Mixing in Haro Strait
Abstract : The long-term goal is to better understand mixing processes in estuaries. Of particular interest are the processes at work in the Haro Strait region between Washington State and British Columbia, which are modulated by a spring/neap cycle in tidal velocities. The field phase of the Haro Strait experiment took place in the summer of 1996 and involved a collaborative effort between MIT, WHOI and IOS. Our objectives are to understand the dynamics associated with intense coastal mixing processes in which separation of tidal flows past topography leads to formation of fronts accompanied by instability and mixing. During this year, we have begun to analyze this data in two different areas. First, we wanted to better quantify the large-scale dynamics. This means estimating horizontal layer transports, rates and amounts of mixing that take place. Second, we want to use these results to understand the importance of smaller-scale mixing that occurs at convergence fronts within this region.
Real-time frontal mapping with AUVs in a coastal environment
A new oceanographic measurement concept is presented, combining a tomographic network with small autonomous underwater vehicles. Using wireless local area network technology, the acoustic tomography data are recorded and processed in real time for achieving a low-resolution estimate oceanographic parameters. The results are used to focus direct measurements by a network of small AUVs in areas of high spatial and temporal variability. By combining the high coverage but low resolution of the tomography with the high resolution capabilities of the AUVs, oceanographic phenomena with small scale dynamics controlled by large scale environmental forcing can be mapped. The feasibility of the new measurement concept has been demonstrated in connection with a June 96 experiment in Haro Strait, BC, aimed at mapping the properties coastal fronts driven by combined estuarine and tidal forcing.
UV-B radiometry and dosimetry for solar measurements.
Biologically effective irradiance or dose of solar UV radiation was determined using a spectroradiometer, two broadband radiometers and two types of passive UV-dosimeters. The absolute erythema irradiance and the actinic irradiance were calculated from the solar spectrum measured with the spectroradiometer. It was demonstrated that the erythema irradiance is proportional to the actinic irradiance of solar radiation. The erythema irradiance was also determined using the two broadband radiometers which utilize a filter transmitting erythema spectra. Personal UV-dosimeters such as polysulphone and CR-39 were used to determine the erythema dose for a selected period of time. These results were used to estimate the accuracy of the broadband radiometers and UV-dosimeters. It was found that the results obtained from the broadband radiometers deviate from the absolute erythema irradiance by less than 20% during clear days between the hours of 11:00 and 13:00 Eastern Standard Time (EST) in Australia. The assessment of the erythema dose using passive dosimeters such as polysulphone and CR-39 could introduce an error as high as 40% if the calibration was not performed before undertaking experimental measurements.