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이주현,진한결,백종진 한국기상학회 2023 Asia-Pacific Journal of Atmospheric Sciences Vol.59 No.2
The raindrop size distribution observed from ground-based or airborne disdrometers has been widely used to understandthe characteristics of clouds and precipitation. However, its variability needs to be studied further and properly consideredfor improving precipitation prediction. In this study, using disdrometer data, the diagnostic relations for the interceptparameter of the exponential raindrop size distribution N0 are derived for different rain types and the impacts of the diagnosticrelations on precipitation prediction are examined. The disdrometer data observed at four sites in South Korea showspatiotemporal variations of N0. Three different derivation methods proposed by previous studies are used to derive thediagnostic relations, and the diagnostic relation that best reproduces the observed N0 is selected. The diagnostic relationis implemented into the WRF single-moment 6-class microphysics (WSM6) scheme, and its impacts are investigatedthrough the simulations of summertime precipitation events in South Korea. Compared to the simulation using the originalWSM6 scheme (WSM6-O) where a constant N0 is used, the simulation where N0 is diagnosed by the diagnostic relationusing the rainwater content at the lowest level (WSM6-L) yields better precipitation prediction. The WSM6-L simulationrepresents the variability of N0. Also, the WSM6-L simulation predicts N0 that is on average smaller than the prescribedvalue in the WSM6-O simulation, agreeing with the observation to some extent. The smaller N0 in the WSM6-L simulationdecreases the rainwater production by the accretion of cloud water and the melting of ice hydrometeors, decreasingthe rainwater mixing ratio.
좌민채,진한결,이주현,문성주,백종진 한국기상학회 2021 Asia-Pacific Journal of Atmospheric Sciences Vol.57 No.3
The raindrop size distribution (RSD) is useful in understanding various precipitation-related processes. Here, we analyze disdrometer data collected in Seoul, South Korea from May 2018 to July 2019 to characterize the RSD according to rain and weather types. Rain types are categorized into stratiform, mixed, and convective rain, and weather types into the Changma front (type CF) and low-pressure system (type L). The slope parameter Λ decreases and the intercept parameter N0 fluctuates with rain rate. Among the rain types, the RSD of stratiform (convective) rain shows the steepest (mildest) slope and the smallest (largest) mean diameter. The logarithm of generalized intercept parameter log10Nw and Λ for stratiform rain have considerably dispersed distributions, which may be attributed to the diversity within the stratiform rain type in Seoul. Mixed-type rain has a larger mean value of log10Nw compared to stratiform and convective rain. Regarding the weather types, the RSD of type CF exhibits a milder slope, a larger mass-weighted mean diameter, and a larger radar reflectivity than type L. These differences between the weather types can be explained by the larger convective proportion in type CF (33%) compared to type L (9%). Possible causes for the differences between the RSD characteristics of the two weather types are examined using reanalysis and satellite data. Type CF has a larger convective available potential energy, a higher cloud top, and more active ice microphysical processes than type L, which can lead to different RSD characteristics.
A Hail Climatology in Mongolia
Jambajamts Lkhamjav,진한결,이현호,백종진 한국기상학회 2017 Asia-Pacific Journal of Atmospheric Sciences Vol.53 No.4
The temporal and spatial characteristics of hail frequency in Mongolia are examined using the hail observation data from 61 meteorological observatories for 1984-2013. The annual number of hail days averaged over all observatories and the entire period is 0.74. It exhibits a decreasing trend, particularly since 1993 with a rate of decrease of 0.214 per decade. Hail occurrence is concentrated in summer, with 72% of the total hail days occurring in June, July, and August. Moreover, hail occurrence is concentrated in the afternoon and early evening, with 89% of the total hail events occurring between 1200 and 2100 local standard time (LST). Spatially, observatories where relatively frequent hail events are observed are concentrated in the north central region where almost all of the land is mountainous or covered by grassland, whereas relatively less frequent hail events are observed in the southern desert region. The relationship between hail frequency and thermodynamic factors including the convective available potential energy (CAPE), the temperature lapse rate between 700 and 500 hPa, the water vapor mixing ratio averaged over the lowest 100 hPa layer, and the freezing-level height is examined using the ERA-Interim reanalysis data. It is found that in summer, CAPE and the low-level water vapor mixing ratio are larger on hail days than on all days, but there is no clear relationship between hail frequency and the 700-500 hPa temperature lapse rate. It is also found that annually, CAPE and the low-level water vapor mixing ratio decrease, while the freezing-level height increases, which seems to be responsible for the annually decreasing trend of hail frequency in Mongolia.
Spatiotemporal Variations of Precipitation in Bangladesh Revealed by Nationwide Rain Gauge Data
AHMED TANVIR,진한결,백종진 한국기상학회 2020 Asia-Pacific Journal of Atmospheric Sciences Vol.56 No.4
Bangladesh is under the strong influence of the South Asian monsoon. Extensive damages caused by frequent severe flood events in this country call for a study of nationwide precipitation climatology. Here, we examine spatiotemporal variations of precipitation in Bangladesh using rain gauge data at 35 stations for the period 2003–2016. The annual precipitation amount in Bangladesh is 2263 mm, and it shows large spatial variations. The annual precipitation amount is large in the southeastern coastal region of the country and the region close to the Meghalaya Plateau, and it is small in the west central region. 17% and 73% of the annual precipitation amount are observed in the pre-monsoon season (March to May) and monsoon season (June to September), respectively. The pattern of the diurnal variation of precipitation differs depending on regions of Bangladesh. In the northern region of the country, the precipitation maximum occurs in the late night to early morning in both the pre-monsoon and monsoon seasons. The late night to early morning maximum of precipitation is associated with the large horizontal convergence of low-level water vapor flux. The Himalaya Mountains and the Meghalaya Plateau together with more nighttime moisture transport due to the strengthened nighttime low-level wind seem to play roles in enhancing nighttime precipitation. In the southwestern region of the country, the precipitation maximum is observed in the early evening in the pre-monsoon season, which is associated with the large convective instability in the afternoon, and it is observed in the early afternoon in the monsoon season. In the southeastern region of the country, the diurnal variability of precipitation is smallest in the pre-monsoon season compared with other regions of the country in the pre-monsoon and monsoon seasons and the precipitation maximum occurs in the late night to early morning in the monsoon season.