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)

Climate Implications of Frontal Scale Air-Sea Interaction (August 5-7, 2013 / NCAR)

Support from the NASA Physical Oceanography Program is gratefully acknowledged.

Meridional heat transport by ocean and atmosphere

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

Trenberth and Caron (2001)

Data: atmospheric transient eddy heat fluxes• 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)

Calculation: atmospheric transient eddy heat fluxes

(1) Two time scales: synoptic (2-8days) and intra-seasonal (8days-3months) Daily variables for each winter (e.g. JFM 1979) at each level

is

is

TTTT

vvvv

''

''

anomalytransientmonthdaynalintraseasoa

anomalytransientdaysynoptica

meanJFMindividualawhere

i

s

)38(:'

)82(:'

,:

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

siisiiss TvTvTvTvTvvT ''''''''

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.

Variables examined(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]

JFM mean northward heat flux by transient eddies (1)(sensible+latent, vertically integrated from surface to 50 hPa)

Synoptic (2-8 days)

Mean WBC positions: Gulf Stream / Kuroshio Extension / Oyashio Extension(from Joyce et al. 2009 & Frankignoul et al. 2011)

Contour Interval : 2 107 W m-1

Intra-seasonal (8-90 days)

Vertical structures of northward heat flux by transient eddies

(Average over a zonal band in 30-50N)

Zonally integrated northward heat transport by transient eddies (2)

(Climatological JFM mean and interannual standard deviation)

Lateral divergence of transient eddy heat fluxes (3)(Vertically integrated climatological mean for JFM)

Synoptic Intra-seasonal Synoptic+Intra-seasonal

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

Interannual standard deviation of JFM lateral divergence of heat flux by transient eddies (3)

Synoptic Intra-seasonal Synoptic+Intra-seasonal

Northward heat transport by synoptic transient eddiesregressed on the GSI, KEI, OEI

GSI KEI OEI

Bjerknes Compensation or Coupled Oscillation?

Summary

• 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 and interannual 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.

Thank you

Regression of intra-seasonal daily 850 hPa variableson the Pacific-North America (PNA) teleconnection index

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

Regression of intra-seasonal daily 850 hPa variableson the Arctic Oscillation (AO) index

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

Indices for the meridional position of theGulf Stream, Kuroshio Extension & Oyashio Extension

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)

Interannual standard deviation of JFM northward heat fluxes by transient eddies (1)

Synoptic Intra-seasonal

Mean contour interval: 4 107 W m-1