Abstract
Previous studies have demonstrated that atmospheric diabatic heating over the Tibetan Plateau (TP) exerts significant influences on the “upstream” climate of the Atlantic-African-European sector in boreal summer. Using the NCAR Community Earth System Model, this study demonstrates that the TP-induced change in North Atlantic sea surface temperature (SST) including evident warming over the mid-latitude North Atlantic and cooling over the south can in turn modulate the above TP impact. Compared with the TP heating experiment without Atlantic SST variation, anomalous wave train pattern appears with north-northeastward downstream influences when the change in Atlantic SST is considered. The wave train pattern is characterized by three positive centers over the North Atlantic, the Arctic Ocean, and east of Japan, and four negative centers over northeastern North America, North Europe, the mid-Atlantic, and the northwestern Pacific. It intensifies the northern portions of the TP-induced tropospheric anticyclones over the extratropical North Atlantic and the cyclones over northeastern North America and North Europe. Correspondingly, precipitation decreases over the northwestern Atlantic but increases over northeastern North America and North Europe. Due to the easterly anomalies on the southern side of the weakened thermal low over subtropical Africa, precipitation over the Sahel decreases, indicating a weakening of TP-induced precipitation dipole over the tropical eastern Atlantic and West Africa when the Atlantic SST influence is considered. Overall, the modulation of Atlantic SST variation accounts for above 20 percent of the upstream climate signals induced by the TP thermal effect.
Highlights
The impacts of the Tibetan Plateau (TP) on regional and large-scale atmospheric circulation have been investigated extensively (Hahn and Manabe 1975; Ye and Wu 1998; Kitoh 2004; Liu et al 2007; Wu et al 2014)
We examine the modulation of Atlantic sea surface temperature (SST) variation on the effect of TP heating on the upstream climate over Afro-Eurasia–Atlantic regions
Previous studies have shown that TP summertime heating can affect the “upstream” climate over the Atlantic-African-European regions
Summary
The impacts of the Tibetan Plateau (TP) on regional and large-scale atmospheric circulation have been investigated extensively (Hahn and Manabe 1975; Ye and Wu 1998; Kitoh 2004; Liu et al 2007; Wu et al 2014). Lu et al (2018) conducted several sensitivity experiments using the NCAR Community Earth System Model with controlled modification of the surface thermal condition in the TP region and demonstrated the influences of summer TP heating on the “upstream” climate over the North Atlantic, South Europe, North Africa, the Middle East, and West Asia. The TP-related climate signals include intensification and northward shift of the subtropical high over the North Atlantic, especially in its northern flank near the Gulf Stream, and a northward shift of the intertropical convergence zone (ITCZ) which causes an increase in the Sahel rainfall The former is due mainly to the TPheating induced Rossby wave response over the extratropics (effect on the rotational motion of the atmosphere) and to the thermally-driven atmospheric circulation over the tropics and subtropics (effect on the divergent flow). All model simulations are conducted with the B2000 component setting; that is, the values of solar forcing, carbon dioxide, aerosol, and ozone concentration are fixed at their levels of Year 2000
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