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- Author or Editor: S. J. Goodman x
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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.
Abstract
The Lake Victoria basin of East Africa is home to over 30 million people, over 200 000 of whom are employed in fishing or transportation on the lake. Approximately 3000–5000 individuals are killed by thunderstorms yearly, primarily by outflow winds and resulting large waves. Prolific lightning activity and thunderstorm initiation in the basin are examined using continuous total lightning observations from the Earth Networks Global Lightning Network (ENGLN) for September 2014–August 2018. Seasonal shifts in the intertropical convergence zone produce semiannual lightning maxima over the lake. Diurnally, solar heating and lake and valley breezes produce daytime lightning maxima north and east of the lake, while at night the peak lightning density propagates southwestward across the lake. Cluster analysis reveals terrain-related thunderstorm initiation hot spots northeast of the lake; clusters also initiate over the lake and northern lowlands. The most prolific clusters initiate between 1100 and 1400 LT, about 1–2 h earlier than the average cluster. Most daytime thunderstorms dissipate without reaching Lake Victoria, and annually 85% of clusters producing over 1000 flashes over Lake Victoria initiate in situ. Initiation times of prolific Lake Victoria clusters exhibit a bimodal seasonal cycle: equinox-season thunderstorms initiate most frequently between 2200 and 0400 LT, while solstice-season thunderstorms initiate most frequently from 0500 to 0800 LT, more than 12 h after the afternoon convective peak over land. More extreme clusters are more likely to have formed over land and propagated over the lake, including 36 of the 100 most extreme Lake Victoria thunderstorms. These mesoscale clusters are most common during February–April and October–November.
Abstract
The Lake Victoria basin of East Africa is home to over 30 million people, over 200 000 of whom are employed in fishing or transportation on the lake. Approximately 3000–5000 individuals are killed by thunderstorms yearly, primarily by outflow winds and resulting large waves. Prolific lightning activity and thunderstorm initiation in the basin are examined using continuous total lightning observations from the Earth Networks Global Lightning Network (ENGLN) for September 2014–August 2018. Seasonal shifts in the intertropical convergence zone produce semiannual lightning maxima over the lake. Diurnally, solar heating and lake and valley breezes produce daytime lightning maxima north and east of the lake, while at night the peak lightning density propagates southwestward across the lake. Cluster analysis reveals terrain-related thunderstorm initiation hot spots northeast of the lake; clusters also initiate over the lake and northern lowlands. The most prolific clusters initiate between 1100 and 1400 LT, about 1–2 h earlier than the average cluster. Most daytime thunderstorms dissipate without reaching Lake Victoria, and annually 85% of clusters producing over 1000 flashes over Lake Victoria initiate in situ. Initiation times of prolific Lake Victoria clusters exhibit a bimodal seasonal cycle: equinox-season thunderstorms initiate most frequently between 2200 and 0400 LT, while solstice-season thunderstorms initiate most frequently from 0500 to 0800 LT, more than 12 h after the afternoon convective peak over land. More extreme clusters are more likely to have formed over land and propagated over the lake, including 36 of the 100 most extreme Lake Victoria thunderstorms. These mesoscale clusters are most common during February–April and October–November.
