Erweiterung der `Localized Near Field' Theorie zur Bestimmung von Quellstärken bei beliebiger thermischer Schichtung in einem Waldbestand

The energy and mass budget of the atmosphere is mainly determined by the exchange at the earths surface. Here plant canopies play a major role. The 'Localized Near Field Theorie' (LNF) of Raupach (1989) describes the relation between concentration profiles and source/sink profiles inside the plant canopy. This work describes a general method based on the LNF to calculate source distributions from measured concentration profiles inside a plant canopy. The LNF is used for the first time to examine the effects of the so called roughness sublayer. To apply the LNF during arbitrary thermal stratification it is necessary to find parametrisations for the input parameters standard deviation of vertical velocity and Lagrangian integral time scale. These are derived from values measured inside a pine forest. Using these parametrisations the distribution of heat sources inside the forest canopy is calculated from measured temperature profiles.Energie- und Stoffumsätze an der Erdoberfläche bestimmen den Energie- und Stoffhaushalt der Atmosphäre. Dabei spielen Pflanzenbestände eine wichtige Rolle. Die 'Localized Near Field Theorie' (LNF) nach Raupach (1989) beschreibt wie Konzentrationsprofile im Pflanzenbestand und die Verteilung der Quellen dort in Beziehung zueinander stehen. In der vorliegenden Arbeit wird ein allgemeines Verfahren auf Basis der LNF zur Berechnung von Quellprofilen aus gemessenen Konzentrationsprofilen vorgestellt. Erstmals werden die Effekte in der sogenannten Rauhigkeitsschicht Mithilfe der LNF untersucht. Um die LNF auf beliebige thermische Schichtung anwenden zu können müssen Parametrisierungen für die Eingangsparameter Standardabweichung der Vertikalgeschwindigkeit und die integrale Lagrangesche Zeitskala gefunden werden. Dies geschieht anhand von in einem Waldbestand gemessenen Werten. Mit dieser Parametrisierung läßt sich schließlich die Verteilung der Wärmequellen im Wald aus gemessenen Temperaturprofilen bestimmen

Erweiterung der `Localized Near Field' Theorie zur Bestimmung von Quellstärken bei beliebiger thermischer Schichtung in einem Waldbestand

The energy and mass budget of the atmosphere is mainly determined by the exchange at the earths surface. Here plant canopies play a major role. The 'Localized Near Field Theorie' (LNF) of Raupach (1989) describes the relation between concentration profiles and source/sink profiles inside the plant canopy. This work describes a general method based on the LNF to calculate source distributions from measured concentration profiles inside a plant canopy. The LNF is used for the first time to examine the effects of the so called roughness sublayer. To apply the LNF during arbitrary thermal stratification it is necessary to find parametrisations for the input parameters standard deviation of vertical velocity and Lagrangian integral time scale. These are derived from values measured inside a pine forest. Using these parametrisations the distribution of heat sources inside the forest canopy is calculated from measured temperature profiles.Energie- und Stoffumsätze an der Erdoberfläche bestimmen den Energie- und Stoffhaushalt der Atmosphäre. Dabei spielen Pflanzenbestände eine wichtige Rolle. Die 'Localized Near Field Theorie' (LNF) nach Raupach (1989) beschreibt wie Konzentrationsprofile im Pflanzenbestand und die Verteilung der Quellen dort in Beziehung zueinander stehen. In der vorliegenden Arbeit wird ein allgemeines Verfahren auf Basis der LNF zur Berechnung von Quellprofilen aus gemessenen Konzentrationsprofilen vorgestellt. Erstmals werden die Effekte in der sogenannten Rauhigkeitsschicht Mithilfe der LNF untersucht. Um die LNF auf beliebige thermische Schichtung anwenden zu können müssen Parametrisierungen für die Eingangsparameter Standardabweichung der Vertikalgeschwindigkeit und die integrale Lagrangesche Zeitskala gefunden werden. Dies geschieht anhand von in einem Waldbestand gemessenen Werten. Mit dieser Parametrisierung läßt sich schließlich die Verteilung der Wärmequellen im Wald aus gemessenen Temperaturprofilen bestimmen

Clear-air lidar dark band

This paper illustrates measurements carried out by the Raman lidar BASIL in the frame of HOPE, revealing the presence of a clear-air dark band phenomenon (i.e. the appearance of a minimum in lidar backscatter echoes) in the upper portion of the convective boundary layer. The phenomenon is clearly distinguishable in the lidar backscatter echoes at 1064 nm. This phenomenon is attributed to the presence of lignite aerosol particles advected from the surrounding open pit mines in the vicinity of the measuring site

Clear-air lidar dark band

Abstract. This paper illustrates measurements carried out by the Raman lidar BASIL in the frame of the HD(CP)2 Observational Prototype Experiment (HOPE), revealing the presence of a clear-air dark band phenomenon (i.e. a minimum in lidar backscatter echoes) in the upper portion of the convective boundary layer. The phenomenon is clearly distinguishable in the lidar backscatter echoes at 532 and 1064 nm, as well as in the particle depolarisation data. This phenomenon is attributed to the presence of lignite aerosol particles advected from the surrounding open pit mines in the vicinity of the measuring site. The paper provides evidence of the phenomenon and illustrates possible interpretations for its occurrence

Long-Term Observations and High-Resolution Modeling of Midlatitude Nocturnal Boundary Layer Processes Connected to Low-Level Jets

Low-level-jet (LLJ) periods are investigated by exploiting a long-termrecord of ground-based remote sensing Doppler wind lidar measurements supported by tower observations and surface flux measurements at the Julich Observatory for Cloud Evolution (JOYCE), a midlatitude site in western Germany. LLJs were found 13% of the time during continuous observations over more than 4 yr. The climatological behavior of the LLJs shows a prevailing nighttime appearance of the jets, with a median height of 375 m and a median wind speed of 8.8 ms(-1) at the jet nose. Significant turbulence below the jet nose only occurs for high bulk wind shear, which is an important parameter for describing the turbulent characteristics of the jets. The numerous LLJs (16% of all jets) in the range of wind-turbine rotor heights below 200 m demonstrate the importance of LLJs and the associated intermittent turbulence for wind-energy applications. Also, a decrease in surface fluxes and an accumulation of carbon dioxide are observed if LLJs are present. A comprehensive analysis of an LLJ case shows the influence of the surrounding topography, dominated by an open pit mine and a 200-m-high hill, on the wind observed at JOYCE. High-resolution large-eddy simulations that complement the observations show that the spatial distribution of the wind field exhibits variations connected with the orographic flow depending on the wind direction, causing high variability in the long-term measurements of the vertical velocity.Peer reviewe

EUREC4A's Maria S. Merian ship-based cloud and micro rain radar observations of clouds and precipitation

As part of the EUREC4A field campaign, the research vessel Maria S. Merian probed an oceanic region between 6° N and 13.8° N and 51° W to 60° W for approximately 32 days. Trade wind cumulus clouds were sampled in the trade-wind alley region east of Barbados as well as in the transition region between the trades and the intertropical convergence zone, where the ship crossed some mesoscale oceanic eddies. We collected continuous observations of cloud and precipitation profiles at unprecedented vertical resolution (7–10 m in the first 3000 m) and high temporal resolution (1–3 s) using a W-band radar and micro-rain radar (MRR-PRO), installed on an active stabilization platform to reduce the impact of ship motions on the observations. The paper describes the ship motion correction algorithm applied to the Doppler observations to extract corrected hydrometeors vertical velocities and the algorithm created to filter interference patterns in the MRR-PRO observations. Radar reflectivity, mean Doppler velocity, spectral width and skewness for W-band and attenuated reflectivity, mean Doppler velocity and rain rate for MRR-PRO are shown for a case study to demonstrate the potential of the high resolution adopted. As non-standard analysis, we also retrieved and provided liquid water path (LWP) from the 89 GHz passive channel available on the W-band radar system. All datasets and hourly and daily quicklooks are publically available. Data can be accessed and basic variables can be plotted online via the intake catalog of the online book "How to EUREC4A".Postprint (author's final draft

Heat and moisture budgets from airborne measurements and high-resolution model simulations

High-resolution simulations with a mesoscale model are performed to estimate heat and moisture budgets of a well-mixed boundary layer. The model budgets are validated against energy budgets obtained from airborne measurements over heterogeneous terrain in Western Germany. Time rate of change, vertical divergence, and horizontal advection for an atmospheric column of air are estimated. Results show that the time trend of specific humidity exhibits some deficiencies, while the potential temperature trend is matched accurately. Furthermore, the simulated turbulent surface fluxes of sensible and latent heat are comparable to the measured fluxes, leading to similar values of the vertical divergence. The analysis of different horizontal model resolutions exhibits improved surface fluxes with increased resolution, a fact attributed to a reduced aggregation effect. Scale-interaction effects could be identified: while time trends and advection are strongly influenced by mesoscale forcing, the turbulent surface fluxes are mainly controlled by microscale processes

Filling the observational gap in the Atacama Desert with a new network of climate stations

The Atacama Desert in northern Chile is the driest place on Earth. In this region, climate models are subject to large biases, especially precipitation is significantly overestimated. Meteorological observations in the region are sparse and limited to inhabited places at the coast or the foothills of the Andes. To fill this gap, a new network of 15 automatic weather stations has been established beginning April 2017. These stations do not only record standard meteorological parameters such as temperature, humidity and wind, but also soil temperatures and humidity, additionally a wetness sensor gives information about the occurrence of fog. Data from the first year(s) of this network show a very regular wind pattern with easterly winds during night and morning and westerly winds from noon to evening. This wind transports moisture from the Pacific Ocean into the desert which forms fog during the night which may account for a moisture supply on the order of the rare precipitation events in the region. A few precipitation events have been observed during the first years. The recorded data allows to distinguish between different sources: convective precipitation above the Altiplano, which in some cases extended to the western slope of the Andes, and troughs extending from mid latitudes to the region, directing moist air from the pacific into the region. Both of these mechanisms brought only some tenths of mm precipitation. In one case the accidental combination of flow over the Andes and a weak cut-off low above the Pacific led to moisture convergence off the coast of northern Chile and initiated a convective system moving south-east ward which brought for the region extreme precipitation of 3-10 mm