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Robert Spirig, Christian Feigenwinter, Markus Kalberer, Eberhard Parlow, and Roland Vogt
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Rainer V. J. Hilland, Christian Bernhofer, May Bohmann, Andreas Christen, Marwan Katurji, Gillian Maggs-Kölling, Matthias Krauβ, Jarl A. Larsen, Eugene Marais, Andrea Pitacco, Benjamin Schumacher, Robert Spirig, Nadia Vendrame, and Roland Vogt

Abstract

The Namib Turbulence EXperiment (NamTEX) was a multi-national micrometeorological campaign conducted in the Central Namib Desert to investigate three-dimensional surface layer turbulence and the spatio-temporal patterns of heat transfer between the sub-surface, surface, and atmosphere. The Namib provides an ideal location for fundamental research that revisits some key assumptions in micrometeorology that are implicitly included in the parameterizations describing energy exchange in weather forecasting and climate models: Homogenous flat surfaces, no vegetation, little moisture, and cloud-free skies create a strong and consistent diurnal forcing, resulting in a wide range of atmospheric stabilities.

A novel combination of instruments was used to simultaneously measure variables and processes relevant to heat transfer: A three km fibre-optic distributed temperature sensor (DTS) was suspended in a pseudo-three-dimensional array within a 300 m x 300 m domain to provide vertical cross-sections of air temperature fluctuations. Aerial and ground-based thermal imagers recorded high resolution surface temperature fluctuations within the domain and revealed the spatial thermal imprint of atmospheric structures responsible for heat exchange. High-resolution soil temperature and moisture profiles together with heat flux plates provided information on near-surface soil dynamics. Turbulent heat exchange was measured with a vertical array of five eddy-covariance point measurements on a 21-m mast, as well as by co-located small- and large-aperture scintillometers.

This contribution first details the scientific goals and experimental set-up of the NamTEX campaign. Then using a typical day, we demonstrate i) the coupling of surface layer, surface, and soil temperatures using high-frequency temperature measurements, ii) differences in spatial and temporal standard deviations of the horizontal temperature field using spatially distributed measurements, and iii) horizontal anisotropy of the turbulent temperature field.

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Robert Spirig, Roland Vogt, Jarl Are Larsen, Christian Feigenwinter, Andreas Wicki, Joel Franceschi, Eberhard Parlow, Bianca Adler, Norbert Kalthoff, Jan Cermak, Hendrik Andersen, Julia Fuchs, Andreas Bott, Maike Hacker, Niklas Wagner, Gillian Maggs-Kölling, Theo Wassenaar, and Mary Seely

Abstract

An intensive observation period was conducted in September 2017 in the central Namib, Namibia, as part of the project Namib Fog Life Cycle Analysis (NaFoLiCA). The purpose of the field campaign was to investigate the spatial and temporal patterns of the coastal fog that occurs regularly during nighttime and morning hours. The fog is often linked to advection of a marine stratus that intercepts with the terrain up to 100 km inland. Meteorological data, including cloud base height, fog deposition, liquid water path, and vertical profiles of wind speed/direction and temperature, were measured continuously during the campaign. Additionally, profiles of temperature and relative humidity were sampled during five selected nights with stratus/fog at both coastal and inland sites using tethered balloon soundings, drone profiling, and radiosondes. This paper presents an overview of the scientific goals of the field campaign; describes the experimental setup, the measurements carried out, and the meteorological conditions during the intensive observation period; and presents first results with a focus on a single fog event.

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Mathias W. Rotach, Pierluigi Calanca, Giovanni Graziani, Joachim Gurtz, D. G. Steyn, Roland Vogt, Marco Andretta, Andreas Christen, Stanislaw Cieslik, Richard Connolly, Stephan F. J. De Wekker, Stefano Galmarini, Evgeny N. Kadygrov, Vladislav Kadygrov, Evgeny Miller, Bruno Neininger, Magdalena Rucker, Eva Van Gorsel, Heidi Weber, Alexandra Weiss, and Massimiliano Zappa

During a special observing period (SOP) of the Mesoscale Alpine Programme (MAP), boundary layer processes in highly complex topography were investigated in the Riviera Valley in southern Switzerland. The main focus was on the turbulence structure and turbulent exchange processes near the valley surfaces and free troposphere. Due to the anticipated spatial inhomogeneity, a number of different turbulence probes were deployed on a cross section through the valley. Together with a suite of more conventional instrumentation, to observe mean meteorological structure in the valley, this effort yielded a highly valuable dataset. The latter is presently being exploited to yield insight into the turbulence structure in very complex terrain, and its relation to flow regimes and associated mean flow characteristics. Specific questions, such as a detailed investigation of turbulent exchange processes over complex topography and the validity of surface exchange parameterizations in numerical models for such surfaces, the closure of the surface energy balance, or the definition and meaning of the “boundary layer height,” are investigated using the MAP-Riviera dataset. In the present paper, we provide details on sites and their characteristics, on measurements and observational strategies, and on efforts to guarantee comparability between different instrumentation at different sites, and we include an overview of the available instrumentation. On the basis of preliminary data and first results, the main research goals of the project are outlined.

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Manuela Lehner, C. David Whiteman, Sebastian W. Hoch, Erik T. Crosman, Matthew E. Jeglum, Nihanth W. Cherukuru, Ronald Calhoun, Bianca Adler, Norbert Kalthoff, Richard Rotunno, Thomas W. Horst, Steven Semmer, William O. J. Brown, Steven P. Oncley, Roland Vogt, A. Martina Grudzielanek, Jan Cermak, Nils J. Fonteyne, Christian Bernhofer, Andrea Pitacco, and Petra Klein

Abstract

The second Meteor Crater Experiment (METCRAX II) was conducted in October 2013 at Arizona’s Meteor Crater. The experiment was designed to investigate nighttime downslope windstorm−type flows that form regularly above the inner southwest sidewall of the 1.2-km diameter crater as a southwesterly mesoscale katabatic flow cascades over the crater rim. The objective of METCRAX II is to determine the causes of these strong, intermittent, and turbulent inflows that bring warm-air intrusions into the southwest part of the crater. This article provides an overview of the scientific goals of the experiment; summarizes the measurements, the crater topography, and the synoptic meteorology of the study period; and presents initial analysis results.

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