Thursday, 8 August 2013
Holladay-Halsey (DoubleTree by Hilton Portland)
Dependency of stratiform precipitation on two-moment scheme is investigated in midlatitude squall line, using one-moment, two-moment and partial two-moment schemes. The results are consistent with existing findings, and show that the two-moment scheme for rain varies rain evaporation which results in mass and buoyancy transport changes leading to the increase of stratiform precipitation. Employment of two-moment scheme for cloud water and cloud ice is found not to have significance on changing amount of stratiform precipitation, but is required for simulating reasonable rain formation. Two-moment treatment for graupel rather than snow is also found to have great impact on the stratiform precipitation through melting process in stratiform region. Horizontally narrow and vertically gradual number concentration change of the graupel along the melting process causes suppression to convective updraft by latent cooling in convective region, and thus increases horizontal rearward buoyancy from convective to stratiform regions, resulting in increase of stratiform precipitation. To simulate these features, decrease of intercept parameter of graupel in convective and its increase in stratiform regions are needed to be simulated simultaneously, thus two-moment scheme for graupel or better diagnostic intercept parameter for graupel is required.
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