Thunderstorm and lightning activities ovThunderstorm and lightning activities ov

er the Tibetan Plateauer the Tibetan Plateau

Xiushu QIEXiushu QIE

ASM-STE, Lhasa, China, July 21-23, 2010

Key Laboratory of Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric Physics,

Chinese Academy of Sciences, Beijing, China

Motivation• Tibetan Plateau exerts profound thermal and dynamical

influence on atmospheric circulation; It also plays an important role in the Asian monsoon circulation.

• Three major programs:– National experiment: May-August, 1979: Qinghai-Xizang

(Tibetan) Plateau Meteorology Experiments (QXPMEX):– National Experiment: May-August 1998, Tibetan Plateau

Experiments (TIPEX)– International Experiment (China-Japan-South Korea):

1997-? May- September, 1998: IOP of GEWEX ASIAN MONSOON EXPERIMENT (GAME-TIBET)

Water cycles; radiation budget; boundary layer; Energy processes; Influence of the plateau thermodynamics on the circulation, monsoon, climate change, and formation and development of disastrous weather system.

• Lightning is one of the main features of severe convection, and can be an indication of deep convection. The knowledge of lightning and thunderstorm is important to understand the heating and convective processes on the Plateau.

• Hydrological cycle maybe difficult to be estimated without a better understanding of variation of thunderstorms.

• Lightning and thunderstorm is important to the stratosphere and troposphere chemistry, and stratosphere-troposphere exchange as well.

• Lightning and thunderstorm could be unique because of the high elevation of the Plateau.

Importance of lightning research on the Plateau

Scientific issues

• What is the lightning distribution on the Plateau? And how does it related to the topography?

• What parameters control the lightning production?

• Are the lightning physics and charge structure inside the thunderstorm different from the lower regions? Why?

Data Sources

• Space-based lightning data: LIS/TRMM & OTD/Microlab-1

•PR radar on TRMM • NCEP data:• First lightning campaign on the Central TP

Spatial distribution of lightning activity over Tibetan Plateau

• The mean flash density is 3 fl·yr-1·km-2, and the max. is around (32ºN， 88ºE) with a peak value of 5.1 fl·yr-1·km-2.

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5.1 fl·yr-1·km-2

Lhasa

NaquAnduo

NCEP climatology of CMAP precipitation on the Tibetan Plateau in summer season.

Topography of the Tibetan Plateau

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NCEP climatology of surface wind field

• Response to the topography and surface thermodynamics.

Lightning distribution

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Seasonal variation of lightningMaximum in June and July

Spreads out to whole TP along the valleys from the southeast of TP

Mainly occurs in the south of Himalayas

Enhancement clearly in JuneThe maximum moves westward

The maximum continues to move westward

Deceases clearly

April May

Jun Jul

Aug Sept

Time of maximum flash rate (LT)

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78 80 82 84 86 88 90 92 94 96 98 100

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Mt. Kokoxili

Diurnal variation of max. flash rate peaks during 14:00-15:00 LT with exceptions of the prominent high mountain region, which peak earlier, and prominent low basins, which peak later.

Seasonal variation of flash rate and precipitation

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ipita

tion

rate

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)

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h (f

l/km

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NCEPCMAPFlash

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fl/r

ain

(10-

8 fl

/kg/

day)

• The flash density and rainfall shows maximum in early July.

• The most striking feature is the large amount of lightning in the relatively dry pre-monsoon season (March to May), 11% in May.

Ratio of lightning to rain • An interesting seasonal change in the lightning activity and rainfall relationship.

• The relative share of lightning activity as a proportion of the precipitation is largest at the beginning of the season.

Seasonal variation of flash rate and Cloud Work Function (Similar to CAPE)

• The cloud work function is much smaller in May than in September, but the flash density is almost the same. The cloud work function therefore only crudely captures the seasonal variation.• Parameterizations based on this variable would significantly underestimate the lightning activity in Spring.

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• Very different seasonality of the two fluxes add to give a smooth seasonal evolution which matches both the Spring and monsoon flash density.

Seasonal variation of products of S*CWF and B*CWF

• The role of the sensible heat

flux appears to primarily

modify the efficiency of

producing lightning for any

given CAPE.

• The cloud buoyancy and rainfall show a better seasonal relationship with flash when they are multiplied by Bowen ratio (ratio of sensible to latent heat flux)

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First Lightning Campaign on the Plateau First Lightning Campaign on the Plateau

• June – Aug, 2003-2004

• Naqu Meteorology Bureau, central Plateau

• 31o28’47”N, 92o03’39.8”E, 4508 m asl

At 5300m asl At 4600m asl

Instrumentations

• Surface E ： Field mill• Field change ： Slow antenna

Fast antenna

• VHF/UHF radiation location: TOA & Interferometer techniques

• Optical ： High speed camera(1000f/s) 、 Spectrum• NOx: NOx Anylazer• Surface meteorology observation• Sounding: at 07:00 and 19:00

• Small• Isolated• Weak• Frequently max: 5 storms/day

Developing stage of typical thundercloud

on the Plateau

Surface E filed underneath thunderstorm

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E (kV/m)

13: 57 14: 13 14: 30 14: 47

Hai l July 7, 2003-CG:3 +CG:0

• Thunderstorms are usually hailstorms on the Plateau with a hail fall period of about 10 min and the diameter of hailstone on the ground is less than 1 cm.

• Surface E field underneath thunderstorm was usually downward pointed on the Plateau, which suggests that there are a large positive charge region at the lower part of Tibetan Plateau thunderstorms.

E

Flash rate for 6 overhead thunderstorms in July

VHF pulse location results by using TOA method for IC discharge at 15:07 (LT) on July 8, 2004

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Elevation evolution Azimuth evolution

E-field changes

• IC flashes take about 78.4% of the total.• IC discharges show polarity-inverted structure, and occur between up

per negative and lower positive charge region

Charge structure inside the thunderstorm over Tibetan Plateau

+-+

-+-

Naqu, Tibetan Plateau Lower altitude region

LPPC

23:12:17 23:32:17 23:52:17 0:12:17 0:32:17-20.0

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Inverted IC

IC

Spectrum

• Discharge is weak on the Plateau

Gungzhou

PlateauLower channel

temperaturenm

nm

Temporal variation of the maximumecho top of per day (From GAME-TIBET)

Uyeda et al., 2001; Feng et al., 2002

• The mean height of cloud base was 1.5-2 km above ground.• The cloud top was 8 km high with a maximum of 17 km. • The cloud is usually tall but thin with a max. echo area of about

2000 km2.

16:39:19 17:12:39 17:45:59 18:19:19 18:52:39 19:25:59Local T im e

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lect

ric fi

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R=0.84, N=9

dC

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Ox(p

pb

v)

Nl

NOx concentration and surface E-field underneath thunderstorm on July 10, 2003.

NOx increase and flash number for 9 thunderstorms in 2003.

ML9841B NOx analyzer and E-field mill

ConclusionsConclusions1. Lightning flashes are found to exhibit a continental-type behavior on the pl

ateau, but shows special characteristics under the thermal and dynamical effect of the Plateau orography.

2. The lightning activity generally peaks in June with a seasonal transition of lightning activity from east to west, showing a seasonal coincidence with the northwestward movement of Indian Monsoon.

3. The diurnal variation of lightning activity shows a single peak at 1600 LT on the plateau, but the maximum occurs earlier on the eastern and southern plateau, and earlier at prominent high mountain region and later at prominent low basins, indicating that the high elevation is conducive to the convection.

4. The surface total heat flux best accounts for the seasonal variation of lightning including the Spring anomalies. The sensible heat flux is important in modifying the efficiency of generating lightning from cloud buoyancy, at least in the Tibetan Plateau.

5. The charge structure inside the storm and lightning activity shows unique characteristics on the Plateau.

ThanksThanks

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Seasonal variation of lightningMaximum in June and July

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April May June

Aug.July Sept.

•The lightning activity in April mainly occurs in the south of Himalayas. •The lightning spreads out to the whole Plateau along the valleys from the southeast of the Plateau in May. •The lightning activities on the Central Plateau increases clearly in June. The most active period of lightning for the whole plateau is from late June to middle July. The maximum flash rate moves westward in July. •The maximum flash rate continues to move westward in August. The seasonal variation peaks in Aug. on the western Plateau. The activity deceases clearly in Sept.

0.3 fl·yr-1·km-2

The diurnal variations of radar echoecho top

echo top heightHeight of max. echo intensityMax. echo intensity

frequency of echoecho area

Flash rate for thunderstorms in August

Surface E filed underneath thunderstorm

20:04:08 20:37:28 21:10:48 21:44:08 22:17:28 22:50:48t

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Aug 13, 2003Hail fall: 21:00-21:09

Hail

IC: 236 +CG: 47 -CG: 1

Lightning flash on July 8, 2003

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• Most of -CG flashes follow long-duration of IC discharge with a

mean duration of about 181.4 ms.

E-field change produced by lightning flash

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17:06:45July 8

• Long duration IC may suggest that -CG can only occur after

partly neutralized the lower positive charge region.