Midtropospheric Flow Regimes and Persistent Wintertime Anomalies of Surface-Layer Pressure and Temperature

The effects on surface-layer temperature, pressure, and circulation of flow regimes defined from parameters related to the midtropospheric flow are examined for Northern Hemisphere (NH) winter. Interregime contrasts identified from modes in the probability density distribution of midlatitude planetary-scale wave amplitude are compared and contrasted with those associated with conventionally defined blocking patterns and those associated with the Pacific/North American (PNA) teleconnection index. The wave amplitude regimes lead to surface pressure contrasts of up to 16 mb, which accompany enhanced meridional surface flow. This meridional flow appears linked to significant low-layer (1000 and 850 mb) temperature contrasts of 4°C to 10°C. Comparison of these results to similar results for blocking and the PNA teleconnection index indicates that all three lead to effects of comparable magnitude in the NH winter low-layer temperature field. These effects are comparable to or greater than the local climatological temperature variability. The amplitude and phase of the interregime temperature and pressure differences implies correspondence between Pacific blocking events and the amplified planetary-wave regime. Conversely, the PNA temperature effects are phase shifted relative to those of both the wave amplitude regimes and the blocking regime.