( 2020) showed that N 0 and N w decreased with altitude when landfalling typhoons passed the 356-m high meteorological tower in Shenzhen, China, where disdrometers are mounted at four different altitudes. ( 2003) also observed the N 0 jump at a disdrometer site in northern Mississippi, USA, when the transition from stratiform to convective rainfall occurred with the disappearance of the radar bright band. Waldvogel ( 1974) observed a sudden change in N 0, called the N 0 jump, during orographic precipitation when a convective portion within a precipitation system moved in to or out from a disdrometer site in Locarno, Switzerland. Many studies have revealed that N 0 or the generalized intercept parameter N w, which is computed from the rainwater content W and mass-weighted mean raindrop diameter D m for a size distribution of any form and is identical to N 0 for an exponential size distribution, has a large spatiotemporal variability (Waldvogel 1974 Uijlenhoet et al. The constant- N 0 assumption in single-moment bulk microphysics schemes is different from reality. In models with single-moment bulk microphysics schemes, which prognose only hydrometeor mixing ratios, the intercept parameter is usually fixed as in the Marshall-Palmer distribution and the slope parameter is determined by the prognosed rainwater mixing ratio. A well-known exponential distribution is the Marshall-Palmer distribution (Marshall and Palmer 1948), where N 0 is a fixed value of 8000 m − 3 mm − 1 and Λ is a function of rain rate. Where N 0 is the intercept parameter and Λ is the slope parameter of raindrop size distribution (RSD). The smaller N 0 in the WSM6-L simulation decreases the rainwater production by the accretion of cloud water and the melting of ice hydrometeors, decreasing the rainwater mixing ratio. Also, the WSM6-L simulation predicts N 0 that is on average smaller than the prescribed value in the WSM6-O simulation, agreeing with the observation to some extent. The WSM6-L simulation represents the variability of N 0. Compared to the simulation using the original WSM6 scheme (WSM6-O) where a constant N 0 is used, the simulation where N 0 is diagnosed by the diagnostic relation using the rainwater content at the lowest level (WSM6-L) yields better precipitation prediction. The diagnostic relation is implemented into the WRF single-moment 6-class microphysics (WSM6) scheme, and its impacts are investigated through the simulations of summertime precipitation events in South Korea. Three different derivation methods proposed by previous studies are used to derive the diagnostic relations, and the diagnostic relation that best reproduces the observed N 0 is selected. The disdrometer data observed at four sites in South Korea show spatiotemporal variations of N 0. In this study, using disdrometer data, the diagnostic relations for the intercept parameter of the exponential raindrop size distribution N 0 are derived for different rain types and the impacts of the diagnostic relations on precipitation prediction are examined. However, its variability needs to be studied further and properly considered for improving precipitation prediction. The raindrop size distribution observed from ground-based or airborne disdrometers has been widely used to understand the characteristics of clouds and precipitation.
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