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Mesoscale Convective Complexes in Southern Africa: A Case studyYemi Adebiyi

MCC event: 07 July 1997 over Nebraska -- GOES-8 IR Jul.(above line) and Jan. (below line) 1985-1986 Jun. Aug. (above line) and Dec.-Feb.(below line) 1974-78 -- Laing and Fritsch, 1997

MCC in Southern AfricaLaing and Fritsch, 1993Definition

A Mesoscale Convective Complex (MCC):

Defined by Maddox (1980) and based entirely on IR satellite observations

IR temperature criteria:

Continuous cold cloud with IR temps < -32C over an area greater the 100,000 km2 Inner cold cloud region with IR temps < -52C over an area > 50,000 km2

Duration: The IR criteria must be met for > 6 hours

Shape: Minor axis / major axis ratio must be > 0.7

Within the MCS spectrum, mesoscale convective complexes are large, long lived, and quasi-circular.Example from Markowski and Richardson, 2011

MCC Evolution and StructureDeveloping Stage:

Often develop in the late afternoon from the merger of storms originating in different locations or squall lines with MCC characteristics

Usually in area of LLJ, surface front with small CIN and large CAPE

Strong vertical motion and heating in lower troposphere

Cotton et al, 1989MCC Evolution and StructureMatured Stage:Reach a mature stage around local midnight or early morning hours (when the nocturnal low-level jet is the strongest)

Level of maximum vertical velocity and heating shift upward producing warm anomaly

Deep layer inflow generates strong mesoscale (and convective) updrafts that produces the large anvil

A low- to mid-level mesoscale convective vortex (MCV) develops as a hydrostatic response to the warm and cold anomalies

Cotton et al, 1989MCC Evolution and StructureDissipating Stage:

Dissipate in the early morning hours or around noon, in response to a more stable environment and a smaller supply of warm, moist air (low-level jet is weakest in the morning)

As the upper-level cold cloud shield and stratiform precipitation dissipate in the early morning, the MCV becomes visible on satellite

Cotton et al, 1989Southern Africa MCC: 29- 30th Dec 2008

Characteristic: size: number of hours:eccentricity and so on

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00Z 30 Dec03Z 30 Dec09Z 30 Dec06Z 30 Dec12Z 30 Dech)

15Z 30 DecMaximum size: ~200,000km2

Duration: >6hours

Eccentricity: >0.7

Cloud-top temperature ~ -80degC

what about the Cloud-top temperature

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Synoptic patternWind speed > 5m/sBlue lines: geopotential heightOrange shade: >1010hPaLight blue: 80mm/day

Moisture con15Mesoscale Convective Complexes in Southern Africa: A Case studyThanks

Basic CharacteristicsPredominantly summer season event

Most often occur downwind of major topographic feature

Often produce severe winds and heavy amounts of rain and localized flash floodingCan produce hail and tornadoesAlmost 25% of MCCs result in injuries or death

Produce ~10% of total annual rainfall in many areasProduce up to ~40% of total rainfall during the growing season

Exhibit high annual variability

Laing and Fritsch, 1997