Cyclonic Rossby Wave Breaking Research Articles

Role of Rossby wave breaking in the west Pacific teleconnection

The dynamical link between the west Pacific (WP) teleconnection and Rossby wave breaking (RWB) events is analyzed during winter months using ERA40 reanalysis data from 1957 to 2002. The WP pattern which is characterized by latitudinal fluctuations of the Pacific jet is closely linked to variations in the nature of RWB, similarly to the North Atlantic Oscillation. More anticyclonic (cyclonic) RWBs than usual occur in the Central Pacific during the positive (negative) WP phase when the Pacific jet is more to the north (south) than usual. Time lag daily composites show that before the occurrence of an anticyclonic RWB event, WP anomalies close to the positive phase preexist that are then reinforced during the breaking leading to an increase of the WP index even few days after the peak of the event. Cyclonic RWB events have similar but opposite effects on the WP pattern since they trigger and maintain the negative phase. Finally, a comparison with the RWB anomalies of the Pacific‐North American (PNA) teleconnection is provided.

Tropospheric Rossby Wave Breaking and the NAO/NAM

Abstract Objective analysis of several hundred thousand anticyclonic and cyclonic breaking Rossby waves is performed for the Northern Hemisphere (NH) winters of 1958–2006. A winter climatology of both anticyclonic and cyclonic Rossby wave breaking (RWB) frequency and size (zonal extent) is presented for the 350-K isentropic surface over the NH, and the spatial distribution of RWB is shown to agree with theoretical ideas of RWB in shear flow. Composites of the two types of RWB reveal their characteristic sea level pressure anomalies, upper- and lower-tropospheric velocity fields, and forcing of the upper-tropospheric zonal flow. It is shown how these signatures project onto the centers of action and force the velocity patterns associated with the North Atlantic Oscillation (NAO) and Northern Hemisphere annular mode (NAM). Previous studies have presented evidence that anticyclonic (cyclonic) breaking leads to the positive (negative) polarity of the NAO, and this relationship is confirmed for RWB over the midlatitudes centered near 50°N. However, an opposite and statistically significant relationship, in which cyclonic RWB forces the positive NAO and anticyclonic RWB forces the negative NAO, is shown over regions 20° to the north and south, centered at 70° and 30°N, respectively. On a winter mean basis, the frequency of RWB over objectively defined regions covering 12% of the area of the NH accounts for 95% of the NAO index and 92% of the NAM index. A 6-hourly analysis of all the winters indicates that RWB over the objectively defined regions affects the NAO/NAM without a time lag. Details of the objective wave-breaking analysis method are provided in the appendix.