PUBLICATION HIGHLIGHT: Seasonal and Latitudinal Variations of Surface Fluxes at Two Arctic Terrestrial Sites
The Arctic is warming faster than other regions of the planet, a phenomena described as Arctic Amplification. Arctic Amplification results in many easily observable environmental changes, such as summer melting of permafrost to deeper levels, certain vegetation zones moving northward, increased sea-ice melt, and decreased snow extent. Although there are many questions about the mechanisms that drive Arctic change, energy and heat exchange processes between the atmosphere and the surface are understood to be key components controlling the system. Observing the exchange processes (or fluxes) is a difficult activity, requiring special micrometeorological flux stations and/or towers to measure high resolution, multiple-level, and synchronized details of atmospheric temperature, moisture, winds and water/carbon dioxide. The problem is made more difficult because the fluxes measured at one site might be quite different those measured at another site.
In a new study published online in Climate Dynamics, NOAA and CIRES researchers from the ESRL Physical Sciences Division, along with collaborators from Canada and Russia, use multi-year measurements from micrometeorological towers in Eureka, Canada and Tiksi, Russia to investigate and compare the annual cycle of fluxes and links to atmospheric and surface processes such as spring onset of melt and autumn onset of freezing.
The researchers found that the primary driver of seasonal and latitudinal variations in the Arctic is the seasonally varying pattern of sunlight that falls directly on a specified area for a specified length of time. For example, Eureka, Canada is located 9 degrees north of Tiksi, Russia, and although it receives a lower cumulative amount of incoming solar radiation over the entire year, there is a brief period during the summer when Eureka receives more net solar radiation than Tiksi. This effect leads to a deeper melting of the permafrost layer in mid-summer at Eureka, despite mitigating factors such as clouds and local soil composition and moisture content. There are also observable differences in the structure of the atmospheric boundary layer at both locations, with Eureka more likely to develop a long-lived, quasi-stationary convective boundary layer in the summer. Finally, differences in soil moisture at each location had an effect; during the transition months in Tiksi, an observed effect resulted in a temporary halt in the fall surface cooling trend when all heat and energy are taken up by freezing processes.
Knowing how atmosphere-surface exchanges contribute to the observed changes in the Arctic allows researchers to better understand how a complex system trades heat and energy between the surface and the atmosphere.. Once these fundamental processes are quantified and understood, physics-based model performance can be evaluated and improved to untangle the effects of human-caused factors and improve predictions of future climate change.