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Lower Tropospheric Processes; A Control on The Global Mean Precipitation Rate
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  • Jacob Hendrickson,
  • Christopher Terai,
  • Michael Pritchard,
  • Peter Caldwell
Jacob Hendrickson
University of California

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Christopher Terai
Lawrence Livermore National Laboratory
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Michael Pritchard
University of California Irvine
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Peter Caldwell
Lawrence Livermore National Laboratory
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The spread in global mean precipitation among climate models is explored in two ensembles using the complementary perspectives of surface evaporation and energy budgets. Models with higher global-mean precipitation have stronger oceanic evaporation, driven by drier near-surface air. The drier surface conditions occur alongside increases in near-surface temperature and moisture at 925 hPa, which point to stronger boundary layer mixing. Correlations suggest that the degree of lower tropospheric mixing explains 18%-49% of the intermodel precipitation variance. To test this hypothesis, the degree of mixing is varied in a single-model experiment by adjusting the relative humidity threshold that controls low-cloud fraction. Indeed, increasing lower tropospheric mixing results in more global mean precipitation. Energetically, increased precipitation rates are associated with more downwelling longwave radiation to the surface and weaker sensible heat fluxes. These results highlight how lower-tropospheric processes must be better constrained to reduce the precipitation discrepancy among climate models.
28 Mar 2021Published in Geophysical Research Letters volume 48 issue 6. 10.1029/2020GL091169