Presentation on theme: "Thunderstorm and lightning activities over the Tibetan Plateau Xiushu QIE ASM-STE, Lhasa, China, July 21-23, 2010 Key Laboratory of Middle Atmosphere and."— Presentation transcript:
Thunderstorm and lightning activities over the Tibetan Plateau Xiushu 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. 63 fl·yr -1 ·km -2 5.1 fl·yr -1 ·km -2 Lhasa Naqu Anduo
NCEP climatology of CMAP precipitation on the Tibetan Plateau in summer season. Topography of the Tibetan Plateau NCEP climatology of surface wind field Response to the topography and surface thermodynamics. Lightning distribution
Seasonal variation of lightning Maximum 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 June The maximum moves westward The maximum continues to move westward Deceases clearly April May Jun Jul Aug Sept
Time of maximum flash rate (LT) Tarmu Base Chaidamu Base Mt. Kala Kunlun 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 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.
Flash rate and heat flux 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)
First Lightning Campaign on the Plateau June – Aug, 2003-2004 Naqu Meteorology Bureau, central Plateau 31 o 28’47”N, 92 o 03’39.8”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 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 2-D development Elevation evolutionAzimuth evolution E-field changes IC flashes take about 78.4% of the total. IC discharges show polarity-inverted structure, and occur between upper negative and lower positive charge region
Charge structure inside the thunderstorm over Tibetan Plateau +-++-+ -+--+- Naqu, Tibetan PlateauLower altitude region LPPC Inverted IC IC
Spectrum Discharge is weak on the Plateau Gungzhou Plateau Lower channel temperature nm
Temporal variation of the maximum echo 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 km 2.
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
Conclusions 1.Lightning flashes are found to exhibit a continental-type behavior on the plateau, 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.
Seasonal variation of lightning Maximum in June and July 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 echo echo top echo top height Height of max. echo intensityMax. echo intensity frequency of echoecho area