The International Satellite Cloud Climatology Project (ISCCP) uses a combination of polar orbiting and geostationary satellites in order to get a three-hourly diurnal sampling. ISCCP has recently released a new dataset (Young et al., 2018, Rossow et al., 2021), with a better spatial sampling (10 km instead of 30 km) and more up-to-date ancillary products (topography and land-water mask, ozone, sea ice and snow cover, atmospheric temperature-humidity profiles). Nighttime cloud properties are adjusted, based on the daytime differences between VIS/IR and IR-only results and interpolation of the VIS retrievals over the nighttime. The ISCCP products are available in several forms, all in NetCDF except for HXS (binary format, image pixel-level separate by satellite, 3 hr, 10 km): HXG (global gridded at 3 hr, 10 km, pixel-level), HGS (gridded separate by satellite, 3 hr, 100 km), HGG (merger of HGS, global gridded at 3 hr, 100 km), HGH (monthly average of HGG for eight times per day at 100 km), HGM (average of HGH at 100 km), plus Ancillary Products used in the rertrieval.
The version of ISCCP-H provided for this assessment is not the standard version as the monthly averages at four specific local times have been built from the ISCCP-HGG data, at 1° spatial resolution, given at eight specific universal times per day in such a way that the results of the two closest times were averaged. In the polar regions during periods without sunlight, only the IR-based results are available in the full ISCCP products, but in the GEWEX database, the height-stratified cloud amounts from VIS/IR analysis are not reported. Furthermore, only the 2-dimensional COD-CP and CEM-CP histograms are constructed from the initial 10 km pixels, while the 1-dimensional histograms are constructed from the 1° averages.
Summary of changes D-to-H-version
Based on all these results, especially the GEWEX Assessment, the following changes in the ISCCP cloud retrieval were made to produce the H-Version: (1) liquid water clouds are now identified by top temperatures ³ 253 K and assumed to be composed of a distribution of droplets with 13 microns average effective radius over land and 15 microns average effective radius over ocean, (2) ice clouds are identified by top temperatures < 253 K and assumed to be composed of crystals with 27 microns average effective radius for optical thicknesses < 3.5 and 34 microns average effective radius for clouds for optical thicknesses ³ 3.5 (this division by optical thickness produces about the right proportion of each type seen in the results and makes microphysical sense, cf. Khvorostyanov and Curry 2014), (3) although these ice crystal properties are used to calculate cloud water paths, the variation of visible reflectivity with viewing-illumination geometry is assumed to follow an empirical model derived from POLDER results (Baran and Labonnote 2007), (4) the cloud layers now have an explicit physical thicknesses, including gas, of 100 mb near the surface increasing linearly to 200 mb at the tropopause, and (5) the availability of a global product quantifying the optical properties of stratospheric and tropospheric aerosol over time was exploited to account for aerosol scattering-absorption in the cloud and surface property retrievals.
Other changes made for the H-Version are:
(1) switching the radiance dataset from B3 (30 km sampling) to B1 (10 km sampling) and mapping results in a 1.0-degree-equivalent equal-area grid,
(2) refining the VIS radiance calibration (Rossow and Ferrier 2015) – also slightly adjusting the IR calibration for AVHRRs on NOAA-14 to NOAA-19,
(3) accounting for aerosol scattering/absorption using a new global product providing tropospheric and stratospheric aerosol optical properties (Kinne et al. 2013),
(4) specifying ozone absorption coefficients specific to each imaging instrument’s spectral response,
(5) accounting for variations of land surface infrared emissivity to retrieve physical surface temperatures,
(6) altering cloud detection categories in nighttime conditions over snow and ice to reflect the results from the comparisons to SHEBA and CALIPSO observations, and
(7) replacing all of the ancillary products (topography and land-water mask, ozone, sea ice and snow cover, atmospheric temperature-humidity profiles) with more up-to-date and homogeneous products based on ones that are being produced in a (nearly) operational mode. As in previous versions, the separate sea ice and snow cover products are merged into a single product (land-water masks reconciled). The new version of the atmospheric temperature-humidity profile product explicitly represents the diurnal variations of temperature in the lower atmosphere over land areas and the occurrence of near-surface temperature inversions over the polar and some nighttime desert regions.
The Level 2 (pixel-level) results are released both as HXS data (separate by satellite like DX data) and new HXG data (globally merged on an equal-angle 0.1 degree map grid). The gridded results separately for each satellite every 3 hours are released as HGS data (like unreleased DS data). The globally merged product every 3 hours is called HGG (like D1 data), the monthly averaged results at each of eight times daily are called HGH, and the total monthly averaged results are called HGM (like D2 data). In the H-Version, an interpolation over the time steps and locations where data are missing is performed directly in the 3-hourly HGG maps, including adjustments of nighttime results based on the daytime differences between VIS/IR and IR-only results, and interpolation of the VIS retrievals over the nighttime.
References
Rossow WB (2017) Climate Data Record (CDR) Program Climate Algorithm Theoretical Basis Document of International Satellite Cloud Climatology Project (ISCCP) Cloud Properties. CDRP-ATBD-0872, available at: https://www.ncei.noaa.gov/pub/data/sds/cdr/CDRs/Cloud_Properties-ISCCP/AlgorithmDescription_01B-29.pdf
Rossow WB, Knapp KR, Young AH (2022) International Satellite Cloud Climatology Project: Extending the record. J Climate 35:141-158. https://doi.org/10.1175/jcli-d-21-0157.1
Young AH, Knapp RK, Inamdar A, Hankins W, Rossow WB (2018) The International Cloud Climatology Project H-Series climate data record product. Earth Syst Sci Data 10:583–593. https://doi.org/10.5194/essd-10-583-2018
Zhang Y, Rossow WB (2023) Global Radiative Flux Profile Data Set: Revised and Extended, J Geophys Res Atmos 128:e2022JD037340. https://doi.org/10.1029/2022JD037340
Distribution of L2 and L3 datasets
The official ISCCP archives reside at NOAA/NESDIS/NCDC.
https://www.ncei.noaa.gov/products/climate-data-records/cloud-properties-isccp