------------------------------------------------------------------------ Data Processing Notes Frontal Air-Sea Interaction Experiment 24 May 2000, AJP ------------------------------------------------------------------------ General ------------------------------------------------------------------------ The five surface moorings within the FASINEX central array were designated F2, F4, F6, F8 and F10. All surface moorings used 3 m discus buoys for flotation. The moored array spacing and orientation were determined based on a shipboard survey of a strong front detected prior to deployment. As initially deployed, mooring F2 was north of the front, F8 was south of the front, and F2-F8 formed a line perpindicular to the front. Mooring F10 was 37 km to the northeast, approximately along the frontal axis. This and other frontal features moved through the array during the experiment. The line on mooring F10 parted on 14 May 1986 and the buoy drifted freely until it was recovered by the Knorr on 10 June 1986. At the time of recovery the buoy was about 60 km to the southwest of the array. Note that data from the free drift period are included in the records from F10. Velocities are relative to the mooring, with no correction for the drift velocity. The sampling interval for the VAWRs and MRs was 7.5 min, and all of the meteorology data files have this sample interval. The nominal sampling interval for VMCMs and VACMs was 3.75 min. However, four VMCMs (F2 and F10 at 120 m; F4 and F6 at 160 m) were restricted to sampling at 7.5 min. These instruments were interpolated so that all of the oceanographic data files have a 3.75 min sample interval. Meteorology ------------------------------------------------------------------------ Wind Speed The VAWRs provided complete records of wind speed at all of the FASINEX surface mooring sites. Wind Direction The VAWRs provided complete records of wind direction at all of the sites. A magnetic variation (also referred to as magnetic declination) of -10 degrees was applied as a rotation to the east and north wind components. Speed and direction were computed from the components. Wind directions are in oceanographic convention (direction towards), opposite to the meteorological convention (direction from). Air Temperature The VAWRs provided complete records of air temperature at all of the sites. Sea Surface Temperature The VAWRs provided complete sea temperature records at all of the sites except F4, where the cable to the sensor was damaged during deployment. The MR temperature from F4 was substituted. Barometric Pressure The VAWRs provided complete records of barometric pressure at all of the sites. Offsets of 2 to 5 mb were detected in post-calibration for four of the five sensors. These were corrected based on a linear fit giving biases of 0.3 to 0.4 mb and drift rates of 0.004 to 0.006 mb/day. Relative Humidity The VAWRs provided complete relative humidity records at all of the sites except for F10, where the VAWR sensor showed erratic behavior. The MR relativel humidity was used for the first 95 days of the F10 record. The relative humidity record from F2 (at the same latitude as F10) was substituted during the last 35 days. Longwave radiation Longwave radiation was not measured during FASINEX. Shortwave radiation The VAWRs provided complete records of shortwave radiation at all of the sites. A bias was removed so that minimum night time values were zero. Precipitation Precipitation was not measured during FASINEX. Calibration and Errors A combination of laboratory calibrations and field comparisons resulted in the following assessment of calibration accuracy and total error of the field measurements for each variable (see Weller et al., 1990, J. Atm. Oc. Technol., 7(1), 85-103). Variable Instrument Accuracy Error --------------- ---------- -------- ----- Wind speed VAWR 2 % +6 % Wind direction VAWR 3 deg 3 deg sea temperature VAWR 0.004 C 0.1 C MR 0.04 C 0.5 C air temperature VAWR 0.008 C 0.4 C barometric pressure VAWR 0.26 mb 0.6 mb relative humidity MR 2 % 3 % shortwave radiation VAWR 3 % 5 % Temperature ------------------------------------------------------------------------ In previous experiments (e.g. LOTUS) VMCM temperature sensors were located inside of the pressure housing. For FASINEX the sensors were relocated to an external pod in order to reduce the response time. Tests a reduction from 80 s in the LOTUS configuration to 10 s in the FASINEX configuration. Performance F6: The record from 40 m on F6 was short due to problems reading the magnetic tape containing the raw data. F10: No temperature data are available from 80 m on F10 due to failure of the magnetic tape. No temperature data are available from 700 m on F10 due to a failure in the VMCM electronics Calibration and Adjustments Careful pre- and post- calibration of VACM and VMCM temperature circuitry over a limited temperature range resulted in very high accuracy: typically 0.0025 C for the VACMs and 0.004 C for VMCMs. It was noted that mooring motion relative to a background temperature gradient may reduce accuracy in the field to 0.01 to 0.04 C. Velocity ------------------------------------------------------------------------ The bearings and load cages used with the VMCMs were modified based on excessive bearing wear experienced during LOTUS. Instruments at the upper three depths on all five moorings used a larger diameter cage (3/4 inch daimeter rods), a cross-brace for the sting, and uprated (type 440 stainless steel) bearings. Instruments at 120 and 160 m used the standard cage (1/2 inch daimeter rods), a cross brace, and uprated bearings. The lower instruments used the standard cage, a cross brace, and standard (type 316 stainless steel) bearings. Performance F2: No velocity data are available from 120 m on F2 due to a mechanical failure of the propeller assembly. F4: The 20 m VMCM on F4 were found to have "sticky" compass and vane follower bearings, but the data were retained. The 120 m record on F4 is short due to a rotor counter failure. F6: The record from 40 m on F6 was short due to problems reading the magnetic tape containing the raw data. F8: The record from 120 m on F8 is short due to flooding of the propeller sensor electronics. F10: No velocity data are available from 80 m on F10 due to failure of the magnetic tape. No velocity data are available from from 120 m and 700 m on F10 due to failures in the VMCM electronics. Velocities during the free-drift phase of the deployment have not been corrected for the drift velocity. Magnetic Variation A magnetic variation (also referred to as magnetic declination) of -10 degrees was applied as a rotation to the east and north velocity components. Speed and direction were computed from the components.