Groundwork in the snow for measurements in the wind
March 21, 2013
It was January 2013 in Toolik, Alaska, about 160 miles north of the Arctic Circle, and the temperature was minus 35 degrees Fahrenheit. Jeff Taylor (NEON atmospheric physicist) and I (NEON micrometeorologist) put on snow shoes to prevent ourselves from sinking into thigh-high snow. After hiking about a mile and a half, we finally reached the ridgeline. Jeff’s eyelashes and beard were covered with frost and his nose dripping with icicles. My hair and mask were also white with frost. Being from the southern part of China, this was my first experience in cold winter temperatures. I was a bit scared, but also excited and looking forward to our task of maintaining the weather station in the field.
We had less than 4 hours of daylight to find our temporary weather station at the future NEON tower site, swap out the battery, clean the solar panel, fix broken wires, and download data. Fortunately, we managed to get it all done and return to the main road before dark. Why couldn’t we wait for a warmer day to maintain the weather station? Well, the weather station is an important NEON pilot study to determine the wind patterns at a particular site, which will inform the site layout design, orientation of the site tower and the location of sensor booms on the tower. We will measure chemicals, energy and momentum exchanges, or fluxes, between ecosystem and atmosphere using instruments mounted on towers at NEON sites. These measurements will help us better understand ecological processes – such as the movement of carbon and pollution between soil, air and water – and the drivers of those processes across the continent. Accurate turbulent wind measurement is a key measurement to enable the determination of the chemical, energy and momentum fluxes. The tower and wind sensor booms must be oriented in such a way that the prevailing winds are unimpeded by any unnatural objects, including tower infrastructure. Because wind direction can change from season to season, we require at least a full year’s wind data to confidently determine the wind patterns at a particular site. Data from the winter is equally important as data from other seasons. Based on the wind data, we can generate wind roses and conduct a footprint analysis, which will tell us the prevailing wind direction and wind speed. For the signals measured at the tower, we can also tell which direction they come from, and from what distance.
This kind of pilot study can help us mitigate the risk of site layout design by telling us how to optimize the location and orientation of tower structure, instrument hut, and soil array to best achieve scientific measurements. We conduct this kind of study at NEON sites like the ones in Moab and Yellowstone, where the historic weather data provided to us don't represent that particular NEON tower site. In addition to the weather station pilot studies, my colleagues and I characterize sites through soil property surveys and ecosystem surveys, which will inform the tower height and the separation of soil plots at each site. As many sites become ready for construction, we work with the facilities and civil construction team and visit each site for pre-construction field review and site acceptance. This activity will ensure the actual site layout follows the determined design, and will help resolve issues that may have scientific impacts, such as tree removal, limb trimming, temporary access route, relocation of soil plot, etc. Another exciting field activity is soil pit digging and soil block sampling, led by NEON soil ecologist Ed Ayres. Ed and his team dig a soil pit at each site while it is under construction. Digging the pits allows us to identify soil horizons, determine the depths for soil sensor installation, and collect site-specific soil blocks to help calibrate soil sensors. I bet Ed and his team will have a lot of stories and photos to share with you about this activity. So, stay tuned!