Influences of Orography and Coastal Geometry on a Transverse-Mode Sea-Effect Snowstorm over Hokkaido Island, Japan

Abstract

Sea-effect snowstorms generated over the Sea of Japan produce consistent and often heavy snowfall throughout the winter season, impacting downstream communities in northern and central Japan. Here, we use observations and Weather Research and Forecasting (WRF) Model simulations to examine the precipitation distribution produced by transverse-mode sea-effect snowbands that interacted with the mountainous terrain circumscribing Ishikari Bay, Hokkaido Island, Japan, on 12 January 2014. The bands observed here were horizontal convective rolls aligned normal to the mean flow and were ~10 km wide and up to ~100 km long. The bands approached Ishikari Bay at intervals of ~10–16 min, intensifying as they progressed through a quasi-stationary, elongated enhancement region that paralleled the Shakotan Peninsula and extended into the Ishikari plain. Hydrometeor advection, through an ascent region over the northeast slope of the Shakotan Peninsula, and along clockwise-turning trajectories steered by the boundary layer directional shear, contributed to sustained precipitation enhancement along a curve in the elongated enhancement region near the entrance to Ishikari Bay. Downstream, orographic flow deflection by the coastal mountains, likely accentuated by thermal and roughness gradients along the Shakotan Peninsula’s shoreline, produced convergence and ascent along the elongated enhancement region. This study demonstrates the impact of downstream topography on sea-effect snowstorms and has implications for improving the prediction of snowfall in this and other lake- and sea-effect regions.

Intrastorm Variability of the Inland and Orographic Enhancement of a Sea-Effect Snowstorm in the Hokuriku Region of Japan

“…YAHI has a minimum elevation angle of 20.58, additional scans up to a maximum elevation angle of 258, and full volumes available at 10-min intervals. We interpolated the volume scans to a Cartesian grid with 0.018 horizontal and 0.25 km vertical resolution using the Radx C11 software package, and produced radarestimated liquid precipitation equivalent (LPE) using the Z-S relationship described by Vasiloff (2001) and Campbell et al (2016) and given by…”

“…The reality can be more complicated, however, as nonlinear mountain-wave dynamics and the release of convective instability heavily influence the trajectory of hydrometeors (Geerts et al 2015). Hydrometeor time scales are also important in lake-effect events, where a maximum in buoyancy occurs at landfall, often accompanied by a maximum in hydrometeor mixing ratio (Alcott and Steenburgh 2013;Campbell and Steenburgh 2017;Campbell et al 2018). This effect is compounded by the tendency for fast-falling particles like graupel to occur more frequently and fall out closer to the shoreline than less-rimed particles (e.g., Harimaya and Sato 1992;Murakami et al 1994;Harimaya and Kanemura 1995;Ohigashi and Tsuboki 2005).…”

“…Watson andLane (2012, 2014) showed that concavities within a barrier can provide additional enhancement beyond that of a straight barrier, with additional effects from the length and steepness of the barrier. Small ridges and corrugations within a mountain range can also provide strong local enhancement (e.g., Garvert et al 2007;Minder et al 2008;Campbell and Steenburgh 2014). In the Hokuriku region, Kusunoki et al (2005) showed that supercooled water maxima were strongly tied to each sub peak in the terrain, with riming from these maxima contributing to orographic enhancement.…”

Characteristics of Sea‐Effect Clouds and Precipitation Over the Sea of Japan Region as Observed by A‐Train Satellites

“…Heavy snowstorms frequently impact the northwest Japanese coast and adjacent topography, disrupting transportation, contributing to structural damage and periods of elevated avalanche risk, and building a snowpack critical for regional water resources and winter tourism (Chechin & Pichugin, 2015;Eito et al, 2005;Nakai et al, 2012;Steenburgh, 2014). Much of this snowfall results from sea-effect precipitation (e.g., Campbell et al, 2018;Eito et al, 2010;Magono et al, 1966;Mizukoshi, 1977;Murakami et al, 1994;Nakai et al, 2005;Tsuchiya & Fujita, 1967), a phenomenon closely related to lake-, sea-, and ocean-effect precipitation in other regions of the world (e.g., Andersson & Nilsson, 1990;Kindap, 2010;Kristovich et al, 2017;Laird et al, 2009;Niziol et al, 1995;Norris et al, 2013;Steenburgh et al, 2000;. Sea effect over the SOJ occurs predominantly during the East Asian winter monsoon, which results from the interaction of the semipermanent Siberian High over northern Asia and the Aleutian Low in the Gulf of Alaska and features mean northwesterly flow over the SOJ during winter (Boyle & Chen, 1987;Dorman et al, 2004).…”

“…Concomitant cold-air outbreaks (Mitnik, 1992) gain heat and moisture over the relatively warm waters of the SOJ and Tsushima current, destabilizing the atmosphere and generating clouds and precipitation (e.g., Hozumi & Magono, 1984;Tsuchiya & Fujita, 1967). Sea-effect precipitation systems then reach the northwest Japanese coast, where they are modified by coastal, inland, and orographic effects (e.g., Campbell et al, 2018;Estoque & Ninomiya, 1976;Kawamoto et al, 1963;Kusunoki et al, 2005;Nakai & Endoh, 1995;Saito et al, 1996;Yoshihara et al, 2004).…”