Non-linear interactions between tropical and Arctic climate variability and change

Abstract

Tropical modes of climate variability remotely interact with high latitudes via their teleconnections. These teleconnections produce a range of impacts, but include altering the state of the stratospheric polar vortex. The quasi-biennial oscillation (QBO) and the El Ni˜no–Southern Oscillation (ENSO) are two prominent examples of tropical variability which weaken the polar vortex when in their easterly QBO and El Ni˜no states respectively. The polar vortex is also found to weaken in response to sea-ice loss in winter, possibly caused by a weakening and equatorward shift of the mid-latitude jet stream. However, it is unclear how these factors impact the polar vortex state when they coincide.

Using climate model data, I show that in the presence of sea-ice loss, the Arctic polar vortex weakens more under easterly QBO conditions than westerly ones. ENSO is also found to modulate the response to sea-ice loss, but instead the polar vortex is stronger under El Ni˜no conditions compared to neutral ENSO.

Finally, a non-linear weakening of the polar vortex is found between the QBO and ENSO teleconnections themselves. Large model ensembles and reanalysis data are used to build on previous research which finds evidence of such non-linearities, although not always of the same nature.

The existence of these non-linearities has implications for seasonal weather prediction, particularly for Northern Hemisphere mid-latitude winters. Given projected future warming and subsequent increased sea-ice loss, and possible changes to the QBO, ENSO and their teleconnections under a warming climate, these non-linear interactions are important to understand in order to accurately predict future climate change impacts.