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?