CIDC FTP Data
Surface Solar Irradiance CIDC Data on FTP

Data Access

Surface Solar Irradiance from NASA GISS
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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

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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

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

Image Files

Name and Directory Information Naming Convention

The file naming convention for the monthly files is

giss.srfrad.1nmegg.[yymm].ddd

where
giss = data product designator (giss)
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:

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:

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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