1. Boundary Layer Clouds

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

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

5. Cooling effect
Warming effect

6. 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= W/m2
Reflected SW radiation
Q= W/m2
Fictitious
climate
system
shortwave cloud forcing
dQ=Q1-Q=-50 W/m2 (cooling)
Present
climate
system
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)

7. 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

8. 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

9. 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

10. Issues Cloud evolution and maintenance. LS Forcing 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

11. 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)

12. 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.

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

14. 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?

15. 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

16. Liquid water content

17. 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

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

19. X-band scanning ARM precipitation radar
Vaisala Ceilometer

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

22. Cloud parameterization
Cloud fraction parameterization

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

24. 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.