SODAR OBSERVATIONS OF THE ATMOSPHERIC BOUNDARY-LAYER OVER THE OCEAN DURING ASTEX-91

A complex marine experiment was conducted in autumn 1991 on the resear ch vessel Dmitry Mendelev in association with the Atlantic Stratocumul us Transition Experiment (ASTEX). A three-axis Doppler sodar designed at the Institute of Atmospheric Physics, Moscow, was used in this expe riment. Total observation time was about 770 hours from 6 October to 2 3 November. Besides facsimile records illustrating spatial and tempora l structure of the turbulence distribution in the atmospheric boundary layer (ABL), routine quantitative measurements of profiles of wind an d echo-signal strength were taken. Some main characteristics of the AB L behavior over the ocean were revealed through an analysis of these d ata as well as the results of other kinds of measurements. An importan t peculiarity of the ABL observed between the Canary Islands and the A zores was the presence of diurnal variation of convective turbulence s trength having a maximum between 04:00 and 07:00 LT. A similar diurnal variation was observed for low-level cloud cover. Occurrence of vario us types of thermal stratification and their diurnal variation were ob tained. Comparison of elevated stable layers and low-level cumulus sho wed that the lower boundary of clouds correlates well with the height of the bottom of elevated inversion layers (at heights of 200-600 m). Canary and Cabo Verde observations showed that islands strongly affect the ABL structure. The strong effect of a surface water temperature g radient on the ABL stability was observed when crossing the Canary, Az ores, and Labrador currents and the Gulf Stream.