Let’s face it. Most of us hope for fair skies when we’re planning to board a plane. The less weather around, the better. If you are DRI’s Dr. Vanda Grubisic’, however, weather is just what you want - and lots of it.

View from the Top Searching for invisible indications of airflow across mountain peaks, Grubi^sic’and her colleagues employed advanced technology aboard aircraft to create a description of the turbulence created by the Alps. Photo by Craig Walther of NCAR/ATD

And she found plenty of it last fall as part of the Mesoscale Alpine Programme, or MAP. The ten-week field campaign was centered in Innsbruck, Austria and Milan Italy, on either side of the European Alps, where each year heavy precipitation, flash floods, and storms cause extensive damage, in particular on the southern side of the Alps. Researchers from Austria, Canada, Croatia, France, Germany, Italy, Slovenia, Spain, Switzerland, the United Kingdom, and the United States were on hand to explore the effects of the complex Alpine terrain on a variety of weather related phenomena and to improve basic understanding and prediction of severe weather.

Grubisic’s research focused on how the terrain affects certain airflow phenomena, particularly something known as potential vorticity (PV) banners which form in conjunction with atmospheric wakes on the downwind sides of mountains. Think of a rock in a stream, and the wake that forms behind it. A similar phenomenon occurs as airflow is disturbed by an obstacle such as a tall mountain. "Our simulations," explains Grubisic’, " show these wakes are divided up into subregions - jets, smaller wakes, etc. The MAP experiment gave us the opportunity to compare predictions of numerical models to what actually happens in nature and to check the scale of the features seen in simulations."

High-Rise Scenery With the towering Alps in the background, NCAR’s Electra research aircraft waited on the ground at the Innsbruck airport in Austria for the next flight to collect airflow data. Photo by Craig Walther of NCAR/ATD

To make these comparisons, Grubisic’ and a team of researchers first had to wait for the right weather conditions. "We looked for conditions that created a simple airflow over obstacles," says Grubisic’. "These were few and far between, as weather patterns in the Alps are often complex and seemed to be especially so this last year." When the weather finally did cooperate, the researchers boarded several specially instrumented research aircraft and flew in formation at various altitudes collecting data and taking measurements. The two American planes involved in the study were NCAR’s (National Center for Atmospheric Research) Electra and the National Oceanic and Atmospheric Administration’s P-3. Instrumentation on the wings and fuselage of these specialized craft collected data along the flight path, measuring such physical quantities as temperature, moisture, wind field, cloud particles, precipitation, and ozone levels. Specialized radar, lidar, dropsondes and ground-based remote sensing devices throughout the region added additional data.

In all, says Grubisic’, the researchers ran six successful PV-banner missions, including one that literally took the Croatian native close to home. During that mission, Grubisic’ made a last-minute decision to change flight plans and fly downstream of the moderately high mountains that run along the Adriatic Coast of Croatia. "It was almost out of desperation that I made the decision to fly south that day. We had not gotten a large amount of good data from our previous missions, and we were running out of chances." Although she admits the experience was "dear to her heart" the decision wasn’t borne of sentimentality, but of her gut feeling that there was to be good data to be had. She was right. That flight coincided with a severe down-slope wind phenomenon in the region known as the Bora and rendered some of the best wake data of the project.

Second-guessing where and when to launch a mission was only the beginning of the challenges faced by Grubisic’ and the other research teams involved in MAP. There was also the direct, albeit friendly, competition for resources, including a total of eight aircraft and various ground instrumentation. When a likely weather system approached, a preselected commission made the decision of which of the eight research teams would fly. Once chosen, says Grubisic’, the team leader’s final decision whether or not to fly was crucial. "If conditions turned out not to be ideal once you were in the air, you’d wasted an opportunity to get good data, and it was not likely your team would be chosen the next time."

Vanda Grubisic’'s DRI office lies in the lee of the Sierra Nevada range, producing many meteorological similarities to the research questions which take her to the Alps.

That meant the pressure was on to get things right the first time and take advantage of every precious minute in the air. "We spent six to seven hours in the air on each mission - the maximum range of our aircraft. Our learning curve had to be very steep. It was important to do things correctly right away, because you never knew when, or if, your next opportunity would be." In this kind of atmosphere, stress levels naturally ran high, but Grubisic’ says, everyone tried to keep a sense of humor. "I had them laughing at the end of one mission with ‘Thank you for flying NCAR. We know you could have chosen another research aircraft . . . .’"

Overall, says Grubisic’, MAP was a very successful field experiment, especially for one so ambitious in scope. "We definitely gained more confidence in our numerical models and found that our ideas based on simpler obstacles, like ocean islands, were right." Precipitation studies conducted by other researchers also went well. "It was a very good weather season for the precipitation guys," she reports. "There were even a couple of instances of severe flash flooding allowing them to observe and record the conditions that led to the flooding."

Part of the credit for MAP’s success goes to the technology, says Grubisic’. Precursors to MAP, such as the 1950s Sierra Wave project and 1980s ALPEX supplied a strong research base, but the remote sensing technology employed in MAP gave researchers the ability to create a more complete picture. "With remote sensing devices, we can get a picture of conditions on various vertical and horizontal planes." The result is a partial three-dimensional representation of airflow patterns and weather phenomena that is much more true-to-life than purely linear data gathered along a flight path.

Once gathered, data must be analyzed and interpreted, and that process has already begun. For instance, almost half of this summer’s five-day Mountain Meteorology Conference sponsored by the American Meteorological Society (AMS) was devoted to MAP and its findings. Always in the center of the storm, so to speak, Grubisic’who is the chair of the AMS Committee on Mountain Meteorology - also chaired that conference of some 130 attendees. The experience, she says, was refreshingly uncomplicated after the rigors of a large-scale field experiment. "It was actually fairly easy to put the program together. We had such a great response from the participating researchers."

In any case, the Mountain Meteorology Conference was just the beginning. According to Grubisic’, researchers will be poring over and assimilating MAP data for the next five years or so, and a conference devoted entirely to MAP is planned for both 2001 and 2002, when it will most likely join the next Mountain Meteorology Conference in the United States. Seems you can learn a lot from a little stormy weather.

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