Take-off time 8:39 am local (2239Z); flight duration 9.1 hours  

Title: High-altitude Asian outflow and sunset MBL chemistry  Objectives:  (1) To sample the warm conveyor belt associated with a frontal passage over Japan; (2) to sample high-altitude biomass burning outflow and subsiding Asian pollution over the central Pacific; (3) to characterize MBL chemistry across sunset; (4) to conduct a MOPITT validation experiment.  

Execution: We flew a straight track from Yokota to Kona with a dog leg to the south towards the end for the sunset MBL experiment.  A series of vertical profiles from cruise altitude (33-37Kft) down to 0.5 Kft were conducted, in coordination with the P-3 (flying the same track) to obtain a  curtain of atmospheric composition.  The sunset MBL chemistry experiment was done in background tropical air from (24N, 173W) to (22N, 166W), and consisted of a sequence of two 1Kft legs on both sides of sunset with a 20-min 10Kft leg in between.   

Results: The MOPITT validation experiment had to be scrapped because of clouds.  The other objectives were met.  Coordination with the P-3 worked well and we achieved a high degree of complementarity in sampling along the flight track.  Climbing out of Yokota we encountered a stratospheric intrusion between 18 and 28Kft (behind the front located east of Japan). Heading south we sampled two principal Asian outflow features: a high-altitude outflow above 20Kft with increasing biomass burning signature as we got further south, and a low-altitude outflow below 8Kft of dominantly industrial origin and which appeared to be due to recirculation of pollution around the western Pacific High.  Crossing the dateline on a 1-hour leg at 31Kft we observed a transition into a highly polluted layer beginning at 177W (CO up to 240 ppbv, ozone 110 ppbv, HCHO 160 pptv, non-volatile aerosol, high CH₃CN, high C₂Cl₄); this layer could be attributed from the forecasts to biomass burning in SE Asia although the high C₂Cl₄ is not consistent with this explanation.  The first 1 Kft leg of the sunset MBL chemistry experiment indicated extremely high concentrations of carbonyls and methylhydroperoxide, dropping with altitude.  Concentrations of HNO₃ were puzzlingly high (150 pptv).  The second 1Kft leg  had higher wind speeds (14 vs. 3 knots).  Going back up to cruise altitude before reaching Kona revealed several high-ozone layers, some correlated with CO while others of stratospheric origin.

Relevant Flow Features:

         Surface-Two frontal systems affected the weather along the flight track.  A developing wave cyclone was centered near 50N, 150E, with a cold front extending southward.  This front had passed through Yokota during the previous afternoon, bringing abruptly cooler temperatures and light rain.  The second system was a deeply occluded low just west of Alaska. Although its trailing cold front influenced the eastern third of the flight track, this southern portion of the front was very weak.  Major surface anticyclones were located near 40N, 170E and 40N, 145W

         Middle Troposphere-Troughs were located just east of Japan and along 175W, in association with the surface lows described above.  A well developed subtropical high was centered near 20N, 160E, while a weaker high was located north of Hawaii, near 35N, 155W.  A weak middle level low was developing southwest of Hawaii.  Middle level winds were predominately westerly over the flight track. The only exception was northwest of Hawaii where southerly and easterly winds were occurring.

         Upper Troposphere-The axis of the jet stream was near 30N over the western two-thirds of the flight track, but extended farther north over the eastern third of the track.  The jet stream was not as intense as during earlier flights.  Winds had a strong westerly component over the entire flight track.

Cloud Features and Other Goodies:

         The flight track was relatively cloudy.  Major comma shaped cloud patterns were associated with each of the major wave cyclones described above.   The flight track of the DC-8 traversed the extensive area of multiple layered clouds associated with the westernmost system.  Mid and high level clouds prevented a MOPITT evaluation between 150-160E.  Flight track clouds associated with the eastern feature were not nearly so widespread.  The region between the two systems-near the date line-was relatively cloud free.

         Stratospheric air was encountered at relatively low levels (~17,000 ft) during the climbout from Yokota, i.e., behind the cold front described above.  This area was in the entrance region of the jet stream. Weaker stratospheric air was encountered just west of Kona.

         The first boundary layer run (near 0025Z) had multiple layered clouds providing overcast conditions.  Winds at 500 ft were from 170 deg at 36 kt-stronger than encountered on most previous runs.  The sea surface exhibited well developed white caps.  This run occurred on the warm side of the westernmost cold front.  The second boundary layer run (near 0217Z) had broken stratocumulus with bases ~3500 ft and tops ~4500 ft, as well as scattered cirrus.  The third boundary layer run (near 0442Z) contained a variety of cumulus, altocumulus, and cirrus, yielding a broken ceiling. Some cumulus reached as high as 15,000 ft, providing rain showers in the area. The chemical effects of these showers were observed during the subsequent leg at 10,000 ft.  The trade wind inversion near 6,500 ft was observed during the ascent/descent of the 3rd run.

         Sunset occurred near 0432Z.  Some clouds were present during the fourth boundary layer run (near 0554Z); however, the darkness prevented a good observation of them.