Cloud-to-Ground Lightning Activity in Mesoscale Convective Complexes

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  • 1 Universities Space Research Association, NASA/MSFC, Huntsville, AL 35812
  • | 2 NOAA/National Severe Storms Laboratory. Norman, OK 73069
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Abstract

A study of cloud-to-ground lightning activity attending an important subclass of mesoscale convective weather systems called the mesoscale convective complex shows that groun discharge flash rates in excess of 1000 h−1 can be sustained on average for more than nine consecutive hours with peak rates of nearly 2700 h−1. Peak rates, averaged over 5 minute intervals, of 60 min−1 are not uncommon and average 42 min−1 for the MCCs analyzed. These rates are comparable to the highest observed rates within other mesoscale storm systems, four times those, observed in severe or multicell storms in Florida, and greater 20 times the rates previously observed in isolated thunderstorms. Peak ground strike densities for individual cells within the MCC of 0.09 strikes km−2 min−1 are comparable to the observed values of Florida storms. However, a single MCC can produce one-fourth of the mean annual lightning strikes to ground at any site it passes over during the most intense phase of its life cycle. Lightning damage occurs with half of the MCCs and is most frequent between the development and mature phases (the most electrically active period) of the MCC life cycle. The most active period is also characterized by the greatest average number of discrete strokes (3–4 component strokes per flash) and largest fraction of multiple stroke discharges, while the fewest multiple stroke discharges occur during the first hour of MCC development. The lightning activity appears to be independent of the size of the total storm system cloud shield at maximum extent and MCC life-cycle duration. The peak flashing rates can vary by a factor of two or more in basically similar, convectively unstable, synoptic environments.

Abstract

A study of cloud-to-ground lightning activity attending an important subclass of mesoscale convective weather systems called the mesoscale convective complex shows that groun discharge flash rates in excess of 1000 h−1 can be sustained on average for more than nine consecutive hours with peak rates of nearly 2700 h−1. Peak rates, averaged over 5 minute intervals, of 60 min−1 are not uncommon and average 42 min−1 for the MCCs analyzed. These rates are comparable to the highest observed rates within other mesoscale storm systems, four times those, observed in severe or multicell storms in Florida, and greater 20 times the rates previously observed in isolated thunderstorms. Peak ground strike densities for individual cells within the MCC of 0.09 strikes km−2 min−1 are comparable to the observed values of Florida storms. However, a single MCC can produce one-fourth of the mean annual lightning strikes to ground at any site it passes over during the most intense phase of its life cycle. Lightning damage occurs with half of the MCCs and is most frequent between the development and mature phases (the most electrically active period) of the MCC life cycle. The most active period is also characterized by the greatest average number of discrete strokes (3–4 component strokes per flash) and largest fraction of multiple stroke discharges, while the fewest multiple stroke discharges occur during the first hour of MCC development. The lightning activity appears to be independent of the size of the total storm system cloud shield at maximum extent and MCC life-cycle duration. The peak flashing rates can vary by a factor of two or more in basically similar, convectively unstable, synoptic environments.

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