Climatological characteristics of planetary boundary layer height over Japan

Based on the 30-year (1988-2017) radiosonde observations, the climatological characteristics of the planetary boundary layer height (PBLH) over Japan, as well as the long-term changes, are investigated. We firstly compared four different methods to determine the PBLH. Results show that the bulk Richardson number method has the best performance among all these methods. At all studied stations, monthly median PBLHs in the morning are generally higher than the ones in the evening. Bimodal structure of seasonal PBLHs are found over Japan. Daytime PBLH peaks in spring and autumn and achieves the minimum in summer and winter. Night-time PBLH shows less seasonal variations. It is found that the PBLHs in the central and southern part of Japan could be dominant by the variations of surface temperature, while the variations of surface relative humidity (RH) may be responsible for the PBLHs in the northern part of Japan. Moreover, sea fog which is associated with high RH and temperature inversion also has an obvious influence on PBLHs in northern Japan. Trend study shows that PBLHs in most stations slightly increased during the past 30years.