Understanding Stratified Turbulence and Greenhouse Gas Exchange in the Stable Boundary Layer of the Arctic Atmosphere

Stratified turbulence is a prominent feature in the Arctic boundary layer, where land surface cooling during the night may induce strong stable stratification. This process significantly alters the transport dynamics of heat, momentum and trace gases, including greenhouse gases , which are critical to understanding Arctic carbon feedback processes. The Arctic is warming at a rate three to four times faster than the global average, threatening to destabilize its permafrost carbon reservoir, which stores about 60% of global soil carbon—an amount three times as large as currently contained in the atmosphere. Accurate estimation of Arctic greenhouse gas fluxes is crucial for understanding the feedback processes between the permafrost carbon cycle and climate, as these processes have the potential to transform the region from a carbon sink into a significant carbon source.

Quantifying greenhouse gas fluxes using the eddy covariance technique, where turbulent vertical fluxes are computed from high-frequency atmospheric data, is particularly challenging under stable stratification, where turbulent mixing is suppressed. This study investigates nighttime greenhouse gas transport dynamics in the Arctic’s stably stratified boundary layer based on Large Eddy Simulation (LES) utilizing the EULAG research model. Site-specific data are incorporated to simulate stable stratification induced by surface cooling.

We employ the "age of air" (AoA) concept, traditionally applied in the stratosphere, to evaluate vertical mixing efficiency in stable conditions. Developing AoA-based methods to interpret the transition from nighttime fluxes to early morning measurements, which are often misinterpreted as outliers, will help to provide new insights into land-atmosphere interactions in the Arctic. These findings contribute to improving Earth System Models (ESMs) and enhance our understanding of Arctic greenhouse gas emissions and their impact on global climate.