Baroclinic Blocking

Atmospheric blocking events, which cause abnormal weather conditions, have been studied from a viewpoint of quasi-stationary barotropic circulation systems because of their apparent lack of vertical tilt. However, this work demonstrates that blocking events often have such structure that anomalies in geopotential height and temperature are horizontally out-of-phase, allowing blocking anomalies to produce fluxes of heat against the climatological-mean gradients for amplifying and maintaining blocking-related temperature anomalies. This process, which represents the baroclinic conversion of energy from the climatological-mean flow to the blocking-related anomalies, is shown to be one of the leading energy sources through an analysis of blocking energetics. In winter, the contribution of the baroclinic energy conversion, especially for North Pacific and Greenland blocks, is substantially larger than the contributions from barotropic energy conversion and feedback forcing by high-frequency eddies. In summer, the baroclinic energy conversion and feedback from high-frequency eddies are more comparable in magnitude.