Five new publications on decadal variability from the ATMOS/MODINI project are here briefly summarised.
In this paper, the authors identify a mode of variability in the southern hemisphere winter atmospheric circulation that is driven by diabatic heating anomalies generated by the East Asian Summer Monsoon in the northern hemisphere in association with the Pacific-Japan pattern. An AGCM driven by observed SST has skill at capturing the variability in this mode suggesting that there is some predictability on interannual time scales.
Ding, H., R.J. Greatbatch, H. Lin, F. Hansen, G. Gollan and T. Jung, 2016: Austral Winter External and Internal Atmospheric Variability between 1980 and 2014 Geophysical Research Letters, 43 (5). pp. 2234-2239. DOI 10.1002/2016GL067862
In this paper, the authors show that the simulation of the Atlantic Multidecadal Variability (AMV) in a model is greatly improved when the cold bias associated with the misplacement of the North Atlantic Current is alleviated. The corrected model shows that in the warm AMV phase, heat is lost by the ocean in the northwestern part of the North Atlantic and gained by the ocean to the east, suggesting an advective transfer of heat by the mid-latitude westerlies. The basin-wide response is consistent with a role for cloud feedback and is in broad agreement with estimates from observations but is poorly represented in the uncorrected model. The corrected model is then used to show that the ocean/atmosphere heat transfer is influenced by low-frequency variability in the overlying atmosphere. We also argue that changing ocean heat transport is an essential feature of our results.
Drews, A. and R. J. Greatbatch, 2016: Atlantic Multidecadal Variability in a model with an improved North Atlantic Current, Geophysical Research Letters, 43 (15). pp. 8199-8206. DOI 10.1002/2016GL069815.
In this paper, we first show that interannual variability of the NAO is best reproduced when perfect knowledge of the Northern Hemisphere (NH) stratosphere is available, together with perfect knowledge of the sea surface temperature and sea ice. A coupled model seasonal forecast experiment is then examined. The model shows a strong bias in the stratospheric polar-night jet associated with a drift in the modelled SSTs resembling the North Atlantic cold bias. After removing the bias statistically, a perfect forecast of the tropical atmosphere and allowing two-way atmosphere–ocean coupling in the extratropics, are found to be key ingredients for successful predictions of stratospheric sudden warmings (SSW). In combination with SSW occurrence, a clear shift of the predicted NAO towards lower values occurs.
Hansen, F., R.J. Greatbatch, G. Gollan, T. Jung and A. Weisheimer, 2017: Remote control on North Atlantic Oscillation predictability via the stratosphere, Quart. J. R. Meteor. Soc., 143 (703B). pp. 706-719. DOI 10.1002/qj.2958.
This paper looks at the difference in the atmospheric response to a specified SST anomaly in the mid-latitude North Pacific in two different decades, 1981-1990 and 1991-2000 using high horizontal resolution (T213) simulations with the ECHAM5 atmospheric model. Of particular interest is the emphasis on the Rossby Wave Source (RWS) and how the RWS differs between the two decades. It is shown that the RWS changes are linked to the decadal reduction of daily SST variability over the eastern North Pacific and strengthening of the Oyashio Extension front over the western North Pacific.
Zhou, G., M. Latif, R. J. Greatbatch and W. Park, 2017: State-Dependence of Atmospheric Response to Extratropical North Pacific SST Anomalies Journal of Climate, 30 (2). pp. 509-525. DOI 10.1175/JCLI-D-15-0672.1.
This paper shows that a linear, multi-mode ocean model driven by wind stress derived from the ERA-Interim reanalysis has considerable skill at reproducing interannual variability in sea surface height in the tropical Pacific as seen by the satellite altimeter. The model successfully captures the observed ENSO events, including the different flavours of ENSO. This model is used to assess different wind forcing products for use with the MODINI initialization system as part of the ATMOS-MODINI project.
Zhu, X., R.J. Greatbatch and M. Claus, 2017: Interannual variability of tropical Pacific Sea level from 1993 to 2014, Journal of Geophysical Research: Oceans, 122 (1). pp. 602-616. DOI 10.1002/2016JC01234