Investigation of Mesoscale Convective Cloud Clusters in South China

1993 ◽  
Author(s):  
Jixi Jiang ◽  
Huiming Ye ◽  
Meizhen Chen
Keyword(s):  
South China ◽  
Convective Cloud ◽  
Cloud Clusters ◽  
Mesoscale Convective

A Wave-Relative Framework Analysis of AEW–MCS Interactions Leading to Tropical Cyclogenesis

2020 ◽  
Vol 148 (11) ◽  
pp. 4657-4671
Author(s):  
Kelly M. Núñez Ocasio ◽  
Jenni L. Evans ◽  
George S. Young
Keyword(s):  
West Africa ◽  
Thermodynamic Characteristics ◽  
Convective Cloud ◽  
Type Systems ◽  
Squall Line ◽  
Tropical Cyclogenesis ◽  
Framework Analysis ◽  
Convective Systems ◽  
Cloud Clusters ◽  
Mesoscale Convective

AbstractAn African easterly wave (AEW) and associated mesoscale convective systems (MCSs) dataset has been created and used to evaluate the propagation of MCSs, AEWs, and, especially, the propagation of MCSs relative to the AEW with which they are associated (i.e., wave-relative framework). The thermodynamic characteristics of AEW–MCS systems are also analyzed. The analysis is done for both AEW–MCS systems that develop into tropical cyclones and those that do not to quantify significant differences. It is shown that developing AEWs over West Africa are associated with a larger number of convective cloud clusters (CCCs; squall-line-type systems) than nondeveloping AEWs. The MCSs of developing AEWs propagate at the same speed of the AEW trough in addition to being in phase with the trough, whereas convection associated with nondeveloping AEWs over West Africa moves faster than the trough and is positioned south of it. These differences become important for the intensification of the AEW vortex as this slower-moving convection (i.e., moving at the same speed of the AEW trough) spends more time supplying moisture and latent heat to the AEW vortex, supporting its further intensification. An analysis of the rainfall rate (MCS intensity), MCS area, and latent heating rate contribution reveals that there are statistically significant differences between developing AEWs and nondeveloping AEWs, especially over West Africa where the fraction of extremely large MCS areas associated with developing AEWs is larger than for nondeveloping AEWs.

scholarly journals Formation of Convective Clouds at the Foothills of the Tropical Eastern Andes (South Ecuador)

2009 ◽  
Vol 48 (8) ◽  
pp. 1682-1695 ◽  
Author(s):  
Jörg Bendix ◽  
Katja Trachte ◽  
Jan Cermak ◽  
Rütger Rollenbeck ◽  
Thomas Nauß
Keyword(s):  
San Francisco ◽  
Cell Formation ◽  
Austral Summer ◽  
Convective Cloud ◽  
Early Morning ◽  
Spatial Extent ◽  
Small Cells ◽  
Target Area ◽  
Convective Clouds ◽  
Mesoscale Convective

Abstract This study examines the seasonal and diurnal dynamics of convective cloud entities—small cells and a mesoscale convective complex–like pattern—in the foothills of the tropical eastern Andes. The investigation is based on Geostationary Operational Environmental Satellite-East (GOES-E) satellite imagery (2005–07), images of a scanning X-band rain radar, and data from regular meteorological stations. The work was conducted in the framework of a major ecological research program, the Research Unit 816, in which meteorological instruments are installed in the Rio San Francisco valley, breaching the eastern Andes of south Ecuador. GOES image segmentation to discriminate convective cells and other clouds is performed for a 600 × 600 km2 target area, using the concept of connected component labeling by applying the 8-connectivity scheme as well as thresholds for minimum blackbody temperature, spatial extent, and eccentricity of the extracted components. The results show that the formation of convective clouds in the lowland part of the target area mainly occurs in austral summer during late afternoon. Nocturnal enhancement of cell formation could be observed from October to April (particularly February–April) between 0100 and 0400 LST (LST = UTC − 5 h) in the Andean foothill region of the target area, which is the relatively dry season of the adjacent eastern Andean slopes. Nocturnal cell formation is especially marked southeast of the Rio San Francisco valley in the southeast Andes of Ecuador, where a confluence area of major katabatic outflow systems coincide with a quasi-concave shape of the Andean terrain line. The confluent cold-air drainage flow leads to low-level instability and cellular convection in the warm, moist Amazon air mass. The novel result of the current study is to provide statistical evidence that, under these special topographic situations, katabatic outflow is strong enough to generate mainly mesoscale convective complexes (MCCs) with a great spatial extent. The MCC-like systems often increase in expanse during their mature phase and propagate toward the Andes because of the prevailing upper-air easterlies, causing early morning peaks of rainfall in the valley of the Rio San Francisco. It is striking that MCC formation in the foothill area is clearly reduced during the main rainy season [June–August (JJA)] of the higher eastern Andean slopes. At a first glance, this contradiction can be explained by rainfall persistence in the Rio San Francisco valley, which is clearly lower during the time of convective activity (December–April) in comparison with JJA, during which low-intensity rainfall is released by predominantly advective clouds with greater temporal endurance.

Large-Scale Environmental Influences on Tropical Cyclone Formation Processes and Development Time

2020 ◽  
Vol 33 (22) ◽  
pp. 9763-9782
Author(s):  
Hsu-Feng Teng ◽  
James M. Done ◽  
Cheng-Shang Lee ◽  
Huang-Hsiung Hsu ◽  
Ying-Hwa Kuo
Keyword(s):  
Large Scale ◽  
Development Time ◽  
Analysis Method ◽  
Short Term ◽  
Convective Systems ◽  
Cloud Clusters ◽  
Mesoscale Convective ◽  
Environmental Transitions ◽  
Cluster Analysis Method ◽  
Low Levels

AbstractThe development of tropical cloud clusters (TCCs) to tropical cyclones (TCs) is the process of TC formation. This study identifies five main environmental transitions for the development of TCCs to TCs in the western North Pacific by using a cluster analysis method. Of these, three transitions indicate TCCs that develop in monsoon environments and two in easterly environments. Their numbers, distributions, and interannual variability differ. On average, the development time, defined as the period from the TCC forming to it developing into a TC, for TCCs that develop in easterly environments is shorter than that in monsoon environments. For the development of TCC to TC in easterly environments, TCCs have fewer embedded mesoscale convective systems (MCSs), which are located closer to the TCC center. Moreover, there is a stronger inward short-term (less than 10 days) angular momentum flux (AMF) at middle levels (800–500 hPa) before TCC formation. Conversely, in monsoon environments, TCCs have more MCSs, which are located farther from the TCC center. A stronger inward short-term AMF at low levels (1000–850 hPa) is observed before TCC formation and develops upward during the development of TCC to TC. The characteristics of MCS and AMF are significantly correlated with the development time of TCC to TC. In summary, large-scale easterly and monsoon environments cause TCCs to have different MCS and AMF characteristics, leading to higher efficiency for TCCs developing into TCs in easterly environments compared to monsoon environments.

scholarly journals The effect of ice nuclei on a deep convective cloud in South China

2018 ◽  
Vol 206 ◽  
pp. 1-12 ◽  
Author(s):  
Xin Deng ◽  
Huiwen Xue ◽  
Zhiyong Meng
Keyword(s):  
South China ◽  
Convective Cloud ◽  
Ice Nuclei ◽  
Deep Convective Cloud

Impacts of Anthropogenic Aerosols on Springtime Mesoscale Convective Systems over Southern China

2020 ◽  
Author(s):  
Lijuan Zhang ◽  
Tzung-May Fu
Keyword(s):  
Southern China ◽  
Convective Cloud ◽  
Mesoscale Convective Systems ◽  
Lower Atmosphere ◽  
Anthropogenic Aerosols ◽  
Cloud Droplets ◽  
Model Simulations ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Radiative Scattering

<p>Precipitation over Southern China for the month of April, which is largely associated with mesoscale convective systems (MCSs), has declined significantly in recent decades. It is unclear how this decline in precipitation may be related to the concurrent increase in anthropogenic aerosols in the atmosphere over this region. Using observation analyses and model simulations, we showed that anthropogenic aerosols significantly reduced MCS occurrences by 21% to 32% over Southern China in April, leading to less and weaker rainfall. Half of this MCS occurrence reduction was due to the direct radiative scattering and the indirect enhancement of non-MCS liquid cloud reflectance by aerosols, which stabilized the regional atmosphere. The other half of the MCS occurrence reduction was due to the microphysical and dynamical responses of the MCS to aerosols. The model simulations showed that the higher levels of aerosols and the resulting increase in liquid cloud droplets both enhance the scattering of sunlight, cool the surface, and stabilize the lower atmosphere. As a result, the occurrence of strong convective systems is suppressed, leading to decreased rainfall in April over Southern China. Our results demonstrated the complex effects of aerosols on MCSs via impacts on both convective systems and non-convective cloud systems in the regional atmosphere.</p>

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