Yong Zhao

Based on the daily precipitation data released by the China Meteorological Data Service Centre, the monthly Sea Surface Temperature (SST) provided by the National Oceanic and Atmospheric Administration (NOAA) and monthly atmospheric reanalysis data extracted from the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) during 1961–2022, we examine the interdecadal change in the relationship between spring Indian Ocean SST (IOSST) and summer extreme precipitation (SEP) in northern Xinjiang of Northwest China. Results show that the IOSST-SEP relationship has experienced an obvious interdecadal change, especially between 1963 and 1983 and 1984–2004, and in the latter period their relationship significantly becomes closer. The meridional movement of the subtropical westerly jet (SWJ) over Central Asia (CA) can well affect the Central Asian cyclone and transport of water vapor and is responsible for the SEP in northern Xinjiang, which plays an important role in linking IOSST and SEP. During 1963–1983, the persistence of anomalous IOSST signals from spring to summer strongly depends on El Niño, so the IOSST is manifested as a heat sink and cannot influence the meridional movement of the SWJ over CA. However, during 1984–2004, the persistence of anomalous IOSST signals from spring to summer is independent of El Niño, and the IOSST is manifested as a heat source and can modulate the meridional movement of the SWJ over CA via Gill-type atmospheric response.

Based on the Global Precipitation Climatology Centre (GPCC) monthly precipitation data, the Extended Reconstructed Sea Surface Temperature (SST) version 5 (ERSSTv5) dataset derived from the National Oceanic and Atmospheric Administration (NOAA), and the Fifth‐generation European Centre for Medium‐Range Weather Forecasts (ECMWF) atmospheric reanalysis (ERA5) monthly dataset, the synergistic influences of the SST anomalies (SSTAs) in the North Atlantic (NA) and the Indian Ocean (IO) on summer precipitation in Central Asia (CA) are investigated. Results show that SST in both the NA and the IO positively correlates with summer precipitation in southern CA. The meridional movement of the subtropical westerly jet (SWJ) plays an important role in linking the SSTAs in the NA and the IO and summer precipitation in southern CA. The positive SSTAs in the NA can excite an eastward‐propagating wave train across Eurasia and cause an anomalous cyclone over CA, which is responsible for the southward movement of the SWJ. The positive SSTAs in the IO can induce an anomalous cyclone in the upper troposphere over the northwestern part of the South Asian summer monsoon region, according to the Gill‐type atmospheric response, and the SWJ over CA also moves southward. The southward movement of the SWJ over CA responds to the simultaneous SST warming in the NA and the IO. Furthermore, it can induce an anomalous cyclone in the middle troposphere over CA and strengthen the transport of water vapour from the Arabian Sea. Therefore, more summer precipitation can be observed in southern CA. In the process of synergistic influences of SSTAs in the NA and the IO on summer precipitation in CA, the former plays a more important role.

Based on the monthly rainfall data at 28 meteorological stations located in the Tarim Basin of Northwest China extracted by the China Meteorological Data Network and JRA‐55 reanalysis atmospheric circulation data released by the Japan Meteorological Agency from 1961 to 2022, the synergetic effects of the Silk Road Pattern (SRP) and East Asian–Pacific (EAP) teleconnection on August precipitation in the Tarim Basin have been investigated, especially in 2016. The Tarim Basin has received the maximum precipitation in August 2016 over the past 60 years, which was contributed by the increase in precipitation days and precipitation intensity. Both SRP and EAP can affect the precipitation in August in the Tarim Basin independently, but there is a better relationship between the synergetic SRP‐EAP index and precipitation, with a correlation coefficient of 0.49 over the 95% confidence level. The positive SRP‐EAP index is associated with the southward movement of the subtropical westerly jet over Central Asia, southerly prevailing over the Tarim Basin, and strengthened water vapour transport from the Arabian Sea and East Asian monsoon region, which are favourable to generating more precipitation in August in the Tarim Basin. During August 2016, the precipitation in the Tarim Basin experienced three obviously distinct processes corresponding to the positive phases of the daily SRP index and negative phases of the daily EAP index, which furthermore indicate that the synergetic variations of the SRP and EAP play very important roles in modulating the maximum precipitation.

Based on observational monthly precipitation data at 21 stations in the eastern part of the arid region of Northwest China (ARNWC), the NCEP/NCAR reanalysis atmospheric circulation data, and ERA5‐land reanalysis surface soil moisture and sensible heat flux data during 1961–2022, we examine the interdecadal change in the relationship between spring Asia‐Pacific Oscillation (APO) and summer precipitation in the eastern part of the ARNWC. Results show the relationship between spring APO and summer precipitation in the eastern part of the ARNWC has weakened significantly since 2000. The southward (northward) shift of the subtropical westerly jet over East Asia and anomalous anticyclone (cyclone) over the Mongolia Plateau play an important role in modulating the dynamical and water vapour conditions responsible for the summer precipitation in the eastern part of the ARNWC during 1961–1999 and 2000–2022. The soil moisture can “memorise” the anomalous signal of APO from spring to summer and feedback to the atmosphere via influencing the summer surface sensible heat in the Tibetan Plateau during 1961–1999. Therefore, the spring APO‐related atmospheric circulation can contribute to favourable dynamical and water vapour conditions responsible for the summer precipitation in the eastern part of the ARNWC. However, the land‐atmosphere interaction in the Tibetan Plateau cannot retain the signal of spring APO and release it in summer during 2000–2022. Therefore, the APO loses its close relationship with summer precipitation in the eastern part of the ARNWC in this period.

The zonal movement of both the western Pacific subtropical high (WPSH) and the North African subtropical high (NASH) correlates well with the summer precipitation in the arid region of Northwest China (ARNWC), but there is not enough understanding of the interdecadal change in the interannual relationship between the zonal position linkage of the two subtropical highs and summer precipitation in the ARNWC under different interdecadal backgrounds. Based on the observed precipitation data at 101 stations in the ARNWC, the NCEP–NCAR reanalysis data, and Hadley Centre surface sea temperature (SST) data for 1961–2022, the interdecadal change in the interannual relationship between the zonal position linkage of the two subtropical highs and summer precipitation in the ARNWC is investigated. Results show that the summer precipitation has experienced two distinct periods (dry period: 1961–1986; wet period: 1987–2022), and the zonal position linkage of the two subtropical highs correlates well with the summer precipitation in the eastern part of the ARNWC in the dry period and the Tarim Basin in the wet period, respectively. When the NASH and the WPSH move in opposite directions, the water vapour is directly (indirectly) transported from the eastern Asian monsoon region (tropical Indo‐Pacific Ocean) in the dry (wet) period. The Asian‐Pacific Oscillation (APO) and the sea surface temperature (SST) in the Indo‐Pacific warm pool both contribute to the zonal movement of the two subtropical highs in the dry period, but in the wet period, only the SST in the Indo‐Pacific warm pool plays an important role in modulating the zonal position linkage of the NASH and the WPSH.

The interdecadal change in the relationship between the Antarctic Oscillation (AAO) and autumn rainfall in the Yunnan–Guizhou Plateau of Southwest China is investigated by using the observed autumn rainfall data at 119 stations and the National Centers for Environment Prediction/National Center for Atmospheric Research reanalysis data for the period 1961–2021. Results show the AAO correlates well with the autumn rainfall in the Yunnan–Guizhou Plateau for the second period (2002–2021) because the AAO becomes stronger. The possible influencing mechanism of AAO on autumn rainfall in the Yunnan–Guizhou Plateau during 2002–2021 is related to the meridional teleconnection pattern and associated convection over the Philippine Sea. The positive AAO can trigger a meridional teleconnection pattern in the upper troposphere to propagate from the southern Pacific to northern Pacific and cause anomalous westerly over the tropical west Pacific, which inhibits the convection over the Philippine Sea. On the one hand, the weakened convection over the Philippine Sea causes the anomalous ascending motion over the Yunnan–Guizhou Plateau; on the other hand, it results in an anomalous anticyclone over the tropical Northwest Pacific and strengthens the transport of water vapor from the tropical Pacific to the Yunnan–Guizhou Plateau.

As a unique climate phenomenon induced by the Tibetan Plateau (TP) heat flux, the TP monsoon is closely connected with the global climate, especially pertaining to the TP. However, the current research focuses more on the influence of the TP monsoon on the TP and eastern China, but not including Central Asia. This paper analyzed the relationship between the TP monsoon index and Central Asia summer precipitation by JRA55 reanalysis data and Global Precipitation Climatology Centre (GPCC) monthly precipitation. The results showed a significant positive relationship between the TP monsoon index and summer precipitation in Central Asia. When the TP monsoon was strong, there was cold advection in the upper troposphere over Central Asia, and the resulting thermal wind caused a cyclonic circulation anomaly in the mid-upper troposphere over Central Asia. This in turn led to a cyclonic circulation anomaly to water vapor transport in the lower troposphere. The abnormal upward movement also caused more precipitation in this area, which explains the positive correlation between the TP monsoon and the precipitation in Central Asia. Based on this physical mechanism, the temperature of the mid-upper troposphere over Central Asia was closely related to the TP monsoon, and it was a key factor that affected summer precipitation changes in Central Asia.

The present study investigated impacts of strong and weak El Niño events on central Asian precipitation variability from El Niño developing years to decaying years. It is found that strong El Niño events persistently enhance central Asian precipitation from the mature winter to decaying summer. Large warm sea surface temperature (SST) anomalies in the tropical central-eastern Pacific induce anomalous upper-level divergence and updraft over central Asia through large-scale convergence and divergence in the mature winter and decaying spring. Meanwhile, the associated wind anomalies induce anomalous eastward and northeastward moisture flux from the North Atlantic and the Arabian Sea to central Asia. Both anomalous ascent and moisture flux convergence favor above-normal precipitation over central Asia in the mature winter and decaying spring. The El Niño events induced central Asian precipitation anomalies that are extended to the decaying summer due to the role of soil moisture. Increased rainfall in winter and spring enhances soil moisture in the following summer, which in turn contributes to more precipitation in summer through modulating regional evaporation. During weak El Niño events, significant wet anomalies are only seen in the developing autumn, which result from anomalous southeastward moisture flux from the Arctic Ocean, and the abnormal signals are weak in the other seasons. The different responses of central Asian precipitation to strong and weak El Niño events may be attributed to the difference in intensity of tropical SST anomalies between the two types of events.

Based on the output data from the Lagrangian flexible particle dispersion model (FLEXPART), we analyze the pathways of moisture to identify the moisture source areas for extreme precipitation in the summer half-year (April–September) over northern and southern Xinjiang, respectively. For both northern and southern Xinjiang, the local evaporation plays a decisive role for extreme precipitation in the summer half-year, of which contribution ratio accounts for 24.5% to northern Xinjiang and 30.2% to southern Xinjiang of all identified source areas. In addition, central Asia and northwestern Asia are the major moisture source areas as well and contribute similarly to extreme precipitation relative to local evaporation. For northern Xinjiang, central Asia surpasses northwestern Asia, and each of them contributes 24.1 and 18.8%, whereas northwestern Asia is somewhat more crucial than central Asia for southern Xinjiang, accounting 22.1 and 19.1%, respectively. Note that the three top-ranked moisture source areas make up a large proportion of total sources. Regarding the remaining source areas that also provide moisture, the contributions are entirely different for southern and northern Xinjiang. Originating from the North Atlantic Ocean, Europe, and the Mediterranean Sea, some water vapor enters northern Xinjiang and converge to precipitate, while this process is barely detectable for extreme precipitation over southern Xinjiang, which is affected by the westerly flow. On the contrary, the Arabian Sea, the Arabian Peninsula, and the Indian Peninsula contribute, even though slightly, to extreme precipitation over southern Xinjiang, which indicates that the meridional transport pathways from the Arabian Sea can carry moisture to this inland region.