The Large-eddy Observatory Voitsumra Experiment 2019 (LOVE19) with high-resolution, spatially-distributed observations of air temperature, wind speed, and wind direction from fiber-optic distributed sensing, towers, and ground-based remote sensing

Abstract

Abstract. The weak-wind Stable Boundary Layer (wwSBL) is poorly described by theory and breaks basic assumptions necessary for observations of turbulence. Understanding the wwSBL requires distributed observations capable of separating between submeso and turbulent scales. To this end, we present the Large Eddy Observatory, Voitsumra Experiment 2019 (LOVE19) which featured 1350 m of fiber optic distributed sensing (FODS) of air temperature and wind speed, as well as an experimental wind direction method, at scales as fine as 1 s and 0.127 m in addition to a suite of point observations of turbulence and ground-based remote sensing. Additionally, flights with a fiber optic cable attached to a tethered balloon provide an unprecedented detailed view of the boundary layer structure with a resolution of 0.254 m and 10 s between 1–200 m height. Two examples are provided demonstrating the unique capabilities of the LOVE19 data for examining boundary layer processes: 1) FODS observations between 1m and ~200 m height during a period of gravity waves propagating across the entire boundary layer and 2) tracking a near-surface, transient submeso structure that causes an intermittent burst of turbulence. All data can be accessed at Zenodo through the DOI https://doi.org/10.5281/zenodo.4312976 (Lapo et al., 2020a).

Distributed sensing of wind direction using fiber-optic cables

“…Exchange mechanisms of momentum, mass, and energy between the surface and the atmosphere in the stable weakwind boundary layer are crucial for our understanding of many processes, including, for example, fog formation (Oke 1987), pollutant dispersal (Hanna 1986(Hanna , 1990, forest-atmosphere gas exchange (Oliveira et al 2013;Freundorfer et al 2019), or frost formation (Whiteman 2000). These exchange processes typically are statistically parameterized using similarity theories (Holtslag and De Bruin 1988).…”

“…Many of the fundamental assumptions made by similarity theories, however, e.g., spatial homogeneity and Taylor's hypothesis of frozen turbulence (Taylor 1938), are not fulfilled in the surface layer, particularly during nocturnal weak-wind situations and during the occurrence of submesoscale processes (Mahrt et al 2009;Thomas 2011;Sun et al 2012Sun et al , 2015Sun et al , 2020Pfister et al 2021b). The inapplicability of these assumptions hampers climate and weather models since it leads to incorrect predictions of turbulent fluxes at the land surface (Holtslag and De Bruin 1988;Holtslag et al 2013;Davy and Esau 2014;Lapo et al 2019). Due to the invalidity of Taylor's hypothesis and the local character of turbulent quantities, spatially and temporally explicit measurements are needed in order to understand the nature of submesoscale processes, building toward the goal of improving model parameterizations (Mahrt et al 2009;Acevedo et al 2014;Thomas 2011;Pfister et al 2021a;Mahrt 2020).…”

“…Due to the invalidity of Taylor's hypothesis and the local character of turbulent quantities, spatially and temporally explicit measurements are needed in order to understand the nature of submesoscale processes, building toward the goal of improving model parameterizations (Mahrt et al 2009;Acevedo et al 2014;Thomas 2011;Pfister et al 2021a;Mahrt 2020). Spatially explicit measurements are also useful in other conditions than during a stable weakwind boundary layer, since internal boundary layers and heterogeneous turbulence can occur during strong wind conditions and in the convective boundary layer in the presence of surface heterogeneities (Mahrt and Vickers 2005;Mott et al 2017;Fritz et al 2021).…”

“…Distributed temperature sensing (DTS) with fiber-optic cables has been shown to be a promising candidate for fulfilling this research need (Thomas et al 2012;Peltola et al 2021). Most often, the Raman scattering method is used for DTS, where some fraction of a light pulse sent into the cable is scattered back at shifted wavelengths (Thomas and Selker 2021). The intensity distribution of the frequency-shifted reflection facilitates calculating the temperature of the optical fiber at the point of the scattering.…”

“…The intensity distribution of the frequency-shifted reflection facilitates calculating the temperature of the optical fiber at the point of the scattering. The location of the scattering event can be obtained from the light pulses time of flight (Selker et al 2006a,b;Thomas and Selker 2021), so that spatially distributed temperature measurements can be achieved. Apart from measuring temperatures, the DTS technique has also been used successfully for spatially and temporally distributed measurements of other atmospheric variables such as solar radiation (Petrides et al 2011), wet-bulb temperature (Euser et al 2014;Schilperoort et al 2018), and wind speed (Sayde et al 2015).…”