RESEARC H ARTICLE C haracteristics of Sea ‐Effect Clo uds a nd Precipitatio n 10.1029/2018J D029586 Over t he Sea of Japa n Regio n as Observed Key Poi nts: by A‐Trai n Satellites • The majority of winter clouds and precipitatio n over t he Sea of Japa n Tyler K. West 1 , W. Ja mes Steenburgh1 , and Gerald G. Mace1 regio n occur duri ng sea‐effect p eri o ds 1 Depart ment of At mospheric Sciences, University of Utah, Salt Lake City, U T, US A • T he distributio n of sea effect varies in the region and is modulated by la nd‐sea i nteractio ns, coastli ne geo metry, and orographic effects A b st r a ct Prolific winter ( Dece mber‐January‐February) sno wfall occurs over north west Japan due to • Sea-effect precipitation is shallo wer freq ue nt sea‐effect precipitatio n t hat develops d uri ng cold‐air o utbreaks over t he Sea of Japa n (S OJ). and more co m mon (deeper and less K no wledge of sea ‐effect clouds a nd precipitatio n across t he S OJ regio n has historically bee n co nstrai ned, co m mon) in the northern (southern a nd ce ntral) Sea of Japa n regio n ho wever, by li mited offs hore i n situ observatio ns a nd re mote ‐se nsi ng li mitatio ns. T his paper uses se nsors fro m National Aeronautics and Space Ad ministration ( N AS A)'s A‐Train Satellite Constellation to exa mine wi nter sea ‐effect properties i n t he S OJ regio n. T he a nalysis s ho ws t hat cloud a nd precipitatio n occurre nce Correspondence to: ge nerally i ncreases across t he S OJ fro m Asia to Japa n, as pote ntial sea‐effect periods wit h a n alo ng‐orbit T. K. West, mean sea surface to 850 ‐hPa te mperature difference ≥ 13 ° C co mprise a majority of the total clouds and tyler.k. west @utah.edu precipitatio n. Sea‐effect clouds a nd precipitatio n occur most freque ntly i n a n arc‐s haped area t hat exte nds fro m the western S OJ, where the Japan‐Sea Polar‐Air mass Convergence Zone (JP CZ) is co m mon, to the Cit ati o n: coast of Honshu, and then north ward to Hokkaido. Radar, lidar, and colu mn water path statistics along West, T. K., Stee nb urg h, W. J., & Mace, A ‐Trai n orbital tracks s ho w t hat sea ‐effect precipitatio n is deepest alo ng t he ce ntral Ho ns hu coast a nd G. G. (2019). C haracteristics of sea‐effect clo uds a nd precipitatio n over beco mes shallo wer but more frequent with north ward extent. Precipitation a mount and frequency maxi mize the Sea of Japan region as observed by along the coast and adjacent mountains but decline with inland extent, most abruptly do wnstrea m of higher A ‐Trai n satellites. Jour nal of mou ntai n barriers. T his work illustrates t hat air ‐sea i nteractio ns, coastal geo metry, a nd regio nal topograp hy Geophysical Research: At mospheres , 124, 1322–1335. https://doi.org/ stro ngly modulate cloud a nd precipitatio n patter ns duri ng sea‐effect periods i n t he S OJ regio n. 10.1029/2018J D029586 Received 30 A U G 2018 1. I ntrod uctio n Accepted 10 J A N 2019 Accepted article online 15 J A N 2019 Copious a mou nts of s no w fall eac h cool seaso n over la nd areas do w nstrea m of t he Sea of Japa n (S OJ), creat- Published online 7 F E B 2019 ing so me of the largest seasonal sno wfalls and deepest seasonal sno wpacks in the world ( Takahashi et al., 2013; Ya maguchi et al., 2011). Heavy sno wstor ms frequently i mpact the north west Japanese coast and adja- ce nt topograp hy, disrupti ng tra nsportatio n, co ntributi ng to structural da mage a nd periods of elevated ava- lanche risk, and building a sno wpack critical for regional water resources and winter touris m ( Chechin & Pic h ugi n, 2015; Eito et al., 2005; Nakai et al., 2012; Stee nb urg h, 2014). M uc h of t his s no wfall res ults fro m sea‐effect precipitatio n (e.g., Ca mpbell et al., 2018; Eito et al., 2010; Mago no et al., 1966; Miz ukos hi, 1977; Muraka mi et al., 1994; Nakai et al., 2005; Tsuc hiya & Fujita, 1967), a p he no me no n closely related to lake ‐, sea‐, and ocean‐effect precipitation in other regions of the world (e.g., Andersson & Nilsson, 1990; Ki ndap, 2010; Kristovic h et al., 2017; Laird et al., 2009; Niziol et al., 1995; Norris et al., 2013; Stee nb urg h et al., 2000; Veals & Steenburgh, 2015). Sea effect over the S OJ occurs predo minantly during the East Asian winter monsoon, which results fro m the interaction of the se miper manent Siberian High over north- ern Asia and the Aleutian Lo w in the Gulf of Alaska and features mean north westerly fl o w over the S OJ dur- ing winter ( Boyle & Chen, 1987; Dor man et al., 2004). Conco mitant cold‐air outbreaks ( Mitnik, 1992) gain heat a nd moisture over t he relatively war m waters of t he S OJ a nd Tsus hi ma curre nt, destabilizi ng t he at mo- sphere and generating clouds and precipitation (e.g., Hozu mi & Magono, 1984; Tsuchiya & Fujita, 1967). Sea‐effect precipitation syste ms then reach the north west Japanese coast, where they are modified by coastal, inland, and orographic effects (e.g., Ca mpbell et al., 2018; Estoque & Nino miya, 1976; Ka wa moto et al., 1963; K us u noki et al., 2005; Nakai & E ndo h, 1995; Saito et al., 1996; Yos hi hara et al., 2004). Previo us st udies have foc used o n sea effect i n portio ns of t he S OJ regio n b ut have bee n li mited i n geograp hic exte nt. Specifi c efforts to describe t he precipitatio n distrib utio n near Japa n ill ustrate a n i ncrease i n precipi- tation fro m the S OJ to the Japanese coast and mountains. Exa mples include Estoque and Nino miya (1976), who present fi gures sho wing mean daily liquid precipitation equivalent during winter 1965 increasing fro m ©2019. A merican Geophysical Union. All Rig hts Reserved. ~1–2 m m/day over the coastal S OJ to 4–7 m m/day over north west Japan. Using regional modeling, WEST ET AL. 1 3 2 2 Journal of Geophysical Research: At mospheres 10.1029/2018J D029586 Fig ure 1. Topograp hy of East Asia a nd Japa n. Terrai n elevatio n ( m mea n sea level) color fi lled as i n scale. T he red colorfi ll represents major urban areas. Adapted fro m maps‐for‐free.co m. Takahashi et al. (2013) found an increase in si mulated liquid precipitation equivalent fro m ~50 –100 m m/ month over the near ‐coast S OJ to ~300–400 m m/ month over the adjacent Japanese mountains. I mportant variations in the distribution of precipitation occur, ho wever, fro m case to case. For exa mple, Magono et al. (1966) distinguish bet ween Satoyuki stor ms, which produce heavier lo wland sno wfalls, and Ya mayuki stor ms, which produce heavier mountain sno wfall, while Nakai et al. (2005) identify a wide range of s no wfall modes t hat i nfl ue nce t he distributio n a nd i nte nsity of s no wfall. Research over the S OJ has identi fied three areas of frequent flo w convergence and enhanced cloudiness and precipitation, although their cli matological contributions to clouds and precipitation have not been quantified. The first is the Japan‐Sea Polar‐Air mass Convergence Zone (JP CZ), which for ms due to flo w interactions with the Korean Highlands just north of the Korean Peninsula (see Figure 1 for geographic locations), the ther mal contrast bet ween the Korean Peninsula and S OJ, and the sea surface te mperature distribution of the S OJ ( Nagata, 1987, 1991; Nagata et al., 1986). The JP C Z nor mally originates near the base of the Korean Peninsula and extends to ward the Japanese coast, but its ter mination location can vary bet ween ~133° E and ~139° E ( Eito et al., 2010). The second area of convergence occurs in the north- ern S OJ to the lee of elevated near‐coast topography in the Sikhote‐Alin Mountains of eastern Russia, with the attendant cloud band usually extending east ward to Hokkaido ( Mura matsu, 1979; Ohtake et al., 2009.) Follo wi ng O htake et al. (2009), we refer to t his as t he Mt. X regio n. T he t hird area of co n- vergence occurs in the northern S OJ when north westerly flo w fro m Asia converges with northeasterly flo w fro m the Sea of Okhotsk just west of Hokkaido and Sakhalin Island ( Katsu mata et al., 1998). Although oriented quasi ‐meridionally, the southern end of this convergence zone and its associated cloud band can curve east ward and intersect Hokkaido.