Meoscale Convective Complexes

Abstract

A particular class of weather system, the Mesoscale Convective Complex (MCC), is identified, defined, and contrasted with other types of convective weather systems. It is found that MCC systems frequently occur over the central United States, grow to tremendous areal extent, and often persist for periods exceeding 12 h. In addition to widespread beneficial rains, a wide variety of severe convective weather phenomena attends these systems. The development and evolution of MCC systems is not explicitly predicted by operational numerical models even though they are shown to be organized in a distinctly nonrandom mode on scales that cannot be considered subgrid. The MCC is a convectively driven weather system whose physics are not yet understood, much less incorporated into operational parameterization schemes. A preliminary conceptual model of the life cycle of these systems is presented using enhanced, infrared satellite imagery in conjunction with conventional surface and radar data. The outlook for further study and ultimately for the prediction of MCC systems is encouraging since their time and space scalescoupled with their frequent occurrence over the central United States-make them highly amenable to detailed investigation. vective clouds. Operational prediction of convective precipitation has traditionally been perceived as a sub-grid scale problem that can best be handled using statistical techniques in combination with numerical model output [see, for example, papers by Glahn and Lowry (1972); Klein and Glahn (1974); and ^Bermowitz and Zurndorfer (1979)]. However, satellite images during warm season months (March-September) show a high frequency of organized, meso-a scale 2 , convective weather systems over the central United States. It is believed that these systems, which have been named Mesoscale Convective Complexes (MCCs), are a class of convective weather system heretofore unrecognized in the literature. Numerous examples are shown and a definition and hypothesized life cycle (based upon physical characteristics and associated circulations) for MCC weather systems are presented in the following sections.

Diurnal Variation of Cb-Clusters over China and Its Relation to Large-Scale Conditions in the Summer of 1979

“…On the other hand, many deep convective clouds in such a horizontal scale also appear to the north of the Baiu frontal zone in China where the time-averaged cloud amount is rather smaller than in the Baiu frontal zone, according to the statistical studies by Ninomiya (1989), Takeda and Iwasaki (1987) and Iwasaki and Takeda (1993). The meso-a-scale convective clouds show multiscale structures in which meso-, Q or 7-scale clouds are embedded, and are considered as significant weather systems (Akiyama, 1984a, b;Madox, 1980Madox, , 1983McAnelly and Cotton, 1986;Ninomiya et al , 1981Ninomiya et al , , 1988a. In the present study we simply refer to such meso-a-scale deep convective clouds (including larger meso-/13-scale ones) as the Cb-clusters, although stratiform clouds might be sometimes embedded in them.…”

Simulating North American mesoscale convective systems with a convection-permitting climate model

“…Our 4 km grid spacing model is too coarse to realistically simulate single cell thunderstorms, however, Mesoscale Convective Systems [MCSs, Houze (2004)] that consist of a complex of thunderstorms that become organized, can be captured. In North America, these storms include squall lines (Rotunno et al 1988), which are storms arranged in a line along a evaporatively generated near-surface cold outflow and Mesoscale Convective Complexes with a large circular cloud shield (Maddox 1980). Despite the advantages of CPCSs, a kilometer scale horizontal grid spacing can only resolve large-scale convective motions and has been shown to result in large convective cells that do not entrain midlevel air (Bryan and Morrison 2012).…”

The propagation and diurnal cycles of deep convection in northern tropical Africa

“…In the United States (USA), studies of the life cycles of mesoscale convective systems (MCSs) have found that most of these systems initiate in the lee of the Rocky Mountains, move eastward and produce an overnight maximum in precipitation across the central plains, sometimes while undergoing various cycles of regeneration (Maddox, 1980;Fritsch et al, 1986;Augustine and Caracena, 1994;Anderson and Arritt, 1998;Trier et al, 2000). Using Weather Surveillance Radar-88 Doppler (WSR-88D) data, Carbone et al (2002) found that clusters of heavy precipitation display coherent patterns of propagation across the continental USA with span and duration that exceed those of any individual MCS.…”