DYCOMS-II Surface: Tanner Banks Buoy Meteorological and Spectral Wave Data 1.0 General Description The Tanner Banks Buoy Meteorological and Spectral Wave Data is one of several surface data sets collected by the University Corporation for Atmospheric Research/Joint Office for Science Support (UCAR/JOSS) as part of the Dynamics and Chemistry of Marine Stratocumulus Phase II: Entrainment Studies (DYCOMS-II) project. Included in the data set are hourly observations of meteorological parameters, 10 min observations of wind parameters, and hourly observations of wave parameters for the Tanner Banks buoy (WMO 46047) located off the California coast. The data cover the period from 7 - 28 July 2001. The data were acquired from the National Data Buoy Center (NDBC). 2.0 Data Contact Scot Loehrer (loehrer@ucar.edu) 3.0 Data and Format Information 3.1 Standard meteorological data (met file) STATION ID five-digit WMO Station Identifier used since 1976. ID's can be reassigned to future deployments within the same 1 degree square. DATE in UTC TIME To the nearest hour, UTC. Sensors that are installed on board moored buoys do not measure and record data for the entire hour. An eight-minute period is used for data collected by sensors on board moored buoys. The end-of- acquisition time is reported as the official observation time. Any data field that contains "9 filled" represents missing data for that observation hour. (Example: 999.0 99.0) ATMP Air temperature (Celsius). Air temperature is measured at 4 m above the site elevation. WTMP Sea surface temperature (Celsius). SST is measured at 0.6 m below site elevation. DEWP Dewpoint temperature taken at the same height as the air temperature measurement. BARO Sea level pressure (hPa). The station pressure is measured at sea level. WSPD Wind speed (m/s) averaged over an eight-minute period for buoys. Reported Hourly. The average wind speed is the simple scalar average of the wind speed observations. A "unit-vector" average is used to calculate the average wind direction. In this technique, unity serves as the length of the vector, and the wind direction observations serve as the orientation of the vector. The u and v components are then calculated for each observation. Next, the average u and v components are computed and the average wind direction is derived from "arctan(u/v)." Note that this technique will produce greater wind speeds than if a true vector average was used. WD Wind direction (the direction the wind is coming from in degrees clockwise from N) during the same period used for WSPD. GST Peak 5 second gust speed (m/s) measured during the eight-minute period. WVHT Significant wave height (meters) is calculated as the average of the highest one-third of all of the wave heights during the 20-minute sampling period. APD Average wave period (seconds) of all waves during the 20-minute period. DPD Dominant wave period (seconds) is the period with the maximum wave energy. MWD Mean wave direction (degrees) corresponding to energy of the dominant period (DOMPD). VIS Station visibility (statute miles) PTDY Pressure Tendency is the direction (plus or minus) and the amount of pressure change (hPa) for a three hour period ending at the time of observation. TIDE The periodic rising and falling of the earth's oceans. Tide is measured in feet. 3.2 Continuous Wind Data (cwind file) DIR Ten-minute average wind direction measurements in degrees clockwise from North. SPD Ten-minute average wind speed values in m/s. GDR Direction, in degrees clockwise from North, of the GUST, reported at the last hourly 10-minute segment. GSP Maximum 5-second peak gust during the measurement hour, reported at the last hourly 10-minute segment. GMN The minute of the hour that the GUST occurred, reported at the last hourly 10-minute segment. 3.3 Spectral Wave Summary Data (spec file) Time Format (YY MM DD HH) The time is shown as DD/HH where DD is the current day and HH is the current hour in GMT. GMT is "London" time and is five hours ahead of Eastern Standard Time. For Daylight Savings Time, the difference is one hour less. In other words, 12 GMT is 7 AM EST (8 AM EDT). For West Coast mariners, Pacific Standard Time = GMT - 8 hours. Swell Direction (SwD) This is the direction that the swells are coming from. Swells are waves not produced by the local wind and come in at a higher period (longer wave length) than waves produced by the local wind. Direction is given on a 16 point compass scale. MM or -99 denote missing data. Less than half of our buoy stations report directional wave data because of the costs involved with additional instrumentation. NO indicates that no swells could be determined. Swell Height (SwH) This is the estimated average height of the highest one-third of the swells. It is estimated from determining how the wave energy is distributed among various periods (frequencies), determining if a separate swell energy peak exists, and then, picking a frequency to separate swell and wind-waves. The swell height is calculated from the wave energies below the separation frequency. Swell Period (SwP) This is the peak period in seconds of the swells. If more than one swell is present, this is the period of the swell containing the maximum energy. Wind-Wave Direction (WWD) This is the direction that the wind-waves are coming from. Wind-waves are produced (or were recently produced) by the local wind. If a swell is present, these waves arrive at a lower period (more frequently) than do the swells. Direction is given on a 16 point compass scale. MM or -99 denote missing data. Less than half of our buoy stations report directional wave data because of the costs involved with additional instrumentation. Wind-Wave Height (WWH) This is the average height of the highest one-third of the wind-waves. Again, it is estimated by the process mentioned under "Swell Height", except that it is the calculated from the energies above the separation frequency. Wind-Wave Period (WWP) This is the peak period in seconds of the wind-waves. Overall Height and Period (H0 and AVP) This is the significant wave height and dominant wave period that has been traditionally available. Significant wave height is the average height of the highest third of the waves. If both swell and wind-waves are present, it should equal the square root of the sum of the squares of the swell and wind-wave heights. Dominant period is the period with maximum energy and is always either the swell period or the wind-wave period. Steepness (STP) Reported as either "VERY STEEP", "STEEP", "AVERAGE", or "SWELL". For a given wave height, steep waves represent a more serious threat to capsizing vessels or damaging marine structures than broad swell. It is determined by examining the significant wave height and the dominant wave period when compared to climatology. 3.4 Station List and Site Information Tanner Banks Buoy 32.43 N 119.53 W (32 26'00"N 119 31'59" W) Site elevation: sea level Air temp height: 4 m above site elevation Anemometer height: 5 m above site elevation Barometer elevation: sea level Sea temp depth: 0.6 m below site elevation Water depth: 1,393.5 m Watch circle radius: 1,700 yards 3-meter discus buoy VEEP payload 4.0 Quality Control Procedures UCAR/JOSS conducted no quality checks on these data. 5.0 File Naming Convention This data set consists of three data files: sfc_20010707_0728_46047cwind.txt sfc_20010707_0728_46047met.txt sfc_20010707_0728_46047spec.txt sfc is the data type the begin date is in yyyymmdd the end date is in mmdd 46047cwind is the continuous wind data 46047met is the meteorological data 46047spec is the spectral wave data 6.0 References Gilhousen, D.B., 1987: A field evaluation of NDBC moored buoy winds. Journal of Atmospheric and Oceanic Technology, 4, 94-104.