C. Fairall J. Hare

Oct 20, 1999

Preliminary bulk fluxes for Nauru99

Readme for flux_nauru.txt

The data file 'flux_nauru,txt' contains computations of bulk meteorological variables and fluxes derived therefrom based on preliminary analysis done during the Nauru99 cruise. Most quantities given are subject to future modification based on accounting for other sources of data and revised calibrations. No direct turbulent flux calculations are included in this present data.

The file is 24 columns and 1632 lines covering Julian days 166 (June 15) through 199 (July 18). The data columns are not labeled so they can be directly acquired with a MATLAB 'load' statement.

x=load('your_local_directory\flux_nauru.txt');%read file with half-hour average data; set your local directory

The columns are as follows:

jdy=x(:,1);%julian day at beginning of half hour average*

U=x(:,2); %true wind speed, m/s; etl sonic anemometer (17.5 m)

dir=x(:,3);%true wind direction (from), deg (clockwise rel north)

tsnk=x(:,4);%sea snake temperature, C (0.05 m depth)

tsg=x(:,5);%tsg water temperature, C (5 m depth)

sal=x(:,6);%tsg salinity, psu (5 m depth)

ta=x(:,7);%air temperature, C (z=14.5 m)

qse=x(:,8);%sea surface specific humidity, g/kg (from snake when in water, see field 17)

qa=x(:,9);%air specific humidity, g/kg (z=14.5 m)

rs=x(:,10);%downward solar flux, W/m^2 (ETL units)

rl=x(:,11);%downward IR flux, W/m^2 (ETL units)

org=x(:,12);%rainrate, mm/hr (ETL STI optical rain gauge, uncorrected)

ushp=x(:,13);%ship speed, m/s (SCS ODEC)

head=x(:,14);%ship heading, deg clockwise rel north (SCS laser ring gyro)

urel=x(:,15);%relative wind speed, m/s (ETL sonic)

reldir=x(:,16);%relative wind direction (from), deg clockwise rel ship's bow(ETL sonic)

Lat=x(:,17);%latitude, DDMM.MMMM (SCS pcode)

Lon=x(:,18);%longitude, DDDMM.MMMM (SCS pcode)

zts=x(:,19);%depth for bulk flux Ts reference, =0.05 when snake is used, 5.0 when tsg is used

sig_u=x(:,20);%std dev of ship speed, m/s (>.2 indicates maneuver during half hour average)

Taub=x(:,21);%bulk wind stress along mean wind, N/m^2

Hsb=x(:,22);%bulk sensible heat flux, W/m^2

Hlb=x(:,23);%bulk latent heat flux, W/m^2 (includes Webb et al. correction)

Hrain=x(:,24);%rain heat flux, W/m^2 as per Gosnell et al

* Please be warned, anyone calling me up and asking if the time denotes the beginning, middle, or end of the period will be hung up on; emails will be deleted before reading.

The data in this file comes from three sources: The ETL sonic anemometer (acquired at 20.83 Hz), the ships SCS system (acquired at 2 sec intervals), and the ETL mean measurement systems (sampled at 10 sec and averaged to 1 min). The sonic is 5 channels of data; the SCS file is 13 channels, and the ETL mean system is 16 channels. A series of programs are run that read these data files, decode them, and write daily text files at 1 min time resolution. A second set of programs reads the daily 1-min text files, time matches the three data sources, averages them to 5 or 30 minutes, computes fluxes, and writes new daily flux files. The 30-min daily flux files have been combined and rewritten as a single file to form flux_nauru.txt.

Further experimental details are as follows:

True wind speed is computed from the sonic anemometer using the ship's Laser ring gyro and the odec doppler log; thus, it is interpreted as the speed relative to the water. Some modest eyeball flow distortion corrections have been used in an attempt to reduce the transitions when stopping for stations.

Air temperature and humidity are combinations of ETL (aspirated Vaisala HMP-235) and IMET (aspirated Rotronic) values, both of which were observed to have problems in strong winds and precipitation. Otherwise, they are within 2% RH and 0.2 C of the CSIRO psychrometer values obtained during the JASMINE experiment..

At some times during the cruise the seasnake may have been removed from the water intermittently. Sea surface temperature measurements often showed contamination by the ship during stops and maneuvers stations. The sensor was airborne a lot in the stronger wind/rougher sea days and the accuracy under those conditions is uncertain.

Longwave flux was obtained from 2 Eppley PIR units, logged and computed as per Fairall et al. Jtech, 1998.

Shortwave flux was obtained from 2 Eppley PSP units.

The rainrate was obtained from the ETL STI optical raingauge. Note, this is model org-815 - not the mini-org used on COARE. No correction for cosine response has been attempted. There is a +0.1 mm/hr bias that should be removed before using this data.

Latitude is recorded without N/S information. The sign should be reversed for the first 1507 points.

Air sea fluxes were computed using the COARE bulk algorithm version 2.6, which differs from the published version in only minor details.