Abstract
In the context of global warming, the frequency and intensity of extreme weather and climate events have increased, especially in Central Asia (CA). In this study, we investigate the characteristics of summer extreme precipitation (SEP) in CA and its relationship with the surface sensible heat (SSH) variation over the central–eastern Tibetan Plateau (CETP). The results suggest that the distribution of SEP in CA is extremely uneven, and the SEP thresholds range from 2 to 32 mm/day, and 80% of them are concentrated in 4–10 mm/day. Both the total amount of SEP and the number of SEP days show significant increasing trends, with the climatic tendencies of 4.4 mm/decade and 0.4 day/decade, respectively. The SSH anomalies over the CETP can affect the SEP and summer drought in CA by regulating the strength of South Asia High (SAH) and the subtropical jet over CA. The strong SSH anomalies over the CETP in late spring (April–May) can be transmitted from the lower to the upper layers through the continuous heating to the atmosphere and lead to the anomalously strong subtropical high over northern Africa and the Arabian Peninsula, the anomalously weak subtropical westerly jet over CA and the anomalously strong SAH in summer. At the same time, the Ural ridge strengthens, the CA trough weakens, and the northern CA is controlled by an anomaly of warm high-pressure ridge. Therefore, the anomaly of water vapor convergence in northern CA weakens. The SEP there will be abnormally less, and the summer drought intensifies. When the SSH over CETP is anomalously weak in late spring, the key circulations are just the opposite. Furthermore, the anomalous water vapor from the Arctic, North Atlantic and western Pacific converges in northern CA and northern Xinjiang, China, which is conducive to the generation of widespread extreme precipitation and the alleviation of summer drought in these regions.
Highlights
Central Asia (CA) is a typical arid and semi-arid climatic region located in the Eurasia inland with complex topography, which is a key region of China's national initiatives of "Silk Road" and "One Belt, One Road"
*, **Statistical significance above the 95 and 99% confidence levels, respectively negative correlations between the sensible heat (SSH) from late spring to early summer over the central–eastern Tibetan Plateau (CETP) and the summer extreme precipitation (SEP) in CA, and the bimonthly correlation in April–May (AM, − 0.51, P < 0.01) is better than that in May − June (MJ, − 0.44, P < 0.01) and June–July (JJ, − 0.34, P < 0.05), which is comparable to the relationship in April-July (AMJJ, − 0.53, P < 0.01)
The SEP threshold, total amount of SEP and the number of SEP days in CA are calculated by the international percentile method
Summary
Central Asia (CA) is a typical arid and semi-arid climatic region located in the Eurasia inland with complex topography, which is a key region of China's national initiatives of "Silk Road" and "One Belt, One Road". Previous studies have shown that the positive SSH anomaly over the TP generates negative vorticity anomaly at high levels, which influences the atmospheric circulation in the Northern Hemisphere by triggering Rossby wave trains (Wu et al 2016; Liu et al 2017b) It is unclear what is the relationship between TP SSH anomalies and the extreme precipitation in CA, and whether the physical mechanisms of thermal influence of the TP on the CA climate are the same as that for the EA monsoon climate? This study starts with the variations of SSH over the CETP to investigate the influence of surface thermal anomalies on the summer extreme precipitation (SEP) in CA and the key circulations.
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