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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-21 21:05 |
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Conference: Bucharest University Faculty of Physics 2008 Meeting
Section: Atmosphere and Earth Science; Environment Protection
Title:
The impact of hail on radial velocities for warning purposes
Authors:
Daniel Carbunaru, Aurora Bell, Bogdan Antonescu
Affiliation:
National Meteorological Administration, Bucharest, Romania
E-mail
Keywords:
convective systems, Mesocyclone,triple reflections,hail
Abstract:
The severe impact of highly organized convective systems, like supercells, can be better anticipated using useful radar pattern recognition software routines such as the Mesocyclone and the Tornado Vortex Signature TVS algorithms. However, while these algorithms do demonstrate some skill they also are susceptible to radar artifacts and sampling limitations. Moreover, they sometimes fail to detect critical signatures that may be subtle or fail to meet certain thresholds in some of the cases radar artifacts can contaminate the reflectivity and velocity structures. For example the Three Body Scatter Signature, TBSS, can be a challenge for the operational environment. This radar echo artifact is the result of triple reflections, caused by non-Rayleigh radar microwaves scattering from a region of large hydrometeors, like wet hail. The triple reflections consist of: (1) a forward scattering by large hydrometeors to the ground below; (2) backscattering from the ground to the large hydrometeor region aloft, and (3) backscattering to the radar. TBSS is also known as flare- or hail-spike due to the appearance of the artifact in plan position indicator.
The general features of TBSS detected in Romania in 2005, 2006 and 2007 are presented. Two special cases are presented where the presence of large hail, produced TBSS and disturbed the radial velocity field detected by the radar. We also examine a particular storm where large hail is responsible for velocity dealiasing. The Romanian experience with an S-band network, confirms that this artifact is associated with hail reports. We present the geographic distribution of the recorded TBSS; we have considered only one TBSS artefact per storm, even if it had a long life, and the position was defined for the moment of maximum detected reflectivity, over 60 dBZ at the third tilt, limited to the warm season (April- September) and only the very clear TBSS structures were counted (isolated storms, well observable spikes). The southern part of Romania (covered by 2 C-band radars), is not sampled.
The TBSS signature is a very important warning tool, although can not give an anticipation of more than 30’ minutes since it is detected at high levels in the storm; however the hail spike can affect the radial velocities and produce disruptions in the radial velocity field that can generate unreal mesocyclonic and tornadic vortex patterns that can be artificially identified by the algorithm.
Ineraction between TBSS and the radial velocities is important because unreal shears are detected by the radar algorithms and artificial labels can be produced (MESO, TVS), or, a real rotational field cand be altered by TBSS overlap in radial field.
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