Abstract
Abstract. Vertical air velocities were estimated from drop size and fall velocity spectra observed by Parsivel disdrometers during intensive field observations from 13 June to 3 August 2016 around Mt. Jiri (1915 m a.s.l.) in the southern Korean Peninsula. Rainfall and wind velocity data measured by Parsivel disdrometers and ultrasonic anemometers, respectively, were analyzed for an orographic rainfall event associated with a stationary front over Mt. Jiri on 1 July 2016. In this study, a new technique was developed to estimate vertical air velocities from drop size and fall velocity spectra measured by the Parsivel disdrometers and investigate characteristics of up-/downdrafts and related microphysics on the windward and leeward sides of the mountain. To validate results from this technique, vertical air velocities between the Parsivel disdrometers and anemometers were compared at different locations and were shown in quite good agreement with each other. It was shown that upward motion was relatively more dominant on the windward side and even during periods of heavy rainfall. In contrast, downward motion was more dominant on the leeward side during nearly the same periods of heavy rainfall. Occurrences of upward and downward motion were digitized as percentage values as they are divided by a total count of occurrences during the entire period. On the windward (leeward) side, the percentages of upward (downward) motion were much larger than those of downward (upward) motion. The mean rainfall intensity on the leeward side was stronger than on the windward side, suggesting that most of the rainfall on the leeward side was relatively more affected by the downward motion. With the estimated vertical air velocities, histogram characteristics of rainfall parameters were also examined between the windward and leeward sides.
Highlights
Drop size distribution (DSD) and related rain parameters from surface disdrometer measurements or indirectly retrieved from remote sensing measurements such as radars, wind profilers, or satellites provide key information for a better understanding of rain microphysics that accounts for drop growth and precipitation processes
Strong horizontal winds, vertical shear, or turbulence can disperse the distribution of drop size and fall velocity, leading to a change in the Parsivel-measured fall velocity averaged over the distribution
At D4, in contrast, most of stratiform rain was associated with downward motion and convective rain was associated with both upward and downward motion (Fig. 7c)
Summary
Drop size distribution (DSD) and related rain parameters from surface disdrometer measurements or indirectly retrieved from remote sensing measurements such as radars, wind profilers, or satellites provide key information for a better understanding of rain microphysics that accounts for drop growth and precipitation processes. Strong horizontal winds, vertical shear, or turbulence can disperse the distribution of drop size and fall velocity, leading to a change (or bias) in the Parsivel-measured fall velocity averaged over the distribution. All these factors would affect DSD integral parameters such as rain rate, the effects of the factors on DSD are complicated and hardly discriminated (Niu et al, 2010). Niu et al (2010) investigated differences in distributions of drop sizes and fall velocities between convective and stratiform rain and ascribed different deviations in Parsivelmeasured fall velocities between small and large drops to vertical air motion and turbulence.
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