a study of ice formation by primary nucleation and ice multiplication in shallow precipitating...
TRANSCRIPT
A study of ice formation by primary nucleation and ice multiplication in
shallow precipitating embedded convection
• T. Choularton1, I. Crawford1, C. Dearden1, K. Bower1, J. Crosier1, A. Blyth2, C. Westbrook3, M. Gallagher1
University of Manchester, UK• University of Leeds, UK• University of Reading, UK
EGU General Assembly - Vienna - 2011
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 Size 3-50 µm2DS - Ultra-fast response shadow imaging 10-1280 µmCIP-15 - Fast response shadow imaging 15-960 µmCIP-100 - Fast response shadow imaging 100-6200 µmCPI - High resolution Cloud particle images 15-2500 µm
In-situ Cloud/Aerosol Microphysics
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Chilbolton Facility for Atmospheric and Radio Research
Chilbolton Remote SensingScanning 3GHz Doppler polarization radar35GHz & 94GHz cloud radar355nm UV lidar1.5μm Doppler lidar905 nm Ceilometer lidar
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Synoptic Situation 00Z 18/02/2009
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MSG Visible Image – 1300 UTC
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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 CConvective Region
Temperature = -11.7 deg CSupercooled Stratus
Hallett-Mossop (Nature, 1974) rime splintering producing high ice number concentrations at relatively warm temperatures•Concentration profile •Crystal habit•Crystal sizesHowever, 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= -11.5 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: AS1.4Poster number: 10876
17:30-19:00