Refining Estimates of the Earth's Radiation Budget
The Earth's climate is determined by flows of energy that smooth out regional differences in the amount of energy the Earth recieves from the sun and the heat it radiates back to space. Excess heat in the tropics must be moved to cold polar regions that continuously lose energy to space. This difference in temperature between tropical and polar regions causes the pattern of rising moist air in the tropics, sinking dry air in the sub-tropics, storminess at the middle latitudes, and strong ocean currents that is responsible for the weather across the planet. This system that governs exchanges of water between the atmosphere, land, and oceans and, in turn, the exchange of energy between the atmosphere and the surface is known as the global energy and water cycle (E&WC). Accurate observational estimates of this cycle is a critical first step toward predicting future climate.
Quantifying Global Energy Balance
Atmospheric radiation is just one component of an intricate system known as the global energy and water cycle (E&WC) that governs exchanges of water between the atmosphere, land, and oceans and, in turn, the exchange of energy between the atmosphere and the surface. Our group is actively engaged in the NASA Energy and Water Cycle Study (NEWS) program that seeks to use satellite observations to improve our characterization of the E&WC, its extremes, and its variability, and to use this knowledge to improve predictive capabilities of global models. As part of the NEWS E&WC Climatology Working Group, we are providing the science community with an important new set of state-of-the art estimates of energy and water fluxes in the climate system based on current NASA satellite observations. When these new datasets are combined, the results suggest that significant imbalances exist in the surface and atmospheric energy budgets as shown in the purple numbers on the right. However, using an innovative optimization procedure that builds off rigorous uncertainty models for each energy flux, energy and water closure constraints can be introduced to derive the balanced budget given in blue. There are a few reasons to favor these new estimates over recently published alternatives. First, they derive from primarily observational or observation-integrating datasets that incorporate state-of-the-art information from NASAs network of Earth observing satellites. In addition, they incorporate explicit estimates of the uncertainties in all component fluxes obtained through rigorous comparisons against high-quality direct measurements, product inter comparisons and sensitivity studies. Most importantly, the energy budget presented here simultaneously satisfies all relevant energy and water cycle closure constraints using an objective variational optimization approach. Additional details concerning the datasets used, the methodology employed, and deeper insights into spatial and temporal variations of the energy budget can be found in L’Ecuyer et al. (2015). These benchmark E&WC estimates will provide a critical resource for evaluating climate models and establishing the primary causes of residual imbalances to target for future improvement.