The top-of-atmosphere, surface and atmospheric cloud radiative kernels
based on ISCCP-H datasets: method and evaluation
Abstract
This study aims to create observation-based cloud radiative kernel (CRK)
datasets and evaluate them by direct comparison of CRK and the
CRK-derived cloud feedback datasets. Based on the International
Satellite Cloud Climatology Project (ISCCP) H datasets, we calculate
CRKs (called ISCCP-FH or FH CRKs) as 2D joint function/histogram of
cloud optical depth and cloud top pressure for shortwave, longwave, and
their sum, Net, at the top of atmosphere (TOA), as well as, for the
first time, at the surface (SFC) and in the atmosphere (ATM). All the FH
CRKs are physically plausible. The direct comparison shows that FH
agrees reasonably well with three other TOA CRK datasets. With cloud
fraction change (CFC) datasets of the same histogram for
doubled-CO2 simulation from 10 CFMIP1 models, we derive
all the TOA, SFC and ATM cloud feedback using the FH CRKs. Our TOA cloud
feedback is highly similar to the previous counterparts. Based on the
comparison for the 4 CRK datasets and the 10 CFC datasets, we estimate
the uncertainty budget for the CRK-derived cloud feedback, which shows
that the CFC-associated uncertainty contributes > 98.5% of
the total cloud feedback uncertainty while CRK’s is very small. Our
preliminary evaluation also shows that some near-zero/small cloud
feedback in the TOA-alone feedback indeed results from the compensation
of sizable cloud feedback of the SFC and ATM feedback, demonstrating how
the SFC- and ATM-CRK derived cloud feedback can be valuable in revealing
some significant surface and atmospheric cloud feedback whose sum
appears insignificant in TOA-alone feedback.