VOCALS2008_soundings_z1_0.readme.txt :: 2009 June 1 :: Simon de Szoeke README metadata for VOCALS2008_soundings_z1_0.nc Title: Rawinsonde data for VOCALS 2008 Version: 1.0 Creation date: 2009-06-30 Author: Simon de Szoeke Data are provided by Simon de Szoeke (Oregon State University), Sandra Yuter (North Carolina State University), and Chris Fairall (NOAA/ESRL/PSD) with funding from the NOAA Climate Program Office. Find this metadata at ftp://precip.meas.ncsu.edu/pub/vocals/VOCALS2008_soundings_z1_0.readme.txt Data Dimensions 1 launch rawinsonde launch number (216, record dimension) 2 altitude altitude in 10-m increments (2501) Data Set Variables Name [units] Description TIME(launch) vectors 1 year [Gregorian year] always 2008 2 yday [day] Decimal year day of sonde launch, since 2008 January 1 00:00 UTC 3 month [month] month of year 4 day [day] day of month 5 hour [hour] hour of day 6 minute [minute] minute of hour 7 lat [degrees] north latitude 8 lon [degrees] east longitude 20 flag quality control flag code (see below) VERTICAL(altitude) vector 9 height [meters] bottom of 10-m vertical averaging interval DATA(launch, altitude) 10 pres [hPa] pressure 11 T [degree C] temperature 12 RH [percent] relative humidity 13 Td [degree C] dew point temperature (*) 14 wnddir [degree] meteorological convention (out-of) wind direction; degrees heading clockwise from north 15 wndspd [m/s] wind speed 16 u [m/s] zonal eastward wind velocity 17 v [m/s] meridional northward wind velocity 18 theta [K] potential temperature (+) 19 q [g/kg] specific humidity (*+) (*) derived from RH (+) derived from temperature In the netcdf(.nc) file, IEEE not-a-number (NaN) values denote missing values. Interpolation to Standard Levels and Derived Variables Data provided here are vertically interpolated to standard 10-m height increments. For a nominal ascent rate of 5 m/s the 10 m height interval corresponds roughly to the 2 s time interval to which the data are interpolated by the Vaisala DigiCORA sonde processing software. The data decorrelation time scale is estimated at about 5 s from the sonde ascent rate and response time of the sensors, so the 10 m and 2 s intervals slightly over-sample the data. Thermodynamic variables pressure, temperature, and relative humidity are measured by sensors on the sonde boom. Other thermodynamic variables Td, theta, and q are computed from these in-situ measurements. Td is computed by the Vaisala software. Variables theta and q are computed in post-processing from T and RH. Winds are calculated from horizontal displacements of the rawinsonde measured by the GPS receiver on the sonde. Wind direction and speed are output at 2 s increments by the Vaisala sounding processing software. These are converted to vector eastward zonal and northward meridional components (u, v) and interpolated to standard 10-m intervals. Wind direction and speed (wnddir, wndspd) are computed from the interpolated wind components. Quality Control Hugely negative relative humidity was found for two sondes. All humidity variables (RH, Td, q) for these sondes are set to NaN, and the launch is flagged H to indicate a humidity issue has been masked out. Three sondes had alternating cycles of RH. This is due to a mismatch between the two hygrometers on the sonde, which are alternately sampled and heated to remove liquid water contamination. Two sondes had alternating shifts of more than 0.1 of their background relative humidity. The humidity variables for these sondes are set to NaN, and they are flagged C for humidity cycling. A third sonde (November 19 12:02) has some humidity cycling with a smaller magnitude. This sonde is flagged c for cycling RH, but no data is expunged. Sonde observations from 20-40 m have been compared with observations from sensors on the ship's forward mast. The 20-40 m level average agrees best with the mast sensors. One sonde has temperature about 3 degrees C warmer than the mast, and 14 sondes have temperature more than 1 C cooler than the mast. The temperature from these 15 sondes is considered outside the range of reasonable agreement with other sensors. They are flagged T for out-of-range temperature, and the temperature data (T, q, theta) are expunged. Sondes sit on the deck of the ship (~7 m) before being launched, and the sonde processing software adjusts the first couple data points to match data entered on a terminal during launch preparation. Since the source of these lower-altitude data is different from the sensors on the rawinsonde itself, data from levels below 30 m are expunged from the rawinsonde data set. Quality Control Flags The variable 'flag' contains a single character for each launch denoting data quality for that sounding. flag code description sonde OK, i.e. no suspect data has been found as of the release c(lowercase) RH has small-amplitude cycles; data not expunged C(uppercase) RH has large-amplitude cycles; humidity data expunged H Seriously out of range humidity values; humidity data expunged T Temperature more than 1 C different from the ship's mast temperature; temperature data expunged