Abstract
AbstractConvection over the Tibetan Plateau (TP) has been linked to heavy rain and flooding in downstream parts of China. Understanding processes which influence the development of convection on the TP could contribute to better forecasting of these extreme events. TP scale (~1000 km) soil moisture gradients have been shown to influence formation of convective systems over the eastern TP. The importance of smaller-scale (~10 km) variability has been identified in other regions (including the Sahel and Mongolia) but has yet to be investigated for the TP. In addition, compared to studies over flat terrain, much less is known about soil moisture–convection feedbacks above complex topography. In this study we use satellite observations of cold cloud, land surface temperature, and soil moisture to analyze the effect of mesoscale soil moisture heterogeneity on the initiation of strong convection in the complex TP environment. We find that strong convection is favored over negative (positive) land surface temperature (soil moisture) gradients. The signal is strongest for less vegetation and low topographic complexity, though still significant up to a local standard deviation of 300 m in elevation, accounting for 65% of cases. In addition, the signal is dependent on background wind. Strong convective initiation is only sensitive to local (tens of kilometers) soil moisture heterogeneity for light wind speeds, though large-scale (hundreds of kilometers) gradients may still be important for strong wind speeds. Our results demonstrate that, even in the presence of complex topography, local soil moisture variability plays an important role in storm development.
Highlights
The Tibetan Plateau (TP) is the highest and most extensive plateau in the world, profoundly affecting climate and weather in the region (Yang et al 2013; Li et al 2014)
For strong convection cases where there is sufficient local LST anomalies (LSTAs) data, we sample an initiation gradient between 210 and 20 km, corresponding to the scale around which we expect the effect of surface heterogeneity on initiations to be maximized (T11)
A comparison of wind direction between the products for our cases reveals a larger spread for lower wind speeds (Fig. S6), as expected. Both ERA-Interim and MERRA2 display a similar disagreement with ERA5, we find the composite LSTA gradient to be more significant for MERRA2 than ERA-Interim (p 5 0.07 and p 5 0.6 respectively, Table 1) suggesting there may be other factors contributing to the worse skill of ERA-Interim
Summary
The Tibetan Plateau (TP) is the highest and most extensive plateau in the world, profoundly affecting climate and weather in the region (Yang et al 2013; Li et al 2014). Due to its average elevation of more than 4000 m, it provides strong thermal and dynamical forcing in the midtroposphere during the summer months, fostering the frequent development of intense storms (e.g., Yang et al 2004). Tibetan convective systems (TCSs) can be associated with extreme rainfall events and contribute up to ;70% of rainfall over the TP and adjacent areas (Hu et al 2016). A better understanding of the processes that impact TCS genesis over the TP could contribute to better forecasting of these extreme events. There is strong evidence for accelerated climate warming on the TP
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