How can the Latent Heat Flux in a Convective Boundary Layer be Described?

We present ongoing work within the Land-Atmosphere Feedback Initiative (LAFI) [1]. LAFI is funded by the Deutsche Forschungsgemeinschaft (DFG) and is located at the University of Hohenheim, Stuttgart. LAFI's objective is to quantify and understand land-atmosphere feedbacks by utilizing synergetic observations and simulations in an interdisciplinary way. One aspect is covered by this work, which aims to provide a better understanding of fluxes in the convective boundary layer (CBL), especially the latent and sensible heat flux. The focus lies on entrainment fluxes in the interfacial layer (IL), the uppermost layer of the CBL, which marks the transition to the free atmosphere (FA).

A key aspect of this work is setting up a comprehensive dataset. This should capture all relevant variables such as temperature, humidity, and wind of the lower atmosphere at high spatial and temporal resolutions for as many cloud-free CBL situations as possible. Accordingly, simultaneous and high-resolution data from the synergetic use of different lidar systems will be used (see [2]) and processed (see [3]). Next, we will analyze this data for the driving variables and possible parameterizations of the latent and sensible heat flux.

We have already started this work by building a dataset containing data from the Atmospheric Radiation Measurement Climate Research Facility (ARM) Southern Great Plains (SGP) site in Oklahoma, USA, and testing a similarity relationship for the latent heat flux in the IL in [4].

Corresponding first results could not confirm the proposed similarity relationship for the latent heat flux in the IL from [2] and will be presented at the conference. Additionally, correlations of the flux with other measured variables, as well as an example case representative for the pool of selected cases will be shown.

In the coming months, we will expand the dataset to other measurement campaigns, like the synergy of Raman and Doppler lidar systems within LAFI in 2025.

References:

[1] https://www.lafi-dfg.de/

[2] Wulfmeyer, Volker et al. (2016): Determination of Convective Boundary Layer Entrainment Fluxes, Dissipation Rates, and the Molecular Destruction of Variances: Theoretical Description and a Strategy for Its Confirmation with a Novel Lidar System Synergy. In Journal of the Atmospheric Sciences 73 (2), pp. 667–692. DOI: 10.1175/JAS-D-14-0392.1

[3] Behrendt, Andreas et al. (2020): Observation of sensible and latent heat flux profiles with lidar. In Atmos. Meas. Tech. 13 (6), pp. 3221–3233. DOI: 10.5194/amt-13-3221-2020

[4] von Klitzing, Linus (2024): Latent Heat Entrainment Flux Similarity Relationships for the Convective Boundary Layer. Master's dissertation. University of Hohenheim, Stuttgart. Institute of Physics and Meteorology