Precipitation Sensor on Duty at North Slope of Alaska

Published: 30 September 2006

Extremely low temperatures and humidity in the northern hemisphere make it very difficult to obtain accurate precipitation measurements. However, because the impacts of climate change are shown to occur most rapidly in the sensitive Arctic environment, these measurements are needed for characterizing boundary layer (surface to 1000-m altitude) conditions and simulating cloud formation as input to climate models. To obtain these measurements, a new precipitation sensor was installed at the ARM North Slope of Alaska site in Barrow. Situated approximately 1/4 mile south and east of the Great White instrument facility, the instrument provides measurements of snow-fall amounts, snow depth (and density), and snow temperature.

Manufactured by Yankee Environmental Systems, the “hot plate” precipitation sensor head consists of two isolated plates positioned one on top of the other. Each plate is about five inches in diameter and both are warmed by electrical heaters. It measures the rate of rain or snow based on how much power is needed to evaporate precipitation on the upper plate to keep its surface temperature constant. The second plate—positioned directly under the evaporating plate and heated to the same temperature—is used to factor out cooling from the wind. The sensor’s electrical components are designed to operate in temperatures spanning ±50°C.

Data collected by the sensor is transferred to the ARM Great White facility via fiber optic cable. The sensor’s close proximity to the Climate Reference Network (CRN) rain gauge allows hour-by-hour comparisons of measured snow rate. If the sensor data are shown to compare well with the CRN gauge, another may be installed at the ARM site in Atqasuk, as well as a second sensor in Barrow, on the top of the 40-m meteorological tower. Because of its height, this sensor would be used to isolate snowfall events from blowing snow events.