DOI: 10.5281/zenodo.5795431
title: PIANO (Penetration and Interruption of Alpine Foehn) – flux station data set

description: ABSTRACT This resource comprises meteorological and turbulence data from four flux stations operated during the PIANO (Penetration and Interruption of Alpine Foehn) field campaign. The campaign took place in and around Innsbruck, Austria, during autumn and early winter 2017. The goal of the PIANO campaign was to study south foehn events, in particular the interaction between cold air pools and foehn, the mechanisms by which foehn can break through to reach the valley floor and the processes affecting the subsequent breakdown of foehn. This dataset provides near-surface turbulence observations (including surface fluxes obtained using the eddy covariance technique), along with radiation and soil measurements, as well as meteorological information. DATA SET DESCRIPTION 1. Spatial coverage and locations Three eddy covariance (EC) stations were operated at grassland sites during the PIANO campaign. One station (‘EC_South’) was installed in the Wipp Valley near to the village of Patsch, south of the city of Innsbruck. Two stations were installed in the Inn Valley, one to the east of Innsbruck in the region of Thaur (‘EC_East’) and one to the west of Innsbruck at Innsbruck Airport (‘EC_West’). Data from a fourth EC station at the Innsbruck Atmospheric Observatory (IAO, Karl et al. (2020)) in the centre of Innsbruck (‘EC_Centre’) was also used. Precise station co-ordinates are provided in the data files. Three of the stations were located on grassland surrounded by mixed agricultural fields: the two stations in the Inn Valley (EC_East, EC_West) were installed on the fairly flat valley floor, while the site in the Wipp Valley (EC_South) gently sloped downwards to the west. During the campaign the vegetation was generally short at 5-10 cm. As far as possible, sites were selected to have a clear fetch for at least a few hundred metres. All three grassland sites experienced snow cover during winter. The urban station (EC_Centre) is a long-term site installed above roof level and representative of the surrounding neighbourhood close to the city centre of Innsbruck. 2. Temporal coverage The temporal coverage of the datasets for the PIANO campaign are as follows: • EC_West: 15 Sep 2017 - 31 Dec 2017<br> • EC_South: 08 Sep 2017 – 15 Dec 2017<br> • EC_East: 13 Oct 2017 – 15 Dec 2017<br> • EC_Centre: 1 Sep 2017 – 31 Dec 2017 The timeseries for EC_East begins later than the other sites because electrical interference thought to be from a nearby transmitter meant there was no useable flux data for the first month. The site was relocated on 13 October 2017 (no data is included before this date). Repeated theft of the batteries at EC_East resulted in gaps for the last few days of the dataset in December 2017. Due to issues with remote data collection, data availability at EC_West is low in September 2017. The PIANO campaign took place during autumn and early winter 2017 but the EC_West station was operated for longer (until 22 May 2018 after which use of the site was no longer permitted) as it provided a useful rural comparison station for the urban measurements (Karl et al., 2020; Ward et al., submitted). Data for 1 January – 22 May 2018 are available from the first author on request. Data collection at the long-term EC_Centre/IAO site began in spring 2017 and is ongoing. 3. Instrument details At EC_West a closed-path eddy covariance system (CPEC200, Campbell Scientific) provided fast response measurements of the three wind components, temperature, water vapour mixing ratio and carbon dioxide mixing ratio. At EC_East and EC_South a sonic anemometer (CSAT3B, Campbell Scientific) and krypton hygrometer (KH20, Campbell Scientific) provided fast response measurements of the three wind components, temperature and water vapour. These fast data were logged at 20 Hz (CR6, Campbell Scientific). All three stations were equipped with a four-component radiometer (CNR4, Kipp and Zonen) to provide incoming and outgoing shortwave and longwave radiation. Meteorological measurements included air temperature and humidity (Rotronic HC2A-S3, mounted in an actively ventilated radiation shield Rotronic RS12T), atmospheric pressure (Campbell CS100, mounted inside the logger box) and precipitation (ARG100 tipping bucket gauge, Campbell Scientific). Soil instruments comprised two soil heat flux plates at 0.05 m depth (HFP01, Hukseflux), two soil temperature sensors (107, Campbell Scientific) at 0.02 and 0.04 m depth and a soil probe (ACC-SEN-SDI, Acclima) providing soil moisture and soil temperature at 0.05 m depth. At each site, the fast-response anemometer and gas analyser were mounted on a tripod at around 2.5 m above ground, while the radiometer and temperature-humidity probe were slightly lower, at around 2.0 m (exact sensor heights are provided in the data files). At EC_Centre a closed-path eddy covariance system (CPEC200, Campbell Scientific) provided fast response measurements of the three wind components, temperature, water vapour mixing ratio and carbon dioxide mixing ratio at 10 Hz (CR3000, Campbell Scientific) measured at 42.8 m above ground level on a lattice mast installed on top of a university building. A four-component radiometer (CNR4, Kipp and Zonen) provided incoming and outgoing shortwave and longwave radiation and air temperature and humidity are also measured (Rotronic HC2A-S3, mounted in a ventilated radiation shield). Atmospheric pressure is measured by a pressure sensor mounted inside one of the electronics boxes supplied as part of the CPEC200 (EC100, Campbell Scientific). No soil or precipitation measurements were made at the urban station. 4. Data processing The fast-response eddy covariance data were processed to 30-min statistics following standard procedures using EddyPro version 7.0.7 (LI-COR Biosciences, 2021). These include despiking of raw data, time-lag compensation using maximum covariance, double coordinate rotation (meaning the 30-min mean vertical wind speed is forced to zero), simple block averaging (i.e. no filtering was applied), humidity correction of sonic temperature (Schotanus et al., 1983), and spectral corrections at low frequencies (Moncrieff et al., 2004) and high frequencies (after Fratini et al. (2012) for the closed-path CPEC200 data and Moncrieff et al. (1997) for the krypton hygrometer data). Oxygen (Tanner et al., 1993; van Dijk et al., 2003) and density (Webb et al., 1980) corrections were also applied at the sites with krypton hygrometers. Automated calibration (zero and span for carbon dioxide and zero for water vapour) was performed for the CPEC instruments once per day at EC_West and twice per day at EC_Centre. In addition to the standard processing described above, gust speeds were calculated from the sonic data. First the instantaneous horizontal wind speed was calculated (neglecting any vertical component). A 3-s running mean of the horizontal wind speed was then obtained, and the gust speed taken as the maximum of this 3-s running mean over a 1-min averaging interval. The dissipation rate of turbulent kinetic energy was obtained from the fast-response measurements of the three wind components (u, v, w) as follows. First, spectra were calculated for u, v and w using evenly spaced logarithmic frequency bins. The inertial subrange was identified as the region around 1 Hz where a local linear fit to the spectral slope was within ±20% of the expected -5/3 slope. The dissipation rate was calculated for each frequency bin in the identified inertial subrange according to Kolmogorov theory (e.g. Kaimal and Finnigan, 1994), using a value of 0.55 for u and 0.73 for v and w for the Kolmogorov inertial subrange constants, and the mean value over the frequency bins was used to provide the dissipation rate for u, v, and w for each 30-min period. Further discussion can be found in Ward et al. (in prep.). Quality control removed data during times of power outage and instrument malfunction and data adversely affected by rainfall (all KH20 data during rainfall were removed). To exclude any potential effects of turbulence distortion, data were removed when the wind direction was within ±10° of the mounting structure. Data falling outside physically reasonable thresholds were removed, including times when the rotation angle exceeded 45°. Stationarity tests following Foken and Wichura (1996) were applied with a threshold of 100 (i.e. data were excluded when the difference between 5-min and 30-min statistics exceeded 100%). For the meteorological, radiation and soil data, quality control removed data during times of power outage and instrument malfunction (including when dew on the radiometer adversely affected readings). 5. Data file structure Two files in netCDF format are provided containing processed and quality-controlled data: • PIANO_EC_MetData_QC_1min_v1-00.nc containing the meteorological, radiation and soil data for each site at 1-min resolution. This file also contains horizontal wind speed (before co-ordinate rotation), wind direction and gust speed for each site at 1-min resolution. • PIANO_EC_FluxData_QC_30min_v1-00.nc containing processed statistics and fluxes for each site at 30-min resolution. There are also quicklook plots (provided in PNG format, monthly and for the whole period) showing the data contained in these files. Four sets of files in ASCII format are provided containing the fast (10/20 Hz) eddy covariance data for each site for every 30-minute period. These files are timestamped with the time corresponding to the end of the period and are named: • PIANO_EC_FastData_SITENAME_yyyymmdd_HHMM.csv. These sets of files are provided as a single .zip folder for each site which is named according to the site. All timestamps are given in UTC (in seconds since 00:00 UTC 01 January 1970) and denote the end of the averaging period. The following variables can be found in the MetData file: air temperature (ta), relative humidity (rh), atmospheric pressure (pa), precipitation (prec), soil temperature (ts1, ts2, ts3), soil volumetric water content (vwc), soil heat flux from each heat flux plate (shf1, shf2), incoming shortwave radiation (swin), outgoing shortwave radiation (swout), incoming longwave radiation (lwin), outgoing longwave radiation (lwout), wind speed (wspeed, i.e. vector average horizontal wind speed before double rotation), wind direction (wdir) and gust speed (gust). The following variables can be found in the FluxData file: friction velocity (ustar), sensible heat flux (h), latent heat flux (le), carbon dioxide flux (fco2), stability parameter (zeta), turbulent kinetic energy (tke), wind speed (wspeed, i.e. vector average wind speed after double rotation), wind direction (wdir), unrotated vertical wind velocity (wunrot, i.e. before double rotation), the standard deviation of the wind components and temperature (sigu, sigv, sigw, sigt), and dissipation rate of turbulent kinetic energy calculated from u, v and w spectra (epu, epv, epw). The following variables can be found in the RawData files: unrotated lateral, longitudinal and vertical wind components (in m s-1), temperature (in degree C), water vapour concentration (supplied for EC_West and EC_Centre as the mixing ratio (in mmol m-1) and supplied for EC_South and EC_East as the absolute humidity (g m-3) and carbon dioxide mixing ratio (in μmol mol-1) for EC_West and EC_Centre. Note that the absolute value of the water vapour concentration from the krypton hygrometers should not be used. These lateral, longitudinal and vertical wind components are as measured in the co-ordinate system of the sonic anemometers and the angle of installation of the sonic needed to convert to north-south east-west co-ordinates is given in the FluxData file. 6. Publications Data from these flux stations have been included in multiple publications as part of the PIANO project (Haid et al., 2020; Haid et al., 2021; Muschinski et al., 2021; Umek et al., 2021; Umek et al., submitted) as well as publications as part of a related study on turbulent exchange in complex environments (Ward et al., in prep.; Ward et al., submitted). 7. Contact Contact helen.ward(at)uibk.ac.at for any questions regarding the data set. 8. Acknowledgements The PIANO campaign was supported by the Austrian Science Fund (FWF) and the Weiss Science Foundation under Grant P29746-N32. Collection of this dataset was also supported by an FWF Lise Meitner project (M2244-N32) and a research stipend from Innsbruck University. Measurements at IAO are supported by the Bundesministerium für Wissenschaft, Forschung und Wirtschaft (Hochschulraum-Strukturmittel grant), the European Commission for funding ALP-AIR within FP7-PEOPLE and the FWF (P30600_NBL, P33701-N). The PIANO campaign was also supported by KIT IMK-IFU, Austro Control GmbH, Zentralanstalt für Meteorologie und Geodynamik (ZAMG), the Hydrographic Service of Tyrol, Innsbrucker Kommunalbetriebe AG (IKB), Bergisel Betriebsgesellschaft m.b.H., Innsbrucker Nordkettenbahnen Betriebs GmbH, T-Mobile Austria GmbH, Unser Lagerhaus Warenhandelsgesellschaft, PEMA Immobilien GmbH, HTL Anichstraße, Hilton Innsbruck, TINETZ-Tiroler Netze GmbH, Land Tirol, and the communities Patsch and Völs. 9. References Foken T, Wichura B (1996) Tools for quality assessment of surface-based flux measurements. Agric. For. Meteorol. 78: 83-105 doi: 10.1016/0168-1923(95)02248-1 Fratini G, Ibrom A, Arriga N, Burba G, Papale D (2012) Relative humidity effects on water vapour fluxes measured with closed-path eddy-covariance systems with short sampling lines. Agric. For. Meteorol. 165: 53-63 doi: 10.1016/j.agrformet.2012.05.018 Haid M, Gohm A, Umek L, Ward HC, Muschinski T, Lehner L, Rotach MW (2020) Foehn–cold pool interactions in the Inn Valley during PIANO IOP2. Q. J. R. Meteorol. Soc. 146: 1232-1263 doi: 10.1002/qj.3735 Haid M, Gohm A, Umek L, Ward HC, Rotach MW (2021) Cold-air pool processes in the Inn Valley during foehn: A comparison of four cases during PIANO. Boundary Layer Meteorology doi: 10.1007/s10546-021-00663-9 Kaimal JC, Finnigan JJ (1994) Atmospheric Boundary Layer Flows: Their structure and management. Oxford University Press, 289 pp. Karl T et al. (2020) Studying urban climate and air quality in the Alps - The Innsbruck Atmospheric Observatory. Bull. Amer. Meteorol. Soc. doi: 10.1175/BAMS-D-19-0270.1 LI-COR Biosciences (2021) Eddy Covariance Processing Software - version 7.0.7, Available at www.licor.com/EddyPro. Moncrieff JB, Clement R, Finnigan JJ, Meyers T (2004) Averaging, detrending and filtering of eddy covariance time series. In: X Lee, Massman WJ and Law BE (Editors), Handbook of Micrometeorology: a guide for surface flux measurements. Moncrieff JB et al. (1997) A system to measure surface fluxes of momentum, sensible heat, water vapour and carbon dioxide. Journal of Hydrology 188-199: 589-611 Muschinski T, Gohm A, Haid M, Umek L, Ward HC (2021) Spatial heterogeneity of the Inn Valley Cold Air Pool during south foehn: Observations from an array of temperature. Meteorol. Z. 30: 153-168 doi: 10.1127/metz/2020/1043 Schotanus P, Nieuwstadt FTM, Bruin HAR (1983) Temperature measurement with a sonic anemometer and its application to heat and moisture fluxes. Bound.-Layer Meteor. 26: 81-93 doi: 10.1007/bf00164332 Tanner B, Swiatek E, Greene J (1993) Density fluctuations and use of the krypton hygrometer in surface flux measurements. Management of irrigation and drainage systems: integrated perspectives. American Society of Civil Engineers, New York, NY: 945-952 Umek L, Gohm A, Haid M, Ward HC, Rotach MW (2021) Large eddy simulation of foehn-cold pool interactions in the Inn Valley during PIANO IOP2. Quart J Roy Meteorol Soc 147: 944-982 doi: 10.1002/qj.3954 Umek L, Gohm A, Haid M, Ward HC, Rotach MW (submitted) Influence of grid resolution of large-eddy simulations on foehn-cold pool interaction. Quart J Roy Meteorol Soc van Dijk A, Kohsiek W, de Bruin HAR (2003) Oxygen Sensitivity of Krypton and Lyman-α Hygrometers. J. Atmos. Ocean. Technol. 20: 143-151 doi: 10.1175/1520-0426(2003)020&lt;0143:osokal&gt;2.0.co;2 Ward HC, Rotach MW, Gohm A, Graus M, Karl T, Haid M, Umek L, Muschinski T (submitted) Energy and mass exchange at an urban site in mountainous terrain – the Alpine city of Innsbruck. Atmos. Chem. Phys. Ward HC, Rotach MW, Graus M, Karl T, Gohm A, Umek L, Haid M (in prep.) Turbulence characteristics at an urban site in highly complex terrain. Webb EK, Pearman GI, Leuning R (1980) Correction of flux measurements for density effects due to heat and water-vapor transfer. Q. J. R. Meteorol. Soc. 106: 85-100