Response of Idealized Baroclinic Wave Life Cycles to Stratospheric Flow Conditions

Abstract

Dynamical stratosphere-troposphere coupling through a response of baroclinic waves to lower stratospheric flow conditions is investigated from an initial value approach. A series of adiabatic and frictionless nonlinear baroclinic wave life cycles in a midlatitude tropospheric jet with different initial zonal flow conditions in the stratosphere is simulated, using a dry primitive equation model with spherical geometry. When a stratospheric jet, located at various latitudes between 35 degrees and 70 degrees, is removed from the initial conditions, the wavenumber-6 life cycle behavior changes from the well-known LC1 to LC2 evolution, characterized by anticyclonic and cyclonic wave breaking, respectively. Linear theory, in terms of refractive index and the structure of the corresponding fastest-growing normal mode, is found to be unable to explain this stratosphere-induced LC1 to LC2 transition. This implies that altered nonlinear wave-mean flow interactions are important. The most significant stratosphere-induced change that extends into the nonlinear baroclinic growth stage is a region of downward wave propagation in the lower stratosphere associated with positive values of the squared refractive index near 20 km. Furthermore, it is demonstrated that the difference between the response of the tropospheric circulation to LC1 and LC2 life cycles closely resembles the meridional and vertical structure of the North Atlantic Oscillation (NAO), with positive (negative) NAO-like anomalies being driven by LC1 (LC2). Thus, a weakened stratospheric jet induces the generation of negative NAO-like anomalies in the troposphere, consistent with the observed stratosphere-NAO connection

Interannual and interdecadal variations in the North Atlantic Oscillation spatial shift

“…b) Numbers in parentheses are correlation coefficients calculated for the period 1958-1997. growth and decay in the NAO variability within a period of approximately two weeks and suggested that the NAO is driven by both high-frequency (period of less than 10 days) and low-frequency (period of more than 10 days) transient eddy fluxes. The intrinsic time scale is closely related to synoptic-scale Rossby wave breaking (RWB) over the North Atlantic, with anticyclone Rossby wave breaking (AWB) leading to a positive NAO event and cyclonic Rossby wave breaking (CWB) leading to a negative event [27][28][29][30][31]. In addition to the phase of the NAO, the RWB also plays a role in determining the NAO spatial pattern.…”

A Climatology of Rossby Wave Breaking on the Southern Hemisphere Tropopause

“…Several subsequent observational and modeling studies have examined the cause and occurrence of these types of RWB (e.g., Hartmann 1995;Hartmann and Zuercher 1998;Hartmann 2000;Peters and Waugh 2003;Moon and Feldstein 2009;Wittman et al 2007;Kunz et al 2009), with most studies focusing on either equatorward or poleward events. One exception is the study of Esler and Haynes (1999), who showed that all four paradigms occurred in an idealized model of the tropospheric circulation.…”

Tropospheric Rossby Wave Breaking and Variability of the Latitude of the Eddy-Driven Jet

“…Finally, no evidence is found in these experiments for the mechanisms proposed by, for example, Wittman et al (2007), Kunz et al (2009), andRivière (2011) in which RWB mediates the jet shift in response to an external forcing; RWB anomalies in response to an external forcing are indistinguishable from those due to internal variability. While this does not necessarily disprove these mechanisms, it does suggest that it will be very difficult to provide evidence for these mechanisms in a data source in which stochastic variability of jet latitude is present.…”

“…Specifically, wave breaking has been linked to the different phases of the North Atlantic Oscillation (Franzke et al 2004;Benedict et al 2004;Rivière and Orlanski 2007), the Pacific-North American pattern (Martius et al 2007;Franzke et al 2011), and hemispheric variations of the large-scale flow such as those diagnosed by the zonal index (e.g., Hartmann 1995;Akahori and Yoden 1997;Gong et al 2010;Wang and Magnustdottir 2011). Changes in wave breaking have been associated with climate change and stratospheric variability (Wittman et al 2004;Kunz et al 2009;Rivière 2011;Barnes and Hartmann 2012;Ndarana et al 2012; Barnes and Polvani 2013;Lu et al 2014). Furthermore, Rossby wave breaking (RWB) is directly associated with stratosphere-troposphere exchange (Sprenger et al 2007).…”

“…For example, changes in wave breaking have been identified as the cause of meridional shifts of the tropospheric jet in response to the polar vortex (Wittman et al 2007; Kunz et al 2009) and to strengthened upper-tropospheric baroclinicity in response to global warming (Rivière 2009(Rivière , 2011Wilcox et al 2012). …”