On the accuracy of analysed low temperatures in the stratosphere

[摘要] The accuracy of ECMWF (European Centre for Medium-Range Weather Forecasts)temperatures has been investigated by comparison to radiosonde temperatures. Particularly,the extent of temperatures below which Polar Stratospheric Clouds (PSCs) consisting of nitricacid trihydrate can exist (T_NAT) has been studied. In the 1999/2000 winter analyses and in the40 year reanalyses (ERA40) from the winter 1996/1997 the analysed extent agrees quite wellwith the radiosondes extent, whereas the 2002/2003 winter analyses considerablyoverestimate the extent from 40-11 hPa due to a general cold bias. Close to the frost pointsmall-scale temperature variations, which ECMWF does not catch, substantially increase theextent of these low temperatures. Some of these small-scale variations are caused by lee-waves.

[学科分类] 大气科学