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

Thursday, 18 December 2014: 9:00 AM
David C Noone1,2, Adriana Raudzens Bailey1, Max B Berkelhammer3, Christopher Cox4 and Aleya Kaushik5, (1)University of Colorado, Cooperative Institute for Research in Environmental Sciences and Dept. of Atmospheric and Oceanic Sciences, Boulder, CO, United States, (2)Oregon State University, College of Earth, Ocean and Atmospheric Sciences, Corvallis, OR, United States, (3)University of Illinois at Chicago, Chicago, IL, United States, (4)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (5)Cooperative Institute for Research in Environmental Sciences, Dept Atmospheric & Oceanic Sciences, Boulder, CO, United States
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.