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[CIDC FTP Data]
[Surface Solar Irradiance CIDC Data on FTP]
Data Access
Surface Solar Irradiance from NASA GISS
[rule]
Readme Contents
Data Set Overview
Sponsor
Original Archive
Future Updates
The Data
Characteristics
Source
The Files
Format
Name and Directory Information
Companion Software
The Science
Theoretical Basis of Data
Processing Sequence and Algorithms
Scientific Potential of Data
Validation of Data
Contacts
Points of Contact
References
[rule]
Data Set Overview
The surface solar irradiance ( 250-4000 nm)is a basic climate and
biosphere parameter which affects the surface temperature and
photosynthesis in both marine and land plants. It is also
important to geochemical cycling because both biological and
photochemical processes strongly perturb distributions of chemical
species on land and in the ocean. Clouds are a major modulator of
the surface solar irradiance. Bishop and Rossow (1991) developed a
fast radiative transfer algorithm for calculating the downwelling
surface solar irradiance which uses the total cloud amount from
the International Satellite Cloud Climatology Project(ISCCP) as an
important input parameter. Their algorithm has gone through three
versions, reprocessing using the version 3 algorithm is in
progress. Eight years (July'83 - June'91) of monthly downward
surface solar irradiance (W/m2) calculated using version 2
algorithm are presented here.
Sponsor
The production and distribution of this data set are funded by
NASA's Earth Science enterprise. The data are not copyrighted;
however, we request that when you publish data or results using
these data please acknowledge as follows:
The authors wish to thank Drs. James Bishop and William
Rossow at the NASA Goddard Institute for Space Studies,
New York, for the production of the original data set,
and the Distribute Active Archive Center (Code 902) at
the Goddard Space Flight Center, Greenbelt, MD, 20771,
for putting these data in the present format and
distributing them. Goddard DAAC's share in these
activities was sponsored by NASA's Earth Science
enterprise.
Original Archive
The original data set on 2.5x2.5 degree grid for the period July
1983 to June 1991 was produced ( Bishop and Rossow, 1991) at the
Goddard Institute for Space Studies (GISS). The daily as well as
the monthly mean data in its original format can be obtained from
the National Center for Atmospheric Research (NCAR) where it is
archived. The monthly mean data in its original format may also be
obtained from GISS. Here we have interpolated the original monthly
mean product at a resolution of 2.5x2.5 degree grid to a 1x1
degree grid for easy comparison to the other Interdiscipline Data
Collections. The south to north orientation of the original data
was reversed, for conformity to our existing datasets. This
reformated data now starts at (89.5N, 179.5W) and runs eastward
and southward to latitude 89.5 S.
Future Updates
This data set will be updated as new data is made available.
The Data
Characteristics
* Parameters: Incident surface solar irradiance
* Units:W/m2
* Temporal Coverage: July 1983 - June 1991
* Temporal Resolution: Gridded monthly means
* Spatial Coverage: Global
* Spatial Resolution: 1 degree x 1 degree
Source
A fast atmospheric radiative transfer program is used to calculate
the downwelling surface solar irradiance. The algorithm assumes a
solar constant of 1367 W/m2 at the mean Earth to Sun distance, and
from this determines the top-of-the-atmosphere instantaneous
insolation as a function of the instantaneous Earth to Sun
distance and the local solar zenith angle. Next the algorithm uses
input data from the ISCCP archive to define regional atmospheric
conditions and surface reflectivity, and calculates the surface
solar irradiance (Bishop and Rossow, 1991). This is done once
every three hours and then daily and monthly means are determined.
The Files
The Surface Solar Irradiances data set consists of 96 data files
(8 years of monthly means) x 259200 bytes per file, and requires
~25 MB of disk storage for the data files plus ~2 MB for the
accompanying GIF images.
Format
Data Files
* File Size: 259200 bytes, 64800 data values
* Data Format: IEEE floating point notation
* Headers, trailers, and delimiters: none
* Fill value: -999.99
* Continent mask: none (data valid over land and water)
* Orientation: North to South
Start position: (179.5W, 89.5N)
End position: (179.5E, 89.5S)
Image Files
* File Size: 20000-23000 bytes
* Data Format: Graphics Interchange Format (GIF)
* Image Orientation: North to South
Start position: (179.5W, 89.5N)
End position: (179.5E, 89.5S)
Name and Directory Information Naming Convention
The file naming convention for the monthly files is
isccp.srfrad.1nmegg.[yymm].ddd
where
isccp = data product designator (isccp)
srfrad = parameter(surface solar irradiance)
1 = number of levels
n = pressure levels for vertical coordinate, (n=not
applicable)
m = temporal period, (m = monthly)
e = horizontal grid resolution, (e = 1 x 1 degree)
gg = spatial coverage, gg = global (land and ocean)
yy = year
mm = month
ddd = file type designation, (bin=binary, ctl=GrADS control
file)
Directory Path
/data/inter_disc/radiation_clouds/solrad_sw/yyyy/
where yyyy is the year.
Companion Software
Several software packages have been made available on the CIDC
CD-ROM set. The Grid Analysis and Display System (GrADS) is an
interactive desktop tool that is currently in use worldwide for
the analysis and display of earth science data. GrADS meta-data
files (.ctl) have been supplied for each of the data sets. A GrADS
gui interface has been created for use with the CIDC data. See the
GrADS document for information on how to use the gui interface.
Decompression software for PC and Macintosh platforms have been
supplied for datasets which are compressed on the CIDC CD-ROM set.
For additional information on the decompression software see the
aareadme file in the directory:
software/decompression/
Sample programs in FORTRAN, C and IDL languages have also been
made available to read these data. You may also acquire this
software by accessing the software/read_cidc_sftwr directory on
each of the CIDC CD-ROMs
The Science
Theoretical Basis of Data
The incident total surface solar irradiance (insolation) is a
vital climate and agricultural parameter. The chief problem in
calculating it arises from the variable cloud cover. Bishop and
Rossow (1991) developed a fast radiative transfer program to
calculate the downwelling surface insolation. International
Satellite Cloud Climatology Project (ISCCP) C1 3-hourly products
are used as input. The original ISCCP world grid consists of
squares 30 km on a side. The visible (~0.6 micrometers) and
infrared (~11 micrometers) satellite measurements have footprints
about 4 to 8 km in diameter. To reduce data volume, ISCCP takes
only one measurement pair in a square for each 3-hour time period.
Mean cloud products are then calculated on a 280x280 km2 world
grid. These form the ISCCP C1 product. Monthly means are also
formed and called the C2 products (Rossow and Schiffer 1991;
Rossow and Garder 1993a&b and Rossow et al. 1993). The ISSCP C1
data was transformed to a 2.5x2.5 degree equal angle grid before
the surface solar irradiance was calculated.
Processing Sequence and Algorithms
The Version 2 algorithm's basic input data consists of 3-hourly
(2.5x2.5 degree) C1 parameters from the International Satellite
Cloud Climatology Project (ISCCP). The input from ISCCP data
include:
* Solar zenith angle (every 3 hr)
(Version 2 algorithm uses cosine of solar zenith angle
averaged over 3 hr)
* Ozone, total precipitable water, surface pressure (daily)
* Clear sky surface reflectance (every 3hr) {in versions 1 &2
the reflectance over the ocean was set to 0.06 to eliminate
any high ISCCP C1 surface reflectance values caused by sun
glint.}
* Cloud cover and optical thickness (every 3hr)
* Land-water fraction
* Snow and ice cover (every 5 days)
ISCCP cloud algorithm combines data from multiple geostationary
and polar orbiting meteorological satellites to provide a global
view of the occurrence and optical properties of clouds. The
algorithm adjusts the radiance measurements from the several
satellites to a common scale. The afternoon NOAA operational
Sun-synchronous satellites were used as calibration standards in
this step. For the period in question these were NOAA-7 (July 1,
1983 - January 31, 1985), NOAA-9 (February 1, 1985 - November 8,
1988) and NOAA-11 (October 18, 1988 - June 1991). Examination of
the Version 1 surface solar irradiance algorithm results showed
that there were calibration offsets at the joining points (see
also Klein and Hartmann, 1993). For this no correction was made in
the archived ISCCP C-Version cloud optical thicknesses. It has
been kept unchanged. However, to correct for this in Bishop's
Versions 2&3 the ISCCP cloud optical thickness (but not the cloud
fraction), was recalculated before being used. In this step ISCCP
C1 radiances were multiplied by 0.945 for the data spanning July
1983 to January 1985 (NOAA-7), unaltered for February 1985 to
October 1988 (NOAA-9), and multiplied by 1.119 for November 1988
to June 1991. These radiance adjustments are also being made in
the ISCCP Version D products where both the cloud amount and the
optical thickness are adjusted (Rossow et al., 1996). The major
adjustment comes in the optical thickness.
In version 2 algorithm of surface solar irradiance, for each
region there are two calculations of the surface solar irradiance
Q, one for the clear sky value Q(clr) and the other for Q(cld) in
the cloud covered portion. Formula 'f ' of Frouin et al. (1989) is
used to calculate Q(clr). It can be written in the form:
Q(clr) = (1-CF) f[S,d,mu,O3,H2O,Rs,Vis,Ps] W/m2 (1)
Here CF is the cloud fraction of the scene, S is the solar
constant taken as 1367 W/m2, d is the Earth to Sun distance, mu is
the cosine of solar zenith angle averaged over three hour period
in question, O3 is ozone, H2O is water vapor, Rs is the surface
reflectivity, Vis is the visibility and Ps is the surface
pressure. The visibility term accounts for atmospheric aerosols
and is assumed constant at 25 km. However it can be varied. In
algorithm Versions 1 & 2 the surface reflectivity is set to 0.06
over the ocean in order to prevent sun glint observations from
creeping into the calculation. In version 3 it is calculated over
ocean regions using theory from Cox and Munk (1956) and Morel and
Gentili (1991). Over land and ice the observed ISCCP value is
used.
The calculation for the cloud covered portion of the scene is:
Q(cld) = CF Q(dir) (1 - Az) (1 + AsRs) W/m2 (2)
Here Q(dir) is the direct solar flux to the cloud top. It is
Q(clr) evaluated with zero surface reflectance and zero cloud
fraction. A fraction of that flux is reflected back to space using
a cloud directional albedo, Az, which depends on the cloud optical
thickness and the solar zenith angle. The remaining flux passes
through the cloud and proceeds to the surface. Here a fraction,
Rs, is reflected upwards and some of this, AsRs, is reflected back
to the surface by the cloud base. The spherical cloud albedo, As,
is a function of the cloud optical thickness. The sum of Q(clr)
and Q(cld) yields the mean downwelling solar irradiance for the
region.
In Versions 2 & 3 of the algorithm a procedure is used to fill in
any gaps in the input data so that calculations can be made for
all daylight 3-hour periods (Bishop et al., 1994). The 3-hourly
values are then averaged to determine the mean daily and monthly
values.
In Version 3 the Photosynthetically Active irradiance (PAR,
400-700 nm) is added as a new product. More details on the
calculation can be found in Bishop and Rossow (1991) and Bishop et
al. (1994).
Resampling of original 2.5x2.5 degree gridded dataset to 1x1
degree grid
For consistency with the other data sets in the Goddard DAAC's
Interdisciplinary Data Collection, the original ISCCP Surface
Solar Irradiance data acquired from the NASA/GISS were reformatted
at the Goddard DAAC from the original integer values into 32-bit
floating point quantities (unscaled values) and regridded to 1 x 1
degree (dimension 360x180) from their original 2.5 x 2.5 degrees
(dimension 144x72). Their south to north orientation was reversed,
again for conformity to existing criteria, and gif images, created
from the resultant files, were visually inspected to assure that
the data was free of artifacts introduced by these procedures.
The following steps were performed in the regridding process:
1. Starting with the first latitude band in the original data
set (87.5N to 90N), the first pair of grid cells (total of 5
degrees in longitude) was partitioned into five cells each of
width 1 degree; cells 1 and 2 were assigned the value of the
first 2.5 degree cell, cells 4 and 5 the value of the second
2.5 degree cell, and cell 3 the arithmetic average of the
values of the first and second 2.5 degree cells.
2. In step 1, if either (but not both) of the original 2.5
degree cells is a fill value, then no average is performed
and cell 3 is assigned the value of the unfilled 2.5 degree
cell. If both of the original cells are fill values, then
cell 3 is likewise assigned this fill value.
3. Steps 1 and 2 were repeated for the remaining 71 pairs of 2.5
grid cells in the original data set
4. Steps 1 through 3 were performed for the remaining 71
latitude bands in the original data set to arrive at a
temporary array of size 360 x 72 (1 degree longitude by 2.5
degrees latitude)
5. The entire procedure above was repeated in the latitudinal
direction using the same grid cell partitioning scheme to
arrive at the final 360 x 180 (1 degree longitude by 1 degree
latitude) array.
6. The regridded data were visually examined to ensure
consistency with the original data.
Scientific Potential of Data
The surface solar irradiance is a basic climate parameter and is
useful in many studies. Some are:
* To study light limitations on the phytoplankton biomass in
the southern ocean (Mitchell et al., 1991)
* The effect of insolation variations on the sea surface
temperature (Seager and Blumenthal, 1994;Liu et al., 1994).
* The Bishop and Rossow insolation calculations (Bishop et al.,
1994) will be used in the Sea-viewing Wide Field-of-view
Sensor (SeaWiFS) project (Hooker and Esaias, 1993) to study
the biological productivity of the oceans.
Validation of Data
GISS has a full radiative transfer model (FRT) which calculates
both the long and short wave radiances both at the surface and in
the atmosphere (Rossow and Lacis, 1991). In this model the
atmosphere is divided into as many as 12 atmospheric layers, up to
eight in the troposphere and four in the stratosphere. All
radiatively significant atmospheric constituents are included and
the effects and vertical variations of atmospheric, aerosol and
cloud multiple scattering are taken into account. The atmospheric
radiative transfer problem is considerably simpler for short wave
than for long wave radiation. Hence Bishop and Rossow (1991)
developed a fast shortwave radiative transfer program to calculate
the downwelling solar radiation at the surface which they called
FAST. FAST runs 100 times faster than FRT. The FAST model
reproduced the detailed global results from full radiative
transfer model calculations to within 6 and 10 W/m2 over the ocean
and land respectively.
Several comparisons have also been made with ground observations.
The first ISCCP Regional Experiment/ Surface Radiation Budget
(FIRE/SRB) experiment was carried out in a 100 km by 100 km region
near (43 N, 89 W) between October 14 and November 2, 1986
(Whitlock et al., 1990). The surface solar irradiance ranged from
13 to 170 W/m2. For a 17 day period, where ground and ISCCP
derived irradiances were spatially and temporally coincident, they
showed an agreement of better than 9 W/m2 on a daily basis and
less than a 4% bias difference in the 17-day mean. This comparison
was done with the Version 1 algorithm but using the 30 km by 30 km
resolution CX data. The test occurred in a period for which the
cloud optical thickness does not change in versions 2 & 3.
A second series of tests was later carried out over the ocean. In
this test daily mean point buoy measurements were compared with
Version 2 C1(280 km x 280 km resolution) results. There were 5
tests which varied in length from 61 to 107 days in the years
1987, 1988 & 1991. Three tests were run for buoy data at (34N,
70W) and two for a buoy at (35-deg. 35.6 min. N, 20-deg. 57.9-min.
W) The observed differences include a strong component due to the
mismatch between the point resolution of the measurements and the
280 km resolution of the C1 data. The biases of the 5 data sets
combined, average +5 W/m2. The worst case, if attributable solely
to the Version 2 retrieved values, is less than 7% of irradiance
under clear sky conditions (Bishop et al., 1994).
Several investigators have calculated the surface insolation and
the surface radiation budget. Two other versions (Darnell et al.,
1992; Pinker and Laszlo, 1992) of the surface short wave radiation
are archived at the NASA Langley Research Center. For the eight
years considered here the full surface radiation budget (short and
long wave) is available from the Goddard Institute of Space
Studies (Zhang, et al., 1995; Rossow and Zhang, 1995) but only for
every third month. Gupta et al. (1992 &1993) have also calculated
the surface longwave radiation.
Contacts
Points of Contact
For information about or assistance in using any DAAC data,
contact
EOS Distributed Active Archive Center (DAAC)
Code 902
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
Internet: daacuso@daac.gsfc.nasa.gov
301-614-5224 (voice)
301-614-5268 (fax)
To inquire about or order the original ( ) data, contact
Dr. James K. B. Bishop
NASA Goddard Institute for Space Studies
2880 Broadway
New York, NY 10025 USA
Internet: cojkb@iO.giss.nasa.gov;
bishop@fireglo.seaoar.uvic.ca
References
Bishop, J. K. B., J. McLaren, Z. Garraffo, and W. B. Rossow, 1994:
Documentation and description of surface solar irradiance data
sets produced for SeaWiFS, A draft document dated (10/30/94), 23
pages, available on the internet at:
http://www.giss.nasa.gov/Data/SeaWiFS/
Bishop, J. K. B., and W. B. Rossow, 1991: Spatial and temporal
variability of global surface solar irradiance, J. Geophys. Res.,
96, 16,839-16,858.
Cox, C., and W. Munk, 1956: Slopes of the sea surface deduced from
photographs of sun glitter, Bull. Scripps Inst. Oceanogr., Univ.
Calif., 6, 401-488.
Darnell, W. L., W. F. Staylor, S. K. Gupta, N. A. Ritchey, and A.
C. Wilber, 1992: Seasonal variation of surface radiation budget
derived from International Satellite Cloud Climatology Project C1
data, J. Geophys. Res., 97, 15,741-15,760.
Frouin, R., D. W. Lingner, C. Gautier, K. S. Baker, and R. C.
Smith, 1989: A simple analytical formula to compute clear sky
total and photosynthetically available solar irradiance at the
ocean surface, J. Geophys. Res., 94, 9731-9742.
Gupta, S. K., W. L. Darnell, and A. C. Wilber, 1992: A
parameterization for longwave surface radiation from satellite
data: recent improvements, J. Appl. Meteorol., 31, 1361-1367.
Gupta, S. K., A. C. Wilber, W. L. Darnell, and J. T. Suttles,
1993: Longwave surface radiation over the globe from satellite
data: An error analysis, Int. J. Remote Sens., 14, 95-114.
Hooker, S. B., and W. E. Esaias, 1993: An over view of the Sea
WiFS project, EOS Transactions A.G.U.,74, 241 & 245. Klein, S. A.,
and D. L. Hartmann, 1993: Spurious changes in the ISCCP dataset,
Geophys. Res. Lett., 20, 455-458, 1993.
Klein, S. A., and D. L. Hartman, 1993: Spurious changes in the
ISCCP dataset, Geophys. Res. Lett., 20>, 455-458, 1993.
Liu, W. T., A. Zhang, and J. K. B. Bishop, 1994: Evaporation and
solar irradiance as regulators of sea surface temperature in
annual and interannual changes, J. Geophys. Res., 99,
12,623-12,637.
Pinker, R. T., and I. Laszlo, 1992: Modeling surface solar
irradiance for satellite applications on a global scale, J. Appl.
Meteorol., 31, 194-211.
Mitchell, B. G., E. A. Brody, O. Holm-Hansen, C. McClain, and J.
Bishop, 1991: Light limitation of phytoplankton biomass and
macronutrient utilization in the Southern Ocean, Limnol Oceanogr.,
36(8), 1,662-1,677.
Morel, A., and B. Gentili, 1991: Diffuse reflectance of oceanic
waters: its dependence on sun angle as influenced by the molecular
scattering contribution, Appl. Opt, 30, 4427-4438.
Rossow, W. B., and R. A. Schiffer, 1991: ISCCP cloud data
products, Bull. Amer. Meteor. Soc., 72, 2-20.
Rossow, W. B., and L. C. Garder, 1993a: Cloud detection using
satellite measurements of infrared and visible radiances for
ISCCP, J. Climate, 6, 2341-2369.
Rossow, W. B., and L. C. Garder, 1993b: Validation of ISCCP cloud
detections, J. Climate, 6, 2370-2393.
Rossow, W. B., A. W. Walker, and L. C. Garder, 1993: Comparison of
ISCCP and other cloud amounts, J. Climate, 6, 2394-2418.
Rossow, W. B., and Y.-C Zhang, 1995: Calculation of surface and
top of atmosphere radiative fluxes from physical quantities based
on ISCCP data sets: 2. Validation and first results, J. Geophys.
Res., 100, 1167-1197.
Rossow, W. B., A. W. Walker, D. E. Beuschel, and M. D. Roiter,
1996: International Satellite Cloud Climatology Project (ISCCP):
documentation of new cloud datasets, draft document dated January
1996, 115 pages, available on internet at :
http://isccp.giss.nasa.gov/documents.html
Seager, R., and M. Benno Blumenthal, 1994: Modeling tropical
Pacific sea surface temperature with Satellite-derived solar
radiative forcing, J. Climate, 7, 1943-1957.
Whitlock, C. H., et al., 1990: Comparison of surface radiation
budget satellite algorithms for downwelled shortwave irradiance
with Wisconsin FIRE/SRB surface-truth data, papers presented at
the Seventh Conference on atmospheric Radiation, Am. Meteorol.
Soc., San Francisco, July 23-27, 1990.
Zhang, Y.-C, W. B. Rossow, and A. A. Lacis, 1995: Calculation of
surface and top of atmosphere radiative fluxes from physical
quantities based on ISCCP data sets: 1. Method and sensitivity to
input data uncertainties, J. Geophys. Res., 100, 1149-1165.
------------------------------------------------------------------------
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