Tropospheric measurements over
the Arequipa, Peru region May 2006

Experimental design
Pilot balloon data
Radiosonde data
Tethersonde data
Averages and plots
Preliminary conclusions
Versión en español
Preliminary conclusions

These comments are very preliminary, but they are a starting point.

Tethersonde data

From the tethersonde data it appears that the cold layer that develops as the sun sets is very shallow (less than 20mb or 200m, and usually less than this) with an increase of about 7°C between about 2m above the surface (lowest level of the radiosonde approximately) and 100m above the ground level. During the afternoon the boundary layer appears to be at least 70mb thick (the dry adiabatic - well mixed layer) but this seems to be variable.

The tethersonde data appear "noisy" because each up- and down-sounding took perhaps 15 minues and cariations over this period add variability to each sounding. The data can be averaged to obtain smoother profiles. Very noisy data sometimes occurred when the battery voltage became very low. The best solution to battery voltage was to build a battery pack with 10 "AA" Alkaline Duracell batteries. These ran at least 15 hours.

Pilot balloon time-height sections

The time-height sections show that the data is fairly good, with only small changes in the profiles over the experiment. Diurnal variations are not easily apparent from these plots, since the winds were fairly strong at upper-levels (above 8 km). Most daytime balloons could be tracked to 12 km, whereas the nighttime soundings extended to about 4-6 km. Although the CORRIGE program was used to process the winds and correct errors, some errors are still present, such as at Pampa de Majes (next to last sounding, near 4.5 km). It should be noted that time-height sections are an effective means of detecting errors in wind soundings, provided that there are frequent observations.

Tethersonde data

The maps show a number of features:

1) The average winds are smoothly varying - at higher levels (above 8km) all three stations show similar mean winds from the NW.

2) La Joya shows the strongest SE winds in the lower troposphere, as expected.

3) On average, the winds below 3500 mASL are westerly at La Pampilla (City of Arequipa) while the winds at Pampa de Majes and La Joya are easterly. This implies that the airflow between the surface and 3500 m approaches Arequipa from the S, then SW, and finally W (in the mean). The air appars to be flowing around the higher terrain (near Cerro Verde) south of the city and approaching the city from the west. This westward flow is most obvious in the afternoon (PM means) and between 2500 and 300 mASL.

4) The difference winds (PM minus AM means) show that there is an upslope flow in the afternoon, but that it is very shallow. The winds at 1750m are clearly towards the higher terrain at Pampa Majes and La Joya but by 2250 they are from the mountins - this is the retur flow of the afternoon upslope (valley) breeze. A second maximum in upslope winds can be seen in the 3000-4000 m layer. Between 6000 and 8000m there s a clear flow from the higher terrain towards the ocean (difference winds from the NE). Above this level the data are fewer, with no nighttime winds.

5) The mean afternoon meridional wind profiles all show a similar feature - the maximum in southerly flow between 3000 and 4000m. This flow towards the higher terrain may be a result of the afternoon heating of the Pacific slopes of the altiplano.