LONG-TERM FALLING TRENDS OF PRESSURE OVER THE KANTO PLAIN AS EVIDENCE OF INCREASING HEAT-CONTENT IN THE LOWER ATMOSPHERE IN THE DAYTIME OF THE WARM-SEASON

Long-term pressure changes in the Kanto plain in the warm season (April-September) are evaluated by using data spanning 32 years (1961-1992). It is found that daytime pressure, defined as departure from nighttime pressure, has fallen over the central and northern Kanto plain at a rate of 0.2 hPa/(30 years) on the average of the warm season, and 0.3-0.4 hPa/(30 years) on sunny days with weak synoptic pressure gradient. Correspondingly, daytime temperature is found to have risen in the central-northwestern Kanto plain at a rate of 1-1.5-degrees-C/(30 years). These facts give observational evidence of widespread warming due to extensive urbanization.