Drop Size Distribution Characteristics by Vertical Wind in Orographic Precipitation

The Drop Size Distribution (DSD) characteristics involved raindrop size, fall-velocity and number concentration reflects the microphysics of precipitation. The vertical wind occurred on the mountainous areas affects the growth and dissipation of raindrops by the collision-coalescence and evaporation, etc. To investigate the DSD characteristics of orographic precipitation passing on Mt.Halla in Jeju Island (oriented west–east; height 1,950 m, width 78 km, length 35 km), intensive field observation were conducted during Changma season (for 3 years, 2012 to 2014). The DSD characteristics of the precipitation systems were investigated using surface PARSIVEL disdrometers installed at different altitudes: 58 m, 140 m, 571 m, 975 m at the western part, and 587 m, 324 m, 57 m at eastern part from Mt. Halla.

The vertical wind on the mountain slope was estimated by the difference between observed fall-velocity and experimental fall-velocity using the disdrometer data. There were measured updraft and downdraft winds at the near coastal region. The downdraft (updraft) was dominant at the highest site (which was installed around the mountain region). The correlation between the vertical wind, mass-weighted diameter (D_m) and normalized intercept parameter (N_w) were examined. The D_m and N_w in the time period of updraft (downdraft) were 1.2 (0.8) mm and 8681 (17352) mm^-1m^-3 at the sites on the slope of mountain. The D_m and N_w at the top of mountain (at the coastal) site were 1.08 (1.39) mm and 9719 (4920) mm^-1m^-3in the updraft (downdraft) region.

The vertical wind measured by parsivel was validated by the wind fields obtained by dual Doppler analysis and ultrasonic anemometer measurement. We will all also present the DSDs characteristics with respect to the vertical winds more detail.

Acknowledgment

This work was funded by the Korea Meteorological Industry Promotion Agency under Grant KMIPA 2015-1050.

This work was financially supported by the BK21 plus Project of the Graduate School of Earth Environmental Hazard System.