A. J. Haklander, P. C. Siegmund, H. M. Kelder

Interannual variability of the
stratospheric wave driving
during northern winter
Alwin J. Haklander 1,2
Supervisor: dr. P.C. Siegmund 2
Promotor: prof. dr. H.M. Kelder 1,2
1 Eindhoven University of Technology (TU/e)
2 Royal Netherlands Meteorological Office (KNMI)
Chapman Conference on RSCCC
Santorini, Greece, Thu 27 Sep 2007

Intro
• Why is the NH midwinter wave driving
relevant
• How is it quantified
• Which factors determine the observed
interannual variability
“Fundamental causes for interannual variability poorly
understood” (2006 WMO/UNEP Ozone assessment,
SPARC Newsletter 29, July 2007)

Why is the NH midwinter wave
driving relevant
• Planetary waves mainly drive
Brewer-Dobson circulation
(BDC)
• BDC draws ozone-rich air
poleward from the Tropics
• Ozone is long lived in polar
night, so little loss there
• Meanwhile, new ozone
production in the Tropics by
the adjustment towards
photochemical equilibrium
• Therefore, BDC causes net
ozone production in NH winter
(Fusco&Salby,1999)
• Adiabatic compression of air
in downward branch at the
pole yields higher early-spring
temperatures → less PSC’s

Why is the NH midwinter wave
driving relevant
Wave driving ~ Extratropical ozone increase
(Ozone increase)
(Wave driving)
• Strong
correlation
January wave
driving at 100
hPa with
extratropical
ozone column
increase
(Fusco &
Salby, 1999)

Why is the NH midwinter wave
driving relevant
Wave driving ~ Adiabatic heating at high latitudes
• Strong
correlation
Jan-Feb wave
driving at 100
hPa with
Feb-Mar mean
T poleward of
60°N at 50 hPa
(Newman,
2005)
(Wave driving)

How is the wave driving
quantified
• F z = net zonal-mean upward flux of wave activity: F z
(upward component Eliassen-Palm flux F)
• F z is proportional to zonal-mean poleward eddy heat
flux [v*T*], with
v
southerly wind component
T
temperature
[] zonal mean
* deviation from zonal mean
• January-February average of [v*T*] over 40-80°N at
100 hPa (~16 km, lower stratosphere) good measure
of total midwinter wave driving in NH (Austin et al.
2003)

How is the wave driving
quantified
• We define H 100 as the January-February
average of [v*T*] over 40-80°N at 100 hPa
(following, e.g., Austin et al., 2003; Newman, 2005)
• ERA-40 reanalysis data for 1979-2002
2.5° × 2.5° lat-lon grid
6-hourly wind and temperature fields
23 levels between 1000 and 1 hPa

How is the wave driving
quantified
• We define
H 100 as the
January-
February
average of
[v*T*] over
40-80°N at
100 hPa

How is the wave driving
quantified
• H 100 ranges
between 11.2 and
19.2 K m/s
• Zonal waves 1-3
account for
>90% of H 100
• Zonal wave 1
dominates the
interannual
variability

Regression
coefficients
Which factors determine
the observed interannual
variability in H 100
– Variable planetarywave
spectrum at
100 hPa
Perform linear regression
analyses of H 100 with
different wave components
constituting H 100
The sum of regression
coefficients for all
wave components is 1.

Which factors determine
the observed interannual
variability in H 100
s = zonal wavenumber
→ Zonal-wave 1
dominates the
interannual
variability of the
total wave driving,
primarily its
stationary
component
→ Waves 1+2
account for about
85% of the
interannual
variability (r=0.88)

• Which factors determine
the observed interannual
variability in H 100
95%
significance
level
[v*T*] poorly defined at lowermost
levels due to extrapolation below the
Earth’s surface
– Variable tropospheric
wave source
Correlation coefficients of
H 100 with [v*T*] averaged
over 20-90°N not significant
in the troposphere.
→ Total tropospheric wave
source probably not a very
important factor

Which factors determine
the observed interannual
variability in H 100
s = zonal wavenumber
→ Fig. a) Only wave
1,2 components of
H 100 significantly
correlated with the
same component of
the upward wave
activity flux in the
troposphere
→ Fig. b) Wave 4
preferred mode for
breaking of very
long waves in
upper stratosphere

Which factors determine
the observed interannual
variability in H 100
So far…
→ Most of the interannual variability of the total wave
driving at 100 hPa can be attributed to stationary
wave 1, about 85% to wave 1+2 (r=0.88)
→ Total heat flux at 100 hPa not significantly
correlated with the total heat flux in the troposphere
→ However, a significant coupling between 100 hPa
and the troposphere does exist for the separate
wave-1 and wave-2 components
→ The variability of the total wave driving at 100 hPa
cannot be significantly attributed to the separate
wave-1 and wave-2 components

Which factors determine
the observed interannual
variability in H 100
Further focus…
Wave 1+2 dominate wave driving
at 100 hPa, both have separate
coupling with troposphere
→ Q: What does this coupling look like in the
meridional plane

• Wave activity is refracted
towards higher index of
refraction
• Stationary wave-1 correlation
maximum ~ coincides with
climatological wave guide

Conclusions
→ Most of the interannual variability of the total wave
driving at 100 hPa can be attributed to stationary
wave 1, about 85% to wave 1+2 (r=0.88)
→ Total heat flux at 100 hPa not significantly
correlated with the total heat flux in the troposphere
→ A significant coupling exists between 100 hPa and
the troposphere for the separate stationary wave-1
and stationary wave-2 components
→ Location of tropospheric stationary-wave 1 source
significantly affects its contribution to wave driving.

Way forward…
→ Analyze the effect of CO 2 doubling on the wave
driving with the MA-ECHAM4 GCM, by comparing a
30-yr doubled CO 2 run with a 30-yr control run
→ Preliminary results:
Highly significant increase of the wave driving
(>12%) in a doubled CO 2 climate:
~25% increase in stationary wave-1 component,
~100% increase in transient wave-5 component.
Stronger heat flux associated with larger zonal
temperature perturbations in the lower stratosphere.
Presented work recently published in ACP:
Haklander, A.J., P.C. Siegmund and H.M. Kelder, 2007: Interannual
variability of the stratospheric wave driving during northern winter.
Atmos. Chem. Phys., 7, 2575-2584.

Questions