Assessment of the impact of the planetary scale on the decay of blocking and the use of phase diagrams and enstrophy as a diagnostic

Abstract

-It was shown that abrupt changes in the large-scale structure of atmospheric flows may lead to the rapid decay of blocking. Analysis of phase diagrams made it possible to identify when sharp changes occurred in the dynamics of the system. The connection of these changes to the decay of blocking was estimated for three blocking events in the Southern Hemisphere. In addition to phase diagrams, enstrophy was used as a diagnostic tool for the analysis of blocking events. From the results of this analysis, four scenarios for the decay mechanisms were determined: (i) decay with a lack of synoptic-scale support, (ii) decay with an active role for synoptic processes, and (iii − iv) either of these mechanisms in the interaction with an abrupt change in the character of the planetary-scale flow.

The Predictability of Northern Hemispheric Blocking Using an Ensemble Mean Forecast System

“…Also, the study by [18] describes blocking as a quasistationary atmospheric state with quasi-barotropic structure, and in a quasi-barotropic flow the sum of the positive Lyapunov exponents is related to IRE. A Lyapunov exponent is the measure of the divergence or convergence of system trajectories that are initially close, and can be approximated by integrating enstrophy over a finite region known as IRE, which is vorticity squared [10,29]. The work of [29] used this technique to determine the stability or predictability within a planetry flow regime.…”

Integrated Regional Enstropy as a Measure of Kolmogorov Entropy

“…IRE conjectures that the blocking domain sum of the flow enstrophy is related to the sum of the positive eigenvalues of the linearization operator of the barotropic voricity equation [2,3]. As such, IRE can also be regarded as a flow stability indicator [2,3]. The work of [2] demonstrated for three case studies of Southern Hemisphere blocking, that IRE increased locally with the decay of each blocking event, and was relatively low during the maintenance period.…”

“…The study of [1] derived a quantity called Integrated Regional Enstrophy (IRE) which can be used as a measure for change in the zonal flow that may indicate blocking. IRE conjectures that the blocking domain sum of the flow enstrophy is related to the sum of the positive eigenvalues of the linearization operator of the barotropic voricity equation [2,3]. As such, IRE can also be regarded as a flow stability indicator [2,3].…”

“…As such, IRE can also be regarded as a flow stability indicator [2,3]. The work of [2] demonstrated for three case studies of Southern Hemisphere blocking, that IRE increased locally with the decay of each blocking event, and was relatively low during the maintenance period. This study and those of [4] and [5] suggest blocking does not survive the transition of large-scale flow regimes.…”

Sensitive versus Rough Dependence under Initial Conditions in Atmospheric Flow Regimes

“…This event was noteworthy as it survived a large-scale flow regime change during early 4-7 February 2014, as the Pacific North American (PNA) teleconnection pattern changed from a positive to negative configuration during early February 2014. Earlier work (e.g., [28,29]) suggested that blocking events should not survive a transition in the large-scale flow regime, but [27] showed that, under certain conditions, these events could survive the transition. Additionally, this event is noteworthy for its longevity and persistence.…”