Distribution of Liquid Water in Orographic Mixed-Phase Clouds

Diana Thatcher Mentor: Linnea Avallone LASP REU 2011

Outline

• Introduction • Experiment • Important Instruments • 1 st Area of Interest • 2 nd 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 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 19 th and 20 th , 2011 • Area over Muddy Mountain, Wyoming • High amounts of snowfall

Flight Path

6 levels – 3 legs each

Features: • Updrafts • Small particles • Liquid water

1

st

Area of Interest

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

2

nd

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