On the Contrasting Decadal Changes of Diurnal Surface Temperature Range between the Tibetan Plateau and Southeastern China during the 1980s–2000s

The diurnal surface temperature range （DTR） has become significantly smaller over the Tibetan Plateau （TP） but larger in southeastern China, despite the daily mean surface temperature having increased steadily in both areas during recent decades. Based on ERA-Interim reanalysis data covering 1979-2012, this study shows that the weakened DTR over TP is caused by stronger warming of daily minimum surface temperature （Tmin） and a weak cooling of the daily maximum surface temper- ature （Tmax）; meanwhile, the enhanced DTR over southeastern China is mainly associated with a relatively stronger/weaker warming of Tmax/Tmin. A further quantitative analysis of DTR changes through a process-based decomposition method-- the Coupled Surface-Atmosphere Climate Feedback Response Analysis Method （CFRAM）--indicates that changes in radia- tive processes are mainly responsible for the decreased DTR over the TR In particular, the increased low-level cloud cover tends to induce the radiative cooling/warming during daytime/nighttime, and the increased water vapor helps to decrease the DTR through the stronger radiative wanning during nighttime than daytime. Contributions from the changes in all radiative processes （over -2℃） are compensated for by those from the stronger decreased surface sensible heat flux during daytime than during nighttime （approximately 2.5℃）, but are co-contributed by the changes in atmospheric dynamics （approximately -0.4℃） and the stronger increased latent heat flux during daytime （approximately -0.8℃）. In contrast, the increased DTR over southeastern China is mainly contributed by the changes in cloud, water vapor and atmospheric dynamics. The changes in surface heat fluxes have resulted in a decrease in DTR over southeastern China.

Decadal Change in the Influence of the Western North Pacific Subtropical High on Summer Rainfall over the Yangtze River Basin in the Late 1970s

It is well known that on the interannual timescale,the westward extension of the western North Pacific subtropical high(WNPSH)results in enhanced rainfall over the Yangtze River basin(YRB)in summer,and vice versa.This study identifies that this correspondence experiences a decadal change in the late 1970s.That is,the WNPSH significantly affects YRB precipitation(YRBP)after the late 1970s(P2)but not before the late 1970s(P1).It is found that enhanced interannual variability of the WNPSH favors its effect on YRB rainfall in P2.On the other hand,after removing the strong WNPSH cases in P2 and making the WNPSH variability equivalent to that in P1,the WNPSH can still significantly affect YRB rainfall,suggesting that the WNPSH variability is not the only factor that affects the WNPSH-YRBP relationship.Further results indicate that the change in basic state of thermal conditions in the tropical WNP provides a favorable background for the enhanced WNPSH-YRBP relationship.In P2,the lower-tropospheric atmosphere in the tropical WNP gets warmer and wetter,and thus the meridional gradient of climatological equivalent potential temperature over the YRB is enhanced.As a result,the WNPSH-related circulation anomalies can more effectively induce YRB rainfall anomalies through affecting the meridional gradient of equivalent potential temperature over the YRB.

DECADAL CHANGES IN WESTERN NORTH PACIFIC TROPICAL CYCLONES ASSOCIATED WITH MADDEN-JULIAN OSCILLATION

This study focuses on the decadal variability of tropical cyclones(TC) over the Western North Pacific(WNP)and how these changes are related to the Madden-Julian Oscillation(MJO).It was done with the help of the Real-time Multivariate MJO index from the Australian Government Bureau of Meteorology of the Centre for Australian Weather and Climate Research,TC data from the Joint Typhoon Warming Center best track datasets,and daily and monthly datasets from the NCEP/NCAR reanalysis center.The results show that the TC frequency in the WNP exhibited a statistically significant decrease during 1998-2010 compared to during 1979-1997.The decrease in TC frequency in the WNP mainly occurred during MJO active phases(i.e.,phases 4,5,6,and 7).Further investigation of the climate background and the propagation differences of the MJO between 1979-1997 and 1998-2010 was performed.The La Nina-like tropical sea surface temperature cooling caused stronger Walker circulation and thus induced unfavorable atmosphere conditions for WNP TC genesis including a low-level easterly anomaly,a negative relative vorticity anomaly,an increase in sea-level pressure,and stronger vertical wind shear.Moreover,shortening of the MJO cycle,decline in the duration of the active phases in the WNP,and easterly anomaly and shrinkage of the convection area during MJO active phases may also partly explain the decadal variation of TC.

Decadal Changes in Climatological Intraseasonal Fluctuation of Subseasonal Evolution of Summer Precipitation over the Korean Peninsula in the mid-1990s

Decadal changes in the subseasonal evolution and the phase-locked climatological intraseasonal fluctuation of summertime rainfall over the Korean Peninsula before and after the mid-1990s are investigated.The activity and the migration speed of the monsoon rain band over the East Asian region are altered in the recent decade,resulting in the drier conditions in late spring and the earlier onset of Changma.In early August when a climatological monsoon break was clear in the earlier decade,the precipitation has increased dramatically with a meridional coherency.The response to the enhanced convection over the South China Sea and southeastern China provides a favorable condition for more precipitation in early August through the changes in moisture transport and tropical cyclone passage.

Dynamic-Analogue Correction of the Decadal Change of East Asian Summer Precipitation in the Late 1990s

This paper systematically evaluates the deviations that appear in the hindcasts of the East Asian summer precipitation（EASP） decadal change in the late 1990 s in two global coupled models（BCC-CGCM and BCC-CSM）.The possible causes for the deviations between the model hindcasts and observations are analyzed.The results show that the hindcasts of EASP by BCC-CGCM and BCC-CSM deviate from observations,with the anomaly correlation coefficient（ACC） being-0.01 and-0.09 for the two models,respectively.The SST anomalies in North and West Pacific and the SST index values predicted by the two models also deviate from the observations,indicating that inconsistent SST fields may be the key factor leading to the deviation in the prediction of the EASP decadal shift.Thus,a dynamic-analogue scheme is proposed to correct the precipitation hindcasts by using SSTs,where SST and EASP are highly correlated,to select historical analogue cases.Cross validations show that the average ACC of the temporal-latitude distribution of the EASP between the corrected hindcasts and observations is 0.18 for BCC-CGCM and0.02 for BCC-CSM;both are much higher than the uncorrected hindcasts.Applying the dynamic-analogue correction scheme in both models successfully improves prediction of the EASP decadal change in the late1990 s.

Decadal (2003–2013) changes in liana diversity,abundance and aboveground biomass in four inland tropical dry evergreen forest sites of peninsular India

In 2013, we re-inventoried all lianas （≥1 cm diameter measured at 1.3 m from the rooting point） in four I-ha permanent plots distributed one each in four sites of inland tropical dry evergreen forest on the Coromandel Coast （Pudukottai district） of peninsular India, established in 2003. Among the four sites, Shanmuganathapuram （SP） and Araiyapatti （AP） were much disturbed and the other two sites （Karisakkadu--KR and Maramadakki--MM） were moderately disturbed. We inventoried a total of 3425 lianas representing 37 species of 33 genera and 22 families. Over a decade （2003-2013） liana species richness increased at two sites （MM and SP） and no changes occurred at the other two sites. Liana abundance increased by 210, 211,164 and 162 individuals at sites AP, KR, MM and SP, respectively, and basal area increased （from 1.09 to 1.76 m2 at AP, 0.67 to 0.86 m2 at KR, 1.68 to 2.06 mz at MM, and from 0.44 to 1.06 m2 at SP）. Over a 10-year period, three species （Abrus precatorius, Canavalia virosa, and Cocculus hirsutus） were lost and five species （Gloriosa superba, Ampelocissus tomentosa, Capparis sepiaria, Aganosma cymosa and Tiliacora acuminata） were newly added. Total aboveground biomass increased by 18.5, 0.74, 3.6 and 9.5 Mg ha-1, respectively, at sites AP, KR, MM and SP.

Decadal Change of the Linkage between Sea Ice over the Barents–Kara Seas in November– December and the Stratospheric Polar Vortex in Subsequent January

The linkage between the sea ice concentration(SIC)over the Barents–Kara Seas in November–December(SIC_BKS_ND)and the stratospheric polar vortex(SPV)in subsequent January(SPV_Jan)is investigated.It is found that SIC_BKS_ND is positively(negatively)correlated with SPV_Jan for the period 1979–1995(1996–2009).Further analyses reveal that,during 1979–1995(1996–2009),SIC_BKS_ND is relatively higher(lower),accompanied by smaller(larger)interannual variability with its center shifting northwest(southeast).Meanwhile,the polar front jet waveguide is relatively stronger(weaker).The simultaneous anomalous eastward-propagating Rossby waves excited by anomalously low SIC_BKS_ND are stronger(weaker),which results in the stronger(weaker)negative–positive–negative wave-train structure of geopotential height anomalies over Eurasia,with the location of these anomalous height centers shifting remarkably westward(eastward).Such changes tend to enhance(suppress)vertically propagating tropospheric planetary waves into the lower stratosphere at high-latitude via constructive(destructive)interference of anomalous tropospheric wave-train structure with the climatological planetary waves,subsequently weakening(strengthening)SPV_Jan.However,in conjunction with anomalously high SIC_BKS_ND,the interference of the tropospheric wave-train structure anomalies and their climatologies shows an opposite distribution to that of low SIC_BKS_ND anomalies,which leads to a strong(weak)SPV_Jan anomaly during 1979–1995(1996–2009).

Forced Decadal Changes in Summer Precipitation Characteristics over China:The Roles of Greenhouse Gases and Anthropogenic Aerosols

We investigated the decadal changes in the different types of summer mean precipitation over China across the mid-1990 s based on observational datasets.The spatial variations in the observed decadal changes were estimated by comparing the present day(PD)time period of 1994–2011 with an earlier period of 1964–1981.The summer total precipitation increased in southern China and decreased in northern China from the early period to the PD.The increases of precipitation in southern China were due to increases in the frequency of heavy and moderate rainfall,whereas the decreases over northern China were mainly due to decreases in the frequency of moderate and light rainfall.Based on a set of numerical experiments using an atmospheric general circulation model coupled with a multilevel mixed-layer ocean model,we found that the increase of precipitation frequency forced by greenhouse gases is the main reason of increasing precipitation over southern and northeastern China,while the decrease of frequency caused by anthropogenic aerosol(AA)induces the decreasing precipitation over northern China.The water vapor flux convergence and water vapor flux strengthen in southern China and northeastern China by anthropogenic greenhouse gases.This distribution is also conducive to precipitation in most of southern China and northeastern China.Under the control of weakened southwesterly winds and 850-h Pa divergence,precipitation decreases over northern and southwestern China by AA.

Impacts of the upper-ocean salinity variations on the decadal sea level change in the Southeast Indian Ocean during the Argo era

In the past nearly two decades,the Argo Program has created an unprecedented global observing array with continuous in situ salinity observations,providing opportunities to extend our knowledge on the variability and effects of ocean salinity.In this study,we utilize the Argo data during 2004–2017,together with the satellite observations and a newly released version of ECCO ocean reanalysis,to explore the decadal salinity variability in the Southeast Indian Ocean(SEIO)and its impacts on the regional sea level changes.Both the observations and ECCO reanalysis show that during the Argo era,sea level in the SEIO and the tropical western Pacific experienced a rapid rise in 2005–2013 and a subsequent decline in 2013–2017.Such a decadal phase reversal in sea level could be explained,to a large extent,by the steric sea level variability in the upper 300 m.Argo data further show that,in the SEIO,both the temperature and salinity changes have significant positive contributions to the decadal sea level variations.This is different from much of the Indo-Pacific region,where the halosteric component often has minor or negative contributions to the regional sea level pattern on decadal timescale.The salinity budget analyses based on the ECCO reanalysis indicate that the decadal salinity change in the upper 300 m of SEIO is mainly caused by the horizontal ocean advection.More detailed decomposition reveals that in the SEIO,there exists a strong meridional salinity front between the tropical low-salinity and subtropical high salinity waters.The meridional component of decadal circulation changes will induce strong cross-front salinity exchange and thus the significant regional salinity variations.

THE DIRECT EFFECTS OF AEROSOLS AND DECADAL VARIATION OF GLOBAL SEA SURFACE TEMPERATURE ON THE EAST ASIAN SUMMER PRECIPITATION IN CAM3.0

Using the CAM3.0 model, we investigated the respective effects of aerosol concentration increasing and decadal variation of global sea surface temperature(SST) around year 1976/77 on the East Asian precipitation in boreal summer. By doubling the concentration of the sulfate aerosol and black carbon aerosol separately and synchronously in East Asia(100-150 °E, 20-50 °N), the climate effects of these aerosols are specifically investigated. The results show that both the decadal SST changing and aerosol concentration increasing could lead to rainfall decreasing in the center of East Asia, but increasing in the regions along southeast coast areas of China. However, the different patterns of rainfall over ocean and lower wind field over Asian continent between aerosol experiments and SST experiments in CAM3.0 indicate the presence of different mechanisms. In the increased aerosol concentration experiments, scattering effect is the main climate effect for both sulfate and black carbon aerosols in the Eastern Asian summer. Especially in the increased sulfate aerosol concentration experiment, the climate scattering effect of aerosol leads to the most significant temperature decreasing, sinking convection anomalies and decreased rainfall in the troposphere over the central part of East Asia. However, in an increased black carbon aerosol concentration experiment, weakened sinking convection anomalies exist at the southerly position. This weakened sinking and its compensating rising convection anomalies in the south lead to the heavy rainfall over southeast coast areas of China. When concentrations of both sulfate and black carbon aerosols increase synchronously, the anomalous rainfall distribution is somewhat like that in the increased black carbon concentration aerosol experiment but with less intensity.

Xigaze: Decade of Change

Ｘｉｇａｚｅ：Ｄｅｃａｄｅ ｏｆ ＣｈａｎｇｅＸｉｇａｚｅ：ＤｅｃａｄｅｏｆＣｈａｎｇｅ￥ＳＯＩＮＡＭＤＡＧＹＩＸｉｇａｚｅ，ｔｈｅｓｅｃｏｎｄｌａｒｇｅｓｔｃｉｔｙｉｎＴｉｂｅｔｌｏｃａｔｅｄｏｎｔｈｅｎｏｒｔｈｅｒｎｓｌｏｐｅｓｏｆｔｈｅＨｉｍａ...

A Decade of Complete Change in a Muslim Community

Talking about changes in the Muslim-inhabited Niu Jie Street of Beijing, every member of the community would be all smiles. ＂Everything has changed; the mosque, the streetscape and the people, too,＂ they would say.

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

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.

Interdecadal Variations of ENSO Impacts over the Indo-Northwest Pacific Region and the Related Mechanisms

Owing to limited observations,it remains unknown whether the impact of El Niño-Southern Oscillation(ENSO)on the Indian Ocean-Northwest Pacific(IO-NWP)climate showed decadal changes in the early 20th century.Using multi-source reanalysis and hindcast datasets from the ECMWF and NOAA extending back to 1901,this study investigates interdecadal variations of the impact of ENSO on the IO-NWP climate from 1901 to 2009.It is found that the influence of ENSO on the IO-NWP climate shows“strong-weak-strong”interdecadal change during 1901-2009.This is characterized by much weaker Indian Ocean sea surface temperature(SST)warming and a weaker NWP subtropical anticyclone(NWPSA)in the following summer of El Ni?o during 1946-1967,compared with those in the other two periods(1901-1945 and 1968-2009).Analyses of the datasets indicate that the interdecadal variation is mainly associated with the change in ENSO amplitude.In contrast to the period of 1946-1967,a greater SST variance occurred in the central-eastern equatorial Pacific during 1901-1945 and 1968-2009.A stronger El Ni?o tends to generate more significant anticyclonic anomalies over the southeast Indian Ocean through teleconnection.The northwesterly anomalies to the south of the anticyclone weaken the southeast trade winds and warm the south Indian Ocean SST via wind-evaporation-SST feedback,and the positive south Indian Ocean SST anomalies trigger westward-propagating oceanic Rossby waves to induce stronger warming of the southwest Indian Ocean,leading to a significant asymmetric wind pattern across the equator in spring.The profound northeastward winds on the north side weaken the southwest monsoon,leading to a“second warming”over the north Indian Ocean in summer,which anchors the eastward-propagating warm Kelvin waves and results in a stronger NWPSA by inducing surface divergence and suppressing deep convection.

The decadal abrupt change in the global land vapor pressure deficit

The vapor pressure deficit(VPD) is an important variable used to characterize atmospheric aridity.This paper analyses the spatial and temporal characteristics of the decadal abrupt change(DAC) in the global land VPD after 1980 using monthly scale data from the Climatic Research Unit.The results show that 60.5% of the global land area underwent a significantly increased decadal abrupt change(IDAC) in the VPD,and the persistent IDAC of the VPD was obvious in the middle and low latitudes of Eurasia,Africa and parts of South America but not in central North America or Western Siberia.From 1980 to 2020,most regions experienced no more than two persistent IDACs,while more than two significant increases occurred mainly around the Mediterranean and in eastern South America.The persistent IDAC occurred relatively early in the middle and low latitudes of Eurasia,Africa,and eastern South America and after 2000 in the high latitude regions,Eastern Europe,and near the Qinghai-Tibet Plateau.The regions where the persistent IDAC lasted longer than 10 years mainly included North Africa,West Asia,eastern South America,and parts of East Asia,indicating that the persistent increases in atmospheric aridity in these regions were obvious.In general,the persistent IDAC that began in 1993–2000 was significantly more than that occurred in other periods and lasted longer than that before 1990,suggesting that the land area experiencing an abrupt increase has an expansion after the 1990s and that the role of water limitation in this persistent IDAC in Central Asia and most of China strengthened.In addition,the VPD showed another large-scale persistent IDAC over the global land region in 2009,indicating that global atmospheric aridity intensified over the last decade.At the same time,in a few global regions,the VPD has exhibited decreased decadal abrupt changes(DDACs) with durations shorter than 2 years.

Has the East Asian Westerly Jet Experienced a Poleward Displacement in Recent Decades?

Previous studies have suggested a poleward shift of the zonally averaged jet stream due to rapid warming over continents.However,the regional characteristics of the change in the jet stream are not yet understood.Here,we present evidence suggesting that the East Asian westerly jet did not shift poleward in past decades（1980-2004 relative to 1958-1979）,both in winter and summer.Rather,the jet axis has moved southward in summer,but its meridional position is steady in winter.The main change of the jet stream in winter is the enhancement of its intensity.These changes in both summer and winter are consistent with the corresponding changes in the large meridional tropospheric temperature-gradient zone.Based on these results,we suggest that the changes of the jet stream over East Asia are unique and are different from the zonal mean jet stream over the Northern Hemisphere and over the North Atlantic region.

Contribution of South China Sea Tropical Cyclones to an Increase in Southern China Summer Rainfall Around 1993

The increase in southern China summer rainfall around 1993 was accompanied by an increase in tropical cyclones that formed in the South China Sea. This study documents the connection of these two features. Our analysis shows that the contribution of tropical cyclones that formed in the South China Sea to southern China summer rainfall experienced a significant increase around 1993, in particular, along the coast and in the heavy rain category. The number of tropical cyclones that formed in the western North Pacific and entered the South China Sea decreased, and their contribution to summer rainfall was reduced in eastern part of southern China （but statistically insignificant）. The increase in tropical cyclone-induced rainfall contributed up to -30＆ of the total rainfall increase along the coastal regions. The increase of tropical cyclones in the South China Sea appears to be related to an increase in local sea surface temperature.

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

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.

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

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.

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

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 s.It 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 s.Different 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 structure.Before 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 latitude.After 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 latitude.These 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 decades.The 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 decades.These results may have important implications for assessing the latitudinal distributions of TC-induced hazards.