The Tropical Lower Stratospheric Response to 11Year Solar Forcing: Dynamical Feedbacks From
the Troposphere-Ocean Response
Lon Hood
Lunar and Planetary Laboratory
University of Arizona
Tucson, Arizona
USA
Acknowledgments: Boris Soukharev
SORCE Science Meeting
Sedona, Arizona
September 14, 2011
The Mean Meridional Circulation Inferred from the Observed
Distributions of Trace Species (Ozone, Water Vapor, Methane, etc.):
The ``Brewer-Dobson’’
Circulation
E. Cordero et al., Stratospheric Ozone Electronic Textbook, NASA/GSFC
C
Solar versus Volcanic Origin:
P
After Hood et al., JGR, 2010
 Timing agrees better with solar origin than with volcanic origin
 Ground-based ozone data prior to 1979 also show a solar cycle variation (WMO, 2006)
Comparison of tropical
column ozone record with
50 hPa temperature record
from NCEP/NCAR
Reanalysis data.
35oS to 35oN:
Deseasonalized
MULTIPLE REGRESSION STATISTICAL MODEL:
Y’(t) = ctrendt + ctrendt’+ cQBO1u30mb(t-lagQBO1)+ cQBO2u10mb(t-lagQBO2)
+ cvolcanicAerosol(t) + csolar MgII(t) + dENSON3.4(t-lagENSO)+ (t)
where:
Y’(t) = deviation of atmospheric quantity from the seasonal mean
t = time measured in 3-month seasonal increments
t , = 0 for t < T0 ; t , = (t - T0) for t ≥ T0 ; T0 = DJF of 1996
U30(10)mb(t- lagQBO) = NCEP 30(10) mb equatorial wind speed (lagged)
Aerosol(t) = Volcanic aerosol index (10 hPa and below only)
MgII(t) = Solar MgII UV index
N3.4(t-lagENSO) = Mean SST, 5oS - 5oN, 120oW - 170oW (lagged)
(t) = residual error term
``Observed’’ Solar Cycle Variation of Stratospheric Ozone:
(Estimated from a Multiple Regression Statistical Analysis of SAGE II Data, 1985-2003)
Positive up to
at least 54 km.
Updated from Soukharev and Hood, JGR, 2006
Shaded areas are statistically significant at 95% confidence.
SAGE II
WACCM3 coupled to CCSM3:
2.5
1.0
1.5
Observations
Model
SAGE II
WACCM3 coupled to CCSM3:
2.5
1.0
1.5
Observations
Model
What is producing the unexpectedly large lower stratospheric
response to the solar cycle?
SAGE II
WACCM3 coupled to CCSM3:
2.5
1.0
1.5
Observations
Model
The observed lower stratospheric response to the solar cycle may imply a
solar-induced weakening of the mean meridional (Brewer-Dobson)
circulation near solar maxima that is not fully simulated by current models.
The observed decadal variation of extratropical wave forcing
has peaks near or approaching solar minima and has troughs
near or approaching solar maxima:
``Top-Down’’ Solar UV Forcing Mechanism:
Solar UV-induced enhancements of
the lower mesospheric subtropical
jet (LMSJ) near the time of winter
solstice lead to changes in
planetary wave propagation and
the strength of the Brewer-Dobson
circulation. The net result for the
tropical stratosphere is relative
downwelling under solar maximum
conditions.
A number of observational and
model studies have supported
this mechanism: Gray et al.,
2001a,b; 2003; 2004; 2007;
Matthes et al., 2004; 2006.
However, the model response in
the lower stratosphere is
generally much weaker than is
seen in the observations.
Transportinduced O3 and
T increase; +
radiative T
increase
Kodera and Kuroda, JGR, 2002:
On the other hand, changes in surface climate can also influence the BDC.
Icelandic
Low
Siberian
High
Aleutian Low
The sea level pressure distribution in the northern winter extratropics forces
planetary-scale Rossby waves (``planetary waves’’) that propagate up into the
stratosphere and drive the mean meridional (Brewer-Dobson) circulation.
``Bottom-Up’’ Solar Forcing Mechanism:
Hypothesis: A significant
troposphere-ocean response to
solar total solar irradiance (TSI)
forcing exists (van Loon et al.,
2007; Meehl et al., 2009). If so,
then the troposphere-ocean
response will modify planetary
wave forcing at the lower
boundary, modify the BDC, and
may produce part or all of the
observed lower stratospheric
response.
Composite averages for DJF during 11 peak
solar years (van Loon et al., [2007]:
The derived response resembles that
during a La Niña (cold ENSO) event.
After Meehl et al., Science, 2009,
and van Loon et al., JGR, 2007.
ENSO Regression
Coefficients:
Sea surface
temperature (SST) and
sea level pressure
(SLP) response to a
moderate La Niña
event (change in the
Niña 3.4 index of -1
unit) during NH
winter.
oC
3.5 hPa
hPa
Sea surface temperature
(SST) and sea level
pressure (SLP) response
to the 11-year solar
cycle (solar max - min)
based on Hadley Centre
data over the 1908-2009
period.
hPa
HADLEY
3.3 hPa
SLP results are
consistent with previous
studies: Christoforou
and Hameed, 1997; van
Loon et al., 2007; Roy
and Haigh, 2010.
oC
3.3 hPa
The sea level pressure
response to the solar
cycle has similarities
to the SLP response to
a moderate La Niña
event (change in the
Niña 3.4 index of -1
unit) during NH
winter.
oC
3.5 hPa
hPa
Solar Regression Coefficient
ENSO Regression Coefficient
Transportinduced NOX
decrease;
photochemic
al O3 increase
Transport-induced
ozone decrease
Reproducibility Test for
ENSO Aliasing:
Solar regression coefficients at
zero lag for Hadley Centre Sea
Level Pressure (SLP) and Sea
Surface Temperature (SST)
over the 1880-1945 period:
SLP Response is centered
on a lag of about -1 year.
Areas enclosed by dark lines are
formally significant at 95%
confidence.
Reproducibility Test for
ENSO Aliasing:
Solar regression coefficients at
zero lag for Hadley Centre Sea
Level Pressure (SLP) and Sea
Surface Temperature (SST)
over the 1946-2009 period:
SLP Response is centered
on a lag of about -1 year.
Areas enclosed by dark lines are
formally significant at 95%
confidence.
Conclusions:
1. There is observational evidence for solar cycle responses of lower
stratospheric ozone and temperature at tropical and subtropical
latitudes.
2. There is observational evidence for solar cycle responses of sea level
pressure and (to a much lesser extent) sea surface temperature in the
North Pacific region over the 1880-2009 period. The SLP response
consists of a weakening and westward shift of the Aleutian low near
and approaching solar maxima. This is similar to the SLP response to
a moderate La Niña event.
3. The weakened Aleutian low near solar maxima reduces the planetary
wave one amplitude near the surface, which results in a reduced planetary
wave flux in the extratropical lower stratosphere. This reduced wave flux
implies a deceleration of the Brewer-Dobson circulation, which reduces the
tropical upwelling rate, leading to increased tropical ozone column
amounts.
4. This ``bottom-up’’ mechanism probably contributes significantly to
producing the tropical lower stratospheric response, including the solar
cycle variation of total ozone.
Extra Slides
Extratropical Wave Forcing of the Brewer-Dobson Circulation:
F  0
u/t < 0
w* > 0
dT/dt < 0
dO3/dt < 0
w* > 0
dT/dt > 0
dO3/dt > 0
Tropopause
Vertically Propagating, Planetary-Scale Rossby Waves
Equator
Pole
Surface
Winter Hemisphere
Extreme wave forcing events can lead to polar stratospheric sudden warmings (SSWs).
Model Simulation of the Solar Cycle Variation of Stratospheric Ozone:
WACCM3 coupled to CCSM3 with imposed QBO:
Multiple regression analysis of WACCM3
model data done by Christian Blume and Katja
Matthes, FUB.
We also know that solar variability can affect planetary wave
propagation, polar vortex strength, and the Brewer-Dobson circulation.
From Gray et al., Reviews of Geophysics, 2010
During the west phase of the QBO near solar maxima, planetary wave
propagation is altered such that more stratospheric warmings occur than
during solar minima.
UARS MLS Water Vapor Mixing Ratio Deviations, ppmV
Alan Brewer, QJRMS, 1949;
Gordon Dobson, PRSL, 1956:
Mote et al.,
JGR, 1996
The water content of air at northern
midlatitudes just above the tropopause is
very low. This is best explained by a
circulation in which air enters the
stratosphere where it is dried by
condensation during passage through the
cold tropical tropopause, travels to
higher latitudes, and sinks into the
troposphere. The same circulation would
simultaneously explain why ozone values
are highest at high latitudes even though
it is produced mainly at low latitudes.
Hence, the ``Brewer-Dobson’’
circulation.
E. Cordero et al., Chapter 6, Stratospheric Ozone, NASA/GSFC