A study of ice formation by primary nucleation and ice multiplication in shallow precipitating embedded convection T. Choularton 1, I. Crawford 1, C. Dearden 1, K. Bower 1, J. Crosier 1, A. Blyth 2, C. Westbrook 3, M. Gallagher 1 University of Manchester, UK University of Leeds, UK University of Reading, UK EGU General Assembly - Vienna

Slightly Supercooled Layer Cloud Small source of precipitation Long lifetime Large area of cloud cover Cloud droplet formation Primary Ice nucleation (heterogeneous) Secondary Ice Production Mechanisms

Slightly Supercooled Layer Cloud Morrison and Pinto, Journal of the Atmospheric Sciences, 2005 Springtime Arctic Mixed Phase Stratiform Cloud Figure removed for copyright purposes

DeMott et al, Proceedings of the National Academy of Sciences, 2010 Ice Nuclei Prediction Figure removed for copyright purposes

DeMott et al, Proceedings of the National Academy of Sciences, 2010 Ice Nuclei Prediction The new DeMott paramaterization includes information on the aerosol population Figure removed for copyright purposes

Slightly Supercooled Layer Cloud Accurate prediction of cloud microphysical properties (esp. Ice Crystal Conc) is necessary for simulated clouds to have observed lifetimes (days) and radiative properties (Arctic Springtime mixed phase stratiform clouds)

FAAM BAe146 aircraft CDP- Droplet Size3-50 µm 2DS- Ultra-fast response shadow imaging µm CIP-15- Fast response shadow imaging µm CIP-100- Fast response shadow imaging µm CPI- High resolution Cloud particle images µm In-situ Cloud/Aerosol Microphysics Figure removed for copyright purposes

Chilbolton Facility for Atmospheric and Radio Research Chilbolton Remote Sensing Scanning 3GHz Doppler polarization radar 35GHz & 94GHz cloud radar 355nm UV lidar 1.5μm Doppler lidar 905 nm Ceilometer lidar Figure removed for copyright purposes

Synoptic Situation 00Z 18/02/2009 Figure removed for copyright purposes

MSG Visible Image – 1300 UTC Figure removed for copyright purposes

MODIS-Terra overpass, 1120 UTC Crosier et al, Atmospheric Chemistry and Physics, 2011 Large region of supercooled (~ -15 deg C) cloud over UK indicated by green Radiosonde stations AB, NT and LK located beneath the same supercooled cloud

Thermodynamic profile – 1200 UTC Low level warm cloud AB, NT and LK have additional cloud layer ~ -13 degC Dry air above Confirmed by BAe146 profile Widespread thin (~300m) supercooled layer clouds with no seeding from above Crosier et al, Atmospheric Chemistry and Physics, 2011

Remote sensing from CFARR Crosier et al, Atmospheric Chemistry and Physics, 2011

BAe146 Flight track – 18/02/2009 Crosier et al, Atmospheric Chemistry and Physics, 2011

CAMRa (3 Ghz Radar) and BAe146 (in-situ) Crosier et al, Atmospheric Chemistry and Physics, 2011

CAMRa (3 Ghz Radar) and BAe146 (in-situ) Crosier et al, Atmospheric Chemistry and Physics, 2011

CAMRa (3 Ghz Radar) and BAe146 (in-situ) Crosier et al, Atmospheric Chemistry and Physics, 2011 Region of embedded convection ~ 15 – 25 km South West of Chilbolton

Crosier et al, Atmospheric Chemistry and Physics, 2011 BAe146 (in-situ)

Crosier et al, Atmospheric Chemistry and Physics, 2011 BAe146 (in-situ) Temperature = -4.3 deg C Convective Region Temperature = deg C Supercooled Stratus Hallett-Mossop (Nature, 1974) rime splintering producing high ice number concentrations at relatively warm temperatures Concentration profile Crystal habit Crystal sizes However, predicted production rates match observations if all droplets can generate splinters, not simply for D>23µm

Conclusions – supercooled layer with embedded convection Steady ice production in slightly supercooled layer cloud (Tmin= deg C, 3.6km altitude) Embedded convection inititiated at mid level convergence (2.5km altitude) HM process highly active in embedded convection region HM process activated by formation of ice in supercooled layer cloud at slightly supercooled temperatures Snowflakes appear to participate in HM process, as do smaller drops than reported (D<23um)

Future work WRF simulations varying the different heterogeneous nucleation mechanisms (Contact vs deposition/condensation etc) to see impact on cloud lifetime etc Impact of HM treatment on precipitation formation Validation of WRF simulations vs observations (in- situ and remote sensing) What particles act as IN at such warm temperatures? Could a stochastic nucleation process be at work?

Thank you for your attention! Poster session: AS1.4 Poster number: :30-19:00