Diurnal variations in lower-tropospheric wind over Japan part II: Analysis of Japan meteorological agency mesoscale analysis data and four global reanalysis data sets

Abstract

Following on from the observation results obtained from Wind profiler Network and Data Acquisition System (WINDAS) data, as reported by Part I of this study, the dynamical processes responsible for the diurnal component in lower-tropospheric winds are examined using Japan Meteorological Agency (JMA) mesoscale analysis data (MANAL) and four global reanalysis data sets (JRA25/JCDAS, ERA-Interim, NCEP1, and NCEP2). Of these data sets, MANAL and JRA25 perform best in reproducing the WINDAS horizontal wind observations, including their diurnal and semidiurnal components. At 1-3 km height, Diurnal Eastward-moving Eddies (DEEs) with a phase speed of 10-15 m s_1 and diameter of∼700 km move eastward over the Sea of Japan and over the Pacific throughout the year. The superposition of winds associated with DEEs over return currents controls the diurnal wind component over the main Japanese islands, generating diurnal amplitude maxima in spring and autumn at this height range. Analysis of global reanalysis data confirmed that the diurnal wind at 3-5 km in winter-spring is controlled mainly by medium-scale eastward-traveling waves with amplitude maxima around the tropopause. The diurnal wind at 3-5 km in summer-autumn is caused primarily by the diurnal tide with zonal wavenumbers ofa10. For stations located on small islands south of the Japanese mainland, the diurnal wind is controlled mainly by the diurnal tide for the entire lower troposphere throughout the year. © 2010, Meteorological Society of Japan.