A nonlinear multiscale interaction model for atmospheric blocking: The eddy-blocking matching mechanism

Abstract

In this article, a nonlinear multiscale interaction (NMI) model is used to propose an eddy-blocking matching (EBM) mechanism to account for how synoptic eddies reinforce or suppress a blocking flow. It is shown that the spatial structure of the eddy vorticity forcing (EVF) arising from upstream synoptic eddies determines whether an incipient block can grow into a meandering blocking flow through its interaction with the transient synoptic eddies from the west. Under certain conditions, the EVF exhibits a low-frequency oscillation on time-scales of 2-3 weeks. During the EVF phase with a negative-over-positive dipole structure, a blocking event can be resonantly excited through the transport of eddy energy into the incipient block by the EVF. As the EVF changes into an opposite phase, the blocking decays. The NMI model produces life cycles of blocking events that resemble observations. Moreover, it is shown that the eddy north-south straining is a response of the eddies to a dipole-or -type block. In our model, as in observations, two synoptic anticyclones (cyclones) can attract and merge with one another as the blocking intensifies, but only when the feedback of the blocking on the eddies is included. Thus, we attribute the eddy straining and associated vortex interaction to the feedback of the intensified blocking on synoptic eddies. The results illustrate the concomitant nature of the eddy deformation, the role of which, as a potential vorticity source for the blocking flow, becomes important only during the mature stage of a block. Our EBM mechanism suggests that an incipient block flow is amplified (or suppressed) under certain conditions by the EVF coming from the upstream of the blocking region. This also suggests that weather and climate models need to be run with a grid size below 100 km in order to simulate the matching EVF and thus atmospheric blocking.

On the dynamics of persistent states and their secular trends in the waveguides of the Southern Hemisphere troposphere

“…6) again shows a midlatitude wavetrain with positive-negative (negative-positive) structures occurring in regions of positive (negative) PV ′ 320 K anomalies. This is indicative of wave breaking occurring where Rossby waves encounter persistent anticyclonic Z ′ g500 hPa anomalies, generating potential vorticity which in turn acts to maintain the anomaly (Luo et al 2014). Significant baroclinic instabilities (PCr) are also associated with the wavetrain most notably in the polar jet between 0°E and 120°E during the summer and with the establishment of the subtropical jet between 60°E and 240°E in the austral winter.…”

“…In this paradigm, growing baroclinic instabilities are largely responsible for the onset of the coherent structure. Both paradigms support the idea that barotropic instability, often in the form of potential vorticity generation due to Rossby waves breaking on the mature coherent structure (Luo et al 2014), determines persistence and that the jets, influenced by meridional temperature gradients, act as waveguides.…”

The dynamics of barotropic vortex merging

“…(9)], is too strong such that no configuration may exist for the complete vortex merger to occur. In practice, it is possible that the vortex dynamics in a 3D space or inclusion of viscosity may allow for a complete merger and subsequent upscale growth of the resulting vortex (Kieu and Zhang, 2009;Huang and Xu, 2010;Luo et al, 2014). However, the barotropic model in this study suffices to demonstrate that an intuitive notion of merging of like-signed vortices, which is often assumed in studies of multiple vortex interaction, is highly intricate and should be taken with caution, as the vortex merger may not lead to an eventually enhanced circulation as one would expect.…”

“…Various fluid processes have been shown to be characterized by well-defined and coherent vortex interactions ranging from minute fluid vortex eddies to large-scale circulations (e.g., Yasuda, 1995;Ferreira and Schubert, 1997;Lansky et al, 1997;Cerretelli and Williamson, 2003;Josser and Rossi, 2007;Rodríguez-Marroyo et al, 2011;Yamazaki and Itoh, 2013;Luo et al, 2014;Tallapragada and Kieu, 2014). For specific mesoscale circulations in the atmosphere, vortex mergers are often connected to swift changes in development of tropical disturbances, which have significant impacts on the formation and subsequent track and intensity changes of tropical cyclones (Lander and Holland, 1993;Simpson et al, 1997;Ferreira and Schubert, 1997;Kieu and Zhang, 2009;Yu et al, 2010;Jang and Chun, 2015).…”

3D Variable Coefficient KdV Equation and Atmospheric Dipole Blocking

“…In the past decades, many investigators have proposed various nonlinear theories such as Rossby soliton [1][2][3][4], envelope Rossby soliton that is described by the Schrodinger equation [5,6], and others to explain the formation of atmospheric blocking and its life process. Although the eddy-forced envelope soliton model can describe a life cycle of atmospheric dipole blocking [7,8], the KdV-type soliton cannot represent the time variation or life of atmospheric dipole blocking [2,3]. However, by considering the time slow-varying basic flow, the KdV-type Rossby solitary wave can represent the life cycle of dipole blocking [9].…”