ソーダによる境界層内の Low Level Jet の観測

Abstract

A phased array 5 beam doppler sodar (AR-400) had been developed by Severe StormDivision of Disaster Prevension Research Institute. We participated with this instrument inISIE (International Sodar Intercoinparison Experiments) held at BAO (Boulder AtmosphericObservatory) in September 1988. Measurement of wind speed and wind direction by thesodar are compared with similar measurements by in situ sensors on a 300 m instrumentedtower. The results indicate the sodar measured wind speeds and wind direction are enoughaccurate.Low Level Jet (LLJ) was observed in early morning of 18 September during ISIE. Theheight of maximum wind speed (hu) is almost the same as the height of temperature profileinflection point. During LLJ event, the fluctuations of wind speed became larger than beforeonset of LLJ, and the wind fluctuations of the period of longer than 500 sec are larger at lowerlevel, and the height of maximum fluctuations of W is at a little below hu and this height isalmost the same as the height of maxium sodar signal intensity. And the momentum fluxdiverges before sunrise and converges after sunrise at the height of maximum wind speed, hu