Through a program of daily visual observations, measurements are made of meteorological and oceanographic parameters. Visual observations are usually collected before 1100 EST. Since these data supplement the instrument data, they are known as Supplementary Observations or SUPOBS.
Oceanographic ObservationsSurface current speed and direction at the FRF are influenced by winds, waves, and, indirectly, by bottom topography. The extent of the respective influences varies daily. However, winds tend to dominate the currents at the seaward end of the pier, whereas waves dominate within the surf zone. Three observations of the surface current are made by timing the movement of small wooden orange floats. Current observations are made at the end of the pier, from the pier at a point midway across the surf zone, and 10 to 15 m from the beach 500 m updrift of the pier. The surf zone width (seaward most breaker position to the shoreline) is determined from the pier deck. Since the pier is 500 m long, surf zones within the length of the pier are accurately estimated, wider surf zones are less so. Photographs of the beach and surf zone are taken each morning, to the north and south from the pier. Visual estimates of the direction of both the primary and secondary wave trains (which must be clearly distinguishable) are observed at the seaward end of the pier. The pier axis (considered perpendicular to the beach at the FRF) is oriented 70 deg east of true north; consequently, wave angles greater than 70 deg indicate that the waves are coming from the south side of the pier. |
Water temperature, density, and salinity
A Bucket Thermometer (shown left) is lowered about 0.3 m (1 ft) into the water and allowed to remain for at least one minute. The temperature is then read, and a hydrometer is used to determine the density. A refractometer is also used to observe water density. Salinity is then computed based on density and water temperature. |
Water visibility
Visibility in coastal near shore waters depends on the amount of salts, soluble organic material, detritus, living organisms, and inorganic particles in the water. These dissolved and suspended materials change the absorption and attenuation characteristics of the water that vary daily and yearly. Visibility is measured with a 0.3-m-diam Secchi disk (shown left) which is lowered at the end of the pier. The depth at which the disk can no longer be seen is recorded. Similar to water temperature, variation invisibility is related to onshore and offshore winds. Onshore winds move warm clear surface water toward shore, whereas offshore winds bring up colder bottom water with large concentrations of suspended matter. Large variations are common, and visibility less than 1 m is expected in any month. |
Atmospheric Pressure: A Weathertronics, Incorporated (Sacramento, CA), recording aneroid sensor (microbarograph) located in the laboratory building also is used to continuously records atmospheric pressure variation. The microbarograph is compared daily with the NWS aneroid barometer, and adjustments are made as necessary. Maintenance of the microbarograph consists of inking the pen, changing the chart paper, and winding the clock every 7 days.
Precipitation: Rain is generally well distributed throughout the year. Precipitation from mid-latitude cyclones (northeasters) predominates in the winter, whereas local convection (thunderstorms) accounts for most of the summer rainfall. An Edward's Manufacturing Company (Alberta Lea, MN) True Check 15-cm-capacity clear plastic rain gage with a 0.025-cm resolution is used to monitor the performance of the electronic weighing rain gage. This gage is located near the weighing gage, and the gages are compared on a daily basis.
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