Observed Soil Moisture Impact on Strong Convection over Mountainous Tibetan Plateau

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  • 1 UK Centre for Ecology and Hydrology, Wallingford, UK
  • 2 UK Centre for Ecology and Hydrology, Wallingford, UK, National Centre for Earth Observation, Wallingford, UK
  • 3 UK Centre for Ecology and Hydrology, Wallingford, UK, Institute of Atmospheric and Cryospheric Sciences, University of Innsbruck, Innsbruck, Austria
  • 4 UK Centre for Ecology and Hydrology, Wallingford, UK
  • 5 Department of Plateau Atmospheric Physics Research, Northwest, Institute of Eco Environment and Resources, Chinese Academy of Sciences, China
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Abstract

Convection 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 (10s of km) soil moisture heterogeneity for light wind speeds, though large scale (100s of km) 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.

Corresponding author: Emma J Barton, emmbar@ceh.ac.uk

Abstract

Convection 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 (10s of km) soil moisture heterogeneity for light wind speeds, though large scale (100s of km) 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.

Corresponding author: Emma J Barton, emmbar@ceh.ac.uk
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