Vol.18, NO.3, 2007
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Xie Jianbiao, Lin Liangxun, Yan Wensheng, et al. Dynamic diagnosis of an infrequent squall line in Guangdong on March 22, 2005. J Appl Meteor Sci, 2007, 18(3): 321-329.
Citation: Xie Jianbiao, Lin Liangxun, Yan Wensheng, et al. Dynamic diagnosis of an infrequent squall line in Guangdong on March 22, 2005. J Appl Meteor Sci, 2007, 18(3): 321-329.
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Dynamic Diagnosis of an Infrequent Squall Line in Guangdong on March 22, 2005

  • Guangzhou Central Meteorological Observatory, Guangzhou 510080

  • Received Date: 2005-11-07
  • Rev Recd Date: 2006-11-02
  • Publish Date: 2007-06-30
    Abstract
  • A dynamic diagnosis and meso-scale analysis of an infrequent squall line on March 22, 2005 in Guangdong is made using the routine observations, automatic weather station data, NCEP/NCAR reanalysis data and Doppler radar images. It's found that the squall line occurs under unstable stratification of environmental conditions and unstable physical mechanism, such as the trough at 500 hPa affecting the region where Guangdong borders Guangxi ahead of the trough at 700 hPa, so the acclivitous trough may be the dynamical trigger mechanism of the squall line's occurrence; the intrusion of the dry and cold air down from the upper troposphere affords the thermal instability field; the westerly jet is overlapped with the low southwest jet over the Guangdong and Guangxi, which brings the strong vertical wind shear, and the squall line develops strongly along the exit area of the low level jet after it is formed at the entrance of the upper jet above the low level jet; in the north and south of the squall line there are many new convection cells which keep building and tend to be combined towards the middle of the bow-shaped echo when the squall line grows; the squall line tends to have a dissy mmetrical structure rather than a symmetrical structure when it weakens, and the comma head and tail of the squall line, which cause disasters, are still growing respectively; the echo's channel of weak reflectivity factor at the rear end of the bow-shaped echo, namely the mesosphere-influx mouth of trough, comes forth, which is a sign to the change when the squall line has turned to dissymmetrical structure from symmetrical structure, and the squall line develops to the most powerful stage; in this process it shows some features such as the bow-shaped echo, the V-shaped mouth of trough, MARC and "long convection line" in front of the squall line. The strong inflow center, velocity convergence zone and small vortex velocity feature from the meridional velocity are also found. It is a good sign to identify the change of multi-cell storms that the long convection line of images occurs and develops all along the squall line; diagnostic analysis shows that the physical measures such as the vertical speed, wet static energy and CAPE can reflect effectively where the squall line has been born and where it has moved to.
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  • Fig. 1  Hourly distribution of severe weather occurrence areas and corresponding locations of squall lines on March 22, 2005

    (thick solid lines denote squall lines, while the thick dashed line indicates convective cloud after the squall line weakened, with the sparse dots, horizontal lines, slash lines, backslash lines, upright lines and dense dots indicating areas of severe weather occurrences at 09:00, 10:00, 11:00, 12:00—13:00, 14:00, 15:00—16:00, respectively; the small squares are stations that observed hailstones.)

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    Fig. 2  The composite diagram for synoptic systems at 08:00 on March 22, 2005

    (the thick solid line represents trough at 500 hPa, while the dashed one for trough at 700 hPa; the big arrow indicates dominant cold flow from the north and the small arrow is for jet line at 850 hPa)

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    Fig. 3  Isotaches at 200 hPa, locations of jet streams (solid line with arrow for 200 hPa while dashed one for 700 hPa) at (a)20:00 on March 21 and (b)08:00 on March 22, 2005 and strong convective occurence areas only for March 22 (shaded area)

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    Fig. 4  Meridional variation of ΔT in upper and lower tropospheres along 110°E at 20:00 on March 21, 2005

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    Fig. 5  Observations by the Yangjiang radar at 08:10 on March 22, 2005

    (a) reflectivity factor, (b) velocity, (c) analyzed flow field corresponding Fig. 5b (elevation:1.5°; the distance between two adjacent circles is 50 km; the echo is observed at 150—200 km northwest to the radar station)

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    Fig. 6  Observations by the Yangjiang radar at 09:11 on March 22, 2005 reflectivity factor with elevation of 0.5°(a) and 1.5° (b), velocity with elevation of 1.5° (c) (the distance between two adjacent circles is 50 km, the echo is observed at 100-150 km northwest to the radar station)

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    Fig. 7  Observations by Guangzhou radar in the direction of 288° on March 22, 2005

    (a) RCS at 10:57, (b) VCS at 11:14 (the center of the strong echo is located in about 15 km from the radar)

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    Fig. 8  Echo intensity and mean relative velocity of the storm at 10:57-12:30, observed by the Guangzhou radar on March 22, 2005

    (the red lines with arrows are analyzed streamlines) (a) 10:57 velocity with elevation of 0.5°, (b) 11:32 CR, (c) 12:14 reflectivity factor with elevation of 0.5°, (d) 12:30 reflectivy factor with elevation of 1.5°, (e) 12:14 velocity with elevation of 0.5°, (f) 12:30 velocity with elevation of 1.5°

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    Fig. 9  Reflectivity factor observed by the Guangzhou Doppler radar at 11:26 on March 22, 2005

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    Fig. 10  Zonal section of vertical velocity along 23°N at 08:00 on March 22, 2005(unit:10 2hPa·s-1)

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    Fig. 11  Surface flow field at 09:00 on March 22, 2005

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    Fig. 12  Distribution of fields at 20:00 on March 21 (a) and 08:00 on March 22 (b) in 2005(unit:J·kg-1)

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    • Received : 2005-11-07
    • Accepted : 2006-11-02
    • Published : 2007-06-30
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