A HEMISPHERIC STUDY OF DAILY PRESSURE VARIABILITY AT SEA LEVEL AND ALOFT

Abstract

The mean spatial distributions of the one-day lag auto-correlation, the standard deviation of interdiurnal pressure change, and the standard deviation of daily pressure are analyzed on maps covering much of the northern hemisphere. Well-defined isopleth patterns, which vary only slightly with season and elevation, are obtained. Although these isopleths are primarily zonal in orientation, they indicate two hemispheric centers of maximum pressure variability associated with the Icelandic and Aleutian lows, and a secondary center near Novaya Zemlya. It is found that the centers of extreme values for each of the three statistics at sea level lie along the principal cyclone track, with the minimum auto-correlation near the Great Lakes, the maximum interdiurnal pressure change in Labrador, and the maximum standard deviation of pressure in the Icelandic area. It is also pointed out that pressure variability in eastern North America generally exceeds that in both Europe and eastern Asia. Vertical cross sections are constructed for the North American region and reveal a level of maximum pressure variability around 500 mb and a level of minimum variability around 700 mb. They also show that pressure variability is least at sea level in low latitudes and around the 100-mb level in high latitudes. This implies that higher-level maps are of special importance in forecasting tropical weather.