COntrails Spreading Into Cirrus (COSIC)

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BACKGROUND In the last fifty years aviation has experienced very rapid development, with air traffic recording an almost 9% yearly growth rate in the first half of the period (approximately 2.5 times the average GDP growth rate) and approximately 5% yearly growth rate in the second half of the period. According to the most recent estimates, aviation climatic impact amounts to 2-8% of the global radiative forcing associated with climate change. As a result of the expected increase in air traffic in the next decades, the relative importance of air traffic on climate change is expected to increase significantly. THE NEED FOR COSIC AND AIMS One of aviation's largest effects is likely to be that due to contrails and their spreading into cirrus. This could be considerably larger than the effects of increased CO2 emissions but this contrail-cirrus remains unquantified. Previous estimates of combined aviation induced cloudiness suggest that spreading contrails could be important. However, these studies rely on correlating air traffic with cirrus coverage and have large uncertainties and methodological problems. The ultimate aim of this proposal is, for the first time, to build a physically based parameterisation of contrail-cirrus - to determine its role in climate change, testing whether it has a larger role than line-shaped contrails. To achieve this ultimate goal, observations of contrail properties and their spreading will be made with FAAM (research aircraft) flights and satellite observations. Then a hierarchy of models will be used to develop a contrail-cirrus cloud parameterisation within the Met Office Unified Model, working closely with both the Met Office and the Deutsches Zentrum für Luft- und Raumfahrt (DLR) partners, and constraining the developed parameterisations by the observations made by University of Manchester and Met Office researchers during the aircraft campaign. WORKPLAN WP1 will perform an aircraft campaign making 6 'case study' observations of spreading contrail during 2009 in an area out of the flight corridor to the southwest of the UK . We will use a novel 'figure of eight' flight pattern to make and monitor our own contrail and, in particular, track its evolution into cirrus. We will measure its radiative forcing by flying cross sections above and below and by monitoring from space using the GERB and SEVIRI geostationary instruments. We will make use of state-of-the-art observations made by the Met Office and University of Manchester groups. We will also rely on ice supersaturation forecasts supplied by the University of Reading group using European Centre forecasts. WP2 will use idealised modelling data supplied by DLR and the detailed observations made during WP1 to simulate specific case studies observed during the aircraft campaign. Particular attention will be made to the later stages of contrail lifecycle. WP3 will again make use of idealised DLR data and our own (and others) case-study data to build a prognostic contrail-cirrus scheme for the Met Office Unified Model. WP4 will employ the Unified Model with this parameterisation to predict the radiative forcing and climate impact from contrail-cirrus, comparing its climate impact to that estimated for line-shaped contrails.