Friday, June 26, 2015
Temperature on the Tundra...
The spatial heterogeneity of Arctic landscapes presents unique challenges to measuring and modeling a wide variety of land surface processes. One that is of particular importance to the NGEE Arctic project is the distribution of temperatures within active layer soils and permafrost. This applies to both the profile of temperature with depth in the soil and variation in temperature across the microtopography of ice-wedge polygons. Many of our team members would like to have good measurements of temperature not only for understanding its importance in controlling CO2 and CH4 flux, but also for validation of our fine-scale models where the challenge is in simulating freeze-thaw processes at fairly high resolution.
Knowing the important role played by temperature in Arctic ecosystems our scientists have deployed a number of temperature probes at field sites on the BEO. Currently we have a dense network of probes that measure temperatures across polygon centers, rims, and troughs to a depth of 1.5 meters. Many of these datasets are available at the NGEE Arctic data portal.
Not surprisingly, every year a suite of new research tasks are added to our existing activities. And when that happens, additional probes also frequently need to be installed. This trip Bob, Go, and Sina each had tasks that required new temperature measurements. Interestingly, their need for new temperature measurements were driven by a range of science questions at fine, intermediate, and large spatial scales.
Sina and Bob were interested in the temperature of shallow soils so they spent much of the last two days installing a dozen Stevens Hydra Probe II sensors within the upper several centimeters of soil at our intensive study sites. Sina placed probes within the soil, ran cables back to the data logger and Bob did the wiring. The data loggers had to be reprogrammed but Bob was able to do that fairly quickly despite surprisingly cold temperatures and intermittent rain. Sina will use these temperature measurements in conjunction with information that she derives from the infrared (IR) camera that is mounted atop a 10-meter tower on the BEO. These measurements taken at two different scales will provide information that will help us interpret spatial heterogeneity in temperatures across the landscape.
Similarly, Go installed temperature and moisture probes at 15 to 20 locations on the BEO last fall. Yesterday and today he downloaded data from each of those and recorded their position with GPS. Go was happy with the quality of data that he has acquired and with the lack of problems encountered given that the probes were left in place over the winter. However, despite his best efforts one or two of the data loggers had been damaged by lemmings or foxes. This kind of damage plagues all researchers, but seems to be an especially acute problem in the Arctic. We should be pleased that only one or two data loggers needed to be replaced. Go plans to continue measuring temperatures at broad spatial scale across the BEO for several more years so he can evaluate surface temperatures from the NASA Soil Moisture Active Passive (SMAP) mission (http://www.nasa.gov/smap/). This will help the NGEE Arctic project in several ways, but most importantly in translating what we measure at fine scales to spatial scales relevant to climate models.