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Lee, Keun-Ok,Uyeda, Hiroshi,Lee, Dong-In Swedish Geophysical Society ; Munksgaard [distribu 2014 Tellus. Series A, Dynamic meteorology and oceanogr Vol.66 No.1
A series of idealised experiments using a cloud-resolving storm simulator (CReSS) was performed to investigate the effects of the isolated elliptically shaped terrain of Jeju Island (oriented east-west), southern Korea, on the enhancement of pre-existing rainfall systems under the influence of prevailing southwesterly moist flows. Control parameters were the low-altitude wind speed (Froude numbers: 0.2, 0.4, 0.55) and the initial location of the elongated (oriented north-east) rainfall system (off the northwestern or western shores of the island). Simulations were conducted for all combinations of initial location and wind regime. Overall, results indicate that weak southwesterlies flowing around the steep mountain on the island (height, 2 km) generate two local convergences, on the northern lateral side and on the lee side of the island, both in regions of moist environments, thus producing conditions favourable for enhanced rainfall. As an eastward-moving rainfall system approaches the northwestern shore of the island, the southwesterlies at low altitudes accelerate between the system and the terrain, generating a local updraft region that causes rainfall enhancement onshore in advance of the system's arrival over the terrain. Thus, the prevailing southwesterlies at low altitudes that are parallel to the terrain are a crucial element for the enhancement. Relatively weak southwesterlies at low altitudes allow system enhancement on the lee side by generating a convergence of relatively weak go-around northwesterlies from the northern island and relatively strong moist southwesterlies from the southern island, thus producing a relatively long-lived rainfall system. As the southwesterlies strengthen, a dry descending air mass intensifies on the northeastern downwind side of the terrain, rapidly dissipating rainfall and resulting in a relatively short-lived rainfall system. A coexisting terrain-generated local convergence, combined with the absence of dry descending air on the downwind side of the terrain, prolongs the lifetime of the rainfall system.
장상민,구지영,이동인,정종훈,박성화,Hiroshi Uyeda 한국지구과학회 2012 韓國地球科學會誌 Vol.33 No.5
To elucidate the mechanism associated with the development of heavy precipitation system, a field experiment was carried out in Jejudo (or Jeju Island) and Marado, Korea from 22 June to 12 July 2006. The synoptic atmospheric conditions were analyzed using the National Centers for Environmental Prediction-National Center for Atmospheric Research’s (NCEP/NCAR) reanalyzed data, weather maps, and sounding data. The kinematic characteristics of each precipitation system were investigated by dual Doppler radar analysis. During the field experiment, data of four precipitation events with more than 20 mm rainfall were collected. In F case (frontal precipitation), a typical Changma front was dominant and the observation field was fully saturated. However there was no convective instability near the surface. LF case (low pressure accompanied with Changma front) showed strong convective instability near the surface, while a strong convergence corresponded to the low pressure from China accompanied with Changma front. In FT case (Changma front indirectly influenced by typhoon), the presence of a convective instability indicated the transport of near surface, strong additional moisture from the typhoon ‘EWINIAR’. The convergence wind field was ground to be located at a low level. The convective instability was not significant in T case (precipitation of the typhoon ‘EWINIAR’), since the typhoon passed through Jejudo and the Changma front was disappeared toward the northeastern region of the Korean peninsula. The kinematic (convergence and divergence) characteristics of wind fields, convective instability, and additional moisture inflow played important roles in the formation and development of heavy precipitation.
You, Cheol‐,Hwan,Kang, Mi‐,Young,Lee, Dong‐,In,Uyeda, Hiroshi John Wiley Sons, Ltd 2014 Meteorological applications Vol.21 No.4
<P><B>ABSTRACT</B></P><P>The empirical relationships used to estimate rainfall amounts from polarimetric radar observations were developed and tested by using long‐period drop size distribution (DSD) data and monitoring of rainfall events prior to operational use in Korea. Rainfall associated with Typhoon Meari in 2011 was selected to assess the performance of these relationships for point and areal rainfall amounts. Data quality was checked in regions of light rain to enable the quantitative use of polarimetric variables. The distributions of the cross‐correlation co‐efficient and standard deviation of the differential phase shift agreed with those established in a previous study, but the absolute average deviation of differential reflectivity (<I>Z<SUB>DR</SUB></I>) was a little distorted. Biases in reflectivity (<I>Z</I>) and differential reflectivity were calculated following established methods and found to be –0.18 and 0.47 dB, respectively. The accuracy of rainfall amounts calculated from <I>R(K<SUB>DP</SUB>)</I> and <I>R(K<SUB>DP</SUB>, Z<SUB>DR</SUB>)</I> was poor. The best estimates of rainfall were obtained using <I>R(Z, Z<SUB>DR</SUB>)</I> based on DSDs from Oklahoma (OKC) in the USA and Busan (BSC) for both the point and areal mean cases. Correlation co‐efficients of <I>R(Z, Z<SUB>DR</SUB>)</I> using the BSC DSDs were better than those using the OKC DSDs for areal mean rainfall amounts. Rainfall amounts in this particular case in Korea were estimated more accurately using the Brandes drop shape for <I>R(Z, Z<SUB>DR</SUB>)</I> than the equilibrium drop shape.</P>
Kim, Hyeon-Joon,Lee, Keun-Ok,You, Cheol-Hwan,Uyeda, Hiroshi,Lee, Dong-In Elsevier Science Publishers 2019 Atmospheric research Vol.222 No.-
<P><B>Abstract</B></P> <P>During the 2012 Changma season of June and July, we conducted an intensive field observation to investigate the microphysical characteristics of orographic precipitation that passed around Mt. Halla (oriented west–east; height: 1950 m; width: 78 km; length: 35 km) in South Korea's Jeju Island. On July 04, 2012, Jeju Island experienced a convective precipitation system that developed in the southern part of a stationary front. With the goal of understanding the microphysical process of this system (precipitation intensity: 70 mm h<SUP>−1</SUP>), we collected detailed data using 7 Parsivel disdrometers, a ground-based dual S-band Doppler radar, and GPS sounding. The convective precipitation developed in a considerably warm and moist environment (near-surface relative humidity: 94%) with dominant southwesterly winds of 4.7 m s<SUP>−1</SUP> at low altitudes. The convective region was formed by a combination of coastal ascending air and considerably warm and moist low-level marine inflow. The coastal warm and moist ascending air activates the warm rain process of moisture uptaken from sea surface, increasing the concentration of large-sized raindrops (diameter: ≥ 5 mm). The continuous development of a convective region extending from the foothill to the upslope highlights that the convective updrafts continuously supply low-level moisture to the convective region. This influx of moisture and the condensation of small-, middle-, and large-sized raindrops combine to create a significant concentration of large-sized raindrops along the upslope of the mountain. Around the mountaintop, the fall of precipitation drives the breakup process aided by convective ascending airs, increasing the concentrations of small-sized raindrops. On the leeward side, the existence of orographically generated stationary wind convergences is notable. As a result and the marine inflow along the southeastern gentle slope, i.e., the convective region, continues to develop, thereby activating cold rain processes. This study sheds light on the variety of raindrop size distributions and moisture processes at locations relative to a single-peak mountain leading to localized heavy precipitation during the passage of an isolated convective precipitation event.</P> <P><B>Highlights</B></P> <P> <UL> <LI> To reveal the microphysical characteristics of orographic precipitation passed around Mt. Halla in moist environment. </LI> </UL> </P>