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.
Meridional heat transport by ocean and atmosphere
Trenberth and Caron (2001)
Large heat is handed over to the atmosphere from
ocean near the western boundary current regions
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:
1/2lat  2/3long 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
v  v   v '  v '
s
T  T   T '  T '
s
where
i
 a  : individual
JFM mean ,
a ' : synoptic ( 2  8 day ) transient anomaly
s
i
a ' : intraseaso nal ( 8 day  3 month ) transient anomaly
i
(2) Covariances: for each winter (JFM) and for the two time scales:
 vT  v  T    v ' T '    v ' T '    v ' T '    v ' T ' 
s
s
Synoptic
transient eddy flux
i
i
s
i
i
s
Intra-seasonal
transient eddy flux
(3) 31-yr time-series: sensible (<vT>) and latent (<vq>) 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)
1 psurface
(C p < v¢T ¢ > +L < v¢q¢ >)dp
ò
g 50hPa
=
[unit: W m-1]
(2) Northward heat transport by transient eddies
(Vertically and zonally integrated)
=
ò
360
0
1 psurface
[ ò
(Cp < v¢T ¢ > +L < v¢q¢ >)dp] dx
g 50hPa
[unit: PW]
(3) Lateral divergence of vertically integrated eddy heat fluxes
=
1
g
¶u¢T ¢ ¶v¢T ¢
¶u¢q¢ ¶v¢q¢
-2]
[W
m
(C
<
+
>
+L
<
+
>
)dp
ò 50hPa p ¶x ¶y
¶x
¶y
psurface
JFM mean northward heat flux by transient eddies (1)
(sensible+latent, vertically integrated from surface to 50 hPa)
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)
Vertical structures of
northward heat flux by transient eddies
(Average over a zonal band in 30-50N)
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)
1
g
Synoptic
ò
psurface
50hPa
(C p <
¶u¢T ¢ ¶v¢T ¢
¶u¢q¢ ¶v¢q¢
+
> +L <
+
>)dp
¶x
¶y
¶x
¶y
Intra-seasonal
Synoptic+Intra-seasonal
Black contours: SST isotherms for 6, 8, 10C
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 eddies
regressed 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+intraseasonal 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 variables
on 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 variables
on 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 the
Gulf Stream, Kuroshio Extension & Oyashio Extension
Gulf Stream Index: 15C at 200 m (1954-2006; Joyce et al. 2000)
Kuroshio Extension Index: 14C 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