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Prediction of visibility and aerosol within the operational Met Office Unified Model. I: Model formulation and variational assimilation
Author(s) -
Clark P. A.,
Harcourt S. A.,
Macpherson B.,
Mathison C. T.,
Cusack S.,
Naylor M.
Publication year - 2008
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.318
Subject(s) - visibility , aerosol , meteorology , advection , environmental science , data assimilation , humidity , geography , physics , thermodynamics
The formulation and performance of the Met Office visibility analysis and prediction system are described. The visibility diagnostic within the limited‐area Unified Model is a function of humidity and a prognostic aerosol content. The aerosol model includes advection, industrial and general urban sources, plus boundary‐layer mixing and removal by rain. The assimilation is a 3‐dimensional variational scheme in which the visibility observation operator is a very nonlinear function of humidity, aerosol and temperature. A quality control scheme for visibility data is included. Visibility observations can give rise to humidity increments of significant magnitude compared with the direct impact of humidity observations. We present the results of sensitivity studies which show the contribution of different components of the system to improved skill in visibility forecasts. Visibility assimilation is most important within the first 6‐12 hours of the forecast and for visibilities below 1 km, while modelling of aerosol sources and advection is important for slightly higher visibilities (1‐5 km) and is still significant at longer forecast times. © Crown Copyright 2008. Reproduced with the permission of the Controller of HMSO. Published by John Wiley & Sons, Ltd.