We use a simple yet Earth-like atmospheric model to propose a new framework for understanding the mathematics of blocking events. Analysing error growth rates along a very long model trajectory, we show that blockings are associated with conditions of anomalously high instability of the atmosphere. Additionally, the lifetime of a blocking is positively correlated with the intensity of such an anomaly, against intuition. In the case of Atlantic blockings, predictability is especially reduced at the onset and decay of the blocking, while a relative increase of predictability is found in the mature phase, while the opposite holds for Pacific blockings, for which predictability is lowest in the mature phase. We associate blockings to a specific class of unstable periodic orbits (UPOs), natural modes of variability that cover the attractor of the system. The UPOs differ substantially in terms of instability, which explains the diversity of the atmosphere in terms predictability. The UPOs associated to blockings are indeed anomalously unstable, which leads to them being rarely visited. The onset of a blocking takes place when the trajectory of the system hops into the neighbourhood of one of these special UPOs. The decay takes place when the trajectory hops back to the neighbourhood of usual, less unstable UPOs associated with zonal flow. This justifies the classical Markov chains-based analysis of transitions between weather regimes. The existence of UPOs differing in the dimensionality of their unstable manifold indicates a very strong violation of hyperbolicity in the model, which leads to a lack of structural stability. We propose that this is could be a generic feature of atmospheric models and might be a fundamental cause behind difficulties in representing blockings for the current climate and uncertainties in predicting how their statistics will change as a result of climate change.
Large-Ensemble Simulations Reveal Links Between Atmospheric Blocking Frequency and Sea Surface Temperature Variability
Department of Atmospheric and Climate Science, University of Washington（大气与气候科学系，华盛顿大学）；Department of Geosciences, Princeton University（地球科学系，普林斯顿大学）；High Meadows Environmental Institute, Princeton University（高梅斯环境研究所，普林斯顿大学）
Elimination of spectral blocking by ensuring rotation-free property of discretised pressure gradient within a spectral semi-implicit semi-Lagrangian global atmospheric model
Zonal asymmetries control the response of atmospheric blocking to Arctic warming in an aquaplanet experiment
University of Trento（特伦托大学）；Istituto Universitario Superiore di Pavia（帕维亚高等大学研究所）；University of Exeter（埃克塞特大学）；Center Agriculture Food Environment, University of Trento（特伦托大学农业食品环境中心）
The Typicality of Regimes Associated with Northern Hemisphere Heatwaves
CSIRO Environment（澳大利亚联邦科学与工业研究组织环境部门）；Department of Meteorology and Bolin Centre for Climate Research, Stockholm University（斯德哥尔摩大学气象系和博林气候研究中心）；School of Computing and Mathematical Sciences, University of Leicester（莱斯特大学计算与数学科学学院）
Mathematical Exploration of Earth Gravitational Field Impact on Seasonal Wind Flux in a Tropical Region
Nigeria Institute of Soil Science（尼日利亚土壤科学研究所）；Institute of Biopaleogeography named under Charles R. Darwin（以查尔斯·达尔文命名的生物古地理学研究所）；University of Abuja（阿布贾大学）；Federal University of Lafia（拉菲亚联邦大学）；Sam Higginbottom University of Agriculture, Technology and Sciences（萨姆·希金博特姆农业、技术与科学学院）；University of Port Harcourt（波特哈科特大学）
