|
CERES Terra Beta3 SYN/AVG/ZAVG |
Investigation: CERES
Data Product: Synoptic Radiative Fluxes and Clouds (SYN), Monthly Regional Radiative Fluxes and Clouds (AVG), Monthly Zonal and Global Radiative Fluxes and Clouds (ZAVG)
Data Set: Terra
Data Set Version: Beta3 These data products are NOT regarded as publishable and will not be maintained in the archives.
The purpose of this document is to inform users of the accuracy of this data product as determined by the CERES Science Team. The document summarizes user applied revisions (e.g. Rev1), key validation results, provides cautions where users might easily misinterpret the data, provides links to further information about the data product, algorithms, and accuracy, and gives information about planned data improvements. This document also automates registration in order to keep users informed of new validation results, cautions, or improved data sets as they become available.
User applied revisions are a method CERES uses to identify improvements to existing archived data products that are simple for users to implement, and allow correction of data products that would not be possible in the archived versions until the next major reprocessing 1 to 2 years in the future. All revisions applicable to this data set are noted in the section User Applied Revisions to Current Edition.
This document is a high-level summary and represents the minimum information needed by scientific users of this data product.
The Synoptic Radiative Fluxes and Clouds (SYN), Monthly Regional Radiative Fluxes and Clouds (AVG), Monthly Zonal and Global Radiative Fluxes and Clouds (ZAVG) archival data product contains 3-hourly (SYN), monthly regional mean (AVG), and monthly zonal & global mean (ZAVG) surface and atmospheric Langley Fu-Liou radiative transfer modeled fluxes consistent with CERES observed fluxes. The SYN/AVG/ZAVG fluxes and cloud properties can be compared directly with climate models results at either the 3-hourly or monthly level. The SYN 3-hourly fluxes are GMT based and the daily fluxes can be obtained by taking the mean of 8 3-hourly-fluxes and the monthly flux is derived from the mean of the daily fluxes. Also, monthly 3-hourly fluxes are provided on the regional, zonal and global levels.
The profile and surface fluxes are obtained from Langley Fu-Liou radiative transfer code using merged CERES (MODIS derived) and 3-hourly geostationary cloud properties, which have been temporally interpolated using the same algorithm as in the CERES-SRBAVG-GEO product. Other input datasets include GEOS4 meteorological data, SMOBA ozone, MODIS MOD04 and MATCH aerosols, apriori ocean spectral albedos, and satellite retrieved broadband surface albedos over land and snow using apriori surface spectral characteristics. The fluxes are derived hourly for pristine (clear-sky no aerosol), clear-sky, all-sky no-aerosol, and all-sky conditions. The radiative transfer fluxes are first computed with the initial input and labeled as “untuned” and then recomputed as “tuned” fluxes, which are partially constrained to CERES TOA observations by slightly changing the initial input, in order to achieve consistent flux and cloud property dataset. The constrainment adjustments to the GEOS4 and cloud properties are also provided. The product also contains UVA, UVB and PAR fluxes. The SYN data product is released by the CERES Surface and Atmosphere Radiation Budget (SARB) working group and the algorithm is similar to the CERES Clouds and Radiative Swath (CRS) data product except for the inclusion of GEO fluxes and cloud properties. Further information can be read in the CERES CRS Data Quality Summary.
CERES data input to the SYN/AVG/ZAVG subsystem is the CERES FSW product and concurrent diurnal data from geostationary satellites. The CERES FSW product contains the instantaneous gridded SSF and CRS archival data product. The 3-hourly geostationary derived fluxes have been normalized with CERES fluxes. The geostationary two-channel cloud property retrieval is a subset of the CERES code. The geostationary dataset provides temporal sampling between CERES measurements. This technique represents a major advancement in the reduction of temporal sampling errors (Young et al. 1998). Both observed and interpolated cloud properties and TOA fluxes are used to provide hourly GMT input to the radiative transfer model. The SYN/AVG/ZAVG is processed only for one CERES instrument, usually the instrument in cross-track mode, which provides uniform footprint spatial sampling.
The purpose of User Applied Revisions is to provide the scientific community early access to algorithm improvements, which will be included in future Editions of the CERES data products. The intent is to provide users simple algorithms along with a description of how and why they should be applied in order to capture the most significant improvements prior to their introduction in the production-processing environment. It is left to the user to apply a revision to data ordered from the Atmospheric Science Data Center. Note: Users should never apply more than one revision. Revisions are independent and the latest, most recent revision to a data set includes all of the identified adjustments.
The CERES Science Team has approved a table of scaling factors, which users should apply to the Beta3 SYN/AVG/ZAVG parameters.
For the CERES observed SYN/AVG/ZAVG TOA SW Fluxes (Up), users should utilize the following equation:
The SYN/AVG/ZAVG1 TOA SW Fluxes (Up) are listed below:
| SYN TOA SW Observed Flux | SYN SDS Index |
|---|---|
| SW TOA Total-Sky | 6 |
| SW TOA Clear-sky | 9 |
| AVG TOA SW observed Flux | AVG SDS Index |
|---|---|
| SW TOA Total-Sky | 6, 226 |
| SW TOA Clear-sky | 9, 229 |
| ZAVG TOA SW Observed Flux | ZAVG SDS Index |
|---|---|
| SW TOA Total-Sky | 1, 210, 419, 628 |
| SW TOA Clear-sky | 4, 213, 422, 631 |
The untuned fluxes do not require any Rev1 corrections since they are strictly modeled results. However, the tuned fluxes, which are partially constrained by the TOA CERES fluxes, did not have the Rev1 corrections applied before the tuning process. Users should be aware of this inconsistency before comparing SYN/AVG/ZAVG with other CERES fluxes from ERBE-like, SRBAVG-nonGEO or SRBAVG-GEO products. For the downwelling profile fluxes no correction should be applied. It is uncertain how this correction would affect the SW upwelling atmospheric and surface fluxes.
This revision is necessary to account for spectral darkening of the transmissive optics on the CERES SW channels. By June 2005, this darkening has reduced the average global all-sky SW flux measurements by 1.1 and 1.8 percent for Terra FM1 and FM2 data respectively. A complete description of the physics of this darkening appears in the CERES BDS Quality Summaries under the Expected Reprocessing section. After application of this revision to the Beta3 SYN/AVG/ZAVG data set, users should refer to the data as Terra Beta3-Rev1 SYN/AVG/ZAVG.
The CERES Science Team notes several cautions regarding the use of CERES Terra Beta3 SYN/AVG/ZAVG data:
There was an error associated in the TOA pristine correction in the Fu-Liou 2-stream algorithm to the higher order COART (8-stream) model and does not contain valid data. The data should have been written out as default values but instead were written out as 0.
Aerosol inputs from MODO4 were interpolated when no retrieval was available. This prevented the SARB subsystem from keying on missing AOT values to bring in daily MATCH AOT assimilation. Large AOT values for MOD04 nearing cloudy time periods caused unrealistically large aerosol forcing values to be computed.
Retrievals of Land, snow and sea-ice surface albedo are not of best quality at non-Terra overpass times, especially at low sun, since TOA clear sky used for surface albedo retrieval is then based on monthly averaged diurnally modeled TOA flux at non-Terra overpass times.
Surface albedo for the cloudy sky portion of the grid box calculation is not moved to the diffuse angle if a clear-sky TOA based retrieval of surface albedo over land or snow is made. This is not a problem for ocean or totally overcast gridboxes.
The GMT-hourly modeled fluxes were computed at the GMT half-hour (0:30) and at the center of the 1° gridbox. The modeled SW fluxes should have been computed for a temporally and spatially integrated solar flux for a particular GMT and region. This may bias the SW fluxes, especially near the terminator and at the global level. Also, the twilight correction that was applied to the SRBVG SW fluxes was not applied to SYN fluxes to account for SW flux for insolation from solar zenith angles greater than 90°. In general, the correction is < 0.5 Wm-2 and the global mean correction is 0.2 Wm-2 (Kato and Loeb 2003). The computation of the solar zenith angle assumed a spherical instead of an oblate spheroid Earth; this could cause a global SW error of up to 0.4 Wm-2. The SYN/AVG/ZAVG modeled computed fluxes are based on a spectral solar flux 1365.04 Wm-2, instead of the CERES reference insolation of 1365 Wm-2.
The SYN/AVG/ZAVG cloud properties differ slightly from the SRBAVG2 (MODIS and GEO clouds) product. The GEO nighttime single-channel IR-only cloud algorithm computes cloud fraction, pressure, temperature and phase. The GEO daytime visible and IR algorithm includes cloud optical depth, emissivity, top and base pressure. The GEO cloud algorithm does not retrieve cloud liquid and ice water path, and particle size. Usually cloud properties are linearly interpolated between cloudy measurements and extrapolated when no cloud information is measured independently for 4 cloud layers based on pressure. However, if there is no MODIS measured particle size or water path for a measured GEO cloud condition, the liquid and ice particle size is assumed to be 10µm and 60µm respectively. For consistency, the water path is recomputed from the optical depth and assumed particle size.
More than 99.5% of all 1-hourly input to the model are consistent in both flux and cloud properties, each parameter being interpolated independently. However for 0.5% of the input cases the modeled fluxes could not be computed. Most of these occur near the terminator, where no CERES SW measurements are available for the month. Rarely, a cloud top may be below the bottom. The total number of modeled flux calculations is available in the "number of observed, untuned, and tuned, for LW and SW hourboxes".
The CERES observed SW and LW clear-sky fluxes are in error, due to a coding mistake. This did not affect the modeled fluxes, but the observed clear-sky SW and LW fluxes should be taken from the SRBAVG dataset.
The adjusted cloud properties (effective temperature, fractional area and visible optical depth) have been miscalculated and should not be used. These are located under the constrainment adjustments HDF vgroup.
The primary goal of the SYN/AVG/ZAVG product is to provide climate quality monthly mean radiative transfer fluxes consistent with the CERES observed fluxes and cloud properties. Users should consult the SSF Data Quality Summary for the accuracy associated with CERES TOA fluxes and cloud properties. The validations of the Langley Fu-Liou radiative transfer modeled fluxes are available in the CRS Data Quality Summary. Validation of the geostationary flux and cloud properties are noted in the SRBAVG Data Quality Summary.
Future validation efforts will focus on consistency of monthly mean regional and global tuned and untuned fluxes with other CERES products such as ERBE-like, SRBAVG nonGEO, SRBAVG-GEO product TOA fluxes over a 5-year time period. Comparison of SYN/AVG/ZAVG surface fluxes with ground observations will be performed. The Data Quality Summary will be updated as these become available.
An overview of the Langley-Fu-Liou radiative transfer algorithm and temporal interpolation algorithms used in CERES can be found in the following references:
Clough, S.A., F.X. Kneizys, and R.W.Davies, 1989: Line shape and the water vapor continuum. Atmos. Res., Vol. 23, 229-241.
d'Almeida, G. A., P. Koepke, and E. P. Shettle, 1991: Atmospheric aerosols - global climatology and radiative characteristics. A. Deepak Publishing, Hampton, Va, 561 pp.
Fu, Q., G. Lesins, J. Higgins, T. Charlock, P. Chylek, and J. Michalsky, 1998: Broadband water vapor absorption of solar radiation tested using ARM data. Geophys. Res. Lett., 25, 1169-1172.
Fu, Q., and K.-N. Liou, 1993: Parameterization of the radiative properties of cirrus clouds. J. Atmos. Sci., 50, 2008-2025.
Fu, Q., and K.-N. Liou, 1992: On the correlated k-distribution method for radiative transfer in nonhomogenous atmospheres. J. Atmos. Sci., 49, 2139-2156.
Fu, Q., K. Liou, M. Cribb, T. Charlock, and A Grossman, 1997: On multiple scattering in thermal infrared radiative transfer. J. Atmos. Sci., 54, 2799-2812.
Fu, Q., W.B. Sun, and P. Yang, 1999: Modeling of scattering and absorption by nonspherical cirrus ice particles at thermal infrared wavelengths. J.Atmos. Sci., 56, 2937-2947.
Hess, M., P. Koepke, and I. Schult, 1998: Optical Properties of Aerosols and Clouds: The software package OPAC. Bull. Amer. Meteor. Soc., 79, 831-844.
Kato, S., T. P. Ackerman, J. H. Mather, and E. E. Clothiaux, 1999: The k-distribution method and correlated-k approximation for a Shortwave Radiative Transfer Model, J. Quant. Spectrosc. Radiat. Transfer, 62, 109-121. Charlock, T. P., and T. L. Alberta, 1996: The CERES/ARM/GEWEX Experiment (CAGEX) for the retrieval of radiative fluxes with satellite data. Bull. Amer. Meteor. Soc., 77, 2673-2683.
Kato, S., and N. G. Loeb, 2003: Twilight irradiance reflected by the earth estimated from Clouds and the Earth's Radiant Energy System (CERES) measurements, J. Climate, 16, 2646-2650.
Kato, S., and F. G. Rose, and T. P. Charlock, 2004: Computation of Domain-averaged Irradiance Using Satellite-derived Cloud Properties, J. Atmos. Oceanic Technol., in press.
Kratz, D. P., and F. G. Rose, 1999: Accounting for molecular absorption within the spectral range of the CERES window channel. J. Quant. Spectrosc. Radiat. Transfer, 48, 83-95.
Loeb, N.G., K. Loukachine, N. Manalo-Smith, B.A. Wielicki, and D.F. Young, 2003: Angular Distribution Models for Top-of-Atmosphere Radiative Flux Estimation from the Clouds and the Earth's Radiant Energy System Instrument on the Tropical Rainfall Measuring Mission Satellite. Part II: Validation, J. Appl. Meteor., 42, 1748-1769.
Rose, F. G., and T. P. Charlock, 2002: New Fu-Liou Code Tested with ARM Raman Lidar and CERES in pre-CALIPSO Exercise. Extended abstract for 11th Conference on Atmospheric Radiation (AMS), 3-7 June 2002 in Ogden, Utah.
Tegen, I., and A. A. Lacis, 1996: Modeling of particle size distribution and its influence on the radiative properties of mineral dust aerosol. J.Geophy. Res., 101, 19237-19244.
Young, D. F., P. Minnis. D. R. Doelling, G. G. Gibson, and T. Wong, 1998: Temporal Interpolation Methods for the Clouds and Earth's Radiant Energy System (CERES) Experiment. J. Appl. Meteorol., 37, 572-590.
A publishable, "Edition" version of the CERES Terra SYN/AVG/ZAVG product is scheduled to be released in Summer 2008. The CERES Team will continue detailed examination and documentation of the ground calibration and characterization data, as well as the in-flight calibration opportunities. Notification of any changes will be sent to registered users.
These data are NOT for publication.
For questions or comments on the CERES Quality Summary, contact the User and Data Services staff at the Atmospheric Science Data Center.
