Earth Radiation Budget Components Research Articles

Planetary Radiation Budgets

The energy state of a planet depends fundamentally on its radiation budget. Measurements made from space over past decades have led to significant revisions of ground-based estimates, both of the reflected fraction (the Bond albedo) of solar radiative flux and of the emitted thermal infrared radiation flux, for the Earth as well as for the other planets. After a brief survey of methods and difficulties in accurately determining planetary radiation budgets, we note contradictions in existing tabulations of global parameters, in particular Bond albedo. For the Earth, such contradictions are unjustified, considering that global and annual means as well as the seasonal cycle of Earth Radiation Budget components have now been determined with high accuracy. The Earth's Bond albedo is close to 0.3. Net storage of energy in the Earth-ocean system is close to zero, with a well-established annual cycle of amplitude close to ±12 Wm−2. Some contradictions remain for the other terrestrial planets. For the giant planets, modern reduced values of the Bond albedo imply reduced but still significant internal energy generation.

The Advanced Very High Resolution Radiometer (AVHRR) Pathfinder Atmosphere (PATMOS) Climate Dataset: Initial Analyses and Evaluations

Abstract As part of the joint National Oceanic and Atmospheric Administration–National Aeronautics and Space Administration (NOAA–NASA) Pathfinder program, the NOAA/National Environmental Satellite, Data and Information Service (NESDIS) has created a research-quality atmospheric, climate-scale dataset through the reprocessing of archived Advanced Very High Resolution Radiometer (AVHRR) observations from four afternoon satellites, in orbit since 1981. The raw observations were recalibrated using a vicarious calibration technique for the AVHRR reflectance channels and an improved treatment of the nonlinearity of the three infrared emittance channels. State-of-the-art algorithms are used in the Pathfinder Atmosphere (PATMOS) project to process global AVHRR datasets into statistics of channel radiances, total cloud amount, components of the earth's radiation budget, and aerosol optical thickness over oceans. The radiances and earth radiation budget components are determined for clear-sky and all-sky condition...

Inversion and space-time-averaging algorithms for ScaRaB (Scanner for the Earth Radiation Budget). Comparison with ERBE

Abstract. Establishment of a uniform long-term record of "top-of-the atmosphere" (TOA) Earth radiation budget (ERB) components, on a scale appropriate to the study of cloud radiation interactions, requires that the data obtained from different observation missions satisfy two basic conditions: (1) the broadband shortwave (SW:0.2–4 µm) and longwave (LW: 4–50 µm) radiances must be demonstrably made on the same absolute scale; and (2) the methods used first to convert the instantaneous (filtered) radiances into (unfiltered) SW and LW radiant fluxes, and then to perform the space-time integrations to yield regional monthly means, must be consistent. Here we consider mainly the second point, with regard to the ScaRaB/Meteor mission in orbit since 25 January 1994 and observing the Earth since 24 February 1994. The objective of this mission is to determine the TOA ERB components and so to provide a continuation of the NASA ERBE scanner mission (November 1984–February 1990). We show how results compatible with ERBE can be obtained by taking into account the instrumental characteristics and the satellite orbit parameters: spectral response of the broadband channels, Earth local time of observation. Considering the spectral response of the ScaRaB broadband channels, we show that no spectral correction is required in the longwave domain, whereas a correction of +4.5% must be applied in the shortwave domain for clear and partly cloudy ocean, in order to compensate for underestimation at the shortest wavelengths. Despite possible differences between ERBE and ScaRaB procedures in values assumed for certain parameters of the scene/cloud identifications, application of these procedures to the same set of ERBE data (spectrally corrected, i.e. "unfiltered" radiances) shows that scene identification agreement is close to 90% and that, where there is disagreement, resulting differences in LW fluxes are negligible, those in SW fluxes small. We show that regional and global mean quantities are in excellent agreement, considering that differences between (ERBS+NOAA-9) and (NOAA-9 only) results may be taken as illustrating time-sampling effects. We find that biases may occur from the undersampling, specifically for the night-time clear-sky estimation over land and desert. Preliminary results using ScaaB data of March 1994 show that clear-sky regional estimates may be less numerous than in ERBE scanner products, due to either the larger pixel size or the auxiliary parameters used in the scene identification, and that expected uncertainties in the global monthly mean values depend mainly on the instrument radiometric calibration.

Shortwave, longwave, and net cloud‐radiative forcing as determined from Nimbus 7 observations

We studied the effect of clouds on the Earth's radiation budget at the top of the atmosphere. Both the northern hemisphere summer and winter are considered in terms of cloud‐radiative forcing, which describes the total effect of clouds on the Earth's radiation budget components. The cloud forcing is obtained by using statistically generated models correlating simultaneous observations of cloud properties and radiation budget parameters obtained from observations from Nimbus 7 satellite observations. The models estimate the broadband albedo and longwave flux throughout the range of variation, including periods of extensive to near‐total cloud cover where more simplistic representations fail. As such, the models are used to estimate period‐averaged clear‐sky radiation budget components. Knowledge of the cloudy‐sky and clear‐sky radiation budget components permits the computation of cloud‐radiative forcing. We show that the net effect of clouds is to cool the Earth. On the average, for an Earth observed to be 52.1% cloud covered, the net cloud forcing is −26.8 Wm−2. This net cooling is obtained from a longwave warming of 24.1 Wm−2 and a shortwave cooling of −50.9 Wm−2. Over much of the Earth there is a general compensation between the warming and cooling effects of clouds. However, over the middle‐ and high‐latitude oceans the albedo effect of clouds is dominant. This is particularly true in each summer hemisphere, where the effects of persistent cloudiness, low oceanic albedos, and high solar insolation combine to drive the net cloud forcing strongly negative. The net effect of cloud forcing cools the Earth, primarily due to the effect of clouds in the summer hemisphere oceans.

Diurnal variation of earth radiation budget components above Africa and the neighboring Atlantic Ocean; Changes between 1983 and 1985, estimated from METEOSAT observations adjusted to ERBS data

METEOSAT observations in the thermal infrared “window” and “water vapor” channels, as well as in the visible channel, reveal diurnal variations over large areas which remain significant in the monthly means. The variations in the infrared correspond to diurnal cycles in the surface skin temperature (over land) and in cloud cover (over both land and sea) at various levels, and they must appear as a more or less significant diurnal variation in the integrated longwave emission to space of the Earth-atmosphere system. The diurnal cycle in the reflected shortwave radiation is influenced by these meteorological variations as well as by the astronomical cycle and the anisotropic reflectance. These must be taken into account in studies of Earth Radiation Budget variations. Using nearly simultaneous and spatially coincident pixel data from the ERBE scanner on ERBS and from METEOSAT in November 1984, we construct provisional transfer functions relating the narrow-band METEOSAT infrared observations to the longwave radiant exitance at the top of the atmosphere. We apply these transfer functions to the METEOSAT ISCCP B2 data sets for the summers of 1983–1985, and compare the resulting longwave radiant exitance estimates, with particular attention to the diurnal variation, which should be relatively insensitive to the inaccuracy inherent in applying the provisional (November 1984) transfer functions to the 1983–1985 data.

The interannual variability of the earth's radiation budget components as observed from space

Based on the 1974–78 NOAA data, characteristic features of the variability of the Earth's radiation budget and its components over the area of the Northern Atlantic have been analyzed. Calculations of the mean square deviation for the ERB and its components have let to the conclusions that anomalous regions of maximum variability may be considered as energy-active zones.

Anisotropy of Longwave Radiation Emergent from a Broken Cloud Field and its Effect on Satellite Estimates of Flux

Abstract Simple geometric considerations suggest that in the same way as broken cloud cover appears practically total near a ground observer's horizon, the anisotropy of the longwave radiation emitted to space from an area of broken cloud should be substantially enhanced. Using a simple model consisting of parallel bands of “black” clouds of rectangular cross section, imbedded in an otherwise horizontally homogeneous vertically stratified atmosphere, we evaluate the longwave radiance emergent in different directions, averaged over the cloud pattern, and find this expectation to be confirmed in a wide range of cases. At large zenith angles, the emergent radiance can exhibit considerable dependence on azimuth, relative to the direction of the band structure. Although such azimuthal dependence practically disappears for many 3-dimensional broken cloud fields (e.g., hexagonal cells), the enhanced zenith angle dependence remains. This can be a source of bias in cloud extractions or Earth radiation budget determinations based on geostationary satellite data, since zenith angle is directly related to geographical location of the point under observation. With our model cloud arrays, and considering radiative transfer in the atmosphere, we have evaluated the bias in the broad-band longwave (3–100 μm) radiant exitance values derived, assuming horizontal homogeneity, from either broad-band or narrow-band (10.5–12.5 μm) radiance data. We find that the bias for near-nadir observations can be as large as 20% (40 W m−2) in extreme cases involving bands of opaque high-level cloud over warm ground. It may remain substantial in situations which are encountered in nature. We examine the dependence of the broken cloud effects on the geometrical parameters of the field. We discuss how such effects might be detected and how they can influence determinations of Earth radiation budget components and of cloud cover. We note that “brokenness” will be a factor in cloud-radiation feedback.