The projection of China＇s near- and long-term future climate is revisited with a new-generation statistically down- scaled dataset, NEX-GDDP （NASA Earth Exchange Global Daily Downscaled Projections）. This dataset presents a high-resolution seamless climate projection from 1950 to 2100 by combining observations and GCM results, and re- markably improves CMIP5 hindcasts and projections from large scale to regional-to-local scales with an unchanged long-term trend. Three aspects are significantly improved： （1） the climatology in the past as compared against the ob- servations; （2） more reliable near- and long-term projections, with a modified range of absolute value and reduced inter-model spread as compared to CMIP5 GCMs; and （3） much added value at regional-to-local scales compared to GCM outputs. NEX-GDDP has great potential to become a widely-used high-resolution dataset and a benchmark of modem climate change for diverse earth science communities.
The overshoot phenomenon of the Atlantic thermohaline circulation(THC) is a transient climate response to meltwater forcing and could induce intense climate change by increasing the magnitudes of Atlantic THC changes at the end of meltwater discharges. This phenomenon was formally presented with the successfully simulated Bφlling–Allerφd(BA) event in the first transient simulation of the last deglaciation with fully coupled model NCAR-CCSM3(TraCE-21K). Currently, not all proxy records of Atlantic THC support the occurrence of the THC overshoot at BA. Commonly used THC proxy from Bermuda Rise(GGC5) does not exhibit THC overshoot at BA but other proxies such as TTR-451 at Eirik Drift do. How to interpret this regional discrepancy of proxy records is a key question for the validation of the Atlantic THC overshoot at BA. Here, we show that the vigor of deep circulation varies regionally during the Atlantic THC overshoot at BA in TraCE-21 K simulation, and this regional discrepancy in the simulation is consistent with that in the marine sediment records in North Atlantic. The consistent model–proxy evidence supports the occurrence of Atlantic THC overshoot at BA.
Jun ChengZhengyu LiuFeng HeBette Otto-BliesnerEsther BradyJean Lynch-Stieglitz
A conceptual coupled ocean-atmosphere model was used to study coupled ensemble data assimilation schemes with a focus on the role of ocean-atmosphere interaction in the assimilation. The optimal scheme was the fully coupled data assimilation scheme that employs the coupled covariance matrix and assimilates observations in both the atmosphere and ocean. The assimilation of synoptic atmospheric variability that captures the temporal fluctuation of the weather noise was found to be critical for the estimation of not only the atmospheric, but also oceanic states. The synoptic atmosphere observation was especially important in the mid-latitude system, where oceanic variability is driven by weather noise. The assimilation of synoptic atmospheric variability in the coupled model improved the atmospheric variability in the analysis and the subsequent forecasts, reducing error in the surface forcing and, in turn, in the ocean state. Atmospheric observation was able to further improve the oceanic state estimation directly through the coupled covariance between the atmosphere and ocean states. Relative to the mid-latitude system, the tropical system was influenced more by ocean atmosphere interaction and, thus, the assimilation of oceanic observation becomes more important for the estimation of the ocean and atmosphere.
