Small-scale Gravity Waves in the Lower Stratosphere Revealed by the MU Radar Multi-beam Observation

[摘要] A multi-beam measurement of winds in the troposphere and lower stratosphere was performed in January 1986 by the MU radar. Twelve beams were used to scan the wind field zonally through the zenith angle from -30° to 30°. Analysing the observation data with high horizontal resolution, we have investigated the small horizontal structure of the wind for the first time.An analysis was made of remarkably strong oscillations of the vertical wind component with a large vertical scale which appeared in the lower stratosphere. Assuming the local wind homogeneity over any neighboring two beam positions in the zonal scan, we make a horizontal time section, which shows that the oscillations are zonally monochromatic. The line-of-sight velocities are fitted to a wavelike structure at each height by the least-squares method, and it is found that the zonal wavelength is 5-30km. According to the phase difference between the zonal and vertical components, it is likely that the oscillations are due to internal gravity waves. The zonal phase veolcity is very small (1-5m/s) compared with the background wind (≈50m/s), indicating that the waves are almost at rest relative to the ground, like a topographic wave. Another interesting feature is that the zonal wavelength changes with height, suggesting that the oscillations are not simply due to a monochromatic gravity wave, but have a complicated three-dimensional structure.

[学科分类] 大气科学