The 2020 Summer Floods and 2020/21 Winter Extreme Cold Surges in China and the 2020 Typhoon Season in the Western North Pacific

China experienced significant flooding in the summer of 2020 and multiple extreme cold surges during the winter of 2020/21.Additionally,the 2020 typhoon season had below average activity with especially quiet activity during the first half of the season in the western North Pacific(WNP).Sea surface temperature changes in the Pacific,Indian,and Atlantic Oceans all contributed to the heavy rainfall in China,but the Atlantic and Indian Oceans seem to have played dominant roles.Enhancement and movement of the Siberian High caused a wavier pattern in the jet stream that allowed cold polar air to reach southward,inducing cold surges in China.Large vertical wind shear and low humidity in the WNP were responsible for fewer typhoons in the first half of the typhoon season.Although it is known that global warming can increase the frequency of extreme weather and climate events,its influences on individual events still need to be quantified.Additionally,the extreme cold surge during 16–18 February 2021 in the United States shares similar mechanisms with the winter 2020/21 extreme cold surges in China.

Analysis of Causes and Seasonal Prediction of the Severe Floods in Yangtze／Huaihe Basins during Summer 1991

The present paper shows that a seasonal prediction for the large scale flooding and waterlogging of the mid-lower Yangtze/ Huaihe River basins in the summer of 1991 made successfully in early April 1991.The seasonal forecasting method and some predictors are also introduced and analyzed herein. Because the extra extent of the abnormally early onset of the plum rain period in 1991 was unexpected,great efforts have been made to find out the causes of this abnormality. These causes are mainly associated with the large scale warming of SST surrounding the south and east part of Asia during the preceding winter,while the ENSO-like pattern of SSTA occurred in the North Pacific.In addition,the possible influence of strong solar proton events is analyzed.In order to improve the seasonal pre4iction the usage of the predicted SOl in following spring/summer is also introduced.The author believes thatthe regional climate anomaly can be correctly predicted for one season ahead only on the basis of physical understanding of the interactions of many preceding factors.

Toward Understanding the Extreme Floods over Yangtze River Valley in June−July 2020:Role of Tropical Oceans

The extreme floods in the Middle/Lower Yangtze River Valley(MLYRV)during June−July 2020 caused more than 170 billion Chinese Yuan direct economic losses.Here,we examine the key features related to this extreme event and explore relative contributions of SST anomalies in different tropical oceans.Our results reveal that the extreme floods over the MLYRV were tightly related to a strong anomalous anticyclone persisting over the western North Pacific,which brought tropical warm moisture northward that converged over the MLYRV.In addition,despite the absence of a strong El Niño in 2019/2020 winter,the mean SST anomaly in the tropical Indian Ocean during June−July 2020 reached its highest value over the last 40 years,and 43%(57%)of it is attributed to the multi-decadal warming trend(interannual variability).Based on the NUIST CFS1.0 model that successfully predicted the wet conditions over the MLYRV in summer 2020 initiated from 1 March 2020(albeit the magnitude of the predicted precipitation was only about one-seventh of the observed),sensitivity experiment results suggest that the warm SST condition in the Indian Ocean played a dominant role in generating the extreme floods,compared to the contributions of SST anomalies in the Maritime Continent,central and eastern equatorial Pacific,and North Atlantic.Furthermore,both the multi-decadal warming trend and the interannual variability of the Indian Ocean SSTs had positive impacts on the extreme floods.Our results imply that the strong multi-decadal warming trend in the Indian Ocean needs to be taken into consideration for the prediction/projection of summer extreme floods over the MLYRV in the future.

THE RELATIONSHIP OF LARGE VOLCANIC ERUPTION IN THE WORLD AND THE SUMMER DROUGHT/FLOOD IN CHINA

Based on data in the last 500 years for strong volwtc aedvity and the sununer drought/flood types available in China, the statistical relatons 0f the volcanic eruptions in seasons and several ropons and the drowtood types and grade index of main wions in China have ban inveStigned. The possible teleconnection bforan flood in the Yangtze hiver and the Huaihe foveL Valleys in 1991 and the volcanic eruption of Mt. Pinatubo in June of 1991 has bam also exathened. It is found that ehas of volcanic eruption in differen ropons in the worid vary on droguood in diffend edons of China, but in some cases the the is absolutely opposite in respect of the summer drowood. Statshcal test shows that in terms of stud confidence levels of the reation for dividing the volcanic eruptions as several ropons are higher than that for volcanic eruPhon in the worid as Whole.

Impacts of 30-60-Day Oscillations over the Subtropical Pacific on the East Asian Summer Rainfall

The relationships between the precipitation over East Asia （20°-45°N, 110°-135°E） and the 30-60-day intraseasonal oscillation （ISO） over the Pacific during the boreal summer are studied in the paper. The dally wind and height fields of NCEP/NCAR reanalysis data, the 24-h precipitation data of 687 stations in China during 1958-2000, and the pentad precipitation of CMAP/NOAA from 1979 to 2002 are all analyzed by the space-time filter method. The analysis results, from every drought and flood summer in four different regions of East Asia respectively during 1958-2000, have shown that the flood （drought） in the East Asian summer monsoon region is absolutely companied with the strongly （weakly） westward propagations of ISO from the central-east Pacific, and depends little on the intensity changes of the East Asian summer monsoon. And the westward ISO is usually the low-frequency cyclones and anticyclones from the Bay of Alaska in northeastern Pacific and the Okhotsk in the northwestern Pacific of mid-high latitudes, and the ISO evolving in subtropical easterlies. In mid-high latitudes the phenomena are related to the westward propagating midocean trough and the retreat of blocking high. Therefore the westward propagating ISO from the central-east Pacific to East Asia is indispensable for more rainfall occurring in East Asia in summer, which results from the long-wave adjustment process in the mid-high latitudes and ISO evolving in tropical easterlies.