Revealing the Morning Transition in the Mountain Boundary Layer Using Fiber-Optic Distributed Temperature Sensing

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Fritz, Antonia M. ; Lapo, Karl ; Freundorfer, Anita ; Linhardt, Tobias ; Thomas, Christoph:
Revealing the Morning Transition in the Mountain Boundary Layer Using Fiber-Optic Distributed Temperature Sensing.
In: Geophysical Research Letters. Bd. 48 (2021) Heft 9 . - e2020GL092238.
ISSN 1944-8007
DOI: https://doi.org/10.1029/2020GL092238

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Abstract

In the morning, the nocturnal stable boundary layer, SBL, transitions into its daytime convective counterpart substantially impacting the distribution of temperature, humidity, and pollutants. Applying distributed temperature sensing (DTS) below a tethered balloon (2–200 m) and along a tower (0–11 m), for the first time we observed three morning transitions (MTs) in a mountain boundary layer with high temporal (<10 s) and spatial (<0.25 m) resolutions. We show that MTs are best derived from a change in static stability from synchronous DTS observations. Our findings confirm that the MT occurs at the SBL top and bottom simultaneously, and identify horizontal heat advection as a main driver aiding solar surface heating in this midrange mountain valley. We conclude that heterogenous land use and mountainous topography cause complex interactions between valley‐scale and local airflows leading to thermal signatures characterized by strong, small‐scale variability. Our study highlights DTS as a crucial tool for investigating complex thermodynamic processes.