Variables for ASTEX experiments : date = year-month-day hour = decimal hour lat = latitude North ( - = South ) lon = longitude East ( - = West ) ws = true wind speed seaT = sea near-surface temperature airT = air temperature qa = air specific humidity swr = short-wave radiation down lwr = long-wave radiation down wdir = wind direction from North rain = precipitation rate shf = sensible heat flux ( see notes below ) lhf = latent heat flux ( see notes below ) Us = ship speed Tru = true wind direction Rel = relative wind direction Hed = the direction the ship's bow is pointing qs = sea surface specific humidity (no cool skin correction) Hsc = covariance sensible heat flux Hsi = inertial sensible heat flux Hsb = bulk sensible heat flux Hlc = covariance latent heat flux Hli = inertial latent heatflux Hlb = bulk latent heat flux Tuc = covariance surface stress (-wu part only) Tui = inertial-dissipation surface stress Tub = bulk surface stress J = ship plume/contamination index ( 0 = good conditions) Oph = standard deviation of OPHIR hygrometer clear channel counts Tlt = mean wind vector tilt Jm = ship maneuver/contamination index Ct = sonic temperature structure function parameter Cq = water vapor structure function parameter Cu = streamwise velocity structure function parameter Cw = vertical velocity structure function parameter Hr = sensible heat flux due to precipitation at droplet wet-bulb T To = OPHIR ait temperature Qo = OPHIR specific humidity Zb = height of turbulence and bulk meteorological measurements skin = calculated skin temperature This is a preliminary distribution of the data intended for internal consumption by my various collaborators. Please do not distribute to anyone else. All turbulent fluxes are subject to change after I reprocess the entire time series. These tables are recent production, but the numbers given here are still based on the realtime computations done at sea. The data format is similar to that used for the COARE Pilot, TIWE, and ASTEX data, with some notable exceptions. (1) The ship speed and course is taken directly from GPS. The true wind has been corrected for the surface current based on IMET data supplied by Bob Weller (WHOI). Thus, these winds are referenced to the surface of the water, not the fixed earth. Typical corrections are on the order of 0.5 m/s. A mean correction of 0.2 m/s has been subtracted from the wind speed based on comparisons with the R/V Franklin. (2) The ship's heading was taken from the ETL gyrocompass. (3) Air temperature and humidities are given from two different sensors (the Vaisala HMP-35 and the OPHIR IR-2000). Both have crude corrections for daytime heating errors based on measured wind speed and solar radiation. The OPHIR mean humidity has been increased by 3% based on calibrations of the OPHIR hygrometer against the CSIRO psychrometer during TOGA/COARE. The factory calibration for the Vaisala humidity sensor has been reduced 2% to force average agreement with the OPHIR. (4) The humidity flux has been increased by 3% as discussed above. The humidity flux has been increased an additional factor of 3.5% to account for the physical separation (1 m) of the hygrometer from the anemometer (as per Kristensen, 1993). (5) Several data quality indicators are given: relwind, J, Oph, Jm, and tilt. Good turbulence data is obtained only when the relative winds are within +/- 90 degrees of 0. Note, sensible heat flux and stress are more sensitive to contamination and flow distortion and this 90 degree limit may not be strict enough. J=1 implies the small scale temperature fluctuations greatly exceeded a reasonable threshold. This implies contamination of the turbulence data by the ship's plume even though the relative wind direction is satisfactory. Oph is the standard deviation of the OPHIR hygrometer clear channel (in counts). When the optics are clean, this is around 5. Values exceeding 15 indicate serious contamination of the latent heat fluxes, either by sea salt or rain. This also occurs with clean optics when sun glint gets into the optics, usually for high solar zenith angles, particularly when the ship is rolling a lot. A tilt exceeding 10 degrees indicates a problem with the covariance fluxes. Jm is a velocity index indicating a maneuver of the ship during the record. Values of Jm exceeding 2 usually result in poor values for covariance stress; latent and sensible heat flux may be unaffected. Note that the turbulent fluxes are not to be used during precipitation exceeding 1 mm/hr. Both the OPHIR hygrometer and the sonic anemometer are subject to rain problems. (6) Structure function parameters for temperature, humidity, streamwise and vertical velocity are given. A Taylor's hypothesis correction has been applied (Wyngaard and Clifford, 1977). These have been determined by a very simple algorithm using the variance spectrum. They have not yet been eyeball checked. The ratio Cw/Cu should be 1.33; deviations of more than 30% from this value suggest problems with the data. (6) Covariance, inertial-dissipation, and bulk values are given for stress and the heat fluxes. (7) The bulk computations use the latest version of the Fairall-Bradley-Rogers algorithm being developed for the COARE program. It uses Smith (JGR, 93,15467-15472,1988) for the drag coefficient, expressed as a Charnock relation for the roughness length: zo =.011 u*^2/g+.11*nu/u* Latent/sensible heat transfer coefficients are from Liu et al. (J.Atmos.Sci.,36,1722-1735,1979), but adjusted as per Fairall et al. (1994a). The mean vector wind is combined with a gustiness velocity equal to 1.25 times the convective scaling velocity (Godrey and Beljaars, JGR, 96, 22043-22048, 1991) is used to give more accurate fluxes at low mean wind speeds. The sea-surface humidity is 0.98 times the saturation humidity for pure water at the sea-surface temperature to account for the effect of sea water salinity. No Webb correction to the latent heat flux is included (it increases Hl an average of 4 W/m^2 for COARE). A cool skin correction to the sea surface temperature has been applied (Fairall et al., 1994b). Because the Moana Wave used a floating sea surface temperature sensor, no warm layer correction has been used. 8) The solar radiation has been increased 3% based on intercomparisons and post calibrations. The interpretation of the headings on the tables is as follows: Instructions on Using the Fluxes This file contains covariance, inertial-dissipation, and bulk flux estimates. For the purposes of producing a smooth estimate of the fluxes for surface energy budget or model inputs, I suggest using the median of the three values. Be warned that the inertial-dissipation sensible heat flux is not very good because to light winds and ship plume contamination. If you are interesting in producing your own bulk parameterization, then you will want to use the turbulent fluxes. In this regard, the covariance fluxes are considered the standard. However, as I mentioned on the previous page, much of the direct turbulence data is invalidated by experimental conditions. As a share resource, the ship was operated to permit simultaneous oceanographic measurements rather than optimizing atmospheric flux measurements. Because the ship was operating in a drift mode for most of the time, turbulence data for wind speeds less than about 2 m/s are difficult to guarantee. The following are a set of rules I suggest to get the best flux estimate from the data file: IF 270.5 OR Tilt>10 or Jm>2 THEN Use the bulk flux for all three fluxes IF Oph>10 THEN Use the bulk flux for the latent heat flux OTHERWISE Use the median of the three fluxes C.Fairall 25 July 1994 NOAA/ERL/R/E/ET7 325 Broadway Boulder, Co 80303 303-497-3253