Linkages of the weather system between over the Pacific and Arctic regions -Importance of the atmospheric river-

For the purpose of improvement of 1-14 day high impact weather forecast, Winter T-PARC (Wintertime THORPEX Pacific-Asia Regional Campaign) was carried out by the lead organization of NOAA from 12 January to the end of February 2009 and continued until the end of March as WSR09 (Winter Storm Reconnaissance in 2009) campaign. As the rapidly deepening low pressure systems in the Northwestern Pacific region strongly affect downstream regions, such as Alaska, Arctic and the North-America, they have a great contribution to the improvement of the forecasting in these region. Therefore, they were one of the main targets of the Winter T-PARC. Stagnating lows in Gulf of Alaska also affect downstream region, they were also a target for WSR09. Winter T-PARC was assigned as a part of International Polar Year (IPY) program in the US. National Institute of Polar Research (NIPR) in Japan supports the Winter T-PARC as a part of Japanese IPY activities.

In this paper, we would like to discuss storm behaviors over the North Pacific Ocean and their linkages to the Arctic weather system. For the rapidly deepening of the low pressure system needs the upper-level forcing and lower-level moisture supply to the low pressure center. All of low pressures entered into the Arctic in the Northwestern Pacific Region associated with “Atmospheric River” of precipitable water. The river became clearly to identify after the explosively deepening (the central SLP became minimum). As the explosively deepening is associated with strong updrafts, Rossby wave breaking is occurred in the upper-level. It enhanced descending air (jets) and also enhanced clockwise circulation in the lower atmosphere. This anti-cyclonic circulation makes clear the river. Stagnating lows in the Gulf of Alaska were also related to “Atmospheric River.” The descending air in the Arctic and/or high latitudes also likely contributes to make an “Atmospheric River.” The “Atmospheric River” has a relationship to the heavy precipitation and flooding in the West coast the North American Continent and moisture supply to the Arctic region.