Mechanisms triggering the regime shi3 in the North Pacific.

Transcription

1 Mechanisms triggering the regime shi3 in the North Pacific. Katerina Giamalaki Claudie Beaulieu (UoS) Stephanie Henson (NOCS) Davide Faranda (LSCE/IPSL) Adrian MarMn (NOCS) Simon Josey (NOCS)

2 Introduc)on Regime Shi2s Shi2 Area Hypothesis Outline 1. Did an extreme atmospheric event ini)ate the shi2? Dynamical Systems Analysis 2. Were there sudden changes in net heat flux that maintained the shi2? Empirical Orthogonal Func)ons (EOFs) & Environmental change- point detec)on analysis (EnvCpt) How is everything connected? - Conclusions 2/21

3 Regime Shi2s Abrupt changes High - amplitude variability Propaga)on through trophic levels Leading to ecosystem restructuring hpp:// com/html/ar)cles/ ar)cle/ brucewrightcolumn1.ht m/ 3/21

4 Posi)ve PDO - Atmosphere 4/21

5 Posi)ve PDO Ocean 5/21

6 What caused the 1977 shi2? Examine the potenmal of dynamical and stamsmcal analyses to reveal new insights. Test the hypothesis: Extreme atmospheric event à forcing Changes in heat budget à maintenance 6/21

7 Outline Introduc)on Regime Shi2s Shi2 Area The 1977 regime shi2 1. Did an extreme atmospheric event inimate the shi3? Dynamical Systems Analysis 2. Were there sudden changes in net heat flux that maintained the shi2? Empirical Orthogonal Func)ons (EOFs) & Environmental change- point detec)on analysis (EnvCpt) How is everything connected? - Conclusions 7/21

8 Dynamical system analysis Sea Level Pressure (SLP) Daily from January 1948 to August 2016 Na)onal Centre for Environmental Predic)on/Na)onal Centre for Atmospheric Research (NCEP/NCAR) reanalysis 2.5 x2.5 Calcula)on of instantaneous proper)es: Instantaneous dimension d(ζ) Persistence θ(ζ) (Faranda et al. 2017) 8/21

9 Instantaneous Proper)es ζ 1 (a state of the system) Field value ζ 2 ζ 3 Daily SLP papern θ(ζ) Time d(ζ) = number of degrees of freedom for each θ(ζ) = indicator of the persistence )me of each 9/21

10 a d(ζ) extreme low Extreme SLP paperns b θ(ζ) extreme high c d(ζ) extreme high d θ(ζ) extreme low 10/21

11 When did the extreme SLP happen? d(ζ) extreme low θ(ζ) extreme high d(ζ) extreme high θ(ζ) extreme low 11/21

12 Is 1977 different? d(ζ) extreme low days per year Average d(ζ) extreme low days per year = 5.3 d(ζ) extreme low days in 77 94% of extreme days occur in winter (Jan- Feb) 12/21

13 Introduc)on Regime Shi2s Shi2 Area The 1977 regime shi2 Outline 1. Did an extreme atmospheric event ini)ate the shi2? Dynamical Systems Analysis 2. Were there sudden changes in net heat flux that maintained the shi3? Empirical Orthogonal FuncMons (EOFs) & Environmental change- point detecmon analysis (EnvCpt) How is everything connected? - Conclusions 13/21

14 Empirical Orthogonal Func)ons (EOFs) Iden)fy large scale paperns governing the region Net heat flux Winter averages from January 1948 to August 2016 NCEP/NCAR reanalysis 2.5 x2.5 14/21

15 Any sudden changes in the net heat flux? EOF 1: 22% Abrupt change /21

16 Environmental change- point detec)on analysis Fits eight models (EnvCpt) Characterizes different types of variability no changes long- term trends changes in mean/variance changes in trend short term memory Net heat flux (First EOF & Pixel- wise) Winter averages from January 1948 to August 2016 NCEP/NCAR reanalysis 2.5 x2.5 (Killick, Beaulieu and Taylor, 2016; hpps://cran.r- project.org/web/packages/envcpt/index.htm) 16/21

17 Any sudden changes in the net heat flux? Trend cpt +AR(1) Trend cpt Mean cpt +AR(1) Mean cpt Trend + AR(1) Trend Mean +AR(1) Mean Data EnvCpt à 1 st EOF of net heat flux AIC 17/21 ß More likely Less likely à

18 Any sudden changes in the net heat flux? Kuroshio Oyashio Extension EOF 1 Net heat flux 40 La)tude Number of pixels per year Longitude 18/21

19 Outline Introduc)on Regime Shi2s Shi2 Area The 1977 regime shi2 1. Did an extreme atmospheric event ini)ate the shi2? Dynamical Systems Analysis 2. Were there sudden changes in net heat flux that maintained the shi2? Empirical Orthogonal Func)ons (EOFs) & Environmental change- point detec)on analysis (EnvCpt) How is everything connected? - Conclusions 19/21

20 How is everything connected? 20/21

21 Conclusions Novel approaches including Dynamical System and Change- point Detec)on Analyses showing: Sta)s)cal evidence that an extreme Aleu)an Low occurred in winter ; Strongest and most persistent Aleu)an Low throughout the whole study period; Abrupt changes detected in the Kuroshio- Oyashio Extension region centred around the year /21