SALLJEX

What is this experiment about?

The Salar de Uyuni is the largest dry/salt "lake" ("salar" in Spanish) in the Americas. As such it (and many other salares on the altiplano) have an effect on the overlying atmospheric conditions. In particular, the highly reflective surface (compared with the surrounding terrain) should produce diurnal circulations that are similar to better known sea-land breezes. The net effect of these breezes, and the associated patterns of vertical motion, are suspected to strongly control the precipitation over the salares and surrounding altiplano. The measurements carried out in November 2002 were designed to measure the atmospheric circulations associated with the Salar de Uyuni and relate these to the diurnal variation of solar radiation and the influence of the varying synoptic-scale winds. As the variations in the synoptic-scale winds over the altiplano are associated with variations in the intensity of the low-level jet and other features of the atmosphere over the region, this experimental activity has been included as a component of the broader SALLJEX activity.

The study of salar-generated atmospheric circulations is important not only for present day and climate studies but also for understanding the past climate of the altiplano. Some 15,000 years ago a very large lake covered the southern altiplano, modifying the local climate to an unknown degree. The altiplano component of SALLJEX should help to interpret past climate conditions associated with large lakes and how the climate changed as the lakes dried out.

Where did it take place?

The Salar de Uyuni is located in southwestern Bolivia, at an altitude of ~3650 m Above sea level (~11980 ft). This salt lake is the largest in the Americas and originated about 10000 years ago, as former Lake Tauca (see fig. 1) dried out. The northern tip of the "salar" is close to 19.5°S; the southern tip around 20.7°S; the westernmost tip around 68.3°W and the easternmost point around 66.9°W, near the town of Uyuni.

Click here to see a larger descriptive map of Altiplano (fig. 2).

Fig. 2. Map of Altiplano, showing main features as Lake Titicaca and Uyuni Salt Lake. Large white spots are salt lakes such as "Coipasa", just north of Uyuni. The greenish spot just east of the word "Altiplano" is Lake Poopó, still a lake, very shallow now.


What kinds of data were collected?

Hourly pilot balloon soundings, 1-2 meter wind direction and velocity estimation every 15 minutes, 3-level Air temperature readings every 15 minutes, sky observations every 15 minutes , cloud photography during the morning hours, occasional tethered balloon launches, and maximum and minimum temperatures at different points on the salar.

When did the experiment take place?

Preparations began for the program in October 2002. The field observation phase took place during the last 7 days of November, 2002. The data quality control and analysis phase is now taking place.

In summary, how was the field experiment part designed?

Four stations were established along the borders of the salar, with one station near the center of the salar; the latter site was also the operations center. The five stations launched pilot balloons at 1 hour intervals, registered temperature observations at 3 levels ( 2 cm, 1.5m, and 4 m above the surface) and also recorded wind and sky conditions, all every 15 min - day and night. At the central site tethersonde measurements were also made under suitable conditions and radiation measurements were also made. More than 45 individuals participated in the experiment; while most came from Bolivia there were participants from Peru, Paraguay, Argentina, Colombia as well as the USA.

Click here to see the station distribution map.

The working conditions during this field campaign were difficult. Strong winds in the afternoon and evening hours blew down tents at most of the sites at least once. The tethersonde activity was particularly difficult due to these winds. Strong sunlight forced observers to use special sunblock and even with these preparations most people were burned - often from the reflected radiation from the surface of the salar. Conditions were cold at night, complicating sleeping in the tents. The operations center staff was luckier - with a room to sleep in and normal bathroom facilities, had to walk the 700 m to the tent/observation site.

After the measurement campaign, all of the participants gathered at the central site at Incahuasi to have a farewell lunch prior to departure for the town of Uyuni.

A more colorful description of the Uyuni Activities can be found here.




Acknowledgements.

All of the participants for their great effort, dedication, patience and hard work, which made possible the execution of field campaign. Much of the coordination and organizational activities within Bolivia were supervised by Guillermina Miranda of the Universidad Mayor de San Andres. The participation of the many AASANA personnel was supervised and organized by Roberto Catecora of AASANA - La Paz. The success of the observations at each site was due to the efforts of each individual at each of the sites (listed in the participant list). A more complete list of acknowledgments is being developed - as there were many contributions not directly evident. The funding for most of the logistical costs associated with the activity came from SALLJEX sounding and raingauge projects sponsored by NOAA's Office of Global Programs.





Links.

  • Uyuni Experiment Homepage's Spanish Version.

  • Titicaca Lake Experiment Homepage.

  • PACS-SONET.

  • SALLJEX HOMEPAGE at NSSL.