COMPARISON OF UK-METEOROLOGICAL-OFFICE AND US-NATIONAL-METEOROLOGICAL-CENTER STRATOSPHERIC ANALYSES DURING NORTHERN AND SOUTHERN WINTER

Meteorological data from the United Kingdom Meteorological Office (UKM O), produced using a data assimilation system, and the U.S, National M eteorological Center (NMC), produced using an objective analysis proce dure, are compared for dynamically active periods during the Arctic an d Antarctic winters of 1992. The differences seen during these periods are generally similar to those seen during other winter periods. Both UKMO and NMC analyses capture the large-scale evolution of the strato spheric circulation during northern hemisphere (NH) and southern hemis phere (SH) winters, Stronger vertical and horizontal temperature gradi ents develop in the UKMO than in the NMC data during stratospheric war mings; comparison with satellite measurements with better vertical res olution suggests that the stronger vertical temperature gradients are more realistic. The NH polar vortex is slightly stronger in the UKMO a nalyses than in the NMC in the middle and upper stratosphere, and mids tratospheric temperatures are slightly lower. The SH polar vortex as r epresented in the UKMO analyses is stronger and colder in the midstrat osphere than its representation in the NMC analyses. The UKMO analyses on occasion exhibit some difficulties in representing cross-polar flo w or changes in curvature of the wind field at very high latitudes. In addition to the above study of two wintertime periods, a more detaile d comparison of lower-stratospheric temperatures is done for all Arcti c and Antarctic winter periods since the launch of the Upper Atmospher e Research Satellite. In the NH lower stratosphere during winter, NMC temperatures are consistently lower than UKMO temperatures and closer to radiosonde temperatures than are UKMO temperatures. Conversely, in the SH lower stratosphere during winter, UKMO temperatures are typical ly lower than NMC and are closer to radiosonde temperature observation s.