M.J. Mahoney and Richard Denning, NASA Jet Propulsion Laboratory & Caltech, standing next to their Microwave Temperature Profiler instrument. This is the first instrument from the US to fly on board the M55 Geophysica. The instrument measures the temperature structure above and below the airplane, which is important for understanding the transport properties of the Arctic stratosphere (e.g., strength of winds) as well as the environmental conditions that promote formation of polar stratospheric clouds.