© Imperial College LondonPage 1 Solar Influence on Stratosphere-Troposphere Dynamical Coupling Isla...
-
Upload
tabitha-washington -
Category
Documents
-
view
216 -
download
1
Transcript of © Imperial College LondonPage 1 Solar Influence on Stratosphere-Troposphere Dynamical Coupling Isla...
© Imperial College LondonPage 1
Solar Influence on Stratosphere-Troposphere Dynamical Coupling
Isla Simpson, Joanna D. Haigh, Space and Atmospheric Physics, Imperial College London
Mike Blackburn, Department of Meteorology, University of Reading
© Imperial College LondonPage 2
• Introduction to the Solar influence on climate over the 11-year cycle.
• Model experiments to investigate how the tropospheric response over the 11-year cycle could be produced by a dynamical response to stratospheric heating.
• Comparison of two different stratospheric heating perturbation cases.
© Imperial College LondonPage 3
Temperature changes over the 11-year cycle
• Non-uniform.• Increase of ~1K in equatorial stratosphere,
decreasing towards the poles.• Banded increase in temperature in mid-latitudes.
Figure: Haigh (2003)
Multiple regression analysis of NCEP/NCAR reanalysis, 1979-2000
© Imperial College LondonPage 4
Circulation changes over the 11-year cycle
• Weakening and poleward shift of the mid-latitude jets.• Weakening and expansion of the Hadley cells.• Poleward shift of the Ferrell cells.
Figure: Haigh and Blackburn (2006)
Multiple regression analysis of NCEP/NCAR reanalysis, DJF, 1979-2002
© Imperial College LondonPage 5
Model Experiments:
• Simplified General Circulation Model (Reading IGCM2.2)– T42L15– Newtonian Relaxation– No Orography
• Haigh et al (2005) - Equatorial Heating gave a similar response to that seen over the Solar cycle.
• Spin-up ensemble:– 200, 50-day runs
5K 0K4.5K0.5K
© Imperial College LondonPage 6
Change in temperature over the spin-up
Control
Equilibrium (Equatorial heating (5K) – Control)
09
2029
4049
© Imperial College LondonPage 7
Change in zonal wind over the spin-upEquilibrium (Equatorial heating (5K) – Control)
Control 09
2029
4049
© Imperial College LondonPage 8
increases
increases
decreases
decreases
Changes in eddy momentum fluxes are in the right sense to drive meridional circulation changes.
y
vuvf
t
u
]''[][
][
y
vu
''
][v
][v
y
vu
''
Mean meridional circulation
Horizontal Eddy Momentum Flux [u’v’]
© Imperial College LondonPage 9
Anomalous meridional circulations are accompanied by zonal wind accelerations in the troposphere:
y
vuvf
t
u
]''[][
][
increases
increases
decreases
decreases
Mean meridional circulation
Zonal mean zonal wind [u]
][v
][u
][v
][u
© Imperial College LondonPage 10
Comparison with zonally symmetric model.
• Eddy forcing remains fixed at its value of the control run.• Heating perturbation applied and the model run as before.
• Not much response in the troposphere, particularly at mid/high latitudes. it is altered eddy momentum fluxes that are important in driving the
tropospheric circulation changes.
Full 3D model No change in Eddy fluxes
[mmc]
[u]
© Imperial College LondonPage 11
What’s causing the change in eddy momentum fluxes?
E-P Flux
]''[
]''[
vF
vuF
p
Refractive Index
222
2
2cosa
NH
f
a
k
cu
qn y
C=8ms-1
© Imperial College LondonPage 12
Days 0 to 9 of the spin-up:
Change in E-P Flux and
Change in
222
2
2cosa
NH
f
a
k
cu
qn y
''vu
Change in : cu
qy
a) Only changing yq
b) Only changing u
© Imperial College LondonPage 13
Days 40 to 49 of the spin-up:
Change in E-P Flux and
Change in
222
2
2cosa
NH
f
a
k
cu
qn y
''vu
Change in : cu
qy
a) Only changing yq
b) Only changing u
© Imperial College LondonPage 14
Contributions to the change in PV gradient(days 0 9):
pp
pyyy
u
T
p
R
fuq
2
yyu
u
Meridional Curvature
Third term (only changing )
Third term (only changing )
Total change in PV gradient
u
© Imperial College LondonPage 15
Outline of mechanism:
Altered vertical temperature gradients Zonal wind accelerations
stratosphere/tropopause
Change in horizontal eddy momentum flux
Changes in mean meridional circulation
Zonal wind accelerations in the troposphere.
Altered horizontal temperature gradients
© Imperial College LondonPage 16
Comparing Uniform and Equatorial Heating:
5K
0K
5K
Equatorial heating (5K) (E5)
Uniform heating (5K) (U5)
Weakening and polewards jet shift.
Weakening and equatorwards jet shift.
© Imperial College LondonPage 17
yq
''vu
E-P Flux
E5 (days 0 9 ) U5 (days 0 9 )
© Imperial College LondonPage 18
E5 (days 40 49 ) U5 (days 40 49 )
u
E-P flux and
n2
© Imperial College LondonPage 19
Conclusions
• The tropospheric response to increased Solar activity could be produced by a dynamical response to increased heating in the stratosphere.
• Changes in eddy momentum flux are important in driving circulation changes in the troposphere.
• Feedback with changing zonal wind in the troposphere influencing eddy propagation.
• Change in vertical temperature gradient around the tropopause and its localisation in latitude is important in determining the direction of the jet shift.
© Imperial College LondonPage 20
© Imperial College LondonPage 21
© Imperial College LondonPage 22
© Imperial College LondonPage 23
© Imperial College LondonPage 24
© Imperial College LondonPage 25
+ = control
* = E5
© Imperial College LondonPage 26
pp
pyyy
u
T
p
R
fuq
2
© Imperial College LondonPage 27
Equilibrium (Equatorial heating (5K) – Control)
Control
Change in mean meridional circulation over the spin-up
09
2029
4049
© Imperial College LondonPage 28
Stratospheric and Tropopause level accelerations:
• Consistent with altered temperature gradients.• Thermal wind balance:
][][ T
z
u
Zonal mean Temperature Zonal-mean zonal wind
Increase Decreased Decreased Increased
][T
][T
z
u
][
z
u
][
© Imperial College LondonPage 29
Momentum Balance:
y
vuvf
t
u
]''[][
][
Acceleration of zonal mean zonal wind Coriolis force on
meridional wind
Convergence of horizontal eddy momentum flux
[u] days 20-29 - control [v] days 20-29 - control
•[u] and [v] terms don’t balance changes in eddy momentum fluxes must be important.
© Imperial College LondonPage 30
© Imperial College LondonPage 31
E5
© Imperial College LondonPage 32
U5