Distribution of Liquid Water
in Orographic Mixed-Phase
Clouds
Diana Thatcher
Mentor: Linnea Avallone
LASP REU 2011
Outline
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Introduction
Experiment
Important Instruments
1st Area of Interest
2nd Area of Interest
Conclusion
Orographic Clouds
• Formed when mountains force moist air upward
• Variety of interesting structures possible
Orographic wave clouds over Long’s Peak
Mixed-Phase Clouds
• Water is present in solid, liquid, and vapor forms
• Typical temperatures: 0 to –30 ºC
– Liquid is supercooled
• Formed in a variety of situations
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Stratiform clouds in polar regions
Frontal systems
Convective cloud systems
Orographic forcing systems
Particle Formation
• Ice particles in areas of
supercooled liquid water can
undergo:
– Riming (growth)
– Splintering (multiplication)
• Affects resulting cloud
structure and precipitation
• Results depend on cloud
temperature and saturation
Example of a Mixed-Phase Cloud
Importance of Study
• Past studies mainly focus on:
– Arctic mixed-phase clouds
– Effect of aerosols on mixed phase clouds
• More knowledge is necessary to create accurate
climate models
– Complex effects of topography
– Microphysics of liquid and solid particle formation
• Results could aid in the prediction of icing
conditions
Icing Hazards
• Supercooled liquid water < 0 ºC
• Easily freezes to outside of aircrafts
– Major difficulties for pilots
Colorado Airborne Mixed-Phase
Cloud Study (CAMPS)
• Includes data from instruments on University of
Wyoming King Air research aircraft
– Numerous sensors
– Wyoming Cloud Radar
– Wyoming Cloud Lidar
• Provides in-situ and remote sensing for liquid water,
ice crystals, and other microphysical properties
Cloud Droplet Spectra - FSSP
Forward Scattering Spectrometer Probe
• Measures particle size distributions
• Detects how a particle scatters light
• 2.0 – 47 μm
Particle Imaging Instruments
2-D Cloud and Precipitation Probes
• Measures particle size distribution
• Image is created from a shadow
when particle passes through a laser
• Pattern recognition algorithms
deduce the shape of particle
• 25 – 800 μm (2-DC)
• 200 – 6400 μm (2-DP)
Icing Indicator
Rosemount Icing Detector (Model 871)
• Detects supercooled liquid water
• Cylinder vibrates at frequency of 40 Hz
– As ice accumulates, the frequency decreases
• Cylinder is heated to melt ice
• Process is repeated
My Area of Study
• February 19th and 20th, 2011
• Area over Muddy Mountain, Wyoming
• High amounts of snowfall
Flight Path
6 levels
– 3 legs each
1st Area of
Interest
Features:
• Updrafts
• Small particles
• Liquid water
Radar and Lidar
Vertical Wind Velocity
Particle Size Distribution
Nearly 100X decrease in mean particle diameter!
Large Particles
Small Particles
Liquid Water Content
• Increase in liquid water content during updrafts,
with a slight lag of less than 1 minute
• Water droplets are much smaller than ice crystals,
coinciding with particle
size distribution
• Temperature: -16 °C
– Icing conditions
2nd Area of
Interest
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Over edge of peak
Updrafts/Downdrafts
Liquid Water
Small Particles
Radar and Lidar
Vertical Wind Velocity
Particle Size and Liquid Water Content
• Increase in small particles
• Increase in liquid water
• Again, particle formation processes are at
work
Conclusion
 In mixed-phase clouds, areas of increased liquid water
content are likely to occur in areas of strong updrafts, with
a slight lag between the peak velocity and peak liquid
water content.
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Sudden increases in liquid water content are
accompanied by a drastic change in the particle size
distribution, with a sharp decrease in the concentration of
ice crystals and a simultaneous increase in small liquid
droplets, indicating the formation of new particles.
Future Work
• Obtain particle image data
– Determine ice crystal structures
– Determine particle formation processes
• Expand to a greater variety of cases
– Determine limits, such as temperature or vapor
saturation
– Further analyze the effects of topography
Questions?
References
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Hogan, R. J., Field, P. R., Illingworth, A. J., Cotton, R. J. and Choularton, T. W. (2002),
Properties of embedded convection in warm-frontal mixed-phase cloud from aircraft and
polarimetric radar. Quarterly Journal of the Royal Meteorological Society, 128: 451–
476. doi: 10.1256/003590002321042054
http://www.eol.ucar.edu/raf/Bulletins/B24/fssp100.html
http://www.eol.ucar.edu/raf/Bulletins/B24/2dProbes.html
http://www.eol.ucar.edu/raf/Bulletins/B24/iceProbe.html
Image Sources
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http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/cld/dvlp/org.rxml
http://www.flickr.com/photos/wxguy_grant/4823374536/
http://www.ucar.edu/news/releases/2006/icing.shtml
http://www.askacfi.com/24/review-of-aircraft-icing-procedures.htm
http://en.wikipedia.org/wiki/Wikipedia:Picture_of_the_day/September_26,_2006
http://www.cas.manchester.ac.uk/resactivities/cloudphysics/results/riming/
http://www.eol.ucar.edu/raf/Bulletins/B24/fssp100.html
http://www.eol.ucar.edu/raf/Bulletins/B24/2dProbes.html
http://www.eol.ucar.edu/raf/Bulletins/B24/iceProbe.html