Study On The Cloud Vertical Structure In Beijing Based On Synchronous Observation Data With Multi-source And High Temporal And Spatial Resolution

As crucial drivers of change in weather and climate systems,Cloud top height(CTH),cloud base height(CBH),cloud layer,cloud thickness and other macroscopic cloud vertical structure(CVS)parameters affect the Earth's energy budget and are closely related to the interaction mechanism between aerosol and atmospheric boundary layer.Based on the multisource remote sensing data with high precision and spatio-temporal synchronization obtained from the Megacities Experiment on Integrated Meteorological Observation in China(MEMO),this paper studied the methods of retrieving CVS based on continuous observation of Ka-band millimeter wave cloud radar(MMCR),a Vaisala CL51 ceilometer(CL51),L-band radiosonde,Himawari-8 geostationary meteorological satellite(HW8),the wind profile radar(WPR)in Beijing Nanjiao weather observatory(BNWO),and analyzed the consistency and discrepancy of CVS by making comparison and verification among different equipments.The climatology of CVS in BNWO were elucidated based on MMCR and radiosonde data,and a comprehensive method for recognizing “cloud frontal zone” based on multi-source data was finally proposed.The main conclusions were as follows:1.retrieval method of CVS based on base data of radionsonde and MMCR were proposed and improved in this thesis.The comparison results of CVS between MMCR retrieval and the collocated radiosonde retrieval showed that CTHs observed by MMCR were lower by 422.0 m on average,while CBHs were higher by 350.7 m.In general,there was a good consistency between them.The main cause of the deviation included the difference of physical theory,balloon drifting,attenuation of MMCR during precipitation and the limitations of algorithm for retrieving CVS and so on.2.MMCR-derived CBHs and CTHs were compared with those derived from CL51 and those retrieved from the HW8.The results showed that the consistency of cloud detection among the three devices was as high as 74.4%.Overall,the MMCR-derived CBHs were slightly higher(by 0.08km)than those derived from the CL51.By contrast,the MMCR-derived CTHs were significantly higher(by 0.82km)than those retrieved from the HW8 satellite.CL51-derived CBHs were generally lower than those observed by MMCR in haze weather.In the presence of precipitation,the MMCR-derived cloud heights were generally lower than those obtained by the CL51 and HW8 due to the much larger rain-induced attenuation of MMCR signals.In particular,the discrepancy between MMCR-and CL51-derived CBHs decreased with rainfall intensity,as opposed to CTHs from the MMCR and the HW8 satellite that increased with rainfall intensity.On the contrary,as the cloud thickness increased,the deviation of CTHs decrease while deviation of CBHs increased.Therefore,CL51 and HW8 data can be used to complement MMCR data when there is rainfall or when MMCR data is missing,and the correction results showed that the mean CBHs in winter was 4.42 km while the mean CTHs in summer was 9.34 km.3.The distribution characteristics of CVSs in Beijing were calculated using the radiosonde base data.the results showed that the cloud occurrence frequency was the highest in in summer(22.7%)while was the lowest in winter(9.9%).The average CTHs,CBHs,cloud thickness and cloud spacing were 6.2 km,4.0 km,2.2 km and 1.7 km,respectively.On the whole,the average cloud heights were higher in spring and summer than in autumn and winter.The mixed clouds including both warm clouds and cold clouds were dorminant in Beijing.In terms of the seasonal distribution,the proportion of warm clouds was the largest in autumn and the smallest in winter while the proportion of cold clouds was the largest in spring and winter and the smallest in summer.4.The vertically resolved cloud structures and their climatological variation based on three-year MMCR measurements in Beijing were elucidated.The results showed that precipitating clouds tended to be located at lower altitudes and exhibited stronger radar reflectivities than non-precipitating clouds.The cloud top height and radar reflectivity intensity in summer and autumn are higher than that in spring and winter.In terms of seasonal variation,CTHs and radar reflectivity were both higher in summer and autumn than spring and winter,which experience less convective precipitation.There were two peaks in the CBH distribution,located at 0–1 km and 5–6 km,whereas the frequency of the CTH peaked at an altitude of 9–10 km.The cloud frequency tended to peak in autumn and reached a minimum in winter.There was a significant diurnal variation of cloud cover in summer,with peak value occurring between15:00 and 20:00 local standard time(LST).In terms of the seasonality of clouds at various levels,middle-and high-level clouds were dominant over Beijing,with high and low(precipitating)clouds concentrated between May and October.Mid-altitude clouds occurred more frequently in winter and spring.5.Based on the frontal theory,"cloud frontal zone" was proposed for the first time which was defined as a dense transition zone between cloud and ambient atmosphere where meteorological elements presented dramatic gradient variation,namely.By using the radiosonde,MMCR and WPR,it was found that meteorological elements in "cloud front zone" had the common characteristics of discontinuous gradient variation and large pulsation amplitude.Finally,the reasonable range of “cloud frontal zone” is given through case studies.