Subdiurnal to Interannual Frequency Analysis of Observed and Modeled Reflected Shortwave Radiation From Earth

Abstract

AbstractEstimates of global top‐of‐atmosphere radiation on monthly, seasonal, annual, and longer time‐scales require estimates of the diurnal variability in both insolation and surface and atmospheric reflection. We compare Earth Polychromatic Imaging Camera (EPIC) and National Institute of Standards and Technology Advanced Radiometer (NISTAR) observations from the Deep Space Climate Observatory (DSCOVR) satellite with Clouds and Earth’s Radiant Energy System (CERES) hourly synoptic fluxes, which are diurnally filled through geostationary observations, and find that their power spectral density functions substantially agree, showing strong relative power at subdiurnal, diurnal, seasonal, and annual time‐scales, and power growing from diurnal to seasonal time‐scales. Frequency analysis of fluxes from several coupled model intercomparison project 5 model (CMIP5) and CMIP6 models shows that they distribute too much power over periods greater than 1 day but less than one year, indicating that a closer look is needed into how models achieve longer‐term stability in reflected shortwave radiation. Model developers can consider using these datasets for time‐varying energetic constraints, since tuning parameter choices will impact modeled planetary shortwave radiation across timescales ranging from subdiurnal to decadal.