observations of Mesocale Wave Disturbances during the Genesis of Atlantic Lows Experiment

Abstract

The Portable Automated Mesonet (PAM) data obtained during the Genesis of Atlantic Lows Fxperiment (GALE) are used to document mesoscale wave activity during the 3-day period from 4 to 6 February 1986. From the surface pressure analyses, four cases of wave activity are identified with wavelengths of 200?400 km, phase speeds of 20?40 m s?1 and trough-to-crest pressure amplitudes of 0.5?3.5 mb. Precipitation was associated with the waves in two of the four cases. Detailed analyses of the horizontal structure show that the waves do not have the pressure-wind relationship expected from linear gravity wave theory. The wind vectors are oriented from high to low pressure with a maximum amplitude between the high and low pressure areas. Low-level inversions were present in three of the four cases. In the raw without a low-level inversion, the amplitude rapidly decreased as the wave moved towards the east. In the case which lasted for the longest time period (at least 8 h). and had the largest pressure amplitude, the sounding bad a critical level (where the wind speed equated the wave speed) and a level where the Richardson number was less than 0.25. Vertical velocities as large as 30 cm s?1 were observed and them was some evidence that the wave was vertically tiled towards its direction of motion. Complex principal component analysis (CPCA) is applied to the surface pressure data to determine the applicability of this technique to the study of mesoscale waves. It is shown that CPCA could be used to generalize the results of this study to the entire 60-day period of GALE.