Static Source Error Calibration of a Nose Boom Mounted Air Data System on an Atmospheric Research Aircraft Using the Trailing Cone Method

This work demonstrates the calibration of an experimental air data probe on an atmospheric research aircraft by means of the Trailing Cone method. The probe under investigation is located on a nose boom in order to minimize the aerodynamic influence of the fuselage on the pressure measurement ahead of the aircraft. However, the data from this experiment proves that this configuration is still subject to significant pressure deviations from the undisturbed atmospheric values. This work demonstrates the determination of this error and presents an appropriate parameterization of the data which is prerequisite to provide accurately corrected pressure readings from this sensor. The experiment covers the determination of the proper configuration (length) for the Trailing Cone assembly, the validation of the method itself and the subsequent calibration of the air data sensor. Several improvements were applied to the Trailing Cone method in order to reduce the flight test effort as well as to significantly enhance the accuracy of the method itself. As a consequence a total of only three test flights was necessary to validate the method and to calibrate the air data sensor. The data analysis shows that the accuracy of the Trailing Cone reference measurement is very close to the pressure sensor calibration limit of 0.1hPa. The resulting accuracy of the corrected pressure measurement by the nose boom mounted pressure probe was demonstrated to be about 0.2 hPa, which represents the 3σ value

Towards improved turbulence estimation with Doppler wind lidar velocity-azimuth display (VAD) scans

The retrieval of turbulence parameters with profiling Doppler wind lidars (DWLs) is of high interest for boundary layer meteorology and its applications. DWLs provide wind measurements above the level of meteorological masts while being easier and less expensive to deploy. Velocity-azimuth display (VAD) scans can be used to retrieve the turbulence kinetic energy (TKE) dissipation rate through a fit of measured azimuth structure functions to a theoretical model. At the elevation angle of 35.3° it is also possible to derive TKE. Modifications to existing retrieval methods are introduced in this study to reduce errors due to advection and enable retrievals with a low number of scans. Data from two experiments are utilized for validation: first, measurements at the Meteorological Observatory Lindenberg–Richard-Aßmann Observatory (MOL-RAO) are used for the validation of the DWL retrieval with sonic anemometers on a meteorological mast. Second, distributed measurements of three DWLs during the CoMet campaign with two different elevation angles are analyzed. For the first time, the ground-based DWL VAD retrievals of TKE and its dissipation rate are compared to in situ measurements of a research aircraft (here: DLR Cessna Grand Caravan 208B), which allows for measurements of turbulence above the altitudes that are in range for sonic anemometers. From the validation against the sonic anemometers we confirm that lidar measurements can be significantly improved by the introduction of the volume-averaging effect into the retrieval. We introduce a correction for advection in the retrieval that only shows minor reductions in the TKE error for 35.3° VAD scans. A significant bias reduction can be achieved with this advection correction for the TKE dissipation rate retrieval from 75° VAD scans at the lowest measurement heights. Successive scans at 35.3 and 75° from the CoMet campaign are shown to provide TKE dissipation rates with a good correlation of R>0.8 if all corrections are applied. The validation against the research aircraft encourages more targeted validation experiments to better understand and quantify the underestimation of lidar measurements in low-turbulence regimes and altitudes above tower heights

A new airborne broadband radiometer system and an efficient method to correct thermal offsets

The instrumentation of the High Altitude and Long Range (HALO) research aircraft is extended by the new Broadband AirCrAft RaDiometer Instrumentation (BACARDI) to quantify the radiative energy budget. Two sets of pyranometers and pyrgeometers are mounted to measure upward and downward solar (0.3&ndash;3 &mu;m) and thermal-infrared (3&ndash;100 &mu;m) irradiances. The radiometers are installed in a passively ventilated fairing to reduce the effects of the dynamic environment, e.g., fast changes of altitude and temperature. The remaining thermal effects range up to 20 W m-2 for the pyranometers and 10 W m-2 for the pyrgeometers; they are corrected using an new efficient method that is introduced in this paper. Using data collected by BACARDI during a night flight, the thermal offsets are parameterized by the rate of change of the radiometer sensor temperatures. Applying the sensor temperatures instead of ambient air temperature for the parameterization provides a linear correction function (200&ndash;600 W m-2 K-1 s), that depends on the mounting position of the radiometer on HALO. Furthermore, BACARDI measurements from the EUREC4A (Elucidating the role of clouds-circulation coupling in climate) field campaign are analyzed to characterize the performance of the radiometers and to evaluate all corrections applied in the data processing. Vertical profiles of irradiance measurements up to 10 km altitude show that the thermal offset correction limits the bias due to temperature changes to values below 10 W m-2. Measurements with BACARDI during horizontal, circular flight patterns in cloud-free conditions demonstrate that the common geometric attitude correction of the solar downward irradiance provides reliable measurements in this typical flight sections of EUREC4A, even without active stabilization of the radiometer.</p

Climate change affects vegetation differently on siliceous and calcareous summits of the European Alps

The alpine life zone is expected to undergo major changes with ongoing climate change. While an increase of plant species richness on mountain summits has generally been found, competitive displacement may result in the long term. Here, we explore how species richness and surface cover types (vascular plants, litter, bare ground, scree and rock) changed over time on different bedrocks on summits of the European Alps. We focus on how species richness and turnover (new and lost species) depended on the density of existing vegetation, namely vascular plant cover. We analyzed permanent plots (1 x 1 m) in each cardinal direction on 24 summits (24 x 4 x 4), with always four summits distributed along elevation gradients in each of six regions (three siliceous, three calcareous) across the European Alps. Mean summer temperatures derived from downscaled climate data increased synchronously over the past 30 years in all six regions. During the investigated 14 years, vascular plant cover decreased on siliceous bedrock, coupled with an increase in litter, and it marginally increased on higher calcareous summits. Species richness showed a unimodal relationship with vascular plant cover. Richness increased over time on siliceous bedrock but slightly decreased on calcareous bedrock due to losses in plots with high plant cover. Our analyses suggest contrasting and complex processes on siliceous versus calcareous summits in the European Alps. The unimodal richness-cover relationship and species losses at high plant cover suggest competition as a driver for vegetation change on alpine summits

Airborne observations of the Eyjafjalla volcano ash cloud over Europe during air space closure in April and May 2010

© Author(s) 2011. This work is distributed under the Creative Commons Attribution 3.0 LicenseAirborne lidar and in-situ measurements of aerosols and trace gases were performed in volcanic ash plumes over Europe between Southern Germany and Iceland with the Falcon aircraft during the eruption period of the Eyjafjalla1 volcano between 19 April and 18 May 2010. Flight planning and measurement analyses were supported by a refined Meteosat ash product and trajectory model analysis. The volcanic ash plume was observed with lidar directly over the volcano and up to a distance of 2700 km downwind, and up to 120 h plume ages. Aged ash layers were between a few 100 m to 3 km deep, occurred between 1 and 7 km altitude, and were typically 100 to 300 km wide. Particles collected by impactors had diameters up to 20 μm diameter, with size and age dependent composition. Ash mass concentrations were derived from optical particle spectrometers for a particle density of 2.6 g cm-3 and various values of the refractive index (RI, real part: 1.59; 3 values for the imaginary part: 0, 0.004 and 0.008). The mass concentrations, effective diameters and related optical properties were compared with ground-based lidar observations. Theoretical considerations of particle sedimentation constrain the particle diameters to those obtained for the lower RI values. The ash mass concentration results have an uncertainty of a factor of two. The maximum ash mass concentration encountered during the 17 flights with 34 ash plume penetrations was below 1 mg m-3. The Falcon flew in ash clouds up to about 0.8 mg m-3 for a few minutes and in an ash cloud with approximately 0.2 mg -3 mean-concentration for about one hour without engine damage. The ash plumes were rather dry and correlated with considerable CO and SO2 increases and O3 decreases. To first order, ash concentration and SO2 mixing ratio in the plumes decreased by a factor of two within less than a day. In fresh plumes, the SO2 and CO concentration increases were correlated with the ash mass concentration. The ash plumes were often visible slantwise as faint dark layers, even for concentrations below 0.1 mg m-3. The large abundance of volatile Aitken mode particles suggests previous nucleation of sulfuric acid droplets. The effective diameters range between 0.2 and 3 μm with considerable surface and volume contributions from the Aitken and coarse mode aerosol, respectively. The distal ash mass flux on 2 May was of the order of 500 (240-1600) kgs -1. The volcano induced about 10 (2.5-50) Tg of distal ash mass and about 3 (0.6-23) Tg of SO2 during the whole eruption period. The results of the Falcon flights were used to support the responsible agencies in their decisions concerning air traffic in the presence of volcanic ash.Peer reviewe

Determination of the Measurement Errors for the HALO Basic Data System BAHAMAS by Means of Error Propagation

Der Forschungsbericht beschreibt die Bestimmung der Messfehler für die meteorologischen Basisdaten des Atmosphären-Forschungsflugzeugs HALO. Diese Daten werden von der vom DLR entwickelten Basismessanlage BAHAMAS erfasst. Die Fehleranalyse basiert auf einer Fehlerfortpflanzungs-Methode, bei der auf die originalen Messdaten ein künstliches weißes Rauschsignal aufsetzt wird, das auf diese Weise die gesamte Datenverarbeitung durchläuft. Die Fehlerrechnung umfasst sowohl statistische Messfehler in den originalen Rohdaten als auch systematischen Fehlerbeiträge in der Datenprozessierung, die durch Sensorkalibrierung, ungenaue Parametrisierungen von physikalischen Zusammenhängen oder Unsicherheiten aus Laborergebnissen herrühren. Die präsentierte Methode stellt eine echte Fehlerfortpflanzung da und basiert nicht auf Vereinfachungen oder Linearisierungs-Ansätzen wie bei einer klassischen Fehlerfortpflanzungsbetrachtung. Das Dokument präsentiert und diskutiert alle bekannten Fehlerquellen für Basismessdaten auf HALO. Abschließend werden Ergebnisse dieser Fehleranalyse für typische Flugszenarien dargestellt und mögliche Ansatzpunkte für eine weitere Minimierung dieser Fehler diskutiert

Does Strong Tropospheric Forcing Cause Large-Amplitude Mesospheric Gravity Waves? A DEEPWAVE Case Study

On 4 July 2014, during the Deep Propagating Gravity Wave Experiment (DEEPWAVE), strong low-level horizontal winds of up to 35 m s−1 over the Southern Alps, New Zealand, caused the excitation of gravity waves having the largest vertical energy fluxes of the whole campaign (38 W m−2). At the same time, large-amplitude mesospheric gravity waves were detected by the Temperature Lidar for Middle Atmospheric Research (TELMA) located at Lauder (45.0°S, 169.7°E), New Zealand. The coincidence of these two events leads to the question of whether the mesospheric gravity waves were generated by the strong tropospheric forcing. To answer this, an extensive data set is analyzed, comprising TELMA, in situ aircraft measurements, radiosondes, wind lidar measurements aboard the DLR Falcon as well as Rayleigh lidar and advanced mesospheric temperature mapper measurements aboard the National Science Foundation/National Center for Atmospheric Research Gulfstream V. These measurements are further complemented by limited area simulations using a numerical weather prediction model. This unique data set confirms that strong tropospheric forcing can cause large-amplitude gravity waves in the mesosphere, and that three essential ingredients are required to achieve this: first, nearly linear propagation across the tropopause; second, leakage through the stratospheric wind minimum; and third, amplification in the polar night jet. Stationary gravity waves were detected in all atmospheric layers up to the mesosphere with horizontal wavelengths between 20 and 100 km. The complete coverage of our data set from troposphere to mesosphere proved to be valuable to identify the processes involved in deep gravity wave propagation

A new airborne broadband radiometer system and an efficient method to correct dynamic thermal offsets

The instrumentation of the High Altitude and Long Range (HALO) research aircraft is extended by the new Broadband AirCrAft RaDiometer Instrumentation (BACARDI) to quantify the radiative energy budget. Two sets of pyranometers and pyrgeometers are mounted to measure upward and downward solar (0.3–3 µm) and thermal–infrared (3–100 µm) irradiances. The radiometers are installed in a passively ventilated fairing to reduce the effects of the dynamic environment, e.g., fast changes in altitude and temperature. The remaining thermal effects range up to 20 W m−2 for the pyranometers and 10 W m−2 for the pyrgeometers. Using data collected by BACARDI during a night flight, it is demonstrated that the dynamic components of the offsets can be parameterized by the rate of change of the radiometer sensor temperatures, providing a greatly simplifying correction of the dynamic thermal effects. The parameterization provides a linear correction function (200–500 W m−2 K−1 s) that depends on the radiometer type and the mounting position of the radiometer on HALO. Furthermore, BACARDI measurements from the EUREC4A (Elucidating the Role of Clouds—Circulation Coupling in Climate) field campaign are analyzed to characterize the performance of the radiometers and to evaluate all corrections applied in the data processing. Vertical profiles of irradiance measurements up to 10 km altitude show that the thermal offset correction limits the bias due to temperature changes to values below 10 W m−2. Measurements with BACARDI during horizontal, circular flight patterns in cloud-free conditions demonstrate that the common geometric attitude correction of the solar downward irradiance provides reliable measurements in this typical flight section of EUREC4A, even without active stabilization of the radiometer.</p

Proximal TCR signaling in self tolerance

This thesis investigates the molecular mechanisms involved in T‐cell receptor (TCR) signaling during thymocyte selection. The T‐cell receptor of developing T‐cells interacts with antigen‐ presenting cells (APCs) that display peptide‐MHC ligands (p‐MHC) of different nature on their surface. The TCR interacts with these ligands and translates the binding affinity for different p‐MHC (characterized by the dissociation constant, KD) into a quantitative readout, thereby providing the basis for downstream signaling. How the TCR distinguishes between high affinity ligands that induce apoptosis of individual thymocytes (negative selection) and low affinity ligands that induce differentiation of thymocytes into single‐positive immature T‐cells (positive selection) has fascinated immunologists and biochemists for many years. This mechanism is critical to establish a self‐MHC restricted, self‐tolerant T‐cell repertoire (central tolerance). The first part of this thesis investigates the molecular interaction between the TCR and the CD8 co‐ receptor in thymic selection. By tagging both molecules with variants of the green fluorescent protein (GFP) and assessing their molecular approximation in the immunological synapse by FRET microscopy (developed by P. Yachi and N. Gascoigne at the Scripps Institute, LaJolla, USA), we found that negative‐selecting p‐MHC ligands induced strong and sustained TCR/CD8 association. In contrast, positive‐selecting ligands induce weak and delayed TCR/CD8 association in the synapse of T‐cell hybridomas with antigen‐presenting cells (APCs). We found that the TCR/CD8 interaction in response to positive‐ or negative‐selecting ligands was reflected in the phosphorylation of the ζ‐ chain. Therefore, the ability of the TCR to tightly associate with the co‐receptor is the critical parameter that determines whether a p‐MHC ligand mediates strong intracellular tyrosine phosphorylation and subsequently induces negative selection signaling. The α‐chain connecting peptide motif (α‐CPM) is a region of 8 conserved amino acids in the membrane‐proximal part of the constant region of the TCR α‐chain. Mutating the α‐CPM did not affect ligand binding since α‐CPM mutant TCRs had similar p‐MHC affinities like wild‐type TCRs. However, TCR/CD8 interaction as measured by FRET microscopy, changed substantially in α‐CPM mutant TCRs. In response to negative‐selecting ligands, TCR/CD8 association was reduced in α‐CPM mutant cells, which was also reflected in decreased ζ phosphorylation. Remarkably, in response to positive‐selecting ligands, α‐ CPM mutant cells displayed no detectable TCR/CD8 interactions and failed to induce ζ phosphorylation. Therefore, the α‐CPM is responsible for the molecular approximation of the CD8 co‐receptor to the TCR complex, allowing efficient signaling initiation. We hypothesize that the TCR and the co‐receptor may act like a molecular zipper. By binding to the same p‐MHC molecule the zippering mechanism allows the two molecules to become tightly associated via the α‐CPM towards the plasma membrane. Inside the cell, the co‐receptor carries the Src kinase, Lck and shuffles it efficiently to the CD3 complex once the zipper is fully closed. Only the zippered configuration allows efficient signaling initiation, emphasizing the importance of the α‐CPM to functionally link the TCR and CD8. In the second part of this thesis we investigated TCR proximal signaling downstream of the TCR complex. The ζ‐chain associated protein of 70 kDa (ZAP‐70) plays a central role in transmitting the TCR‐generated signal to downstream signaling molecules. ZAP‐70 binds to phosphorylated immunoreceptor tyrosine activation motifs (ITAMs) located on the ζ or CD3 molecules of the TCR complex. The tyrosine kinase activity of ZAP‐70 is triggered if the molecule binds to doubly phosphorylated ITAMs via its tandem SH2‐domain and subsequently becomes phosphorylated at several tyrosine residues. We wondered whether ZAP‐70 would function as molecular switch in TCR signaling, converting varying TCR inputs (by binding p‐MHC ligands of different binding affinity) into discrete signaling responses by generating distinct levels of ZAP‐70 kinase activity. In response to negative‐selecting ligands, ZAP‐70 was efficiently recruited to the immunological synapse. In the synapse, ZAP‐70 became phosphorylated at critical tyrosine residues, which induced its kinase activity. In vitro kinase assays revealed a discrete 2‐fold increase in ZAP‐70 kinase activity precisely at the negative selection threshold. In contrast, ZAP‐70 recruitment to the synapse and its kinase activity remained low in response to positive‐selecting ligands. Therefore, we speculate that a discrete elevation of ZAP‐70 activity occurs at the threshold of positive and negative selection. Further evidence for such a mechanism came from fetal thymic organ cultures (FTOCs), where negative selection was converted into partial positive selection by reducing ZAP‐70 kinase activity with a specific inhibitior. We also asked whether the increased ZAP‐70 kinase activity in negative selection is generated by an increase in the ratio of ZAP‐70 / TCR in the synapse. This idea seamed reasonable since multiple ITAMs and therefore potential ZAP‐70 binding sites exist among the CD3 molecules. However, we did not detect an increase in the ZAP‐70 / TCR ratio. Relative to positive selecting ligands, negative selectors induced a 2‐fold increase in the amount of TCR and ZAP‐70 recruited to the immunological synapse. However, the ZAP‐70 / TCR ratio was similar in both forms of selection and therefore, the number of TCR molecules recruited to the synapse determines the selection outcome. We postulate a model of TCR‐proximal signaling, where TCR‐associated ZAP‐70 is recruited into the synapse proportionally to the TCR’s ability to bind p‐MHC ligands and recruit the co‐receptor. According to the zipper model, only negative‐selecting ligands mediate efficient co‐ receptor association and therefore, increased ζ phosphorylation. ZAP‐70 becomes phosphorylated accordingly, which initiates a 2‐fold increase in its kinase activity in response to p‐MHC ligands above the negative selection threshold. This step‐wise increase in ZAP‐70 kinase activity is sufficient to mediate higher levels of LAT phosphorylation, which assembles a negative selection signaling comple