Diagnosis of systematic differences between multiple parametrizations of warm rain microphysics using a kinematic framework

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Abstract
This paper introduces the Kinematic Driver Model (KiD) and its application. KiD is a 1D modelling framework developed at the UK Met Office to facilitate a consistent intercomparison of the microphysics parametrizations employed in a number of cloud‐resolving models and numerical weather prediction models. The development of the KiD model was born out of GCSS intercomparison results, which show a wide range of microphysical behaviour and a need to explain the behaviour of different microphysics schemes without the complication of dynamic or radiative feedbacks. This paper describes the KiD model and one of the standard test cases for warm microphysics. Results from a comparison of warm microphysics schemes are presented. The schemes tested produce very different surface precipitation rates and onset timings, as well as different accumulated precipitation. In general, single‐moment bulk schemes produce the most rapid onset of precipitation and the widest range in accumulated surface precipitation. Sensitivity tests within the KiD show that including a diagnostic intercept parameter for the rain size distribution reduced variation between the single‐moment schemes. However, the early onset of precipitation is a persistent feature of single‐moment schemes. Double‐moment bulk schemes exhibit improved timing for the precipitation onset relative to an explicit bin model and comparison of accumulated precipitation shows much better agreement. However, double‐moment schemes tend to produce relatively large peak precipitation rates, particularly with the deeper cloud. Further sensitivity tests within the KiD demonstrate that using a three‐moment scheme, with variable shape parameter, significantly improves the simulation peak precipitation rate relative to an explicit bin model. The tests and results presented in this paper are described to act as a reference for other users to compare with their microphysics schemes and aid microphysics parametrization development. Copyright © 2012 British Crown copyright, the Met Office. Published by John Wiley & Sons Ltd.

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