The influence of the 1997-99 El Nino Southern Oscillation on extratropical baroclinic life cycles over the eastern North Pacific

The role of linear wave refraction in the transient eddy–mean flow response to tropical Pacific SST anomalies

“…However, it is possible that the planetary-scale low-frequency waves extend the eddy-driven response even further polewards, meaning that their mutual interaction is important. It is also possible that transient eddy nonlinearities in the GCM act to extend the zonal mean wind anomalies polewards, in line with observations that link ENSO-induced changes in wave breaking to changes in the mean flow (Shapiro et al, 2001;Orlanski, 2003;Martius et al, 2007). Despite these differences, our results suggest that simple linear refraction can give rise to a positive wave-mean flow feedback in midlatitudes, which can explain a large part of the mean flow anomalies there, but that stationary wave anomalies and nonlinearities which are included in the GCM, but not in the QG model, are needed to fully account for the spreading of the positive U PAC anomalies to high latitudes during EN.…”

“…Straus and Shukla (1997) and Orlanski (2005) argue that increased baroclinicity in the eastern Pacific, which is part of the direct response to tropical Pacific heating, is responsible for displacing the storm track southward and extending it eastward in that region. Orlanski (2003Orlanski ( , 2005 also argues that central to the response is a change in the nonlinear decay stage of eddy life cycles, which is observed to occur (Shapiro et al, 2001;Martius et al, 2007;Gong et al, 2010).…”

Adjustment of the atmospheric circulation to tropical Pacific SST anomalies: Variability of transient eddy propagation in the Pacific–North America sector

“…Both Straus and Shukla (1997) and Orlanski (2005) argue that the southward-displaced and eastwardextended storm track over the eastern Pacific during El Niños arises from increased baroclinic instability in that region that follows from the direct response of the atmospheric temperature and circulation to the central and eastern tropical Pacific heating anomalies (Trenberth et al, 1998). Orlanski (2005) and Shapiro et al (2001) also argued for the possible importance of differences in nonlinear wave breaking during the different phases of the ENSO cycle. These authors recognize that these changes will in turn alter the mean flow and have a subsequent impact on wave propagation.…”

The role of cold fronts in the onset of the monsoon season in the South Atlantic convergence zone

“…These so-called 'anticyclonic behaviour' midlatitude cyclones tend to produce strong, elongated, slower-moving surface cold fronts and little or no warm front signature. Shapiro et al (2001) [1997][1998] El Niño, the midlatitude jet was stronger and displaced southward so that 'cyclonic' shear was present and more 'broadening trough' or 'cyclonic behaviour' events were observed. Incidentally they find that 'anticyclonic' or 'thinning trough' events had lower predictability than their cyclonic counterparts.…”