Flight 19: Yokota Local 5 (2 April, 2001)

This was the second of two flights coordinated with the ACE-Asia science team.  The two aircraft again planned to sample both as a team and separately in outflow over the Sea of Japan.  Model predictions indicated an axis of low level outflow predominantly below 2 km over the Sea of Japan.  The NCAR C-130 planned to fly three stacked walls along the outflow at 133E, 135E, and 137E.   A rendezvous with the NCAR C-130 was planned for (38.5N, 134E)  to execute a joint spiral under the Terra satellite and jointly execute the stacked wall at 135E across the outflow axis.  This was to be followed by extended wall sampling by the P-3B along the axis of outflow.

Results: The P-3B transited at 18Kft from Yokota AFB to the rendezvous point over the Sea of Japan.  Conditions along this leg were clean (e.g., O3 50-60 ppbv, CO 90-100 ppbv, NOy 200-400 pptv).  After joining the NCAR C-130, the joint spiral was performed with some degree of interference from broken clouds.  Flight along the stacked wall was performed at altitudes of 500, 2000, and 4500 feet.  Along each of these legs, more polluted conditions were encountered to the north, verifying the presence of the low level outflow (e.g., 320 vs 250 ppbv CO, 4 vs 2.5 ppbv NOy, 2.5 vs 1 ppbv SO2).  Although the low level outflow was detected, along-axis profiling exposed an unexpected and more polluted layer at a higher altitude.  This layer was extensively sampled (e.g., CO >400 ppbv, SO2 up to 8 ppbv, NOy up to 4 ppbv, PAN 1 ppbv, etc.) and determined to be between 8.5 and 12.5 Kft.  Toward the end of the flight, a descent was performed at 41N, 137E.  During this profile, the polluted layer was found to be entirely within a cloud layer between 8.5 and 12.5 Kft.  This was followed by a 20 minute leg at 500 feet heading due south.  During this leg, a shift in wind direction from 305 to 235 degrees signalled our crossing of the surface front.  An ascent at the end of this leg at 39N, 138E resulted in a much cleaner profile providing a stark contrast to the profile at 41N (e.g., CO <100 ppbv and NOy <400 pptv).