A Classification of Snow Clouds by Doppler Radar Observations at Nagaoka, Japan

Abstract

A classification of snow clouds, called the "snowfall mode," is proposed based on Doppler radar observations at 10-minute intervals at Nagaoka in 1999/2000 winter season. Using 795 hours of data at an altitude of 1.6 km, six snowfall modes were defined: longitudinal line (Lmode), transversal line (T-mode), spreading precipitation (S-mode), meso-scale vortex (V-mode), mountainslope precipitation (M-mode), and local-frontal (discontinuity) band (D-mode). In migrating snow clouds, a subclass, referred to as snowfall with coastal intensification (xI-mode, where x is L, T, S and V) was defined. A sample snapshot and the mean Ze are shown for each snowfall mode. The frequency of occurrence of the snowfall modes indicated that both of the longitudinal cloud streets and the mesoscale disturbances occupied about 1/3 of the analysis period. About 18% of the precipitation in the analysis period was considered to be under orographic effects. The prevailing wind direction differed between the snowfall modes although a west-northwesterly wind dominated. IntroductionSnow clouds developing over the Sea of Japan generate a wide variety of radar echo patterns, which suggests that there are a number of mechanisms involved in the development of snow clouds. In the 1970s, some classifications of snow clouds were made using conventional radars (e.g., Nanasawa 1975). However, their time resolution was low that the motion and duration of the specific patterns were not analyzed. Since then, many theoretical and observational case studies have been conducted. There are several wellknown structures of snow clouds. Longitudinal (Lmode) snowbands often correspond to "cloud streets" that appear during cold outbreaks. The structure of the transversal (T-mode) snowbands was recently elucidated (Murakami et al. 2002). Vortex disturbances often appear around the Japan Sea Polar-Airmass Convergence Zone (JPCZ) (Asai 1988; Tsuboki and Asai 2004). They were also observed as radar echoes (e.g., Asai and Miura 1981). Moreover, land breezes contribute to the formation of snowbands and significantly affect the snowfall (e.g., Ishihara et al. 1989;Ohigashi and Tsuboki 2005).Thus, various structure and development processes of the snow clouds have been analyzed. However, systematic morphological terminology has not been established, and the frequency of occurrence has not been thoroughly analyzed.The Nagaoka Institute of Snow and Ice Studies (NISIS) locates in the central part of the Niigata Prefecture (Fig. 1). The NISIS makes it possible to observe snow clouds throughout the winter season. In this paper, we propose a classification of snow clouds or "snowfall modes" based on Doppler radar winter observations. ObservationAn X-band Doppler radar, X-POL (Iwanami et al. 1996), was set up on the roof of the NISIS. The observation area was a northwestern-side semicircle with a radius of 64 km. The radar operation consisted of 15 steps of a PPI scan, repeated at about 10-minute intervals. Three-dimensional distributions of the equivalent radar reflect...

Modification of misovortices during landfall in the Japan Sea coastal region

“…All of the misovortices analyzed here were embedded in rain or snow clouds. We subjectively classified the clouds using JMA radar into two well-known modes (e.g., Nakai et al, 2005): "L-mode" and "T-mode," i.e., lines (bands running or cells aligned) longitudinal and transversal to the prevailing northwesterly wind, respectively. L-mode was observed on four dates and T-mode on two dates ( Table 2).…”

Climatology of cold season lake‐effect cloud bands for the North American Great Lakes

“…The approach used in this study should have widespread application as similar mesoscale systems and cloud bands have been observed in a large number of locations beyond the Great Lakes region. These systems develop in similar atmospheric environments where boundary layer destabilization occurs from cold air masses moving over relatively warm water, and have been observed and investigated in regions including: the English Channel and Irish Sea (Norris et al , ), the Gulf of Finland (Mazon et al , ; Savijärvi, ), the Baltic Sea (Andersson and Nilsson, ; Andersson and Gustafsson, ), the Labrador Sea (Renfrew and Moore, ; Liu et al , ), the Greenland Sea (Brümmer et al , ; Brümmer and Pohlmann, ), the Beaufort Sea (Mourad and Walter, ), the Bering Sea (Walter, ), the Sea of Japan (Asai and Miura, ; Tusboki et al , ; Nakai et al , ) and several other North American bodies of water, such as the Chesapeake and Delaware Bays (Sikora and Halverson, ), Lake Champlain (Laird et al , ), the Finger Lakes (Laird et al , ), Lake Tahoe and Pyramid Lake (Laird et al ., ), and the Great Salt Lake (Alcott et al , ).…”

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

“…Results for individual over‐water profiles with Δ T sea‐850 ≥ 13 °C were compared to results for overpasses with sea‐850 ≥ 13 °C, and no major qualitative differences were found (not shown). In addition, although some non‐sea‐effect clouds may produce precipitation when sea‐850 ≥ 13 °C, studies indicate that most of the precipitation falling on the west coast of Japan during DJF is produced by clouds generated over the SOJ (e.g., Nakai et al, ).…”

“…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).…”