Abstract
AbstractCumulonimbus clouds, which cause local heavy rainfall and urban floods, can develop within 20 min after being detected by operational centimeter-wavelength (X-, C-, or S-band) weather radars. To detect such clouds with greater lead times, Ka-band radars at a wavelength of 8.6 mm together with operational X-band radars were used in this study. The vertically averaged radar reflectivity (VAR) of convective echoes detected by the Ka-band and X-band radars were defined as mesoscale cloud echoes (MCEs) and mesoscale precipitation echoes (MPEs), respectively. The time series of each echo was analyzed by an echo tracking algorithm. On average, MCEs that developed into MPEs (denoted as developed MCEs) were detected 17 min earlier than the MPEs and 33 min earlier than the peak time of the area-averaged VAR (VARa) for MPEs. Some MCEs dissipated without developing into MPEs (denoted as non-developed MCEs). There were statistically significant differences between the developed and non-developed MCEs in terms of the maximum VARa values, maximum MCEs areas, and increase amounts of the VARa values and MCE areas for the first 6–12 min after their detection. Among these indicators, the maximum VARa for the first 9 min showed the most significant differences. Therefore, an algorithm for predicting MCE development using this indicator is discussed.
Highlights
IntroductionMeso-g-scale (spatial scale 2–20 km) cumulonimbus clouds can cause localized heavy rainfall
In summer, meso-g-scale cumulonimbus clouds can cause localized heavy rainfall
We studied local heavy rainfall events that occurred in the study area in August 2016 and 2017
Summary
Meso-g-scale (spatial scale 2–20 km) cumulonimbus clouds can cause localized heavy rainfall. If such a heavy rainfall event occurs in an urban area, even over a short time, it can result in flooding. Because cumulonimbus clouds develop very quickly, heavy rainfall sometimes occurs only 20 min after such clouds are detected by conventional (S-, C-, or X-band) weather radars (Ishihara 2012; Kim et al 2012). Operational X-band radars have been used in Japan to observe cumulonimbus clouds in urban areas. X-band phased array weather radars (PAWRs), which can obtain a threedimensional observation within 30 s, have been developed (Yoshikawa et al 2013; Yoshida et al 2013; Ushio et al 2015)
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