Clouds and Aerosols
Jón Egill Kristjánsson
Key Concepts
• Radiative Forcing: Change in Energy Fluxes from
1750 to 2011
• Response: Associated with temperature changes;
time scales of decades to centuries. Very sensitive
to feedbacks in the climate system
Key Concepts
• Radiative Forcing: Change in Energy Fluxes from
1750 to 2011
• Rapid Adjustments: Not related to temperature
changes. Time scale less than 1 yr
• Response: Associated with temperature changes;
time scales of decades to centuries. Very sensitive
to feedbacks in the climate system
*) Effective Radiative Forcing (ERF)
*
How do we determine ‘Effective
Radiative Forcing’?
The ‘Gregory method’
Forcing and Feedbacks related to
Clouds and Aerosols
How do Aerosols exert a Radiative
Forcing on Climate?
Cloud Regimes vs Latitude
Where do we find clouds?
- ITCZ
- Storm Tracks
- Cold ocean currents
Location of the clouds in the vertical
(CloudSat/CALIPSO)
- 38°C
0°C
Cloud Water Content and Precipitation
NB! Frequency of Occurrence of
Precipitation ≠ Amount of Precipitation
Precipitation
986 mm yr-1
Where do we find High Clouds?
- ITCZ, especially Summer Hemisphere
- Storm Tracks
Where do we find Mid-level Clouds?
- Low-latitude land regions, especially Summer Hemisphere
- Storm Tracks
Where do we find Low Clouds?
- Storm Tracks
- Cold ocean currents – Why?
Vertical Velocity in mid-troposphere
- How high is mid-troposphere?
- What pressure?
- Why mid-troposphere?
Rising Motion
Sinking Motion
SW Cloud Radiative Effect
The Radiative Cooling Effect of Clouds in the Current Climate
LW Cloud Radiative Effect
The Radiative Warming Effect of Clouds in the Current Climate
Net Cloud Radiative Effect (SW + LW)
The Net Radiative Effect of Clouds in the Current Climate
Types of models for simulating clouds
- The Global Climate Models do not resolve individual clouds
- The Cloud Resolving Models are not global
What can be done?
Water Vapor Feedback
- Positive
feedback
due to
more WV in
a warmer
climate
- Negative
feedback
due to
reduced
lapse rate
- Net WV
feedback is
positive
Cloud Response to Global Warming
Cloud Feedback
Main Components of Cloud Feedback
• Changes in Altitude of High Clouds
• Changes in the Amount of Middle and High
Clouds
• Changes in Low Clouds
• Changes in Cloud Opacity
• Changes in Arctic Low Clouds
Aerosols and Climate Forcing
Anthropogenic Aerosols
Natural Aerosols
Aerosol Optical Depth in ECMWF model
with assimilation of MODIS retrievals
CALIPSO: Aerosol Extinction
Coefficient vs Height and Latitude
What’s this?
Vertical Profiles of Black Carbon: Obs
and Models
Huge Model Biases
Vertical Profiles of Black Carbon: Obs
and Models
Huge Model Biases