Characteristics of cloud cluster over the steep southern slopes of the Himalayas observed by CloudSat

Abstract

ABSRACT A cloud cluster (CC) dataset is presented using CloudSat Cloud Profile Radar (CPR) observations from June to August, between 2006 and 2010. The CCs were defined by grouping contiguous cloud pixels using a defined criteria, including reflectivity, ‘cloud mask’, and topographic information. The characteristics of identified CCs were then analysed. Based on the complex topography of the southern Himalayas, four adjacent regions were selected, including the flat Gangetic Plains (FGP), the foothills of the Himalayas (FHH), the steep slope of the southern Himalayas (SSSH), and the Himalayan‐Tibetan Plateau (HTPT). The characteristics of the CCs in the four regions were different, and the distribution of the cloud‐top height gradually changed from bimodal (3 and 15 km) over the FGP and FHH, to unimodal (7–9 km) over the HTPT. From the plain to the Plateau, the average cloud‐top height and cloud‐base height increased after an initial decrease. The maximum reflectivity increased from −6 (plain) to 2 dBZ (slope areas), and then decreased to −2 dBZ (Plateau), which suggests that the CCs may produce precipitation on the slope. Maximum CCs occurred over the FHH. The characteristics of the CCs also showed semidiurnal variation, which may have been affected by the variation of the monsoon and the circulation over the mountain valley. According to the physical principles of the cloud‐type definitions from ISCCP, high‐level cirrus, deep convective CCs, and mid‐ to low‐level CCs were categorized. As the elevation increased, the cloud‐top height of the mid‐ to low‐level CCs also significantly increased to 8 km, whereas the cloud‐top height of the high‐level cirrus clouds decreased. Our results suggest that the different characteristics of CCs may be caused by a strong upward motion interacting with the terrain of the Himalayas.

Diurnal Variation of Meiyu Rainfall in the Yangtze Plain During Atypical Meiyu Years

“…Contoured frequency by altitude diagrams (CFADs) of radar echoes are a good indicator of the threedimensional structural characteristics of clouds or precipitation events (Chen, Fu, et al, 2017). Figure 4c shows the CFAD distribution of the Ku-band echo for this precipitation event.…”

Retrieval of the vertical evolution of the cloud effective radius from the Chinese FY-4 (Feng Yun 4) next-generation geostationary satellites

“…In the process of gridding, R e was taken as the arithmetic mean of all the cloud pixels in the grid. In view of the physical meaning of τ itself, direct arithmetic averaging without considering the pattern of distribution within the grid produced a maximum error of 20 % (Chen et al, 2019). We therefore used the logarithmic mean to average τ to a 1 • grid.…”

Trumpet‐Shaped Topography Modulation of the Frequency, Vertical Structures, and Water Path of Cloud Systems in the Summertime Over the Southeastern Tibetan Plateau: A Perspective of Daytime–Nighttime Differences

“…Due to thermal and orographic forcing, the summertime QTP is dominated by convective cloud systems, which exist at a small horizontal scale, and are relatively shallow and very local (Kurosaki & Kimura, ; Gao et al, ; Fu et al, ; Luo et al, ; Rüthrich et al, ; Pan & Fu, ; Li & Zhang, ; Shang et al, ; Wang & Guo, ). Note that the warm and humid summer monsoon frequently reaches the steep southern slope of the QTP, making it conducive to the formation of unique cloud–precipitation distributions (Chen et al, ; Chen et al, ; Fu et al, ; Qie et al, ; Yan et al, ; Yan & Liu, ; Zhang et al, ). In particular, the southeastern QTP (SETP) exhibits high‐frequency convective cloud systems consisting of very high cloud cover and large‐areal precipitation (Kurosaki & Kimura, ; Li et al, ; Maussion et al, ; Tan et al, ; Tong et al, ; Yu & Fu, ), and is the source of many large rivers in Asia, including the Jinsha, Lancang, and Nujiang rivers (Tan et al, ).…”

“…The analysis of observations from active and passive satellite instrumentation has enabled significant progress in the quantitative understanding of the horizontal and vertical spatial distribution of cloud systems over the southern QTP (Qie et al, ; Chen et al, ; Fu et al, ; Zhang et al, ; Chen et al, ; Yan & Liu, ; Luo et al, ; Li et al, ). For instance, Chen et al () revealed that the distribution of cloud top heights (CTH) gradually changes from bimodal (3 and 15 km) over the foothills of the Himalayas, to unimodal (7–9 km) over the QTP. There are two reflectivity peaks of cloud clusters over the steep slope of the southern Himalayas, corresponding to cirrus (stratus) and strong convection, whereas only a single peak occurs for cirrus (stratus) over the foothills of the Himalayas.…”

“…There are two reflectivity peaks of cloud clusters over the steep slope of the southern Himalayas, corresponding to cirrus (stratus) and strong convection, whereas only a single peak occurs for cirrus (stratus) over the foothills of the Himalayas. Chen et al () pointed out that the different characteristics of cloud clusters may be caused by a strong upward motion interacting with the Himalayan topography. Chen et al () found that the deep convection systems over the Tibetan Plateau and its southern slope have a higher main detrainment height (about 10–16 km) than in other regions at the same latitude.…”