Keywords:Boundary layer height, radiosonde, trend reversal, China
Our knowledge concerning the trend in boundary layer height (BLH) in China is limited due to the unavailability of reliable and high-resolution radiosonde measurements. In this talk, we will present the trend of BLH over China, using the radiosonde observations (at 08:00 pm) at 89 stations for the period 1979–2016. Overall, the annual mean BLH averaged over all the available stations in China exhibits a distinct west-to-east negative gradient. Most stations exhibit an increasing trend in BLH during 1979-2003 and shift to a declining trend in BLH during 2004-2016. The trend of seasonal mean BLH bears resemblance to annual mean BLH. The meteorological influence on the temporal disparity of the BLH trend is investigated as well, showing that BLH at most sounding sites is negatively associated with the soil moisture, lower tropospheric stability (LTS) and surface relative humidity, but positively associated with the near-surface temperature. An increase of BLH (9.4m yr-1 during 1981-1988,14.0m yr-1during 1989-2003) from 1979 to 2003 is found to be related to an increase in near-surface temperature (mean=0.04 ºC yr-1), a reduction of soil moisture (mean=-2.18 kg m-2yr-1), a reduction of LTS (mean=-0.03 K yr-1), a decrease in surface relative humidity (mean=-0.007 % yr-1) during 1979-2003.A weakening of near-surface temperature and the increase of soil moisture, LTS and surface relative humidity are found to contribute to the decreasing trend of BLH during 2004-2016. The major findings obtained from this study help us better understand the climatology of BLH over China and its association with related meteorological variables.