A complicated mesoscale convective system Lightning flashes (ICs, CGs) happen both inside and outside convective regions (“cells”), sometimes in stratiform regions, or anvil regions

Motivation What kind convective systems have lightning? What properties of convective systems are best correlated with the lightning flash rate? Using TRMM observations, we may: Find convective regions (“cells”) within precipitation systems Find convective regions (“cells”) with lightning flashes Find correlations between lightning flash rates to various properties of precipitation systems

Find convective cells in precipitation systems Three “cell” definitions: Convective pixels (red color fill) 40 dBZ pixels in any levels (black line) 30 dBZ pixels at 6 km (white line)

Simple statistics of convective “cells” “Cell” definitionPopulation% with flash% of flashes Within “cell” Convective pixels ~67 million1%81% 40 dBZ in any level ~14 million5%66% 30 dBZ at 6km~6 million12%68% From 12 year TRMM observations ( )

Giant “cells” and giant lightning “cells”

What kind of systems have more flashes? More ice in the charging zone from -10 o C to -20 o C  more charge separation  higher flash rate From radar and radiometers: Higher reflectivity at altitudes Lower microwave brightness temperature (Williams et al., 1987 JGR, Lang et al 2000 MWR, Toracinta et al MWR Cecil et al MWR … ) Updraft volume  flash rate Mass flux of ice in mixed-phase region  flash rate (Deierling et al. 2008, Deierling and Petersen, 2008 JGR) Flash rate vs. properties of precipitation systems

Which parameter best correlates with flash rate? TRMM Precipitation radar Correlation coefficient with flash rate Echo top height0.42 Max 20 dBZ height0.42 Max 30 dBZ height0.48 Max 40 dBZ height0.59 Max near surf dBZ0.41 Maximum reflectivity Over US (30-36N, 80-95W)

Which parameter best correlates with flash rate Area of high reflectivity at altitudes

Which parameter best correlates with flash rate? regional differences Argentina DJF US JJA Central Africa Tropical ocean 35 dBZ -10 o C 35 dBZ -20 o C

Which parameter best correlates with flash rate?

Flash rate vs. 35 dBZ at -10 o C

Lightning rate vs. convective cells Differently defined convective “cells” have large differences. However, the thunder “cells” share the same properties. It is not the maximum amount of ice at one location, but the total amount of ice through the charging zone that lead to higher flash rate. Therefore, areas of high reflectivity at altitudes and areas of cold microwave TB are better correlated to the flash rate than the maximum reflectivity and the minimum TB. There are obvious differences between land and oceanic thunderstorms. This is THE topic for the future investigation.

Relative Contributions of Electrified Shower Clouds and Thunderstorms to the Global Circuit: Can 10 Years of TRMM Data Help Solve an Old Puzzle?

Fair Weather Charge In fair weather there is a natural separation of charge in the atmosphere Upper troposphere is positively charged. Ground is negatively charged.

The atmosphere normally has a voltage gradient of 100 volts/meter… … which may sound like a lot, but what happens when you stand one meter from a 110 volt outlet ?

Old Puzzle / Hypothesis 90 years ago “A thundercloud or shower-cloud is the seat of the electromotive force which must cause a current to flow through the cloud between the Earth’s surface and the upper atmosphere... In shower-clouds in which the potentials fall short of what is required to produce lightning discharges, there is no reason to suppose that the vertical currents are of an altogether different order of magnitude.” Wilson (1920)

Carnegie Curve vs. thunder days 80 years ago Diurnal variation of electric field seems reproduced by the thunder days (after add an arbitrary uniform oceanic storms to bring the amplitude down)

Thunderstorms observed by TRMM Thunderstorms over different regions have different lightning flash rates AsianAfricaAmericas

Carnegie curve vs. flash count Good correlation in phase, but much higher amplitude Same as pointed out by Bailey et al. 2007

Carnegie curve vs. rainfall in thunderstorms Good correlation in both phase and amplitude

Diurnal variation of flashes Asian Africa Americas

Diurnal variation of rainfall in thunderstorms Asian Africa Americas

Vostok electric field vs. rainfall in thunderstorms Good correlation between Thunderstorm rain vs. electric field in different seasons DJF Vostok electric field might be contaminated by weathers

End of story? It seems that the diurnal variation of rainfall in thunderstorms has a very good correlation with the Carnegie curve both in the phase and the amplitude. However, this is not the end of the story. What about the shower clouds without lightning as mentioned by Wilson 90 years ago?

ER-2 overflight of Emily

In-situ storm current observations Storm current from 850 ER-2 overflights Courtesy of Mach et al. 2010

A VERY rough way to identify the electrified shower clouds 30 dBZ echo top colder than -10 o C over land, -17 o C over ocean

Rainfall from thunderstorms, electrified show clouds and others

Carnegie vs. electrified shower clouds

Thunderstorm + electrified shower?

A different approach define convective cells Three “cell” definitions: Convective pixels (red color fill) 40 dBZ pixels in any levels (black line) 30 dBZ pixels at 6 km (white line)

Global distribution of convective cells

(Solid line) Rain in cells defined by 30 dBZ at 6 km has the best correlation

Electric field vs. Rainfall from convective cells defined by area of 30 dBZ at 6km

Summary of the Carnegie curve With more observations available today, we have better tools to play the same game as Whipple (1929) played 80 years ago: relating the diurnal variation of thunderstorms to that of the electric field. Diurnal variation of rainfall from thunderstorms has a good correlation with the Carnegie curve both in the phase and the amplitude. The role of electrified shower clouds is still hard to describe due to the difficulty of identifying them and quantifying the electric field that they contribute. A different approach of adding convective cells gives more hints to this puzzle.

Let’s talk about the final project Written reports have to be submitted to me in before end of Monday Dec 13. Late report is not accepted. If you insist to give me a paper report, you have to hand the report to me on Friday Dec 10. We have 7 students Each one have about 10 minutes of presentation and a few minutes for questions. So we need 1.5 class time. Who will volunteer to present the results next Tuesday? If you have presentation on the day, come to classroom 5 minutes early to upload your slides onto my laptop.