Statistical Characteristics of Long-Lived Large-Scale Disturbances in the Northern Hemisphere 500hPa Height Fields

Abstract

Disturgances of intermediate time-scale (10-30 days) were studied by use of twice daily data of geopotential heights for 11 years from 1969 to 1979. The disturbances with an amplitude of height of more than 150m were analyzed. High and low pressure systems with durations of longer than 7 days and sizes of larger than about 1, 000km in diameter were selected for the analysis. The number of them was fifty. Most of them occur in the two regions of the North Pacific and the North Atlantic, and migrate eastward, southward and westward. Their three dimensional structures show that baroclinic energy conversion from potential to kinetic energy plays a significant role in their life span.