Influence of Late Springtime Surface Sensible Heat Flux Anomalies over the Tibetan and Iranian Plateaus on the Location of the South Asian High in Early Summer

摘要

Variation in the location of the South Asian High(SAH) in early boreal summer is strongly influenced by elevated surface heating from the Tibetan Plateau(TP) and the Iranian Plateau(IP). Based on observational and ERA-Interim data,diagnostic analyses reveal that the interannual northwestward–southeastward(NW–SE) shift of the SAH in June is more closely correlated with the synergistic effect of concurrent surface thermal anomalies over the TP and IP than with each single surface thermal anomaly over either plateau from the preceding May. Concurrent surface thermal anomalies over these two plateaus in May are characterized by a negative correlation between sensible heat flux over most parts of the TP(TPSH)and IP(IPSH). This anomaly pattern can persist till June and influences the NW–SE shift of the SAH in June through the release of latent heat(LH) over northeastern India. When the IPSH is stronger(weaker) and the TPSH is weaker(stronger)than normal in May, an anomalous cyclone(anticyclone) appears over northern India at 850 hPa, which is accompanied by the ascent(descent) of air and anomalous convergence(divergence) of moisture flux in May and June. Therefore, the LH release over northeastern India is strengthened(weakened) and the vertical gradient of apparent heat source is decreased(increased)in the upper troposphere, which is responsible for the northwestward(southeastward) shift of the SAH in June.