C. Fairall, J. Hare, Frank Bradley

Oct 2, 2001

Preliminary bulk fluxes for EPIC2001

Readme for flux30_sum.txt

The data file 'flux30_sum.txt' contains computations of bulk meteorological variables and fluxes derived the ETL system based on preliminary analysis done during the EPIC2001 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 31 columns and 1187 lines covering Julian days 253 (September 10) through 278 (October 5). There are two versions, one with and one without column labels (flux30_sum_nohd.txt). The data columns are not labeled so they can be directly acquired with a MATLAB 'load' statement.

x=load('your_local_directory\flux30_sum_nohd.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 (18.5 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=15.5 m)

qse=x(:,8);%sea surface specific humidity, g/kg

qa=x(:,9);%air specific humidity, g/kg (z=15.5 m)

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

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

org1=x(:,12);%rainrate, mm/hr (ETL STI optical rain gauge #1, 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

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

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

org2=x(:,25);%rainrate, mm/hr (ETL STI optical rain gauge #2,uncorrected)

org3=x(:,26);%rainrate, mm/hr (CSIRO STI optical rain gauge #1,uncor)

org4=x(:,27);%rainrate, mm/hr (CSIRO STI optical rain gauge #2, uncor)

org1_c=x(:,28);%ORG1 quality index, 4-5= operating

org2_c=x(:,29);%ORG2 quality index, 4-5= operating

aspir=x(:,30);%backflow indicator (=5) when aspirator fails

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 31 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 flux30_sum.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 experiment..

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 two ETL STI optical raingauge (Model 705) and two CSIRO guages (mini-org). Data have not been corrected for cosine response. Gauges 1 and 3 are mounted long axis oriented abeam, 2 and 4 at 90 deg.

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