A new mathematical framework for atmospheric blocking events
File(s)
Author(s)
Lucarini, Valerio
Gritsun, Andrey
Type
Journal Article
Abstract
We use a simple yet Earth-like hemispheric atmospheric model to propose a new framework for the mathematical properties of blocking events. Using finite-time Lyapunov exponents, we show that the occurrence of blockings is associated with conditions featuring anomalously high instability. Longer-lived blockings are very rare and have typically higher instability. In the case of Atlantic blockings, predictability is especially reduced at the onset and decay of the blocking event, while a relative increase of predictability is found in the mature phase. The opposite holds for Pacific blockings, for which predictability is lowest in the mature phase. Blockings are realised when the trajectory of the system is in the neighbourhood of a specific class of unstable periodic orbits (UPOs), natural modes of variability that cover the attractor the system. UPOs corresponding to blockings have, indeed, a higher degree of instability compared to UPOs associated with zonal flow. Our results provide a rigorous justification for the classical Markov chains-based analysis of transitions between weather regimes. The analysis of UPOs elucidates that the model features a very severe violation of hyperbolicity, due to the presence of a substantial variability in the number of unstable dimensions, which explains why atmospheric states can differ a lot in term of their predictability. Additionally, such a variability explains the need for performing data assimilation in a state space that includes not only the unstable and neutral subspaces, but also some stable modes. The lack of robustness associated with the violation of hyperbolicity might be a basic cause contributing to the difficulty in representing blockings in numerical models and in predicting how their statistics will change as a result of climate change. This corresponds to fundamental issues limiting our ability to construct very accurate numerical models of the atmosphere, in term of predictability of the both the first and of the second kind in the sense of Lorenz.
Date Issued
2019-11-01
Date Acceptance
2019-10-14
Citation
Climate Dynamics, 2019, 54, pp.575-598
ISSN
0930-7575
Publisher
Springer (part of Springer Nature)
Start Page
575
End Page
598
Journal / Book Title
Climate Dynamics
Volume
54
Copyright Statement
© The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000493640000001&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Subjects
Science & Technology
Physical Sciences
Meteorology & Atmospheric Sciences
Atmospheric blockings
Unstable periodic orbits
Covariant Lyapunov vectors
Lyapunov exponents
Predictability
Numerical modelling
UNSTABLE PERIODIC-ORBITS
LOW-FREQUENCY VARIABILITY
WEATHER REGIME TRANSITIONS
NORTHERN-HEMISPHERE WINTER
MULTIPLE FLOW REGIMES
STATISTICAL PROPERTIES
LYAPUNOV VECTORS
ATLANTIC BLOCKING
NATURAL MEASURE
ERROR GROWTH
Publication Status
Published
Date Publish Online
2019-11-01