Post on 18-Jan-2016
transcript
Distribution of Liquid Water in Orographic Mixed-Phase Clouds
Diana ThatcherMentor: Linnea Avallone
LASP REU 2011
Outline
• 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– 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 Instruments2-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 IndicatorRosemount 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
Large Particles Small Particles
Nearly 100X decrease in mean particle diameter!
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
• 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.
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
• 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
• 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