Relationships between lightning flash rates over the tropics and subtropics and the vertical...

Relationships between lightning flash rates over the tropics and subtropics and the vertical

structures of precipitation radar reflectivity

Chuntao Liu

Department of Atmospheric sciences, University of Utah

Contributors:Edward Zipser1 , Daniel Cecil2

1. University of Utah2. University of Alabama at Huntsville

Riming electric charge separation

Takahashi and Miyawaki, 2002, JAS

Keys :

Graupel

Temperature

Super-cooled liquid water

Why there is a relationship between radar reflectivity and lightning flash?

Define precipitation features using TRMM Precipitation Radar

Radar Precipitation Features (RPFs)

Contiguous area with rainfall

Properties of precipitation features

Flash rateTemperature at 20, 30, 40 dBZ

echo topsMaximum reflectivity at temperatures

Area of 20, 30, 40 dBZ at temperaturesVolume of 20, 30 40 dBZ at -5oC - -35oC

IWC of 20, 30 40 dBZ at -5oC - -35oC

PR echo top height (km)

Population of RPFs and those with lightning

• 1998-2010

Land Coast Open ocean All 36S-36N

RPF 3.7 million 6.4m million 11.8 million 22.2 million

With flash 11.5% 2.6% 0.5% 3%

Correlation between radar reflectivity vs. flash rate in precipitation features

Echo top temperature vs. Flash rate

Correlation coefficient to flash rate in precipitation features

Ocean Coast Land All 36S-36N

Maximum 20 dBZ echo top Temperature

-0.12 -0.18 -0.27 -0.24

Maximum 30 dBZ echo top Temperature

-0.30 -0.36 -0.40 -0.38

Maximum 40 dBZ echo top Temperature

-0.49 -0.50 -0.49 -0.50

Correlation coefficient to flash rate in precipitation features

area of reflectivity at temperatures vs. Flash rate

Solid : land dotted: ocean

area of reflectivity at temperatures vs. Flash rateauto-correlation among different part of storms removed

Solid : land dotted: ocean

Regional variation of correlations (I)Correlation coefficients

Regional variation of correlations (II)Slope of linear relationship

Summary• Flash rate is best correlated with the volume of the high reflectivity (> 30 dBZ) in the mixed phase region, confirming the importance of the presence of large particles in the charging process.

• More flashes are generated over land than over ocean given the same volume of 30-35 dBZ in the mixed-phase region.

• There are large regional differences in the correlations between radar reflectivity properties vs. flash rate.

• Even with the similar radar reflectivity profiles to the oceanic systems, it is still easier to have lightning flashes over Amazon. Other factors must play important roles besides the graupel at mixed phase region in the lightning generation.

2-D histogram of RPFs and probability with lightning

Temperature of 20 dBZ echo top vs. Temperature of 30 dBZ echo top

Regional variation of lightning probability in precipitation systems

Correlation coefficient to flash rate in precipitation features

maximum reflectivity at altitudes vs. Flash rate

Correlation coefficient to flash rate in precipitation features

area of reflectivity at temperatures vs. Flash rate

Solid : land dotted: ocean