Abstract
Clouds are significant in the global radiation budget, atmospheric circulation, and hydrological cycle. However, knowledge regarding the observed climatology of the cloud vertical structure (CVS) over Beijing is still poor. Based on high-resolution radiosonde observations at Beijing Nanjiao Weather Observatory (BNWO) during the period 2010–2017, the method for identifying CVS depending on height-resolved relative humidity thresholds is improved, and CVS estimation by radiosonde is compared with observations by millimeter-wave cloud radar and ceilometer at the same site. Good consistency is shown between the three instruments. Then, the CVS climatology, including the frequency distribution and seasonal variation, is investigated. Overall, the occurrence frequency (OF) of cloudy cases in Beijing is slightly higher than that of clear-sky cases, and the cloud OF is highest in summer and lowest in winter. Single-layer clouds and middle-level clouds are dominant in Beijing. In addition, the average cloud top height (CTH), cloud base height (CBH), and cloud thickness in Beijing are 6.2 km, 4.0 km, and 2.2 km, respectively, and show the trend of reaching peaks in spring and minimums in winter. In terms of frequency distribution, the CTH basically resides below an altitude of 16 km, and approximately 43% of the CBHs are located at altitudes of 0.5–1.5 km. The cloud OF has only one peak located at altitudes of 4–8 km in spring, whereas it shows a trimodal distribution in other seasons. The height at which the cloud OF reaches its peak is highest in summer and lowest in winter. To the best of our knowledge, the cloud properties analyzed here are the first to elucidate the distribution and temporal variation of the CVS in Beijing from a long-term sounding perspective, and these results will provide a scientific observation basis for improving the atmospheric circulation model, as well as comparisons and verifications for measurements by ground-based remote sensing equipment.
Highlights
As critical driving forces of climate systems, clouds play a significant role in modulating the energy budget, atmospheric circulation, and hydrologic cycle of the Earth [1,2,3,4]
The results showed that the consistency between cloud vertical structure (CVS) by radiosonde and other observations was further improved
It is necessary to verify the accuracy of CVS retrieved from the ZHA18 method based on radiosonde observations before proceeding further
Summary
As critical driving forces of climate systems, clouds play a significant role in modulating the energy budget, atmospheric circulation, and hydrologic cycle of the Earth [1,2,3,4]. Atmospheric circulation is significantly affected by the vertical and horizontal gradients in the radiative and latent heat fluxes induced by clouds [5]. There are large uncertainties in the net impact of clouds on the energy budget due to two opposite effects, depending on cloud thickness [6] and the interaction with aerosols [7,8,9]; Atmosphere 2020, 11, 401; doi:10.3390/atmos11040401 www.mdpi.com/journal/atmosphere. CVS played an important role in modifying the radiative cooling profile and latent heating profile of the atmosphere. Explicit knowledge about CVS seems to be elusive because of the large temporal and spatial variability in CVSs, leading to considerable difficulty in global weather and climate prediction [2,11]
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