1 / 24

Boundary Layer Clouds

Boundary Layer Clouds. St & Sc. St & Sc. subsidence. Trade wind inversion. Stratus and stratocumulus. Transition. Trade cumulus. Intertropiccal Convergence Zone (ITCZ). SGP Low cloud coverage (ceilometer & MPL): 27.8% (Lazarus et al. 2000). Cooling effect. Warming effect.

rheah
Download Presentation

Boundary Layer Clouds

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Boundary Layer Clouds

  2. St & Sc St & Sc subsidence Trade wind inversion Stratus and stratocumulus Transition Trade cumulus Intertropiccal Convergence Zone (ITCZ)

  3. SGP Low cloud coverage (ceilometer & MPL): 27.8% (Lazarus et al. 2000)

  4. Cooling effect Warming effect

  5. NASA: The Earth Radiation Budget Experiment (ERBE) It measures the energy budget at the top of the atmosphere. Energy budget at the top of atmosphere (TOA) Incoming solar radiation 340 W/m2 Incoming solar radiation 340 W/m2 Reflected SW radiation Q1= 50 W/m2 Reflected SW radiation Q= 100 W/m2 Fictitious climate system Present climate system shortwave cloud forcing dQ=Q1-Q=-50 W/m2 (cooling) Emitted LW radiation F1= 270 W/m2 Emitted LW radiation F= 240 W/m2 with clouds No clouds longwave cloud forcing dF=F1-F=30 W/m2 (warming)

  6. SW cloud forcing = clear-sky SW radiation – full-sky SW radiation LW cloud forcing = clear-sky LW radiation – full-sky LW radiation Net cloud forcing (CRF) = SW cloud forcing + LW cloud forcing Current climate: CRF = -20 W/m2 (cooling) But this does not mean clouds will damp global warming! The impact of clouds on global warming depends on how the net cloud forcing changes as climate changes. Direct radiative forcing due to doubled CO2, G = 4 W/m2

  7. e.g. If the net cloud forcing changes from -20 W/m2 to -16 W/m2 due to doubling CO2, the change of net cloud forcing will add to the direct CO2 forcing. The global warming will be amplified by a fact of 2. Cloud radiative effects depend on cloud distribution, height, and optical properties. Low cloud High cloud SW cloud forcing dominates LW cloud forcing dominates

  8. In GCMs, clouds are not resolved and have to be parameterized empirically in terms of resolved variables. water vapor (WV) cloud surface albedo lapse rate (LR) WV+LR ALL

  9. Issues Cloud evolution and maintenance. Cloudiness . Radiative and microphysical properties. Cloud entraining processes and cloud mass transport. Cloud mesoscale organizations. Cloud-aerosol-drizzle interactions LS Forcing Radiation Turbulence Microphysics Surface Processes

  10. Mesoscale cellular convection (MCC) Pockets of open cell (POCS) Variations of MCCs and POCs are much larger than the individual variations within the structures (Jensen et al. 2008)

  11. Aerosol feedback Direct aerosol effect: scattering, reflecting, and absorbing solar radiation by particles. Primary indirect aerosol effect (Primary Twomey effect): cloud reflectivity is enhanced due to the increased concentrations of cloud droplets caused by anthropogenic cloud condensation nuclei (CNN). Secondary indirect aerosol effect (Second Twomey effect): 1. Greater concentrations of smaller droplets in polluted clouds reduce cloud precipitation efficiency by restricting coalescence and result in increased cloud cover, thicknesses, and lifetime.

  12. 2. Changed precipitation pattern could further affect CCN distribution and the coupling between diabatic processes and cloud dynamics.

  13. Parameterization Development and Testing Strategy GCM/NWP PAR CRMS LES OBS Hi-Res simulation s and 3-D Observations Traditional LES: idealized initial profiles and prescribed horizontal homogeneous large-scale forcings. Representativeness of clean cloud cases?

  14. Clouds Liquid water mixing ratio Liquid water density of clouds Cloud droplet distribution Number density N (D): the number of droplets per nit volume (concentration) in an interval D + ΔD

  15. Liquid water content

  16. Variables that are useful for cloud research Mixing ratio, saturated mixing ratio, liquid water mixing ratio, total mixing ratio Equivalent potential temperature Liquid water potential temperature Saturated quivalent potential temperature

  17. Instrumentation Latest version W-band (95 GHz)cloud radar Millimeter Wave Cloud Radar (35 GHz)

  18. X-band scanning ARM precipitation radar Vaisala Ceilometer

  19. Mechanisms of maintaining cloud-topped boundary layer • Surface forcing • Cloud top radiative cooling • Cloud top evaporative cooling

  20. Cloud parameterization • Cloud fraction parameterization

  21. Shallow cumulus parameterization: Mass-flux approach 1. How to close the system? 2. How to determine entrainment and detrainment rates?

  22. Stratocumulus parameterization Cloud top entrainment parameterization Eddy viscosity A1, A2: empirical coefficients. V: turbulent velocity scale. ΔF: cloud-top radiative flux divergence. ΔB: buoyance jump across the inversion.

More Related