Inferring Katabatic Jet Height with Near-Surface Measurements

Understanding the development of katabatic wind systems above mountain glaciers is essential to better constrain the response of the local glacier microclimate and surface melting to large-scale climate forcing. The vertical turbulent flux profiles, and consequently turbulent fluxes at the glacier surface during katabatic flow, depend strongly on the height of the near-surface katabatic jet. However, direct measurements of jet heights are rare as they require balloon soundings or meteorological towers; neither of which are appropriate for long-term installation on glaciers. In this study, we conduct a multi-month field campaign in the summer of 2023 on the Kaskawulsh Glacier in the Yukon, Canada, measuring mean meteorological variables (up to 5m above the glacier surface), and turbulent fluxes at three heights (1m, 2m, and 3m above the surface) derived from eddy-covariance measurements. Over 30 hours of atmospheric  profiling with wind and temperature sensors tethered to a kite provides temporally and spatially high-resolution vertical profiles of katabatic flow. Using Multi-Resolution Flux Decomposition (MRD) applied to the eddy-covariance data from only one near-surface sonic anemometer, we introduce a method to infer the height of the katabatic wind speed maximum using the length scales of the most energetic eddies contributing to the heat flux. The inferred katabatic height for each 30-min interval of observations agrees with the corresponding measured 30-min average height from the atmospheric profiling, with a correlation of 0.73 and a mean bias error of 0.3m between the two datasets. We demonstrate that turbulent mixing lengths of momentum and heat fluxes can also be quantified with the use of MRD on the eddy-covariance data, and we propose a simple modification in the parametrizations of mixing-length models accounting for the near-surface katabatic jet. We corroborate these findings with data collected as part of the Second Meteor Crater Experiment (METCRAX II), providing tower-based measurements of deep katabatic flow at non-glacier terrain in the Arizona Meteor Crater.