Every so often, the southward-flowing winds off the coast of California switch direction with almost no warning, causing clouds and fog that can cover hundreds of miles. For scientists, these “southerly surges” have remained mysterious. So John Bane decided to fly straight into one.

No one had ever measured the temperature or direction of airflow inside a southerly surge,” says Bane, professor and chair of the Marine Sciences Program. “They had only measured it at the coastline or possibly at a buoy at the surface of the ocean.”

Bane wanted to get better measurements to help develop more accurate computer models, which meteorologists use in forecasting. “If the fog is not forecast well, and you’re at an airport or in a boat offshore when it comes in, you could be in trouble,” he says.

But he needed an airplane that could measure air temperature, humidity, and pressure, and the plane’s airspeed, position, and altitude. There were some of those around, but they were expensive. And Bane needed to keep one handy, ready to go whenever a southerly surge came up.

Bane, a pilot with almost 25 years of flying experience, decided to rig one himself. He arranged to use a privately owned six-seater, a Piper Seneca III he could keep on standby at relatively low cost. He wanted to turn it into a convertible, so to speak—something he could quickly transform into a sophisticated research craft, then back into an ordinary plane.

Next, Bane recruited Jim Miller, an aviation technician, and Meredith Sessions, an engineer at Scripps Institution of Oceanography. Their challenge was to measure the same kinds of things as large, expensive planes, but with instruments that were small, lightweight, low-power.

After two months of experimenting, they ended up putting most of the sensors on a removable panel on the underside of the plane. “Then we had all these wires coming from the sensors,” Bane says. “How do we handle all that information?” Miller designed a console to receive the signals and convert them into digital form. “The box,” as Bane calls it, is made from simple materials—metal, screws, wire, and circuit breakers.

The wiring leads to a plug in the airplane’s floor. Installation takes twenty minutes—remove a couple of passenger seats, bolt the box down, and attach the plug. During a flight, the box feeds new measurements to two laptop computers every second. Sara Haines, a research specialist who works with Bane at UNC-CH, spent several months designing computer software to record all the measurements and display the data in flight.

With Bane in the pilot’s seat and Sessions as co-pilot, the team has flown 42 research missions. In more than 200 hours of flight, “every instrument, every switch, every computer program has worked every time,” Bane says proudly. “Now we know a little more about how the real world acts.”

And it turns out that southerly surges act differently than anyone thought. The pattern of airflow isn’t in the lower layer of air, but up higher. And the leading edge of the disturbance is out in front of the resulting clouds, rather than even with them. They also found that the clouds come right down onto the surface of the ocean, which means that they’re really fog. “Fog is simply a cloud with the bottom extending down to the surface of the land or water,” Bane explains.

Since I’ve presented these results at professional meetings,” he adds, “several people have come up to me and asked, `Can you build one of those airplanes for us?’”

This work was supported by the Office of Naval Research. Bane, chair of the Marine Sciences Program in the College of Arts and Sciences, also conducts research on the ocean circulation off the Carolinas and winter storms along the U.S. east coast.