[strat_list] paper on NAO hindcast with stratospheric model

[Yvan Orsolini]

Dear all,

You might be interested in our recent article

Orsolini, Y. J., Kindem, I.T and N.G. Kvamsto, On the potential impact of 
the stratosphere upon seasonal dynamical hindcasts of the North Atlantic 
Oscillation: a pilot study, Clim. Dyn.,  doi: 10.1007/s00382-009-0705-6, 
2009.

http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s00382-009-0705-6

Abstract
We have investigated the importance of the stratosphere-troposphere 
linkage on the seasonal predictability of the North Atlantic Oscillation 
in a pilot study using a high horizontal resolution atmospheric general 
circulation model, and covering the 14 winters from 1979/80 to 1992/93. We 
made an ensemble of simulations with the Meteo-France .Arpege Climat. 
model (V3.0) with a well-resolved stratosphere, and a broad comparison is 
drawn with hindcasts from previously published experiments using low-top 
and lower horizontal resolution models, but covering the same winters with 
the same ensemble size and verification method.

For the January-February-March North Atlantic Oscillation index, the 
deterministic hindcast skill score is 0.59, using re-analyses as 
verification. It is comparable to the reported multi-model skill score 
(0.57). The largest improvement originates from the winter 1986/87 
characterised by a major stratospheric sudden warming. We demonstrate that 
there is then a high-latitude zonal-mean zonal wind decrease in the 
stratosphere-troposphere hindcasts over a broad pressure range. This is 
consistent with a composite analysis showing that model anomalous vortex 
events, either weak or strong, lead to a North Atlantic Oscillation index 
anomaly in the troposphere, which persists, on average, for 1 month after 
the anomaly peaked in the stratosphere.



Dr. Yvan J. ORSOLINI, Senior Scientist
Norwegian Institute for Air Research (NILU) 
Instituttveien 18, P.O.Box 100,
N-2027 Kjeller, 
Norway

e-mail: orsolini at nilu.no
Phone:  +47 63898183 (NILU) | Fax:    +47 63898050