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The development of science in the former German Democratic Republic (GDR) experienced some disruptions with the reunification of Germany. Nevertheless, it was possible to maintain a certain continuity in climate research, which can be seen as a personal merit of Prof. Dr. Peter Hupfer. The development of climate research from the 1950s to the present and his part in it will be acknowledged in the present article.

One hundred and fifty years ago, a meteorological conference was held in Leipzig as part of the anniversary meeting of the Society of German Natural Scientists and Physicians (Gesellschaft Deutscher Naturforscher und Ärzte), founded in Leipzig in 1822. This meeting, intended as a preparatory meeting for the 1st International Meteorological Congress held in Vienna a year later, ultimately laid the foundation for today's World Meteorological Organization. The organizers of the Leipzig Conference (was held on 14–16 August 1872) were the German Carl Christians Bruhns (1830–1881), the Austrian Carl Jelinek (1822–1876) and the Swiss Heinrich von Wild (1833–1902). The discussions at the conference were conducted on the basis of a catalogue of 26 questions on the most pressing issues of the use of measuring instruments, observation periods, and data exchange (catalog in English translation in the appendix) that were sent together with the invitation. The main concern here was to enable consistency between individual states. Based on the Report on the Negotiations of the Meteorological Assembly at Leipzig (Vienna, 1872), which also contains opinions expressed by meteorologists who were not present at the conference, the results of this trend-setting Leipzig assembly are presented here, that was a milestone in international meteorological cooperation.

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.

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-Ålesund (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.

The possibility to use footprint models, which are well established in micrometeorology and ecology, is discussed also for the fine-tuning of the location of wind turbines. A selection of possible models is given. In an example it is shown that differences in the wind power of two nearby located wind turbines can be explained by the presence of forested areas within the footprint.

Two models for predicting near-surface flux and concentration footprints are compared concerning their performance in the presence of heterogeneous surface conditions. One of the models is a conventional Lagrangian backward model and the second an LES model with an embedded Lagrangian footprint model. The latter model reveals generation of thermally induced secondary circulation under such surface heterogeneity. The conventional Lagrangian backward model with simple parameterization of flow conditions mostly performs well in footprint predictions for concentrations and somewhat worse for fluxes, and fails only in areas where flow patterns are dominated by pronounced secondary circulations.

Commonly used measuring methods only allow for a closure of the energy balance at the Earth's surface except for a residual. Models, in contrast, inherently demand an entirely closed energy balance, which they achieve in different ways. This paper examines the model simulations depending on the methods used for closing the energy balance, the optimization of the parameters, and the equations used. The one-dimensional surface vegetation atmosphere transfer (SVAT) models REMO, SEWAB and TERRA, which were made available by the GKSS Institute in Geesthacht, are examined and compared with measured data from the LITFASS-2003 experiment. LITFASS-2003 took place during May and June 2003 in the experimental fields of the Meteorological Observatory Lindenberg. Parameter sets optimized with regard to the turbulent fluxes yield better results, but are often not consistent with site characteristics and differ within the models. We ran the models with the optimized parameter sets, and with a set of selected parameters which agree with the respective sites. SEWAB closes the energy balance by using an iteration of the surface temperature, through which the influence of the residual is distributed over all fluxes. In REMO and TERRA the soil heat flux is estimated as the residual of the other components of the energy balance equation. This results in an extreme overestimation of this heat flux. Parameter optimization has an impact on the partitioning of the available energy and its distribution to the turbulent heat fluxes. It does not influence the effect of the residual on the results. Currently we do not know how to close the measured energy balance at the surface appropriately because of the underestimation of the turbulent fluxes by eddy-covariance measurements and the unknown partitioning of the residual between the sensible and latent heat flux. Therefore, the method used in SEWAB yields better results than the one used in REMO and TERRA. The method used to close the energy balance has more impact on the simulated surface energy balance components than does their parameterization. For this reason it is not possible to attribute the differences in the calculated heat fluxes to particular differences in the equations and parameters.

Most sensors do not perfectly reproduce changes of the measured quantity with respect to time and intensity. Delays and damping effects cause the signal to deviate from the true value. These deviations are often caused by combined impacts of the probe itself, the probe's housing, the sensor's inlet system and more. In this work, we will (a) evaluate correction schemes already known from aircraft temperature measurements for their performance on measured vertical temperature profiles, and (b) present an alternative, simpler correction scheme. The temperature profiles were measured with an elevator system at a 99 m mast from 2 m to 98 m a.g.l., parallel to a stationary high quality reference temperature profile. Besides laboratory tests, we will demonstrate and quantify the effect of the corrections applied to the mobile temperature sensor's data in direct comparison with the reference temperature data. This direct comparison (a) exceeds the potential of aircraft measurements, where comparisons with stationary in-situ sensors are hard to realize, and (b) clearly shows the effectiveness and correct magnitude of the corrections. It is demonstrated with temperature measurements, that a mobile sensor can satisfactorily substitute a profile of stationary sensors.

In this paper we present one year of meteorological and flux measurements obtained near Ny-Ålesund, Spitsbergen. Fluxes are derived by the eddy covariance method and by a hydrodynamic model approach (HMA) as well. Both methods are compared and analyzed with respect to season and mean wind direction. Concerning the wind field we find a clear distinction between 3 prevailing regimes (which have influence on the flux behavior) mainly caused by the topography at the measurement site. Concerning the fluxes we find a good agreement between the HMA and the eddy covariance method in cases of turbulent mixing in summer but deviations at stable conditions, when the HMA almost always shows negative fluxes. Part of the deviation is based on a dependence of HMA fluxes on friction velocity and the influence of the molecular boundary layer. Moreover, the flagging system of the eddy covariance software package TK3 is briefly revised. A new quality criterion for the use of fluxes obtained by the eddy covariance method, which is based on integral turbulence characteristics, is proposed.

This study evaluates the impact of post-field data processing methods on eddy covariance flux estimates and the resulting energy balance residual. To that end, a dataset from the LITFASS-2003 field campaign was analysed using an experimental software package. Widely discussed issues in data processing like an adequate flux averaging time, coordinate transformations and alternative approaches for the correction of density effects were examined. The impact of all the single processing steps on the turbulent flux estimates of sensible heat, latent heat and CO2 as well as the impact on the resulting energy balance residual is demonstrated. The mean energy balance residual could be reduced by 17 % compared to 30-min covariances without any conversions or corrections if all necessary procedures were applied to the test dataset. Important procedures for the reduction of the experimental energy balance closure problem were the correction for spectral loss and the correction for density effects. Furthermore, the energy balance residual vanished almost completely if the covariance averaging time was extended from 30 minutes over 24 hours to five days. The low-frequency flux contributions could be explained through effects which were caused by the strong heterogeneity of the landscape surrounding the measurement site. The dependence of CO2 flux estimates on the post-field data processing was stronger. Their mean value was changed by a factor of 2 through the correction for density effects.

Variables describing the heat transport in soils are usually determined indirectly from soil temperature and/or moisture measurements. Alternatively, they can be measured using repeatedly heated sensors like the self-calibrating heat flux plate HFP01SC and the thermal properties sensor TP01 from Hukseflux (Delft, NL). This study aims to validate the data recorded with these instruments for three variables: The Philip correction (factor fP), the soil heat conductivity (λs), and the volumetric soil heat capacity (cν). All of these were measured in a short experiment with the HFP01SC and/or the TP01 sensor and were simultaneously calculated from reference methods using soil temperature and moisture measurements. For the data set on which this study is based, the HFP01SC's self-correction agrees with the Philip correction, but the sensor cannot be recommended for measuring λs. The TP01 seems to underestimate λsand should not be used to quantify cν.

A micrometeorological field experiment was performed within the frame of the STINHO-project (structure of turbulent transport under inhomogeneous conditions) at the boundary layer field site of the Meteorological Observatory Lindenberg of the German Meteorological Service (Deutscher Wetterdienst) in the summer of 2002 in order to investigate the interaction of thermally heterogeneous surfaces with the turbulent atmosphere. The intention was to compare conventional meteorological point and vertically integrated measurements with area-covering air flow observations and numerical simulations. To observe horizontally variable flow and temperature fields above a heterogeneous land surface, simultaneous acoustic methods (travel time tomography), optical observation methods (IR-camera and line-integrated scintillometer-measurements), as well as the airborne measurement system Helipod were used. The data set will be applied in future to validate large-eddy simulations adjusted to the area of investigation.

After an historical introduction into the research activities of Prof. Hinzpeter and the author, because of their roots in the Meteorological Observatory Potsdam the investigation of the molecular temperature sublayer over the ocean was selected as one field of a common interest. The experimental investigations made in Kiel and Leipzig are presented. It is shown that the thickness of the molecular sublayer depends on the friction velocity and the conditions of the wavy surface. Based on this data, parametrizations of the viscous sublayer on the basis of these investigations and of hydrodynamical measurements are discussed. Possibilities to use this parametrizations in air-sea interaction models are considered. Nach einer historischen Einleitung zu den wissenschaftlichen Wurzeln von Prof. Hinzpeter und dem Autor im Meteorologischen Observatorium Potsdam wird die Untersuchung der molekularen Grenzschicht über dem Ozean als ein gemeinsames wissenschaftliches Interessengebiet näher betrachtet. Dabei werden die in Kiel und Leipzig durchgeführten Untersuchungsergebnisse dargestellt. Es wird gezeigt, dass die Dicke der molekularen Temperaturgrenzschicht von der Schubspannungsgeschwindigkeit und von der Entwicklung der Oberflächenwellen abhängt. Auf Grund dieser experimentellen Befunde werden Parametrisierungen für die viskose Unterschicht auf der Basis dieser Daten und hydrodynamischer Untersuchungen sowie Möglichkeiten zu deren Einbeziehung in Wechselwirkungsmodelle Meer-Atmosphäre diskutiert.

It is now accepted that large-scale turbulent eddies impact the widely reported non-closure of the surface energy balance when latent and sensible heat fluxes are measured using the eddy covariance method in the atmospheric surface layer (ASL). However, a mechanistic link between large eddies and non-closure of the surface energy balance remains a subject of inquiry. Here, measured 10 Hz time series of vertical velocity, air temperature, and water vapor density collected in the ASL are analyzed for conditions where entrainment and/or horizontal advection separately predominate. The series are decomposed into small- and large- eddies based on a frequency cutoff and their contributions to turbulent fluxes are analyzed. Phase difference between vertical velocity and water vapor density associated with large eddies reduces latent heat fluxes, especially in conditions where advection prevails. Enlarged phase difference of large eddies linked to entrainment or advection occurrence leads to increased residuals of the surface energy balance.

Micrometeorological measurements of radiation, atmospheric and soil parameters, and turbulent energy and momentum fluxes, ozone and carbon dioxide fluxes have been conducted over a maize field at Freising-Weihenstephan in Southern Germany during the total solar eclipse on August 11, 1999. For the period 30 minutes before and after the totality the weather conditions at the location where the micrometeorological measurements were made was satisfactory. Several connections between the irradiation and other meteorological parameters over a maize field have been found. The time response between irradiation and the long-wave upward radiation was only a few minutes, whereas almost all parameters caused by the turbulent transport had a time shift of up to 30 minutes. A period of nearly 30 minutes with reduced turbulence regime after the totality was found. Using a wavelet transformation for the time series, a change of time scales from longer to shorter ones was observed before the totality, and after the turbulence increased in the short time scales. The investigation of the residuum of the closure of the energy balance showed that with a time shift for the latent heat flux (unlike the net radiation) after the totality, a better energy budget closure was obtained.

The total solar eclipse of August 11, 1999 provided a unique opportunity to observe the input of fast day-night and night-day transitions, under high solar elevation around noon, on the earth-atmosphere-biosphere system. Within the interdisciplinary field campaign BAYSOFI, measurements of radiation, boundary layer micrometeorology and photochemistry, photosynthesis and transpiration were carried out at Freising-Weihenstephan and several locations nearby focusing on short-term effects of the eclipse. Although the overall grosswetterlage on August 11 was not favourable for viewing the eclipse, with clouds covering most of central Europe, observational conditions at Weihenstephan were fair due to a large hole in the cloud layer which appeared just half hour before totality lasting for more than one hour. Thus significant effects of the eclipse on radiation, photolysis rates, OH, the temperature, wind, turbulence structure and stratification, ozone and CO2 fluxes, photosynthesis, transpiration and sap flow of trees could be observed which are reported and discussed in the following sequence of papers.

The sensible heat flux (H) and the latent heat flux (λE) were measured above a grassland during June, 1997 (LINEX-97/1 Experiment), using the eddy covariance method (EC) and the Bowen ratio/Energy balance method (BREB). The results indicate that HBREB is about (30 ± 20) Wm-2 higher than HEC, and λEBREB is about (180 ± 40) Wm-2 higher than λEEC during the daytime, and this is mainly caused by an imbalance in the closure of the surface energy balance in the BREB. In order to avoid the inaccuracies associated with the surface energy balance method, we propose a modified Bowen ratio method (MBR) to determine sensible and latent heat fluxes without using the surface energy balance equation. The results and error analysis show that MBR can give more accurate results than BREB. For the MBR, a measurement system using a sonic anemometer together with temperature and humidity measurements at two levels is being recommended to obtain sensible and latent heat fluxes.

On the basis of the integral turbulence characteristics observed at the Melpitz measuring field as a part of the SANA project in 1991, the measuring conditions at the site were found to be mainly influenced by inhomogeneities of the surface roughness. Also present was a weakly developing internal boundary layer caused by a change of the surface roughness between bare soil and dry grass. The importance of using different tests to classify the conditions of the underlying surface is emphasized for measuring sites where fundamental research is planned.

The paper gives a survey of the concepts, the methods and the measuring devices currently used to determine the dry deposition and emission of trace gases. Furthermore, problems inherent in these methods are pointed out and discussed. A short description of the essential micrometeorological measurements to determine fluxes for different compounds and to qualify errors is given, too. The so-called direct flux method for basic research as well as the progress in the development of accumulation methods are explained. To assess area-averaged mean values of dry deposition, an extensive explanation of the inferential method being used to estimate the dry deposition of inert and reactive trace gases is given.

Mit Dr. Günter Steib, Ehrenmitglied der Deutschen Meteorologischen Gesellschaft, feierte am 16. September 1999 ein Meteorologe und Polarforscher seinen 80. Geburtstag, der seine wissenschaftliche Entwicklung in der Nachkriegszeit nahm. Wie wahrscheinlich nur wenige Wissenschaftler im geteilten Deutschland war er in Ost und West nicht unbekannt und wurde für seine Leistungen ausgezeichnet. Neben zahlreichen Anerkennungen in der DDR ist hier besonders die Verleihung des ersten Preises für Polarmeteorologie der Alfred-Wegener-Stiftung im Oktober 1987 in Köln zu nennen.