The role of surface energy fluxes in determining mixing layer heights

• Published in: Agricultural and forest meteorology 2023-11, Vol.342, p.109687, Article 109687
• Main Authors: Beamesderfer, Eric R., Biraud, Sebastien C., Brunsell, Nathaniel A., Friedl, Mark A., Helbig, Manuel, Hollinger, David Y., Milliman, Thomas, Rahn, David A., Scott, Russell L., Stoy, Paul C., Diehl, Jen L., Richardson, Andrew D.
• Format: Article
• Language: English
• Subjects: AmeriFlux; Boundary layer height; climate; ecosystems; Eddy-covariance; energy; forests; heat; Land-atmosphere interactions; latent heat; meteorology; Phenology; summer; Surface energy budget; vapor pressure deficit
• ISSN: 0168-1923
• DOI: 10.1016/j.agrformet.2023.109687

•Mixing layer heights were assessed from radiosonde, ceilometer, and reanalysis data.•The relative influence of daily surface fluxes was examined for all sky conditions.•Results emphasized the complexity of bi-directional land-atmosphere interactions. The atmospheric mixing layer height (MLH) is a critical variable for understanding and constraining ecosystem and climate dynamics. Past MLH estimation efforts have largely relied on data with low temporal (radiosondes) or spatial (reanalysis) resolutions. This study is unique in that it utilized continuous point-based ceilometer- and radiosonde-derived measurements of MLH at surface flux tower sites to identify the surface influence on MLH dynamics. We found a strong correlation (R2 = 0.73-0.91) between radiosonde MLH and ceilometer MLH at two sites with co-located observations. Seasonally, mean MLH was the highest at all sites during the summer, while the highest annual mean MLH was found at the warm and dry sites, dominated by high sensible heat fluxes. At daily time scales, surface fluxes of sensible heat, latent heat, and vapor pressure deficit had the largest influence on afternoon MLH. However, at best, the identified forcing variables and surface fluxes only accounted for ∼38-65% of the variability in MLH under all sky conditions, and ∼53-76% of the variability under clear skies. These results highlight the difficulty in using single-point observations to explain MLH dynamics but should encourage the use of ceilometers or similar atmospheric measurements at surface flux sites in future studies.