The New Long-term, Global, 3-hourly, High-Resolution Atmospheric Radiative Flux Profile Product: ISCCP-FH

Based on the radiative transfer part of the NASA GISS GCM ModelD (called RadD) and the ISCCP D-series product, a global, 3-hourly, 280-km equal-area, atmospheric radiation profile product, ISCCP-FD, was produced starting at the end of the 20th century and continuing in parallel with ISCCP processing until it covered the period 1983 to 2009. Since then the GISS GCM modelD has evolved into ModelE including improvements of the radiation model into RadE. ISCCP has also evolved from the D-series to its third version, the H-series. The ISCCP H-series is being produced now to cover more than three decades. Given the substantial advances in various aspects of the atmospheric, cloud and radiation research, the time is right to produce a new, better radiation profile product, ISCCP-FH, whose preliminary results and new features will be reported at the conference.

The new radiation code, RadH, is based on RadE so it bears all the improvements of RadE (over RadD) and, moreover, incorporates more recent improvements. The major advanced features of RadH include: (1) Reformulation of the SW line absorption for H2O, O2, CO2, CH4 and N2O etc. using the most up-to-date HITRAN2012, which corrects some H2O deficiencies and greatly improves the accuracy, spectral coverage, additional absorption phenomena and validity, (2) Use of a new aerosol compilation, HAC-v1, that is based AeroCom's advances, (3) Improvement of the LW model includes better representation of H2O continua, CFC cross sections and SO2 line absorption, better CH4 and N2O overlap treatments and polar region profile calculations. The diagnostic tests show that all these improvements are all in the right direction based on comparisons with in situ and direct flux measurement, and therefore, will improve ISCCP-FH product.

ISCCP H-series is the third generation of ISCCP projects that is based on a 10-km sampling of the satellite radiance data in place of the 30-km-sampled B3 data. The major shortcoming of the D-series products was caused by inhomogeneities of temperature and humidity profiles from the operational TOVS product that has now been improved by a reprocessing of the original HIRS data by NCDC using a new algorithm based on a neural network. There are other noticeable improvements in radiance QC, calibration, cloud detection (especially high, thin and polar clouds), surface property retrievals and temperature inversion treatment with better ancillary datasets, e.g., more accurate surface type and topography, snow/ice datasets, reprocessed ozone data, etc. The retrievals are now based on more realistic atmosphere with aerosols (HAC-v1) so the uncertainties are much reduced. The temperature and humidity profiles have increased vertical resolution and have been statistically adjusted to represent the diurnal variations in the lower atmosphere. The new ISCCP H-series also has more products (e.g., five for L3) with a new globally gridded pixel-level data. The D1-like product, now called HGG, is the input for ISCCP-FH with a spatial resolution of ~100 km equal area.

As concluded by the GEWEX-Radiation Panel assessment of radiation products, the uncertainties of ISCCP-FD and other major flux products are largely driven by the uncertainties or errors of the input datasets, not by the flux calculations by radiative model. Although the total changes of the improved flux values are only a few W/m2 at TOA, surface and in the atmosphere, their uncertainties are significantly reduced. The details of all the major improvements and features of ISCCP-FH will be illustrated at the conference.