Pre-operational testing of the new boundary layer and MOSES-1 surface exchange schemes in the UK Mesoscale Model
Best, M.J. ; CHALCRAFT, B.V. ; WILSON, C.A. ; Radcliffe, J. ; Macpherson [B.] ; Jones C.P. ; Cox [P.M.]
New boundary layer and surface flux schemes were developed and tested in the UK Mesoscale Model. Verification showed them to have an overall beneficial effect and they were implemented operationally on 5th May 1999. The new boundary layer scheme has a non-local specification of the turbulent mixing coefficients, categorizing the structure into one of six predetermined types. It also explicitly parametrizes entrainment at the top of the turbulent mixing layer. The Met Office surface exchange scheme, called MOSES, uses a Penman-Monteith-type surface energy balance, has four deep soil levels and follows an interactive canopy resistance model. The version of MOSES discussed here is known as MOSES-I. (Its extension to allow for non-uniformity of the land surface in a grid box is known as MOSES-II and was implemented operationally in October 2000, as reported by best et al., 2000). The soil moisture analysis from MORECS data had to be considerably revised for MOSES. Of the impacts seen in forecast fields over the course of the trial, greatest improvements came in predicting low cloud and fog and improving the diurnal cycle of screen temperature.
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