The impact of boreal surface thermal anomalies on January Central Asian moist vortex

Central Asian vortex (CAV) is a kind of typical regional cyclonic vortex in the North Hemisphere and its important component, Central Asian moist vortex (CAMV), is one of the key systems causing Central Asian heavy precipitation. This study focused on the main characteristics and interannual forcing sources of January CAMV, which has led to rapid increase of Central Asian heavy snowfall during several decades, mainly discussing about the individual and cooperative effect of boreal surface thermal anomalies on CAMVs. The results indicate that the January CAMV demonstrates significantly interannual variability in its annual activity days, moreover, this interannual variability has been experiencing decadal enhancement since 2004, which explains the decadal increase in contemporaneous Central Asian heavy snowfall amount. The “northern moist vortex” (NMV) featuring the low vortex in the northern Central Asia accompanying the European and Tibetan Plateau Ridge, represents the typical circulation configuration of January CAMV. The interannual frequency of NMV is highly related to preceding North Pacific Victoria mode (VM), mid-latitude North Atlantic sea surface temperature (MNA) as well as the land-sea temperature contrast (LSTC) between Africa and eastern North Atlantic. Among them, VM and MNA could respectively stimulate circumglobal and Atlantic-Eurasian wave train structures into northern Central Asia. While, LSTC could excite anomalous lower-level cyclonic circulation over the Mediterranean entrance, accelerating and lifting the entrance of African-Asian jet stream via the way of “eddy-driven jet stream”, thereby strengthening the docking of the African-Asian jet stream with the North Atlantic jet stream and enhancing the waveguide effect of two jet streams. When these three surface thermal factors coexist on the interannual scale, VM tends to play a leading role for contributing more than 50% to NMVs in three factors. While, MNA and LSTC play unneglected roles of “relay” to further modulate NMVs, and the cooperative effect of multiple surface thermal anomalies is the key to impacting January CAMVs.