Study On The Diurnal Variation Of Cloud Radiative Property And The Relationship With Meteorology

The Diurnal cycle of clouds(DCC)is a critical cloud property for weather and climate systems,determining the strength of net cloud radiative forcing(CRF).Nevertheless,this property is not well simulated in current climate models and lacks understanding on its vertical structure and its links to meteorological factors,and thus contributing to the largest cloud uncertainties in climate models.In this paper,we combine ground-based and satellite instruments with high precision and temporal-spatial resolution together,to describe diurnal variations of cloud macrophysical and microphysical properties and their impacts on the CRF thoroughly.Furthermore,the links between clouds and meteorological factors(i.e.temperature,stability,vertical velocity and relative humidity)on the diurnal timescale and the response of diurnal centroid are discussed.First,we take advantage of the cloud observation of Ka-band Zenith Radar(KAZR)at Semi-Arid Climate and Environment Observatory of Lanzhou University(SACOL)and the fifth state-of-the-art reanalysis(ERA5)with hourly resolution derived from European Centre for Medium-Range Weather Forecasts(ECMWF),to analyze the diurnal variation of cirrus and its radiative forcing.By principal component analysis(PCA),variations of meteorological factors are better evaluated to link cloud variations on the diurnal timescale.It is found that cirrus can produce 20.1W/m² net radiative forcing and impose strong warming effects on the Earth,which can be attributed to diurnal cycle of cirrus.Moreover,we investigated the diurnal cycle of cloud vertical structure and its impact on the CRF on global scale by Clouds-Aerosol Transport System(CATS)lidar and Clouds and Earth Radiant Energy System(CERES)geostationary imagery.It is found that high clouds and oceanic low clouds have the feature of nighttime development,whereas continental low clouds develop at noon.By computing the correlation relationship between daily mean cloud amount,amplitude and centroid and their impacts on the CRF,the daily mean cloud amount and amplitude are highly correlated and they all have competing impacts on the CRF.Especially,there is a slope about-13.3Wm^-2h^-1 between diurnal centroid and net CRF.In consideration of cold point temperature and vertical velocity at 300h Pa,high clouds are more likely to peak during the period from afternoon to midnight.On the contrary,high clouds peak during the period from midnight to morning.This presents fundamental factors for controlling diurnal centroid.According to the record of geostationary imagery from 2001 to 2018,the diurnal centroid is significantly correlated with global mean temperature,with 0.70 correlation coefficient.This indicates under global warming,the diurnal centroid will shift to the period between midnight to morning,especially in summer.On average,with temperature raising 1?,the centroid will shift about 2 hour 47 minutes.