The Precipitation Process in Convective Cells Embedded in Deep Snow Bands over the Sea of Japan

Abstract

Convective cells in two deep snow bands were examined over the Sea of Japan with an instrumented aircraft and dual-Doppler radars. A combination of the relatively warm air stream (westerly) at lower levels secluded near the center of the low and the polar air stream (west-southwesterly) at middle and upper levels produced a deep unstable stratification to the southwestern quadrant of a well-developed low, where snow bands A1 and B1 were respectively observed at around 1600 and 1700 JST on 28 Jan. 1993.Radar data showed that both snow bands were in quasi-steady state within a dual Doppler radar observation area. However, the two snow bands showed quite different development; the maximum reflectivities in bands A1 and B1 were 15 dBZ and 30 dBZ, respectively.Aircraft data showed that the accretional growth of snow particles was the primary precipitation formation mechanism in the convective cells embedded in both snow bands.From aircraft and radar data, it appears that vertical wind shear within the cloud layer influenced the precipitation process. In the cell embedded in snow band A1, the updraft at middle and upper levels tilted downshear due to a strong wind shear and precipitation embryos initiated in the updraft were advected downshear from the main supercooled cloud water region. Therefore, these embryos did not grow to large graupel particles. By comparison, in the cell embedded in snow band B1, the updraft tilted upshear at lower levels and stood almost erect at middle and upper levels due to weak wind shear. Therefore, precipitation embryos initiated in the updraft grew into 5 mm graupel particles as they descended through the main supercooled cloud water region. In addition, re-circulation of graupel particles, which had descended in a vicinity of the updraft core, seemed to play an important role to efficiently produce larger graupel particles.

Comparison of Snow Water Equivalent Estimated in Central Japan by High-Resolution Simulations Using Different Land-Surface Models

“…References for the main physical processes in our simulation are provided in Table 2. We did not use cumulus parameterization options because the horizontal grid interval we used was fine enough to resolve the well-developed snow band above the Sea of Japan in winter (Murakami et al 2003).…”

“…Therefore, cumulus formed above the Sea of Japan would be modeled as flowing too far inland, reaching the area where many of the observation sites are above 1000 m elevation. Second, the 3.3 km grid was not fine enough to resolve micro-scale convective clouds and narrow snow band (Murakami et al 2003); thus, water that should be precipitated from small cumulus over the lowlands on the Sea of Japan side of the study area would be modeled as falling in the mountainous area. Third, under-recording of precipitation by rain gauges is much higher for snow than for rain, and increases with increasing wind speed even when there is a wind shield installed (Larson and Peck 1974).…”

Kinematic and Thermodynamical Structures of Longitudinal-Mode Snow Bands over the Sea of Japan during Cold-Air Outbreaks Part I: Snow Bands in Large Vertical Shear Environment in the Band-Transverse Direction

“…They are, for example, associated with cold-air outbreaks, cold fronts, a largescale convergence zone between two polar air masses (Okabayashi 1969), the Japan Sea Polar-air mass Convergent Zone (Asai 1988), shallow and deep convective snow bands behind synoptic lows Murakami et al 2003), and wind-speed increase zones . Among these, snow clouds forming during cold-air outbreaks are very common, and they organize into various forms at mesoscale.…”

Microphysical Structures of Early-Winter Snow Clouds during a Cold Air Outbreak of December 23-25, 2010

“…Many observations within snow clouds via balloon-borne sondes have been conducted (e.g., Magono and Lee 1973;Matsuo et al 1994;Murakami et al 1994Murakami et al , 2003Kusunoki et al 2004Kusunoki et al , 2005.…”