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Stephanie JamesDepartment of Marine and Environmental Systems
Florida Institute of TechnologyMelbourne, FL 32901
The Effect of Divergence on Cloud-to-Ground Lightning in Cape
Canaveral, Florida
Overview
• What is divergence?
• Why does it matter?– Florida is the lightning capital of the United States– Does surface divergence play a role in the amount of
lightning?
Divergence Convergence
UpdraftDowndraft
++ ++ ++
- -----
Overview
• A relation between surface divergence and total strikes?
• 20 cases of thunderstorms in the Cape Canaveral region between May 23, 2008 and June 30, 2008
Different Charges over Florida
Positive Strikes Negative Strikes
Methods
• Distinguished days with storms and recorded lat/lon
• Looked at daily, hourly, and five minute lightning for the area
• Compared lightning to thunderstorm based on NEXRAD radar
imagery
• Counted the amount of lightning as well as the location of the
first strike in each storm in the region
• Determined the value of minimum, maximum, and average
divergence for each case
Minimum, Maximum, and Mean Divergence
June 28, 2008Latitude LongitudeTime Divergence Time
28.81 -80.83 1807 -70 028.80 -80.86 1822 -70 528.81 -80.84 1816 -60 928.80 -80.80 1820 -70 1328.78 -80.78 1824 -50 1628.76 -80.76 1829 -50 2028.77 -80.76 1833 -50 2428.75 -80.75 1837 -60 2828.74 -80.77 1842 -50 3328.74 -80.74 1846 210 3728.71 -80.72 1850 150 4128.69 -80.69 1855 65 4628.69 -80.67 1900 65 5128.70 -80.62 1904 0 5528.69 -80.58 1908 20 5928.69 -80.56 1912 20 63
June 23, 2008 Case Study
June 23, 2008 Case Study
Latitude LongitudeTime (EDT)
Divergence (s-1*10-5) Total Strikes
28.46 -80.90 1754 -60 460
28.48 -80.88 1758 -60
28.46 -80.84 1803 -270
28.47 -80.79 1809 -235
28.48 -80.76 1814 -200
28.48 -80.73 1819 -30
28.50 -80.67 1824 -70
28.51 -80.64 1829 -140
28.51 -80.61 1834 -125
28.51 -80.58 1839 -105
28.54 -80.54 1844 -60
28.55 -80.50 1848 -50
28.57 -80.49 1853 0
High values of Convergence
High values of Divergence
Results for All Cases
Conclusions
• Higher minimum convergence usually means more lightning strikes
• Maximum divergence vs. total strikes showed the least amount of relation
• The first strike tends to initiate near zero divergence
References• Ahrens, C.D., 2003. Meteorology Today: An Introduction to Weather, Climate, and the Environment. (7th Edition)• Camp, J.P., A.I. Watson, and H.E. Fuelberg, 1998: The Diurnal Distribution of Lightning over North Florida and Its Relation to
the Prevailing Low-Level Flow. Wea. Forecasting, 13, 729–739. • Hodanish, S., D. Sharp, W. Collins, C. Paxton, and R.E. Orville, 1997: A 10-yr Monthly Lightning Climatology of Florida: 1986–
95. Wea. Forecasting, 12, 439–448.• Paluch, I.R., and J.D. Sartor, 1973: Thunderstorm Electrification by the Inductive Charging Mechanism:II. Possible Effects of
Updraft on the Charge Separation Process. J. Atmos. Sci., 30, 1174–1177.
Questions?