Variations of the summer Somali and Australia cross-equatorial flows and the implications for the Asian summer monsoon

Abstract

The temporal variations during 1948-2010 and vertical structures of the summer Somali and Australia cross-equatorial flows (CEFs) and the implications for the Asian summer monsoon were explored in this study. The strongest southerly and northerly CEFs exist at 925 hPa and 150 hPa level, respectively. The low-level Somali (LLS) CEFs were significantly connected with the rainfall in most regions of India (especially the monsoon regions), except in a small area in southwest India. In comparison to the climatology, the lowlevel Australia (LLA) CEFs exhibited stronger variations at interannual time scale and are more closely connected to the East Asian summer monsoon circulation than to the LLS CEFs.The East Asian summer monsoon circulation anomalies related to stronger LLA CEFs were associated with less water vapor content and less rainfall in the region between the middle Yellow River and Yangtze River and with more water vapor and more rainfall in southern China. The sea-surface temperature anomalies east of Australia related to summer LLA CEFs emerge in spring and persist into summer, with implications for the seasonal prediction of summer rainfall in East Asia. The connection between the LLA CEFs and East Asian summer monsoon rainfall may be partly due to its linkage with El Nino-Southern Oscillation. In addition, both the LLA and LLS CEFs exhibited interdecadal shifts in the late 1970s and the late 1990s, consistent with the phase shifts of Pacific Decadal Oscillation (PDO).Citation: Zhu, Y. L., 2012: Variations of the summer Somali and Australia cross-equatorial flows and the implications for the Asian summer monsoon.

Interannual and long term variability of low level jetstream of the Asian summer monsoon

“…This is linked to the increasing frequency of break monsoon days of the monsoon season in the recent decades (Joseph and Simon, 2005;Rameshkumar et al, 2009) as the LLJ axis shift towards the equator east of longitude 70°E during (cold) phase of ENSO. Zhu (2012) has also found similar relationship. The cross equatorial flow, EIm and WPm are connected to the strength of two highs, Mascerene High and Australian High respectively as shown by Wang and Li (1982) and Xue et al (2004).…”

“…4b). Zhu (2012) found that the strength of the cross-equatorial flow near the Somali coast is negatively related to the SST over western tropical Indian Ocean and Arabian Sea. When the along-shore winds off the coasts of Somalia and Arabia become weak the coastal upwelling reduces generating warm SST anomalies there.…”

The relation of cross‐equatorial flow during winter and spring with South China Sea summer monsoon onset

“…CEF is one of the main components in Asian monsoon system, and is related closely with Asian climate. Therefore, much attention has been paid on impacts of CEF on Asian summer monsoon Li and Wu, 2002;Ding and He, 2006;Gao and Xue, 2006;Qiu and Sun, 2013), rainfall over China Wang and Xue, 2003;Lei and Yang, 2008;Zhu, 2012;Li and Li, 2014), and weather systems, such as subtropical high over western North Pacific (Bi et al, 2004;Xu et al, 2006;Lin et al, 2007), Typhon (Wang and Leftwich, 1984;Huang et al, 2008;Feng et al, 2014), etc. CEF over Western Hemisphere is related closely with distribution of seasonal rainfall over its adjacent area as well as over Eastern Hemisphere (Wang and Fu, 2002).…”

Characteristics of intercontinental transport of tropospheric ozone from Africa to Asia

“…Located north to the enhanced Mascarene Anticyclone, on the east coast of Somali, Somali cross-equatorial flow served as an essential component of the Asian monsoon system (Joseph and Sijikumar, 2004). Peaked at 925 hPa (Zhu, 2012), the Somali jet carries ozone in eastern Africa to India in the lower troposphere (Figs. 10c and 11b).…”