Boundary layer features of the 1994 hot summer in Japan

By using data for 34 years (1961-1994), climatological features of the 1994 hot summer in Japan were examined with attention to boundary-layer processes. The thermal anomaly in the boundary layer was analyzed in terms of two parameters: screen height-850 hPa temperature difference (delta T) and day-night pressure difference (Delta p). It was found that the 1994 summer was characterized by a positive anomaly of delta T and a negative anomaly of Delta p, namely a larger temperature anomaly in the daytime boundary layer than in the free atmosphere. The anomalies of delta T and Delta p were found to be correlated with the precipitation and sunshine during the preceding days. This indicates that the high temperature in the 1994 summer is partly referred to the reduction of soil moisture due to persistent sunny weather. On the other hand, there was little indication of urban warming in the daytime except at some stations, although a warming trend in the nighttime was found for many stations. It is therefore unlikely that urban warming was the main cause of the high temperature in the daytime of the 1994 summer.