Infrared (IR) measurements of cloud tops from geostationary satellites are commonly used to study the occurrence, structure, motion, and precipitation characteristics of mesoscale convective systems (MCSs). Although there is no direct physical link between cloud top irradiance and the internal precipition structure of an MCS, the high temporal and spatial resolution of the data has made geo-IR data uniquely suited to study MCSs on time and space scales of convection. Yet, few studies have examined whether the basis of many IR studies of convection, that the coldest cloud tops represent heavy-raining deep convective cells, is actually valid for MCSs.
Recent studies of squall line MCSs from shipboard radar and satellite data from the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE) suggest a complex relationship between the precipitation structure (from radar reflectivity) and the cloud top pattern, and that the assumed relationship between cold cloud and deep convection is not strictly valid. The cloud pattern appears to be determined by the evolution of convection along the leading edge and by the differential advection of the cloud shield from the leading edge in strong directional shear. This evolution leads to recognizable signatures in the cloud shield, which suggests that there may be sufficient information in the cloud pattern to derive an automated method to track MCSs from IR data.
In this study, the cloud pattern of an evolving, squall line MCS which has a cloud pattern not contaminated by cloudiness from nearby convection is characterized by several parameters derived from the IR data. The goal is to develop an automated, physically based technique which can recognize the cloud signatures of an evolving, propagating MCS. The texture, eccentricity, and fractal dimension of cloud features are tracked, and related to the radar reflectivity structure of the underlying precipitation. These parameters may be used to distinguish the active convective cells from the associated anvil cloud in MCSs without relying on arbitrary temperature thresholds.