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Die Entwicklung kostengünstiger Sensoren und die Verfügbarkeit massenhaft vorhandener meteorologischer Messdaten, vorwiegend des Luftdrucks, der Lufttemperatur und der Luftfeuchte, ermöglichen eine räumliche und zeitliche Verdichtung herkömmlicher Messnetze. Dies eröffnet damit neben der Wissenschaft auch Kommunen, Betrieben und anderen Einrichtungen völlig neue Möglichkeiten, z. B. bei der Umweltüberwachung und Beschreibung des Lokalklimas. Die leichte Verfügbarkeit und Bedienung der Sensoren ermöglicht es auch dem Laien, diese zu betreiben und sich an den Messprogrammen zu beteiligen oder sogar an der Auswertung mitzuwirken. Diese neue Möglichkeit der Sammlung und Einbeziehung von Messdaten außerhalb der Standardmessnetze wird als Crowdsourcing bezeichnet. Der Beitrag dient der Vorbereitung einer entsprechenden VDI-Richtlinie und beschreibt die zur Verfügung stehende Sensortechnik, die Sicherung der Datenqualität und die Möglichkeiten der Datenbearbeitung.

The WPL (Webb, Pearman, and Leuning) correction is fully accepted to correct trace gas fluxes like CO2 for density fluctuations due to water vapour and temperature fluctuations for open-path gas analysers. It is known that this additive correction can be on the order of magnitude of the actual flux. However, this is hardly ever included in the analysis of data quality. An example from the Arctic shows the problems, because the size of the correction is a multiple of the actual flux. As a general result, we examined and tabulated the magnitude of the WPL correction for carbon dioxide flux as a function of sensible and latent heat flux. Furthermore, we propose a parameter to better estimate possible deficits in data quality and recommend integrating the quality flag derived with this parameter into the general study of small carbon dioxide fluxes.

It has been repeatedly assumed that Heinz Lettau found the Obukhov length in 1949 independently of Obukhov in 1946. However, it was not the characteristic length scale, the Obukhov length L, but the ratio of height and the Obukhov length (z/L), the Obukhov stability parameter, that he analyzed. Whether Lettau described the parameter z/L independently of Obukhov is investigated herein. Regardless of speculation about this, the significant contributions made by Lettau in the application of z/L merit this term being called the Obukhov–Lettau stability parameter in the future.

Der Boden als untere Randbedingung für Modelle der Ausbreitungsrechnung wird wegen der langsamen Veränderungen nur wenig beachtet. Durch den Klimawandel bedingte stärkere Austrocknung der oberen Bodenschichten und der geringeren Wasserverfügung in der Wurzeltiefe ergeben sich markante Auswirkungen auf die Stabilität der Schichtung in der Atmosphäre. In diesem Artikel werden Temperatur- und Feuchteverhältnisse und die damit im Zusammenhang stehenden physikalischen Prozesse beschrieben, mit denen mögliche Auswirkungen auf atmosphärische Prozesse besser abgeschätzt werden können.

Quantitative knowledge of the surface energy balance is essential for the prediction of weather and climate. However, a multitude of studies from around the world indicate that the turbulent heat fluxes are generally underestimated using eddy-covariance measurements, and hence, the energy balance is not closed. This energy-balance-closure problem, which has been heavily covered in the literature for more than 25 years, is the topic of the present review, in which we provide an overview of the potential reason for the lack of closure. We demonstrate the effects of the diurnal cycle on the energy balance closure, and address questions with regard to the partitioning of the energy balance residual between the sensible and the latent fluxes, and whether the magnitude of the flux underestimation can be predicted based on other variables typically measured at micrometeorological stations. Remaining open questions are discussed and potential avenues for future research on this topic are laid out. Integrated studies, combining multi-tower experiments and scale-crossing, spatially-resolving lidar and airborne measurements with high-resolution large-eddy simulations, are considered to be of critical importance for enhancing our understanding of the underlying transport processes in the atmospheric boundary layer.

A maritime pine plantation in Central Portugal that has been continuously monitored using the eddy-covariance technique for carbon fluxes since a wildfire in 2017, was significantly affected by two storms during December 2019 that resulted in a large-sale windthrow. This study analyses the impacts of this windthrow on the aerodynamic characteristics of zero-plane displacement and roughness length, and, ultimately, their implications for the turbulent fluxes. The turbulent fluxes were only affected to a minor degree by the windthrow, but the footprint area of the flux tower changed markedly, so that the target area of the measurements had to be re-determined.

Strong temperature gradients with stable stratification immediately above the surface are typical for radiation cooling, but near-surface temperature inversions (hereinafter referred to as inversions) have hardly been studied. Both phenomena are examined in more detail by means of measurements in the Caspian Sea and Antarctica and compared with measurements made by other authors. For this purpose, tests for decoupling are applied in the first case. In the second case, the inversions can be explained in the context of counter-gradient fluxes and turbulent Prandtl numbers greater than one.

Der Datensatz des Surface Heat Budget of the Arctic Ocean (SHEBA) Experimentes 1997/98 wird häufig für die Berechnung von universellen Funktionen für stabile Schichtung herangezogen. Für eine nicht-iterative Modellierung (Louis-Ansatz) können diese Funktionen neu berechnet werden. Allerdings haben diese Funktionen viele empirische Faktoren, die sich aus der Anpassung an den ursprünglichen Datensatz ergeben. Ein interessantes Ergebnis bei der Analyse der Daten des SHEBA-Experimentes ist, dass die Daten für die oberen Messpunkte des Experiments einer lokalen Skalierung mit den klassischen universellen Funktionen folgen, während die Daten der unteren Messpunkte eine große Streuung aufweisen. Somit könnten für den oberen Teil des Profils ein allgemein üblicher Louis-Ansatz verwendet werden. Es ist davon auszugehen, dass unter besonderen Bedingungen der untere Teil des Profils vom oberen Teil entkoppelt ist, wie es bei anderen Experimenten bereits gezeigt werden konnte. Ein einfacher Test für die Entkopplung durch Vergleich der experimentellen Daten mit einem hydrodynamischen Modellansatzes wird in der Präsentation gezeigt. Es wird daher empfohlen, den SHEBA Datensatz auf Entkopplung zu testen und eine wahrscheinlich viel einfachere universelle Funktion zu erstellen. Allerdings ist der Umgang mit entkoppelten Situationen noch im Bereich der Forschung. Es ist allerdings für die meisten Fälle zu erwarten, dass bei Berücksichtigung der Entkopplung kleinere Flüsse bestimmt würden.

The differences between one classical and three state-of-the-art formulations of the mass density of humid air were quantified. Here, we present both the calculi for direct determination of the humid-air mass density employing the virial form of the thermodynamic equation of state, and a sufficiently accurate look-up-table for the quick-look determination of the humid-air mass density, which is based on the advanced Thermodynamic Equation of Seawater 2010.

The WPL (Webb, Pearman, and Leuning) correction is fully accepted to correct trace gas fluxes like CO2 for density fluctuations due to water vapor and temperature fluctuations for open-path gas analysers. It is known that this additive correction can be in the order of magnitude of the actual flux. However, this is hardly ever included in the analysis of data quality. An example from the Arctic shows the problems, because the size of the correction is a multiple of the actual flux. As a general result, we examined and tabulated the magnitude of the WPL correction for carbon dioxide flux as a function of sensible and latent heat flux. Furthermore, we propose a parameter to better estimate possible deficits in data quality and recommend integrating the quality flag derived with this parameter into the general study of small carbon dioxide fluxes.

With 450,000 km2 Kobresia (syn. Carex) pygmaea dominated pastures in the eastern Tibetan highlands are the world's largest pastoral alpine ecosystem forming a durable turf cover at 3000–6000 m a.s.l. Kobresia's resilience and competitiveness is based on dwarf habit, predominantly below-ground allocation of photo assimilates, mixture of seed production and clonal growth, and high genetic diversity. Kobresia growth is co-limited by livestock-mediated nutrient withdrawal and, in the drier parts of the plateau, low rainfall during the short and cold growing season. Overstocking has caused pasture degradation and soil deterioration over most parts of the Tibetan highlands and is the basis for this man-made ecosystem. Natural autocyclic processes of turf destruction and soil erosion are initiated through polygonal turf cover cracking, and accelerated by soil-dwelling endemic small mammals in the absence of predators. The major consequences of vegetation cover deterioration include the release of large amounts of C, earlier diurnal formation of clouds, and decreased surface temperatures. These effects decrease the recovery potential of Kobresia pastures and make them more vulnerable to anthropogenic pressure and climate change. Traditional migratory rangeland management was sustainable over millennia, and possibly still offers the best strategy to conserve and possibly increase C stocks in the Kobresia turf. (Less)

The vertical and horizontal structure of the atmosphere and the typical timescales of atmospheric phenomena and processes largely determine the design and performance of atmospheric measurement techniques. Each meteorological process can be characterized by typical spatial and temporal scales. This is based on the spectral organization of atmospheric turbulence and on wavelike processes, where relevant wavelength ranges (spatial dimensions) relate to distinct durations (frequencies). The development of a suitable measurement strategy for any observational task should therefore be based on a careful consideration of the specific processes to be described and resolved. This should govern the decision on, e.g., the measurement range, the measurement levels / range resolution, the horizontal spacing of sensors or sites, the measurement frequencies and averaging times, and sensor characteristics such as response time, resolution, accuracy, sensitivity etc. When using in-situ technologies, a wide variety of measuring platforms can be used, from the classic weather station arrangements, masts, and towers to balloons or controlled airborne platforms (including both manned and remotely piloted aerial vehicles). With remote sensing technology, various measurement systems (both passive and active) are available in terms of measured variables, pointing and scanning options, altitude range, spatial and temporal resolution. It will be shown that the extensive overview tables in the recently published Springer Handbook of Atmospheric Measurements can provide guidance on how in-situ and remote sensing techniques can be optimally used for both routine observations and process studies (field campaigns) for a large variety of applications and how measurement concepts, strategies and networks can be designed.

Extensive studies are available that analyse time series of carbon dioxide and water flux measurements of FLUXNET sites over many years and link these results to climate change such as changes in atmospheric carbon dioxide concentration, air temperature and growing season length and other factors. Many of the sites show trends to a larger carbon uptake. Here we analyse time series of net ecosystem exchange, gross primary production, respiration, and evapotranspiration of four forest sites with particularly long measurement periods of about 20 years. The regular trends shown are interrupted by periods with higher or lower increases of carbon uptake. These breakpoints can be of very different origin and include forest decline, increased vegetation period, drought effects, heat waves, and changes in site heterogeneity. The influence of such breakpoints should be included in long-term studies of land-atmosphere exchange processes.

The eddy-covariance method represents the only direct way to measure the turbulent fluxes of momentum, temperature, trace gases, and particles between the land surface and the atmosphere. It is a direct measurement of the net carbon-dioxide budget and dry deposition. For that purpose, it is widely used in networks of long-term ecosystem observatories around the world and is the centerpiece of intensive field campaigns investigating biosphere–atmosphere exchange processes. The instrumentation typically consists of a 3-D sonic anemometer/thermometer and one or more additional gas analyzers that are able to measure the high-frequency fluctuations of the scalar to be transported. These instruments are mounted on a meteorological mast to sample the turbulent field under the assumption that eddies are carried along with the mean wind. Further prerequisites of the method are horizontal homogeneity, steady-state conditions and well-developed turbulence. For successful application of the method, a series of quality tests and flux corrections is required, which will be presented together with commonly used instrumentation and postprocessing software. Moreover, we will provide a historical overview and provide guidelines for site selection and setup and the necessary maintenance procedures.

Actual and maximum rates of evaporation (E) and evapotranspiration (ET) are important to the operation of atmospheric process models and for hydrologic and agricultural modeling. Because rates of evapotranspiration are limited by both the available energy at the surface and the availability of water, a variety of techniques can be used for estimation. The near-maximum ET under nonlimiting water availability can be closely approximated by the reference ET concept using near-surface observations of air temperature, humidity, wind speed, and solar radiation via the Penman–Monteith or a similar method. The determination of actual rates of ET when water is limiting demands a more complex approach, and often requires daily (or even more frequent) water balance data for the upper soil layers. An alternative is to measure the actual ET using micrometeorological techniques such as the eddy-covariance and Bowen ratio methods. The application of standardized calculations for the reference ET is discussed, as are iterative surface energy balance–aerodynamic combinations, which are useful in conditions where water is limiting.

Measurements in the atmosphere differ from measurements in other media because of the thermodynamic and radiative properties of air (e. g., low density, low heat capacity, and transparency to a large part of the electromagnetic spectrum) and the fact that the air is almost always in (often turbulent) motion. The vertical and horizontal distributions of meteorological elements and the spatial and temporal scales of processes strongly influence the selection of appropriate measurement methods and devices. This chapter gives a brief overview of the different ways of classifying atmospheric measurements, the relevant states and processes that influence measurements in the atmosphere, and basic measurement techniques (including some fundamental aspects of the performance and interpretation of these techniques). It focuses in particular on the so-called atmospheric boundary layer, since most measurements are performed in this region and most human activities take place there.

Meteorological measurements are performed by various types of stations, including synoptic weather and climate monitoring stations, agrometeorological stations, and stations that require meteorological data for other purposes, such as to monitor traffic or air pollution or for private use. This chapter describes the history of stations that carry out atmospheric measurements, as well as recent developments in this field, mostly involving the use of new technologies to measure meteorological parameters. The specifics of the installation of stations for different purposes and the main parameters measured are summarized. The accuracy of the atmospheric measurements and the sensor system maintenance required vary depending on the intended application of the data. Therefore, the requirements for the measured meteorological parameters may differ from those defined in the corresponding parameter-specific chapters of this Handbook.

Quality assurance and control is fundamental to ensuring the scientific usefulness of atmospheric measurements. Quality is relevant to all stages of data generation, from site selection and system design to all physical components of a measurement system (including their calibration, operation, and maintenance) as well as data handling and processing. This chapter describes useful practices and techniques for a comprehensive quality management program that is designed to minimize problems and quantify quality along the entire data generation chain. Widely applicable methods of post-field data quality control for instrumented (in-situ), visual, and remotely sensed observations are presented. The chapter concludes with example applications of QA/QC in measurement networks, and a discussion of common data problems. Finally, future developments in quality assurance and quality control are presented.

CO2 release from thawing permafrost is both a consequence of, and a driver for, global warming, making accurate information on the Arctic carbon cycle essential for climate predictions. Eddy covariance data obtained from Bayelva (Svalbard) in 2015, using well‐established processing and quality control techniques, indicate that most of the annual net CO2 uptake is due to high CO2 flux events in winter that are associated with strong winds and probably relate to technical limitations of the gas analyzer. Emission events may relate to either (unidentified) instrumental limitations or to physical processes such as CO2 advection. Excluding the high winter uptake events yields an annual CO2 budget close to zero; whether or not these events are included can, therefore, have a considerable effect on carbon budget calculations. Further investigation will be crucial to pinpoint the factors causing these high CO2 flux events and to derive scientifically substantiated flux processing standards.

Wildfires typically affect multiple forest ecosystem services, with carbon sequestration being affected both directly, through the combustion of vegetation, litter and soil organic matter, and indirectly, through perturbation of the energy and matter balances. Post-fire carbon fluxes continue to be poorly studied at the ecosystem scale, especially during the initial window of disturbance when changes in environmental conditions can be very pronounced due to the deposition and subsequent mobilization of a wildfire ash layer and the recovery of the vegetation. Therefore, an eddy-covariance system was installed in a burnt area as soon as possible after a wildfire that had occurred on 13 August 2017 and has been operating from the 43rd post-fire day onwards. The study site was specifically selected in a Mediterranean woodland area dominated by maritime pine stands with a low stature that had burned at high severity. The carbon fluxes recorded during the first post-fire hydrological year tended to be very low so that a specific procedure for the analysis and, in particular, gap filling of the eddy-covariance data had to be developed. Still, the carbon fluxes varied noticeably during the first post-fire year, broadly revealing five consecutive periods. During the rainless period after the wildfire, fluxes were reduced but, somewhat surprisingly, indicated a net assimilation. With the onset of the autumn rainfall, fluxes increased and corresponded to a net emission, while they became insignificant with the start of the winter. From the midwinter onwards, net fluxes became negative, indicating a weak carbon update during spring followed by a strong uptake during summer. Over the first post-fire year as a whole, the cumulative net ecosystem exchange was −347 g C m−2, revealing a relatively fast recovery of the carbon sink function of the ecosystem. This recovery was mainly due to understory species, both resprouter and seeder species, since pine recruitment was reduced. Specific periods during the first post-fire year were analyzed in detail to improve process understanding. Perhaps most surprisingly, dew formation and, more specifically, its subsequent evaporation were found to play a role in carbon emissions during the rainless period immediately after fire, involving a mechanism distinct from degassing the ash–soil pores by infiltrating water. The use of a special wavelet technique was fundamental for this inference.

While stationary measurements can be performed relatively frequently, they do not permit detailed spatial analyses of meteorological variables, particularly air temperature. This problem can be resolved by making the sensor mobile and then taking measurements at a variety of locations within the area of interest. Mobile measurements have therefore been used in climatological research since the early twentieth century. Due to improvements in and the miniaturization of the relevant measurement technologies, mobile measurements have undergone a renaissance since the 1970s. Urban climatology has become an important field of great scientific interest. The realization that the measurements of just one urban weather station—generally located (in line with the recommendations of the World Meteorological Organization) on short-cut lawn—is not sufficient to represent all of the climates present in an urban area has led to the acceptance of and even the need for mobile measurements taken on cars, bikes, or buses. New methodologies have been implemented, and advances in digital measurement and storage on data loggers have made mobile measurements an important tool for spatially distributed studies of air temperature, air humidity, and air pollution.

This study investigates turbulence characteristics as observed at a 200 m tall mast at a hilly and complex site. It thereby concentrates on turbulence statistics, which are important for the site suitability analysis of a wind turbine. The directional variations in terrain are clearly reflected in the observed turbulence intensities and drag. Integral turbulence statistics showed some variations from their typical flat terrain values. Footprint modelling was used to model the area of effect and to relate the observed turbulence characteristics to the ruggedness and roughness within the estimated fetch area. Among the investigated turbulence quantities, the normalised standard deviation of the wind velocity along the streamlines showed the highest correlation with the effective roughness and ruggedness within the footprint followed by the normalised friction velocity and normalised standard deviation of the vertical wind speed. A differentiation between the effects of roughness and ruggedness was not possible, as forest cover and complex orography are highly correlated at the investigated site. An analysis of turbulence intensity by wind speed indicated a strong influence of atmospheric stability. Stable conditions lead to an overall reduction in turbulence intensity for a wind speed range between approx. 6–12 m s−1 when compared to neutral stratification. The variance of the horizontal wind speed strongly varied over the height range which is typical for a modern wind turbine and was in the order of the differences between different standard turbulence classes for wind turbines.

On 20 March 2015, a total solar eclipse occurred over Ny-Alesund (78.9° N, 11.9° E), Svalbard, under ideal conditions with clear sky. The cycle of the radiation fluxes is comparable with other experiments during eclipses, with even the upward longwave radiation showing significant changes, with a delay to the shortwave radiation and a slowly linear increase after the totality. Also, under polar conditions, an increase of the wind velocity before and a decrease after the totality was found, which is an indicator of the generation of an “Eclipse cyclone”. This change of the wind direction generated a local wind system with a near-surface-layer katabatic flow. During the eclipse, a remarkably large sensible heat flux was observed. The turbulent fluxes were analysed using a wavelet technique with 1-minute time resolution, which is the ideal method for investigating these highly non-steady conditions. No influences on the boundary layer structure as measured with radiosondes were found, with the exception of a wind direction change during the eclipse cyclone below the shallow inversion layer.

This study aimed at quantifying potential negative effects of instrument heating to improve eddy covariance flux data quality in cold environments. Our overarching objective was to minimize heating-related bias in annual CO2 budgets from an Arctic permafrost system. We used continuous eddy-covariance measurements covering three full years within an Arctic permafrost ecosystem with parallel sonic anemometers operation with activated heating and without heating as well as parallel operation of open- and closed-path gas analyzers, the latter serving as a reference. Our results demonstrate that the sonic anemometer heating has a direct effect on temperature measurements while the turbulent wind field is not affected. As a consequence, fluxes of sensible heat are increased by an average 5 W m-2 with activated heating, while no direct effect on other scalar fluxes was observed. However, the biased measurements in sensible heat fluxes can have an indirect effect on the CO2 fluxes in case they are used as input for a density-flux WPL correction of an open-path gas analyzer. Evaluating the self-heating effect of the open-path gas analyzer by comparing CO2 flux measurements between open- and closed-path gas analyzers we found systematically higher CO2 uptake recorded with the open-path sensor, leading to a cumulative annual offset of 96 gC m-2, which was not only the result of the cold winter season but also due to substantial self-heating effects during summer. With an inclined sensor mounting, only a fraction of the self-heating correction for vertically mounted instruments is required.