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TSI data@ http://spot.colorado.edu/~koppg/TSI/
Modeling Climate Response to Variations in
Spectral Solar Irradiance
Bob Cahalan, NASA/Goddard/Climate&RadiationLab
Guoyong Wen, NASA/Goddard & Morgan State U
David Rind & Jeff Jonas, NASA/GISS & Columbia U
Spectral Solar Irradiance (SSI) Forcing Scenarios
Simple Radiative-Convective Model (RCM)
Time Lags for 11-year and multi-decadal changes
Conclusions
SORCE Observations of Spectral Solar Irradiance (SSI)
Harder et al, 2009: GRL 36, L0701, doi:10.1029/2008GL036797
TSI & SSI do not vary in-phase
–
–
Before Sorce, models assumed fixed spectral shape
T<Tave brightening, T>Tave dimming
Near-UV and Visible Are Compensating
–
UV variability much larger, but offset by the Visible
Large UV variability impacts stratospheric temperature and ozone
SORCE-SIM Better Explains Mesospheric Ozone Trends
Results from Merkel et al. (GRL, 2011)
O3 Difference (%)
Avg. 15ºN-15ºS
•
•
•
Using NCAR’s Whole Atmosphere Community Climate Model
 Modeled equatorial atmospheric ozone changes, forced by NRL and SORCE SSI.
 Compared to SABER ozone observations.
Higher SORCE UV variability improves model/data agreement
of mesospheric ozone.
Latitude
Enhanced HOx photochemistry with greater SORCE solar UV variability
But solar max – min equilibrium simulations neglect timelags!
Absorption of Solar Radiation
O3
Hartley bands
Huggins bands
Chappuis bands
O2-A band
H2O
0.72 m
0.82 m
0.94 m
1.14 m
1.38 m
1.87 m
175nm
1
2
3
2
------UV-C
UV
4 5 6 7
UV-B
8
9
VIS
NIR
UV-A
%TSI: 8% UV (6% UV-A), 39% VIS, 53% NIR
10
11
10 m
Radiative Convective Model (RCM)


•
Tropical Atmosphere: Convective adjustment scheme with water vapor feedback
(Manabe and Weatherald, 1967) with 18 vertical layers (2 hPa ≈ 43 km)
Set Cloud Fraction = 0.0, tune Horizontal Flux to get T(Sfc) = 300 K
Ocean: Heat diffusion with 4 layers, coupled with atmosphere through energy exchange
(Schlesinger et al., 1985)
Model Inputs
SSI at 11 bands as a function of time
Surface albedo
Convective scheme (fixed lapse rate)
Water vapor property (fixed RH)
Net horizontal flux
Cloud Fraction, LWP/IWP, heights
Aerosol optical thickness
Thickness ΔZ
(m)
Heat capacity Co
(Wm-2yrK-1)
Atmos. - Ocean
Heat Transport
λa,o, λk (Wm-2yrK1)
Diffusivity (ΔZ λk/ρCo)
(cm2s-1)
8.00
Ocean layer k=1
50
6.25
10.84
3.23
2
200
26.57
4.60
3.84
3
500
66.44
0.98
1.52
4
800
106.30
Atmosphere–Ocean Response to Instantaneous CO2 Doubling
Atmosphere: initial rapid response, followed by slow response slaved to ocean
Atmospheric temperature
responses to instantaneous
CO2 doubling in first 16
years. Dashed lines for
stratospheric temperatures
from theoretical
computation with e-folding
time of 7 days for upper
stratosphere (~2 mb) and
18 days for the middle
stratosphere (~20mb).
RCM 2xCO2 Climate Change
Surface air and ocean temperature responses for 16y & 1600y.
RCM Centennial Climate Change - Forcing
(Left): In-phase spectral solar forcing (blue for UV, green for VIS, and red for
NIR). Top panel: at the TOA (upper panel), thicker curves for incoming radiation,
thinner curves for the net radiative flux (down minus up). Bottom panel: the net
radiative flux at the tropopause.
(Right): Similar to the left panel except for the out-of-phase scenario.
RCM Centennial Climate Change - Response
(Left) Temperature responses to the in-phase spectral solar forcing scenario. Top panel:
stratospheric responses, dark blue for upper stratosphere at ~2mb, lighter blue for
middle stratosphere at ~20 mb. Middle Panel: tropospheric responses, red for
tropopause at ~100 m, brown for surface. Bottom Panel: temperature responses of four
ocean layers. The curve with largest amplitude is for top layer. The curve with smallest
amplitude is for bottom layer. (Right): Similar to left panel except for out-of-phase
forcing scenario
UV,VIS,NIR, TSI
Forcing at TOA Left: Krivova; Right: Harder
Blue: UV; Green: VIS; Red:NIR; Black: TSI
20mb
Surface
2mb
100mb
0-50m
750-1550m
Left Panel: Temperature responses to the SATIRE-T (Krivova, 2010) reconstructed in-phase SSI. Top
panel: stratospheric responses, dark blue for upper stratosphere at ~2mb, light blue
for middle stratosphere at ~20 mb. Middle Panel: tropospheric responses, red for tropopause at
~100 mb, brown for surface. Bottom Panel: temperature responses of four ocean layers. The
curve with largest amplitude is for the top layer. The curve with smallest amplitude is for the bottom layer.
Right Panel: similar to the left panel except for responses to SIM-derived out-of-phase SSI in the right
panel for solar forcing.
RCM Multi-decadal Climate Change
 Both in-phase and out-of-phase forcings lead to warming.
 Out-of-phase forcing leads to ~0.7 K
increase in upper
stratosphere temperature, about 5 times larger than in-phase.
 Out-of-phase forcing leads to ~0.05K increase in surface
temperature, about half as large as in-phase forcing.
 Even for constant TSI, atmospheric temperatures can have
responses to spectral solar forcing.
 Out-of-phase SSI changes may cause atmospheric stability to
vary from solar max to solar min, leading to cloud feedbacks
that may amplify climate responses.
GCM Model
for Centennial Studies
• GISS GCMAM (Rind, D., J. Lerner, J. Jonas, and C.
McLinden, 2007: The effects of resolution and model physics on
tracer transports in the NASA Goddard Institute for Space
Studies general circulation models. J. Geophys. Res., 112,
D09315, doi:10.1029/2006JD007476)
• 4x5, 53 Layers, top at ~85 Km
• LINOZ simplified ozone chemistry in
stratosphere
• Coupled Atm-Ocean version, using Russell et
al. ocean (updated from: Russell, G.L., J.R. Miller, and D.
Rind, 1995: A coupled atmosphere-ocean model for transient
climate change studies. Atmos.-Ocean, 33, 683-730.)
GCM Experiments
for Centennial Studies
• 2 Coupled atmosphere-ocean control runs
with 1600 pre-industrial conditions
(atmosphere composition and solar
irradiance)
– One control run for each solar spectrum
– Integrated for 500 years
• 2 Transient solar irradiance experiments
started from year 100 of the respective
control runs
– Integrated for 410 years
GCM Multi-decadal Climate Change
 Global
average temperature responses to the two
scenarios are similar. The difference is large in surface
temperatures. This is different from the RCM.
 Snow
and ice cover has larger and different responses in
the two scenarios. Out-of-phase forcing leads to ~0.05K
increase in surface temperature, about half as large as in-phase
forcing.