"THIRTY YEARS OF AIRBORNE RESEARCH
AT THE UNIVERSITY OF WASHINGTON: A RETROSPECTIVE"
NOTES FOR COLLOQUIUM GIVEN BY PETER V. HOBBS
TO THE UW ATMOSPHERIC SCIENCES DEPT.,
OCTOBER 24, 2002
1. INTRODUCTION
A story is told about Sherlock Holmes and Dr. Watson:
They are on a camping trip together, when Holmes suddenly wakes up in the middle of the night and says
"Watson, look at all those stars, what do you deduce from that?"
"Well, Holmes, I deduce there must be billions of galaxies out there, each containing billions of suns, and billions of planets, and therefore there must be life out there. What do you conclude, Holmes?"
"Watson, you idiot, someone has stolen our tent!"
I tell this joke mainly because it is amusing, but also because it contains an important lesson for researchers, which is that one can easily become involved in excessive detail while missing the big picture.
Therefore, I think it is useful from time to time to stand back from the fray and ask oneself: What have I achieved in the overall scheme of things? One test of that might be: Is anything you have done likely to find its way into a textbook (written by someone else that is, rather than yourself!)?
Of course, we must not be so foolish as to think that anything we do will have any real permanence. As Rick says to Ilsa in "Casablanca"
"It doesn't take much to see that what we do amounts to a hill of beans in this crazy world."
Well, all of this is by way of an apology for the self-indulgent retrospective on which I'm about to launch.
WHY LOOK BACK NOW?
Now is a particularly appropriate time for me to look back, because after some 30 years of maintaining and using aircraft for research purposes, our aircraft research facility was closed down last year.
Why did I start this program in the first place?
Well, for the first half-dozen years or so after I joined the Department in 1963, my group carried out laboratory experiments on various aspects of cloud physics. Also we did some field studies in the Olympic Mountains, but with our feet firmly planted on the ground.
It was a result of the latter studies that I decided that one had to be mobile, both in the horizontal and the vertical, to properly observe the atmosphere. That meant an aircraft (or possibly a balloon, but I also wanted some control over where we went).
In 1970 we acquired our first aircraft--a Douglas B-23.
We instrumented the B-23 for cloud and aerosol studies, and used it for a large number of studies through 1984.
I will return to a few of these studies in a little more depth later.
In 1984 the B-23, was replaced by a Convair C-131A.
Since this was a considerably larger aircraft than the B-23, it allowed us to expand the payload considerably with more chemistry and radiation instrumentation.
In 1997 we acquired a twin-turbo prop Convair-580, which we used very successfully in a number of field projects around the world.
I will now describe briefly a few of the topics from the long list I've just been through.
Choice of these topics was difficult, but I have chosen several quite different areas of research. Also, I have chosen topics where I think we have had some impact. However, one should be circumspect in such evaluations because often it takes several decades before the importance of research can be properly assessed.
2. THE CASCADE PROJECT (1969-1974)
The first project I have chosen to describe is the CASCADE Project.
Although this project was carried out some 25 years ago, the results it produced on the mico- and mesoscale structures of storm systems were not surpassed until last year when we carried out the IMPROVE field studies.
One thing to notice is that the CASCADE project extended over 5 years. This is quite different from the "one-shot" field studies and "three years to analyze your results" that is typical these days.
The principal goals of the Cascade Project were to study the structures of clouds in winter storms over the Cascade Mountains and to carry out some exploratory studies on how snowfall in the Cascades might be modified by cloud seeding.
In the CASCADE Project we used our B-23 aircraft to study the micro-structures of clouds across the Cascades, simultaneously with observations on the ground of snow crystal types and precipitation rates, and measurements of the vertical fallspeeds of precipitation particles with a vertically-pointing Doppler radar located at Snoqualmie Pass.
An important result that emerged from these studies was that growth of ice particles by riming (that is by supercooled drops colliding with and freezing onto ice particles) was an important mechanism for the formation of precipitation.
As a result of the larger fallspeeds of rimed particles compared to unrimed, most of the snowfall over the Cascades falls on the western (windward) slopes.
This led us to hypothesize that if we could eliminate growth by riming, the crystals would have lower fallspeeds and should be carried on westerly winds over to the drier leeward slopes of the Cascades. Growth by riming can be eliminated if the supercooled drops in the clouds are eliminated, and that, in turn, can be achieved by heavy seeding with a glaciogenic material (such as silver iodide or dry ice).
We carried out a number of seeding experiments to test this hypothesis, with the following results:
3. THE CYCLES PROJECT (1973-1986)
Following the CASCADE Project, we moved west to study winter cyclones as they came onto the Washington Coast, in what we called the CYCLES Project.
The CYCLES Project was the first detailed study of the structures of cyclonic storms on the micro- and meso-scales.
I will mention here just a few results that came out of this long and productive project.
The first is this classification of rainbands, which is still in widespread use.
We also documented the structures and dynamical mechanisms responsible for the various rainbands, for example:
Here we see an example of the S-pattern that we showed is associated with the veering of the wind with height, and therefore warm air advection. Pattern recognition of mesoscale features is now common; we first showed its utility in a paper published in 1977.
Another important accomplishment of CYCLES was the scheme proposed by Steve Rutledge and myself for parameterizing cloud and precipitation processes in mesoscale models.
4. CLOUD CHEMISTRY AND CLOUD-AEROSOL INTERACTIONS
In the early days of the B-23, Larry Radke and I decided that wave clouds such as these, which commonly form over Mt. Rainier and elsewhere, provide an excellent natural laboratory for studying the effects of clouds on aerosols and particles.
The way we went about these studies was to measure the particles and gases that entered the inflow into the cloud and compared them with what came out of the exhaust region.
Shows that concentrations of CCN are greater in outflows.
Attributed this to chemical reactions in cloud droplets that produce sulfate, which is deposited onto the original CCN and increases its size and therefore activity as a CCN.
Subsequently, we extend our studies of cloud chemistry to other cloud types (stratiform and cumulus) from which we were able to derive the scavenging efficiencies of sulfate and nitrate particles by clouds.
Since these early measurements, cloud chemistry has become a major area of research, mainly by theoreticians and modelers (while progress in measurements has been relatively slow). Cloud models now exist in which hundreds of chemical reactions are hypothesized to occur in the droplets.
In some more recent field studies, we discovered that clouds can also affect chemical reactions in the air surrounding them. There are several reasons for this:
Clouds can transport gases and particles from low levels and vent them to cleaner regions at higher levels, where the gases may react to form other species.
The solar flux in the vicinity of clouds can be enhanced, which will promote photochemical reactions (by producing OH for example).
The evaporation of cloud water moistens the ambient air, which can also enhance the reactions of gases.
5. EMISSIONS FROM NATURAL AND ANTHROPOGENIC SOURCES
The next topic I have chosen to describe briefly is our work on emissions of particles and gases from various sources.
I'll start with volcanoes.
(a) Volcanoes
We have studied many volcanoes, all around the world.
Prior to these early studies, measurements of the effluents from volcanoes derived primarily from intrepid volcanologists scrambling up the side of an erupting volcano and sticking an instrument down the throat of the volcano.
The biggest eruption we studied was Mt. St. Helens on 18 May 1980. Although this eruption seems like just yesterday to many of us who lived through it, most our first year graduate students were just entering the world in 1980. So, just to remind you:
Here we are approaching this monster in our 2nd WW B-23 aircraft.
Hands-up of anyone aboard that wants to enter this plume?
Did not execute for Mt. St. Helens!
But we did enter side of plume, and were immediately bombarded by "volcanic hail."
(b) Oil Wells
If Mt. St. Helens was the largest natural source of emissions that we studied, then the over 600 oil wells, set alight by the Iraqi army as it fled Kuwait in February 1991, was certainly the biggest natural source.
(c) Biomass Fires
Since I have given seminars to the department on SCAR-B and SAFARI 2000 fairly recently, I will not say much about these processes here, except that we obtained the most comprehensive data on emissions from fires to date.
Of particular importance are measurements we obtained in southern Africa of the effects of aging on various species emitted by biomass fires.
6. CONCLUSIONS
I called this talk "A Retrospective," which may give the impression my group has come to the end of its research. In fact, this is just a progress report. Although we no longer have a research aircraft, my research team is alive and well, and we look forward to many years of productive research analyzing the unique data sets we have collected.
As T. S. Eliot put it:
Finally, I would be remiss if I did not acknowledge the many fine people with whom I have worked over the years.
Peter V. Hobbs
October 21, 2002
HALO; LOWER TANGENT ARCS (LTA), SUN DOGS