CLIMATOLOGICAL CHARACTERISTICS OF SPRINGTIME LOWER TROPOSPHERIC AIRFLOW OVER CENTRAL AND EASTERN NORTH AMERICA

Abstract

A climatology of springtime lower tropospheric airflow, as represented by 850 hPa observed winds and 1000 hPa geostrophic winds, is presented for central and eastern North America. The climatology is based on twice-daily grid-point values for 1969–1989 from the operational analyses for the Northern Hemisphere prepared by the USA National Weather Service's National Meteorological Centre. Sixteen-point wind roses are used to show the spatial and temporal distributions by direction category of wind frequency, average speed, and wind run. These analyses are supplemented by resultant wind vector and streamline maps for each month. Evident in the climatological distributions is the declining strength of the circulation from March to May, the northward migration and strengthing of the North Atlantic subtropical anticyclone in late spring, and the nocturnal strengthening and veering of southerly airflow over the southern Great Plains. Additionally, areas of cyclonic and/or anticyclonic resultant flow correspond well with earlier identified centres of cyclogenesis and anticyclogenesis. The results presented here may provide a useful climatological baseline for future studies involving lower tropospheric airflow.