Vol.32, NO.5, 2021
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Article Navigation >  Journal of Applied Meteorological Science  > 2021  >  32(5): 567-579
Wang Hong, Li Ying, Wen Yongren. Observational characteristics of a hybrid severe convective event in the Sichuan-Tibet Region. J Appl Meteor Sci, 2021, 32(5): 567-579. DOI:  10.11898/1001-7313.20210505.
Citation: Wang Hong, Li Ying, Wen Yongren. Observational characteristics of a hybrid severe convective event in the Sichuan-Tibet Region. J Appl Meteor Sci, 2021, 32(5): 567-579. DOI:  10.11898/1001-7313.20210505.
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Observational Characteristics of A Hybrid Severe Convective Event in the Sichuan-Tibet Region

DOI: 10.11898/1001-7313.20210505
  • 1.

    State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081

  • 2.

    Ningbo Meteorological Bureau of Zhejiang Province, Ningbo 351000

  • 3.

    Chinese Academy of Meteorological Sciences, Beijing 100081

  • Received Date: 2021-05-21
  • Rev Recd Date: 2021-07-09
  • Publish Date: 2021-09-30
    Abstract
  • The Sichuan-Tibet Region is a key area for the development of western China, where severe convective weather such as thunderstorm gales occur frequently. However, due to the complex terrains, synoptic systems, and the lack of meteorological observations, it is especially challenging to make accurate prediction. To better understand the mechanism of severe convective weather over the plateau, a rare severe convective event in the Sichuan-Tibet Region on 8 Sep 2016 is analyzed with weather reports, hourly and minutely surface observations, sounding data and Doppler weather radar data from China Meteorological Administration and ERA-Interim 0.5°×0.5° reanalysis data from European Centre for Medium-Range Weather Forecasts (ECMWF). The result shows that hourly rainfall of over 10 mm and hails of over 18 mm are observed at several weather stations, indicating a hybrid moist convective event. The meso-scale convective system (MCS) occurs near a shear line at low level with weak cold advection at 500 hPa. Large environmental convective available potential energy (CAPE), vertical wind shear, and the thick moist atmospheric layer are conductive to the formation of supercell. The initial convection is generated along a surface convergence line, with multiple γ meso-scale cells embedded in stratiform cloud in the north and cluster cells in the south. They move to the southeast, enter the favorable environment and merge with each other, enabling the cell on the south side to quickly develop into a supercell. When the supercell grows matured, the characteristic of front inflow gap, hook echoes and mesoscale cyclone at low levels are clear. The strong echo region tilts forward with height. There is significant overshooting top with the echo top height up to 15 km above ground in the upper troposphere, and obvious echo overhang capping bounded weak-echo region (BWER) in the middle layer. Mid-altitude radial convergence, weakening of updrafts and rapid drop of the reflectivity core indicate the occurrence of downbursts inside the storm. The cooling effect due to the entrainment of midlevel dry air is favorable to the growing of big hails and raindrops, and the formation of downdrafts. Moreover, the drag effect related to the rapid drop of heavy raindrops and hails, and the narrow tube effect of the canyon terrain, contribute to the formation of thunderstorm gales near the ground.
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  • Fig. 1  Moving paths of strong convection centers(the time interval is 30 min, the black and red lines denote the reflectivity factor ranging from 35-60 dBZ and more than 60 dBZ) from 0500 UTC to 0900 UTC on 8 Sep 2016(a) and probability distribution of hail diameter in the Qinghai-Tibet Region during 2010-2017(b)

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    Fig. 2  Geopotential height(the contour, unit:dagpm) and wind at 0000 UTC on 8 Sep 2016

    (the red rectangle denotes convection area)
    (a)500 hPa(the shaded denotes temperature, the brown curve denotes trough), (b)600 hPa(the shaded denotes relative humidity, the brown curve denotes shear line, the grey denotes terrain), (c)200 hPa(the barb denotes upper level jet stream with wind velocity no less than 30 m·s-1, the shaded denotes divergence), (d)surface(the contour denotes sea-level pressure, unit:hPa;the shaded denotes temperature)

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    Fig. 3  Environmental convective available potential energy(the shaded) and 500-700 hPa vertical wind shear(the blue contour, unit:m·s-1) on 8 Sep 2016

    (the red rectangle indicates mature supercell area)

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    Fig. 4  Radar and surface observations at Ganzi on 8 Sep 2016

    (the dot denotes surface temperature, the number denotes relative humidity(unit:%), the brown curve denotes surface convergence lines, the red ellipse denotes convection positions)

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    Fig. 5  Observation at 0.5°elevation angle by Ganzi radar on 8 Sep 2016

    (a)reflectivity factors(the white ellipse denotes hook echo, the white arrow indicates inflow gap), (b)vertical cross-section along line AB in Fig. 5a(the white ellipse denotes echo overhang), (c)reflectivity factors(the white ellipse denotes mesocyclone), (d)vertical cross-section along line AB in Fig. 5c(the white arrow denotes storm inflow direction)

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    Fig. 6  Observation at 0.5°elevation angle by Ganzi radar on 8 Sep 2016

    (the white circle denotes mesocyclone, the white arrow denotes supercell inflow direction)

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    Fig. 7  Vertical cross-section along line AB in Fig. 6 by Ganzi radar on 8 Sep 2016

    (the red dot denotes Yajiang Station, the white arrow denotes low-level air flow direction)

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    Fig. 8  Surface meteorological elements evolution from 0745 UTC to 0825 UTC on 8 Sep 2016

    (a)precipitation(the column) and temperature(the curve) at Yajiang station, (b)pressure(the curve) and wind(the barb)at Yajiang Station, (c)precipitation(the column) at auto weather station 838181, (d)hourly extreme wind(the barb) at auto weather station 838181

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    Fig. 9  Topographical sketch map around the stations(a) and 3 h pressure change(the blue contour, unit:hPa) and 24 h temperature change(the shaded) on surface at 0900 UTC 8 Sep 2016(b)

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    • Received : 2021-05-21
    • Accepted : 2021-07-09
    • Published : 2021-09-30
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