Travelling planetary waves extracted from UKMO and ECMWF assimilated fields and simulated with COMMA-LIM model

Details Travelling planetary waves extracted from UKMO and ECMWF assimilated fields and simulated with COMMA-LIM model Travelling planetary waves extracted from UKMO and ECMWF assimilated fields and simulated with COMMA-LIM model

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....1842p&link_type=abstract

EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #1842

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Scientific paper

The analysis of UKMO data shows that these assimilated fields can be used to study a long-term variability of planetary waves in the stratosphere (Fedulina et al., 2002). However, this daily data set can not be used to consider the planetary waves with periods shorter then of about 4~days. The ECMWF operational analysis 6-hourly data set gives us a possibility to investigate the shorter-period planetary waves. Both of these assimilated stratospheric geopotential height fields have been analyzed to investigate the shorter-period (T< 10 days) planetary waves during June/September 2001 time interval. The results of this analysis show that in the northern (summer) hemisphere the westward-propagating waves with zonal wave numbers m=1-3 are dominant and the observed maxima in wavelet spectra can be identified with the normal atmospheric modes, the so-called 5-, 4-, and 2-day waves. There exists also a substantial westward-propagating wave with m=4 and period of about 40~hours. In the southern (winter) hemisphere at high latitudes the maxima in wavelet spectra are obtained for the eastward-propagating waves with m=1 (period of about 4~days) and m=2 (period of about 2~days). It is suggested that these two waves, as well as the 40-hour westward-propagating wave in the northern hemisphere, are excited in the result of an instability of stratospheric jets. Wavelet spectra show also a presence of the eastward-propagating wave with m=1 and period between 4 and 6 days above the equator, which can be interpreted as a manifestation of the Kelvin wave. There is a good agreement between the results obtained using UKMO and ECMWF data sets. The results of the planetary-wave simulation with COMMA-LIM model are discussed. It is shown that this mechanistical model is capable of reproducing the propagation and main properties of Rossby normal-mode and Kelvin waves up to the lower thermosphere, but unstable modes are absent in the climatological background wind fields. It is suggested that to simulate the unstable planetary modes an internal variability of the stratospheric flow (for instance, the stratospheric warming events) has to be taken into consideration. Reference Fedulina I.N., Pogorletsev A.I. and G. Vaughan, Seasonal, interannual and short-term variability of planetary waves in UKMO assimilated fields, Quarter. J. Roy. Meteorol. Soc., 128, 2002, submitted for publication.

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