Sheffield
Justin
Sheffield
Justin
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ArticleThe observed state of the water cycle in the early twenty-first century(American Meteorological Society, 2015-11-01) Rodell, Matthew ; Beaudoing, Hiroko K. ; L’Ecuyer, Tristan S. ; Olson, William S. ; Famiglietti, James S. ; Houser, Paul R. ; Adler, Robert ; Bosilovich, Michael G. ; Clayson, Carol A. ; Chambers, Don P. ; Clark, Edward A. ; Fetzer, Eric J. ; Gao, X. ; Gu, Guojun ; Hilburn, K. A. ; Huffman, George J. ; Lettenmaier, Dennis P. ; Liu, W. Timothy ; Robertson, Franklin R. ; Schlosser, C. Adam ; Sheffield, Justin ; Wood, Eric F.This study quantifies mean annual and monthly fluxes of Earth’s water cycle over continents and ocean basins during the first decade of the millennium. To the extent possible, the flux estimates are based on satellite measurements first and data-integrating models second. A careful accounting of uncertainty in the estimates is included. It is applied within a routine that enforces multiple water and energy budget constraints simultaneously in a variational framework in order to produce objectively determined optimized flux estimates. In the majority of cases, the observed annual surface and atmospheric water budgets over the continents and oceans close with much less than 10% residual. Observed residuals and optimized uncertainty estimates are considerably larger for monthly surface and atmospheric water budget closure, often nearing or exceeding 20% in North America, Eurasia, Australia and neighboring islands, and the Arctic and South Atlantic Oceans. The residuals in South America and Africa tend to be smaller, possibly because cold land processes are negligible. Fluxes were poorly observed over the Arctic Ocean, certain seas, Antarctica, and the Australasian and Indonesian islands, leading to reliance on atmospheric analysis estimates. Many of the satellite systems that contributed data have been or will soon be lost or replaced. Models that integrate ground-based and remote observations will be critical for ameliorating gaps and discontinuities in the data records caused by these transitions. Continued development of such models is essential for maximizing the value of the observations. Next-generation observing systems are the best hope for significantly improving global water budget accounting.
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ArticleNorth American climate in CMIP5 experiments. Part II: evaluation of historical simulations of intraseasonal to decadal variability(American Meteorological Society, 2013-12-01) Sheffield, Justin ; Camargo, Suzana J. ; Fu, Rong ; Hu, Qi ; Jiang, Xianan ; Johnson, Nathaniel ; Karnauskas, Kristopher B. ; Kim, Seon Tae ; Kinter, Jim ; Kumar, Sanjiv ; Langenbrunner, Baird ; Maloney, Eric ; Mariotti, Annarita ; Meyerson, Joyce E. ; Neelin, J. David ; Nigam, Sumant ; Pan, Zaitao ; Ruiz-Barradas, Alfredo ; Seager, Richard ; Serra, Yolande L. ; Sun, De-Zheng ; Wang, Chunzai ; Xie, Shang-Ping ; Yu, Jin-Yi ; Zhang, Tao ; Zhao, MingThis is the second part of a three-part paper on North American climate in phase 5 of the Coupled Model Intercomparison Project (CMIP5) that evaluates the twentieth-century simulations of intraseasonal to multidecadal variability and teleconnections with North American climate. Overall, the multimodel ensemble does reasonably well at reproducing observed variability in several aspects, but it does less well at capturing observed teleconnections, with implications for future projections examined in part three of this paper. In terms of intraseasonal variability, almost half of the models examined can reproduce observed variability in the eastern Pacific and most models capture the midsummer drought over Central America. The multimodel mean replicates the density of traveling tropical synoptic-scale disturbances but with large spread among the models. On the other hand, the coarse resolution of the models means that tropical cyclone frequencies are underpredicted in the Atlantic and eastern North Pacific. The frequency and mean amplitude of ENSO are generally well reproduced, although teleconnections with North American climate are widely varying among models and only a few models can reproduce the east and central Pacific types of ENSO and connections with U.S. winter temperatures. The models capture the spatial pattern of Pacific decadal oscillation (PDO) variability and its influence on continental temperature and West Coast precipitation but less well for the wintertime precipitation. The spatial representation of the Atlantic multidecadal oscillation (AMO) is reasonable, but the magnitude of SST anomalies and teleconnections are poorly reproduced. Multidecadal trends such as the warming hole over the central–southeastern United States and precipitation increases are not replicated by the models, suggesting that observed changes are linked to natural variability.
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ArticleThe observed state of the energy budget in the early twenty-first century(American Meteorological Society, 2015-11-01) L’Ecuyer, Tristan S. ; Beaudoing, Hiroko K. ; Rodell, Matthew ; Olson, William S. ; Lin, B. ; Kato, S. ; Clayson, Carol A. ; Wood, Eric F. ; Sheffield, Justin ; Adler, Robert ; Huffman, George J. ; Bosilovich, Michael G. ; Gu, Guojun ; Robertson, Franklin R. ; Houser, Paul R. ; Chambers, Don P. ; Famiglietti, James S. ; Fetzer, Eric J. ; Liu, W. Timothy ; Gao, X. ; Schlosser, C. Adam ; Clark, Edward A. ; Lettenmaier, Dennis P. ; Hilburn, K. A.New objectively balanced observation-based reconstructions of global and continental energy budgets and their seasonal variability are presented that span the golden decade of Earth-observing satellites at the start of the twenty-first century. In the absence of balance constraints, various combinations of modern flux datasets reveal that current estimates of net radiation into Earth’s surface exceed corresponding turbulent heat fluxes by 13–24 W m−2. The largest imbalances occur over oceanic regions where the component algorithms operate independent of closure constraints. Recent uncertainty assessments suggest that these imbalances fall within anticipated error bounds for each dataset, but the systematic nature of required adjustments across different regions confirm the existence of biases in the component fluxes. To reintroduce energy and water cycle closure information lost in the development of independent flux datasets, a variational method is introduced that explicitly accounts for the relative accuracies in all component fluxes. Applying the technique to a 10-yr record of satellite observations yields new energy budget estimates that simultaneously satisfy all energy and water cycle balance constraints. Globally, 180 W m−2 of atmospheric longwave cooling is balanced by 74 W m−2 of shortwave absorption and 106 W m−2 of latent and sensible heat release. At the surface, 106 W m−2 of downwelling radiation is balanced by turbulent heat transfer to within a residual heat flux into the oceans of 0.45 W m−2, consistent with recent observations of changes in ocean heat content. Annual mean energy budgets and their seasonal cycles for each of seven continents and nine ocean basins are also presented.