Author of report: MIKE DOUGLAS and ED ZIPSER
Mission Number: 030128I
Type of Mission: Altiplano-Pacific
Start time of Mission(UTC): 2003/01/28 11:57
End time of Mission(UTC): 2003/01/28 20:44
This flight was called to describe the diurnal variations of the mixed layer over varying terrain of the Bolivian altiplano and to describe variations in the boundary layer west of the coast of Chile. The flight involved ferrying to a point in the northern Bolivian altiplano, flying southward across the altiplano at varying altitudes, and then crossing into Chile. The aircraft then descended to the moist oceanic boundary layer, porpoising between 500 ft and about 6000 ft on average to the point 20S 74W. The aircraft then returned to the coast at Arica, ascending and carrying out a second traverse of the altiplano before returning to Santa Cruz. The first pass over the altiplano showed a shallow, moist mixed layer with dry air above. This was much deeper 5 hours later, during the second traverse. Low-level winds over the Salar de Uyuni showed strongly divergent flow during the afternoon (~ 19Z) pattern, including a sharp lake breeze front. The over-Pacific portion of the flight showed cyclonic flow at 850 mb, with some differences evident between the AVN analyses and the observations. The cloud tops were very close to 860 mb throughout the flight. Cloud bases were near 1000m AGL. No problems were encountered during the flight, except for minor delays due to air traffic control communications and minor deviations from the route due to the need to deviate around high topography.
This is a brief summary of some of the highlights of the Altiplano-Pacific flight, taken from my flight notes, photos, and a short time browsing through the printout. Any conclusions are my own, and should be regarded as HIGHLY preliminary. It is written on 30 January, 2 days after the flight. Note: There is a great TERRA overpass at 1440 UTC/28 January over the Altiplano at about the time we were approaching the Bolivia-Chile border. Check it out at http://184.108.40.206/production/ (Browse images from TERRA. about 10local time, and AQUA about 14 local time daily are available from this site, as well as highlights selectable from each region from the ‘gallery’ tab. If you have the capacity, you can look at resolutions from 250 m to 2000 m.) In a previous e-mail, Rene thought that the generally weak convection on this day would be associated with some westerly flow, but this flight measured little if any westerly flow at any level at any time. The approach to the Altiplano during the morning had steady flow from the SE, very moist east of 66W but very dry west of 66W, with wind speeds as high as 30 knots. In the afternoon, the flow was still easterly on ferry back to VVI in the afternoon, but lighter with variable directions, and in spite of ample moisture, only a few convective cells east of 65W were observed.
ALTIPLANO: Flight pattern was carried out close to the plan, with porpoising at low levels from 1300-1430 UTC and from 1800-1940 UTC, over nearly the same track providing significant diurnal changes. These are summarized below. Winds: In the morning, generally from SE to E, mostly 5-15 knots. In the afternoon, generally from E to NE, mostly 5-15 knots. There may have been some slight changes with altitude, but they are subtle and will require more careful analysis. Temperatures: At 300 m (~636 mb): Theta 47C morning, 52C afternoon At 1500 m (~547 mb): Theta 51C morning, 53C afternoon Mixing Ratios: At 300 m:(~636 mb): 7 g/kg morning, 4 g/kg afternoon At 1500 m (~547 mb): 0.6-3 g/kg morning, 4 g/kg afternoon Cloud Base: About 1000 m (~580 mb) morning, >2200 m, afternoon Obviously, the shallow moist layer in the morning quickly mixed out through a deep layer by afternoon, with deep well mixed soundings with respect to both theta and mixing ratio.
SALAR: Excellent data both morning and afternoon. Down radiometer about 16C morning, ranging from 21-27C afternoon. Little AIR temperature gradient between Salar and surroundings but whopping down radiometer gradient, with ~38C in afternoon over dry ground. Mike Douglas has analysis of afternoon wind pattern showing clear divergent outflow from Salar.
PACIFIC OCEAN portion: There was a narrow (~20 km?) clear zone near the coast, then stratocumulus. Bases hard to define but mostly ~1000 m (900 mb), while tops were extremely sharp and always close to 865 mb. Each and every time, the temperature inversion from 11-19C was equally sharp, with dew point depressions just above the SC layer reaching 40C. Wind pattern was too complex to describe in a few words- the flight notes are posted and the wind data are now on line.