Analysis of some meteorological variables recorded at 4000 m in the Argentinian subtropical Andean region

Next to the Destacamento La Gruta de Gendarmería Nacional, Province of Catamarca (26° 52' 35”S – 68° 18' 37”W, 4000 m, Argentina) at the Subtropical Andes an automatic weather station was installed in January 2004. This task was achieved within the framework of an interdisciplinary project which emphasized on defining climatic changes during the Holocene. From April to December, meteorological conditions in the mountain were observed in order to better understand the atmospheric signals in altitude. This work documents the design, installation and operation of the station, and presents the first discussion of measurements of the collected data. Technical and human problems reduced the information registered to the period from mid April to January 2005. The analyzed variables were air temperature, maximum and minimum temperatures, humidity, precipitation, wind, as well as the snow accumulation, registered by the staff of Gendarmería. Daily mean values of air temperature above 0°C were registered for spring and summer. Winter was the most disturbed period; for the times of higher daily temperature range, daily NCEP fields of geopotential heights showed a ridge to the west of the Pacific coast and a trough extending southeastward from the subtropics into the South Atlantic Ocean. These so-called cold surges have a marked impact on regional weather. Atmospheric humidity at 4000 m varied notably during the recording period. The median of the relative humidity was under 40%. According to the daily median of the water pressure, August turned out to be the most humid month with rainfall records of 1.8 mm, higher to those registered in November or December. Actually during August, snowfalls were registered, which, in agreement to the emitted reports by Gendarmería Nacional, they were intense and of long duration. Hourly frequency of winds show preferential directions of SW-NW, presenting the largest variability during November and December that allows to presume a dampness contribution to the region from different sources. This experience was as an interdisciplinary effort which not only involved researchers but also inhabitants of a complete community and its environment at 4000 m.