The Trend Of Cloud Cover In North China Plain And Its Influence On Diurnal Temperature Range

This paper analyzes the distribution and trend of cloud cover in the North China Plain(NCP)using the data of cloud cover,temperature and sunshine duration in the NCP from 1960 to 2014,and analyzes the distribution and trend of diurnal temperature range(DTR)and the impact of cloud on DTR.In addition,the correlation between DTR and meteorological elements is also analyzed(e.g.sunshine duration(SSD)).The main conclusions are as follows:(1)The average total cloud cover(TCC)in the NCP is 58 %,and the average low cloud cover(LCC)is 19 %.Cloud cover in the south is more than in the north,with the most in summer and the least in winter.TCC trend in the NCP was-0.89 %/10 a,and 98 stations in 137 stations showed a downward trend.The LCC trend was-3.07 %/10 a,with 111 stations showing a downward trend.TCC turned into a significant upward trend in the 1990 s,while LCC showed a continuous downward trend.(2)The average DTR trend is-0.19 °C/10 a,which is due to the fact that the daily minimum temperature growth is faster than the daily maximum temperature.By comparing DTR under overcast and clear-sky conditions,it was found that DTR under the overcast condition decreased more rapidly than under the clear-sky.It is believed that the upward trend of high cloud cover after the 1990 s may be one of the reasons why DTR trend is more rapidly under overcast conditions.In addition,the interaction between aerosol and cloud makes the cloud liquid water in the NCP increase,and the cloud albedo increases,which makes DTR decrease.It may be another reason for the temperature difference under overcast conditions.(3)There is a significant spatial correlation between trend of sunshine duration(SSD)and the trend of DTR in the North China Plain,which means that the change of SSD has a significant impact on the trend of DTR.The SSD are used as a variable to characterize the radiation,and the changes have a great influence on DTR that is very sensitive to radiation changes.There was a negative correlation between the specific humidity and DTR,specific humidity shows a increase trend in most stations.The increase of water vapor can absorb the solar radiation in the near-infrared part,which leads to the decrease of solar radiation reaching the ground during the day.The nighttime water vapor can absorb the long-wave radiation released from the surface,resulting DTR decrease in the NCP.Therefore,the influence of the humidity on the DTR is not negligible.