Arctic Clouds and Radiation Part 2

Transcription

1 Arctic Clouds and Radiation Part 2 Glen Lesins Department of Physics and Atmospheric Science Dalhousie University Create Summer School, Alliston, July 2013

2 No sun Arctic Winter Energy Balance 160 W m -2 Outgoing Long-Wave at Top of Atmosphere Atmospheric Meridional Heat and Moisture Flux Atmosphere 120 W m -2 Infrared Up (Skin Temp) Clouds (Optical Depth) Infrared Down (Temp and Greenhouse Gases) Sensible and Latent Heat (Surface Winds) Aerosols Surface Energy Balance Net IR Up = Conduction + SH + LH Snow Ground Heat Conduction Sea Ice Ocean Heat Conduction Freezing releases 20 W m W m -2 Oceanic Meridional Heat and Water Flux 10 W m -2

3 Sounding plotted on a SkewT-LogP Diagram Typical winter sounding at Eureka Strong surface based temperature inversion

4 Winter ice clouds reduce surface IR cooling and enhance TOA IR flux Solid Lines Clear Dotted Lines Cloud Layer Optical depth ~ 1.3 Note the increase in downward IR when clouds are added.

5 Thin Ice Clouds (TIC-1) visible by lidar but not by radar (type 1) Consists of very small but likely numerous ice crystals Lidar (532 nm) Mostly TIC-1 Mie Regime TIC-1 mostly invisible in radar backscatter Cloud Radar (8.7 mm) Rayleigh Regime

6 Deep Precipitating Ice Systems Lidar Cloud Radar

7 Deep Non-Precipitating Ice Systems Lidar Cloud Radar

8 Supercooled liquid water layer Lidar (532 nm) Precipitating ice crystals (TIC-2c) Cloud Radar (8.7 mm)

9 Classifying particle type using lidar and cloud radar backscattering cross-sections and lidar depolarization Bourdages et al., 2009

10 Rayleigh/Mie/Raman Lidar Feb 9, 2010 case NOAA Cloud Radar EC Cloud Radar

11 Microwave Humidity Sounder MHS Retrieving Arctic Winter Precipitable Water Polar orbiting satellites 16 km nadir resolution 2 pan-arctic analyses a day To sample the entire water vapour column the precipitable water must be less than 15 mm. NOAA 18 N operational Aug 30, 2005 METOP-A operational May 21, 2007

12 Contributions to the upward microwave brightness temperature at the satellite T ext T B τ T down T up ε T sfc T = T 1 ε e + T + T 1 ε e + T εe ( ) 2 ( ) τ τ τ B ext up down sfc τ, the optical thickness at the rotational water line. It is proportional to the total water vapour path.

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14 Example of a retrieval

15 Can follow the intrusions, movement and evolution of water vapour in the Arctic.

16 Water Vapour Intrusions Reaching Eureka in the Winter Water vapour profiles from Raman Lidar Impact of intrusions on downward longwave Time series of intrusion events Doyle et al., 2011

17 Water Vapour Intrusion Gateways Arctic Haze Serreze & Barry, 2009

18 60 o N Western Arctic Areas picked for average water column results. Eastern Arctic

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20 Northward transport of water vapour across 70 o N Winter average (Dec-Apr) is about 1.3 x kg yr -1 This translates to 35 cm of snow over the 5 months. Annual average fluxes crossing 70 o N (in units kg yr -1 ): Water vapour +2 River water +4 Sea Ice -3 Ocean water -3 Net energy gain = (2 l s + 4 l f 3 l f ) x kg yr -1 = (2 l v + 3 l f ) x kg yr -1 = 6 x J yr W m -2 Peixoto & Oort, 1992

21 The SIFI and DGF Effects Anthropogenic Sulphates (Arctic Haze) Coats and inhibits ice forming nuclei (IFN) Sulphate-Induced Freezing Inhibition Effect (SIFI) Fewer but larger ice crystals can now precipitate out The air becomes drier allowing more longwave cooling to space Colder air leads to higher vapour super-saturation and continued deposition on the few larger ice crystals that fall out Dehydration Greenhouse Feedback (DGF) Grenier et al., 2009

22 How to detect the influence of air pollution on Arctic ice clouds? A lidar uses visible light (either ground based or satellite CALIOP) The backscattering from aerosols and ice crystals can be measured. A cloud radar at a wavelength of about 3 mm cannot detect aerosols, cloud droplets or ice crystals less than about 25 µm (either ground based MMCR or satellite CloudSat). Blanchet s thin Arctic ice cloud classification scheme: TIC-1 Can only be seen by lidar (small non-precipitating ice crystals) TIC-2 Can be detected by both the lidar and cloud radar (more likely precipitating) TIC-2a TIC-2 cloud extending below a TIC-1 cloud TIC-2b TIC-2 right to cloud top (explosive ice crystal growth) TIC-2c TIC-2 cloud below a supercooled liquid water layer Test for the SIFI effect by correlating enhanced aerosol pollution with a greater frequency of TIC-2 clouds at the expense of TIC-1 clouds. (Jean-Pierre Blanchet claims this is happening but it is not conclusive)

23 Backscatter cross-section at 532 nm from CALIOP Retrieved ice particle effective radius (uses CloudSat at 3.2 mm) Polluted TIC-2B Clean TIC-1 Cloud Type TIC-2C TIC-2A Grenier et al., 2009

24 TIC-1 and TIC-2A are most frequent in Greenland, North Atlantic and Kara Sea sectors (clean air) while TIC-2B are most frequent in Beaufort Sea, Eastern Russia and Canadian Archipelago sectors (polluted air) Arctic Haze Frequency

25 What is the cause of diamond dust events with high optical depth? (Can increase downward longwave radiation by up to 30 W m -2 ) Lidar Aerosol Diamond Dust? Cloud Radar

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29 Thank you

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31 Extra Slides

32 Knuteson et al., 2010 ITSC-17 Monterey, CA

33 Knuteson et al., 2010 ITSC-17 Monterey, CA

34 Microwave detection of water vapour is based on the pure rotational transitions of the water vapour molecule. Chahine, 1983

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36 Radiance Solution to Plane Parallel Radiative Transfer Equation 1 ( ) ( ) τ + + τ τ τ ν, = ν 0, exp + ν (, ) exp µ µ µ 0 I τ µ I µ S τ µ dτ ( ) ( ) 0 ν, = ν 0, exp + ν (, ) exp τ 0 τ τ 1 τ τ I τ µ I τ µ S τ µ dτ µ µ µ Where the source function includes both emission and scattering 1 0 ω S (, ) ( 1 ) B T( ) ν + ν τ µ = ων ν τ + p( µ, µ ) Iν ( τ, µ ) dµ + p( µ, µ ) Iν ( τ, µ ) dµ Simplifications and assumptions for microwave transfer: 1. No scattering (single scattering albedo = 0) 2. Use the Rayleigh-Jeans approximation (I ν ~ T v ) 3. Surface has specular reflection

37 Rewriting the solution following Guissard and Sobieski (1994) T = mt T T 1 ε e τ µ B P sfc a ext ( )( ) 2 0 where m P Skin temperature effect Lapse rate effect Scattering surface effect ( T T S ) 0 = 1+ 1 εe + T T T T ( ) 2τ 0 µ τ µ a sfc J 1 ε e J 1 2 sfc sfc sfc sfc sfc τ0 τ µ J 1 e dz 1 ( ) dt = dz 0 τ 0 µ τ µ τ0 τ µ J = e e 1 e dz 2 0 ( ) dt dz

38 How do we determine the precipitable water (W)? The total optical depth in the water line is proportional to W as long as the surface is visible (not saturated). τ 0i = κ i W Kappa is the water vapour mass absorption coefficient. B A W T = mt T T 1 ε e τ µ B P sfc a ext ( )( ) unknowns: A, B and W 3 measured T B at 3 frequencies Problem: m P has a weak dependence on frequency. So the solution for W is a bit more complicated. Use the tables generated for the AMSU-B instrument (Melsheimer and Heygster, 2008)

39 Fu Liou Radiative Transfer Code Correlated-k plane-parallel calculation. 2-stream in short-wave and 2- or 4-stream in long-wave. 6 short-wave bands, 12 long-wave bands. Absorption by O 3, H 2 O, CO 2, CH 4, N 2 O and water continuum. Rayleigh molecular scattering. Can input aerosol and water and ice cloud profiles. Agrees with line by line to within 1 W m -2 Very fast.

40 Serreze & Barry, 2009

41 Mean Net Longwave Radiation at the Surface (W m -2 ) About -20 to -40 W m -2 Serreze & Barry, 2009

42 Net cooling in winter Arctic atmosphere is about 10 W m -2 de = dt c p p dt dt g Gives a cooling rate of about 2.5 K per month (reasonable) s