EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

The seasonal teleconnections of the Indian Ocean Dipole to the North Atlantic region

Tim Hempel1, Antje Weisheimer1,2, and Tim Palmer1
Tim Hempel et al.
  • 1University of Oxford, Physics, Atmosperic, Oceanic and Planetary Physics, United Kingdom of Great Britain – England, Scotland, Wales
  • 2European Centre for Medium-Range Weather Forecasts, Reading, United Kingdom of Great Britain – England, Scotland, Wales

The Indian Ocean Dipole (IOD) is a major source of seasonal climate variability in the
Indian Ocean. This dipole has major impacts on the Indian Ocean region and through
teleconnections can influence the seasonal climate of remote regions as well. In late 2019 a
major IOD event contributed to a strong positive North Atlantic Oscillation (NAO) of that
winter. Thus, a good understanding of the mechanism that transports information from
the Indian Ocean to the North Atlantic is desirable. In this contribution we investigate
the special teleconnection of the winter of 2019 and analyse the transport mechanism.

In model experiments with the OpenIFS from ECMWF we show that the NAO in the
winter 2019 is influenced by the Indian Ocean Dipole. We use hindcast ensemble model
experiments to analyse the behaviour of the IOD and its impact on the NAO. These
seasonal hindcast experiments are started from the 01. November 2019 and run for the
DJF season 2019/2020. Since the OpenIFS is uncoupled we change the Sea Surface
Temperature (SST) boundary conditions in regions of importance to the NAO (like the
ENSO region, the North Atlantic, and also the Indian Ocean). With these perturbations
we identify the relative importance of individual ocean regions to the state of the NAO
in the winter of 2019.

We contrast the experiments with the perturbed SST conditions to a control forecast and
ERA5 reanalysis. We find that removing the IOD has a significant impact on the NAO of
the 2019/2020 DJF season, pushing the NAO to a more negative state. Additionally the
contrast between control forecast and model experiments shows Rossby Waves emanating
from the Indian Ocean over the North Pacific and the Arabian Peninsular.

Experiments with perturbations in other ocean regions show that some signals, like ENSO,
can suppress the impact of the IOD on the NAO, but in their absence the positive IOD
event of 2019 did likely contribute to the strong positive NAO of 2019/2020.

How to cite: Hempel, T., Weisheimer, A., and Palmer, T.: The seasonal teleconnections of the Indian Ocean Dipole to the North Atlantic region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7631,, 2022.