ALBERT

Description: Results of a lake model intercomparison study conducted within the framework of Lake Model Intercomparison Project are presented. The investigated lake was Großer Kossenblatter See (Germany) as a representative of shallow, (2 m mean depth) turbid midlatitude lakes. Meteorological measurements, including turbulent fluxes and water temperature, were carried out by the Lindenberg Meteorological Observatory of the German Meteorological Service (Deutscher Wetterdienst, DWD). Eight lake models of different complexity were run, forced by identical meteorological variables and model parameters unified as far as possible given different formulations of processes. All models generally captured diurnal and seasonal variability of lake surface temperature reasonably well. However, some models were incapable of realistically reproducing temperature stratification in summer. Total heat turbulent fluxes, computed by the surface flux schemes of the compared lake models, deviated on average from those measured by eddy covariance by 17–28 W m−2. There are a number of possible reasons for these deviations, and the conclusion is drawn that underestimation of real fluxes by the eddy covariance technique is the most probable reason. It is supported by the fact that the eddy covariance fluxes do not allow to close the heat balance of the water column, the residual for the whole period considered being ≈–28 W m−2. The effect of heat flux to bottom sediments can become significant for bottom temperatures. It also has profound influence on the surface temperatures in autumn due to convective mixing but not in summer when the lake stratification is stable. Thus, neglecting sediments shifts the summer–autumn temperature difference in models lacking explicit treatment of sediments considerably. As a practical recommendation based on results of the present study, we also infer that in order to realistically represent lakes in numerical weather prediction and climate models, it is advisable to use depth-resolving turbulence models (or equivalent) in favor of models with a completely mixed temperature profile.

Description: Vertical profiles of temperature, humidity and wind up to a height of 1500 m a.g.l. (above ground level) were measured with the automatically operating small unmanned research aircraft M2AV (Meteorological Mini Aerial Vehicle) during the LITFASS-2009 (LIndenberg-To-Falkenberg: Aircraft, Scintillometer and large-eddy Simulation) experiment. The campaign took place in July 2009 over the heterogeneous landscape around the Meteorologcial Observatory Lindenberg – Richard-Aßmann-Observatory in the eastern part of Germany. Due to a high vertical resolution of about 10 cm the M2AV data show details of the turbulent structure of the atmospheric boundary layer (ABL). One profile takes about 10–15 min allowing for a continuous monitoring of certain phases of ABL development by successive ascents and descents during one flight (50–60 min duration). Two case studies of measurements performed during the morning and evening ABL transition periods are discussed in detail. Comparison of the aircraft-based temperature, humidity and wind profiles with tower, sodar/RASS, wind profiler/RASS, radiosoundings and microwave radiometer profiler measurements show good agreement taking into account the different sampling strategies of these measurement systems.

Description: The objective of this study is to assess the feasibility and quality of eddy-covariance flux measurements from a weight-shift microlight aircraft (WSMA). Firstly, we investigate the precision of the wind measurement (σu,v ≤ 0.09 m s−1, σw = 0.04 m s−1), the lynchpin of flux calculations from aircraft. From here, the smallest resolvable changes in friction velocity (0.02 m s−1), and sensible- (5 W m−2) and latent (3 W m−2) heat flux are estimated. Secondly, a seven-day flight campaign was performed near Lindenberg (Germany). Here we compare measurements of wind, temperature, humidity and respective fluxes between a tall tower and the WSMA. The maximum likelihood functional relationship (MLFR) between tower and WSMA measurements considers the random error in the data, and shows very good agreement of the scalar averages. The MLFRs for standard deviations (SDs, 2–34%) and fluxes (17–21%) indicate higher estimates of the airborne measurements compared to the tower. Considering the 99.5% confidence intervals, the observed differences are not significant, with exception of the temperature SD. The comparison with a large-aperture scintillometer reveals lower sensible heat flux estimates at both tower (−40 to −25%) and WSMA (−25–0%). We relate the observed differences to (i) inconsistencies in the temperature and wind measurement at the tower and (ii) the measurement platforms' differing abilities to capture contributions from non-propagating eddies. These findings encourage the use of WSMA as a low cost and highly versatile flux measurement platform.

Description: Vertical profiles of temperature, humidity and wind up to a height of 1500 m a.g.l. (above ground level) were measured with the automatically operating small unmanned research aircraft M2AV (Meteorological Mini Aerial Vehicle) during the LITFASS-2009 LIndenberg-To-Falkenberg: Aircraft, Scintillometer and large-eddy Simulation) experiment. The campaign took place in July 2009 over the heterogeneous landscape around the Meteorological Observatory Lindenberg – Richard-Aßmann-Observatory in the eastern part of Germany. Due to a high vertical resolution of about 10 cm the M2AV data show details of the turbulent structure of the atmospheric boundary layer (ABL). One profile took about 10–15 min allowing for a continuous monitoring of certain phases of ABL development by successive ascents and descents during one flight (50–60 min duration). Two case studies of measurements performed during the morning and evening ABL transition periods are discussed in detail. Comparison of the aircraft-based temperature, humidity and wind profiles with tower, sodar/RASS, wind profiler/RASS, radiosoundings and microwave radiometer profiler measurements show good agreement taking into account the different sampling strategies of these measurement systems.

Description: Results of a lake model intercomparison study conducted within the framework of Lake Model Intercomparison Project are presented. The investigated lake was Großer Kossenblatter See (Germany) as a representative of shallow (2 m mean depth) midlatitude turbid lakes. Meteorological measurements, including turbulent fluxes and water temperature, were carried out by the Lindenberg Meteorological Observatory of the German Meteorological Service (Deutscher Wetterdienst, DWD). Eight lake models of different complexity were run, forced by identical meteorological variables and model parameters unified as far as possible given different formulations of processes. All models generally captured diurnal and seasonal variability of lake surface temperature well. However, some models were incapable of realistically reproducing temperature stratification in summer. Total heat turbulent fluxes, computed by surface flux schemes of lake models, deviated on average from those measured by eddy covariance by 17–28 W m−2. To realistically represent lakes in numerical weather prediction and climate models, it is advisable to use depth-resolving turbulence models (or equivalent) in favour of models with a completely mixed temperature profile. While the effect of heat flux to bottom sediments can become significant for bottom temperatures, it has no important influence on the surface temperatures.

Description: The objective of this study is to assess the feasibility and quality of Eddy-Covariance flux measurements from a weight-shift microlight aircraft (WSMA). Firstly we investigate the precision of the wind measurement (σu,v≤ 0.09 m s−1, σw = 0.04 m s−1), the lynchpin of flux calculations from aircraft. From here the smallest resolvable changes in friction velocity (0.02 m s−1), and sensible- (5 W m−2) and latent (3 W m−2) heat flux are estimated. Secondly a seven-day flight campaign was performed near Lindenberg (Germany). Here we compare measurements of wind, temperature, humidity and respective fluxes between a tall tower and the WSMA. The maximum likelihood functional relationship (MLFR) between tower and WSMA measurements considers the random error in the data, and shows very good agreement of the scalar averages. The MLFRs for standard deviations (SDs, 2–34%) and fluxes (17–21%) indicate higher estimates of the airborne measurements compared to the tower. Considering the 99.5% confidence intervals the observed differences are not significant, with exception of the temperature SD. The comparison with a large-aperture scintillometer reveals lower sensible heat flux estimates at both, tower (−40–−25%) and WSMA (−25–0%). We relate the observed differences to (i) inconsistencies in the temperature and wind measurement at the tower and (ii) the measurement platforms differing abilities to capture contributions from non-propagating eddies. These findings encourage the use of WSMA as a low price and highly versatile flux measurement platform.