Take-off time 7:15 am local (1715Z); flight duration 6.8 hours    

Title: Aircraft intercomparison, stratus chemistry, and jet stream  transport    Objectives:  (1) To conduct an extensive intercomparison with the P-3; (2)  to examine chemical processing in stratus clouds; (3) to sample Asian  pollution transported in the jet stream around the east Pacific ridge and  southward over California.    

Execution: We flew from Kona (20N, 156W) to (22.5N, 151.5W) for the  intercomparison, which consisted of a 20-min leg at 17Kft, a descent to  1Kft at 500fpm, and a 20-min leg at 0.5Kft.  We then did a 20-min leg in  stratus (6Kft) and headed to Dryden (35N, 118W) with a spiral followed by  a climb to 39Kft along the way.    

Results: The intercomparison was a success; all instruments were on-line  and the aircraft flew within 200-400 ft from each other most of the time.  Steady concentrations were observed on both the 17Kft and the 1Kft  intercomparison legs.  The stratus deck extended from 3 to 7 Kft.  The  20-min leg at 6Kft following the intercomparison was conducted in  almost-continuous stratus.  No particularly strong pollution layers were  observed in the flight; there were layers at 5-15Kft with CO up to 240  ppbv, and the boundary layer was enhanced in CO and CO2 also (typically  170 ppbv CO, 377.2 ppbv CO2, 56 ppbv O3).  The atmosphere was featureless  above 15Kft and did not reveal any structure that would be associated with  jet stream transport of Asian pollution.  Approaching California we flew a  long leg in the stratosphere (39Kft) and sampled a major stratospheric  intrusion extending down to 20Kft and capping thunderstorm activity over  southern California.  

Meteorological Summary DC-8 Kona to Dryden Transit 9 April 2001

Relevant Flow Features:
         Surface-A strong anticyclone was centered near 40N, 145W.  A weak surface low was passing over southern California.  Although not strong at the surface, this low was better defined aloft and associated with a strong short wave trough.  Due to these pressure systems, surface winds were from the east on the western part of the flight track and mostly northerly on the eastern part of the track.
         Middle troposphere-The high northeast of Hawaii, and the low over southern California persisted into the middle levels.  Easterly winds continued along the westerly portion of the track and northerly winds along the western portions.
         Upper troposphere-Due to the closed anticyclone, the polar jet stream was displaced far to the north of most of the flight track. However, the jet plunged southward along the California Coast.  The subtropical jet stream extended from south of Hawaii to Baja California. The flight track was north of this jet. Winds along the western portion of the track were from the west, but from the northwest over eastern portions.
         Backward trajectories at all levels showed considerable circular transport over much of the flight track.  This was due to the persistent anticyclone noted above.  Only near California did the trajectories show well defined transport from Asia.  This air had traveled around the strong anticyclone located farther west.

Relevant Cloud Patterns and Other Goodies:
         Most of the flight track was devoid of middle and high clouds. The only exception was near California-in association with the low pressure described above.  However, much of the flight track was blanketed by broken layers of cumulus and stratocumulus.
         The area of the DC-8/P-3 intercomparison had only broken cumulus and stratocumulus clouds  At 17,500 ft, the winds were from 087deg at ~25 kt.  During the descent to 500 ft, two major cloud layers were observed. Stratocumulus had bases of 5100 ft and tops of 7250 ft.  The tops were uniform, and this level marked the trade wind inversion.  A cumulus deck was below, with bases of ~3700 ft and varying tops that occasionally reached ~7000 ft.  Some of these clouds produced light rainshowers.  The intercomparison leg at 500 ft had winds from ~ 070 deg at ~27 kt-stronger than many runs at  this altitude.  The cloud level run at ~6000 ft remained in the clouds at most times, but some breaks did occur.
         The second boundary layer run ( near 2129Z) had an almost overcast cover of stratocumulus.  Bases were near 3500 ft and tops near 5100 ft.  A broken layer of cumulus was below, with bases near 2600 ft.  The winds at this run were somewhat weaker than in the previous run, ~20 kt here.  The direction was northeasterly at the beginning of the run, but shifted to northerly by the end.
         The stratosphere was entered near 2225Z as the DC-8 was passing 35,700 ft for 39,000 ft.  We remained in the stratosphere until the descent into Dryden.  A line of weak thunderstorms was located off the California Coast and near Dryden .