Abstract
Abstract. A method for forecasting very short-term rainfall to detect potentially hazardous convective cloud that produces heavy local rainfall was developed using actual volumetric C-band polarimetric radar data. Because the rainfall estimation algorithm used in this method removed the effect of ice particles based on polarimetric measurements, it was immune to the high reflectivity associated with hail. The reliability of the algorithm was confirmed by comparing the rainfall rate estimated from the polarimetric radar measurements at the lowest elevation angle with that obtained from optical disdrometers on the ground. The rainfall rate estimated from polarimetric data agreed well with the results obtained from the disdrometers, and was much more reliable than results derived from reflectivity alone. Two small cumulus cells were analyzed, one of which developed and later produced heavy rainfall, whereas the other did not. Observations made by polarimetric radar with a volumetric scan revealed that a high vertical maximum intensity of rainfall rate and a vertical area of enhanced differential reflectivity extending above the freezing level, often termed a high ZDR column, were clearly formed about 10 min prior to the onset of heavy rainfall on the ground. The onset time of the heavy rainfall could be estimated in advance from the polarimetric data, which agreed fairly well with observations. These polarimetric characteristics were not observed for the cumulus cell that did not produce heavy rainfall. The results suggest that both the vertical maximum intensity of the rainfall rate and a high ZDR column, estimated from polarimetric measurements, can be used to identify potentially hazardous clouds. Furthermore, this study shows that polarimetric radar measurements with high spatial and temporal resolutions are invaluable for disaster reduction.
Highlights
Heavy convective rainfalls, in conjunction with accompanying phenomena such as rainstorms, hail, and flash flooding, have an immediate and often devastating impact on a broad range of human activities, especially in urban areas
This suggests that the quality of the ZDR measured with this radar is suitable for reliable quantitative precipitation estimates (QPE), especially for the long-pulse observations, even with a sample number of 20, because rainfall rates greater than 10 mm h−1 can be estimated with an accuracy of 25 % if the ZDR measurement error is less than 0.2 dB (e.g. Illingworth, 2004; Illingworth and Blackman, 2002)
Rainfall rate (R) was estimated using a method based on Gorgucci et al (1994) but with parameters proposed by Bringi and Chandrasekar (2001) from the corrected ZDR and ZH data, with an ice fraction of less than 0.2 and a ZDR greater than 0.5 dB as
Summary
In conjunction with accompanying phenomena such as rainstorms, hail, and flash flooding, have an immediate and often devastating impact on a broad range of human activities, especially in urban areas. The efficacy of dual-polarization radar for quantitative precipitation estimation (QPE) has been demonstrated in a number of previous studies (see Bringi and Chandrasekar, 2001 for a review) These studies have shown that rainfall retrieval using combinations of polarimetric variables have an advantage over traditional R(ZH) methods because more information regarding DSD is available They recorded this peak value with a sample number of 20, which enabled volumetric scans with a time resolution of 4 minutes for their system This radar may have the capability to investigate the evolution of cloud in the development stage, as is required for very short-term forecasts.
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