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Interannual Variation of Tropical Night Frequency in Beijing and Associated Large-Scale Circulation Background

Advances in Atmospheric Sciences 2012年第2期29卷 295-306页

作者： Jong-Kil PARK 陆日宇李超凡 Eun Byul KIM Department of Atmospheric Environment Information Engineering Atmospheric Environment Information Research Center Inje University State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric Physics Chinese Academy of Sciences

This study examined the variability in frequency of tropical night occurrence （i.e., minimum air tem- perature 25℃） in Beijing, using a homogenized daily temperature dataset during the period 1960–2008. Our results show that tropical nights occur most frequently in late July and early August, which is consis- tent with relatively high air humidity associated with the rainy season in Beijing. In addition, year-to-year variation of tropical night occurrence indicates that the tropical nights have appeared much more frequently since 1994, which can be illustrated by the yearly days of tropical nights averaged over two periods： 9.2 days of tropical nights per year during 1994–2008 versus 3.15 days during 1960–1993. These features of tropical night variations suggest a distinction between tropical nights and extreme heat in Beijing. We further investigated the large-scale circulations associated with the year-to-year variation of tropical night occurrence in July and August, when tropical nights appear most frequently and occupy 95% of the annual sum. After comparing the results in the two reanalysis datasets （NCEP/NCAR and ERA-40） and considering the possible effects of decadal change in the frequency of tropical nights that occurred around 1993/94, we conclude that on the interannual time scale, the cyclonic anomaly with a barotropic structure centered over Beijing is responsible for less frequent tropical nights, and the anticyclonic anomaly is responsible for more frequent occurrence of tropical nights over Beijing.

关键词： tropical night large-scale circulation interannual variability decadal change Beijing

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Strengthened Relationship between the Antarctic Oscillation and ENSO After the Mid-1990s during Austral Spring

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Advances in Atmospheric Sciences 2017年第1期34卷 54-65页

作者： Tingting HAN Huijun WANG Jianqi SUN Nansen-Zhu International Research Centre Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China Climate change Research Center Chinese Academy of SciencesBeijing 100029China Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Key Laboratory of Meteorological Disaster Ministry of EducationNanjing University for Information Science and TechnologyNanjing 210044China University of Chinese Academy of Sciences Beijing 100049China

This paper documents a decadal strengthened co-variability of the Antarctic Oscillation （AAO） and ENSO in austral spring after the mid-1990s. During the period 1979-93, the ENSO （AAO） spatial signatures are restricted to the tropicsmidlatitudes （Antarctic-midlatitudes） of the Southern Hemisphere （SH）, with a weak connection between the two oscillations. Comparatively, after the mid-1990s, the E1 Nifio-related atmospheric anomalies project on a negative AAO pattern with a barotropic structure in the mid-high latitudes of the SH. The expansion of E1 Nifio-related air temperature anomalies have a heightened impact on the meridional thermal structure of the SH, contributing to a weakened circumpolar westerly and strengthened subtropical jet. Meanwhile, the ENSO-related southern three-cell circulations expand poleward and then strongly couple the Antarctic and the tropics. Numerical simulation results suggest that the intensified connection between ENSO and SST in the South Pacific since the mid-1990s is responsible for the strengthened AAO-ENSO relationship.

关键词： ENSO Antarctic Oscillation South Pacific SST austral spring decadal change

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Recent Weakening in Interannual Variability of Mean Tropical Cyclogenesis Latitude over the Western North Pacific during Boreal Summer

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Journal of Meteorological Research 2020年第6期34卷 1183-1198页

作者： Minmin WU Lei WANG Baiyang CHEN Laboratory for Coastal Ocean Variation and Disaster Prediction College of Ocean and MeteorologyGuangdong Ocean UniversityZhanjiang 524088 Key Laboratory of Climate Resources and Environment in Continental Shelf Sea and Deep Sea of Department of Education of Guangdong ProvinceGuangdong Ocean UniversityZhanjiang 524088 Marine Resources Big Data Center of South China Sea Southern Marine Science and Engineering Guangdong Laboratory(Zhanjiang)Zhanjiang 524025

The intensity of the interannual variability(IIV)of the mean tropical cyclone(TC)genesis latitude over the western North Pacific(WNP)has been weakening significantly since the late 1990 *** is found that the IIV of the mean TC genesis latitude depends largely on the strength of the out-of-phase relationship between TC genesis numbers in the north(north of 15°N)and south(south of 15°N)of the WNP.A weaker(stronger)north–south TC see-saw has led to a smaller(larger)IIV of the mean TC genesis latitude after(before)the late 1990 *** configurations of sea surface temperature(SST)anomalies are found to be responsible for the decadal changes in the north–south TC see-saw and dipole *** the late 1990 s,the joint effect of SST anomalies over the tropical Pacific and tropical North Indian Ocean dominated,rendering the obvious north–south TC see-saw and larger IIV of the mean TC genesis *** the late 1990 s,however,the dominant SST anomalies associated with TC genesis shift to the tropical central Pacific(CP)and tropical North Atlantic Ocean,which have weakened the north–south TC seesaw and reduced the IIV of the mean TC genesis *** observed decadal changes in the configuration of SST anomalies are considered to be closely associated with the shift of the El Ni?o–Southern Oscillation(ENSO)from eastern Pacific(EP)type to the CP type during the recent *** results suggest that the increased influences from the tropical Atlantic Ocean have become more important to the variations of TC activity in the WNP during the recent *** results may have important implications for assessing the latitudinal distributions of TC-induced hazards.

关键词： tropical cyclone cyclogenesis latitude decadal change shifting El Nino–Southern Oscillation(ENSO) western North Pacific(WNP) tropical Atlantic sea surface temperature(SST)

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Inhomogeneous trends in the onset date of extreme hot days in China over the last five decades

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Atmospheric and Oceanic Science Letters 2021年第6期14卷 33-40页

作者： Yang Yang Zhaohui Lin Lifeng Luo Yan Zhang Zhen Li International Center for Climate and Environment Sciences Institute of Atmospheric PhysicsChinese Academy of SciencesBeijingChina University of Chinese Academy of Sciences BeijingChina Department of Geography Environmentand Spatial SciencesMichigan State UniversityEast LansingMIUSA Key Laboratory of Regional Climate-Environment for Temperate East Asia Institute of Atmospheric PhysicsChinese Academy of SciencesBeijingChina

Using a homogenized daily maximum temperature(T_(max))dataset across China,this study characterized the spatiotemporal variation of the onset date of extreme hot days in a year(i.e.,FirstEHD)during *** trends of FirstEHD over China during 1960-2018 can be found,with the advanced trend of FirstEHD over most parts in China,while a number of stations in North-Central China(NC)show the delayed trend of ***,there exist interdecadal changes of FirstEHD trend,with a remarkable difference in the trend magnitude before and after the 1990s over South China(SC),and the sign of trend can even reverse from negative to positive after the 1990s in Xinjiang(XJ)and Yangtze River Basin(YR),and from positive to negative in *** overall trends of FirstEHD over NC,YR,and XJ during 1960-2018 are dominated by the trends before the 1990s,while they are dominated by the sharp advance after the 1990s over *** is further found that the trend of FirstEHD can generally be explained by the long-term trend in T_(max) over most parts of China,but the contribution from T_(max) variabilities is also non-negligible and can even account for more than 75% of the overall trend over *** possible factors responsible for the decadal changes in FirstEHD trends are also discussed.

关键词： Extreme hot days Onset date Trend decadal change Variability of maximum temperature

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Long-term changes in wintertime persistent heavy rainfall over southern China contributed by the Madden-Julian Oscillation

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Atmospheric and Oceanic Science Letters 2019年第5期12卷 361-368页

作者： LIU Yu HSU Pang-Chi Key Laboratory of Meteorological Disaster of Ministry of Education Joint International Research Laboratory of Climate and Environment Change/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters Nanjing University of Information Science& Technology

During the boreal winter,abundant persistent heavy rainfall(PHR)amount and significant rainfall variability at subseasonal timescale are generally observed over the southern sector of East China,where the large-scale circulation and moisture transport are tightly connected with the equatorial Madden-Julian Oscillation(MJO).As the MJO convections occur over the equatorial Indian Ocean(MJO phases 1-4),the low-level moisture convergence is enhanced over southern China(SC,108°-120°E,21°-26°N)with the divergence to the ***,a positive anomaly of PHR amount appears in SC but a negative anomaly of PHR amount is seen in the Yangtze River valley(YR,113°-122°E,28°-30°N).In contrast,the divergence(convergence)of moisture flux anomalies in the SC(YR)associated with the western equatorial Pacific MJO convections(phases 5-8)limits(benefits)the occurrence of PHR in the SC(YR).The wintertime PHR over southern China is found to undergo a long-term change over the past three decades(1979-2011)with a decreasing(an increasing)trend of PHR amount in the SC(YR).The change in PHR amount occurs consistently with the decadal change in MJO *** the earlier decade(1979-1994,E1),the active Indian Ocean(western Pacific)MJO events appeared more frequently while they became less frequent in the recent decade(1995-2011,E2).Accordingly,the Indian Ocean(western Pacific)MJO-related moisture convergence(divergence)anomalies in the SC tend to be weakened(enhanced),contributing to the decrease in PHR amount over the SC in the recent decade.

关键词： Persistent heavy rainfall southern China MaddenJulian Oscillation decadal change

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Interdecadal Variations of Winter Temperatures in East China During the Past 100 Years and Related Atmospheric Circulation

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Atmospheric and Oceanic Science Letters 2013年第5期6卷 290-294页

作者： ZHU Ya-Li Nansen-Zhu International Research Centre Institute of Atmospheric Physics Chinese Academy of Sciences Climate change Research Center Chinese Academy of Sciences

The winter temperature changes in East China during the past 100 years are investigated by using the Twentieth Century Version 2(20th-v2)*** typical warm(P1,1911–30;P4,1991–2010)and cold(P2,1938–57;P3,1961–80)periods are identified for the East China winter temperature *** of160-station observational data,NCAR sea level pressure(SLP)data,and NCEP/NCAR Reanalysis shows that the20th-v2 Reanalysis can successfully depict the major features of the warming from P3 to P4,which is part of the global warming *** cooling from P1 to P2is a regional phenomenon under global ***,both changes are consistent with the phase change of the Arctic Oscillation(AO),while the second change is also accompanied by the phase change of Antarctic Oscillation(AAO)from negative to *** sources of the interdecadal shifts of the AO and winter temperature in East China require further research.

关键词： East China winter temperature global warming decadal change

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Estimating Tree Canopy Cover and Identifying Deforestation Patterns in Meghalaya (1990-2021) through ML Classifiers

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Journal of Geographic Information System 2023年第3期15卷 309-333页

作者： Tapan Dhar Sengalvarayan Aravindan Basudeb Bhatta Department of Earth Sciences Annamalai University Annamalai Nagar India CAD Centre Jadavpur University Kolkata India

This study utilizes ML classifiers to estimate canopy density based on three decades of data (1990-2021). The Support Vector Machine (SVM) classifier outperformed other classifiers, such as Random Tree and Maximum Likelihood. Satellite data from Landsat and Sentinel 2 was classified using a developed python model, providing an economical and time-saving approach. The accuracy of the classification was evaluated through a confusion matrix and area computation. The findings indicate a negative trend in the overall decadal change, with significant tree loss attributed to jhum cultivation, mining, and quarry activities. However, positive changes were observed in recent years due to the ban on illegal mining. The study highlights the dynamic nature of tree cover and emphasizes the need for biennial assessments using at least five time-series data. Micro-level analysis in Shallang, West Khasi hills, revealed a concerning trend of shortening jhum cycles. Automation in canopy change analysis is crucial for effective forest monitoring, providing timely information for law enforcement proposals and involving forest managers, stakeholders, and watchdog organizations.

关键词： Meghalaya Forest Cover ML SVM Python Script decadal change Biennial change

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