Intraseasonal Soil Moisture–Atmosphere Feedbacks on the Tibetan Plateau Circulation

Abstract

Substantial intraseasonal precipitation variability is observed across the Tibetan Plateau (TP) during boreal summer associated with the subtropical jet location and the Silk Road pattern. Weather station data and satellite observations highlight a sensitivity of soil moisture and surface fluxes to this variability. During rain-free periods of two or more days, skin temperatures are shown to rise as the surface dries, signalling decreased evaporative fraction. Surface fluxes are further enhanced by relatively clear skies. In this study we use an atmospheric reanalysis to assess how this surface flux response across the TP influences local and remote conditions. Increased surface sensible heat flux induced by decreased soil moisture during a regional dry event leads to a deepening of the planetary boundary-layer and the development of a heat low. Consistent with previous studies, heat low characteristics exhibit pronounced diurnal variability driven by anomalous daytime surface warming. For example, low-level horizontal winds are weakest during the afternoon and intensify overnight when boundary-layer turbulence is minimal. The heat low favours an upper-tropospheric anticyclone which induces an upper-level Rossby wave and leads to negative upperlevel temperature anomalies across southern China. The Rossby wave intensifies the upper-level cyclonic circulation across central China, whilst upperlevel negative temperature anomalies across south China extends the west Pacific subtropical high westward. These circulation anomalies influence temperature and precipitation anomalies across much of China. The association between land-atmosphere interactions across the TP, large-scale atmospheric circulation characteristics, and precipitation in east Asia highlights the importance of intraseasonal soil moisture dynamics on the TP.

The Role of Mesoscale Convective Systems in Precipitation in the Tibetan Plateau Region

“…The systems that made the greatest contributions to precipitation $$ > $$5 mm hr −1 over the TP (including both MCSs and TCSs) were located in the eastern part of the TP. This regional pattern may be related to surface properties, such as soil moisture and vegetation, which can regulate heat fluxes in the boundary layer (Talib et al., 2021) and thereby increase the convective instability at higher altitudes. This has, for instance, been suggested by Sugimoto and Ueno (2012) who found that soil moisture played a crucial role for convection initiation over the eastern TP.…”

Satellite‐Observed Vegetation Responses to Intraseasonal Precipitation Variability

“…The stronger vegetation response to precipitation is expected to dominate any weaker impacts in the opposing direction. Moreover, the impact of intraseasonal surface variability on precipitation may be non-local (Chug & Dominguez, 2019;Talib et al, 2021Talib et al, , 2022. Water controls on transpiration (rather than direct evaporation) provide the dominant pathway for atmospheric feedbacks on these timescales.…”

The sensitivity of the West African monsoon circulation to intraseasonal soil moisture feedbacks

“…(2005) who showed that West African monsoon winds maximise overnight when the convective boundary layer is diminished and boundary‐layer turbulence is weak. The diurnally varying atmospheric response is similar to those found in modelling (Rácz and Smith, 1999; Smith and Spengler, 2011) and observational (Hoinka and Castro, 2003; Parker et al ., 2005; Howard and Washington, 2018; Talib et al ., 2021) studies of the dynamical atmospheric response to surface warming in the Sahel and other regions of the world. The southward monsoon shift also leads to substantial humidity perturbations with specific humidity decreasing by up to 1.6 g$$$ \cdotp $$$kg$$$ {}^{-1} $$$ to the north of maximum warming (Figure 7h).…”