Cirrus Coupled Cloud-Radiation Experiment: CIRCCREX

Climate and weather prediction models demand understanding of how cirrus clouds, high in the troposphere (6-14km in altitude) affect our climate. Cirrus covers up to 30% of the globe and its effects should be accurately included in global climate models. Clouds have two main effects; they are the main atmospheric component in the hydrological cycle, but they also trap radiation, both reflecting sunlight back to space (cooling the Earth's surface) and trapping the thermal energy emitted from the surface (as they are cold, emitting less energy to space than an equivalent cloudless sky). The balance between the shortwave (sunlight) and longwave (thermal radiation) effect depends on factors such as altitude and thickness of the cloud, and the size and shape of the ice crystals that make up the cloud. The crystals can take on myriad shapes, and the shapes existing in particular clouds depend on conditions and on the evolutionary sequence that the particles experience; growing, aggregating and/or dissipating over time, dependant on the changes in temperature, humidity and meteorological environment they experience. Different crystal sizes and shapes reflect and scatter light in different ways. Some crystal shapes are efficient at reflecting sunlight, but not thermal radiation and some the other way round. The net effect of a cloud on the radiation budget depends on the microscopic shapes of the crystals inside it. By measuring both the heat emitted by the cloud and its internal crystal properties ('microphysics') we can determine the link between the two, and hence the overall effect the cloud is having on the climate.
Cirrus models have been derived that calculate expected response of different crystal types across the spectrum, and these are usually combined with predicted particle size and shapes (Particle Size Distributions, PSD) found from in-situ flight campaign measurements using cloud probes. These are parameterised (simplified) and used in climate models and general circulation models (GCMs), eg. in numerical weather prediction (NWP) and climate change, but these cirrus models have not been tested across the full spectrum. Some studies have been made of specific radiative properties of some crystal types in the shortwave, and of other crystal types in parts of the longwave, but there has not been a successful measurement covering the full spectrum simultaneously measuring the precise make up of the crystal sizes and types in a cloud.
We plan a novel flight campaign combining full spectrum radiative measurements (125-0.3 microns) from longwave to shortwave, with state-of-the-art measurements of crystal PSDs, the ice water content and temperature etc. We will test scattering models and PSD parameterisations used to describe cirrus cloud in atmospheric models, such as the UK MetOffice (MO) Unified model Numerical Weather Prediction (NWP) with model improvements implemented by our MO project partners. Our project is possible because of NERC funded research that led to: state-of-the-art cloud probe instruments and software tools that addressed problems of ice crystal shattering at the inlet apertures and the great uncertainty in ice crystal size distributions of the past; and the development of the unique far-IR instrument TAFTS at Imperial College (IC). The ability to measure the entire spectrum from an aircraft, and so simultaneously measure the cirrus crystal types, sizes, temperature and IWC, roughness etc., is a unique facility only available on the UK FAAM aircraft. We combine radiometry in the far-IR of IC, in mid-IR to solar of MO, cloud microphysics instrumentation and expertise of Manchester and Hertfordshire Universities, and UKMO/FAAM with complementary cloud and atmospheric state measurements. This will give a leap forward to cirrus modelling, our datasets allowing testing and development of models and parameterizations used to predict the effect of cirrus in climate models and NWP.

1)Specific users this work might be of interest to and how they will benefit:

Immediate beneficiaries are given in "Academic Beneficiaries".

The Intergovernmental Panel on Climate Change has identified understanding of the effects of cloud as one of the key uncertainties in climate change predictions. The most direct users of our cirrus project are atmospheric scientists, climate and numerical weather prediction (NWP) modellers, who will use the anticipated improved and validated cirrus parameterizations to improve GCM ability to capture cirrus impact and evolution. The new cirrus parameterizations will be available through our project partner,the Met Office, for incorporation into global climate models. We will demonstrate the accuracy improvement possible for NWP models by tests with the new cirrus models. The expected result will be improved ability to capture correctly cirrus effects on weather forecasts and climate predictions. We will work directly with modellers to facilitate this, with:

(i)The Met Office (MO) who run the Unified Model (UM), used internationally, http://www.metoffice.gov.uk/research/collaboration/um-collaboration, for weather prediction and climate models. The MO will use evidence from our CIRCCREX collaborative project to inform on including paradigm shift cloud-radiation coupled cirrus parameterizations in the UM.

(ii) USA cirrus modellers (Baum, Yang and ice cloud research team http://www.ssec.wisc.edu/ice_models/) who will provide us with their cirrus models for testing with our observational data (see support letter). This allows them to improve their models using unique datasets. These cirrus models are used in climate models and satellite retrievals, ensuring wide impact internationally.

Other impacts follow indirectly,eg from studies of cirrus, contrails,aerosols, chemical transport, to studies using energy transport, radiative transfer, and climate change. Indirect users include those reliant on climate and atmospheric models, or satellite retrieval data for clouds.

Results will be published in international journals with press releases to raise profile of our research.The greatest impact will be incorporation of the new cirrus cloud-radiation parameterizations into climate and NWP model codes used worldwide.

2)Wider user benefits:
Most relevant is the impact for Government policy makers responsible for action on climate change, who benefit from more reliable climate models (eg MO UM), strengthening the international community's case for taking action to avert climate change -the IPCC highlighted clouds as a key uncertainty. Improved MO weather forecasting accuracy has societal and economic benefits to the wider public.

Wider user benefit is achieved by:
A project website suitable for scientists and the general public including school children, with "news releases" ,press articles on CIRCCREX research and its impacts, for example on climate models.
Public Outreach: IC staff are involved in engaging with the next generation, for example giving outreach lectures 'The Science of Climate Change' to schools.
our strong links to our project partners at the UK MetOffice, who advise the Government regarding climate change.

3)Other impacts: UK competitiveness.The NERC funded TAFTS instrument is the only high resolution far-IR spectrometer for in-situ measurements of up- and down-welling radiances in the troposphere. The far-IR region has great uncertainties in radiative transfer and climate models.To realise the impact of TAFTS in terms of new science, and to maintain our position at the forefront of this field internationally we continue to seek support for science with TAFTS. Far-IR expertise of TAFTS scientists is forming a strong base for future world class instrumentation projects: eg. our involvement in recent bids for new IR satellite instrumentation and membership of the Science Definition Team of NASA's proposed far IR satellite instrument CLARREO.