By Dr. Douglas Hardy, Geosciences Dept., University of Massachusetts
High-altitude weather stations in the Andes
Ice cores recently recovered from high-elevation sites within the Tropics are providing long, detailed records of past climate. These histories contain information about global-scale changes in climate as well as environmental changes in areas where most human activities occur.
Climatic information is reconstructed from ice cores by analysis of geochemical measurements made sequentially down-core, including oxygen isotopic ratios, chemistry, and the concentration of dust. Two ice cores were drilled to bedrock (each 435 ft) in July 1997 at the summit of an ice cap in the Andes of Bolivia, by Dr. Lonnie Thompson, Ohio State University, and his team. Climatologists from the University of Massachusetts (UMass) are collaborating with these scientists to document the ice cap climate, and to better understand the atmospheric sources of geochemical variability in snow accumulating at the site.
In support of the ice core calibration, weather stations are operating near the drill site on Sajama (21,464 ft; 18°06’S and 68°53’W), the highest peak in Bolivia, and on Nevado Illimani (20,555 ft; 16°39’S and 67°47’W), which is 200 km essentially upwind of Sajama. Both stations measure snow accumulation and ablation hourly, along with snow temperature and a variety of meteorological variables. Analysis of these data is closely tied to the results of annual snowpack studies carried out in the vicinity of the stations, and with data from NCEP global analyses (National Centers for Environmental Protection of NOAA).
The design of these stations required balancing competing goals. For example, global solar irradiance can exceed 1100 W m-2 at mid-day, requiring mechanical aspiration of the temperature and humidity sensors. While abun-has been an adventure — it is no mys-date — this in spite of unusually heavy dant radiation could easily provide con-tery to us why so few weather stations snow accumulation (13 ft) during the tinuous power to the fans, we limited operate at high altitudes. 1996-97 wet season. Data from the stathe system design to two 10 W solar Upon arrival at the summit, one is tions now encompass one of the most panels to reduce wind loading. Con-not inclined to dig down six feet significant El Niño events of the centusequently, the fans are operated for only through wind-packed snow in search of ry, and is providing valuable insight into one minute out of every ten. Both sta-the enclosures. Several nights were the record of tropical ice cores. tions are designed around CR10X data-spent at the summit on each visit, often Details on the stations and first-year loggers. Data are stored on-site in the in winds so strong that flapping tents results are available in the September dataloggers and on SM716 storage mod-precluded conversation. Prior to depar-1998 issue of the American ules, and both sites use GOES telemetry ture, a call to UMass by satellite phone Meteorological Society Bulletin, and to deliver data in near-real time to provided a reassuring check on satellite from our Web site at http://www.geo. UMass. The Sajama station maximizes telemetry. umass.edu/climate/bolivia.html. CR10X capacity, with duplicates of The performance of the stations has We would like to acknowledge the most sensors and an AM416 multiplexer been quite remarkable. After 26 financial support of NOAA, logistical for thermistors and thermocouples. months, the Sajama record for most help from Carlos Escobar, and the devo-
Installing and servicing the stations variables is 100 percent complete to tion of Campbell engineers!