DC-8 Flight Report for 14 December 1999

Expectations:

Takeoff: 7:50 UT, 8:50 LT

Duration:About 8 hrs 10 min.

Goals:

  1. To underfly the POAM observation point at 63°45´N, 11°56´W (1307) and photograph any clouds that may be in the line of sight. We will first fly over the cloud with LASE and find the top altitude, then make several "sun runs" as the sun sets, then fly along the tangent path at altitude, then do a descent to about 10 kft.
  2. Search for activated chlorine in vortex air. We will fly along the coast of Norway across the vortex edge and into a tongue of air that is predicted to be exiting the vortex.
  3. Experiment with fumes leaking from the forward head on the DC-8. Close the restroom and investigate methane spikes.

Flight Repor:

Took off on time at 7:52 UT, 8:52 LT.

The most recent forecast suggests that clouds over the POAM point are marginal. Near 63°N and 16°E, the tropopause was located near 30 kft. Light cirrus was present to the east, overlying a dense lower cloud deck. However, it was essentially clear below the aircraft. During the sun run, the sun was well above the horizon and above the clouds as seen from the aircraft near 63°N and 16°E, where nav and the aircraft said the angle should be zero. Evidently this angle is measured relative to the ground. AROTEL sees a lot of structure in the ozone in the region from 14 to 16 km, but the in situ data is relatively constant. At 09:10, the DC-8 is laying a contrail, at 33 kft. The MTP tropopause is about 30 kft. LASE sees cirrus below the aircraft at about 8 km which are not visible to the eye.

Across southern Norway for the last 30 min before 9:45 or so, there are multiple indications of waves. They are present in DIAL ozone and aerosol, AROTEL ozone, MTP temperature, and in situ aerosols. So we see these oscillations in both the vertical and horizontal. In the horizontal they have a period of about 5 min. In the vertical the wavelength is about 1 km, and the amplitude in the lower stratosphere is several hundred ppb. There are lots of convective clouds off the southern coast of Norway prior to 10:00 UT. LASE indicates the cloud tops are near 6 km. After 10:00 UT, the clouds thinned and the icy ocean was visible. LASE sees cloud tops dropping to about 2 km at 61°41´N and a large pool of dry air in the upper troposphere.

There is no evidence from DIAL ozone that we are entering the vortex as we fly north along the coast of Norway. The predicted vortex location suggests we should be in the vortex in this region.

LASE observed subvisible cirrus near 6 to 8 km around 10:30 UT. The top appeared close to the tropopause. The water in the upper troposphere gradually increased as we flew northward. The DC-8 was laying a contrail in the stratosphere from 10:30 to 10:45. The sun passing through the contrail left flickering shadows on the left wing.

A region of lowered ozone was seen near 10:40 UT. Possibly this corresponds to the filament of vortex air which we hoped to observe. However, there is no evidence of high ClO in the lower stratosphere. The OH instrument is functioning on this flight, and seems to be observing HO2. DIAL sees interesting structure in ozone in the lower stratosphere. At 16 km there seemed to be a period of about 10 min. AROTEL sees a vertical wavelength of about 1 km. In situ ozone also saw some variation during this period.

Between 10:40 and 10:55 or so, we passed below a region of relatively low ozone near 23 km according to DIAL and relatively low temperature according to MTP. ASUR did not see any ClO in the lower stratosphere. Maybe this was the vortex fragment of possibly processed air that we were searching for.

At 11:22 LASE saw the cirrus near the tropopause disappear. Cloud tops were then at about 2 km. The tropopause also fell rapidly as we approached the coast of Norway. So far predicted tropopause heights have been grossly in error.

At the POAM tangent point it is clear down to nearly the surface. However, there are clouds to the south. Based upon our earlier pass to the south, we decided to remain just above the tropopause during the first POAM underflight. LASE finds that the cloud tops here are around 5 km. So we decided to make the second solar observation at about 25 kft. We did the first three passes at the same location. The sun was still above the cloud, so we did a fourth and fifth loop. From NOy in situ we passed through our contrail at about 13:03 and several times later. The contrail was also seen in particles and in HO2. Apparently 92°sun angle at the ground is about the best for getting clouds on the disk of the sun at our altitude. The disk is almost gone at 30 kft, with a sun angle of 92.9 to 93.3, depending on the clouds on the horizon. From the satellite image obtained by DADS it would seem that the cloud in the field of view of POAM was localized to a small area of Norway and Sweden, and was essentially the only cloud present anywhere.

We did a spiral descent over the POAM tangent point beginning at 41 kft, descending to 10 kft.