Increased eddy activity in the northeastern Pacific during

Transcription

1 Increased eddy activity in the northeastern Pacific during Mengrong Ding 1,2,Pengfei Lin 1,2*, Hailong Liu 1,2*,and Fei Chai 3,4 1 LASG, IAP, CAS, Beijing, China 2 UCAS, Beijing, China 3 School of Marine Sciences, UMO, Maine, USA 4 SOED, SOA, Zhejiang, China Reference : Ding, M., Lin, P., Liu, H., and Chai, F.,2017: Increased eddy activity in the northeastern pacific during Journal of Climate, doi: /jcli-d

2 What are ocean mesoscale eddies? cyclonic anticyclonic Mesoscale eddies almost exist everywhere in the ocean; - Horizontal scale : O(10)-O(100) km; - Time scale : weeks-months.

3 Why to analyze the trends of eddies in the NEP? The non-uniform distribution of wind-related changes in the eddy activity could affect the regional patterns of ocean circulation and biogeochemical responses to future climate change. Patara et al.,2016 Where the large variances of both Pacific Decadal Oscillation(PDO) and North Pacific Gyre Oscillation(NPGO) happen. Di Lorenzo et al,2008

4 Two problems to be settled: To examine the long-term variabilities of eddy activity in the NEP and the dynamic mechanisms behind it; To discuss the relationship between the long-term variabilities of eddy activity and the dominate climate modes, i.e., the Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO).

5 The increasing trend of eddy activity in the NEP Left. Linear trends (yr -1 ) of (a) normalized EKE;(b) EON; (c) CEON; (d) AEON. Right: Top: Linear trends (ms -1 yr -1 ) of wind anomalies. Bottom: Comparison of 10m wind and SLP between ( ) and ( ).

6 Decadal variabilities of eddy activity in the NEP Right: Annual average of the EON (shading), EKE (contour, units: cm 2 /s 2 ) and ERA-interim 10-m wind field (vector, units: m/s) for (a) and (b) (c) Difference between and Left: The lead and lag correlation coefficients between the NPGO(red lines) or the PDO(blue lines) index and the 4- year-low-pass-filtered regionally-averaged EKE time series with linear trend (solid lines) or without linear trend (dashed lines) in the study domain.

7 Conclusions Significant increasing linear trends of eke and eon in the NEP, caused by the increase of eddy lifetime; The weakening trend of surface winds can explain the prolongation of eddy lifetime; The enhanced anticyclonic WSC anomaly is found to provide a more suitable environment for the growth of AEs; The large-scale surface wind anomaly is also linked to the decadal variation associated with the climate modes (PDO and NPGO) in the North Pacific.

8 Future Work To evaluate the global eddy activity with the model output(licom/cesm); To analyze the long-term behaviors of eddy activity with the model dataset AVISO CORR. = 0.85 LICOM

9 Questions?

10 Eddy occurrence number: (mean state)

11 Eddy occurrence number: (trend)

12 An Eddy-resolving OGCM LICOM2.0 FGOALS LASG/IAP Climate system Ocean Model ICE ATM CPL OCN LND LICOM Low To High 1. Model domain: 66 N 78 S, Increase the resolution: 1/10, 55 levels 2. Modify biharmonic viscosity 3. Improve the barotropic and baroclinic split methods 4. Optimize parallel algorithm and memory.

13 Experiments Model: LICOM version 2 Resolution : 1/10, 55 levels Domain: 78 S-66 N (no Arctic Ocean) Spinup Experiments (OMIP forcing) 8 years ( ) QUIK Experiments (CORE2 heat flux + QUIK wind) 12 years Hindcast 60 years ( ) Spinup CORE Experiments (CORE2 forcing) Satellite SLA from merged gridded Data weekly from

14 Mechanism for the increase: Increases of eke and eon Increases of eddy Existence (lifetime) dissipation of eddy energy Candidates for the dissipation of eddy energy: 1) bottom friction dissipation; 2) interaction with the internal wave field; 3) continental margin scattering/absorption ; 4) suppression by wind work. (Ferrari and Wunsch, 2009)

15 Mechanism for the increase: Increases of eke and eon Increases of eddy Existence (lifetime) dissipation of eddy energy Candidates for the dissipation of eddy energy: 1) bottom friction dissipation; 2) interaction with the internal wave field; 3) continental margin scattering/absorption ; 4) suppression by wind work. (Ferrari and Wunsch, 2009)

16 Mechanism for the increase: Top: Linear trends (ms -1 yr -1 ) of wind anomalies. The hatched areas indicate the linear trend exceeding the 95% confidence level. Bottom: Comparison of 10m wind and SLP between ( ) and ( ). TT ee ~ 2ρρ oodd 3ρρ aa CC DD UU aa TT ee : the eddy attenuation time scale TT ee, ρρ oo : The density of surface seawater, ρρ aa : the density of surface air, DD: the vertical scale of mesoscale eddy, CC DD :the drag coefficient. (Gaube et al., 2015)

17 Figure S1. Linear trends of eddy lifetime (units: weeks/year) for (a) all eddies, (b) CEs and (c) AEs from 1993 to The hatched area indicates the linear trend exceeding the 95% confidence level.

18 Figure S2. The linear trends of (a) eddy kinetic energy (EKE) (units: cm -2 s -2 yr -1 ) and (b) normalized EKE (units: yr -1 ) during The hatched areas indicate the linear trend exceeding the 95% confidence level.

19 Figure S3. Time series of region-averaged EON calculated for Chelton et al. (2013) (C13, black curve) and Faghmous et al. (2015) (F15, blue curve). Linear fitting lines of the time series are plotted, and the trends are noted, with the p value in the parentheses, which means exceeding 95% confidence level if p value is < 0.05.

20 Figure S4. Time series of regionally averaged (black curves) (a) EKE, (b) EON, (c) CEON, and (d) AEON from 1993 to The blue curves denote the regionally averaged existence number of eddies for (b) all eddies, (c) CEs, and (d) AEs. The STD of the regionally averaged EKE is noted in (a). Linear fitting lines of the time series are plotted, and the trends are also noted, with the p values in parentheses; the 95% confidence level is exceeded when p values are less than 0.05.