Light scattering in the atmospheric near-water layer above areas of long-living hydrodynamic disturbances of the marine environment

Abstract

The influence of the marine environment hydrody namic disturbances on near water aerosol optic char acteristics was studied in the course of field experi mental investigations. The research vessel was the source of hydrodynamic disturbances of the marine environment. In the course of the experiment, we recorded aerosol light scattering when the trace falling behind the vessel was crossed 40 min after it was formed. The aerosol light scattering level decreased in the vessel trace turbulence zone relative to background values.Hydrodynamic processes proceeding in the marine environment layer are inaccessible to direct observa tion with the help of remote sounding devices operat ing in the optical and radio ranges. Because of this, such processes can be recorded only indirectly by the effects they cause in the near surface areas. The effect of the marine environment hydrodynamic distur bances spreads over the atmospheric near surface layer and results in variations of the aerosol concentra tions [1]. Measurement of aerosol concentrations at different heights with lidar in the shelf zone indicated their dependence on surface agitation, the wind rate, and bottom relief [2, 3]. The idea [2, 3] about applica tion of laser methods to study the aerosol formation process under the effect of different hydrodynamic disturbance sources in the marine environment was executed in the course of a field experiment [4] accompanied by increase in the flow of laser radiation scattered from near water aerosol in the coastal zone relative to the submerged jet. This paper contains the data obtained in the course of further investigations of the influence of hydrody namic disturbances of the marine environment on the near water aerosol optic characteristics carried out by the research vessel in the open sea. The equipment used to conduct the complex experiments was arranged on the upper deck of the vessel. The vessel itself was used as a source of hydrodynamic distur bance of the marine environment. Its turbulent wake was crossed two times in the course of experimental measurements. To decrease the influence of possible aerosol emissions produced by the research vessel, the aerosol light scattering recording zone was moved 10 m forward in the direction of the vessel movement.A paraxial optical scheme including laser illumina tion and receiving electrooptical channels was used in the developed aerosol locator. The laser illumination channel contained a laser with an operation wave length of 0.532 µm and power of 100 mW in the con stant radiation regime. Its radiation was interrupted by a mechanic modulator performing periodic modula tion with a frequency of 1.5 kHz. The receiving chan nel represented an electrooptical system including a camera lens and photodetectors based on a photomul tiplier. Synchronous signal accumulation was applied to increase the device sensitivity.The figure demonstrates the dependence of the aerosol concentration on time. Time counting starts about five minutes before crossing the turbulent wake of the vessel. It...