Climatology of Cloud Vertical Structures from Long-Term High-Resolution Radiosonde Measurements in Beijing

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.

Important Role of Low Cloud and Fog in Sulfate Aerosol Formation During Winter Haze Over the North China Plain

“…In Beijing, for instance, the frequency of low clouds in winter is 20.8% of the whole season, among which the probability of low clouds with the cloud base height (CBH) below 500 m is the highest at 12.5%, accounting for half of the total low cloud frequency (Figure 1b). Due to the low SO 2 concentration and high CBH in the medium and high clouds, as well as the middle and uppermost layers of the multilayer clouds (Q. Zhou et al., 2020), the transport of sulfate aerosol to the surface becomes difficult, so this study focuses on the impact of low clouds on sulfate aerosol formation. The sulfate oxidation ratio (SOR, molar ratio of sulfate to the sum of sulfate and SO 2 ), which has been extensively used to indicate the conversion efficiency of sulfur in the atmosphere (P. Liu et al., 2020; X. Wang et al., 2019; R. Zhang et al., 2018), increased with increasing relative humidity (RH) for conditions both with and without low clouds when pollution occurs (PM 2.5 concentration greater than 100 μg/m 3 ) in Beijing.…”

“…Water vapor accumulates in front of Taihang Mountain and Yanshan Mountain, prone to form low clouds in the NCP (L. Wang et al, 2014;Wu et al, 2017;R. Zhang et al, 2014;Q. Zhou et al, 2020).…”

“…In Beijing, for instance, the frequency of low clouds in winter is 20.8% of the whole season, among which the probability of low clouds with the cloud base height (CBH) below 500 m is the highest at 12.5%, accounting for half of the total low cloud frequency (Figure1b). Due to the low SO 2 concentration and high CBH in the medium and high clouds, as well as the middle and uppermost layers of the multilayer clouds (Q Zhou et al, 2020),. the transport of sulfate aerosol to the surface becomes difficult, so this study focuses on the impact of low clouds on sulfate aerosol formation.…”

Characteristics and Formation Mechanism of the Cloud Vertical Structure Over the Southeastern Tibetan Plateau in Summer

“…Similar problems also exist in other regions. For example, it is found that the CTH detected by radiosonde in Beijing is at most 2,500 m higher than that measured by ground–based millimeter–wave cloud radar (Zhou et al., 2020). In the Southern Great Plains and the Alaska region of the United States and the tropical Western Pacific, the CTH measured by the radiosonde is higher than that detected by ground–based cloud radar, with a standard deviation of about 2 km (Zhang et al., 2013).…”

“…The ascending radiosonde collects the temperature, pressure, relative humidity, wind and other meteorological elements as well as the latitude and longitude deviation at every 1.2 s (corresponding to a vertical resolution of about 8 m). Therefore, based on the radiosonde data during June-August from 2015 to 2021 from the 7 radiosonde sites, the relative humidity threshold method, which is commonly applied in studying the cloud of China and even the world (Cai et al, 2014;Li, Cai, & Zhou, 2021;Narendra Reddy et al, 2018;Wang et al, 2000;Wang & Rossow, 1995;Zhang et al, 2010Zhang et al, , 2018Zhou et al, 2020;Zhou & Ou, 2010), is used to detect the cloud layers over the SETP in this study. The details for the method to detect CVS can be found at the Text S1 and Table S1 in Supporting Information S1.…”