• 作者： 蔣志才
• 作者服務機構： 中央氣象局
• 中文摘要： Clear Air Turbulence (CAT) For-ecast Section of USAF is located atKansas City, Missouri, which is respo-nsible for forecasting the CAT andMountain Wave Over the ContinentalUnited States. The CAT occurred atthe height over 16000 ft. is not associa-ted with visible convective activity.On the other hand, when turbulencebelow 16000 ft. is called mountain wave,but the working procedures of CATand mountain wave are quite different. Mountain wave often occurredwhere wind speed across known terrainbarriers equal or exceed 25 knots andsurface pressure differences across bar-riers are noted. The CAT often occur-red by horizontal or/and vertical windshear in space which wind speeds are60 knots or greater. The followingcreteria are considered to exhibit CATin the indicated intensities: Horizontal Vertical CAT Shear Shear Intensity 25 kts/1.5° 3-9 Light (Lat. degree) kts/1000' 25 kts/1.5° 9-12 Moderate (Lat. degree) kts,11000' 25 kts/1.5° 12-15 Moderate (Lat. degree) kts/1000' Occasionally Severe 25 kts/1.5° above 15 Severe (Lat. degree) kts/1000' Besides daily surface and constantpressure level charts, the working pr-ocedure to forecast CAT have to addsome other charts, namely: wind-aloftprofile analysis, wind shear index,500-300 mb temperature difference and200 mb temperature difference chartsfor 24 hrs., 500mb and tropopause chart,maximum wind chart an Max. windprognostic chart. The maximum windlevel and possible location of the jetstream are decided by making wind-aloft profile analysis, the propose ofdrawing 500-300 mb temperature dif-ference and 200 mb temperature dif-ference charts for 24 hrs. are searchingfor the aerial stability. In addition, thestructure of the tropopause and dis-tribution of the maximum wind canbe find out from the rest auxiliarycharts, then the movement or develop-ment of the jet stream will be readeasily. Theoretically, the prognosticchart can be sketch out. Using available data and actualcharts in hand, analysis of the flightaccident of CAL dated Dec. 4, 1975over Kagoshima was made by followingmentioned process. The retults in thisstudy shown an acceptable agreementwith the existence of CAT over Kago-shima.
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