Extended Abstract (1.3M)1B.6a
Bow echo embedded within a squall line
Wen-Chau Lee, NCAR, Boulder, CO; and R. M. Wakimoto and J. F. Gamache
An intense squall line occurred on 7 May 1995 in Texas penhandle during VORTEX-95. This north-south oriented squall line moved from Texas into Oklahoma and produced downburst type damages on the ground near Willow, Oklahoma. Both NCAR Electra and NOAA P-3 flew ~60 km legs on the eastern side of this squall line at two different altitudes. With additional data source from Amarillo WSR_88D data and surface measurement from NSSL ground team, the evolution and fine scale structure of this squall line segment and its accompanied mesocyclone were well documented in a two-hour period.
This squall line exhibit complex structures. A distinct mesocyclone and hook echo signature were identified within this squall line but no tornado was reported. From the Amarillo WSR-88D low-level scans, a bow echo was identified near the location of the mesocyclone. The relationship between this mesocyclone and the distortion of the squall line will be studied by evaluating the vorticity equations. The depth of the approaching flow (the so-called storm outflow) reached 2-3 km depth in scan plane (RHI) data on the south flank of the mesocyclone and was associated with an upright updraft. The outflow of the squall line north of the mesocyclone was shallow and accompanied with slopping updraft. Multiple horizontal vortex tubes (Doppler velocity dipoles in RHI scans) with speed exceeding 30 m/s were clearly shown along the interface between the receding flow (inflow) and approaching flow (outflow). Similar horizontal vortex tubes also existed on the front end of the updraft vault which was associated with curling of reflectivity factor.
The purpose of this paper is to present the evolution and find scale structure within this squall line using primarily the dual-Doppler radar analyses from the NCAR ELDORA data. ELDORA's 300 m along track resolution is able to resolve features in about 2 km wavelength. The fine structures of this squall line will be illustrated in both the radar scan plane data and reconstructed dual-Doppler radar winds. A 3-D variation method enabled plausible airflow in the anvil and vault region (at elevation angles exceeding 45 degrees) to be deduced that could be obtained in the traditional dual-Doppler analyses. The wind field that is associated with the Willow downburst type damage will be discussed.
Session 1B, MCS/Orographic Precipitation
Wednesday, 6 August 2003, 10:45 AM-12:30 PM
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