1. Buoyancy driven turbulence in the atmosphere
Stephan de Roode (TU Delft)
Applied Physics Department
Clouds, Climate and Air Quality
eastern Pacific island of Guadalupe. The rugged terrain of this volcanic Mexican island reaches a maximum elevation of 1.3 kilometers. The island is about 35 kilometers long

2. Clouds, Climate and Air Quality
Harm Jonker, Pier Siebesma and Stephan de Roode
cloud-climate feedback
detailed numerical simulation
N2O
CH4
new methods for measuring emission rates
atmospheric boundary layer in the laboratory

3. Length scales in the atmosphere
Earth 103 km
Landsat 60 km 65km
LES 10 km
~1mm-100mm
~mm
~100m
courtesy: Harm Jonker

4. Global mean turbulent heat fluxes
source: Ruddiman, 2000

5. No single model can encompass all relevant processesmm
10 m
100 m
1 km
10 km
100 km
1000 km
10000 km
Cloud microphysics 
turbulence
Cumulus
clouds
Cumulonimbus
clouds
Mesoscale
Convective systems
Extratropical
Cyclones
Planetary
waves
DNS
Subgrid
Large Eddy Simulation (LES) Model
Cloud System Resolving Model (CSRM)
Numerical Weather Prediction (NWP) Model
Global Climate Model

6. DALES: Dutch Atmospheric Large-Eddy Simulation Model
Dry LES code (prognostic subgrid TKE, stability dependent length scale)
Frans Nieuwstadt (KNMI) and R. A. Brost (NOAA/NCAR, USA)
Radiation and moist thermodynamics
Hans Cuijpers and Peter Duynkerke (KNMI/TU Delft, Utrecht University)
Parallellisation and Poisson solver
Matthieu Pourquie and Bendiks Jan Boersma (TU Delft)
Drizzle
Margreet Van Zanten and Pier Siebesma (UCLA/KNMI)
Atmospheric Chemistry
Jordi Vila (Wageningen University)
Land-surface interaction, advection schemes
Chiel van Heerwaarden (Wageningen University)
Particle dispersion, numerics
Thijs Heus and Harm Jonker (TU Delft)

7. Contents Governing equations & static stability
Observations, large-eddy simulations and parameterizations:
- Clear convection
- Latent heat release & shallow cumulus
- Longwave radiative cooling & stratocumulus

8. z Temperature Static stability Q: what will happen with the air
measured
vertical
temperature profile
Q: what will happen with the air
parcel if it is vertically displaced? z
Temperature

9. First law of thermodynamics: Conservation of energy
added heat
internal energy
work
cv = specific heat of dry air at constant volume (718 J kg-1K-1 at 0 oC)
T = temperature
p = air pressure
r = air density

10. Equation of state for dry air: gas law
Combine gas law and energy conservation
cp = specific heat of dry air at constant pressure (1005 J kg-1K-1 at 0 oC)
Rd = gas constant for dry air (287 J kg-1K-1 )

11. Hydrostatic equilibrium
Gas law, energy conservation and hydrostatic equilibrium
Adiabatic process dq=0  dry adiabatic lapse rate

12. z T Atmospheric stability: dry air measured vertical
temperature profile
Atmospheric stability: dry air
dry adiabatic
lapse rate:
–10K/km
A dry air parcel, moved upwards, cools according to the dry adiabatic lapse rate.
But now it is warmer than the environmental air, and experiences an upward force.
A dry air parcel, moved downwards,
warms according to the dry adiabatic lapse rate. But now it is cooler than the environmental air,
and experiences a downward force. F z
unstable
situation
for dry air F T

13. z T Atmospheric stability: dry air F F stable situation for dry air
A dry air parcel, moved downwards, warms according to the dry adiabatic lapse rate.
But now it is warmer than the environmental air, and experiences an upward force.
A dry air parcel, moved upwards,
cools according to the dry adiabatic lapse rate.
But now it is cooler than the environmental air,
and experiences a downward force.
Atmospheric stability: dry air
stable
situation
for dry air F F z
dry adiabatic
lapse rate:
–10K/km
measured
environmental
temperature profile
unstable
situation
for dry air T

14. Harm Jonker's saline convective water tank
Initial state:
tank is filled with salt water
Convection driven by
a fresh water flux at the surface
Schematic by Daniel Abrahams

15. Convective water tank
Movie by Phillia Lijdsman

16. Adiabatic process dq=0  dry adiabatic lapse rate (2)
The potential temperature q is the temperature if a parcel would be brought adiabatically to a reference pressure p0

17. Balloon observations at Cabauw during daytime
Q: what makes this case challlenging for modeling?

18. LES results of a convective boundary layer: Buoyancy flux
warm air going down
entrainment of warm air
warm air going up
Q: what is sign of the mean tendency for qv?

19. LES results
Buoyancy flux and vertical velocity variance

20. LES results of a convective boundary layer -
resolved TKE budget

21. LES results Humidity flux Flux-jump relation: w'q'T = -weDq Dq H
we and wls are of the order 1 cm s-1

22. Entrainment scaling Large-scale subsidence Entrainment atmospheric
boundary layer
Photograph: Adriaan Schuitmaker

23. Conservation of energy: saturated case
heat released
by condensation
internal energy
work
ql = liquid water content
Lv = enthalpy of vaporization of water (2.5x106 J kg-1 at 0 oC)

24. For a moist adiabatic process, the liquid water static
energy (sl) is a conserved variable
meteorologists sl

25. z T Atmospheric stability: conditional instability measured F
wet adiabatic
lapse rate
measured
environmental
temperature profile F
A moist air parcel, moved upwards, cools according to the wet adiabatic lapse rate. But now it is warmer than the environmental air, and experiences an upward force.
A dry air parcel, moved upwards, cools according to the dry adiabatic lapse rate. But now it is cooler than the environmental air, and experiences a downward force. F
dry adiabatic
lapse rate F z T

26. z T Atmospheric stability: conditional instability stable for dry and
moist air
stable
for dry air
possibly
unstable
for moist air z T
Q: why possibly unstable for moist air?

27. Convective transport in Shallow Cumulus: Characteristics
Courtesy Bjorn Stevens
LES
Heus
TU Delft

28. Shallow cumulus movie by Thijs Heus

29. Stratocumulus
1100 km

30. Longwave radiative flux (FL) profile in cloud
Cloud top cooling!

31. Turbulence in stratocumulus: LES results and observations
Nighttime Daytime

32. Standard transport parameterization approach:
This unwanted situation can lead to:
Double counting of processes
Inconsistencies
Problems with transitions between different regimes:
dry pbl  shallow cu
scu  shallow cu
shallow cu deep cu

33. How to estimate updraft fields and mass flux?
Betts JAS
Arakawa&Schubert JAS
Tiedtke MWR
Gregory & Rowntree 1990 MWR
Kain & Fritsch 1990 JAS
And many more……..
The old working horse:
Entraining plume model: M e d
Plus boundary conditions
at cloud base.

34. Downgradient-diffusion models

35. Downgradient-diffusion models
Analytical solutions for stable stratifications see Baas et al. (2008)

36. Stable boundary layer solutions
Nieuwstadt's (1984)
z/L  ∞

37. Turbulence and clouds:
do we care?

38. Climate Model Sensistivity estimates of GCM’s participating in IPCC AR4
Source: IPCC Chapter
Spread in climate sensitivity:
concern for many aspects of climate change research, assesment of climate extremes, design of mitigation scenarios.
What is the origin of this spread?
Radiative Forcing, Climate feedbacks,

39. Relative Contributions to the uncertainty in climate feedbacks
Cloud feedback
Surface albedo feedback
Water vapor feedback
Radiative effects only
Source: Dufresne & Bony, Journal of Climate 2008
Uncertainty in climate sensitivity mainly due to (low) cloud feedbacks