The Spectral Radiative Effects of Inhomogeneous Clouds and Aerosols

Transcription

1 The Spectral Radiative Effects of Inhomogeneous Clouds and Aerosols S. Schmidt, B. Kindel, & P. Pilewskie Laboratory for Atmospheric and Space Physics University of Colorado SORCE Science Meeting, Sep Clouds & Aerosols Schmidt page 1

2 Wavelength-dependent deposition of solar irradiance in atmosphere atmospheric heating rates This example shows where in the atmosphere solar irradiance is depleted for a clear-sky scene. This is important for dynamics and shortwave radiative energy budget. This presentation: What happens if clouds and aerosols are added to the picture. Most of the time, the spatial structure of cloud-aerosol fields is complex, which leads to formerly unknown spectral effects. SORCE Science Meeting, Sep Clouds & Aerosols Schmidt page 2

3 The contribution of aerosols to atmospheric optical thickness SORCE Science Meeting, Sep Clouds & Aerosols Schmidt page 3

4 Aerosol Optical Properties Bergstrom et al., 2003; 2007; Pilewskie et al., 2005; 2010; Russell et al. 2010

5 Cloud Optical Properties optical thickness & effective radius = 7 r e = 27 μm can be determined from two wavelengths for homogeneous scenes. The cloud radiative effects (forcing, absorption) can then be calculated from passive imager observations + scenedependent angular distribution of radiance Kindel et al., 2010 SORCE Science Meeting, Sep Clouds & Aerosols Schmidt page 5

6 For heterogeneous clouds = 53 r e = 30 μm the spectral dependence of albedo (reflectance) can no longer be re-calculated from the two retrieved parameters, optical thickness and effective radius. Consequently, spectral and broadband forcing and absorption cannot be based on these parameters alone. Kindel et al., 2010 SORCE Science Meeting, Sep Clouds & Aerosols Schmidt page 6

7 A new method for deriving spectral shortwave cloud absorption from aircraft Kindel, Pilewskie, et al., 2011 SORCE Science Meeting, Sep Clouds & Aerosols Schmidt page 7

8 that agrees well with modeled absorption Model 2% residual SORCE Science Meeting, Sep Clouds & Aerosols Schmidt page 8

9 Contributions to Absorbed Irradiance In Cloud Kindel, Pilewskie, et al., 2011; Schmidt & Pilewskie, 2011 SORCE Science Meeting, Sep Clouds & Aerosols Schmidt page 9

10 Heterogeneous Clouds Need to understand the relationship between spatial structure and spectral radiative cloud effects. Aircraft data (TC 4 ) 3D radiative transfer model SORCE Science Meeting, Sep Clouds & Aerosols Schmidt page 10

11 Heterogeneous Clouds Reproduce Apparent Absorption colored horizontal flux divergence Schmidt et al., 2010 SORCE Science Meeting, Sep Clouds & Aerosols Schmidt page 11

12 3-D Clouds and Aerosols What is the combined radiative effect of clouds and aerosols? Can the radiative forcing of a cloud-aerosol field be calculated from that of aerosols and clouds individually? F, F SORCE Science Meeting, Sep Clouds & Aerosols Schmidt page 12

13 PDF 3-D Clouds and Aerosols 0.03 SSFR 16: LES runs 19:48 "CLD" cloud+aerosol cloud only "GAP" Extreme cloud edge effect (individual cloud) Downward Irradiance [W m -2 nm -1 ]

14 3-D Clouds and Aerosols Aerosols decrease direct irradiance / increase diffuse irradiance clouds enhance irradiance

15 3-D Clouds and Aerosols These observations lead to the conclusion (Schmidt et al., GRL, 2009) that for heterogeneous scenes: f cld-aer (λ) f cld (λ) + f aer (λ) In summary: Inhomogeneous clouds introduce spectral biases that need to be considered in the deposition of solar irradiance in the atmosphere and at the surface. Optical thickness and effective radius alone are not sufficient to determine radiative effects. In heterogeneous scenes, aerosols superimpose their radiative signature, and the cloud-aerosol radiative properties cannot be obtained from the sum of cloud and aerosol effects. None of these effects have been validated on a global scale. Need full spectral imagery from space. More detail: Schmidt and Pilewskie, 2011: Airborne Measurements of Spectral Shortwave Radiation in Cloud and Aerosol Remote Sensing and Energy Budget Studies, Light Scattering Reviews, 6, A. Kokhanovsky (ed.), Springer ftp://laspftp.colorado.edu/pub/schmidt/lsr/ SORCE Science Meeting, Sep Clouds & Aerosols Schmidt page 15