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P9. Wind induced anomalies in the ocean heat transport over the North
Atlantic
Francesco Emanuele Bucci
University of Copenhagen – Niels Bohr Institute fra.ema.bucci@gmail.com
Results are presented from a study on the relationship between atmospheric blocking effects above
the North Atlantic and the variability of the North Atlantic ocean. In the article entitled
“Atmospheric Blocking and Atlantic Multidecadal Ocean Variability” (Sirpa Haekkinen, Peter B.
Rhines and Denis L. Worthen, Science 2011) it is proposed that there is a connection between the
frequency of atmospheric blocking events above the North Atlantic ocean and the circulation of the
North Atlantic ocean. It is proposed that the persistence of blocking effect for many days during one
winter could affect the variability of the ocean for decades: one explanation could be that the wind
forcing over the northern North Atlantic changes significantly and this would affect the wind driven
circulation of the North Atlantic and modify the extension of the subpolar gyre circulation. This
would imply changes in the northward heat transport and increased influx of warm water from
subtropical latitudes into the northern North Atlantic.The influence from the relatively short term
blocking effects, with time scales of days to weeks, on the large scale circulation is analysed in a
sensitivity study with the ocean general circulation model NEMO. The chosen configuration
includes the ocean module and the sea-ice module; an atmospheric forcing is applied from the
NCAR/NCEP reanalysis. The ocean model works on a global configuration, with an horizontal
resolution of 1 degree at the equator and 46 vertical levels. The atmospheric forcing comes from
one of the dataset analyzed by Haekkinen, the NCEP/NCAR reanalysis (Kalnay et al.,The
NCEP/NCAR 40-year reanalysis project, Bull. Amer. Meteor. Soc., 77, 437-470, 1996) derived
from an analysis-forecast system with the assimilation of data since the 1948.
An EOF analysis has been done on the curl of the wind stress above the North Atlantic: the wind
stress curl is used as index of the strength of the gyre circulation. A seasonal signal propagates over
the decades and a correlation with the anomalous blocking events is examined.
A sensitivity experiment is performed through the model in order to find a correlation between
anomalous blocking events and the variability of the ocean circulation. The meridional heat
transport is investigated in order to study the mechanism of influx of warm waters due to the wind
anomalies.
Program 17. danske havforskermøde, 126