BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:The Tropical Tropopause Layer - Stephan Borrmann (Mainz)\, Neil Ha rris (Cambridge)\, Alison Ming (Cambridge) and Amanda Maycock (Cambridge) DTSTART:20150421T133000Z DTEND:20150421T163000Z UID:TALK58328@talks.cam.ac.uk CONTACT:Dr Amanda Maycock DESCRIPTION:An afternoon CCfCS meeting on 'The Tropical Tropopause Layer'. \n\n\n1430 Neil Harris - The influence of convective transport on TTL com position\n\n1500 Alison Ming - The structure of the upwelling and diabatic heating in the tropical lower stratosphere\n\n1530 Tea\n\n1600 Stephan Bo rrmann - Results and questions arising from recent in-situ measurements\n\ n1645 Amanda Maycock - The future of the TTL as simulated in global models \n\n1715 Discussion \n\n1730 Close/wine reception\n\n--------------------- ---------\n\nThe influence of convective transport on TTL composition\n\nN eil Harris (University of Cambridge)\n\nPassage of air through the Tropica l Tropopause Layer (TTL) is the major route for troposphere to stratospher e transport. The UK CAST campaign took place in the West Pacific in Januar y/February 2014. The field campaign was based mainly in Guam (13.5˚N\, 14 4.8˚E) and had three components: CAST with the NERC FAAM BAe-146 research aircraft\; the NASA ATTREX project based around the Global Hawk\; the NCA R-led CONTRAST campaign based around the Gulfstream V (HIAPER) aircraft. T ogether\, these aircraft made detailed measurements of atmospheric structu re and composition from the ocean surface to 20 km. An overview of the cam paigns will be given along with the results of high resolution global Unif ied Model studies and NAME trajectory calculations to look at the transpor t of air into the TTL in convective systems over the Maritime continent an d West Pacific. The focus will be on the transport of air from in and arou nd the boundary layer and will assess the possible importance of natural a nd anthropogenic emissions for TTL composition. \n\n---------------------- --------\n\nResults and questions arising from recent in-situ measurements \n\nStephan Borrmann (Johannes Gutenberg-Universität Mainz and MPI-Chemis try)\n\nIn-situ measurements were performed up to 21 kilometers altitude within the SCOUT-O3 and the AMMA-SCOUT framework in the tropical and mid- latitude UT/LS utilizing the Russian high altitude research aircraft M-55 "Geophysica". Results of ultrafine particle measurements are discussed fr om three tropical campaigns in Brazil\, Northern Australia and Burkina Fas o. The emphasis here is on new particle formation processes in clear air\, within anvils of mesoscale convective systems\, and within convective out flows from clouds. With respect to clouds results from measurements in cir rus over West African MCS systems and Cb overshoots in Australia are discu ssed as well as thin and subvisible cirrus cloud events. \n\n---------- --------------------\n\nThe structure of the upwelling and diabatic heatin g in the tropical lower stratosphere\n\nAlison Ming (University of Cambrid ge)\n\nThe upward velocity in the Brewer-Dobson circulation in the lower s tratosphere (~70 hPa) has a double-peak structure\, with the maximum upwar d velocity at about 20 N and 20 S and a minimum over the equator. This str ucture is evident in diabatic heating rates and vertical velocities calcul ated from ERA-Interim data and also in many model simulations. We analyse the different contributions to the localized maxima in diabatic heating ra tes and find an important contribution to the double-peak from ozone absor ption\, with secondary contributions from temperature structure and from l atitudinal variations in upper tropospheric clouds. \n\nAs required by the angular momentum balance\, the double-peak structure in upwelling corresp onds to a certain latitudinal structure in wave driving. However we argue that the structure in the wave driving cannot be considered to be the pri mary cause of the double peak and that the cause is instead some component of the diabatic heating field. We look at the consequence of imposing a d ouble peak structure in the heating in an idealized general circulation mo del and find that the circulation responds in such a way to produce two co rresponding peaks in the upwelling with a temperature change that has a we ak meridional gradient. There is a corresponding change in the wave drivin g but this is part of the dynamical response to the imposed heating.\n\n-- ----------------------------\n\nThe future of the TTL as simulated in glob al models\n\nAmanda Maycock (University of Cambridge)\n\nOzone and water v apour are particularly powerful greenhouse gases in the upper troposphere/ lower stratosphere. Thus changes in TTL composition may affect how surface climate responds to future anthropogenic greenhouse gas emissions. Howeve r\, climate models often struggle to capture the present day structure of the TTL\, raising questions about the reliability of future projections in this region. This talk will review some features of the TTL in global mod els under present day conditions and discuss simulated changes under clima te change with reference to possible implications for surface climate proj ections.\n LOCATION:MR3\, Centre for Mathematical Sciences END:VEVENT END:VCALENDAR