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**Description of "Historic Data"**

Table of Contents:

:InstantaneousThe instantaneous flux are available at hourly interval. They are reported at the nominal time of satellite observations viz. 00:15 utc, 01:15 utc, 02:15 utc, ..., 23:15 utc from the year 1996 onward. :Hourly averageThe hourly average flux is an estimate of the flux averaged for an hour ending at the hour in local standard time. It is obtained from the instantaneous flux by normalizing it to the average solar zenith angle for the hour. :Daily averageThe daily average flux is the 24-hour average of the flux for a day.

In calculating the daily average, missing day-time hours are filled in by replicating data from non-missing hours one hour before the missing ones. If the hour one before the missing one is also missing filling is done from the closest hour after the missing one. If all day-time hours are missing no filling is done. Fluxes at a missing hour are obtained by multiplying the non-missing fluxes by the ratio of the solar zenith angle cosine at the missing hour to that at the non-missing hour. In addition, the daily average flux, obtained from summing up the hourly values, is multiplied by the ratio of numerical-to-analytical integral of the daily top of the atmosphere downward flux. The latter procedure is intended to correct for potential inaccuracies in the numerical integration of hourly fluxes.Non-filled and non-corrected daily averages can be obtained from the hourly averages.

:Monthly averageThe monthly average flux is the average of daily fluxes for a month.

It is the arithmetic mean of daily averages for the non-missing days. Potential errors in this numerical "integral" are corrected by multiplying the arithmetic mean by the ratio of numerical-to-analytical integral of the monthly top of the atmosphere downward flux.Non-filled and non-corrected monthly averages can be obtained from the hourly averages.

[Top]In addidtion to fluxes, instantaneous, hourly, daily and monthly averages of the surface albedo and cloud cover fraction are provided.

:AlbedoThe albedo is obtained as the ratio of the upward flux to the downward flux. :Cloud coverThe cloud cover fraction is calculated as the ratio of the number of cloudy pixels within a grid cell to the total number of pixels (cloudy+clear) in that cell. [Top]

Before July 2001: Each file has information for 5661 (0.5 by 0.5 degree, equal-angle) cells (51 latitudes and 111 longitudes). All cells are present, even when data are missing. The cells are written sequentially, proceeding eastward through the latitude zone, then northward to the next latitude zone. The center lat/lon coordinates of the first cell are 25 N, 125 W, and those of the last cell are 50 N, 70 W.

The following Fortran statements could be used to calculate the center coordinates of cells:

INTEGER Nlat, Nlon, Lat, Lon

REAL Lat1, Lon1, Reslat, Reslon

PARAMETER ( Nlat=51, Nlon=111 )

REAL Glat( Nlat ), Glon( Nlon )

C ** Calculate latitude and longitude coordinates of

C ** cell centers

Reslat = 0.5

Reslon = 0.5

Lat1 = 25.0

Lon1 = -125.0

DO 20 Lat = 1, Nlat

Glat( Lat ) = ( Lat-1 ) * Reslat + Lat1

20 CONTINUE

DO 30 Lon = 1, Nlon

Glon( Lon ) = ( Lon-1 ) * Reslon + Lon1

30 CONTINUEHere Glat and Glon are the latitude and longitude coordinates of cell-centers, Reslat and Reslon are the distances between cell-centers in latitude and longitude (resolution), Lat1 and Lon1 are the latitude and longitude coordinates of the center of first cell , respectively. All quantities are in degrees.

[Top]Since July 2001:

Each file has information for 7381 (0.5 by 0.5 degree, equal-angle) cells (61 latitudes and 121 longitudes). All cells are present, even when data are missing. The cells are written sequentially, proceeding eastward through the latitude zone, then northward to the next latitude zone. The center lat/lon coordinates of the first cell are 24 N, 126 W, and those of the last cell are 54 N, 66 W.

The following Fortran statements could be used to calculate the center coordinates of cells:

INTEGER Nlat, Nlon, Lat, Lon REAL Lat1, Lon1, Reslat, Reslon PARAMETER ( Nlat=61, Nlon=121 ) REAL Glat( Nlon, Nlat ), Glon( Nlon, Nlat )C ** Calculate latitude and longitude coordinates of C ** cell centersReslat = 0.5 Reslon = 0.5 Lat1 = 24.0 Lon1 = -126.0 DO 20 Lat = 1, Nlat Glat( Lat ) = ( Lat-1 ) * Reslat + Lat1 20 CONTINUE DO 30 Lon = 1, Nlon Glon( Lon ) = ( Lon-1 ) * Reslon + Lon1 30 CONTINUEHere Glat and Glon are the latitude and longitude coordinates of cell-centers, Reslat and Reslon are the distances between cell-centers in latitude and longitude (resolution), Lat1 and Lon1 are the latitude and longitude coordinates of the center of first cell , respectively. All quantities are in degrees.

[Top]

Before July 2001: Data for a particular parameter and time resolution for a month are contained in a single file.

Instantaneousandhourly averagefiles contain all 24 hours for a day, and all days for a month, even if data are missing. For theinstantaneousfiles the hours are UTC (0-23), while those for thehourly averagefiles are local standard time (1-24).Daily averagefiles also include all days for a month, even if data are missing.In the

instantaneousandhourly averagefiles, all cells are written for a given hour of a given day. Writing of data proceeds from the first hour to the last of a day, and is repeated for all days in the month. That is:(lon1,lat1,h1,d1) (lon2,lat1,h1,d1) ... (lon111,lat1,h1,d1)

...

(lon1,lat51,h1,d1) (lon2,lat51,h1,d1) ... (lon111,lat51,h1,d1)

(lon1,lat1,h2,d1) (lon2,lat1,h2,d1) ... (lon111,lat1,h2,d1)

...

...

(lon1,lat51,h24,d1) (lon2,lat51,h24,d1) ... (lon111,lat51,h24,d1)

...

...

...

(lon1,lat51,h24,d31) (lon2,lat51,h24,d31) ... (lon111,lat51,h24,d31)n the

daily averagefiles, days are written sequentially, that is:(lon1,lat1,d1) (lon2,lat1,d1) ... (lon111,lat1,d1)

...

(lon1,lat51,d1) (lon2,lat51,d1) ... (lon111,lat51,d1)

...

...

(lon1,lat51,d31) (lon2,lat51,d31) ... (lon111,lat51,d31)The structure of the

monthly averagefile is as follows:(lon1,lat1) (lon2,lat1) ... (lon111,lat1)

...

(lon1,lat51) (lon2,lat51) ... (lon111,lat51)where lon=longitude, lat=latitude, h=hour, and d=day.

All files are written unformatted with direct access. The logical record length is 444 bytes (111 columns times 4 bytes). The floating point binary data conform to the

little endianspecification, and were written on a DEC workstation. Here is a sample Fortran statement to open a file (e.g., 9606sda.m):OPEN ( Unit=1, File='9606sda.m', Status='OLD', & Form='UNFORMATTED', Access='DIRECT', Recl=Lrec )where Lrec is the record length (444 for compilers that require bytes for Recl, or 111 for those that need words for Recl).

Please Note:

If your machine uses Big endian representation of binary data (e.g. SGI, IBM), the instructions of reading data can be found at:

http://metosrv2.umd.edu/~srb/gcip/faq.htm

[Top]Since July 2001:

Data for a particular parameter and time resolution for a month are contained in a single file.

Instantaneousandhourly averagefiles contain all 24 hours for a day, and all days for a month, even if data are missing. For theinstantaneousfiles the hours are UTC (0-23), while those for thehourly averagefiles are local standard time (1-24).Daily averagefiles also include all days for a month, even if data are missing.In the

instantaneousandhourly averagefiles, all cells are written for a given hour of a given day. Writing of data proceeds from the first hour to the last of a day, and is repeated for all days in the month. That is:(lon1,lat1,h1,d1) (lon2,lat1,h1,d1) ... (lon111,lat1,h1,d1)

...

(lon1,lat61,h1,d1) (lon2,lat61,h1,d1) ... (lon111,lat61,h1,d1)

(lon1,lat1,h2,d1) (lon2,lat1,h2,d1) ... (lon111,lat1,h2,d1)

...

...

(lon1,lat61,h24,d1) (lon2,lat61,h24,d1) ... (lon111,lat61,h24,d1)

...

...

...

(lon1,lat61,h24,d31) (lon2,lat61,h24,d31) ... (lon111,lat61,h24,d31)n the

daily averagefiles, days are written sequentially, that is:(lon1,lat1,d1) (lon2,lat1,d1) ... (lon111,lat1,d1)

...

(lon1,lat61,d1) (lon2,lat61,d1) ... (lon111,lat61,d1)

...

...

(lon1,lat61,d31) (lon2,lat61,d31) ... (lon111,lat61,d31)The structure of the

monthly averagefile is as follows:(lon1,lat1) (lon2,lat1) ... (lon111,lat1)

...

(lon1,lat61) (lon2,lat61) ... (lon111,lat61)where lon=longitude, lat=latitude, h=hour, and d=day.

All files are written unformatted with direct access. The logical record length is 484 bytes (121 columns times 4 bytes). The floating point binary data conform to the

little endianspecification, and were written on a DEC workstation. Here is a sample Fortran statement to open a file (e.g., 9606sda.m):OPEN ( Unit=1, File='0109sda.m', Status='OLD', & Form='UNFORMATTED', Access='DIRECT', Recl=Lrec )where Lrec is the record length (484 for compilers that require bytes for Recl, or 121 for those that need words for Recl).

Please Note:

If your machine uses Big endian representation of binary data (e.g. SGI, IBM), the instructions of reading data can be found at:

http://metosrv2.umd.edu/~srb/gcip/faq.htm

[Top]

Fluxes are given in Wm ^{-2}.

Albedo and cloud cover fraction are dimensionless, their values range from 0 to 1.[Top]

Missing data are represented by -999. [Top]

instantaneous : yymmppp.i

hourly :yymmppp.h

daily :yymmppp.d

monthly :yymmppp.m

where

yy: year (two digits),

mm: month (two digits)

ppp: parameter (three characters), their values are:

sda: surface downward flux,

par: photosynthetically active radiation,

tda: top of atmosphere downward flux,

tua: top of atmosphere upward flux,

sal: surface albedo,

ccf: cloud cover fraction.All files are compressed using the gzip utility, and all have the extension ".gz" attached to the above names.

[Top]

File typeUncompressed size (bytes)Compressed size(bytes)

(varies, an example is given)instantaneous: 15.5M 2.5M hourly: 15.5M 2.5M daily: 663K 196K monthly: 22K 7K

[Top]

**Sample Fortran Read Statements**

http://metosrv2.umd.edu/~srb/g cip/faq.htm

[Top]

Before July 2001:

INTEGER Day, Hour, Irec, Lat, Lon, Maxday, Ndays, Nhours, Nlat, & Nlon PARAMETER ( Maxday=31, Nhours=24, Nlat=51, Nlon=111 ) REAL Fluxi( Nlon, Nlat, Nhours, Maxday ), Minute, TimeC ** Ndays is the number of days in the month C ** open for read, Minute is the minutes after the C ** hour when satellite observation is taken CNdays = 30 Minute = 15.0 Irec = 0 DO10 Day = 1, NdaysDO 20 Hour = 1, NhoursC ** Time is the nominal time of the satellite C ** observationTime = Hour + Minute / 60.DO 30 Lat = 1, Nlat Irec = Irec + 1 READ ( 1, Rec=Irec ) ( Fluxi(Lon,Lat,Hour,Day), Lon=1, & Nlon ) 30 CONTINUE 20 CONTINUE 10 CONTINUE

Since July 2001:

INTEGER Day, Hour, Irec, Lat, Lon, Maxday, Ndays, Nhours, Nlat, & Nlon PARAMETER ( Maxday=31, Nhours=24, Nlat=61, Nlon=121 ) REAL Fluxi( Nlon, Nlat, Nhours, Maxday ), Minute, TimeC ** Ndays is the number of days in the month C ** open for read, Minute is the minutes after the C ** hour when satellite observation is taken CNdays = 30 Minute = 15.0 Irec = 0 DO10 Day = 1, NdaysDO 20 Hour = 1, NhoursC ** Time is the nominal time of the satellite C ** observationTime = Hour + Minute / 60.DO 30 Lat = 1, Nlat Irec = Irec + 1 READ ( 1, Rec=Irec ) ( Fluxi(Lon,Lat,Hour,Day), Lon=1, & Nlon ) 30 CONTINUE 20 CONTINUE 10 CONTINUE

Sample output and sample Fortran program are also available.

**[Read statements] [Top]**

Before July 2001:

INTEGER Day, Hour, Irec, Lat, Lon, Maxday, Ndays, Nhours, Nlat, & Nlon PARAMETER ( Maxday=31, Nhours=24, Nlat=51, Nlon=111 ) REAL Fluxh( Nlon, Nlat, Nhours, Maxday )C ** Ndays is the number of days in the month C ** open for read CNdays = 30 Irec = 0 DO 10 Day = 1, NdaysDO 20 Hour = 1, Nhours DO 30 Lat = 1, Nlat Irec = Irec + 1 READ ( 1, Rec=Irec ) ( Fluxh(Lon,Lat,Hour,Day), Lon=1, & Nlon ) 30 CONTINUE 20 CONTINUE 10 CONTINUE

Since July 2001:

INTEGER Day, Hour, Irec, Lat, Lon, Maxday, Ndays, Nhours, Nlat, & Nlon PARAMETER ( Maxday=31, Nhours=24, Nlat=61, Nlon=121 ) REAL Fluxh( Nlon, Nlat, Nhours, Maxday )C ** Ndays is the number of days in the month C ** open for read CNdays = 30 Irec = 0 DO 10 Day = 1, NdaysDO 20 Hour = 1, Nhours DO 30 Lat = 1, Nlat Irec = Irec + 1 READ ( 1, Rec=Irec ) ( Fluxh(Lon,Lat,Hour,Day), Lon=1, & Nlon ) 30 CONTINUE 20 CONTINUE 10 CONTINUE

Sample output and sample Fortran program are also available.

**[Read statements] [Top]**

Before July 2001:

INTEGER Day, Irec, Lat, Lon, Maxday, Ndays, Nlat, NlonPARAMETER ( Maxday=31, Nlat=51, Nlon=111 )REAL Fluxd( Nlon, Nlat, Maxday ) Ndays = 30 Irec = 0 DO 10 Day = 1, NdaysDO 20 Lat = 1, Nlat Irec = Irec + 1 READ ( 1, Rec=Irec ) ( Fluxd(Lon,Lat,Day), Lon=1, Nlon ) 20 CONTINUE 10 CONTINUE

Since July 2001:

INTEGER Day, Irec, Lat, Lon, Maxday, Ndays, Nlat, NlonPARAMETER ( Maxday=31, Nlat=61, Nlon=121 )REAL Fluxd( Nlon, Nlat, Maxday ) Ndays = 30 Irec = 0 DO 10 Day = 1, NdaysDO 20 Lat = 1, Nlat Irec = Irec + 1 READ ( 1, Rec=Irec ) ( Fluxd(Lon,Lat,Day), Lon=1, Nlon ) 20 CONTINUE 10 CONTINUE

Sample output and sample Fortran program are also available.

**[Read statements] [Top]**

Before July 2001:

INTEGER Nlat, NlonPARAMETER ( Nlat=51, Nlon=111 )REAL Fluxm( Nlon, Nlat ) Irec = 0 DO 10 Lat = 1, Nlat Irec = Irec + 1 READ ( 1, Rec=Irec ) ( Fluxm(Lon,Lat), Lon=1, Nlon ) 10 CONTINUE

Since July 2001:

INTEGER Nlat, NlonPARAMETER ( Nlat=61, Nlon=121 )REAL Fluxm( Nlon, Nlat ) Irec = 0 DO 10 Lat = 1, Nlat Irec = Irec + 1 READ ( 1, Rec=Irec ) ( Fluxm(Lon,Lat), Lon=1, Nlon ) 10 CONTINUE

Sample output and sample Fortran program are also available.

**[Read statements] [Top]**

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Last modified on *Nov 4, 2000*