Zonal Extension of the Middle East Jet Stream and Its Influence on the Asian Monsoon

Abstract

Investigation into the interannual variation of the Middle East jet stream (MEJS) and its influence on the Asian monsoon indicates that the eastward extension of MEJS is closely related with a wetter and colder winter in southern China and a later onset of the subsequent Asian summer monsoon, compared with normal conditions. When the MEJS extends eastward, a significant barotropic anomalous anticyclone is located over the Arabian Sea (AS), associated with the southeastward propagating wave train from Europe. Intense divergence in the southwest of the AS anomalous anticyclone favors more convection over the western tropical Indian Ocean, which excites an anomalous upper-level anticyclone to the north as a Rossby wave response, further intensifying the AS anticyclonic anomaly. This positive feedback loop maintains the AS anomalous anticyclone and results in the eastward extension of the MEJS. Accordingly, intense northeasterly anomalies over the Mediterranean Sea and the subtropical westerly anomalies bring abundant cold air from the middle-higher latitudes to subtropical regions, resulting in a widespread cooling in subtropical Eurasia including southern China. Barotropic anomalous westerlies occur around the Tibetan Plateau in the south and deepen the India-Burma trough, favoring more water vapor transport from the Bay of Bengal to southern China. This wetter and colder conditions in subtropical Eurasia can persist from winter to spring, leading to the much later onset of the Asian summer monsoon. Therefore, the winter MEJS variability can be considered as an important indicator for the Asian monsoon.

Predictability of Extremely Pluvial Winters Over the Yangtze–Huai River Basin in China

“…The increased circulation anomaly and moisture convergence in the northern YHRB during the 1997–1998 winter season were primarily attributed to the quasi‐barotropic structure of the intensified anticyclone near the northern YHRB and northwest of Japan (Figures 7d and 7e). The results are in agreement with earlier findings (e.g., Wei et al., 2022). We also investigated the ensemble co‐variability between the WIO SST and the GH anomaly at 200 hPa in the YHRB for all winters and found that the possible teleconnection from the WIO strongly depends on the amplitude of the WIO SST (Figure 9).…”

“…The tropical Indian Ocean (IO) can also influence winter precipitation in the YHRB (e.g., Abid et al., 2021; Annamalai et al., 2007). The warm SST anomalies in the tropical IO could intensify a Kelvin wave response located to the east (e.g., Li et al., 2015), as well as a zonal extension of the upper‐level Middle East Jet Stream (e.g., Wei et al., 2022) and finally more precipitation in the YHRB region. Additionally, it has been observed that a warm tropical Atlantic could result in the northward extension of the Western North Pacific (WNP) anticyclone through the formation of an upper‐tropospheric Rossby wave train stretching from the tropical Atlantic to the mid‐latitudes of East Asia.…”

11-year solar cycle influences on the late-wintertime South Asian jet variability

“…Previous studies suggested that the SAJLWT pattern can be modulated by SST and convection anomalies over the Indo-Pacific sector (Hu et al, 2018;Wei et al, 2022). To demonstrate this, Figure 9 shows regressed SST, precipitation, and 850-hPa wind anomalies onto PC1.…”

“…Previous studies have found that the SAJLWT pattern is closely associated with the upstream circulation patterns over the NAE region, as well as SST and convection anomalies over the tropical Indo-Pacific region (Wei et al, 2022). Coincidentally, significant solar signals exist in two regions, including a NAOlike pattern in the NAE region and a weakened Walker Circulation in the Indo-Pacific region.…”

“…In general, the SAJLWT is associated with El Niño-Southern Oscillation (ENSO)-like patterns. Through the Gill-Matsuno mechanism, sea surface temperature (SST) and convection anomalies in the tropical eastern Pacific (EP), western Pacific (WP), and Indian Ocean (IO) were found to excite circulation anomalies along the SAJ (Leung et al, 2017;Hu et al, 2018;Wei et al, 2022). However, whether the SAJLWT can be driven by external forcing factors remains unclear.…”