Diagnosing concurrent drivers of weather extremes: application to hot and cold days in North America

International audienceA fundamental challenge in climate science is decomposing the con-7 current drivers of weather extremes in observations. Achieving this would pro-8 vide insights into the drivers of individual extreme events as well as into pos-9 sible future changes in extreme event frequencies under greenhouse forcing. 10 In the present work, we exploit recent results from dynamical systems the-11 ory to study the co-variation and recurrence statistics of different atmospheric 12 fields. Specifically, we present a methodology to quantify the recurrences of 13 bivariate fields, the repeated co-occurrences of distinct univariate fields, and 14 the dependence between two fields. The dependence is defined by a coupling 15 parameter, which varies according to the chosen fields, season, and domain 16 and can be understood in terms of the underlying physics of the atmosphere. 17 For suitably chosen fields, this approach enables to decompose the different 18 drivers of weather extremes. Here, we compute the above metrics for near-19 surface temperature and sea level pressure, and use them to study hot or cold 20 days over North America. We first identify states where temperature extremes 21 are strongly and weakly coupled to the large-scale atmospheric circulation, 22 and then elucidate the interplay between coupling and the occurrence of tem-23 perature extremes