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The Response of geopotential height Anomalies to El Niño and La Niña Conditions and Their Implications to Seasonal Rainfall Variability over the Horn of Africa

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Atmospheric and Climate Sciences 2022年第2期12卷 475-492页

作者： Solomon Gunta Hejamady Gangadhara Bhat Busnur Rachotappa Manjunatha Department of Physics College of Natural and Computational Sciences Wolaita Sodo University Wolaita Sodo Ethiopia Remote Sensing and Geo-Informatics Division Department of Marine Geology Faculty of Science and Technology Mangalore University Karnataka India

In this study, we unveil atmospheric circulation anomalies associated with the large-scale tropical teleconnections using National Center for Environmental Prediction (NCEP) reanalysis dataset. Composite analyses have been performed to know the impact of large-scale tropical circulations on the Horn of Africa. The composite analysis performed at the geopotential height of 850 Mb and 200 Mb, and precipitation rate (mm/day) during six strong El Niño and La Niña episodes revealed that the large-scale tropical variability induced climate anomalies in space and time. A substantial decrease in upper-level height (200 Mb) has been observed in the study area during El Niño composite years as compared to the La Niña years. During El Niño conditions, the upper-level divergence initiates low-level vertical motion, thereby enhancing convection, however, during La Niña composite years, nearly contrasting situations are noticed in Belg (February to May) season in Ethiopia. However, geopotential height anomalies at 850 Mb are above-normal during the strong El Niño years, suggesting suppressed convection due to vertical shrinking and enhancement of divergence at the lower level. Compared to the Belg (February to May), geopotential anomalies were generally positive during the Kiremt (June to September) season, thereby suppressing the rainfall, particularly in Southern Ethiopia and Northern Part of Kenya. In contrast, an increase in rainfall was observed during the Belg season (February to May).

关键词： geopotential height Composite Analysis ENSO Atmospheric Circulations NCEP Reanalysis Tropical SST Anomalies Teleconnections Belg Kiremt

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Future Changes in Various Cold Surges over China in CMIP6 Projections

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Advances in Atmospheric Sciences 2024年第9期41卷 1751-1768页

作者： Li MA Zhigang WEI Xianru LI Shuting WU Key Laboratory of Environmental Change and Natural Disasters of Chinese Ministry of Education Beijing Normal UniversityBeijing 100875China State Key Laboratory of Earth Surface Processes and Resource Ecology(ESPRE) Beijing Normal UniversityBeijing 100875China Academy of Disaster Reduction and Emergency Management Ministry of Emergency Management and Ministry of EducationBeijing 100875China Faculty of Geographical Science Beijing Normal UniversityBeijing 100875China

Cold surges(CSs)often occur in the mid-latitude regions of the Northern Hemisphere and have enormous effects on socioeconomic *** report that the occurrences of CSs and persistent CSs(PCSs)have rebounded since the 1990s,but the trends related to the frequencies of strong CSs(SCSs)and extreme CSs(ECSs)changed from increasing to decreasing after *** highest-ranked model ensemble approach was used to project the occurrences of various CSs under the SSP1-2.6,SSP2-4.5,and SSP5-8.5 *** frequencies of the total CSs show overall decreasing ***,under the SSP1-2.6 scenario,slight increasing trends are noted for SCSs and ECSs in *** circulations that are characterized by an anomalous anticyclonic circulation with a significantly positive 500-hPa geopotential height(Z500)anomaly at high latitudes along with significant negative anomalies in China were favorable for cold air intrusions into *** addition,the frequencies of all CS types under the SPP5-8.5 scenario greatly decreased in the long term(2071-2100),a finding which is thought to be related to negative SST anomalies in the central and western North Pacific,differences in sea level pressure(SLP)between high-and mid-latitude regions,and a weaker East Asian *** terms of ECSs,the decreasing trends observed during the historical period were maintained until 2024 under the SSP1-2.6 *** to the SSP1-2.6 scenario,the Z500 pattern showed a trend of strengthened ridges over the Ural region and northern East Asia and weakened troughs over Siberia(60°-90°E)under the SSP2-4.5 and SSP5-8.5 scenarios,contributing to the shift to increasing trends of ECSs after 2014.

关键词： cold surge “highest-ranked”model ensemble anticyclonic circulation geopotential height China

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Analysis of the Simulated Climatic Characters of the South Asia High with a Flexible Coupled Ocean-Atmosphere GCM

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Advances in Atmospheric Sciences 2007年第1期24卷 136-146页

作者：黄樱钱永甫 Department of Atmospheric Sciences Nanjing UniversityNanjing 210093

The ability of a climate model to reproduce the climatic characters of the South Asia High （SAH） is assessed by analyzing the 110-yr output of a Flexible Coupled GCM, version 0 （FGCM-0）. Comparing the results of FGCM-0 with the NCEP/NCAR reanalysis data, the major findings show that FGCM-0 has better results in simulation of the geopotential height field at 100 hPa, and reproduces fairly the main atmospheric circulation centers. However, there are still some differences in the simulated results compared with the reanalysis data. The coupled model also successfully reproduces the mean seasonal variation of the SAH, that is, it moves from the Pacific Ocean to the Asian continent, remaining over the Tibetan Plateau from winter to summer, and then withdraws from the Tibetan Plateau to the Pacific Ocean from summer to winter. However, such observed relationships between the SAH positions and the summer precipitation patterns cannot be fairly reproduced in the FGCM-0.

关键词： South Asia High (SAH) FGCM-0 geopotential height seasonal variation SAH characteristic parameters

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The Climatic Effects of the Stratospheric Volcanic Ash

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Advances in Atmospheric Sciences 1993年第2期10卷 135-146页

作者：钱永甫 Department of Atmospheric Sciences Nanjing University Nanjing

The climatic effects of the stratospheric volcanic ash are simulated. The model we used is a primitive equation model with the P-σ incorporated coordinate system. The model has 5 layers in the atmosphere and 2 layers in the soil. The volcanic ash is introduced to the first (highest) model layer with a fixed optical thickness of 0.1275. Two comparative numerical experiments with and without the volcanic ash are made. Results show that the effects of the stratospheric volcanic ash on the formations of the mean climatic fields are much smaller than those of the land-sea distribution and the large scale topography. However, it does have contributions to the anomalies of the basic climatic states. The direct effect of the volcanic ash is to increase the temperature in the stratosphere. It can also influence the temperature and the height fields of isobaric surfaces, horizontal and vertical motions, precipitation and the surface climate through dynamic and thermodynamic processes in the atmosphere.

关键词： Tibetan Plateau Vertical Motion geopotential height Upward Motion Meridional Circulation

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Rainfall spectrum change in North China and its possible mechanism

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Progress in Natural Science:Materials International 2004年第7期 46-52页

作者： DAI Xingang 1,2*, WANG Ping 3, ZHANG Peiqun 4 and CHOU Jifan 1(1. College of Resources and Environmental Sciences, Lanzhou University, Lanzhou 730000, China 2. State Key Laboratory LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China 3. College of Physics, Peking University, Beijing 100871, China 4. National Climate Center, Beijing 100081, China) College of Resources and Environmental Sciences，Lanzhou University，Lanzhou 730000，China State Key Laboratory LASG，Institute of Atmospheric Physics，Chinese Academy of Sciences，Beijing 100029，China College of Physics，Peking University，Beijing 100871，China National Climate Center，Beijing 100081，China College of Resources and Environmental Sciences，Lanzhou University，Lanzhou 730000，China

The seasonal distribution of the rainfall in North China has changed greatly since 1977, with more rainfall in spring and less in July, August, and September (JAS). Wavelet analysis showed that the JAS rainfall underwent an abrupt spectrum change in the mid-1960s. Its interannual variability has declined while the interdecadal component has become the dominant mode, associated with the dry climate. Correlation analysis found that the JAS rainfall is negatively correlated with the departures of the 500 hPa geopotential height significantly over the northwest and southwest of China, and positively correlated with the summer monsoon over eastern China. Therefore, the interdecadal ascending of the air pressure in northwestern China and the monsoon decaying over East Asia in the past 20 years may be the two major causes of North China drought.

关键词： North China drought wavelet spectrum abruption monsoon geopotential height interdecadal change.

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