Atmospheric Circulation 2008
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Autumn 2008 Atmospheric Circulation Newsletter of the University of Washington Atmospheric Sciences Department Let It Snow! by Mark Stoelinga produced 180% of normal snow- trailer (see photo) to assess the relative percent- pack in the central Washington ages of habit types seen, and degrees of riming. Cascades, made for a very good At the same time, a series of other manned and winter of observations. automated observations were taken of precipita- The research endeavor was tion rate, new snow depth, particle size distribu- motivated by an increasing rec- tions, and particle fall speeds. Other tests were ognition of the importance of conducted on accumulated snow, such as rate snow microphysical processes in of compaction under load, and shear strength. precipitation production, coupled The key goal was to be able to relate all these with a lack of data on the prop- properties to the habit and riming composition erties of snow that relate to the of the snow particles. physics of precipitation growth, The data set collected during the observa- and a general oversimplification tional studies provides an unprecedented long- of the representation of snow term record of snow particle types that occurred properties in computer weather throughout many different orographic winter prediction models. Essentially, storms in the Cascades. One application of the most computer models treat data set is to estimate the total mass of different snow particles as “little snow habit types that comprise the snow accumula- The snow study research site at Stevens Pass balls,” or spheres of constant tion during typical storms in the Cascades. The during winter 2007/2008. density, regardless of the condi- analysis indicates that, for example, dendritic tions that lead to their growth. (intricately branched) crystals comprise around s was widely reported in the local me- However, snow particles are known to take on a 40% of the total mass of Cascade snow fall, Adia, the winter of 2007/2008 witnessed variety of shapes and densities. This variability whereas hexagonal plates comprise only about a bountiful snow season in the Cascade Moun- is related to both the habit type of ice growth 2%. This kind of information is valuable for de- tains, providing a boon to skiers, utility provid- (e.g., “dendrites,” “plates,” “needles,” etc.), termining which habits are important to predict ers, and Research Associate Professor Mark which is determined by the temperature and and which are not. Another important parameter Stoelinga. Stoelinga’s research group conduct- humidity conditions at which the particle grew that was measured is particle fall speed. These ed field studies at Stevens Pass this past winter by vapor deposition; and by the degree of rim- measurements were gathered with an automated to study the microscopic properties of falling ing growth, which occurs when a snow particle imaging instrument known as a video disdrom- and accumulating snow particles, with an eye encounters and collects supercooled liquid wa- eter, mounted on the roof of the research trailer, toward improving weather forecasts produced ter cloud droplets that subsequently freeze onto which measured the size and fall speed of every by the computer weather prediction models on the snow particle, making it denser. Different particle that fell through a 6"×6" opening. In which the National Weather Service, and ulti- habit types and degrees of riming can result in conjunction with the habit type observations, mately the public, rely. large differences in important properties of fall- the disdrometer observations allowed the re- The field work actually began in the previ- ing snow particles such as their mass, fall speed, searchers to develop relationships between par- ous winter of 2006/2007, during which Stoe- and ability to grow further by deposition or rim- ticle fall speed and both habit type and degree linga’s research team, which included Research ing. Also, the properties of the snow that accu- (Continued on page 4) Scientist John Locatelli and graduate students mulates on the ground, such Hafen McCormick and Jerry Casson, resided as density, depth, and struc- at Snoqualmie Pass for three months in two tural strength, are affected small A-frame cabins immediately adjacent to by the shapes and densities of snow particles that fell. their research trailer. While that winter pro- These properties of accumu- vided near normal snowfall in the Washington lated snow are important for Cascades, the low elevation of Snoqualmie Pass forecasting of snow depth (3020 ft/920 m) resulted in significant portions and avalanche potential. of the precipitation falling as either wet snow or During both winter sea- even rain, not ideal for studying the behavior of sons, observations were con- snow crystals. So the team decided to relocate ducted with essentially the to Stevens Pass for this past winter’s observa- same routine and strategy. tions. Stevens Pass Ski Area took an interest Particle samples were col- in the scientific endeavor, and generously al- lected by an observer on a lowed the research team to locate their research glass slide every 15 minutes trailer at the base of the ski area, with unlim- during snowfall events, and ited electric power and snow removal services examined under stereomi- Graduate student Hafen McCormick examines snow particles provided. The higher elevation of Stevens Pass croscope within the research under a stereomicroscope. (4060 ft/1240 m), coupled with a snow year that 1 Department of Atmospheric Sciences Chair’s Column teorological Society and recruiting faculty. The Featured Professor: repair was evidently successful, as was Mike, ne of my who soon received a job offer from UW. Mike favorite fea- Mike Wallace O took the job, married Susie, and headed west. tures, in both Atmo- spheric Circulation Once at UW, Mike began work with Dick and the alumni news- Reed, Jim Holton and grad student Vern Kousky letters I receive from that led to Mike and Vern’s seminal paper on my alma maters, is the quasi-biennial oscillation. In the early 1970s the section on alumni the department began to attract physics students news. So I’d like who had little background in atmospheric sci- to begin by thank- ence, so Mike developed the ATMS 501 course ing David Mechem (Fundamentals of Physical Meteorology) that (Ph.D. 2003) for he continues to teach to this day. Mike must sending us the news about his daughter’s sci- have really figured out how to present that ma- ence fair project. I hope that many more of you terial, because he was honored with the depart- will send us bits on news about your current mental teaching award in both 1990 and 2003. family or activities that we can share in next Mike, collaborating with Peter Hobbs, used his year’s edition of Atmospheric Circulation. 501 course notes to write the first edition of At- Aside from the consistency of the Husky mospheric Science: An Introductory Survey in football program this fall, perhaps the biggest 1977. A thoroughly reworked second edition of piece of news at UW is the creation of a new Wallace and Hobbs appeared in 2006. College of the Environment. This is likely to Mike served as chairman of our department impact our department in many ways. The first from 1983–1988, during which time he also be- way is that it has drawn Dennis Hartmann, who Mike Wallace came the director of the Joint Institute for the just finished a five-year term as our departmen- Study of the Atmosphere and Ocean (JISAO). tal chairman, back into the treacherous rapids of ohn Michael Wallace began his prepara- Although he remained very active in the depart- university administration. Dennis has agreed to Jtion for graduate school in meteorology by ment, he moved his office over to JISAO after serve as the Interim Dean for the new college. obtaining a B.S. in Naval Architecture in 1962 stepping down as chair. We finally welcomed Due to his busy administrative schedule, winter from the Webb Institute of Naval Architecture Mike back into his current fifth-floor office in 2009 is likely to be the first quarter since 1994 in Glenn Cove, N.Y. Even as an undergraduate, the ATG building in early 2006, and we have during which Dennis does not teach ATMS 552 Mike’s first love was meteorology, which he loved having him so available ever since. (Objective Analysis). proved during his time at Webb by staying up There is also a reasonable chance that our all night to watch a blizzard instead of studying department will find itself moving from the Col- for a final exam in Boiler Design. After gradu- lege of Arts and Sciences to the College of the ation, Mike had offers to study atmospheric Environment. Forecasting future administrative science from two graduate schools: M.I.T. and decisions, some of which may be influenced by UW. Having roots in the northeast, he elected the economy, is not a whole lot easier than fore- to attend the school closest to his neighbor- casting the weather, so you may need to wait hood. While at M.I.T., Mike was an early user for the next issue of Atmospheric Circulation of computers, starting with a Librascope Gen- to find out how the College of the Environment eral Precision 30, a twin to the machine used by Ed Lorenz in his studies of predictability. Soon develops. In the mean time you can read more ATMS May Join New about the new college on this page. after his arrival at M.I.T., Mike, working under Before closing I’d like to call your attention the guidance of Reggie Newell, switched to the College of the Environment new super computer of its day, an IBM 7090 to our new effort to put alumni theses online by Dennis Hartmann (see p.