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第 0 回 大気海洋圏物理系セミナー のおしらせ

日 時:1999年 1月 28日(木) 午前 9:30 〜 12:00
場 所:低温科学研究所 2F 大講義室

発表者:Joshua Wurman (オクラホマ大学助教授)
題 目:

発表者:Seelye Martin (School of Oceanography, University of Washington)
題 目:

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(Joshua Wurman) 発表要旨:

  
 The Doppler On Wheels (DOW) mobile radars were used in the Radar  
 Observations of Tornadoes And Thunderstorms Experiment (ROTATE) in 1998.   
 Three tornadoes were observed.  One was observed by both DOWs, permitting  
 dual-Doppler retrievals.  One was observed intermittently for over 30 minutes  
 as it intensified into a violent tornado.  The tornado was observed as it  
 destroyed the town of Spencer, South Dakota, killing 6 and injuring 50% of  
 the population.  Winds of 115 m/s were observed, representing the highest  
 ever recorded near the ground.  Sub tornado structures, possibly indicating  
 multiple-vortex structure were observed.  A third tornado was observed from  
 extremely close range as the center of rotation passed within 170 m of a DOW,  
 with the outer flow region passing through the radar.  At the center of the  
 tornado the radar beamwidth was only 3 m (though radar gates were 38 m),  
 constant elevation observations were repeated every 12-14 s. 
  
 The DOW radars intercepted hurricanes Bonnie (North Carolina) and Georges 
  (Mississippi) as the eyes passed onshore.  Dual-Doppler data were  
 retrieved in George with a baseline of 14 km.  Small scale structures and  
 wind streaks that had been recently discovered in hurricane Fran (1996,  
 North Carolina) were observed. 
  

(Seelye Martin) 発表要旨:

     Using remote sensing and oceanographic data, we describe the  
 properties of the northern Okhotsk polynyas, which occur on the northwest  
 shelf between Ayun and Okhotsk City, on the northern shelf between  
 Okhotsk City and Magadan, and in Shelikhov Bay. In the satellite  
 analysis, we use a passive microwave algorithm to derive for each polynya  
 the area of thin ice and open water, and a heat flux algorithm to derive  
 the ice and brine production. From our analysis, the NWS polynya is the  
 dominant ice and brine producer, contributing on average about 55% of the  
 total production. Shelikhov Bay is the second largest producer with about  
 25% of the total, and the northern shelf produces the final 20%. For our  
 observational period, we found that the total polynya productivity varied  
 by a factor of two, and that of the dominant NWS polynya varied by a  
 factor of three. The source of the NWS variability is due to the  
 winter-averaged angle at which the surface pressure isobars intersect the  
 NWS coast. When the isobars are parallel to the coast, there is little  
 offshore transport. When the isobars are at an angle such that there is  
 an offshore flow, the polynya size and ice production are much larger, so  
 that a small change in angle yields a large change in ice and brine  
 production. For the 1996 and 1997 winters, we also compare satellite  
 estimates of polynya ice and brine production with Russian CTD surveys  
 provided by Gladyshev. For Shelikhov Bay, the surveys show that this  
 region produces large amounts of dense water, which flows into the Tinro  
 Basin. For the northern and northwest shelves, the observations show that  
 much of the generated dense water circulates on the shelf around to the  
 east to enter the East Sakhalin Current. Our satellite estimates show  
 that the total polynya ice production for 1996 and 1997 was respectively  
 230 and 120 cubic kilometers, with the NWS contributing 60 - 70% of the  
 total. For the same years, ship survey estimates of ice production yield  
 comparable values of 210 and 130 cubic kilometers in 1996 and 1997. This  
 agreement suggests that the satellite observations provide reasonable  
 estimates of the ice and brine production, and can be used to monitor the  
 polynya response to changes in regional climate. 
  

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連絡先

水田 元太 @北海道大学大学院地球環境科学研究科
大気海洋圏環境科学専攻大循環力学講座
mail-to:mizuta@ees.hokudai.ac.jp / Tel: 011-706-2357