Observation of aerosols and clouds
To reduce uncertainty in our understanding of aerosols and clouds and to improve our predictions of their current and future impact on climate, we need observational systems that can provide constraint on our model tools.
Climate models seek to replicate the state of the global system and predict its future change on timescales of years to decades. To test our models, very diverse observational systems are required.
Global observations
Global observations, either from long term continuous in-situ observations or continuous global data from satellites, provide the long-term data sets and global coverage of a range of cloud and aerosol properties.
– Satellites use visible light scattered from clouds to obtain information such as the cloud droplet size, droplet number and the amount of liquid water through the depth of cloud and infra-red wavelengths can help to determine cloud top height.
– Space-borne radar can retrieve precipitation and whether the clouds contain liquid or ice phase water. Aerosol optical depth can be measured using scattered visible radiation. Active remote sensing using lidars can obtain vertically resolved information of aerosol layers and cloud top heights.
Ground-based long-term observations
Ground-based long-term observations combine in-situ observations and remote sensing methods using a wide range of active and passive sensors.
– CERTAINTY works closely with ACTRIS, a pan-European research infrastructure that includes a number of long-term observations sites that produce high-quality data and information on aerosols and clouds.
– Radars and lidars are widely used to provide detailed information on clouds of different types and can be used to examine the role of aerosols in cloud formation and development.
– The combination of ground-based data with remote sensing can provide detailed information on the physical, chemical and optical properties of aerosols on a continuous basis. Where these stations are located on mountains at altitude, in-situ observations of clouds are also possible, as well as constraining climate scale models. These detailed observations also shed light on important processes and can be used to inform and constrain regional models and computational tools that examine cloud systems on small scales that resolve clouds and their microphysical properties.
Airborne observations
While satellite data provides global coverage, they cannot retrieve all the important properties that are important and lower clouds and aerosols may be masked by upper-level cloud cover. Ground based stations provide long term observations but since aerosol and cloud processes take place through the atmospheric column cannot always capture important interactions.
– Airborne observations are expensive but can deliver in situ and remotely sensed observations in regions where important cloud types exist and these datasets are an important additional source of data.
Laboratory and chamber studies
These elements of the atmospheric observing system are all important and may be combined to offer a strong test of our understanding of atmospheric processes. However, the atmosphere is complex and often important microphysical processes that drive cloud development cannot be constrained in the real atmosphere.
– Laboratory and chamber studies that simulate these processes in the absence of atmospheric variability are therefore used to underpin this understanding and develop new parameterisations that can be included in the next generation of models.
