Atmospheric waveguides, quasi-stationary waves, and temperature extremes

Atmospheric waveguides can affect the propagation of Rossby waves, and have been hypothesized to be associated with amplified quasi-stationary waves and thus to extreme weather events in the mid-latitudes. Here, we compare different methods of calculating temporally and spatially varying waveguides, including different ways of separating the waveguides (background flow) from waves, and show that upstream PV waveguides are often present in the days prior to heatwaves. We compare waveguides from potential vorticity (PV) gradients (“PV waveguides”) with barotropic waveguides based on what is known as the stationary wavenumber, or KS (“KS waveguides”). Composites of days with high waveguide strength over particular regions show distinct differences between the two waveguide definitions. Strong KS waveguides in many regions are associated with a double-jet structure, consistent with previous research; this structure is rarely present for strong PV waveguides. The presence of high geopotential heights occurs with the double-jet anomaly, consistent with atmospheric blocking creating the KS waveguide conditions through the influence on local zonal winds, highlighting that this methodology does not sufficiently separate non-linear perturbations (i.e. blocking) from the waveguides, or background flow. Significant positive correlations exist between local waveguide strength and the amplitude of quasi-stationary waves; these correlations are stronger and more widespread for PV waveguides than for KS waveguides, and they are strongest when the rolling-zonalization background flow method is used. We caution against using KS waveguides on temporally and/or zonally varying scales and recommend rolling-zonalization PV waveguides for the study of waveguides and their connections to quasi-stationary atmospheric waves. Using PV waveguides, we find strong connections with heatwaves, with enhanced waveguides upstream from 1-6 days prior to heatwave days.