Global Characteristics of Medium-Scale Tropopausal Waves Observed in ECMWF Operational Data

Abstract

Abstract Global characteristics and seasonal variation of medium-scale (zonal wavelengths of 2000–3000 km) waves observed around the midlatitude tropopause are examined using 6-hourly European Centre for Medium-Range Weather Forecasts operational data over four years (1990–93), covering both hemispheres. Medium-scale waves and synoptic-scale waves are extracted using time filters and their characteristics are compared. Hovmoller diagrams indicate the existence of medium-scale waves in the Southern Hemisphere as well as in the Northern Hemisphere. The zonal wavelengths of medium-scale waves are slightly larger in the Southern Hemisphere than in the Northern Hemisphere. Medium-scale waves are mostly active in three regions: the North Atlantic in winter (Dec–Jan–Feb), the North Pacific in spring (Mar–Apr–May, MAM), and the south Indian Ocean in autumn (MAM). These regions are roughly corresponding to and slightly downstream of storm tracks where synoptic waves are dominant. Significant differences in seasona...