Transcript Pinatubo, time constants and TOA net flux

A natural experiment:
The Mt. Pinatubo eruption; net flux;
time constants; and the ERB
Professor John Harries,
Space and Atmospheric Physics group,
Blackett Laboratory,
Imperial College,
London,
UK
3 May 2007
GIST May 2007
1
o Work reported in Harries and Futyan GRL, 33, L23814,
2006
o Acknowledge provision of data by Prof. Brian Soden,
U.Miami, USA]
3 May 2007
GIST May 2007
2
Some Background
Climate may be described in terms of ‘Forcing’
and ‘feedback’ processes.
Forcing processes (External processes which impose a
change of climate balance):
•greenhouse gas changes;
•solar variations;
•volcanic eruptions.
Feedback processes (Internal processes which respond to
a forced change):
•water vapour feedback;
•cloud feedback;
•land surface feedback;
•ice feedback;
•ocean feedback.
3 May 2007
GIST May 2007
3
Terrestrial Energy Budget (per unit surface area) and
greenhouse forcing
Input SW Power Pin = ITS (1 – A) / 4 = S (1 – A)
Output LW Power Pout =  TE4 =  (1 – g)TS4
Power deposited/lost = p
G = greenhouse
How bigradiative
is p = forcing
FN =(in
PinWm-2)
– Pout=? (TS4- TE4)
g = normalised greenhouse effect, g = G / (TS4 )  G / 390  0.40
Does it vary with time?
A = planetary albedo  0.31
Can volcanic
eruption help?
 = Stefan-Boltzmann constant = 5.6696  10-8 Wm-2K-4
TE = effective temperature of Earth / atmosphere  254K
TS = mean surface temperature of Earth  288K
 235 Wm-2
(ITS 1366 Wm-2)
3 May 2007
Pin
=
Pout
+
Pin - Pout = p = FN
GIST May 2007
p
 1 Wm-2
(Hansen et al.,
Science, 2005)
4
Terrestrial Energy Budget: feedbacks and
volcanic forcing
Direct
decrease in A
(and smaller
increase in g)
due to volcano
hydrological cycle,
circulation patterns,
cloud cover & type
SW
delayed
responses
LW
S (1 – A) =  (1 – g) TS + p1 + p2 + …
Volcanic
eruption forces
greenhouse
a direct effect
forcing
Delay due to feedback
on A, and a
processes: eg. deep
response in g
In this experiment, we use
ocean warming
on scale of
Pinatubo to “ping” the system,
days to years and we watch how the system
4
responds
3 May 2007
GIST May 2007
5
Pinatubo: A natural perturbation to the system
Pinatubo (Phillipines,
June 12 1991) was
powerful (20 Mt), and
directed vertically: so,
a large mass of injecta
quickly reached the
stratosphere.
Tropospheric material
was quickly washed
out.
Stratospheric zonal
circulation is strong,
and particles quickly
circulated equatorial
zone, spreading N and
S more slowly. Decay
from stratosphere slow.
3 May 2007
GIST May 2007
6
http://en.wikipedia.org/wiki/Mount_Pinatubo
Pinatubo: A natural perturbation to the system
Pinatubo (Phillipines,
June 12 1991) was
powerful (20 Mt), and
directed vertically: so,
a large mass of injecta
quickly reached the
stratosphere.
Tropospheric material
was quickly washed
out.
Stratospheric zonal
circulation is strong,
and particles quickly
circulated equatorial
zone, spreading N and
S more slowly. Decay
from stratosphere slow.
3 May 2007
GIST May 2007
7
Some Context:
Net Flux, FN
Recent work in
USA has attempted
to make
measurements of
stability of TOA
radiation balance,
and of evidence for
“stored energy”,
p, by measuring
net flux anomaly at
TOA…..
p =  FN
Mt. Pinatubo,
20N -20S: Wielicki et al,
(2001): revision in press
3 May 2007
June 1991
GIST May 2007
8
Combination of ERBE and CERES data (Wong et
3 May 2007
GIST May 2007
al 2005; Loeb et al, 2006)
9
FN
(stored energy)
Pinatubo
(lost energy)
3 May 2007
GIST May 2007
…and to model it
10
(Hansen, 2005)
• Following work on Pinatubo by Soden et al. [2002], we
have used the perturbation caused by Pinatubo to study
some of the process time constants in the system;
• We have analysed the time series of the parameters
shown in next Figure, and measured the (assumed
exponential) rise and decay of the perturbation in each
parameter;
• Results produce characteristic time constants for
certain processes, which ought to be captured by models.
3 May 2007
GIST May 2007
11
Figure 1.
The time series of the anomalies
of the following parameters
[adapted from Soden et al., 2002]:
(top to bottom)
SW and LW flux anomalies
•observed longwave and
shortwave TOA
fluxes for latitudes 60N–60S and
for 1991–1996**;
Net flux anomalies
(“stored energy”)
•Observed net flux formed from
the difference between absorbed
SW and emitted LW fluxes;
•Observed total column water
vapour and lower tropospheric
temperature for 90N–90S; (NVAP
project; Randel et al., 1996).
Water vapour column and T
•Observed 6.7 mm brightness
temperature for 90N–90S (TOVS
Radiances Pathfinder project:
Bates et al., 1996).
3 May 2007
T6.7
GIST May 2007
12
3 May 2007
GIST May 2007
13
Concluding remarks:
• Pinatubo offers a natural perturbation to the climate
system;
•
FN –ve for volcanic eruption: +ve for stored energy;
• Processes which can respond immediately to the
“instantaneous” insertion of aerosol from the volcano show
very short time constants (few months), driven by the time
taken for aerosols to become distributed;
• Processes which involve slower dynamical processes, eg
moving water vapour around, take much longer (1-2 years);
• Rise and decay process time constants differ;
• Models ought to reproduce these relaxation times as
validation.
3 May 2007
GIST May 2007
14
End
3 May 2007
GIST May 2007
15
Some of the evidence for climate
change,
and the uncertainties
3 May 2007
GIST May 2007
16
The
temperature
signal at the
surface and
the
coincident
changes in
CO2 , CH4 ,
sulphates,
etc…
3 May 2007
GIST May 2007
17
CERES (polar orbiter) monthly averages :
SW
LW
3 May 2007
GIST May 2007
18
Do we have
evidence of
“climate
forcing” by
increasing
greenhouse
gases?
Yes!
Harries et al.,
Nature, March 15
2001
3 May 2007
GIST May 2007
19
There are, of course, uncertainties
in many forcing processes…..
IPCC
3 May 2007
GIST May 2007
20
But the major uncertainties are in
feedbacks, not the forcings: Should we
believe that we understand “climate
change” well enough to predict our future?
No!
Climate change
runs by different
models for same
conditions
3 May 2007
GIST May 2007
The feedback
processes,
especially
clouds, water
vapour, oceans,
cause large
uncertainty 21
Terrestrial Energy Budget
Shortwave
Longwave
Albedo  1/3
3 May 2007
GIST May 2007
22
Variability and complexity
in climate
3 May 2007
GIST May 2007
23
• Climate
is of
highly
variable:
Studies
the Physics
of the Earth’s Climate Balance, and
+ Many processes arethe
non-linear;
new
+ Some processes are chaotic;
EarthinRadiation
Budget experiment
+Geostationary
Natural variability
climate components;
(GERB)
+ Feedback processes
cause variability.
•Climate is very complex:
Professor John Harries
+ Many greenhouse absorbers (CO2, CH4, H2O,
Head,O3,
Space
and Atmospheric Physics
FCC,
clouds..);
+ Many SW scatterers (clouds, aerosols, dust);
+ Both Forcing and Feedback processes;
+ Wide range of time and space scales are significant;
• Variability is in spectral, spatial and temporal space.
3 May 2007
GIST May 2007
24