Road Map for the Next Decade of Earth System Reanalysis in the United States Bulletin of the American Meteorological Society

Reanalysis combines historical observations with modern Earth system models (ESMs) to generate a spatially and temporally complete history of the Earth system. It is an essential infrastructure that supports mission-critical activities across multiple U.S. agencies [including the National Oceanic and Atmospheric Administration (NOAA), National Aeronautics and Space Administration (NASA), National Science Foundation (NSF), Department of Energy (DOE), and Department of Defense (DOD)], industry (including energy, resource management, agriculture, infrastructure, insurance, information technology, and finance), and academia. In particular, reanalysis products can be used as initial conditions to evaluate and calibrate environmental forecasts produced by NOAA, NASA, and DoD and research institutions that investigate predictability on subseasonal to decadal time scales. Reanalyses can also provide an essential climate record of past weather conditions, extremes, and trends and can serve as verification datasets for ESMs. Reanalyses can quantify storage within and fluxes across the Earth system components essential to livelihood and commerce, such as heat, radiation, water, air quality, and carbon. Most recently, reanalysis datasets are also used for training of the machine learning models and as critical ingredient of emerging digital twins of the Earth system.