Documentation

This is the documentation for the deprecated HOAPS-3 data set from the CERA data base.
Please check the ››Data Access page on how to download the new HOAPS-3.2 data.

File Format

The HOAPS-3 datafiles are available in standard netCDF format. The files are created using CF Metadata conventions. If you are not familiar with the netCDF format please refer to the netCDF Homepage. There you will find all necessary documentation and software or links to software for reading, manipulating and displaying netCDF files.

Naming conventions

Monthly means:
All monthly mean products are distributed in separate yearly files. Therefore one monthly mean netCDF datafile consists of 12 time records and the shortest time period available is one year. The files extracted from the CERA archive, will follow this naming conventions:

HOAPS3_MONTHLY_PPPP_X.nc:  PPPP  - four letter parameter code (››see "HOAPS Code Table")
   X  - Time period index 1987=1, 2005=19

Pentad means:
All pentad (5-day) mean products are distributed in separate monthly files. The first day of a 5-day average period determines the monthly file wherein it is saved. Each year is subdivided in 73 pentads starting at the same day of the year. During leap years, the twelfth pentad (starting at February 25) is the average of six days. The files extracted from the CERA archive, will follow this naming conventions:

HOAPS3_PENTAD_PPPP_x.nc:  PPPP  - four letter parameter code (››see "HOAPS Code Table")
   X  - Time period index 1987-01=1, 2005-12=228

Twice daily composites:
All twice daily composite products are distributed in separate monthly files containing two timesteps per day. The time steps (variable "time") are 0UTC and 12UTC for each day. For these timesteps in each grid cell contains pixels from 0-12UTC and 12-24UTC, respectively. The variable "dtime" holds the exact observation time (in seconds from midnight) for each gridbox. The files extracted from the CERA archive, will follow this naming conventions:

HOAPS3_DAILY_PPPP_X.nc:  PPPP  - four letter parameter code (››see "HOAPS Code Table")
   X  - Time period index 1987-01-01=1, 2005-12-31=228

Decoding of Parameters

In order to save disk space, all time dependent 2-dimensional fields are stored with netCDF data type short (16 Bit). The encoding/decoding follows the standard netCDF conventions. If the attributes scale_factor and add_offset are present for a variable, the data has to be scaled first and then the offset is added. Missing values have to be filtered before decoding.

Variables

Each netCDF datafile contains the following variables (unless otherwise noted):

timefirst day of average time period, days counted from 01-01-1987
latitudegeographical latitude of grid-box centre
longitudegeographical longitude of grid-box centre
ppppmonthly mean, the name depends on the parameter (››see "HOAPS Code Table" for the code table)
numonumber of observations counted during the average period (not available for budg)
numdnumber of days with at least one observation counted during the average period (not available for budg) (HOAPS-G only)
stdvroot mean squared variance (not available for budg) (HOAPS-G only)
sidscomma separated satellite id string of all SSM/I instruments used to compute this monthly mean (HOAPS-G only)
dtimeTime of day for observation in gridbox (HOAPS-C only)
satidsatellite id SSM/I instrument used to compute values in gridbox (HOAPS-C only)

Global attributes

Each netCDF datafile contains the following global attributes:

titledataset title, "HOAPS-G" for all files containing gridded averages
Conventionsconventions followed, "CF-1.0" for all files
referenceslink to the HOAPS homepage
institutioninstitution where the data was produced
sourcedata source, "satellite observations"
Major_Version_NumberMajor release version
Minor_Version_NumberMinor release version
Parameter_Namespecific parameter name (››see "HOAPS Code Table" for the code table)
Parameter_IDspecific parameter ID (››see "HOAPS Code Table" for the code table)
Average_Periodperiod of average: month for monthly means, day for x-day means
Average_Period_Lengthlength of one average period: 1 for monthly means, 5 for pentade means, ...
Average_Originorigin of average period, "year" for all files
Average_Orbit_Segmentsatellite orbits used for this mean, "ascending+descending" for all files
Average_Map_Resolutionspatial resolution in arc minutes, default HOAPS resolution is 30 arc minutes (0.5 degrees)
File_Typetemporal file splitting, "year": all means of one year are stored in this file, "month": all means of one month are stored in this file
historycreation time of this file, format is: DD/MM/YYYY (JLD) hh:mm:ss

Variable attributes

The netCDF variables can contain one ore more of the following attributes:

long_namelong descriptive name
unitphysical unit
C_formatformat string that should be used for C applications to print values for this variable, applies to the scaled (internal) type and value
FORTRAN_formatformat string that should be used for FORTRAN applications to print values for this variable, applies to the scaled (internal) type and value
valid_minsmallest valid value of a variable
valid_maxlargest valid value of a variable
scale_factorThe data are to be multiplied by this factor after it is read.
add_offsetThis number is to be added to the data after it is read. If scale_factor is present, the data are first scaled before the offset is added.
_FillValueThis number represent missing or undefined data. Missing values are to be filtered before scaling.

HOAPS Code Table

AcronymDescriptionUnitPar. IDCM SAF IDCM SAF code
WINDWind speed at 10m heightm/s0CM-142NSW
HAIRNear surface specific humidityg/kg1CM-141NSH
RAINPrecipitationmm/d2CM-144PRE
WVPAVertically integrated water vapourkg/m**23*HTW
TWPAVertically integrated total (ice+liquid) waterkg/m**24*TWP
ASSTSea surface temperaturedeg C30*SST
HSEASea surface saturation specific humidityg/kg31*SSH
FNETSurface net longwave radiationW/m**260*SNL
DHUMDifference in humidityg/kg61*SHD
TRCELatent heat transfer coefficient (Dalton number)-64*LTC
LATELatent heat flux at sea surfaceW/m**265CM-143LHF
HEATSensible heat flux at sea surfaceW/m**266*SHF
EVAPEvaporationmm/d67CM-145EVA
BUDGFreshwater fluxmm/d68CM-146EMP
      * parameter not operationally supported by CM SAF