14.20 o7 r davies

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Research 5: Roger Davies

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  • 12-month running mean of anomalies (h-hbar(time,space))overall decrease 45 m/decade. Sampling uncertainty 8 m,
  • 14.20 o7 r davies

    1. 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. 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 NZIP_11 2
    3. 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 driftTerra: 10:30 am sun-synchronous,pole-pole, 14.6 orbits per day 3
    4. 4. NZIP_11 4
    5. 5. 300 km NZIP_11 5
    6. 6. NZIP_11 6
    7. 7. NZIP_11 7
    8. 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 NZIP_11 8
    9. 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 NZIP_11 9
    10. 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 effectaltitude (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) NZIP_11 10
    11. 11. the simplest of equilibrium climate models 20 15 raising tropopause height by 154m (≈2xCO2) increases surface temperature by ≈1°Caltitude (km) 10 5 0 -70 -60 -50 -40 -30 -20 -10 0 10 20 temperature (°C) NZIP_11 11
    12. 12. The Effect of Carbon Dioxide on Equilibrium Surface Temperature 3Change 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) NZIP_11 12
    13. 13. The Effect of Carbon Dioxide on Equilibrium Surface Temperature 3Change 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) NZIP_11 13
    14. 14. Annual Mean Effective Height meters NZIP_11 14
    15. 15. Interannual rms Fluctuation of Cloud-top Heights meters NZIP_11 15
    16. 16. Correlation of anomalies in cloud-top height with anomalies in sea level pressure rsea level pressure from NCEP reanalysis Mar 2000–Feb 2010 cloud-top heights from MISR NZIP_11 16
    17. 17. Correlation of anomalies in cloud-top height with anomalies in surface temperature rsurface temperature from NCEP reanalysis Mar 2000–Feb 2010 cloud-top heights from MISR NZIP_11 17
    18. 18. Correlation of anomalies in cloud-top height with anomalies in Southern Oscillation Index rSOI from Australian Bureau of Meteorology Mar 2000–Feb 2010 cloud-top heights from MISR NZIP_11 18
    19. 19. Central Pacific, –Indonesia, –SOI 1500 15 1000 10 500 5Height anomalies (m) 0 0 2000 2002 2004 2006 2008 2010 -500 -5 -1000 -10 -1500 -15 Year Indonesian heights inverted SOI inverted NZIP_11 19
    20. 20. global cloud height anomalies 60 40 20height 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 NZIP_11 20
    21. 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 12height (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 NZIP_11 21
    22. 22. Standard Atmosphere with Clouds 1pressure (hPa) 10 RCE RE 100 1000 190 210 230 250 270 290 310 330 350 370 390 temperature (K) NZIP_11 22
    23. 23. Standard Atmosphere with Clouds 1pressure (hPa) 10 RCE RE 100 1000 190 210 230 250 270 290 310 330 350 370 390 temperature (K) NZIP_11 23
    24. 24. relative trapping of longwave emission from the surface (adapted from Kiehl and Trenberth) clouds 45% water vapour 33% carbon dioxide 15% others 7% NZIP_11 24
    25. 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 NZIP_11 25
    26. 26. The Effect of Carbon Dioxide on Equilibrium Surface Temperature 3 with water vapour feedback @8%/1°CChange 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) NZIP_11 26
    27. 27. The Effect of Carbon Dioxide on Equilibrium Surface Temperature 3Change 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) NZIP_11 27
    28. 28. The Effect of Carbon Dioxide on Equilibrium Surface Temperature 5 4Change 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) NZIP_11 28
    29. 29. Standard Deviation of Annual Average of Cloud-top Heights metersPacific box: 30°S–30°N, 100°E–230°E (130°W)Area: 1/6 of globe NZIP_11 29
    30. 30. Local Height Anomalies: Pacific Box (30°N–30°S, 100°E–130°W) rest of world 250 200 150Height anomaly (m) 100 50 0 2000 2002 2004 2006 2008 2010 -50 -100 -150 Year NZIP_11 30
    31. 31. Normalized Height anomalies: Pacific Box/6, Remainder*5/6, Total 80 60 40 20Height anomaly (m) 0 2000 2002 2004 2006 2008 2010 -20 -40 -60 -80 -100 Year NZIP_11 31
    32. 32. Zonal annual mean fraction by height 20 18 16 14 12height (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 NZIP_11 32
    33. 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 NZIP_11 33

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