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Impact of Antarctic mixed-phase clouds on climate
R Paul Lawson1, Andrew Gettelman2
1SPEC Incorporated, Boulder, CO 80301; and plawson@specinc.com.
Summary
Low-level Antarctic clouds, often mixed-phase, are more common than previously thought. Improving climate models with these findings significantly impacts climate predictions, especially over the Southern Ocean.
Area of Science:
- Atmospheric Science
- Climate Science
- Cloud Physics
Background:
- Low-level clouds over the Antarctic Plateau are poorly understood, yet crucial for climate.
- Existing global climate models (GCMs) inadequately represent mixed-phase clouds.
- This underrepresentation leads to significant uncertainty in climate change projections.
Purpose of the Study:
- To investigate the composition and incidence of low-level clouds over the Antarctic Plateau.
- To assess the impact of these clouds on climate predictions using modified GCMs.
- To evaluate the radiative effects of improved mixed-phase cloud representation.
Main Methods:
- Conducted in situ measurements at the South Pole using a tethered balloon system and ground-based lidar.
- Modified the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) GCM.
- Evaluated continental-scale radiative effects and performed sensitivity tests.
Main Results:
- Observed a higher incidence of low-level, mixed-phase clouds (containing supercooled liquid water and ice crystals) than anticipated.
- Incorporating these findings into the CESM GCM increased net cloud radiative effects (CREs) over Antarctica by +7.4 Wm(-2).
- Extended model simulations revealed substantial net CRE over Southern Ocean storm tracks, sensitive to mixed-phase clouds below -20 °C.
Conclusions:
- The study highlights the significant role of mixed-phase clouds in Antarctic and Southern Ocean climate.
- Accurate representation of these clouds in GCMs is essential for reliable climate predictions.
- Further research into supercooled liquid water in clouds is critical for refining climate models.
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