The Impact of Positive-Definite Moisture Transport on NWP Precipitation Forecasts

Skamarock, William C.; Weisman, Morris L.
January 2009
Monthly Weather Review;Jan2009, Vol. 137 Issue 1, p488
Academic Journal
A positive-definite transport scheme for moisture is tested in a nonhydrostatic forecast model using convection-permitting resolutions. Use of the positive-definite scheme is found to significantly reduce the large positive bias in surface precipitation forecasts found in the non-positive-definite model forecasts, in particular at high precipitation thresholds. The positive-definite scheme eliminates spurious sources of water arising from the clipping of negative moisture values in the non-positive-definite model formulation, leading to the bias reduction.


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