Naohiko Hirasawa

1. Reasearch and activities

     A part of water vapor in the atmosphere becomes rain or snow through condensation or sublimation and moves to the ground surface (ocean or land) as precipitation. Water moves from the ground surface to the atmosphere again by evaporation. Such a moisture circulation is performed in the surface layer of the earth including the atmosphere. The characteristics of the moisture circulation in the polar regions are summarized as follows due to the low temperature.

1) Small amount of moisture circulation: The amount of water vapor that can exist in the atmosphere (= that which can pass through the atmosphere) is small, and the amount of precipitation and evaporation is also small. And

2) Accumulation of moisture: The phase change tends to a solid and stays there for a long time, creating a huge ice body like the Antarctic ice sheet.

     There are interesting phenomena in the polar meteorological processes related to the moisture circulation, which are different from those in the middle latitudes and low latitudes. A temperature inversion layer (the atmospheric layer in which the temperature rises with the altitude) has developed in the lower layer up to about 1000 m from the ground. Small ice crystals that sublimate in that layer become precipitation (Clear Sky Precipitation = Diamond Dust). It continues almost continuously in winter. It has long been thought that this Clear Sky Precipitation contributed significantly to supply of moisture to the Antarctic ice sheet, but in recent years, its recognition has changed significantly. It became clear that a large amount of water vapor was brought in from the lower latitude side at once (in about one day) in association with the synoptic-scale disturbances such as the occasional blocking phenomenon, and it occurred about 10 times a year. It has become clear from the observations of several inland areas that such events contribute about half of the total precipitation. Numerical model evaluation has come to be carried out.

     I would like to clarify such changes in the polar moisture circulation and related atmospheric circulation in a wide space-time range from regional scale to global scale, events to yearly or daily changes. In promoting research, field observation and satellite data receiving at Syowa Station will be conducted based on participation in the Japanese Antarctic Research Expedition (JARE) and also in research in the Arctic region, and internationally shared satellite data archives and global atmospheric re-analysis data will be used. Numerical model experiments are carried out to advance theoretical consideration of observation data.

     Furthermore, for the purpose of expanding the research community, I have made some collaboration such as organizing Research Group of Polar and the Cold Regions established in the Meteorological Society of Japan, symposiums, editing and reviewing journals and websites, and exhibiting something in the Polar Science Museum.

2. Field experiences

[Antarctic]

・JARE-38 Wintering team, At Dome Fuji Station,  Nov. 1996 - Mar. 1998

・JARE-48 Summer team for Japan-Germany airplane observation of aerosols, At S17 on the ice sheet near Syowa Station, Dec. 2006 - Mar. 2007

・JARE-56 Summer team for UAV observation of aerosols, On board of Shirase & Syowa Station & S17, Dec. 2014 - Mar. 2015

・JARE-58 Summer team for UAV observation of aerosols, On board of Shirase & S17, Dec. 2016 - Mar. 2017

・JARE-59 Wintering team, On board of Shirase & Syowa Station & S17 & Relay Point, inland of Antarctic ice sheet, Dec. 2017 - Mar. 2019

[Arctic]

・NyAlesund, Norway, 1995/96 winter, 1998/99 winter, 1999/2000 winter

・Rikubetsu, Hokkaido, North Japan, Snowfall experiment, 2012 - present (a observation site of WMO SPICE project, 2012 - 2016)

・Yakutsk, Rossia, Snowfall experiment, 2012 - present

・PFRR, Alaska, US, Snowfall experiment, 2015 - present