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What kind of clouds have lightning?. Observing storms from space. Riming electric charge separation. Why there is a relationship between radar reflectivity and lightning flash?. Keys : Graupel Temperature Super-cooled liquid water. Takahashi and Miyawaki , 2002, JAS. - PowerPoint PPT Presentation
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What kind of clouds have lightning?
Observing storms from space
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 dBZecho topsMaximum reflectivity at temperaturesArea of 20, 30, 40 dBZ at temperaturesVolume of 20, 30 40 dBZ at -5oC - -35oCIWC 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-36NRPF 3.7 million 6.4m million 11.8 million 22.2 million
With flash 11.5% 2.6% 0.5% 3%
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
Echo top temperature vs. Flash rate
Correlation coefficient to flash rate in precipitation features
Ocean Coast Land All 36S-36NMaximum 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
Maximum reflectivity does not have good correlation with Flash rate neither ( < 0.5 )
Correlation between radar reflectivity vs. flash rate in precipitation features
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 : landDotted: 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.
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 ispositively charged.
Ground is negativelycharged.
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 amplitudeSame 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 betweenThunderstorm 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 observationsStorm 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 -10oC over land, -17oC 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 e-mail before
end of Tuesday Feb 26. Late report is not accepted. If you insist to give me a paper report, you have to hand the report to me on Monday Dec 25.
• We have 8 studentsEach one have about 10 minutes of presentation and a few minutes for questions.
So we need 2 class time. We do a lottery on who present first.
If you have presentation on the day, come to classroom 5 minutes early to upload your slides onto my laptop.