The driving of North American climate extremes by North Pacific stationary-transient wave interference

Droughts figure among the extreme weather events that have increased since the pre-industrial period. Credit: NOAA

The occurrence of extreme weather events, such as heatwaves, droughts, and floods, has increased substantially since the pre-industrial period, but this trend has large regional variations. An important driver of the regional climate variability is the zonally asymmetric atmospheric circulation, or stationary waves, forced by the zonal asymmetries in the Earth’s surface such as the land-sea thermal contrast and elevated terrain (e.g., hills and mountains).

The authors show that North Pacific wave interference is a useful diagnostic for estimating the magnitude of stationary waves therein, which is tightly linked to North American weather extremes through regulating heat and moisture advection.  This research also shows that the spatial structure of these regional impacts is expected to change under a high greenhouse gas emissions scenario.

Because stationary waves regulate the poleward transport of heat and moisture and influence storm track strength and location, the projected stationary wave changes in response to increasing greenhouse gas concentrations are key to understanding how regional climate may change in the future. Transient waves, or daily atmospheric circulation anomalies, in midlatitudes can contribute to regional climate variability on intraseasonal time scales through their interference with climatological stationary waves.