ACD Participates in TREX

ACD participated in the Terrain-Induced Rotor Experiment (T-REX) with airborne measurements of O3, CO, and H2O in waves in the lee of the Sierra range in California. The primary objective of T-REX is to study the structure and evolution of intense low-level horizontal vortices (rotors) over the Owens Valley immediately downstream of the mountain range. These waves have chemical implications as well as dynamical. Wave-breaking can lead to turbulence and mixing of chemical constituents among different layers of the atmosphere. In particular, they may promote mixing across the tropopause region and so contribute to bi-directional stratosphere-troposphere exchange. Our instruments were deployed on NCAR's new G5 (HIAPER) aircraft.

Figure 1, a photo by Carlye Calvin, shows the O3 instrumentation rack as it was flown on the G5. The main detector unit has been flown many times previously, but other components were recently built as part of a new HAIS fast-ozone instrument currently under development as a facility instrument for the G5.

Figure 2 (PDF Download) shows data obtained in a wave during T-REX. The tropopause region is one of steep vertical gradients in mixing ratios. As a result, the vertical wave motions lead to a pronounced wave structure when sampled by a horizontally-flying aircraft, as evident in the figure. Air that is displaced upward brings low-O3 air up from below, while downward moving air brings O3-rich air from above. Water and CO have vertical gradients opposite in sign from O3, so they vary together in a manner opposite to O3.