Wavelet Scale Analysis of Mesoscale Convective Systems for Detecting Deep Convection From Infrared Imagery

Abstract

Mesoscale convective systems (MCSs) are frequently associated with rainfall extremes and are expected to further intensify under global warming. However, despite the significant impact of such extreme events, the dominant processes favoring their occurrence are still under debate. Meteosat geostationary satellites provide unique long‐term subhourly records of cloud top temperatures, allowing to track changes in MCS structures that could be linked to rainfall intensification. Focusing on West Africa, we show that Meteosat cloud top temperatures are a useful proxy for rainfall intensities, as derived from snapshots from the Tropical Rainfall Measuring Mission 2A25 product: MCSs larger than 15,000 km2 at a temperature threshold of −40°C are found to produce 91% of all extreme rainfall occurrences in the study region, with 80% of the storms producing extreme rain when their minimum temperature drops below −80°C. Furthermore, we present a new method based on 2‐D continuous wavelet transform to explore the relationship between cloud top temperature and rainfall intensity for subcloud features at different length scales. The method shows great potential for separating convective and stratiform cloud parts when combining information on temperature and scale, improving the common approach of using a temperature threshold only. We find that below −80°C, every fifth pixel is associated with deep convection. This frequency is doubled when looking at subcloud features smaller than 35 km. Scale analysis of subcloud features can thus help to better exploit cloud top temperature data sets, which provide much more spatiotemporal detail of MCS characteristics than available rainfall data sets alone.

Earlier Seasonal Onset of Intense Mesoscale Convective Systems in the Congo Basin Since 1999

“…Following T17, we define MCSs as contiguous areas of cold cloud exceeding 25,000 km 2 for a given temperature threshold. At the event time scale, MCSs at colder thresholds (higher altitudes) are associated with an increased probability of intense rainfall (T17, Klein et al, ). Here we focus on thresholds of −40 and −70 °C and term these systems respectively MCSs, and intense MCSs.…”

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

“…Globally, the spatial distribution and evolution characteristics of MCSs have been intensively documented in a variety of pioneering studies from the perspective of space-borne and ground-based observations (e.g., Anderson & Arritt, 2001;Blamey & Reason, 2012;Hodges & Thorncroft, 1997;Meng et al, 2013). For instance, infrared data from the Geostationary Operational Environmental Satellite have been commonly applied to explore the initiation, propagation, and regional variations in South and North America (e.g., Anabor et al, 2008;Durkee & Mote, 2010;Mecikalski et al, 2008), and the Meteosat Second Generation (MSG) has been extensively used in characterizing the MCSs in Europe and Africa (e.g., Feidas, 2017;Klein et al, 2018;Senf et al, 2015). In the Asian monsoon region, the detailed survey with regard to spatial distributions and lifecycles of MCSs was mainly conducted by Fengyun-2 geostationary meteorological satellite (e.g., Ai et al, 2016;J.…”

Dry soils can intensify mesoscale convective systems

“…Not only does dry soil enhance the frequency of convective cores, but also those cores are more intense, as measured by cloud-top temperature ( 30 ). On average, cores in DRY are 2.4 °C cooler than in WET ( SI Appendix , Fig.…”