Tropical Cloud Cluster Climatology, Variability, and Genesis Productivity

Abstract

Tropical cloud clusters (TCCs) are traditionally defined as synoptic-scale areas of deep convection and associated cirrus outflow. They play a critical role in the energy balance of the tropics, releasing large amounts of latent heat high in the troposphere. If conditions are favorable, TCCs can develop into tropical cyclones (TCs), which put coastal populations at risk. Previous work, usually connected with large field campaigns, has investigated TCC characteristics over small areas and time periods. Recently, developments in satellite reanalysis and global best track assimilation have allowed for the creation of a much more extensive database of TCC activity. The authors use the TCC database to produce an extensive global analysis of TCCs, focusing on TCC climatology, variability, and genesis productivity (GP) over a 28-yr period . While global TCC frequency was fairly consistent over the time period, with relatively small interannual variability and no noticeable trend, regional analyses show a high degree of interannual variability with clear trends in some regions. Approximately 1600 TCCs develop around the globe each year; about 6.4% of those develop into TCs. The eastern North Pacific Ocean (EPAC) basin produces the highest number of TCCs (per unit area) in a given year, but the western North Pacific Ocean (WPAC) basin has the highest GP (;12%). Annual TCC frequency in some basins exhibits a strong correlation to sea surface temperatures (SSTs), particularly in the EPAC, North Atlantic Ocean, and WPAC. However, GP is not as sensitive to SST, supporting the hypothesis that the tropical cyclogenesis process is most sensitive to atmospheric dynamical considerations such as vertical wind shear and large-scale vorticity.

Mesoscale Convective Systems in the Asian Monsoon Region From Advanced Himawari Imager: Algorithms and Preliminary Results

“…Figure shows the spatial distributions of SCSs, where several regions with high frequency stand out. In the tropics, SCSs mainly locate at the Bay of Bengal, South China Sea, and the western Pacific, consistent with Hennon et al (). The spatial pattern of SCS occurrence seems to be closely related with large‐scale circulations.…”

Influence of ENSO on formation of tropical cloud clusters and their development into tropical cyclones in the western North Pacific

“…Hennon et al . [] showed that ENSO influenced the number, location, and development of TCCs (the precursors of TCs). Thus, for better understanding of the influence of ENSO on TC formation in the WNP, the connection between ENSO and TCC activity must be investigated.…”

Observing Convective Aggregation

“…The primary source of data for this observational work is infrared and visible images from geostationary satellites, dating back to at least Arkin (1979) and encompassing Velasco and Fritsch (1987), Miller and Fritsch (1990), Laing and Fritsch (1993a, b), Machado and Rossow (1993), Mapes and Houze (1993), Laing and Fritsch (1997), Zuidema (2003), and Hennon et al (2012), but some more recent studies have also used other types of satellite data such as precipitation radar (Nesbitt et al 2000;Schumacher and Houze 2003;Futyan and Genio 2007;Peters et al 2009), microwave measurements of column water vapor (CWV) (Mapes et al 2009), and scatterometer winds (Mapes et al 2009). While cloud clusters are often identified by searching for large, contiguous cold cloud shields, more advanced techniques search for the combined signature of deep convection and extensive stratiform cloud and precipitation area.…”

“…This includes studies on the structural characteristics and radiative properties of tropical high cloud systems (Machado and Rossow 1993), the life cycles of deep convective systems (Futyan and Genio 2007;Mapes et al 2009), the size distribution of cloud clusters (Mapes and Houze 1993;Roca and Ramanathan 2000;Zuidema 2003;Peters et al 2009), and the spatial and temporal variability in cloud clusters and their efficiency at producing tropical cyclones (Hennon et al 2012). Studies have also pointed out significant self-similarity between MCSs and convectively coupled equatorial waves Kiladis et al 2009).…”

“…There is observational evidence that the frequency of organized convection has increased across the tropics over the past $ 30 years (Tselioudis et al 2010) and that most of the regional increases in tropical precipitation over that period are associated with this increase (Tan et al 2015). In addition to their contribution to tropical cloudiness and precipitation, tropical cloud clusters also play an important role as precursors to tropical cyclones, with globally 6.4% of tropical cloud clusters developing into tropical cyclones each year (Hennon et al 2012). Another observational finding which may be relevant to self-aggregation is the evidence that tropical precipitation has properties like those of a critical phenomenon.…”