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 2000.It 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 July.When 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 July.It 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 EASM.Moreover,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 hPa.All the above tend to suppress the precipitation in the Yangtze and Huaihe River valley.The 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.
Against a background of climate change, Macao is very exposed to sea level rise(SLR) because of its low elevation,small size, and ongoing land reclamation. Therefore, we evaluate sea level changes in Macao, both historical and, especially,possible future scenarios, aiming to provide knowledge and a framework to help accommodate and protect against future SLR. Sea level in Macao is now rising at an accelerated rate: 1.35 mm yr-1over 1925–2010 and jumping to 4.2 mm yr-1over 1970–2010, which outpaces the rise in global mean sea level. In addition, vertical land movement in Macao contributes little to local sea level change. In the future, the rate of SLR in Macao will be about 20% higher than the global average, as a consequence of a greater local warming tendency and strengthened northward winds. Specifically, the sea level is projected to rise 8–12, 22–51 and 35–118 cm by 2020, 2060 and 2100, respectively, depending on the emissions scenario and climate sensitivity. Under the +8.5 W m-2Representative Concentration Pathway(RCP8.5) scenario the increase in sea level by2100 will reach 65–118 cm—double that under RCP2.6. Moreover, the SLR will accelerate under RCP6.0 and RCP8.5, while remaining at a moderate and steady rate under RCP4.5 and RCP2.6. The key source of uncertainty stems from the emissions scenario and climate sensitivity, among which the discrepancies in SLR are small during the first half of the 21 st century but begin to diverge thereafter.
In this paper, we mainly summarize and review the progresses in recent climatological studies(by CMSR,IAP/CAS and some associated domestic and international institutions) on the interannual and interdecadal variabilities of monsoon troughs and their impacts on tropical cyclones and typhoons(TCs) geneses over the western North Pacific Ocean. The climatological characteristics of monsoon troughs and four types of circulation patterns favorable to TCs genesis over the western North Pacific Ocean in summer and autumn are given in this paper. It is also shown in this paper that the monsoon trough over the western North Pacific Ocean has obvious interannual and interdecadal variabilities. Especially, it is revealed in this paper that the interannual and interdecadal variabilities of the monsoon trough over the western North Pacific Ocean influence the TCs genesis not only through the impact on distributions of the vorticity in the lower troposphere and the divergence in the upper troposphere, the water vapor in the mid-and lower troposphere and the vertical shear of wind fields between the upper and lower troposphere over the western North Pacific Ocean, but also through the dynamical effects of the transition between convectively coupled tropical waves and providing disturbance energy. Besides, some climatological problems associated with TCs activity over the western North Pacific Ocean that need to be studied further are also pointed out in this paper.
This study investigated interdecadal variability of June–October(JJASO) the large and small warm pools in western Pacific and their association with rainfall anomalies using station and reanalysis data from 1958 to 2008.The results indicated that the large and small warm pools in western Pacific showed an interdecadal shift around 1986.The large warm pool years over western Pacific were found after 1986,whereas the small warm pool years were often seen throughout the periods before 1986.The analysis results also showed that there were obvious interdecadal variability in JJASO rainfall in Southeast China and warm pool in western Pacific.During 1958–1985(small warm pool years),the decrease in rainfall was associated with tropospheric moisture divergence and sinking motion over Southeast China and warm pool in western Pacific.However,during 1986–2008(large warm pool years),the increase in rainfall was associated with tropospheric moisture convergence and ascending motion.Further analysis showed that large warm pool contributed to the increase in surface latent heat fluxes over warm pool in the western Pacific.Thus,there was an increase in the amount of water vapor over Southeast China and warm pool in western Pacific,which contributed to increased rainfall in these regions.
The clustering of severe and sustained droughts in Southwest China(SWC)during the last decade has resulted in tremendous losses,including crop failure,a lack of drinking water,ecosystem destruction,health problems,and even deaths.Various attempts have been made to explore the variability and causes of drought in SWC.Here,the authors summarize and integrate this accumulated but fragmented knowledge.On the whole,general agreement has been reached on the evolution of drought in SWC,which has become more frequent and intense during the past 50 years and is projected to continue throughout the 21st century.However,it is unclear and even disputable as to what and how sea surface temperatures and circulation oscillation patterns affect the drought condition.Meanwhile,the presence of strong nonlinearity places considerable challenges in both understanding and predicting drought in SWC.Therefore,much remains to be learned concerning the mechanisms responsible for drought disasters in SWC and accurate forecast practice.In addition to pursuing research on factors and processes involved in drought formation,above all,there is an urgent need to develop appropriate strategies and plans for mitigating the threats of drought.
The effect of uniform zonal winds on tropical cyclone(TC)genesis is examined on a beta plane using an idealized mesoscale model.The simulation results show that uniform easterly and westerly flows are both favorable for TC genesis.However,uniform easterly flows result in a faster TC genesis rate compared with uniform westerly flows.It is found that faster TC genesis is associated with greater surface heat fluxes and convection during the early stage.The superposition of uniform easterly flows and the beta effect results in greater surface heat fluxes and convection around the TC center compared with uniform westerly flows.Meanwhile,TC genesis is closely associated with the size and intensity of a mid-level circulation.The joint greater convection induced by the easterly flows and beta effect results in enhancement of the vertical temperature gradient,which is associated with the intensification of mid-level circulation.The strong and compact mid-level circulation is more favorable for efficient conversion of latent heat energy to the kinetic energy of the lower-level cyclonic winds.Thus,uniform easterly flows are more favorable for TC genesis than uniform westerly flows.
In the last decade, a series of severe and extensive droughts have swept across Southwest China, resulting in tremendous economic losses, deaths, and disruption to society. Consequently, this study is motivated by the paramount importance of assessing future changes in drought in Southwest China. Precipitation is likely to decrease over most parts of Southwest China around the beginning of the century, followed by widespread precipitation increases; the increase in potential evapotranspiration(PET), due to the joint effects of increased temperature and surface net radiation and decreased relative humidity,will overwhelm the whole region throughout the entire 21 st century. In comparative terms, the enhancement of PET will outweigh that of precipitation, particularly under Representative Concentration Pathway(RCP) 8.5, resulting in intensified drought. Generally, the drying tendency will be in the southeast portion, whereas the mountainous region in the northwest will become increasingly wetter owing to abundant precipitation increases. Droughts classified as moderate/severe according to historical standards will become the norm in the 2080 s under RCP4.5/RCP8.5. Future drought changes will manifest different characteristics depending on the time scale: the magnitude of change at a time scale of 48 months is nearly twice as great as that at 3 months. Furthermore, we will see that not only will incidences of severe and extreme drought increase dramatically in the future, but extremely wet events will also become more probable.
Based on several reanalysis and observational datasets,this study demonstrates that the East Asian winter monsoon(EAWM)recovered from its weak epoch and reamplified in the mid-2000s.Accordingly,East Asia has experienced more cold winters and significant negative surface air temperature anomalies during the recent strong EAWM epoch spanning the period 2004–2012.The associated cooling was mainly located over inland northern East Asia with a west–east orientation.The cooling generally coincided with negative winter temperature trends in eastern Eurasia in the last two decades,possibly contributing to the observed regional cooling trend when the global mean temperature is still trending up.Enhanced wintertime blocking activity around the Ural mountain region and diminished Arctic sea ice concentration in the previous September are suggested to be the responsible internal atmospheric process and external driver for the recent re-amplification of the EAWM,respectively.
An interdecadal shift in the onset date of the South China Sea summer monsoon(SCSSM) is identified during the late 1990 s by using the European Centre for Medium-Range Weather Forecasts Interim Reanalysis dataset. The mean onset date was brought forward by two pentads during 1999–2013 compared to that during 1979–1998. The large-scale atmospheric and oceanic change associated with this shift exhibits a significant interdecadal variation signal around 1998/1999, indicating that the shift during the late 1990 s is robust. Different from the well-known mid-1990 s shift, this shift carried more important systematical significance. Diagnostic analysis suggests that the earlier outbreak of the SCSSM was due to the interdecadal warming of the warm pool, which brought stronger convection anomalies and led to a weak western Pacific subtropical high(WPSH) during boreal spring(March–May). The earlier retreat of the WPSH was a direct cause of this shift.
This study documents a weakening of the relationship between the spring Arctic Oscillation(AO) and the following summer tropical cyclone(TC) formation frequency over the eastern part(150?–180?E) of the western North Pacific(WNP). The relationship is strong and statistically significant during 1968–1986,but becomes weak during 1989–2007. The spring AOrelated SST,atmospheric dynamic,and thermodynamic conditions are compared between the two epochs to understand the possible reasons for the change in the relationship. Results indicate that the spring AO leads to an El Ni ?no-like SST anomaly,lower-level anomalous cyclonic circulation,upper-level anomalous anticyclonic circulation,enhanced ascending motion,and a positive midlevel relative humidity anomaly in the tropical western–central Pacific during 1968–1986,whereas the AOrelated anomalies in the above quantities are weak during 1989–2007. Hence,the large-scale dynamic and thermodynamic anomalies are more favorable for TC formation over the eastern WNP during 1968–1986 than during 1989–2007.
CAO XiCHEN ShangfengCHEN GuanghuaCHEN WenWU Renguang
