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[CIDC FTP Data]
[ISCCPC2 IDC Data on FTP]
Data Access
ISCCP C2 Cloud Data
Cloud fraction Cloud top pressure Cloud optical
thickness
Cloud top Clear sky surface Clear sky surface
temperature reflectance temperature
[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
Clouds play an important role in the climate change by affecting
the heat exchange between the Sun, Earth and atmosphere. Also,
they modulate the solar irradiance incident on the Earth's surface
(the insolation) and this affects the productivity of plants both
on land and in the water as well as the surface temperature and
heat budget. Numerous efforts to form cloud climatologies from
both surface and satellite observations have been made. At present
the most important of these is the ongoing International Satellite
Cloud Climatology Project (ISCCP), established in 1982 as part of
the World Climate Research Program (WCRP). A combination of
satellite-measured radiances, ice/snow cover dataset and TOVS
atmospheric temperature/humidity are used by ISCCP to produce a
global dataset on cloud and surface variables. Operational data
collection and processing for ISCCP have been underway since July
1983. An overview of the project and the data products is given in
Rossow and Schiffer (1991); the algorithm and its effectiveness
are described by Rossow and Garder (1993a&b) while Rossow et al.
(1993) compare the resulting products to other cloud
climatologies. The ISCCP C2-series data products, briefly
described here(more extensively in Rossow et al. (1996)), are
gridded data averaged over each month. These data (spanning over
the period July 1983 to June 1991) are originally produced on an
equal area map grids which has a constant 2.5 degree latitude
increments and varaiable longitude increments ranging from 2.5
degree at the equator to 120 degree at the pole The Goddard DAAC
has regridded these dataset to 1x1 degree equal angle grid for
inclusion in the Interdisciplinary data collection.
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 William B. Rossow, and the
Goddard Institute for Space Studies (GISS),New York, NY,
USA, for the production of this data set, and the
Distributed Active Archive Center (Code 902) at the
Goddard Space Flight Center, Greenbelt, MD, 20771, for
putting these data in their present format and
distributing them. These distribution activities were
sponsored by NASA's Earth Science enterprise.
Original Archive
The original ISCCP C2 cloud dataset was produced by the Goddard
Institute for Space Studies (GISS) at New York, NY. This data set
in its original format can be obtained from NASA Langley Research
Center, Distributed Active Archive Center. This is the long term
archive for the data and also the source for detailed information
concerning the ISCCP C-series and other data products.
Note: The format of the data in the GISS and LaRC archives is
different than that stored at the Goddard DAAC. The Goddard DAAC
regridded the original equal area grid to a 1 by 1 degree
(lat/lon) equal angle grid for only a subset of total parameters.
For more details see Processing Sequence and Algorithms.
Future Updates
Since the improved ISCCP cloud-products (series-D) are now being
produced at GISS, the production of C-product for data beyond June
1991 has stopped. However, additional years of the ISCCP D-2 data
are being processed at GISS and Goddard DAAC maintains a subset of
the D2 Cloud Data (regridded to 1x1 degree equal angle grid) as a
part of the other Interdisciplinary data collection products.
The Data
The ISCCP C2 monthly mean data presented here is on 1x1 degree
latitude-longitude world grid that starts at (89.5N, 179.5W) and
runs eastward and southward to latitude 89.5 S.
The original ISCCP C2 (monthly mean) and C1 (daily) products were
calculated on an approximately equal area world grid ( equivalent
to an area of a 2.5x2.5 degree latitude-longitude grid at the
equator). The latitude band widths were fixed to 2.5 degree and
grid size along the longitude was varied to provide an integer
number of cells in a latitude zone and grid cell area as close to
an equatorial grid cell as possible. Map grids started from south
pole to north pole. In each latitude zone, all longitudes were
indexed in order from the Greenwich meridian eastward(0 - 360
degree) before going to the next latitude zone. Here we have
interpolated a subset (6 out of the original 132 parameters) of
the equal-area monthly mean product to a 1x1 degree grid for easy
comparison to the other Interdisciplinary Data Collection
products.
Characteristics
* Parameters:
Parameter Description Range Units
cldfrc mean cloud fraction 0 - 100 percent
cldprs mean cloud top pressure 35 - 985 millibars
cldtau mean cloud optical 0.09 - dimensionless
thickness 119
cldtmp mean cloud top 190 - Kelvin
temperature 310
srfref mean clear sky surface 0 - 1 fraction
reflectance
srftmp mean clear sky surface 199 - Kelvin
temperature 325
* Temporal Coverage: July 1983 - June 1991
* Temporal Resolution: Gridded monthly means
* Spatial Coverage: Global
* Spatial Resolution: 1 degree x 1 degree equal angle grid
Source
ISCCP was established in 1982 as part of the World Climate
Research Programme (WCRP) to collect and analyze satellite
radiance measurements to infer the global distribution of clouds,
their properties, and their diurnal, seasonal, and interannual
variations.
The first phase of the project produced the gridded, 3-hourly
(stage C1) and monthly (stage C2) datasets (Rossow, and Schiffer
1991, Rossow et al. 1989). A subset of the monthly mean C2 data,
consisting of six parameters and covering the period of July 1983
to June 1991 (regridded and reformated), is available as part of
the Interdesciplinary Dataset Collection.
There are four principle product levels:
* Reduced Resolution Radiance Data(B3)
These data are a reduced resolution version (in both time and
space) of the original visible and infrared images from all
of the operational weather satellites. The data consist of
radiances (4-7 km pixels) spaced at 30 km interval, every 3
hours, from the individual satellites. The calibration and
navigation data are also appended (Rossow et al., 1987). When
the D algorithms were introduced, a new (BT) calibration
table product was also added.
* Pixel Level Cloud Product(CX)
These products consist of calibrated radiances and viewing
geometry, cloud detection results, cloud and surface
properties from radiative analysis for individual satellite
at a 30 km resolution.
* Gridded Cloud Product(C1)
These are spatial averages of the 3-hourly CX quantities and
statistical summaries on a global equal area grid (
approximate 280 km by 280 km cell size). These products are
obtained by merging the results from all satellites. The
atmosphere and surface properties from TOVS are appended as
well.
* Climatological Summary Product(C2)
The C2 products are monthly averages of C1 quantities and
statistics including the data sets corresponding to eight
3-hourly monthly means( periods centered on, 0, 3, 6, 9, 12,
15, 18, and 21 hours UTC) for each product at equal area
grid. There are a total of 132 parameters for each map grid
cells in the original C2 data set. We have chosen 6 of these
and only the monthly means (average of the eight 3-hour
monthly mean sets) to include in the Interdisciplinary Data
Collection.
The resulting datasets and analysis products are being used to
improve understanding and modeling of the role of clouds in
climate, with the primary focus being the elucidation of the
effects of clouds on the radiation balance. These data can also
used to support many other cloud studies, including understanding
of the hydrological cycle.
Data are collected from the suite of weather satellites operated
by several nations and processed by several groups in government
agencies, laboratories, and universities. For each operational
satellite, a Satellite Processing Center (SPC) collects the raw
satellite data and sends it to the Global Processing Center (GPC).
The Correlative Data Center coordinates the delivery of other
satellite and conventional weather data to the GPC. The Satellite
Calibration Center (SCC) normalizes the calibration of the
geostationary satellites with respect to a polar orbiter satellite
standard. All ISCCP data products are archived at the NASA Langley
Research Center, Distributed Active Archive Center.
The satellites involved in the C-version products are listed in
the table below:
>
Temporal and Regional Coverage
Satellite Sensor C1 start C1 end Longitudes
NOAA-7 AVHRR 07/01/83 01/31/85 global (1)
NOAA-8 AVHRR 10/01/83 06/24/84 global
NOAA-9 AVHRR 02/01/85 11/08/88 global
NOAA-10 AVHRR 11/17/86 08/30/91 global
NOAA-11 AVHRR 10/18/88 6/30/91 global
GOES-5 VISSR 07/01/83 07/30/84 15W-135W
GOES-6 VISSR 07/01/83 01/21/89 75W-165E (2)
GOES-7 VISSR 04/26/87 6/30/91 15W-135W (3)
METEOSAT-2 MIR 07/01/83 08/11/88 60W-60E
METEOSAT-3 MIR 08/11/88 01/25/91 60W-60E (4)
METEOSAT-4 MIR 06/19/89 06/30/91 60W-60E
GMS-1 VISSR 01/21/84 06/30/84 160W-80E
GMS-2 VISSR 07/01/83 09/27/84 160W-80E
GMS-3 VISSR 09/27/84 12/04/89 160W-80E
GMS-4 VISSR 12/04/89 06/30/91 160W-60E
Notes: NOAA-7, 9 & 11 were afternoon satellites, while NOAA 8 & 10
were morning satellites.
1. Global coverage required 24 hours.
2. For better coverage of seasonal weather events, GOES-6 was
moved to 98W on August 30, 1984, to 108W on November 22,
1984, back to 98W on July 28, 1986, and to 135W from April
1987 until its failure on 1/21/89.
3. For better coverage of seasonal weather events, GOES-7 is
positioned between 98W and 108W, with a position of 98W
during the tropical convective season.
4. METEOSAT-3 was positioned to 50W longitude in early August
1991 to supplement the coverage of GOES-7. This move was
necessary in order to provide coverage of Atlantic weather
events during the absence of a GOES East Satellite.
The Files
The ISCCP subset presented here consists of 576 datafiles (96
monthly mean data filess per parameter x 6 parameters). Though
size of single data file is only .259 MB but if whole eight years
worth of data is downloaded it would require ~150 MB of disk
storage.
Format
* 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)
Name and Directory Information
Naming Convention:
The file naming convention for the monthly files is
isccp_c2.pppppp.1nmegg.[yymm].ddd
where
isccp = data product designator(isccp_c2)
pppppp = parameters(cldfrc,cldtmp,cldprs,cldtau,srftmp,srfref
1 = number of levels(=1)
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/isccp_c2/pppppp/yyyy/
where pppppp is the parameter and yyyy is 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 ISCCP cloud algorithm starts with independent visible and
infrared estimates as to whether a region is clear, cloud covered
or on the border and therefore uncertain. The two estimates are
then merged to make a final clear or cloudy judgment. At night
only the infrared algorithm can be used. Key features of the cloud
detection algorithm are
* use of space and time radiance variation tests over several
different space and time domains to account for the global
variety of cloudy and clear characteristics
* estimation of clear radiance values for every time and place,
and
* use of radiance thresholds that vary with type of surface and
climate regime, (Rossow and Garder, 1993a).
The ISCCP products include the infrared estimates for both day and
night observations but the bispectral products and the cloud
optical thickness estimate are available only during the day. The
bispectral algorithm is more accurate. Therefore a correction is
made to the infrared only nighttime cloud products when the mean
diurnal total cloud fraction is calculated. The correction is
determined from a comparison of daytime bispectral and infrared
only cloud fractions. The ISCCP products include low, mid, and
high altitude cloud fractions, and several daytime cloud types
based on cloud height and brightness. It also includes the 3-hour
as well as the diurnal means. Here we include only the C2 monthly
mean diurnal cloud fraction and optical thickness together with
the cloud top temperature and pressure. The mean clear sky
reflectance and skin temperature are also included.
Processing Sequence and Algorithms
ISCCP collects visible (~0.6 micrometer)and infrared (~11
micrometers) data from several geostationary weather satellites
and from the National Oceanic and Atmospheric Administration
(NOAA) operational meteorological satellites which are in
Sun-synchronous near polar orbits. The data collection started
with July 1, 1983 and is still continuing. The geostationary
satellites on a three hourly basis monitor the Earth from 60 N to
60 S latitude and each covers 120 degrees of longitude. Those
involved are the GOES 5-7, METEOSAT 2-5, GMS 1-4, and the INSAT
series. Ideally these would have given full global coverage from
60 N to 60 S, but due to numerous problems 3-hourly coverage is
not always available in some regions. This is particularly true
around India. The NOAA 7,9 & 11 satellites each observe all
regions on the Earth at least twice a day. Normally there are two
operating at any one time, one crosses the Equator about 7:30 AM &
PM local time and the other crosses in the early afternoon and
morning. The Polar regions are viewed several times a day. The
project used the afternoon satellites, NOAA 7,9&11, as calibration
standards to ensure a uniform calibration among the numerous
satellites used. The original C-version algorithms (Rossow and
Garder, 1993a) were used to produce cloud products for the period
(July 1983-June 1991). The current version of the ISCCP C2-series
was released in 1991. Since then the C-series data has gone
through an extensive review and a number of improvements have been
recommended. The D-series data was developed as a result of this
process. Validation of the products and comparison with other
cloud climatologies are given by Rossow and Garder (1993b) and
Rossow et al. (1993). Some improvements both in the calibration
corrections and in the cloud algorithms have been made and a new
D-series of cloud products are now being produced (Rossow et al.,
1995). Eventually the D-series products will cover the entire
period July 1, 1983 to June 2000.
Rergridding from an equal area world grid to 1 x 1 degree equal
angle grid
For consistency with the other data sets in the Goddard DAAC's
Interdisciplinary Data Collection, the original ISCCP C2 data for
a subset of parameters were extracted from the ISCCP anonymous FTP
site and reformatted at the Goddard DAAC from the original 8 bit
quantities (scaled integer values) into 32-bit floating point
quantities (unscaled values) and regridded to 1 x 1 degree equal
angle grid from their original approximate 280 km x 280 km equal
area grid maps.
In the regridding process the original data at equal area grid
with constant 2.5 degree latitudinal increments and variable
longitudinal increments, ranging from 2.5 degree at the equator to
120 degree at the pole were replicated as many time as needed to
produce a 1 by 1 degree latitude-longitude equal angle product. A
weighted average was used in cases where two equal area grid cells
overlapped a single one degree grid cell. This weighting was based
on the percent area each original equal area grid cells covered in
the 1 degree area. Changes in grid area due to changing latitude
were taken into consideration in this procedure. This regridding
method is different from the one used by ISCCP to convert their
data from approximate 280 km x 280km equal area to 2.5 by 2.5
degree equal angle. Their method did not use a weighted average in
cases where grid cells overlapped, but instead chose one of the
grid cell values over another. As a result the values from the
statistical files in the original dataset can not be related to
all of the grid values in this regridded dataset.
Also, the south to north orientation was reversed, and for each
latitude zone, data along the longitude was made to start from 180
west going towards east,again for conformity to the 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.
Scientific Potential of Data
The monthly mean summary of the data set given here can be used
for many types of climate studies including:
* Study of global, seasonal, and interannual cloud variability
(Rossow et al., 1993)
* Correlation with other climate parameters (Kyle et al., 1995)
* Investigation of global energy transport (Sohn and Smith,
1992).
Validation of Data
The validation of the data is discussed in some detail in Rossow
and Garder 1993b with some additional details given in Rossow and
Garder (1993a) and Rossow et al. (1993). The following summary of
error estimates is given in Table 1 in Rossow et al. (1993):
Summary of error estimates
Surface Temperature - open water <2 K
Surface Temperature - land 4 K
Surface Temperature - sea ice 4 K
Surface Reflectance - open water 3%(except in glint
regions)
Surface Reflectance - snow-free
land 3%-5%
Surface Reflectance - snow cover 10%
Surface Reflectance - sea ice 10%
Cloud amount <10%
ISCCP new product( D-series) was produced in part as a result of
intensive research done on the C-series data, in which over 200
research articles have been written.
Similar research is continuing with the D-series product and
includes comparison of observations from an on-going series of
field experiments. Rossow et al. (1996) discuss the differences
between the ISCCP C series and D series algorithms, as well as
on-going validation efforts being made on the D-series product.
The ISCCP project has documented known and fixed data errors in
their dataset.
Contacts
Points of Contact
For information about or assistance in using any DAAC data,
contact
EOS Goddard Distributed Active Archive Center (DAAC)
Code 902
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
e-mail: daacuso@daac.gsfc.nasa.gov
301-614-5224 (voice)
301-614-5268 (fax)
For questions about ISCCP science, contact
Dr. William B. Rossow
NASA Goddard Institute for Space Studies
2880 Broadway
New York, NY 10025 USA
e-mail: clwbr@giss.nasa.gov
(212) 678-5567
The long term archives for the ISCCP data products are at:
(Not including the Stage CX 30 km resolution data)
ISCCP Central Archives
National Climatic Data Center
Federal Building 151 Patton Ave.
Asheville, NC 28801-5001
email: satorder@ncdc.noaa.gov
(704) 271-4800 (option #5) (voice)
(704) 271-4876
(Including the Stage CX 30 km resolution data)
Langley DAAC
Mail Stop 157B
NASA Langley Research Center
Hampton, VA 23681-0001
e-mail: userserv@eosdis.larc.nasa.gov
telnet eosdis.larc.nasa.gov
(804) 864-8656 (voice)
(804) 864-9807 (fax)
References
Brest, C.L., and W.B. Rossow, 1992. Radiometric calibration and
monitoring of NOAA AVHRR data for ISCCP. Int. J. Remote Sens.,
13:235-273.
Brest, C.L., W.B. Rossow, and M.D. Roiter, 1996. Update on ISCCP
calibration for visible and infrared radiances. J. Atmos. Ocean.
Tech., (submitted).
Kyle, H. L., M. Weiss, and P. Ardanuy, 1995. Cloud, surface
temperature, and outgoing longwave radiation for the period from
1979 to 1990, J. Climate, 8:2644-2658.
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
detection, J. Climate, 6: 2370-2393.
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., E. Kinsella, A. Wolf, and L. Garder, 1987.
International satellite Cloud Climatology Project (ISCCP)
Description of Reduced Resolution Radiance Data. In, WMO/TD No.
58, (eds), World Meteorological Organization, Geneva, 143 pp.
Rossow, W.B., L.C. Garder, and A.A. Lacis, 1989. Global seasonal
cloud variations from satellite radiance measurements. Part I:
Sensitivity of Analysis. J. Climate, 2:419-458.
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., A. W. Walker, D. E. Beuschel, and M. D. Roiter,
1996. International Satellite Cloud Climatology Project (ISCCP):
documentation of new cloud datasets, 115 pages, available on
internet at : http://isccp.giss.nasa.gov/documents.html
Sohn, B. J., and E. A. Smith, 1992. Global energy transports and
the influence of cloud on transport requirements: A satellite
analyses, J. Climate, 5:717-734.
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Page Author: Page Author: H. Lee Kyle -- lkyle@daac.gsfc.nasa.gov
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