A low Level Jet Observed by a Doppler Sodar during the International Sodar Intercomparison Experiment (ISIE)

Abstract

The present authors have developed a phased array Doppler sodar and participated with it in the International Sodar Intercomparison Experiment (ISIE) at Boulder Atmospheric Observatory (BAO) in 1988. During the period of ISIE, a significant low-level jet (LLJ) was observed in the morning of September 18, 1988. The turbulent structure of an LLJ was analyzed using sodar observations as well as tower observations, and is summarized as follows; (1) Low frequency fluctuations (<0.002 Hz) increase in the time period of LLJ appearance. (2) The turbulent momentum flux in this frequency range shows divergence from the jet core in the developing stage and convergence toward the jet core in the decelerating stage. (3) This shows that turbulence acts as the resisting force to the development of an LLJ.