Influence of Temperature Inversions and Turbulence on Land-Atmosphere Exchange for Irrigated Farmland in Rolling Terrain

Surface energy fluxes are exchanged between the surface of the earth and the atmosphere and impact weather, climate, and air quality. The concentrations of atmospheric greenhouse gasses are increasing leading to changes in atmospheric boundary layer (ABL) dynamics as a result of the changing surface energy balance. The ABL processes are important to characterize because they are difficult to parameterize in global and regional scale atmospheric models. Empirical data can be collected using eddy covariance micrometeorological methods to measure turbulent fluxes (e.g., sensible heat, moisture, and CO2) and quantify the land-atmosphere exchange. The objective of this work is to calculate surface fluxes using observational data collected during one week in September 2014 from a monitoring site in Echo, Oregon. The site is located in the Columbia Basin with rolling terrain, irrigated farmland, and over 100 wind turbines. The 10m tower was placed in a small valley depression to isolate nighttime temperature inversions. This work presents observations of momentum, sensible heat, moisture, and carbon dioxide fluxes from data collected at a sampling frequency of 10Hz at four heights. Results show a strong correlation between temperature inversions and CO2 concentrations. The impact of the irrigated farmland near the measurement site was observed in the latent heat flux, where the advection of moisture was evident in the tower moisture gradient. A strong relationship was also observed between sensible heat flux, latent heat flux, CO2 flux and atmospheric stability. The average nighttime CO2 concentration observed was approximately 400ppm and daytime around 390ppm; compared to the 2013 global average CO2 concentration of 395ppm. The maximum CO2 concentration (465ppm) was observed on the strongest temperature inversion night.