Cloud Radiative Effect Variability in the Recent Satellite Record and Associated Cloud Radiative Response

Abstract

We investigate changes in the shortwave (SW) and longwave (LW) cloud radiative effect (CRE) according to 20+years of measurements by NASA’s CERES and MODIS instruments, and attempt to distinguish and quantify the contributions of radiative flux anomalies due to cloud and non-cloud changes. Trends in flux anomalies due to presumed cloud changes, collectively termed “cloud radiative response” (CRR) are examined under both the cloud radiative kernel (CRK) and the so-called “adjusted CRE” frameworks. We compare CRK-based CRR estimates from pre-calculated time-invariant kernels and from means of temporally varying observed kernels, both operating on observed monthly 1° cloud anomalies resolved by cloud type. We show that temporally varying kernels enable reconstruction of observed SW and LW CRE trends. When comparing CRR from kernels with that from the adjusted CRE method we find broad agreement in geographical patterns, both resembling those of CRE. Global-mean values are however quite different, due to either unaccounted CRR in the former method and/or imperfect cloud masking corrections in the latter method. Global values of CRE trends and CRR from either method are also quite different. The SW CRR from observed kernels is about half of the CRE trend (+0.16 Wm −2 decade −1 vs +0.34 Wm −2 decade −1 ), implying that a substantial part of the positive trend in SW absorption is due to variability in both clear-skies and cloud masking (radiative flux anomalies under invariant cloud types). In the LW the difference is about 0.5 Wm −2 decade −1 , with LW CRE trends implying additional cooling due to non-cloud variability.