Extreme Moisture Transport into the Arctic Linked to Rossby Wave Breaking

Water vapor plays an important role in the energetics of the Arctic. We demonstrate that the bulk of the poleward moisture transport by transients across 60N is driven by extreme transport events. These events are shown to be closely related to two types of Rossby wave breaking (RWB) – anticyclonic wave breaking (AWB) and cyclonic wave breaking (CWB). Using a RWB tracking algorithm, we determine that these two types can account for 47% of the total poleward moisture transport by transients across 60$^\circ$N in winter and 37% in summer.

Additional analysis suggests that the seasonality of this RWB-related moisture transport is determined equally by the strength of RWB transport, and the frequency of RWB occurrence. The seasonality of RWB occurrence is, in turn, dictated by the seasonal variation of the latitude of the jet-streams – AWB (CWB) related transport occurs more frequently when the jet is shifted poleward (equatorward).

The interannual variability of RWB-related transport across 60N in winter is shown to be strongly influenced by climate variability captured by ENSO and the NAO. In the positive (negative) phase of ENSO, AWB transports less (more) moisture through the Bering Strait and CWB transports more (less) through Canada. In the positive (negative) phase of the NAO, AWB transports more (less) moisture through the Norwegian Sea and CWB transports less (more) along the west coast of Greenland. These results highlight how low-frequency climate variability outside of the polar region can influence Arctic water vapor by modulating extreme synoptic transport events.