Influence of the Asian-Pacific Oscillation on Spring Precipitation over Central Eastern China

The linkage between the Asian-Pacific oscillation(APO)and the precipitation over central eastern China in spring is preliminarily addressed by use of the observed data.Results show that they correlate very well,with the positive(negative)phase of APO tending to increase(decrease)the precipitation over central eastern China.Such a relationship can be explained by the atmospheric circulation changes over Asia and the North Pacific in association with the anomalous APO.A positive phase of APO,characterized by a positive anomaly over Asia and a negative anomaly over the North Pacific in the upper-tropospheric temperature,corresponds to decreased low-level geopotential height(H)and increased high-level H over Asia,and these effects are concurrent with increased low-level H and decreased high-level H over the North Pacific.Meanwhile,an anticyclonic circulation anomaly in the upper troposphere and a cyclonic circulation anomaly in the lower troposphere are introduced in East Asia,and the low-level southerly wind is strengthened over central eastern China.These changes provide advantageous conditions for enhanced precipitation over central eastern China.The situation is reversed in the negative phase of APO,leading to reduced precipitation in this region.     

ASIAN-PACIFIC OSCILLATION IN AUTUMN AND ITS RELATIONSHIPS WITH THE SUBTROPICAL MONSOON IN EAST ASIA

Based on the 1961-2010 NCEP/NCAR reanalysis, this work uses empirical orthogonal function(EOF) and composite analysis to study the distributions of zonal land-sea thermal contrast between Asia and the Pacific during transitions from the summer monsoon to the winter monsoon in East Asian subtropics, and investigates the interannual variations of the thermal contrast and their relationships with circulation systems over the East Asian subtropics. The findings are as follows. 1) In autumn, the interannual variations of the temperature deviation in the middle and upper troposphere show significant east-west out-of-phase teleconnection over Asia and the central and eastern Pacific, i.e. the Asian-Pacific Oscillation, or APO. 2) While not as significant as in summer with regard to coverage and intensity, the APO shows interannual variations in autumn that well depicts the change in the intensity of the subtropical monsoon. In the high(low) APO year, the current subtropical summer monsoon is strong(weak) and the winter monsoon is weak(strong) in East Asia as derived from the general circulation and wind field of the East Asian-Pacific region.     

On the relationship between the winter Eurasian teleconnection pattern and the following summer precipitation over China

The Eurasian teleconnection pattern(EU) is an important low-frequency pattern with well-known impacts on climate anomalies in Eurasia. The difference of low-level v-winds in several regions in the Eurasian mid–high latitudes is defined as the EU index(EUIV). In this study, the relationship between the winter EUIVand precipitation in the following summer over China is investigated. Results show that there is a significant positive(negative) correlation between the winter EUIVand the following summer precipitation over North China(the Yangtze River–Huaihe River basins). Meanwhile, an interdecadal variability exists in the interannual relationship, and the correlation has become significantly enhanced since the early 1980 s.Thus, the proposed EUIVmay have implications for the prediction of summer precipitation anomalies over China. In positive winter EUIVyears, three cyclonic circulation anomalies are observed—over the Ural Mountains, the Okhotsk Sea, and the subtropical western North Pacific. That is, the Ural blocking and Okhotsk blocking are inactive, zonal circulation prevails in the mid–high latitudes, and the western Pacific subtropical high tends to be weaker and locates to the north of its normal position in the following summer. This leads to above-normal moisture penetrating into the northern part of East China, and significant positive(negative) precipitation anomalies over North China(the Yangtze River–Huaihe River basins), and vice versa. Further examination shows that the SST anomalies over the Northwest Pacific and subtropical central North Pacific may both contribute to the formation of EUIV-related circulation anomalies over the western North Pacific.     

Statistical Downscaling for Multi-Model Ensemble Prediction of Summer Monsoon Rainfall in the Asia-Pacific Region Using Geopotential Height Field

The 21-yr ensemble predictions of model precipitation and circulation in the East Asian and western North Pacific （Asia-Pacific） summer monsoon region （0°-50°N, 100° 150°E） were evaluated in nine different AGCM, used in the Asia-Pacific Economic Cooperation Climate Center （APCC） multi-model ensemble seasonal prediction system. The analysis indicates that the precipitation anomaly patterns of model ensemble predictions are substantially different from the observed counterparts in this region, but the summer monsoon circulations are reasonably predicted. For example, all models can well produce the interannual variability of the western North Pacific monsoon index （WNPMI） defined by 850 hPa winds, but they failed to predict the relationship between WNPMI and precipitation anomalies. The interannual variability of the 500 hPa geopotential height （GPH） can be well predicted by the models in contrast to precipitation anomalies. On the basis of such model performances and the relationship between the interannual variations of 500 hPa GPH and precipitation anomalies, we developed a statistical scheme used to downscale the summer monsoon precipitation anomaly on the basis of EOF and singular value decomposition （SVD）. In this scheme, the three leading EOF modes of 500 hPa GPH anomaly fields predicted by the models are firstly corrected by the linear regression between the principal components in each model and observation, respectively. Then, the corrected model GPH is chosen as the predictor to downscale the precipitation anomaly field, which is assembled by the forecasted expansion coefficients of model 500 hPa GPH and the three leading SVD modes of observed precipitation anomaly corresponding to the prediction of model 500 hPa GPH during a 19-year training period. The cross-validated forecasts suggest that this downscaling scheme may have a potential to improve the forecast skill of the precipitation anomaly in the South China Sea, western North Pacific and the East Asia Pacific regions, wh     

Summer Asian-Pacific Oscillation and Its Relationship with Atmospheric Circulation and Monsoon Rainfall

Using the ERA-40 data and numerical simulations, this study investigated the teleconnection over the extratropical Asian-Pacific region and its relationship with the Asian monsoon rainfall and the climatological characteristics of tropical cyclones over the western North Pacific, and analyzed impacts of the Tibetan Plateau （TP） heating and Pacific sea surface temperature （SST） on the teleconnection. The Asian-Pacific oscillation （APO） is defined as a zonal seesaw of the tropospheric temperature in the midlatitudes of the Asian-Pacific region. When the troposphere is cooling in the midlatitudes of the Asian continent, it is warming in the midlatitudes of the central and eastern North Pacific; and vice versa. The APO also appears in the stratosphere, but with a reversed phase. Used as an index of the thermal contrast between Asia and the North Pacific, it provides a new way to explore interactions between the Asian and Pacific atmospheric circulations. The APO index exhibits the interannual and interdecadal variability. It shows a downward trend during 1958-2001, indicating a weakening of the thermal contrast, and shows a 5.5-yr oscillation period. The formation of the APO is associated with the zonal vertical circulation caused by a difference in the solar radiative heating between the Asian continent and the North Pacific. The numerical simulations further reveal that the summer TP heating enhances the local tropospheric temperature and upward motion, and then strengthens downward motion and decreases the tropospheric temperature over the central and eastern North Pacific. This leads to the formation of the APO. The Pacific decadal oscillation and El Nino/La Nina over the tropical eastern Pacific do not exert strong influences on the APO. When there is an anomaly in the summer APO, the South Asian high, the westerly jet over Eurasia, the tropical easterly jet over South Asia, and the subtropical high over the North Pacific change significantly, with anomalous Asian monsoon rainfall and tropical cyclon     

Tropical Cyclones over the Western North Pacific Strengthen the East Asia–Pacific Pattern during Summer

The contribution of tropical cyclones(TCs)to the East Asia–Pacific(EAP)teleconnection pattern during summer was investigated using the best track data of the Joint Typhoon Warning Center and NCEP-2 reanalysis datasets from 1979 to2018.The results showed that the TCs over the western North Pacific(WNP)correspond to a strengthened EAP pattern:During the summers of strong convection over the tropical WNP,TC days correspond to a stronger cyclonic circulation anomaly over the WNP in the lower troposphere,an enhanced seesaw pattern of negative and positive geopotential height anomalies over the subtropical WNP and midlatitude East Asia in the middle troposphere,and a more northward shift of the East Asian westerly jet in the upper troposphere.Further analyses indicated that two types of TCs with distinctly different tracks,i.e.,westward-moving TCs and northward-moving TCs,both favor the EAP pattern.The present results imply that TCs over the WNP,as extreme weather,can contribute significantly to summer-mean climate anomalies over the WNP and East Asia.     

Diversity of the Coupling Wheels in the East Asian Summer Monsoon on the Interannual Time Scale: Challenge of Summer Rainfall Forecasting in China

Two types of three-dimensional circulation of the East Asian summer monsoon(EASM) act as the coupling wheels determining the seasonal rainfall anomalies in China during 1979–2015. The first coupling mode features the interaction between the Mongolian cyclone over North Asia and the South Asian high(SAH) anomalies over the Tibetan Plateau at 200 hPa. The second mode presents the coupling between the anomalous low-level western Pacific anticyclone and upperlevel SAH via the meridional flow over Southeast Asia. These two modes are responsible for the summer rainfall anomalies over China in 24 and 7 out of 37 years, respectively. However, the dominant SST anomalies in the tropical Pacific, the Indian Ocean, and the North Atlantic Ocean fail to account for the first coupling wheel's interannual variability, illustrating the challenges in forecasting summer rainfall over China.     

Relationship Between Upper-Ocean Heat Content in the Tropical Indian Ocean and Summer Precipitation in China

An analysis of the Ishii ocean heat content(OHC) in the tropical Indian Ocean from the surface to 700-m depth shows that the OHC changes dramatically on the interannual timescale in the Indian Ocean.The first mode of empirical orthogonal function(EOF1) of the OHC shows that there is a strong air-sea interaction pattern in the Indian Ocean with a positive(negative) loading in the east and a negative(positive) loading in the west.This seesaw oscillation pattern influences the summer precipitation in China with a North-South reversed distribution.Composite analysis shows that during a positive(negative) OHC episode,an anomalous cyclonic(anticyclonic) circulation over the western Pacific and South China weakens(enhances) the monsoonal northward flow in the lower troposphere;meanwhile,anomalous meridional circulation connects the descending(ascending) branch over the Southeast Indian Ocean and the ascending(descending) branch in South China as well as a descending(ascending) branch over North China.Analysis of the mechanism behind these features suggests that(1) the accumulation of OHC-induced vorticity is related to the wave activity over the mid-latitudes and that(2) the meridional teleconnection induced by the Indo-Pacific air-OHC interaction appears over East Asia and the western Pacific.Both of these patterns can cause summer precipitation anomalies in China.     

Interannual Variability of Autumn Precipitation over South China and its Relation to Atmospheric Circulation and SST Anomalies

The interannual variability of autumn precipitation over South China and its relationship with atmospheric circulation and SST anomalies are examined using the autumn precipitation data of 160 stations in China and the NCEP-NCAR reanalysis dataset from 1951 to 2004. Results indicate a strong interannual variability of autumn precipitation over South China and its positive correlation with the autumn western Pacific subtropical high （WPSH）. In the flood years, the WPSH ridge line lies over the south of South China and the strengthened ridge over North Asia triggers cold air to move southward. Furthermore, there exists a significantly anomalous updraft and cyclone with the northward stream strengthened at 850 hPa and a positive anomaly center of meridional moisture transport strengthening the northward warm and humid water transport over South China. These display the reverse feature in drought years. The autumn precipitation interannual variability over South China correlates positively with SST in the western Pacific and North Pacific, whereas a negative correlation occurs in the South Indian Ocean in July. The time of the strongest lag-correlation coefficients between SST and autumn precipitation over South China is about two months, implying that the SST of the three ocean areas in July might be one of the predictors for autumn precipitation interannual variability over South China. Discussion about the linkage among July SSTs in the western Pacific, the autumn WPSH and autumn precipitation over South China suggests that SST anomalies might contribute to autumn precipitation through its close relation to the autumn WPSH.     

RESEARCH ON THE INTERANNUAL AND INTERDECADAL VARIABILITIES OF THE MONSOON TROUGH AND THEIR IMPACTS ON TROPICAL CYCLONE GENESIS OVER THE WESTERN NORTH PACIFIC OCEAN

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.     

The Oscillation between Tropical Indian Ocean and North Pacific:Evidence and Possible Impact on Winter Climate in China

This paper provides evidence that the variation of boreal winter sea level pressure (SLP) over the North Pacific is out-of-phase with SLP fluctuation over the tropical Indian Ocean on both the interdecadal and interannual time scales.Subsequently,a SLP between tropical Indian Ocean and North Pacific (TIO-NP) oscillation index is defined to indicate the variation of such out-of-phase fluctuation.Moreover,the simultaneous surface air temperature and precipitation anomalies in China are closely related to TIO-NP oscillations.Below-normal surface air temperature anomalies in the northern and the eastern part of China,and less rainfall in southern China,correspond to positive TIO-NP oscillation phase with negative SLP anomalies in tropical Indian Ocean and positive anomalies in North Pacific.The TIO-NP oscillation affects China’s winter climate anomalies,possibly through modulating the northeast East Asia winter monsoon.     

On the Relationship between the Northern Limit of Southerly Wind and Summer Precipitation over East China

The relationship between the summer northernmost position of southerly wind and precipitation over East China is investigated. The northern limit of summer southerly wind index(INLSSW) over East China is defined as the latitude where the zonal-averaged(105–120°E)low-level meridional wind is equal to zero. Results show that there is a significant negative(positive) correlation between INLSSW and summer precipitation over the Yangtze River(North China) region. Thus, the proposed INLSSW may have implications for the prediction of summer precipitation anomalies in these regions. In positive INLSSW years, a cyclonic circulation anomaly is observed over the tropical western North Pacific and an anticyclonic circulation anomaly is seen over the subtropics of East China,accompanied by southerly anomalies over East China.This leads to above-normal moisture penetrating into the northern part of East China. In addition, significant upward(downward) motion anomalies can be found over the North China(Yangtze River) region. As a result, there are significant positive(negative) precipitation anomalies over the North China(Yangtze River) region. Further examination shows that sea surface temperature anomalies over the tropical eastern Pacific and Indian Ocean both contribute to the formation of INLSSW-related circulation anomalies over the tropical western North Pacific.     

The Summer Snow Cover Anomaly over the Tibetan Plateau and Its Association with Simultaneous Precipitation over the Mei-yu–Baiu region

The summer snow anomalies over the Tibetan Plateau （TP） and their effects on climate variability are often overlooked,possibly due to the fact that some datasets cannot properly capture summer snow cover over high terrain.The satellite-derived Equal-Area Scalable Earth grid （EASE-grid） dataset shows that snow still exists in summer in the western part and along the southem flank of the TP.Analysis demonstrates that the summer snow cover area proportion （SCAP） over the TP has a significant positive correlation with simultaneous precipitation over the mei-yu-baiu （MB） region on the interannual time scale.The close relationship between the summer SCAP and summer precipitation over the MB region could not be simply considered as a simultaneous response to the Silk Road pattern and the SST anomalies in the tropical Indian Ocean and tropical central-eastern Pacific.The SCAP anomaly has an independent effect and may directly modulate the land surface heating and,consequently,vertical motion over the western TP,and concurrently induce anomalous vertical motion over the North Indian Ocean via a meridional vertical circulation.Through a zonal vertical circulation over the tropics and a Kelvin wave-type response,anomalous vertical motion over the North Indian Ocean may result in an anomalous high over the western North Pacific and modulate the convective activity in the western Pacific warm pool,which stimulates the East Asia-Pacific （EAP） pattern and eventually affects summer precipitation over the MB region.     

A Simulation of the Upper-Tropospheric Temperature Pattern in BCC_CSM1.1

A simulation of the upper-tropospheric temperature (UTT) by the Beijing Climate Center Climate System Model version 1.1 (BCC_CSM1.1) model is evaluated through a comparison with NCEP/NCAR reanalysis data. It is shown that this model has the ability to simulate the climate pattern of the UTT in all four seasons. The spatial correlation on the climatological distribution between the simulation and the observation is 0.92, 0.93, 0.90, and 0.93 for spring, summer, autumn, and winter, respectively. The first leading mode of the UTT in the simulation agrees with that in the observation, except that the simulated second leading mode corresponds to the observed first leading mode in spring. The standard deviation distribution of the simulation is also roughly consistent with the observation, with a pattern coefficient of 0.82, 0.78, 0.82, and 0.82 in spring, summer, autumn, and winter, respectively. The potential UTT change in the second half of the 21st century under the Representative Concentration Pathway 8.5 (RCP8.5) scenario is examined. The prominent change is that the summer UTT will increase over Eurasia and decrease over the North Pacific compared with the present, indicating that the zonal thermal contrast between Asia and the North Pacific will be strengthened within the context of future global warming. The intensity of the interannual variability of the UTT over the Asian-Pacific region is also generally increased. The zonal thermal contrast between Asia and the North Pacific will tend to be enhanced in winter, concurrent with the intensified interannual variability.     

The interannual variation in monthly temperature over Northeast China during summer

The interannual variations of summer surface air temperature over Northeast China （NEC） were investigated through a month-to-month analysis from May to August. The results suggested that the warmer temperature over NEC is related to a local positive 500-hPa geopotential height anomaly for all four months. However, the teleconnection patterns of atmospheric circulation anomalies associated with the monthly surface air temperature over NEC behave as a distinguished subseasonal variation, although the local positive height anomaly is common from month to month. In May and June, the teleconnection pattern is characterized by a wave train in the upper and middle troposphere from the Indian Peninsula to NEC. This wave train is stronger in June than in May, possibly due to the positive feedback between the wave train and the South Asian rainfall anomaly in June, when the South Asian summer monsoon has been established. In July and August, however, the teleconnection pattern associated with the NEC temperature anomalies is characterized by an East Asia/Pacific （EAP） or Pacific/Japan （PJ） pattern, with the existence of precipitation anomalies over the Philippine Sea and the South China Sea. This pattern is much clearer in July corresponding to the stronger convection over the Philippine Sea compared to that in August.     

Response of the Asian summer monsoon to weakening of Atlantic thermohaline circulation

Various paleoclimate records have shown that the Asian monsoon was punctuated by numerous suborbital time-scale events, and these events were coeval with those that happened in the North Atlantic. This study investigates the Asian summer monsoon responses to the Atlantic Ocean forcing by applying an additional freshwater flux into the North Atlantic. The simulated results indicate that the cold North Atlantic and warm South Atlantic induced by the weakened Atlantic thermohaline circulation （THC） due to the freshwater flux lead to significantly suppressed Asian summer monsoon. The authors analyzed the detailed processes of the Atlantic Ocean forcing on the Asian summer monsoon, and found that the atmospheric teleconnection in the eastern and central North Pacific and the atmosphere-ocean interaction in the tropical North Pacific play the most crucial role. Enhanced precipitation in the subtropical North Pacific extends the effects of Atlantic Ocean forcing from the eastern Pacific into the western Pacific, and the atmosphere-ocean interaction in the tropical Pacific and Indian Ocean intensifies the circulation and precipitation anomalies in the Pacific and East Asia.     

Joint Effect of East Asia–Pacific and Eurasian Teleconnections on the Summer Precipitation in North Asia

The East Asia-Pacific(EAP) and Eurasian(EU) teleconnections are independent of each other on the seasonal timescale(with a correlation coefficient of only 0.03).But they may occur concurrently with consistent or opposite phases.This paper investigates their synergistic effect on the summer precipitation in North Asia.Based on the signs/phases of EAP and EU indices,the EAP and EU teleconnection anomalies occur in four cases:(Ⅰ) positive EAP+positive EU,(Ⅱ) negative EAP+negative EU,(Ⅲ) positive EAP+negative EU,and(Ⅳ) negative EAP+positive EU.Further analyses show that these four configurations of EAP and EU anomalies are coherently related to different atmospheric circulations over the midlatitude Eurasian continent,leading to different summer precipitation modes in North Asia.Category Ⅰ(Ⅱ) corresponds to a zonal tripole structure of the geopotential height at 500 hPa over eastern Europe and the Sea of Japan,leading to less(more) than normal precipitation in eastern Europe,Japan,and the surrounding areas,and more(less) precipitation from central China to Lake Baikal and eastern Russia.Category Ⅲ(Ⅳ) corresponds to a meridional dipole structure of the geopotential height at 500 hPa over North Asia,leading to more(less) precipitation in the northern North Asia and less(more) precipitation in most of the southern North Asia.Independent analysis reveals that the EAP teleconnection itself is positively correlated with the precipitation in the region between the eastern part of Lake Baikal and Okhotsk Sea,and negatively correlated with the precipitation in the region between Northeast China and Japan.Coincidently,the EU pattern and precipitation have negative correlations in Ural Mountain and Okhotsk Sea areas and positive correlations in the Lake Baikal area.The respective relations of EAP and EU with the summer precipitation in North Asia suggest that the EAP northern lobe overlapped with the EU central and eastern lobes could extend the geopotential anomalies over Lake Baikal to Russian Far East,creating an EAP-EU synergistic effect on the summer precipitation in North Asia.     

Interdecadal Variability of the Afro-Asian Summer Monsoon System

The Afro-Asian summer monsoon is a zonally planetary-scale system, with a large-scale rainbelt covering Africa, South Asia and East Asia on interdecadal timescales both in the past century(1901–2014) and during the last three decades(1979–2014). A recent abrupt change of precipitation occurred in the late 1990 s. Since then, the entire rainbelt of the Afro-Asia monsoon system has advanced northwards in a coordinated way. Consistent increases in precipitation over the Huanghe–Huaihe River valley and the Sahel are associated with the teleconnection pattern excited by the warm phase of the Atlantic Multidecadal Oscillation(AMO). A teleconnection wave train, with alternating cyclones/anticyclones, is detected in the upper troposphere. Along the teleconnection path, the configuration of circulation anomalies in North Africa is characterized by coupling of the upper-level anticyclone(divergence) with low-level thermal low pressure(convergence), facilitating the initiation and development of ascending motions in the Sahel. Similarly, in East Asia, a coupled circulation pattern also excites ascending motion in the Huanghe–Huaihe River valley. The synchronous increase in precipitation over the Sahel and Huanghe–Huaihe River valley can be attributed to the co-occurrences and in-phase changes of ascending motion. On the other hand, the warm phase of the AMO results in significant warming in the upper troposphere in North Africa and the northern part of East Asia. Such warming contributes to intensification of the tropical easterly jet through increasing the meridional pressure gradient both at the entrance region(East Asia) and the exit region(Africa). Accordingly, precipitation over the Sahel and Huanghe–Huaihe River valley intensifies, owing to ageostrophic secondary cells. The results of this study provide evidence for a consistent and holistic interdecadal change in the Afro-Asian summer monsoon.     

An East Asian Subtropical Summer Monsoon Index and Its Relationship to Summer Rainfall in China

Using the monthly mean NCEP/NCAR reanalysis data and the monthly rainfall observations at 160 rain gauge stations of China during 1961 1999, and based on major characteristics of the atmospheric circulation over East Asia and the western Pacific, a simple index for the East Asian subtropical summer monsoon （EASSM） is defined. The relationship between this index and summer rainfall in China and associated circulation features are examined. A comparison is made between this index and other monsoon indices. The results indicate that the index defined herein is reflective of variations of both the thermal low pressure centered in Siberia and the subtropical ridge over the western Pacific. It epitomizes the intensity of the EASSM and the variability of summer rainfall along the Yangtze River. Analysis shows that the Siberian low has a greater effect on the rainfall than the subtropical ridge, suggesting that the summer rainfall variability over the eastern parts of China is to a large extent affected by anomalies of the atmospheric circulation and cold air development in the midlatitudes. Taking into account of the effects of both the Siberian low and the subtropical ridge can better capture the summer rainfall anomalies of China. The index exhibits interannual and decadal variabilities, with high-index values occurring mainly in the 1960s and 1970s and low-index values in the 1980s and 1990s. When the EASSM index is low, the Siberian low and the subtropical ridge are weaker, and northerly wind anomalies appear at low levels over the midlatitudes and subtropics of East Asia, whereas southwesterly wind anomalies dominate in the upper troposphere over the tropics and subtropics of Asia and the western Pacific. The northerly wind anomalies bring about frequent cold air disturbances from the midlatitudes of East Asia, strengthening the convergence and ascending motions along the Meiyu front, and result in an increase of summer rainfall over the Yangtze River.     

Persistence of Snow Cover Anomalies over the Tibetan Plateau and the Implications for Forecasting Summer Precipitation over the Meiyu-Baiu Region

The present reported study investigated the persistence of snow anomalies over the Tibetan Plateau（TP） from the preceding seasons to summer and the relationship between the previous snow cover anomaly and summer precipitation over East Asia. The results showed that, relative to other snow indices, such as the station observational snow depth（SOSD） index and the snow water equivalent（SWE） index, the snow cover area proportion（SCAP） index calculated from the SWE and the percentage of visible snow of the Equal-Area Scalable Earth Grids（EASE-grids） dataset has a higher persistence in interannual anomalies, particularly from May to summer. As such, the May SCAP index is significantly related to summer precipitation over the Meiyu-Baiu region. The persistence of the SCAP index can partly explain the season-delayed effect of snow cover over the TP on summer rainfall over the Meiyu-Baiu region besides the contribution of the soil moisture bridge. The preceding SST anomaly in the tropical Indian Ocean and ENSO can persist through the summer and affect the summer precipitation over the Meiyu-Baiu region. However, the May SCAP index is mostly independent of the simultaneous SSTs in the tropical Indian Ocean and the preceding ENSO and may affect the summer precipitation over the Meiyu-Baiu region independent of the effects of the SST anomalies. Therefore, the May SCAP over the TP could be regarded as an important supplementary factor in the forecasting of summer precipitation over the Meiyu-Baiu region.