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Discussion papers
https://doi.org/10.5194/acp-2019-154
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-154
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 Apr 2019

Research article | 08 Apr 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Drier spring over the US Southwest as an important precursor of summer droughts over the US Great Plains

Amir Erfanian and Rong Fu Amir Erfanian and Rong Fu
  • Department of Atmosphericand Oceanic Sciences, University of California Los Angeles, CA, USA

Abstract. This study addresses the role of atmospheric moisture budget in determining the onset and development of the summer droughts over the North American Great Plains (GP) using two state-of-the-art reanalysis datasets. We identified zonal moisture advection as the major cause of the severe tropospheric drying during the extreme droughts of southern GP 2011 and northern GP 2012. For both events, an eastward advection of anomalously dry and warm air in the free troposphere in spring sets the stage for the summer drought, leading to a sharp drop of relative humidity above the boundary layer, enhancing dry entrainment, and suppressing deep convection. Further breakdown of the zonal advection into the dynamic (caused by circulation anomalies) versus thermodynamic (caused by moisture anomalies) contributions revealed dominance of the thermodynamic advection in the tropospheric drying observed during the onset of both 2011 and 2012 droughts. The dependence of thermodynamic advection on moisture gradient links the spring precipitation in the Rockies and southwestern US, the source region of the anomalous dry advection, to the GP summer precipitation (with correlations > 0.4 using gauged-based data). The results of this study improve our predictive understanding of summer drought onset mechanisms over the GP.

Amir Erfanian and Rong Fu
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Amir Erfanian and Rong Fu
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Short summary
An eastward advection of dry and warm air in spring was identified as a major drought onset mechanism over the US Great Plains (GP). Further breakdown of the zonal advection into the dynamic versus thermodynamic contributions revealed dominance of the latter in the tropospheric drying observed during the onset of GP 2011 and 2012 droughts. The dependence of thermodynamic advection on moisture gradient links the spring precipitation in the Rockies and US southwest to the GP summer precipitation.
An eastward advection of dry and warm air in spring was identified as a major drought onset...
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