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In our study, we analysed a period from 2003 to 2012 with micrometeorological data measured at a boundary-layer field site operated by the Lindenberg Meteorological Observatory – Richard-Asmann-Observatory of the German Meteorological Service (DWD). Amongst others, these data consist of real evapotranspiration (ETr) rates measured by eddy covariance and soil water contents determined by time domain reflectometry. Measured ETr and soil water contents were compared with those simulated by a simple soil–vegetation–atmosphere transfer (SVAT) scheme consisting of the FAO56 Penman-Monteith equation and the soil water flux model Hydrus-1D. We applied this SVAT scheme using uncompensatory and compensatory root water uptake (RWU). Soil water contents and ETr rates calculated using uncompensatory RWU showed an acceptable fit to the measured ones. In comparison, the use of compensatory RWU resulted in lower model performance due to higher deviations between measured and simulated soil moisture values and ETr...

The study analyses a 2-year period of hourly rates of real evapotranspiration (ETr) derived from eddy covariance measurements and soil water contents at depths from 8 to 90 cm, monitored by time do...

We introduce a simple, physically consistent method to predict nocturnal wind and temperature profiles from external forcing parameters such as the geostrophic wind. As an indicator of the radiative ‘forcing’ the net longwave radiative cooling is used as a proxy. Surface fluxes are expressed in terms of these parameters by coupling an Ekman model to a rudimentary surface energy balance. Additionally the model assumes validity of Monin-Obukhov similarity in order to predict near-surface wind and temperature profiles up to a height equal to the Obukhov length. The predictions are validated against an independent dataset that covers 11-years of observations at Cabauw, The Netherlands. It is shown that the characteristic profiles in response to external forcings are well-captured by the conceptual model. For this period the observational climatology is in close agreement with ECMWF re-analysis data. As such, the conceptual model provides an alternative tool to giving a first-order estimate of the nocturnal wind and temperature profile near the surface in cases when advanced numerical or observational infrastructure is not available.

The transport of atmospheric pollutants in the planetary boundary layer over East Germany was studied during the SADE-94 experiment using airborne and ground-based observations of meteorological and chemical parameters. Strong jump-like changes of the SO2 and NOx mixing ratios measured at Melpitz, a rural site about 50 km northeast and 90 km west of two major lignite-coal mining and industrial areas, demonstrate the influence of high emissions and mesoscale transport on the air quality at a rural location. Data of two days with prevailing winds from east and southwest, respectively, were used to determine the origin of plumes from their characteristic species or their specific trace gas concentration ratios. An attempt has been made to establish emitter–receptor relationships between the emittants and the measured plumes of SO2 and NOx. It is shown that not only in complex terrain, where trace gas dispersion is guided in many cases by the terrain structure but also over flat country sites the trace gases of single-point sources are traceable over distances of more than 100 km in the PBL. Furthermore 75 km downstream the source area surface concentrations of air pollutants caused by downdrafts are measured, which exceed 25% of the value registered direct in the lee of the source. Data of a third day describe the mixing ratio of air pollutants in the convective boundary layer at Melpitz. NOx and SO2 are used to depict bottom–up and top–down mixing processes mainly in the entrainment zone. Under low-wind conditions, neutral or stable PBL and a capping inversion single air pollution plumes are detectable over long ranges in time (>6 h) and space (>100 km) over flat terrain. The characteristic features of the plumes keep unchanged during transport. So high stacks only displace the problem of near-surface air pollution from the source region to areas far downstream.

Measurements are presented of the development of the convective boundary layer in the transition zone from the Upper Rhine valley to the Northern Black Forest during one special observation period of the TRACT campaign conducted in September 1992. The data used in this study were obtained from airborne instruments as well as from ground-based stations. The analysed boundary layer structure shows a strong influence of the underlying terrain. Until noon, a nearly terrain following capping inversion developed. However, advective processes proved to play an important role in the boundary layer structure over the hilly terrain. So, the large-scale air flow caused suppression of the convective boundary layer growth at the mountain ridge by forcing the capping inversion towards the elevation of the terrain. A mountain induced secondary circulation system was observed on the western facing slopes of the Black Forest. This secondary circulation system affected the heat budget and therefore the growth of the convective boundary layer over the mountain slopes. The advection of cold air by up-slope winds lowered the heating rate near the ground and was able to generate an inversion above the up-slope wind layer. In the late afternoon, the terrain following structure of the capping inversion diminished and the capping inversion tended to form a horizontal plane. Prognostic formulae for boundary layer growth are discussed for different sites of the terrain. While in the valley good agreement is found between calculated and observed boundary layer depths, the calculations for the mountain ridge overestimate the obserations by up to a factor of 5 if a boundary layer growth equation derived for homogeneous terrain is used.

The paper presents selected results from a field experiment which has been carried out in the Erzgebirge Mountains at the frontier between Saxony (Germany) and the Czech Republic in February and March, 1995. This campaign was aimed to investigate certain aspects of the transport of sulphur dioxide (SO2) from industrial sources in Northern Bohemia across the Erzgebirge under conditions of prevailing southeasterly flow. The regional distribution of SO2 in the Upper Erzgebirge is shown, and the influence of meteorological conditions on observed ground-level concentrations is discussed. DOAS measurements are used to assess the representativeness of ground-level concentration measurements carried out at some valley sites within the Saxonian air quality monitoring network. Estimation of the magnitude of the SO2-flux is attempted based on aircraft concentration measurements.

Sodar measurements have been used to estimate the mixing height for about 20 yr, nevertheless the issue is still the subject of controversial discussion. The paper attempts to critically examine the methods and results of mixing height determination from sodar data that have been reported in the literature. The theoretical base, the methods suggested, the automatization of algorithms, and the intercomparison of sodar-based mixing height values with data from independent measurements and models are briefly discussed. An assessment is given of sodar capabilities in comparison with other profiling techniques. It is concluded that sodar data may be used to derive reliable mixing height information in many situations which are of special relevance for environmental monitoring, namely in stagnant weather situations with low mixing height values between about 50 and 500–1000 m, depending on the type of the sodar. However, the algorithms available up to now for their automatic evaluation appear not yet reliable enough to be recommended for operational purposes, and a control of the output by a trained analyst is advisable. Simultaneous operation of sodars and other remote sensing systems (lidar, wind profiler) is shown to be a promising way to overcome the range limitations of sodars and to allow continuous mixing height estimation throughout the complete diurnal cycle.

Results from a field campaign that has been performed in summer 1993 to study photochemical pollution in the Harz Mountains, Germany, are presented. During a five-day, fair-weather period, a steady increase of the daily maximum ozone concentration up to values around 100 ppb was observed in the Harz region. The results of ozone measurements at two surface stations (404 m a.s.l. and 1142 m a.s.l., respectively) are discussed with respect to both the transport and dispersion conditions during the period and the local structure of the atmospheric boundary layer. Remarkable similarities in the time series of the ozone mixing ratio at the two places have been found which indicate some kind of quasi-homogeneity even over complex terrain. The trace gas concentrations at the top of Mt. Brocken, the highest summit of the Harz Mountains, are shown to be strongly influenced by vertical transports due to convection (at daytime) and subsidence of inversion layers (at nighttime).

The Baltic Sea Experiment (BALTEX) is one of the five continental-scale experiments of the Global Energy and Water Cycle Experiment (GEWEX). More than 50 research groups from 14 European countries are participating in this project to measure and model the energy and water cycle over the large drainage basin of the Baltic Sea in northern Europe. BALTEX aims to provide a better understanding of the processes of the climate system and to improve and to validate the water cycle in regional numerical models for weather forecasting and climate studies. A major effort is undertaken to couple interactively the atmosphere with the vegetated continental surfaces and the Baltic Sea including its sea ice. The intensive observational and modeling phase BRIDGE, which is a contribution to the Coordinated Enhanced Observing Period of GEWEX, will provide enhanced datasets for the period October 1999-February 2002 to validate numerical models and satellite products. Major achievements have been obtained in an improved understanding of related exchange processes. For the first time an interactive atmosphere-ocean-land surface model for the Baltic Sea was tested. This paper reports on major activities and some results.

Estimation of the mixing height is one of the most common applications of SODAR data for more than twenty years and SODAR has been shown to provide reliable results under a great variety of meteorological and site conditions. Nevertheless there are still some unsolved questions. The paper gives a brief review of results obtained during the last two decades. Additionally some of the open problems are discussed in more detail. These are the determination of the stable boundary layer height from digitized SODAR data, its relation to other common height scales, its parameterization, and finally the estimation of the height of a deep convective boundary layer, exceeding the SODAR probing range.

Remote sensing forms an essential part of the MOL-RAO boundary-layer measurements. Special emphasis will be put on the place of scintillometry as a technique to derive the sensible turbulent heat flux at the regional scale thus bridging the gap between local micrometeorological measurements and the typical spatial resolution of regional-scale meteorological models and of satellite images.

An improved non-stationary two-layer model is presented for the simulation of wind speed maxima in the nocturnal boundary layer. The model is based on the idea of Blackadar (1957), who proposed as forcing mechanism an inertial oscillation of the ageostrophic component of the wind vector in the levels above the top of the nocturnal radiation inversion. First, the time-dependent variation of the nocturnal boundary-layer height is studied by means of prognostic equations; there is a good agreement between observed and calculated height data for three days of the Wangara experiment. Furthermore, a diurnal variation of the drag coefficient is considered in the lower layer by decreasing the coefficient by a factor of 10–20 due to stabilization of this layer during the night. The marked temporal decrease (increase) of the drag coefficient in the first hours after sunset (sunrise) is described by a function $$C_{D(t)} = C_{DN} - A\sqrt[4]{{\sin ({\pi \mathord{\left/ {\vphantom {\pi {2T}}} \right. \kern-\nulldelimiterspace} {2T}})t}}$$ . The incorporation of these two effects into the model gives results which are in good agreement with observed wind data for Wangara days 13/14, 30/31, and 33/34.

Aspects of atmospheric turbulence related to scintillometry Atmospheric turbulence is the main vertical transport mechanism in the atmospheric boundary layer. The surface fluxes related to this turbulent transport are the sensible () and latent heat fluxes (). The area-averaged values of and are of interest to evaluate mesoscale numerical weather models and in water budget studies. Natural landscapes are often heterogeneous, i.e. and differ among fields. The fluxes can be obtained with a scintillometer system, which consists of an electromagnetic beam transmitter at one end of a propagation path and a receiver at the other end. The intensity of the electromagnetic signal at the receiver varies due to fluctuations in the refractive index of air () caused by turbulence along the path. From the magnitude of these fluctuations the structure parameter of temperature () and of humidity () can be derived. Finally, and are used to determine path-averaged and via Monin-Obukhov similarity theory (MOST). The advantage of scintillometry is that the obtained fluxes are path-averaged, which makes scintillometry a more suitable method for obtaining area-averaged fluxes over natural landscapes than traditional point measurements. However, the disadvantage is that the fluxes are not directly measured. Therefore in this thesis four questions are answered related to the applicability of MOST and to the behaviour of structure parameters over heterogeneous surfaces. The latter is important because MOST assumes homogeneous surface conditions. For our studies we used meteorological data measured at three sites (Cabauw; the Netherlands, CASES-99 experiment; Leon; Kansas; USA, LITFASS-2009 and LITFASS-2010 experiments; Lindenberg; Germany) under unstable conditions (day-time). MOST is restricted to the part of the atmosphere close to the surface: the atmospheric surface layer (ASL). The depth of the ASL is not constant during the day, and is relatively shallow during the morning. At those moments, the scintillometer observation level can be located outside the ASL, which can question the validity of MOST. Therefore, we proposed and compared two variations in MOST (MOST using local fluxes and MOST using surface fluxes). We found that during the afternoon when both concepts have to be valid, the values of are comparable. During the morning, the data do not unequivocally support one of the two concepts: MOSTl shows the correct temporal behaviour in, but underestimates by a factor of ten. The universal function that links the surface fluxes with the structure parameter in MOST needs to be determined empirically. In literature a great variety of these function can be found. Therefore, we investigate to what extent the expression for this function depends on the specific regression approaches, stability range and observation level. First, we found that applying various regression approaches has an impact on the expression. This means that studies always should specify their regression approach, when presenting new functions. We advise to use an orthogonal distance regression method, applied to the logarithmic transformation of both dimensionless groups, and weighted such that unreliable data points have a smaller influence on the fit. Second, we found that the observation height and the stability range have an impact on the coefficients too. This implies that variations found in literature may result from variations in the height and stability ranges among the datasets. Furthermore, application of a given expression on a dataset measured at a different height or within a different stability range has to be done with care. In order to investigate whether variations in and along a scintillometer path or aircraft flight leg are within the range of local variability, or could be attributed to surface heterogeneity, we analysed the amount of local variability in the structure parameters at different heights and under different stability regimes. We found that the variability is determined by stability and by the size of the averaging window over which the structure parameters are calculated. If instability increases, differences in structure parameters between upward motions and downward motions increase. If the averaging window size increases, the variance of the logarithmic structure parameters decreases. A rough estimation of this decrease is made by fitting a simple linear regression between this variances and the averaging window size. From this we found that for various stability classes both the offset and slope (in absolute sense) decrease with increasing instability. The offset and slope can be used to quantify the local variability, which in turn can give an indication if variations in the structure parameters along a scintillometer or flight path might be attributed to surface heterogeneity. Finally, our last study is an elaboration of the study of Beyrich et al. (2012). They compared obtained with the unmanned meteorological mini aerial vehicle (M2AV) with obtained with the large-aperture scintillometer (LAS) for five flights on one single day during LITFASS-2009 experiment. We investigated if the systematically larger values of the M2AV as observed by them, can be found for other days, and if these differences could be reduced or explained through a more elaborate processing of the data of both instruments. We concluded that the difference can be found for other days during LITFASS-2009 and LITFASS-2010 as well. obtained from the M2AV data is larger, which is not improved by the more elaborate data analysis. Moreover, an exact synchronization of the LAS data with the time intervals of the M2AV data does not eliminate the discrepancy between both datasets. All in all, this thesis defines better the borders of MOST and shows the behaviour of the structure parameters in the atmospheric surface layer. Beyrich F, Bange J, Hartogensis OK, Raasch S, Braam M, van Dinther D, Gräf D, van Kesteren B, van den Kroonenberg AC, Maronga B, Martin S, Moene AF (2012) Towards a validation of scintillometer measurements: The LITFASS-2009 experiment. Boundary-Layer Meteorol 144:83-112