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Evaluation of key microphysical parameters in three‐dimensional cloud‐model simulations using aircraft and multiparameter radar data
Author(s) -
Brown Philip R. A.,
Swann Hugh A.
Publication year - 1997
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49712354406
Subject(s) - parametrization (atmospheric modeling) , graupel , radar , precipitation , environmental science , meteorology , cloud physics , cloud computing , cloud top , atmospheric sciences , convection , computer science , physics , radiative transfer , telecommunications , quantum mechanics , operating system
A 3‐d numerical model is being used for the development of improved parametrizations of convective transport processes in climate and numerical weather‐prediction models. In common with similar cloud‐resolving models, it uses a 3‐phase bulk‐water parametrization of the microphysical processes. the comparison of results from such models with observed case‐studies represents an important step in their development and a key activity of the Global Energy and Water Cycle Experiment Cloud System Study. This paper presents observations and model results from the case of a weakly convective precipitating cloud that occurred on 22 June 1990 over central southern England. the cloud was observed by both an instrumented research aircraft and a dual‐polarization radar. the combination of these measurements provides information on the dominant precipitation particle types, their density, number concentration, and characteristic size, and enables the identification of key microphysical processes. the observations were used to provide guidance on the numerical values of some of the variable parameters in the microphysics scheme. Observed values of N o,G , the intercept parameter for graupel, lay in the range 10 4 to 10 7 m −4 . the comparison of observed radar reflectivities with those calculated from in situ particle size spectra suggests that the density of rimed precipitation particles decreased from around 0.5 g cm −3 in the most intense precipitation to around 0.1 g cm −3 towards the cloud edges. A number of model sensitivity studies were performed to examine the impact of changes in these parameters on the model cloud and precipitation fields. For this case‐study, it was found that the total surface precipitation was generally insensitive to such changes, varying by less than 10%. Reductions of 35% occurred for model runs in which the graupel fall speed was reduced and for a model run with only ‘warm‐rain’ microphysics. Much larger variations in the range 50‐100% occurred in the total cloud ice and snow contents. The modelling study identifies a number of differences between runs which could not be resolved owing to the lack of in situ data in certain regions of the cloud. Some of the requirements for improved observational methods and procedures are discussed.