Evidence of Thermal Equilibration in Large-scale Atmospheric Blocking Episodes over Europe and the North Atlantic

The Earth's atmosphere consistently mixes to achieve an equilibrated state. Atmospheric thermal equilibration occurs when all thermal forcings diminish and temperature gradients vanish. Although the atmosphere never equilibrates completely, it exhibits specific features in areas that are more equilibrated than others. For example, characteristics of equilibration include low diabatic heating and relatively calm conditions throughout the atmospheric column. Large-scale planetary waves can remain in these equilibrated states for several weeks, as identified in previous work.

This study focuses on the relevance and intensity of thermal equilibration in large-scale atmospheric blocking episodes. Other studies have not explored the relationships between long-duration blocking events and equilibration in much detail. We evaluate whether or not thermal equilibration becomes more evident in blocking episodes. We identify both wintertime and summertime large-scale blocking episodes over the North Atlantic and Europe using a dynamical blocking index on the NCEP/NCAR Reanalysis dataset. After identifying episodes, evidence of thermal equilibration is presented and analyzed through regional composites of atmospheric variables in blocked and non-blocked situations. Relationships between potential vorticity (PV) and streamlines are also described and presented through scatter plots. The results provide significant evidence that thermal equilibration is more probable in blocking episodes than in non-blocked states.