Vertical Variation of Z-R Relationship at Hallasan Mountain during Typhoon Nakri in 2014

Abstract

Hallasan Mountain is located at the center of Jeju Island, Korea. Even though the height of the mountain is just 1,950m, the orographic effect is strong enough to cause heavy rainfall. In this study, a rainfall event, due to Typhoon Nakri in 2014, observed in Jeju Island was analyzed fully using the radar and rain gauge data. First, the Z-R relationship (Z = AR(b)) was derived for every 250m interval from the sea level to the mountain top. The resulting Z-R relationships showed that the exponent b could be assumed as constant but that the parameter A showed a significant decreasing trend up to an altitude around 1,000m before it increased again. Theorographic effect was found to bemost significant at this altitude of 1,000 m. Second, the derived Z-R relationships were applied to the corresponding altitude radar reflectivity data to generate the rain rate field over Jeju Island. This rain rate field was then used to derive the areal-average rain rate data. These data were found to be very similar to the rain gauge estimates but were significantly different fromthose derived fromthe application of theMarshall-Palmer equation to the 1.5 kmCAPPI data, which is the data type that is generally used by the Korea Meteorological Administration (KMA).