Research 5: Roger Davies

1. Radiative-Convective Modelling of the Earth’s Climate:The
Effect of Observed Changes in Cloud Amounts
Roger Davies, Physics Department, The University of Auckland
http://www.physics.auckland.ac.nz/uoa/professor-roger-davies

2. climate physics at Auckland
• observations • theory
– MISR on Terra (global) – equilibrium climate sensitivity
• albedos, heights, winds – global balance of energy
– cloud heights – radiative transfer
– ‘effective’ height, H = ò f (h)h dh • shortwave (albedo)
• H´ = H – <H> • longwave (greenhouse effect)
– decadal time series of H´ • gases
• clouds
– correlations of H´ with SOI (El
Niño/La Niña) – cloud physics
– hints of decreasing H – convection
– radiative-convective
equilibrium (RCE)
• with detailed clouds
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3. MISR: Multiangle Imaging SpectroRadiometer
• 9 fixed view angles
– +70.5° to –70.5°
– reflected solar radiances (4 bands)
• climate data records
– self-consistent: 5/2000 – present
• deseasonalized interannual
variations
– albedo anomalies
• onboard calibration ≈1% relative
radiometric accuracy
– height anomalies
• geometrically (stereo) derived: no
calibration drift
Terra: 10:30 am sun-synchronous,
pole-pole, 14.6 orbits per day
3

4. NZIP_11 4

5. 300 km
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6. NZIP_11 6

7. NZIP_11 7

8. Cloud-Top Heights measured by MISR
• stereo pattern-matching from the A-cameras (±26°)
– measurements with horizontal resolution 275 m: heights every 2.2 km
– effective height: max contrast in SW reflectivity, may include surface
– rms instantaneous height uncertainty: ≈500 m (validated)
– O(108) measurements per month, globally at 10:30 am local time
– global sampling error: ≈30 m/month; ≈8 m/year
• March 2000 — February 2010: the first 10 years
• consistent climate data record of cloud heights
– insensitive to radiometric calibration
– high resolution measurements
– uniform technique from pole-pole (no view angle effects)
• deseasonalized anomalies, globally and regionally
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9. Why bother with global cloud heights?
• Cloud-Climate feedback
• Changes in effective height, H
– emitted longwave radiation to space controls temperatures at z > H
• this temperature is fixed for a given albedo, in equilibrium
– if H decreases, the convective layer is reduced
• results in lower equilibrium surface temperature
• In radiative-convective equilibrium (RCE)
– height increase implies warming, decrease implies cooling
• Over 1 decade, CO2 forcing ≈0.28 W m-2 (IPCC)
– In RCE this is equivalent to an increase of ≈28 m in global average
effective height
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10. the simplest of equilibrium climate models
the simplest of equilibrium climate models
20
20
temperature controlled by albedo
Tmin temperature controlled by albedo, a
15
15
altitude controlled by thethe greenhouse effect
he altitude controlled by greenhouse effect
altitude (km)
altitude (km)
10
10
convection, with lapse rate G
convection
5
5
0
0
-70
-70 -60
-60 -50
-50 -40
-40 -30
-30 -20
-20 -10
-10 0
0 10
10 20
20
temperature (°C)
temperature (°C)
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11. the simplest of equilibrium climate models
20
15 raising tropopause height by 154m (≈2xCO2)
increases surface temperature by ≈1°C
altitude (km)
10
5
0
-70 -60 -50 -40 -30 -20 -10 0 10 20
temperature (°C)
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12. The Effect of Carbon Dioxide on Equilibrium Surface Temperature
3
Change of Equilibrium Surface Temperature °C
2
784
1
change CO2 only 554
keep clouds constant
0 keep albedo constant 392
keep water vapour constant
277
-1 190
-2
-3
100 1000
CO2 concentration (parts per million)
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13. The Effect of Carbon Dioxide on Equilibrium Surface Temperature
3
Change of Equilibrium Surface Temperature °C
with water vapour feedback at 8%/K
2 and cloud fraction at 5%/K
change CO2, water vapour
and low cloud fraction
784
1 and cloud height by ±300 m/K
554
0 392
277
-1 190
-2
-3
100 1000
CO2 concentration (parts per million)
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14. Annual Mean Effective Height
meters
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15. Interannual rms Fluctuation of Cloud-top
Heights
meters
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16. Correlation of anomalies in cloud-top height with
anomalies in sea level pressure
r
sea level pressure from NCEP reanalysis
Mar 2000–Feb 2010
cloud-top heights from MISR
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17. Correlation of anomalies in cloud-top height with
anomalies in surface temperature
r
surface temperature from NCEP reanalysis
Mar 2000–Feb 2010
cloud-top heights from MISR
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18. Correlation of anomalies in cloud-top height with
anomalies in Southern Oscillation Index
r
SOI from Australian Bureau of Meteorology
Mar 2000–Feb 2010
cloud-top heights from MISR
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19. Central Pacific, –Indonesia, –SOI
1500 15
1000 10
500 5
Height anomalies (m)
0 0
2000 2002 2004 2006 2008 2010
-500 -5
-1000 -10
-1500 -15
Year
Indonesian heights inverted
SOI inverted
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20. global cloud height anomalies
60
40
20
height anomaly (m)
0
-20
-40
-60
-80
-100
2000 2002 2004 2006 2008 2010
year
12-month running mean overall decrease: 45 ±5 m max departure: –80 m
sampling error ±8 m interannual rms: 26 m
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21. mean annual global stereo height distribution
clouds+surface (12/05-6/08)
WITHOUT THIN CIRRUS
20
18
16
Total fractions
14
surface: 0.366
non-surface: 0.634
12
height (km)
low (0-3 km): 0.363
mid (3-7 km): 0.144
high (>7 km): 0.128
all
10
cloud only
8
6
4
2
0
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40
fraction/km
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22. Standard Atmosphere with Clouds
1
pressure (hPa)
10
RCE
RE
100
1000
190 210 230 250 270 290 310 330 350 370 390
temperature (K)
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23. Standard Atmosphere with Clouds
1
pressure (hPa)
10
RCE
RE
100
1000
190 210 230 250 270 290 310 330 350 370 390
temperature (K)
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24. relative trapping of longwave emission from
the surface
(adapted from Kiehl and Trenberth)
clouds 45%
water vapour 33%
carbon dioxide 15%
others 7%
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25. Equilibrium Surface Temperatures: with constant albedo
Observed 288 K
No Atmosphere 255 K
Model, no clouds 278 K
Model, observed clouds 291 K
Model, no high clouds 286 K
Model, observed clouds, 50% CO2 290 K
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26. The Effect of Carbon Dioxide on Equilibrium Surface Temperature
3
with water vapour feedback @8%/1°C
Change of Equilibrium Surface Temperature °C
2
change CO2 and water vapour
keep relative humidity constant
keep clouds constant 784
1 keep albedo constant
554
0 392
277
-1 190
-2
-3
100 1000
CO2 concentration (parts per million)
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27. The Effect of Carbon Dioxide on Equilibrium Surface Temperature
3
Change of Equilibrium Surface Temperature °C
with water vapour feedback at 8%
2 and cloud fraction at 5%/degree
change CO2, water vapour
and low cloud fraction 784
1
554
0 392
277
-1 190
-2
-3
100 1000
CO2 concentration (parts per million)
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28. The Effect of Carbon Dioxide on Equilibrium Surface Temperature
5
4
Change of Equilibrium Surface Temperature °C
Maximum Arctic ice-albedo feedback
3
2
784
1 change CO2 only
keep clouds constant 554
0 keep albedo constant 392
keep water vapour constant
277
-1 190
-2
-3
Last Glacial Maximum
-4
-5
100 1000
CO2 concentration (parts per million)
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29. Standard Deviation of Annual Average of
Cloud-top Heights
meters
Pacific box: 30°S–30°N, 100°E–230°E (130°W)
Area: 1/6 of globe
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30. Local Height Anomalies: Pacific Box (30°N–30°S, 100°E–130°W)
rest of world
250
200
150
Height anomaly (m)
100
50
0
2000 2002 2004 2006 2008 2010
-50
-100
-150
Year
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31. Normalized Height anomalies: Pacific Box/6, Remainder*5/6, Total
80
60
40
20
Height anomaly (m)
0
2000 2002 2004 2006 2008 2010
-20
-40
-60
-80
-100
Year
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32. Zonal annual mean fraction by height
20
18
16
14
12
height (km)
58°S
10 9°N
21°N
8
6
4
2
0
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
fraction/km
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33. In Summary
• MISR cloud heights provide a useful climate data record
• additional CO2 forcing over the last decade ≈ +0.28 W m-2
– equivalent to an increase in effective emission altitude of ≈28 m in
RCE
• globally averaged effective height shows this level of
fluctuation at the annual level (26 m rms)
– heights have decreased by ≈45 m over the last decade
• the major event of the decade is coincident with the 2007-8
La Niña
– offsetting height changes between Indonesia and Central Pacific
– teleconnections elsewhere appear to dominate the global result
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