Sampling Marine Atmosphere Surface Layer in Undisturbed Environment

Unlike the atmospheric surface layer over land, the marine atmospheric surface layer lies over a constantly evolving ocean surface with surface currents and waves. It is then questionable whether the surface layer profiles of the mean wind, temperature, and water vapor content follows the empirical flux-profile relationship derived from measurements over land. Furthermore, the effects of surface waves on the near surface profiles are unclear although some limited measurements indicated a modification of the mean wind profiles in case of low wind and high swell conditions. However, measurements of the near surface profiles or fluxes are difficult to obtain as the lower atmosphere are inevitably affected by the platforms such as research vessels and/or large buoys. In an effort to sample the marine surface layer in minimally disturbed environment, utilized an instrumented small vessel such as a Rigid Hull Inflatable Boat (RHIB). The RHIB is 20 feet long and 8 feet beam width and thus introduce minimum flow distortion in the immediate environment. In addition of a small mast instrumented for mean wind, pressure, temperature, and relative humidity measurements at a single level, the RHIB is also equipped with a small tethered balloon with an Imet rawinsonde modified to record data on a microchip data disk. Profiling with the tethered balloon provided multiple vertical profiles of temperature and humidity of the marine surface layer between 0.5 m to about 50 m level. This sampling technique revealed the significant temperature and humidity gradients near the surface, which is not seen from the conventional profiling measurements based on medium or large vessels. Comparison of these measured profiles with those diagnosed from a surface layer model will be discussed.