The characteristics of the North Atlantic jet stream play a key role in the weather and climate of western Europe. By combining model-based predictions of the sea surface temperature with the observed relationship between precipitation and sea surface temperature, Simpson and colleagues demonstrate a great potential for skilful predictions of decadal average March precipitation over western Europe.

Predicting near-term variability in ocean carbon uptake

In order to assess the potential to predict interannual to decadal changes in the components of Earth’s carbon cycle, decadal prediction systems must be developed that include prognostic biogeochemistry models. Nicole Lovenduski (CU Boulder) collaborated with NCAR scientists S. Yeager, K. Lindsay, and M. Long to assess the potential to predict air-sea fluxes of CO2 on multi-year timescales using the CESM Decadal Prediction Large Ensemble (DPLE). The results show that initialization improves lead year 1 forecasts in all regions, and that some ocean biomes exhibit significant improvements out to lead year 3. The potential skill of globally-integrated air-sea CO2 flux is high (r > 0.6) and significantly improved by initialization out to lead year 2, but such high skill is not seen when verifying against observational global flux products. Nevertheless, this study suggests that multi-year predictions of ocean carbon uptake could be viable in the future as prediction systems improve.

Figure: Temporal evolution of area-averaged air-sea CO² flux anomalies in the biomes shown (mol m^-2 yr^-1). The following time series are shown: (black) forced ocean reconstruction, (red) CESM-DPLE ensemble mean for lead year 1, (red dotted) CESM-LENS uninitialized ensemble mean, and (blue) Landschützer et al. (2016) observationally based product.

Decadal predictability of North Atlantic blocking and the NAO

Recent advances in seasonal forecasting suggest that mid-latitude atmospheric circulation variability in the North Atlantic exhibits significant predictability in boreal winter, but it remains an open question whether multi-year predictions of the NAO and/or atmospheric blocking activity are viable or not. In this study, high-frequency output from the CESM Decadal Prediction Large Ensemble (DPLE) is used to determine the skill at forecasting winter blocking events in the subpolar region of the North Atlantic. Such blocking events contribute to the occurrence of climate extremes over western Europe. Results show significant skill at predicting decadal fluctuations in blocking activity (r > 0.6 for lead years 1-8), and the large ensemble size (40 members) is found to be key to achieving such high skill. Given the close relation between blocking activity and the NAO, similar skill levels are obtained for predicting decadal fluctuations in winter NAO. In both cases, the DPLE skill when verifying against observations is much higher than when verifying against single ensemble members, indicating that this decadal prediction system exhibits the signal-to-noise “paradox” first identified in seasonal prediction systems.

References

• Lovenduski, N. S., S. G. Yeager, K. Lindsay, and M. C. Long, 2019: Predicting near-term variability in ocean carbon uptake. Earth Syst. Dynam., 10, 45-57, doi:10.5194/esd-10-45-2019
• Simpson, I.R., Yeager, S.G., McKinnon, K.A. et al. Decadal predictability of late winter precipitation in western Europe through an ocean–jet stream connection. Nat. Geosci. 12, 613–619 (2019) doi:10.1038/s41561-019-0391-x
• Athanasiadis, P. J., S. G. Yeager, Y.-O. Kwon, A. Bellucci, D. W. Smith, and S. Tibaldi, 2019: Decadal predictability of North Atlantic blocking and the NAO, in review.