A Study on Variability of ZDR and KDP Maxima According to Microphysical Processes through Dual-Polarization Radar and Distrometers Observation

Many snow storms have been observed by using dual-polarization radar. The observation results show that Z_DR and K_DP maxima zone in snow storm strongly relate to heavy snowfall period. Therefore, understanding the variability of Z_DR and K_DP maxima is very important for expectation of snowfall amount. In this paper, we attempted to explain the variability of Z_DR and K_DP maxima due to the change of microphysical processes. Observations of three snow storms in Colorado, USA were performed by using CSU-CHILL radar, distrometers and radio-sonde.

Range height indicator (RHI) scans of CSU-CHILL radar were performed toward to Easton site near Greeley, Colorado. The timeseries of vertical profile (TVP) are extracted from RHI data over Easton site. 2D-video distrometer (2DVD) and multi angle snowflake cameras (MASC) were co-located at Easton site.

We used two approaches to explain the variability of Z_DR and K_DP maxima due to microphysical processes. First, we examined the relationships between the maxima and snowfall characteristics. The maxima values were extracted from TVP over Easton site. Characteristics of snowfall were analyzed by using snow habits using MASC, snow size distribution (SSD) and its moments obtained from 2DVD data. Second, we examined the relationships between the maxima and precipitation system. Precipitation system was classified as the shallow system or the deep system.

In each event, we analyzed two periods in which the microphysical processes changed. Z_DR maximum decreases when microphysical processes change from aggregation to riming. Both Z_DR and K_DP maxima decrease when snow habits are changed from dendrite to plate. We compared maxima values between shallow system group and deep system group. Shallow system is characterized by relatively large Z_DR maximum whereas deep system is characterized by relatively small Z_DR maximum.

We will interpret the results from the viewpoint of microphysics. In addition, simulation results based on microphysical interpretation will be compared with the observed vertical profile.