Abstract
Bobohalma Doppler radar reflectivity fields are analyzed using data recorded during the September 2003 – August 2005 period. Hourly and monthly relative frequencies of occurrence of echoes greater than or equal to 40 dBZ are calculated. This reflectivity threshold is used to highlight areas conducive to deep convection. The relative frequencies of occurrence for echoes greater than or equal to 50 dBZ are also determined. This threshold is used to identify areas with mature storms, which can produce severe weather phenomena. The results reveal the spatial distribution of high and low monthly relative frequencies, and its variations from month to month. Topographic convergence zones are identified, which can activate under some specific synoptic and meso-scale patterns, but these are not explored in this study. Diurnal variations of relative frequencies for summer months June-July-August are treated by Fourier decomposition, featuring only the zero, first and second harmonics. These correspond to the daily mean, diurnal and semi-diurnal cycles. Areas in which convection is more likely to be triggered are identified, and the amplitude and time of the occurrence of maximum in the first harmonic are calculated. The results show that the diurnal cycle of convective phenomena varies with altitude, and the convective cells frequently organize over high orography and then propagate to lower orography. In addition, the results reveal strong semi-diurnal signals in the reflectivity field. The amplitude and time of the occurrence of maximum in the semi-diurnal variations are determined. It is shown that in the analyzed domain for echoes greater than or equal to 50 dBZ more than 27% of pixels have the maximum amplitude of the semi-diurnal variations greater than the maximum amplitude of the diurnal variations. Then an explanation of the origins of semi-diurnal signals is proposed.
Authors
C. Vamos
Tiberiu Popoviciu” Institute of Numerical Analysis, Romanian Academy, Cluj-Napoca, Romania
C. Pavai
Regional Forecast Center Cluj, Cluj-Napoca, Romania
Keywords
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Paper coordinates
C. Pavai, C. Vamoş, Statistical characteristics of reflectivity field in areas covered by the Bobohalma WSR-98D RADAR, Romanian Journal of Meteorology, v. 8 (2006) no. 1-2, pp. 1-20.
About this paper
Journal
Journal of Meteorology
Publisher Name
DOI
Print ISSN
2284-6220
Online ISSN
1223-1113
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