Clouds & aerosols over the Southern Ocean

Reducing biases in the representation of clouds and aerosols in the NZESM

Clouds have a massive effect on climate. Cloud cover reflects radiation from the sun that would otherwise be absorbed by oceans, raising their temperatures. Cloud cover can also act as a blanket, keeping warmth near the surface.

Clouds

Despite their significant influence on climate, clouds still represent the largest source of uncertainty in modern climate models. For example, the frequency of clouds over the Southern Ocean is often underestimated, causing models to predict warmer sea surface temperatures than observed, which in turn means the models predict the strength and position of the storm tracks incorrectly. These biases also affect the sensitivity of the model to human-induced climate drivers, such as increasing greenhouse gases.

It is vital to correct these biases, so we can increase our certainty in climate projections.

This project is improving our understanding of the chemistry and physics of clouds and aerosols in the Southern Ocean. By combining detailed measurements made during voyages with satellite observations and modelling studies, we're able to pinpoint model biases and identify the underlying errors. We recently completed our second dedicated measurement voyage on the RV Tangaroa, which saw researchers travel deep into the Southern Ocean, while making observations from the ship and launching instrumented balloons. We're now beginning to compare the measurements from the voyage with NZESM model output to identify differences and their underlying causes.

The project team has also developed new ways of using satellite data - using machine learning to identify different cloud types (not in itself a new strategy, but which has never before been used in model evaluation and improvement). This helps us determine whether the right amount of cloud is represented in the model and also, crucially, whether it's the right kind of cloud and if it's in the right place, relative to satellite observations. Results are suggesting that climate models predict a higher abundance of ice cloud than is found in reality, and we're now working on understanding the mechanisms that form ice in clouds.

Improving our understanding of clouds and incorporating this understanding into the NZ Earth System Model is critical, as these processes significantly affect New Zealand’s climate and have influences as far away as the tropics.

This is a joint project with the ESMP programme.

 

This project in the media:
Super-cooled liquid clouds: Why researchers want to know more Radio NZ
New Zealand's Next Top Model, New Zealand Geographic
New Zealanders out to uncover icy secrets, Scoop.co.nz
Breaking the ice, NIWA
 

Journal articles:

  • McDonald, A. J., and Parsons, S. (2018). “A Comparison of Cloud Classification Methodologies: Differences between Cloud and Dynamical Regimes.” Journal of Geophysical Research – Atmospheres, 123. doi:10.1029/2018JD028595
  • Jolly, B., Kuma, P., McDonald, A. J., and Parsons, S., (2018). "An analysis of the cloud environment over the Ross Sea and Ross Ice Shelf using CloudSat/CALIPSO satellite observations: the importance of synoptic forcing." Atmospheric Chemistry and Physics. 18(13): 9723-9739. Doi:10.5194/acp-18-9723-2018.
  • Schuddeboom, A. McDonald, A. J., Morgenstern, O., Harvey, M., and Parsons, S.(2018). "Regional Regime-Based Evaluation of Present-Day General Circulation Model Cloud Simulations Using Self-Organizing Maps." Journal of Geophysical Research-Atmospheres 123(8): 4259-4272. doi:10.1002/2017JD028196.
  • McDonald, A. J., Cassano, J. J., Jolly, B, Parsons, S.  and Schuddeboom A. (2016) “An automated satellite cloud classification scheme using Self-Organizing Maps: Alternative ISCCP weather states.” Journal of Geophysical Research – Atmospheres, 13,009–13,030, doi:10.1002/2016JD025199.

Presentations:
Shipborne and ground-based observations of clouds in the sub-antarctic and Southern ocean, Peter Kuma et al, Antarctic Science Conference Dunedin
Clouds and aerosols: Understanding processes –informing models, Mike Harvey et al, Deep South Symposium
Clouds and aerosols: a modelling perspective, Vidya Varma et al, Deep South Symposium