Asia-Pacific J. Atmos. Sci., 48(3), 259-273, 2012 DOI:10.1007/s13143-012-0026-2 The Effect of Topography and Sea Surface Temperature on Heavy Snowfall in the Yeongdong Region: A Case Study with High Resolution WRF Simulation Sun-Hee Jung, Eun-Soon Im, and Sang-Ok Han National Institute of Meteorological Research, Korea Meteorological Administration, Korea (Manuscript received 4 November 2011; revised 5 April 2012; accepted 6 April 2012) © The Korean Meteorological Society and Springer 2012 Abstract: An analysis of the heavy snowfall that occurred on 11-14 to traffic flow, agriculture, and fishery. The total snow amount February 2011 in the Yeongdong region along the eastern coast is in Donghae (DH) was 134.7 cm (11-14 Feb.), and the 24-hour presented. Relevant characteristics based on observation and model accumulated fresh snow in Gangneung (GN) was 77.7 cm (11 simulations are discussed with a focus on the times of maximum Feb.), which is the highest value recorded since observations snowfall in Gangneung (GN) and Daegwallyong (DG). This event was considered part of the typical snowfall pattern that frequently started in 1911. This event, considered the heaviest snowfall in a occurs in the Yeongdong region due to the prevailing northeasterly century on South Korea’s east coast, paralyzed the community flow. The control simulation using the high resolution Weather and caused widespread chaos. Hundreds of houses collapsed Research and Forecasting (WRF) model (1 km × 1 km) showed under the weight of the snow while hundreds of motorists were reasonable performance in capturing the spatial distribution and stranded in deep drifts. The cost of the damage was expected temporal evolution of precipitation. The area of precipitation maxima to run to approximately US 65,000,000 dollars (http://www. appeared to propagate from the plain coastal region further into the safekorea.go.kr). inland mountainous region, in relation to the location of convergence zone. In addition, a series of sensitivity experiments were performed According to the brief press release by the Korea Meteor- to investigate the effect of topography and sea surface temperature ological Administration, several typical factors contributed to (SST) on the formation of heavy snowfall. The change of topography this unprecedented event. First, a well developed Siberian High tended to modulate the topographically induced mechanical flow, expanding over the East Sea formed a synoptic pressure pattern and thereby modify the precipitation distribution, which highlights that blew the cold northeasterly winds onto the eastern coastal the importance of an elaborate representation of the topography. On region. Secondly, as this continental cold air mass persistently the other hand, the sensitivity experiment to prescribe positive advected and passed over the relatively warm sea surface, it (negative) SST forcing shows the enhanced (suppressed) precipi- tation amount due to the change of the sensible and latent heat was rapidly modified by large oceanic heat and moisture fluxes. fluxes, which enhanced the vertical instability. In addition, the Low pressure located in the southeastern Sea of Japan played a Key words: Heavy snowfall, topography and SST effect, WRF role in keeping the persistent northeasterly flow in the eastern simulation coastal region from blocking the closed meso-scale Low developing at the eastern Sea of the Korean peninsula. These 1. Introduction factors combined to provide a favorable condition for extended heavy snowfall. The Yeongdong region frequently suffers various severe Several previous studies have examined heavy snowfalls in weather events such as heavy precipitation and downslope the Yeongdong region based on both observations and windstorm, mostly due to the combined effect of its steep numerical model experiments. Most of these studies indicated mountain slopes (Taebaek mountain range) and close proximity that the orographic lifting due to the Taebaek mountain range to the ocean (East Sea) (Chung et al., 2004; Kim et al., 2005; and the abundant moisture and heat from the East Sea were the Kim and Chung, 2006; Lee et al., 2006; Han and Lee 2007; causes of the more frequent and heavier snowfall compared to Lee and Kim 2008b; Chang et al., 2009; Lee and In, 2009). Of other regions. Lee and Kim (2008a) postulated topographic particular concern is the heavy snowfall during the winter effect as the key factor in the formation of heavy snowfall in season because of its frequent occurrence and negative impacts the Yeongdong region through an experiment that removed the on the ecosystem and economy. Recently, exceptionally heavy topography over the Taebaek Mountains. Lee and Lee (1994) snowfall occurred on 11-14 February 2011 in the Yeongdong also showed that the height of the topography significantly region along the eastern coast, resulting in tremendous damage affects the amount of snowfall. On the other hand, Ahn and Cho (1998) highlighted the importance of sea surface tempera- ture (SST) in the simulation of heavy snowfall events in the Corresponding Author: Eun-Soon Im, 401 Education Service Center, Gangnueng-Wonju National University, 7, Jukheon-gil, Gangneung- Yeongdong region based on a meso-scale model experiment. si, Gangwon-do 201-702, Korea. In this study, we attempt to simulate the snowfall event that E-mail: [email protected] occurred on 11-14 February 2011 in the Yeongdong region 260 ASIA-PACIFIC JOURNAL OF ATMOSPHERIC SCIENCES Fig. 1. The model domain and topography (upper panels), and vertical transects of the surface elevation along the line between points A and B (lower panels) used for the CONT (a, c) and EXP_T1 (b, d) simulations. Topography is represented with shading based on scale at right of the (b). using the high resolution Weather Research and Forecasting Table 1. Summary of numerical experiments. (WRF) system (1 km × 1 km). The model results are evaluated Experiment Topography SST by comparison with station observations in terms of spatial distribution and temporal evolution. Assessing the model sys- CONT 30sec. resolution data set Default tem’s capability of capturing observed features can provide EXP_T1 10-min. resolution data set Default some confidence in interpreting the following sensitivity experi- EXP_S1 Same as CONT + 2 K ments. To better understand the effect of the topography and EXP_S2 Same as CONT − 2K SST on the formation of heavy snowfall, a series of ex- periments are performed. In the sensitivity experiment for EXP_S3 Same as CONT No horizontal gradient (SST = constant) topography effect, the topography is smoothed by using 10-min United States Geological Survey (USGS) dataset (EXP_T1) while the control experiment (CONT) uses 30-sec data, resultant snowfall intensity. resulting in different topographic features despite the same In section 2 we briefly describe the model configuration and resolution of the two experiments (See Fig. 1). In the sensitivity experiment design. The synoptic condition and the relevant experiment investigating the SST effect, SST is uniformly characteristics of the snowfall event are explained in section 3. increased (decreased) by 2 K over the ocean areas within the The results for the control (CONT) and four kinds of sensitivity interior domain when interpolating the initial and lateral experiment (EXP_T1 and EXP_S1-3) were then validated and boundary conditions (EXP_S1 & EXP_S2). Additionally, a compared in section 4. Finally, the summary and discussion sensitivity experiment is performed to prescribe the SST as a are presented in section 5. constant in order to examine the effect of horizontal gradient of the SST distribution (EXP_S3, See Table 1). By comparison 2. Model configuration and experiment design with CONT, EXP_T1 present an ideal of the topography effect while EXP_S1-3 reveals the influence of SST condition on the The numerical model used in this study is the WRF (version 31 August 2012 Sun-Hee Jung et al. 261 3.2.1) described by Skamarock et al. (2008). The WRF model Iacono et al., 2008), Goddard shortwave radiation scheme (Tao is a next-generation meso-scale numerical weather prediction et al., 1989), the Double-Moment (WDM) 6-class microphysics system designed to serve both operational forecasting and scheme (Lim and Hong, 2010), and none cumulus parameter- atmospheric research needs. The Advanced Research WRF ization scheme. The WDM 6-class scheme consists of six solver developed at the National Center for Atmospheric Re- hydrometeors: vapor, cloud water, cloud ice, rain, snow, and search was used for the dynamic core, which is a fully com- graupel. This scheme is considered the most suitable for cloud- pressible and non-hydrostatic model. The physical parameter- resolving grid. Through various sensitivity experiments, we izations employed in this simulation include the 5-layer thermal determined the optimal selection and combination among the diffusion land-surface model (Chen and Dudhia. 2001), the variety of physical parameterizations. Yonsei University (YSU) planetary boundary layer scheme Figure 1a shows the model domain and topography for the (Hong et al., 2006), the Rapid Radiative Transfer Model CONT experiment. The domain focused on the eastern part of (RRTMG) longwave radiation scheme (Malwer et al., 1997; Korean peninsula where the snowfall event selected in this Fig. 2. Spatial distribution of SST used in (a) CONT, (b) EXP_S1, (c) EXP_S2 and the difference field between CONT and (d) EXP_S3. 262 ASIA-PACIFIC JOURNAL OF ATMOSPHERIC SCIENCES study was concentrated. The horizontal resolution was 1 km × SST affects the simulation of the vertical and horizontal 1 km with 400 × 400 grid points while 31 vertical levels were meteorological fields and the resultant snowfall amount. employed up to 50 hPa. We also carefully selected the domain The initial and time-dependent lateral boundary conditions area through several sensitivity tests since the simulation were interpolated using the Korea Local Analysis and Predic- results may have been affected by the domain size and location tion System (KLAPS) with a horizontal resolution of 5 km × of the lateral boundaries (Seth and Giorgi, 1998).