Drying tendency over the southern slope of the Tibetan Plateau in recent decades: role of a CGT-like atmospheric change

Abstract

A significant drying tendency over the southern slope of the Tibetan Plateau (SSTP) in summer (especially in July–September) during 1980–2018 is identified in this study. Moisture budget analysis reveals that the drying tendency is dominated by a decreased vertical moisture advection due to weakened upward motion, which is mainly resulted from an anticyclonic trend appeared over the northeastern TP. This anomalous anticyclone can weaken the upper-tropospheric divergence pumping over the SSTP. In addition, moist static energy diagnosis indicates that the southern branch of the anomalous anticyclone advects low moist enthalpy air into the SSTP, which also suppresses local upward motion and convection. Moreover, the anticyclonic trend over the northeastern TP is found not a local phenomenon, but is rather associated with the large-scale atmospheric change in the middle latitudes that shows a circumglobal teleconnection (CGT)-like pattern. Our results highlight that the long-term CGT-like trend of atmospheric circulation plays a crucial role in triggering the drying tendency over the SSTP in recent decades.

Different mechanisms for the extremely hot central-eastern China in July–August 2022 from a Eurasian large-scale circulation perspective

“…The easterly anomalies led to sinking motions through air isentropic sliding and a more important mechanism called 'wind-induced moist enthalpy advection' . The latter actually has been shown in one of our recent works (Wang et al 2022b), which was used to explain the weakened ascent and drying tendency over the TP's southern slope. In fact, significant drought was also observed over the southern TP in summer 2022 (figures 1(e) and (g)), a similar critical factor is the westward-extended easterlies associated with the above-mentioned anomalous anticyclone over northern CEC and the obvious invasion of negative moist enthalpy advection (figures 2(b) and (d)).…”

“…Furthermore, we diagnose the moist static energy (MSE) budget equation (Neelin and Held 1987), in which the wind-induced moist enthalpy advection (−V ′ • ∇ h (C p T + L v q)) has been extensively shown to be the critical mechanism for anomalous vertical motion in monsoon regions (e.g. Wu et al 2017, Hu et al 2021, Wang et al 2022b. Here, V ′ is anomalous horizontal wind; T and q are the climatological air temperature and specific humidity, respectively; C p and L v are the specific heat at constant pressure and latent heat of vaporization, respectively; and C p T + L v q is the climatological moist enthalpy.…”

The westerlies control the zonal migration of rainy season over the Tibetan Plateau

“…Precipitation over the TP exhibits variations on a wide range of timescales and the origins varies for various time scales. While the intraseasonal and interannual variability of summertime precipitation is linked to interactions of the SASM anomalies and wave-like atmospheric circulation anomalies over midlatitude 9,10 , the interdecadal variability of the summertime precipitation over the TP was suggested to be linked to the westerlies 24,25,26 . This study investigates the annual cycles of precipitation over the TP and mid-latitude westerlies, suggesting that summer weakening of westerlies favors more precipitation over the TP and westward extension of main precipitation zone in the southeastern TP.…”

Spatial Heterogeneity of Summer Rainfall Trends over the Tibetan Plateau Contributed by Different Rainfall Intensities

“…And weaker surface sensible heating from 1980 to 2008 led to reduced rainfall along the TP's southern and eastern slopes [25]. Recent decades showcased intensified rainfall over northern TP but not in the south [26][27][28]. Yue et al [29] reported decreased summer rainfall and lake shrinkage in the southern TP post 1998, linked to a dipolar sea surface temperature pattern between the equatorial central Pacific and Indo-Pacific warm pool.…”