadal dry-wet variations are depicted by natural proxies for the

Decline and poleward shift in Indian summer monsoon synoptic activity in a warming climate.

PubMed

Sandeep, S; Ajayamohan, R S; Boos, William R; Sabin, T P; Praveen, V

2018-03-13

Cyclonic atmospheric vortices of varying intensity, collectively known as low-pressure systems (LPS), travel northwest across central India and produce more than half of the precipitation received by that fertile region and its ∼600 million inhabitants. Yet, future changes in LPS activity are poorly understood, due in part to inadequate representation of these storms in current climate models. Using a high-resolution atmospheric general circulation model that realistically simulates the genesis distribution of LPS, here we show that Indian monsoon LPS activity declines about 45% by the late 21st century in simulations of a business-as-usual emission scenario. The distribution of LPS genesis shifts poleward as it weakens, with oceanic genesis decreasing by ∼60% and continental genesis increasing by ∼10%; over land the increase in storm counts is accompanied by a shift toward lower storm wind speeds. The weakening and poleward shift of the genesis distribution in a warmer climate are confirmed and attributed, via a statistical model, to the reduction and poleward shift of low-level absolute vorticity over the monsoon region, which in turn are robust features of most coupled model projections. The poleward shift in LPS activity results in an increased frequency of extreme precipitation events over northern India. Copyright © 2018 the Author(s). Published by PNAS.

Seasonal Transitions and the Westerly Jet in the Holocene East Asian Summer Monsoon

NASA Astrophysics Data System (ADS)

Kong, W.; Chiang, J. C. H.

2015-12-01

The Holocene East Asian Summer Monsoon (EASM) was characterized by a trend to weaker monsoon intensity paced by orbital insolation. Here, we attribute the stronger EASM intensity in the early-mid Holocene to changes in the timing of the transition between the EASM seasonal stages - Spring, pre Mei- Yu, Mei-Yu, and Summer - during that time. Following the recent 'jet transition hypothesis' (Chiang et al., 2015), we explore the role of north-south displacement of the westerlies relative to the Tibetan Plateau that is hypothesized to control the downstream EASM seasonality changes across the Holocene. To this end, we analyze model simulations of the Holocene EASM, compare the simulated Holocene climate with the paleodata observations, and examine the role of atmospheric circulation and specifically the westerlies in modulating the East Asia summer climate. The PMIP3 climate model simulations suggest that, compared to the pre-industrial, the Mei-Yu onset and the transition from Mei-Yu to Summer rainfall occur earlier in the mid-Holocene. The advanced seasonal rainfall transition is accompanied by the weakened and northward-shifted upstream westerlies. In our atmospheric general circulation model (coupled to a slab ocean) simulations of various time periods across the Holocene (9ka, 6ka, 3ka, and pre-industrial), we quantitatively show that the timing and the length of each rainfall stage are closely related to the jet position over East Asia. We also show that the simulated changes in the maximum annual rainfall band and dust emission over East Asia largely agree with the paleo-proxy observations. In addition, we find that changes to the seasonal rainfall transitions, latitudinal westerly position, and stationary eddy activity over East Asia co-vary across the Holocene. In particular, we argue that the changes in the rainfall seasonal transitions are tied to an altered stationary wave pattern, resembling today's the so-called 'Silk Road Pattern', riding along the

On the Predictability of Northeast Monsoon Rainfall over South Peninsular India in General Circulation Models

NASA Astrophysics Data System (ADS)

Nair, Archana; Acharya, Nachiketa; Singh, Ankita; Mohanty, U. C.; Panda, T. C.

2013-11-01

In this study the predictability of northeast monsoon (Oct-Nov-Dec) rainfall over peninsular India by eight general circulation model (GCM) outputs was analyzed. These GCM outputs (forecasts for the whole season issued in September) were compared with high-resolution observed gridded rainfall data obtained from the India Meteorological Department for the period 1982-2010. Rainfall, interannual variability (IAV), correlation coefficients, and index of agreement were examined for the outputs of eight GCMs and compared with observation. It was found that the models are able to reproduce rainfall and IAV to different extents. The predictive power of GCMs was also judged by determining the signal-to-noise ratio and the external error variance; it was noted that the predictive power of the models was usually very low. To examine dominant modes of interannual variability, empirical orthogonal function (EOF) analysis was also conducted. EOF analysis of the models revealed they were capable of representing the observed precipitation variability to some extent. The teleconnection between the sea surface temperature (SST) and northeast monsoon rainfall was also investigated and results suggest that during OND the SST over the equatorial Indian Ocean, the Bay of Bengal, the central Pacific Ocean (over Nino3 region), and the north and south Atlantic Ocean enhances northeast monsoon rainfall. This observed phenomenon is only predicted by the CCM3v6 model.

Progress Towards Achieving the Challenge of Indian Summer Monsoon Climate Simulation in a Coupled Ocean-Atmosphere Model

NASA Astrophysics Data System (ADS)

Hazra, Anupam; Chaudhari, Hemantkumar S.; Saha, Subodh Kumar; Pokhrel, Samir; Goswami, B. N.

2017-10-01

Simulation of the spatial and temporal structure of the monsoon intraseasonal oscillations (MISOs), which have effects on the seasonal mean and annual cycle of Indian summer monsoon (ISM) rainfall, remains a grand challenge for the state-of-the-art global coupled models. Biases in simulation of the amplitude and northward propagation of MISOs and related dry rainfall bias over ISM region in climate models are limiting the current skill of monsoon prediction. Recent observations indicate that the convective microphysics of clouds may be critical in simulating the observed MISOs. The hypothesis is strongly supported by high fidelity in simulation of the amplitude and space-time spectra of MISO by a coupled climate model, when our physically based modified cloud microphysics scheme is implemented in conjunction with a modified new Simple Arakawa Schubert (nSAS) convective parameterization scheme. Improved simulation of MISOs appears to have been aided by much improved simulation of the observed high cloud fraction and convective to stratiform rain fractions and resulted into a much improved simulation of the ISM rainfall, monsoon onset, and the annual cycle.

Evaluation of NCMRWF unified model vertical cloud structure with CloudSat over the Indian summer monsoon region

NASA Astrophysics Data System (ADS)

Jayakumar, A.; Mamgain, Ashu; Jisesh, A. S.; Mohandas, Saji; Rakhi, R.; Rajagopal, E. N.

2016-05-01

Representation of rainfall distribution and monsoon circulation in the high resolution versions of NCMRWF Unified model (NCUM-REG) for the short-range forecasting of extreme rainfall event is vastly dependent on the key factors such as vertical cloud distribution, convection and convection/cloud relationship in the model. Hence it is highly relevant to evaluate the vertical structure of cloud and precipitation of the model over the monsoon environment. In this regard, we utilized the synergy of the capabilities of CloudSat data for long observational period, by conditioning it for the synoptic situation of the model simulation period. Simulations were run at 4-km grid length with the convective parameterization effectively switched off and on. Since the sample of CloudSat overpasses through the monsoon domain is small, the aforementioned methodology may qualitatively evaluate the vertical cloud structure for the model simulation period. It is envisaged that the present study will open up the possibility of further improvement in the high resolution version of NCUM in the tropics for the Indian summer monsoon associated rainfall events.

Interdecadal variations of East Asian summer monsoon northward propagation and influences on summer precipitation over East China

NASA Astrophysics Data System (ADS)

Jiang, Z.; Yang, S.; He, J.; Li, J.; Liang, J.

2008-08-01

The interdecadal variation of northward propagation of the East Asian Summer Monsoon (EASM) and summer precipitation in East China have been investigated using daily surface rainfall from a dense rain gauge network in China for 1957 2001, National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis, European Center for Medium-Range Weather Forecast (ECMWF) reanalysis, and Global Mean Sea Level Pressure Dataset (GMSLP2) from Climatic Research Unit (CRU). Results in general show a consistent agreement on the interdecadal variability of EASM northward propagations. However, it appears that the interdecadal variation is stronger in NCEP than in ECMWF and CRU datasets. A newly defined normalized precipitation index (NPI), a 5-day running mean rainfall normalized with its standard deviation, clearly depicts the characteristics of summer rainbelt activities in East China in terms of jumps and durations during its northward propagations. The EASM northward propagation shows a prominent interdecadal variation. EASM before late 1970s had a rapid northward advance and a northern edge beyond its normal position. As a result, more summer rainfall occurred for the North China rainy season, Huaihe-River Mei-Yu, and South China Mei-Yu. In contrast, EASM after late 1970s had a slow northward movement and a northern edge located south of its normal position. Less summer precipitation occurred in East China except in Yangtze River basin. The EASM northernmost position (ENP), northernmost intensity (ENI), and EASM have a complex and good relationship at interdecadal timescales. They have significant influences on interdecadal variation of the large-scale precipitation anomalies in East China.

Simulation of the Central Indian Ocean Mode in CESM: Implications for the Indian Summer Monsoon System

NASA Astrophysics Data System (ADS)

Zhou, Lei; Murtugudde, Raghu; Neale, Richard B.; Jochum, Markus

2018-01-01

The simulation of the Indian summer monsoon and its pronounced intraseasonal component in a modern climate model remains a significant challenge. Recently, using observations and reanalysis products, the central Indian Ocean (CIO) mode was found to be a natural mode in the ocean-atmosphere coupled system and also shown to have a close mechanistic connection with the monsoon intraseasonal oscillation (MISO). In this study, the simulation of the actual CIO mode in historical Community Earth System Model (CESM) outputs is assessed by comparing with observations and reanalysis products. The simulation of the Madden-Julian Oscillation, a major component of tropical intraseasonal variabilities (ISVs), is satisfactory. However, the CIO mode is not well captured in any of the CESM simulations considered here. The force and response relationship between the atmosphere and the ocean associated with the CIO mode in CESM is opposite to that in nature. The simulated meridional gradient of large-scale zonal winds is too weak, which precludes the necessary energy conversion from the mean state to the ISVs and cuts off the energy source to MISO in CESM. The inability of CESM to reproduce the CIO mode seen clearly in nature highlights the CIO mode as a new dynamical framework for diagnosing the deficiencies in Indian summer monsoon simulation in climate models. The CIO mode is a coupled metric for evaluating climate models and may be a better indicator of a model's skill to accurately capture the tropical multiscale interactions over subseasonal to interannual timescales.

Why the Australian Monsoon Strengthened During the Cold Last Glacial Maximum?

NASA Astrophysics Data System (ADS)

Yan, M.; Wang, B.; Liu, J.; Ning, L.

2017-12-01

The multi-model ensemble simulation suggests that the global monsoon and most sub-monsoons are weakened during the Last Glacial Maximum (LGM) due to the lower green-house gases concentration, the presence of the ice-sheets and the weakened seasonal distribution of insolation. In contrast, the Australian monsoon is strengthened during the LGM. The precipitation there increases in austral summer and decreases in austral winter, so that the annual range or monsoonality increases. The strengthened monsoonality is mainly due to the decreased precipitation in austral winter, which is primarily caused by circulation changes, although the reduced atmospheric water vapor also has a moderate contribution. On the other hand, the strengthened Australian summer monsoon rainfall is likely caused by the change of land-sea thermal contrast due to the alteration of land-sea configuration and by the asymmetric change in sea surface temperature (SST) over Indo-Pacific warm pool region. The strengthened land-sea thermal contrast and Western Pacific-Eastern Indian Ocean thermal gradients in the pre-summer monsoon season triggers a cyclonic wind anomaly that is maintained to the monsoon season, thereby increasing summer precipitation. The increased summer precipitation is associated with the increased cloud cover over the land and decreased cloud cover over the ocean. This may weaken the land-sea thermal contrast, which agrees with the paleoclimate reconstruction. The biases between different models are likely related to the different responses of SST over the North Atlantic Ocean in the pre-summer monsoon season.

Regional-scale relationships between aerosol and summer monsoon circulation, and precipitation over northeast Asia

NASA Astrophysics Data System (ADS)

Yoon, Soon-Chang; Kim, Sang-Woo; Choi, Suk-Jin; Choi, In-Jin

2010-08-01

We investigated the regional-scale relationships between columnar aerosol loads and summer monsoon circulation, and also the precipitation over northeast Asia using aerosol optical depth (AOD) data obtained from the 8-year MODIS, AERONET Sun/sky radiometer, and precipitation data acquired under the Global Precipitation Climatology Project (GPCP). These high-quality data revealed the regional-scale link between AOD and summer monsoon circulation, precipitation in July over northeast Asian countries, and their distinct spatial and annual variabilities. Compared to the mean AOD for the entire period of 2001-2008, the increase of almost 40-50% in the AOD value in July 2005 and July 2007 was found over the downwind regions of China (Yellow Sea, Korean peninsula, and East Sea), with negative precipitation anomalies. This can be attributable to the strong westerly confluent flows, between cyclone flows by continental thermal low centered over the northern China and anticyclonic flows by the western North Pacific High, which transport anthropogenic pollution aerosols emitted from east China to aforementioned downwind high AOD regions along the rim of the Pacific marine airmass. In July 2002, however, the easterly flows transported anthropogenic aerosols from east China to the southwestern part of China in July 2002. As a result, the AOD off the coast of China was dramatically reduced in spite of decreasing rainfall. From the calculation of the cross-correlation coefficient between MODIS-derived AOD anomalies and GPCP precipitation anomalies in July over the period 2001-2008, we found negative correlations over the areas encompassed by 105-115°E and 30-35°N and by 120-140°E and 35-40°N (Yellow Sea, Korean peninsula, and East Sea). This suggests that aerosol loads over these regions are easily influenced by the Asian monsoon flow system and associated precipitation.

Factors affecting the inter-annual to centennial timescale variability of Indian summer monsoon rainfall

NASA Astrophysics Data System (ADS)

Malik, Abdul; Brönnimann, Stefan

2017-09-01

The Modes of Ocean Variability (MOV) namely Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), and El Niño Southern Oscillation (ENSO) can have significant impacts on Indian Summer Monsoon Rainfall (ISMR) on different timescales. The timescales at which these MOV interacts with ISMR and the factors which may perturb their relationship with ISMR need to be investigated. We employ De-trended Cross-Correlation Analysis (DCCA), and De-trended Partial-Cross-Correlation Analysis (DPCCA) to study the timescales of interaction of ISMR with AMO, PDO, and ENSO using observational dataset (AD 1854-1999), and atmosphere-ocean-chemistry climate model simulations with SOCOL-MPIOM (AD 1600-1999). Further, this study uses De-trended Semi-Partial Cross-Correlation Analysis (DSPCCA) to address the relation between solar variability and the ISMR. We find statistically significant evidence of intrinsic correlations of ISMR with AMO, PDO, and ENSO on different timescales, consistent between model simulations and observations. However, the model fails to capture modulation in intrinsic relationship between ISRM and MOV due to external signals. Our analysis indicates that AMO is a potential source of non-stationary relationship between ISMR and ENSO. Furthermore, the pattern of correlation between ISMR and Total Solar Irradiance (TSI) is inconsistent between observations and model simulations. The observational dataset indicates statistically insignificant negative intrinsic correlation between ISMR and TSI on decadal-to-centennial timescales. This statistically insignificant negative intrinsic correlation is transformed to statistically significant positive extrinsic by AMO on 61-86-year timescale. We propose a new mechanism for Sun-monsoon connection which operates through AMO by changes in summer (June-September; JJAS) meridional gradient of tropospheric temperatures (ΔTTJJAS). There is a negative (positive) intrinsic correlation between ΔTTJJAS (AMO) and

Factors affecting the inter-annual to centennial timescale variability of Indian summer monsoon rainfall

NASA Astrophysics Data System (ADS)

Malik, Abdul; Brönnimann, Stefan

2018-06-01

The Modes of Ocean Variability (MOV) namely Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), and El Niño Southern Oscillation (ENSO) can have significant impacts on Indian Summer Monsoon Rainfall (ISMR) on different timescales. The timescales at which these MOV interacts with ISMR and the factors which may perturb their relationship with ISMR need to be investigated. We employ De-trended Cross-Correlation Analysis (DCCA), and De-trended Partial-Cross-Correlation Analysis (DPCCA) to study the timescales of interaction of ISMR with AMO, PDO, and ENSO using observational dataset (AD 1854-1999), and atmosphere-ocean-chemistry climate model simulations with SOCOL-MPIOM (AD 1600-1999). Further, this study uses De-trended Semi-Partial Cross-Correlation Analysis (DSPCCA) to address the relation between solar variability and the ISMR. We find statistically significant evidence of intrinsic correlations of ISMR with AMO, PDO, and ENSO on different timescales, consistent between model simulations and observations. However, the model fails to capture modulation in intrinsic relationship between ISRM and MOV due to external signals. Our analysis indicates that AMO is a potential source of non-stationary relationship between ISMR and ENSO. Furthermore, the pattern of correlation between ISMR and Total Solar Irradiance (TSI) is inconsistent between observations and model simulations. The observational dataset indicates statistically insignificant negative intrinsic correlation between ISMR and TSI on decadal-to-centennial timescales. This statistically insignificant negative intrinsic correlation is transformed to statistically significant positive extrinsic by AMO on 61-86-year timescale. We propose a new mechanism for Sun-monsoon connection which operates through AMO by changes in summer (June-September; JJAS) meridional gradient of tropospheric temperatures (ΔTTJJAS). There is a negative (positive) intrinsic correlation between ΔTTJJAS (AMO) and

Revised cloud processes to improve the mean and intraseasonal variability of Indian summer monsoon in climate forecast system: Part 1

NASA Astrophysics Data System (ADS)

Abhik, S.; Krishna, R. P. M.; Mahakur, M.; Ganai, Malay; Mukhopadhyay, P.; Dudhia, J.

2017-06-01

The National Centre for Environmental Prediction (NCEP) Climate Forecast System (CFS) is being used for operational monsoon prediction over the Indian region. Recent studies indicate that the moist convective process in CFS is one of the major sources of uncertainty in monsoon predictions. In this study, the existing simple cloud microphysics of CFS is replaced by the six-class Weather Research Forecasting (WRF) single moment (WSM6) microphysical scheme. Additionally, a revised convective parameterization is employed to improve the performance of the model in simulating the boreal summer mean climate and intraseasonal variability over the Indian summer monsoon (ISM) region. The revised version of the model (CFSCR) exhibits a potential to improve shortcomings in the seasonal mean precipitation distribution relative to the standard CFS (CTRL), especially over the ISM region. Consistently, notable improvements are also evident in other observed ISM characteristics. These improvements are found to be associated with a better simulation of spatial and vertical distributions of cloud hydrometeors in CFSCR. A reasonable representation of the subgrid-scale convective parameterization along with cloud hydrometeors helps to improve the convective and large-scale precipitation distribution in the model. As a consequence, the simulated low-frequency boreal summer intraseasonal oscillation (BSISO) exhibits realistic propagation and the observed northwest-southeast rainband is well reproduced in CFSCR. Additionally, both the high and low-frequency BSISOs are better captured in CFSCR. The improvement of low and high-frequency BSISOs in CFSCR is shown to be related to a realistic phase relationship of clouds.