Application of Stable Isotope Tracers to Determine Latent Heat Exchange in Stable and Condensing Boundary Layers

David Noone, University of Colorado, Cooperative Institute for Research in Environmental Sciences and Dept. of Atmospheric and Oceanic Sciences, Boulder, CO, United States; Oregon State University, College of Earth, Ocean and Atmospheric Sciences, Corvallis, OR, United States, Adriana Raudzens Bailey, University of Colorado, Boulder, United States, Max B Berkelhammer, University of Illinois Chicago, Department of Earth and Environmental Sciences, Chicago, United States, Christopher Cox, Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States and Aleya Kaushik, Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, United States
Abstract:
Understanding the manner in which material is exchanged between the planetary boundary layer and the free troposphere is essential for evaluating many aspects of climate, including the distribution of trace gases, the transport of energy and water, cloud types, climate sensitivity, and the surface energy balance. However, neither observations nor parameterized numerical models constrain the interplay between moist processes and joint exchanges of water and heat adequately. Advance in understanding is limited in part by the complex controls on turbulence and, in the case of cloudy boundary layers, the interplay between turbulent mixing and latent heating, which is difficult to observe. Recent theoretical and observational advances now allow stable isotope ratios of water vapor and cloud condensate to be used to isolate the transport component from other thermodynamic controls, including condensation. Here we expose the role of latent heat exchanges that would be difficult to determine without a method to track water vapor transport. Analysis of case of a very stable boundary layer shows sustained downward latent heat fluxes during the development of a radiative inversion, and which establishes a new basis for parameterizing turbulence under stable conditions. The case of a capped convective marine boundary layer highlights the role of transport processes and condensation, which are critical for maintaining the temperature and humidity structure of the lower atmosphere over tropical oceans. While a variety of trace gases can be used to identify air mass exchange, water stable isotope ratios are particularly useful because they can identify latent heat exchanges, which are necessary to fully account for the coupling of water and energy in the boundary layer. The use of isotopic tracers explicitly captures this coupling even in the case of weak turbulence when important terms needed to resolve the local energy balance would otherwise be lost.
Back to: Atmospheric Boundary Layer Processes and Turbulence I