[1] In this study, we estimate a time series of geocenter anomalies from a combination of data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission and the output from ocean models. A matrix equation is derived relating total geocenter variations to the GRACE coefficients of degrees two and higher and to the oceanic component of the degree one coefficients. We estimate the oceanic component from two state-of-the-art ocean models. Results are compared to independent estimates of geocenter derived from other satellite data, such as satellite laser ranging and GPS. Finally, we compute degree one coefficients that are consistent with the processing applied to the GRACE Level-2 gravity field coefficients. The estimated degree one coefficients can be used to improve estimates of mass variability from GRACE, which alone cannot provide them directly.
The current Earth's Energy Imbalance (EEI) is mostly the result of human activities and is driving global warming. The absolute value of EEI represents the most fundamental metric defining the status of global climate change and will be more useful than using global surface temperature. EEI can best be estimated from Ocean Heat Content changes, complemented by radiation measurements from space. Sustained observations from the Argo array of autonomous profiling floats and further development of the ocean observing system to sample the deep ocean, marginal seas, and the sea ice regions are crucial to refining future estimates of EEI. Combining multiple measurements in an optimal way holds considerable promise for estimating EEI and thus assessing the status of global climate change, improving climate syntheses and models, and testing the effectiveness of mitigation actions. Progress has been and can be achieved with a concerted international effort. Earth's energy imbalanceWeather and climate on planet Earth arise primarily from differential radiative heating and resulting movement of energy by the dynamic components of the climate system: the atmosphere and the oceans. Both of these fluids can move heat and moisture through advective processes by atmospheric winds and ocean currents, as well as through eddies, large-scale atmospheric jet streams and convection. Other major components of the climate system include sea ice, the land and its features (including albedo, vegetation, other biomass, and ecosystems), snow cover, land ice (including the ice sheets of Antarctica and Greenland, and mountain glaciers), rivers, lakes, and surface and ground water. About 30% of the incoming solar radiation is reflected and scattered from clouds and the Earth's surface back to space. The remaining absorbed solar radiation (ASR) in the climate system is transformed into various forms (internal heat, potential energy, latent energy, kinetic energy, and chemical forms), moved, stored and sequestered primarily in the ocean, but also in the atmosphere, land and ice components of the climate system. Ultimately it is radiated back to space as outgoing longwave radiation (OLR) [1][2][3] . In an equilibrium climate there is a global balance 2 between the ASR and OLR, which determines the Earth's radiation budget 1-2 . Perturbations of this budget from internal or external climate variations create EEI 4 , manifested as a radiative flux imbalance at the top of the atmosphere (TOA).The EEI is shaped by a number of climate forcings, some of which occur naturally and others that are anthropogenic in origin. A sense of the relative importance of these factors for a given timescale is obtained through estimates of their "Effective Radiative Forcing" (ERF, Fig. 1). The phenomena giving rise to changes in ERF vary regionally and over time. Internal climate variability occurs from day-to-day and month-to-month associated with weather systems and phenomena like the MaddenJulian Oscillation (MJO) that cause short-term changes in cloudiness 5 . On ...
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