Nevado Sajama

Weather station configuration

SAJAMA Weather Station configuration

Location: 18°06' S; 68°53' W at 6542 m (21,464 ft)

This weather station is designed and equipped for year-around data collection at the summit of this Andean volcano. It was installed 1 October 1996 on the summit of Sajama by a team from the Climatology Lab (D. Hardy, C. Braun and M. Vuille), with assistance from B. Francou and ORSTOM. All measurements are stored in digital form on-site in two independent locations, and transmitted to the University of Massachusetts via GOES satellite. The station was serviced and upgraded in June/July of 1997.

Data acquisition, storage and transmission

• Campbell Scientific CR10X measurement and control module (temperature tested -55° to 85°C; 1MB memory)
• Campbell Scientific storage module (358,000 data points) (temperature tested -55° to 85°C)
• Satellite telemetry via GOES

Power

• 12 V regulated power supply to datalogger and satellite transmitter with rechargeable gel cell battery (24 Ahr) and 10W solar panel (Solarex)
• Independent 12V power supply to aspirated radiation shield with 25 Ahr rechargeable gel cell and 10W solar panel (Solarex)

Instrument enclosure/mounting

• Water-tight enclosure (16 × 18") for datalogger, satellite transmitter and peripherals
• Extendible and adjustable instrument tower

Sensors

• Setra barometric pressure: 400 to 700 mb special pressure range, with extended temperature compensation over -25° to 66°C
• Vaisala temperature and relative humidity probe (thermistor/ capacitive polymer) with Gill Aspirated Radiation Shield (w/airflow monitoring switch)
• Vaisala temperature and relative humidity probe (thermistor/ capacitive polymer) with Gill Multi-Plate Radiation Shield (experimental comparison with aspirated shield)
• RM Young Wind Monitors (two heights)
• Campbell Scientific Canada ultrasonic snow depth sensors (2 locations)
• Eppley Black & White pyranometer
• LI-COR silicon pyranometer
• Everest Interscience infrared temperature transducer to measure snow surface temperature
• Type E thermocouples to measure air temperature gradients (4 heights)
• Thermometrics thermistors (Ultrastable) to measure snow temperature (2 depths)

Additional notes and information:

• The CR10X is a modular datalogger with proven durability. Flash memory provides 1 MB of internal data storage, backed by a lithium battery.

• Data are transferred hourly from the CR10X to a solid-state, sealed storage module. The module has it's own lithium-battery backed RAM, providing a second data storage location and an important back-up to the data transmitted via GOES. Sufficient storage capacity exists for approximately 13 months of data collection, if necessary. Upon visitation of the station an empty module can be connected to replace the module with data, which is then taken down to a more hospitable environment and downloaded to a computer.

• The TGT1 is a relatively new transmitter from Telonics. It supports one-way communication via a GOES satellite to the NESDIS receiving site at Wallops Station, Virginia. Data are then immediately available via modem. Transmission of data from the station takes place during approximately one minute every 3 hours, and is collected from NESDIS and archived by Climatology Lab computers daily. Frank Keimig has completely automated this procedure.

• This system includes two independent power systems. The datalogger, transmitter and most sensors are be powered by a Campbell Scientific Canada BP25 battery (made by Gates). This sealed, rechargeable gel cell is designed to be charged at cold temperatures (here using a 10W solar panel), and has been well proven in the Canadian High Arctic. Another gel cell, housed within the enclosure, provides power to the blower of the Aspirated Radiation Shield and is float charged by a 10W solar panel. A relay is used to switch power on and off to the blower, which draws approx. 450 mA.

• The instrument tower is an adaptation of a design used on the Greenland Ice Sheet (K. Steffan). The mast (3" diameter) and cross-arms are 6061 T6 aluminum alloy tubing, and were assembled on-site by drilling into the snow/firn. The tower is additionally secured by anchored guy wires. The design allows additional height to be added to the tower in subsequent years (if required), and allows the sensor positions to be reset easily.

• Duplicate wind sensors are used as insurance against equipment failure due to the harsh environment at 6500 m. Two snowdepth sensors measure accumulation over slightly different areas, which will also help account for snowdepth variability.

• Extreme solar irradiance and low humidity on Sajama requires aspiration of the temperature and humidity sensor. As a comparison experiment, and as insurance against electrical or mechanical failure, a naturally ventilated sensor has also been deployed.

• The thermocouples will gradually be buried as the 1997-98 accumulation season progresses, providing additional snow temperature data. Additional thermocouples will be installed in 1998 to replace those that are buried.

• The total weight of the Weather Station is approximately 350 lbs.