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Altocumulus Cloud Sortie
Paul Barrett, Phil Brown, Alan Blyth
© Crown copyright Met Office
Altocumulus Sortie – PiknMix 2014
Mixed Phase supercooled layer cloud
measurements in the mid-troposphere
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Motivation: Investigate the turbulence and ice properties in
supercooled altocumulus clouds
Typical Weather conditions:
Frontal systems:
• ahead of warm fronts
• within humid warm sectors
• occluding fronts
• within large scale upper
troughs (500hPa down to
800hPa)
• No embedded waves
Cloud Top Temperature
• -10°C to -30°C (ideal -20°C)
© Crown copyright Met Office
Key Instruments:
(possible Go / no-go)
• AIMMS / 5-port turbulence,
• CDP, SID2, CIP15/100, 2DC,
WVSS2, TWC, Nevzorov
Nice to have:
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LIDAR, Dropsonde, Video, MARSS,
BCPd, 3V-CPI,
Aerosol Measurements – PCASP,
GRIMM, CPC, CAS?
T-Amdar (icing, humidity)
Altocumulus Model and Flight
Strategy
• Cellular Liquid Cloud structure underneath temperature
inversion – very thin liquid layer <1000ft
• Ice virga falling from liquid layer
• Turbulence Structure c.f. Stratocumulus
• Sloping Cloud top along constant potential temperature
surfaces – difficult to fly through!
© Crown copyright Met Office
Flight Strategy
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SLRs become “slant” profiles w.r.t inversion altitude – 1,3,4,7
dog-leg stack of straight and level runs: Along and across wind
legs
Profiles, wings level, at 1000ft/min to minimise horizontal contam.
of vertical structure
Aircraft to drift with the wind
LIDAR to measure CTH
If high LWC expected then Cloud Top Runs last! (warmer clouds)
Sample the inversion at regular intervals in time and space
B674 Altitude Time Series
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