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Advances in Atmospheric Sciences 2013年第1期30卷 153-166页

作者： debashis nath 陈文 Center for Monsoon System Research Institute of Atmospheric PhysicsChinese Academy of Sciences

Over the tropics, convection, wind shear （i.e., vertical and horizontal shear of wind and/or geostrophic adjustment comprising spontaneous imbalance in jet streams） and topography are the major sources for the generation of gravity waves. During the summer monsoon season （June August） over the Indian subcontinent, convection and wind shear coexist. To determine the dominant source of gravity waves during monsoon season, an experiment was conducted using mesosphere-stratosphere-troposphere （MST） radar situated at Gadanki （13.5°N, 79.2°E）, a tropical observatory in the southern part of the Indian subcontinent. MST radar was operated continuously for 72 h to capture high-frequency gravity waves. During this time, a radiosonde was released every 6 h in addition to the regular launch （once daily to study low-frequency gravity waves） throughout the season. These two data sets were utilized effectively to characterize the jet stream and the associated gravity waves. Data available from collocated instruments along with satellite-based brightness temperature （TBB） data were utilized to characterize the convection in and around Gadanki. Despite the presence of two major sources of gravity wave generation （i.e., convection and wind shear） during the monsoon season, wind shear （both vertical shear and geostrophic adjustment） contributed the most to the generation of gravity waves on various scales.

关键词： convection wind shear gravity waves MST radar radiosonde

Impact of Planetary Wave Reflection on Tropospheric Blocking over the Urals–Siberia Region in January 2008

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Advances in Atmospheric Sciences 2016年第3期33卷 309-318页

作者： debashis nath Wen CHEN Center for Monsoon System Research Institute of Atmospheric Physics Chinese Academy of Sciences

Planetary wave reflection from the stratosphere played a significant role in changing the tropospheric circulation pattern over Eurasia in mid-January 2008. We studied the 2008 event and compared with composite analysis （winters of 2002/2003, 200412005, 200612007, 200712008, 201012011 and 2011/2012）, when the downward coupling was stronger, by employing time-lagged singular value decomposition analysis on the geopotential height field. In the Northern Hemisphere, the geopo- tential fields were decomposed into zonal mean and wave components to compare the relative covariance patterns. It was found that the wavenumber 1 （WN1） component was dominant compared with the wavenumber 2 （WN2） component and zonal mean process. For the WNI field, the covariance was much higher （lower） for the negative （positive） lag, with a prominent peak around ＋15 days when the leading stratosphere coupled strongly with the troposphere. It contributed to the downward coupling due to reflection, when the stratosphere exhibited a partially reflective background state. We also analyzed the evolution of the WNI anomaly and heat flux anomaly, both in the troposphere and stratosphere, during January- March 2008. The amplitude of the tropospheric WN 1 pattern reached a maximum and was consistent with a downward wave coupling event influenced by the stratospheric WN1 anomaly at 10 hPa. This was consistent with the reflection of the WN1 component over Eurasia, which triggered an anomalous blocking high in the Urals-Siberia region. We further clarified the impact of reflection on the tropospheric WNI field and hence the tropospheric circulation pattern by changing the propagation direction during and after the event.

关键词： planetary wave reflection singular value decomposition (SVD) Eliassen-Palm (EP) flux blocking circulation

Long-Term Trend in Potential Vorticity Intrusion Events over the Pacific Ocean： Role of Global Mean Temperature Rise

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Journal of Meteorological Research 2017年第5期31卷 906-915页

作者： debashis nath Wen CHEN Xiaoqing LAN Center for Monsoon System Research Institute of Atmospheric Physics Chinese Academy of Sciences

In this study, we examine a long-term increasing trend in subtropical potential vorticity （PV） intrusion events over the Pacific Ocean in relation to the global mean temperature rise, based on multiple reaualysis datasets. The fre- quency of the PV intrusions is closely related to the upper-tropospheric equatorial westerly duct and the subtropical jet （STJ）. An overall strengthening of the westerly duct and weakening of the STJ are found to be driven by the warming-induced strengthening of Walker circulation and regional changes in Hadley circulation on multi-dccadal timescalc, leading to an increase in the PV intrusion frequency over the tropics. The results are robust in all datasets. The multi-decadal strengthening in the Pacific Walker circulation is consistent with the global mean temperature rise. In this way, the PV intrusions are correlated with the wanning related global mean temperuate rise. When the interan- nual variability of ENSO is removed from the intrusion time series, the long-term trend in PV intrusions due to ex- ternal forcing associated with anthropogenic warming （global mean temperature rise） becomes clearer. The link between the global mean temperature rise and intrusion frequency is further verified by performing a correlation ana- lysis between the two. The significant （〉 95%） correlation coefficient is 0.85, 0.94, 0.84, 0.83, and 0.84 for ERA-40, ERA-Interim, NCEP-NCAR, JRA-55, and JRA-25, respectively. This unequivocally indicates that the global mean temperature rise can explain around 69%--88% of the variance related to the lung-term increase in PV intrusion fre- quency over the Pacific Ocean.

关键词： potential vorticity (PV) intrusion Pacific Ocean westerly duct subtropical jet Walker circulation glob-al warming

Impact of Drought on Agriculture in the Indo-Gangetic Plain,India

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Advances in Atmospheric Sciences 2017年第3期34卷 335-346页

作者： Reshmita nath debashis nath Qian LI Wen CHEN Xuefeng CUI Center for Monsoon System Research Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China School of System Sciences Beijing Normal UniversityBeijing 100875China Key Laboratory of Middle Atmosphere and Global Environmental Observations Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China Meteorology and Climate Unit School of Mathematical ScienceUniversity College DublinDublin 4Ireland

In this study, we investigate the spatiotemporal characteristics of drought in India and its impact on agriculture during the summer season （April-September）. In the analysis, we use Standardized Precipitation Evapotranspiration Index （SPEI） datasets between 1982 and 2012 at the six-monthly timescale. Based on the criterion SPEI 〈 -1, we obtain a map of the number of occurrences of drought and find that the humid subtropical Upper Middle Gangetic Plain （UMGP） region is highly drought-prone, with an occurrence frequency of 40%-45%. This UMGP region contributes at least 18%-20% of India＇s annual cereal production. Not only the probability of drought, but the UMGP region has become increasingly drought-prone in recent decades. Moreover, cereal production in the UMGP region has experienced a gradual declining trend from 2000 onwards, which is consistent with the increase in drought-affected areas from 20%-25% to 50%-60%, before and after 2000, respectively. A higher correlation coefficient （-0.69） between the cereal production changes and drought-affected areas confirms that at least 50% of the agricultural （cereal） losses are associated with drought. While analyzing the individual impact of precipitation and surface temperature on SPEI at 6 month timescale [SPEI （6）] we find that, in the UMGP region, surface temperature plays the primary role in the lowering of the SPEI. The linkage is further confirmed by correlation analysis between SPEI （6） and surface temperature, which exhibits strong negative values in the UMGP region. Higher temperatures may have caused more evaporation and drying, which therefore increased the area affected by drought in recent decades.

关键词： drought agriculture SPEI Indo-Gangetic Plain temperature precipitation potential evapotranspiration

Planetary Wave Reflection and Its Impact on Tropospheric Cold Weather over Asia during January 2008

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Advances in Atmospheric Sciences 2014年第4期31卷 851-862页

作者： debashis nath CHEN Wen WANG Lin MA Yin Center for Monsoon System Research Institute of Atmospheric Physics Chinese Academy of Sciences

Reflection of stratospheric planetary waves and its impact on tropospheric cold weather over Asia during January 2008 were investigated by applying two dimensional Eliassen-Palm （EP） flux and three-dimensional Plumb wave activity *** planetary wave propagation can clearly be seen in the longitude-height and latitude-height sections of the Plumb wave activity flux and EP flux,respectively,when the stratospheric basic state is partially ***,a wave packet emanating from Baffin Island/coast of Labrador propagated eastward,equatorward and was reflected over Central Eurasia and parts of China,which in turn triggered the advection of cold wind from the northern part of the boreal forest regions and Siberia to the *** wide region of Central Eurasia and China experienced extreme cold weather during the second ten days of January 2008,whereas the extraordinary persistence of the event might have occurred due to an anomalous blocking high in the Urals-Siberia region.

关键词： planetary wave reflection reflective index advection blocking cold weather

Relationship Between Soil Temperature in May over Northwest China and the East Asian Summer Monsoon Precipitation

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Acta meteorologica Sinica 2013年第5期27卷 716-724页

作者：王远皓陈文张井勇 debashis nath Center for Monsoon System Research Institute of Atmospheric Physics Chinese Academy of Sciences University of Chinese Academy of Sciences

This study investigates the relationship between the soil temperature in May and the East Asian summer monsoon （EASM） precipitation in June and July using station observed soil temperature data over Northwest China from 1971 to *** is found that the memory of the soil temperature at 80-cm depth can persist for at least 2 months,and the soil temperature in May is closely linked to the EASM precipitation in June and *** the soil temperature is warmer in May over Northwest China,less rainfall occurs over the Yangtze and Huaihe River valley but more rainfall occurs over South China in June and *** is proposed that positive anomalous soil temperature in May over Northwest China corresponds to higher geopotential heights over the most parts of the mainland of East Asia,which tend to weaken the ensuing ***,in June and July,a cyclonic circulation anomaly occurs over Southeast China and Northwest Pacific and an anticyclonic anomaly appears in the Yangtze and Huaihe River valley at 850 *** the above tend to suppress the precipitation in the Yangtze and Huaihe River *** results also indicate that the soil temperature in May over Northwest China is closely related to the East Asia/Pacific （EAP） teleconnection pattern,and it may be employed as a useful predictor for the East Asian summer monsoon rainfall.

关键词： soil temperature the East Asian summer monsoon precipitation the EAP teleconnection pattern

Improvement of a Snow Albedo Parameterization in the Snow–Atmosphere–Soil Transfer Model:Evaluation of Impacts of Aerosol on Seasonal Snow Cover

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Advances in Atmospheric Sciences 2017年第11期34卷 1333-1345页

作者： Efang ZHONG Qian LI Shufen SUN Wen CHEN Shangfeng CHEN debashis nath Center for Monsoon System Research Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China University of Chinese Academy of Sciences Beijing 100049 China State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China

The presence of light-absorbing aerosols （LAA） in snow profoundly influence the surface energy balance and water budget. However, most snow-process schemes in land-surface and climate models currently do not take this into consider- ation. To better represent the snow process and to evaluate the impacts of LAA on snow, this study presents an improved snow albedo parameterization in the Snow-Atmosphere-Soil on snow. Specifically, the Snow, Ice and Aerosol Radiation Transfer （SAST） model, which includes the impacts of LAA （SNICAR） model is incorporated into the SAST model with an LAA mass stratigraphy scheme. The new coupled model is validated against in-situ measurements at the Swamp Angel Study Plot （SASP）, Colorado, USA. Results show that the snow albedo and snow depth are better reproduced than those in the original SAST, particularly during the period of snow ablation. Furthermore, the impacts of LAA on snow are esti- mated in the coupled model through case comparisons of the snowpack, with or without LAA. The LAA particles directly absorb extra solar radiation, which accelerates the growth rate of the snow grain size. Meanwhile, these larger snow particles favor more radiative absorption. The average total radiative forcing of the LAA at the SASP is 47.5 W m-2. This extra radiative absorption enhances the snowmelt rate. As a result, the peak runoff time and ＂snow all gone＂ day have shifted 18 and 19.5 days earlier, respectively, which could further impose substantial impacts on the hydrologic cycle and atmospheric processes.

关键词： light-absorbing aerosols snow albedo SAST SNICAR

Atmospheric diabatic heating–induced wave train from the Caspian Sea to South and East Asia during the summer monsoon season

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Atmospheric and Oceanic Science Letters 2020年第5期13卷 381-389页

作者： CHOUDHURY Devanil nath debashis CHEN Wen Center for Monsoon System Research Institute of Atmospheric PhysicsChinese Academy of SciencesBeijingChina College of Earth and Planetary Science University of Chinese Academy of SciencesBeijingChina

During the summer monsoon season,the authors observe a wave train that stretches from the northern Arabian Peninsula and Caspian Sea to the Indo-Gangetic plains along the foothills of the Himalaya and extending further east of the Tibetan *** trend analysis between 1979 and 2018 with NCEP–NCAR reanalysis data show that the diabatic heating flux(averaged over 1000 to 500 hPa)tends to decrease significantly over the Caspian Sea and its surrounding *** addition,the sea level pressure is increasing by^0.1 hPa yr-1 over the Caspian Sea,forming a high-pressure divergent center over *** divergent center is collocated with an anticyclonic circulation trend at 850 hPa over the Caspian *** decreasing diabatic heating flux modulates the local atmospheric circulation by increasing the surface pressure around the center of divergence,which further facilitates a wave train to propagate towards South and East *** wave train transports the moisture fluxes at 925 h Pa from the Caspian Sea,southeastward towards the South and East Asian monsoon region.

关键词： Moisture transport wave train diabatic heating Indian summer monsoon Caspian Sea

Biases of the wintertime Arctic Oscillation in CMIP5 models

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Biases of the wintertime Arctic Oscillation in CMIP5 models

Study of Secondary Cosmic Rays and Astronomical X-Ray Sources using Small Stratospheric Balloons

第35届中国气象学会年会

作者： Hainan Gong Lin Wang Wen Chen Xiaolong Chen debashis nath Center for Monsoon System research Institute of Atmospheric PhysicsChinese Academy of Sciences The State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric PhysicsChinese Academy of Sciences

Distinct biases are found in the pattern and teleconnections of the Arctic Oscillation（AO） in 32 climate models that participate the Coupled Model Intercomparison Project Phase 5（CMIP5）.Compared with observations,the Pacific（Atlantic） center of AO is excessively strong（weak） in most of the 32 CMIP5 models,and the AO-related surface air temperature anomalies are generally weak over the Eurasian continent and North *** biases are closely tied to the excessively strong linkage,which is marginal in observations,between AO and the North Pacific mode（NPM）—the leading variability of the North Pacific sea level *** implies that the AO in CMIP5 models may be compounded with some regional mode over the North ***,a bias-correction method was proposed via correcting the AO index（AOI） to improve the diagnostic estimates of the AO *** results suggest that the biases in the pattern and teleconnections of AO can be significantly reduced when the NPM variability is linearly removed from the AOI.

关键词： Arctic Oscillation(AO) CMIP5 North Pacific Pacific-North America(PNA) empirical orthogonal function(EOF)

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Research in Astronomy and Astrophysics 2024年第6期24卷 94-109页

作者： Rupnath Sikdar Sandip K.Chakrabarti debashis Bhowmick Indian Centre for Space Physics 466BarakholaSingabari RoadNetai NagarKolkata700099West BengalIndia

The X-ray sources of the universe are extraterrestrial in nature which emit X-ray *** closest strong X-ray source is the Sun,which is followed by various compact sources such as neutron stars,black holes,the Crab pulsar,*** this paper,we analyze the data received from several low-cost lightweight meteorological balloon-borne missions launched by the Indian Centre for Space *** main interest is to study the variation of the vertical intensity of secondary cosmic rays,the detection of strong X-ray sources,and their spectra in the energy band of^(1)0–80 keV during the complete *** to the lack of an onboard pointing system,low exposure time,achieving a maximum altitude of only~42 km,and freely rotating the payload about its axis,we modeled the background radiation flux for the X-ray detector using physical *** also present the source detection method,observation of the pulsation of the Crab(^(3)3 Hz),and spectra of some sources such as the quiet Sun and the Crab pulsar.

关键词： X-rays:stars balloons instrumentation:detectors