Nan-Gaussian Distributions of TOA SW Flux as Observed by MISR and CERES

The Top of Atmosphere (TOA) shortwave (SW) flux, converted from Terra Multi-angle Imaging SpectroRadiometer (MISR) narrow band albedos, is compared with that measured from Clouds and the Earth's Radiant Energy System (CERES). We describe the probability density function (PDF) of the monthly TOA SW flux and how the statistical third moment, skewness, can impact the quantification of the flux. The PDF of the SW flux is not normally distributed but positively skewed. In both sets of observations, the near-global (80S-80 N) median value of the SW flux is similar to 3 W/m(2) less than the mean value, due to the positive skewness of the distribution. The near-global mean TOA SW flux converted from MISR is about 7 W/m(2) (similar to 7%) less than CERES measured flux during the last two decades. Surprisingly, a hemispheric asymmetry exists with TOA SW observations from the Terra platform. SH reflects 3.92 and 1.15 W/m(2) more mean SW flux than NH, from MISR and CERES Single Scanner Footprint products, respectively. We can infer that the offsetting by morning clouds in the SH is greater than the effect of hemispheric imbalance of SW flux caused by different land masses in two hemispheres. While the characteristics of the two SW fluxes broadly agree with each other, differences in the regional PDF from two different SW fluxes are substantial over high cloud regions and high altitude regions. Our analysis shows that some parts of the different skewness from the two measurements may be attributed to the different calibration of the radiance anisotropy over high cloud scenes. Plain Language Summary In this work, we describe the non-Gaussian probability density functions (PDFs) of the Top of Atmosphere (TOA) reflected shortwave (SW) flux. For non-Gaussian PDFs, the frequency of occurrence is not symmetric with respect to the mean. The TOA SW PDFs are relatively thick in the left tail because there exists a low boundary of zero reflectance when the Earth don't get solar insolation during the polar nights. In a comparison of two satellite measurements, we show how the statistical third moments of the TOA SW flux can impact the quantification of the averaged flux. Gaussian distributions are naturally assumed in atmospheric data analysis. This, however, is not always true for the TOA SW flux distribution. The two instruments, Multi-angle Imaging SpectroRadiometer (MISR) and Clouds and the Earth's Radiant Energy System (CERES), on the Earth Observing System Terra satellite (launched in December of 1999) offer a rare opportunity to observe the TOA reflected SW flux from the same constellation. Hemispheric asymmetry exists at 10:30 a.m. local time TOA SW observations from Terra platform. SH reflects about 1-4 W/m(2) more SW flux than NH, with the MISR and CERES Single Scanner Footprint (SSF1deg) products observed from Terra.