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
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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.
Key wordsTibetan Plateau Iranian Plateau surface sensible heat flux latent heat of condensation South Asian High
青藏高原和伊朗高原地表加热作用对初夏南亚高压位置影响显著. 基于观测资料与ERA-Interim资料, 通过诊断分析发现在年际尺度上, 6月南亚高压位置的西北-东南向摆动与前期5月份青藏高原和伊朗高原地表感热异常协同作用密切相关. 5月青藏高原地表感热与伊朗高原地表感热为负相关, 这种两高原的感热异常模态可持续至6月从而影响印度东北部上空的凝结潜热释放大小并造成6月南亚高压位置的西北-东南向变化. 当5月伊朗高原感热偏大(小)而青藏高原感热偏小(大)时, 5月和6月印度北部上空850hPa大气出现气旋式(反气旋)异常环流, 伴随着大气的异常上升(下沉)运动和异常水汽辐合(辐散). 因此, 印度东北部上空凝结潜热释放增强(减弱)而对流层上层大气显热源的垂直梯度减小(增大), 最终造成6月南亚高压位置偏西北(东南).
关键词青藏高原 伊朗高原 地表感热通量 凝结潜热 南亚高压
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This work was supported by the National Natural Science Foundation of China (Grant Nos. 91437219, 41275075 and 41175005) and the National Basic Research Program of China (Grant No. 2013CB430203).
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