Ice supersaturation in the ECMWF integrated forecast system

被引:160
作者
Tompkins, A. M.
Gierens, K.
Radel, G.
机构
[1] European Ctr Medium Range Weather Forecasts, Reading RG2 9AX, Berks, England
[2] DLR, Inst Phys Atmosphare, Oberpfaffenhofen, Germany
[3] Univ Reading, Dept Meteorol, Reading RG6 2AH, Berks, England
关键词
cirrus clouds; ice nucleation; microphysics;
D O I
10.1002/qj.14
中图分类号
P4 [大气科学(气象学)];
学科分类号
0706 ; 070601 ;
摘要
A parametrization for ice supersaturation is introduced into the ECMWF Integrated Forecast System (IFS), compatible with the cloud scheme that allows partial cloud coverage. It is based on the simple, but often justifiable, diagnostic assumption that the ice nucleation and subsequent depositional growth time-scales are short compared to the model time step, thus supersaturation is only permitted in the clear-sky portion of the grid cell. Results from model integrations using the new scheme are presented, which is demonstrated to increase uppertropospheric humidity, decrease high-level cloud cover and, to a much lesser extent, cloud ice amounts, all as expected from simple arguments. Evaluation of the relative distribution of supersaturated humidity amounts shows good agreement with the observed climatology derived from in situ aircraft observations. With the new scheme, the global distribution of frequency of occurrence of supersaturated regions compares well with remotely sensed microwave limb sounder (MLS) data, with the most marked errors of underprediction occurring in regions where the model is known to underpredict deep convection. Finally, it is also demonstrated that the new scheme leads to improved predictions of permanent contrail cloud over southern England, which indirectly implies upper-tropospheric humidity fields are better represented for this region. Copyright (c) 2007 Royal Meteorological Society
引用
收藏
页码:53 / 63
页数:11
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