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Young-Oh Kwon and Terrence M. Joyce (Woods Hole Oceanographic Institution)

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Climate Implications of Frontal Scale Air-Sea Interaction

(August 5-7, 2013 / NCAR)

Northern Hemisphere Atmospheric Transient Eddy Fluxes and their Co-variability with the Gulf Stream and Kuroshio-Oyashio Extensions

Young-Oh Kwon and Terrence M. Joyce

(Woods Hole Oceanographic Institution)

Support from the NASA Physical Oceanography Program

is gratefully acknowledged.

Trenberth and Caron (2001)

Large heat is handed over to the atmosphere from ocean near the western boundary current regions

- Source:
NASA MERRA (Modern Era Retrospective-analysis for Research and Applications)

- Period and temporal resolution:
Daily mean for 1979-2009 (31 years)

- Season: Winter (JFM:all the analysis shown here is for the winter only!)
- Spatial domain and resolution:
1/2lat 2/3long in the Northern Hemisphere only.

- Levels:
Sea-level, 850 hPa, 500 hPa, 250 hPa, 200 hPa, and 100 hPa

- Variables:
Winds (u, v), temperature (T), and specific humidity (q)

(1) Two time scales: synoptic (2-8days)and intra-seasonal (8days-3months)

Daily variables for each winter (e.g. JFM 1979) at each level

(2) Covariances: for each winter (JFM) and for the two time scales:

Synoptic

transient eddy flux

Intra-seasonal transient eddy flux

(3) 31-yr time-series: sensible (<vT>) and latent (<vq>) for each time scale.

Climatological mean and interannual standard deviation.

(1) Northward heat flux by transient eddies

(Vertically integrated from the surface to 50 hPa)

= [unit: W m-1]

(2) Northward heat transport by transient eddies

(Vertically and zonally integrated)

= [unit: PW]

(3) Lateral divergence of vertically integrated eddy heat fluxes

= [W m-2]

Synoptic (2-8 days)

Intra-seasonal (8-90 days)

Contour Interval : 2 107 W m-1

Mean WBC positions: Gulf Stream / Kuroshio Extension / Oyashio Extension

(from Joyce et al. 2009 & Frankignoul et al. 2011)

Synoptic

Intra-seasonal

Synoptic+Intra-seasonal

Black contours: SST isotherms for 6, 8, 10C

Synoptic

Intra-seasonal

Synoptic+Intra-seasonal

GSI

KEI

OEI

BjerknesCompensation or Coupled Oscillation?

- Synoptic and intra-seasonal time scales contribute comparably to the zonally integrated northward heat transport by transient eddies, though with very distinct spatial patterns.
- Lateral divergence of transient eddy heat fluxes : synoptic+intra-seasonal mean distribution andinterannual variability are remarkably coincident with the ocean fronts.
- Greater than 50% of the interannual variance of the winter northward heat flux and transport by transient eddies in the synoptic bands are correlated with interannual variability for the positions of the KE, OE and GS as the forcing as well as the response to the ocean front changes.

v regression

(C.I.= 0.5 m s-1)

T regression

(C.I.=0.5 K)

v regression T regression

(C.I.=0.5 106 W m-2)

=

H regression

(C.I. 10m / gray: negative )

Red: positive regressions / Blue: negative regressions

v regression

(C.I.= 0.5 m s-1)

T regression

(C.I.=0.5 K)

v regression T regression

(C.I.=0.5 106 W m-2)

=

H regression

(C.I. 10m / gray: negative )

Red: positive regressions / Blue: negative regressions

Gulf Stream Index: 15C at 200 m (1954-2006; Joyce et al. 2000)

Kuroshio Extension Index: 14C at 200 m (1980-2006; Joyce et al. 2009)

Oyashio Extension Index: maximum dSST/dy based on 1/4 SST (1983-2007; Frankignoul et al. 2011)

Synoptic

Intra-seasonal

Mean contour interval: 4 107 W m-1