Winter Time 10-20 Day Variations in the Upper Troposphere

Abstract

The 10-20 day variations in the northern hemisphere winter-time wind field in the upper troposphere have been examined using FGGE data. Previous study by Pan and Zhou (1985) has demonstrated the importance of the upper tropospheric long-synoptic scale waves in the modulation of the cold air outbreak over the winter monsoon domain. Results of this study indicate that these longsynoptic scale waves are part of a hemispheric wavetrain that propagates slowly eastward. Coherent wave movement can be traced from the Atlantic Ocean eastward to the central Pacific Ocean where the waves move equatorward. Teleconnection type response in the western Pacific Ocean is observed to be strong when a cyclonic or an anticyclonic center of the wave moves near the dateline. Singlelevel regional kinetic energy budget has been examined for these long-synoptic waves and, to a first order-of-magnitude approximation, the maintenance of the long-synoptic waves can be viewed as a balance of the flux-divergence by pressure-work and the barotropic energy conversion to mean flow.