A Study of In-Cloud and Cloud-to-Ground Lightning in Tornado-Bearing Supercells in the Midwest

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3 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

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A Study of In
-
Cloud and

Cloud
-
to
-
Ground Lightning in
Tornado
-
Bearing Supercells in
the Midwest

Ben Herzog and Patrick S. Market

Dept. of Soil, Environmental & Atmospheric
Sciences

University of Missouri

Columbia, MO


Introduction


Knapp (1994) indicated a correlation
between cloud to ground (CG) lightning
flash frequency and the time of tornado
touchdown



Objectives


To verify Knapp’s (1994) work


To determine if identifying CG as well as in
cloud (IC) lightning flash frequency trends
could be used as an effective forecasting
tool to determine tornado touchdown.


Methodology


Find tornadic thunderstorms


Storm Prediction Center storm reports


Verify tornadoes from the National Climatic Data
Center


Obtain Data


March 2007


June 2007


Rocky
-

Appalachian Mountains


Radar data from National Climatic Data Center


Lightning data from Vaisala, Inc


Methodology (cont.)


Break each storm into 5 minute periods to identify
flash trends


Start 60 minutes before first touchdown


Create spread sheets on each storm containing:


Total number of flashes per five minutes


Number of cloud to ground (CG) flashes per five minutes


Number of in cloud (IC) flashes per five minutes


Number of negative CG (CGN) flashes per five minutes


Number of positive CG (CGP) flashes per five minutes


Create a spread sheet containing all data from every
storm



Analysis


30 total storms analyzed


26092 total flashes analyzed


Some five minute spans had 0 flashes


Some five minute spans had over 300 flashes


53.4% of flashes were CG


89.7% of CG flashes were negative


10.3% of CG flashes were positive


46.6% of flashes were IC


Analysis

Total Flashes

Analysis

CG Flashes

Analysis

IC Flashes

Analysis

Negative CG Flashes

Analysis

Positive CG Flashes

Analysis

CGN Flashes






CGP Flashes

Results


As suggested in the study by Knapp, there is
an identifiable pattern before tornado
touchdown


Approximately 30 minutes before touchdown, there
is a maxima in flash frequency


Approximately 20 minutes before touchdown, there
is a minima in flash frequency


Approximately 10 minutes before touchdown, there
is another maxima in flash frequency


Approximately 5 minutes before touchdown, there
is another minima in flash frequency



Results (cont.)


The cloud to ground flashes show this pattern
especially well


The negative CG flashes also show this pattern


There are very few PCG flashes, so finding a
pattern in the flash trend may be of little utility.
However, at T
-
30 minutes before touchdown, we
found 0 total PCG flashes. At that same time, the
maximum number of NCG flashes occurred.


Results (cont.)


There is a pattern associated with the in cloud
flashes


There is a pattern of maxima and minima of
flashes in IC storms, but it is not nearly as
pronounced of a pattern as the CG flashes


Future Work


Obtain data on storms from different years
and see is the flash frequency pattern
matches 2007


Classify the storms into different categories


High precipitation supercells


Low precipitation supercells


Classic supercells


Squall lines


Mesoscale convective complexes


Acknowledgements



Knapp, David I., 1994: Using Cloud
-
to
-
Ground Lightning Data to

Identify Tornadic Thunderstorm Signatures and Nowcast

Severe Weather.
National Weather Digest,
19(2), 35
-
42