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

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

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

Gravity-wave-induced cross-isentropic mixing: a DEEPWAVE case study

Orographic gravity waves (i.e., mountain waves) can potentially lead to cross-isentropic fluxes of trace gases via the generation of turbulence. During the DEEPWAVE (Deep Propagating Gravity Wave Experiment) campaign in July 2014, we performed tracer measurements of carbon monoxide (CO) and nitrous oxide (N2O) above the Southern Alps during periods of gravity wave activity. The measurements were taken along two stacked levels at 7.9 km in the troposphere and 10.9 km in the stratosphere. A detailed analysis of the observed wind components shows that both flight legs were affected by vertically propagating gravity waves with momentum deposition and energy dissipation between the two legs. Corresponding tracer measurements indicate turbulent mixing in the region of gravity wave occurrence. For the stratospheric data, we identified mixing leading to a change of the cross-isentropic tracer gradient of N2O from the upstream to the downstream region of the Southern Alps. Based on the quasi-inert tracer N2O, we identified two distinct layers in the stratosphere with different chemical composition on different isentropes as given by constant potential temperature 2. The CO–N2O relationship clearly indicates that irreversible mixing between these two layers occurred. Further, we found a significant change of the vertical profiles of N2O with respect to 2 from the upstream to the downstream side above the Southern Alps just above the tropopause. A scale-dependent gradient analysis reveals that this cross-isentropic gradient change of N2O is triggered in the region of gravity wave occurrence

Airborne limb-imaging measurements of temperature, HNO3, O3, ClONO2, H2O and CFC-12 during the Arctic winter 2015/2016: characterization, in situ validation and comparison to Aura/MLS

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) was operated on board the German High Altitude and Long Range Research Aircraft (HALO) during the PGS (POLSTRACC/GW-LCYCLE/SALSA) aircraft campaigns in the Arctic winter 2015/2016. Research flights were conducted from 17 December 2015 until 18 March 2016 within 25–87°N, 80°W–30°E. From the GLORIA infrared limb-emission measurements, two-dimensional cross sections of temperature, HNO3, O3, ClONO2, H2O and CFC-12 are retrieved. During 15 scientific flights of the PGS campaigns the GLORIA instrument measured more than 15000 atmospheric profiles at high spectral resolution. Dependent on flight altitude and tropospheric cloud cover, the profiles retrieved from the measurements typically range between 5 and 14km, and vertical resolutions between 400 and 1000m are achieved. The estimated total (random and systematic) 1σ errors are in the range of 1 to 2K for temperature and 10% to 20% relative error for the discussed trace gases. Comparisons to in situ instruments deployed on board HALO have been performed. Over all flights of this campaign the median differences and median absolute deviations between in situ and GLORIA observations are −0.75 K ± 0.88K for temperature, −0.03 ppbv ± 0.85ppbv for HNO3, −3.5 ppbv ± 116.8ppbv for O3, −15.4 pptv ± 102.8pptv for ClONO2, −0.13 ppmv ± 0.63ppmv for H2O and −19.8 pptv ± 46.9pptv for CFC-12. Seventy-three percent of these differences are within twice the combined estimated errors of the cross-compared instruments. Events with larger deviations are explained by atmospheric variability and different sampling characteristics of the instruments. Additionally, comparisons of GLORIA HNO3 and O3 with measurements of the Aura Microwave Limb Sounder (MLS) instrument show highly consistent structures in trace gas distributions and illustrate the potential of the high-spectral-resolution limb-imaging GLORIA observations for resolving narrow mesoscale structures in the upper troposphere and lower stratosphere (UTLS)

Proceedings of the 4th International Conference on Transport, Atmosphere and Climate

The "4th International Conference on Transport, Atmosphere and Climate (TAC-4)" held in Bad Kohlgrub (Germany), 2015, was organised with the objective of updating our knowledge on the impacts of transport on the composition of the atmosphere and on climate, three years after the TAC-3 conference in Prien am Chiemsee (Germany). The TAC-4 conference covered all aspects of the impact of the different modes of transport (aviation, road transport, shipping etc.) on atmospheric chemistry, microphysics, radiation and climate, in particular

The Coexistence of Gravity Waves From Diverse Sources During a SOUTHTRAC Flight

We use observations from one of the SOUTHTRAC (Southern Hemisphere Transport, Dynamics, and Chemistry) Campaign flights in Patagonia and the Antarctic Peninsula during September 2019 to analyze possible sources of gravity waves (GW) in this hotspot during austral late winter and early spring. Data from two of the instruments onboard the German High Altitude and Long Range Research Aircraft (HALO) are employed: the Airborne Lidar for Middle Atmosphere research (ALIMA) and the Basic HALO Measurement and Sensor System (BAHAMAS). The former provides vertical temperature profiles along the trajectory, while the latter gives the three components of velocity, pressure, and temperature at the flight position. GW-induced perturbations are obtained from these observations. We include numerical simulations from the Weather Research and Forecast (WRF) model to place a four-dimensional context for the GW observed during the flight and to present possible interpretations of the measurements, for example, the orientation or eventual propagation sense of the waves may not be inferred using only data obtained onboard. We first evaluate agreements and discrepancies between the model outcomes and the observations. This allowed us an assessment of the WRF performance in the generation, propagation, and eventual dissipation of diverse types of GW through the troposphere, stratosphere, and lower mesosphere. We then analyze the coexistence and interplay of mountain waves (MW) and non-orographic (NO) GW. The MW dominate above topographic areas and in the direction of the so-called GW belt, whereas the latter waves are mainly relevant above oceanic zones. WRF simulates NOGW as mainly upward propagating entities above the lower stratosphere. Model runs show that deep vertical propagation conditions are in general favorable during this flight but also that in the upper stratosphere and lower mesosphere and mainly above topography there is some potential for wave breaking. The numerical simulations evaluate the GW drag for the whole flight area and find that the strongest effect is located in the zonal component around the stratopause. The general behavior against height resembles that obtained with a local fixed lidar data. According to WRF results, up to 100 km horizontal wavelength MW account for about half of the force opposing the circulation of the atmosphere

A Spectral Rotary Analysis of Gravity Waves: An Application During One of the SOUTHTRAC Flights

To understand the main orographic and non-orographic sources of gravity waves (GWs) over South America during an Experiment (Rapp et al., 2021, https://doi.org/10.1175/BAMS-D-20-0034.1), we propose the application of a rotational spectral analysis based on methods originally developed for oceanographic studies. This approach is deployed in a complex scenario of large-amplitude GWs by applying it to reanalysis data. We divide the atmospheric region of interest into two height intervals. The simulations are compared with lidar measurements during one of the flights. From the degree of polarization and the total energy of the GWs, the contribution of the upward and downward wave packets is described as a function of their vertical wavenumbers. At low levels, a larger downward energy flux is observed in a few significant harmonics, suggesting inertial GWs radiated at polar night jet levels, and below, near to a cold front. In contrast, the upward GW energy flux, per unit area, is larger than the downward flux, as expected over mountainous areas. The main sub-regions of upward GW energy flux are located above Patagonia, the Antarctic Peninsula and only some oceanic sectors. Above the sea, there are alternating sub-regions dominated by linearly polarized GWs and sectors of downward GWs. At the upper levels, the total available GW energy per unit mass is higher than at the lower levels. Regions with different degrees of polarization are distributed in elongated bands. A satisfactory comparison is made with an analysis based on the phase difference between temperature and vertical wind disturbances

Non-orographic gravity waves and turbulence caused by merging jet streams

Jet streams are important sources of non-orographic internal gravity waves and clear air turbulence (CAT). We analyze non-orographic gravity waves and CAT during a merger of the polar front jet stream (PFJ) with the subtropical jet stream (STJ) above the southern Atlantic. Thereby, we use a novel combination of airborne observations covering the meso-scale and turbulent scale in combination with high-resolution deterministic short-term forecasts. Coherent phase lines of temperature perturbations by gravity waves stretching along a highly sheared tropopause fold are simulated by the ECMWF IFS (integrated forecast system) forecasts. During the merging event, the PFJ reverses its direction from approximately antiparallel to parallel with respect to the STJ, going along with strong wind shear and horizontal deformation. Temperature perturbations in limb-imaging and lidar observations onboard the research aircraft HALO during the SouthTRAC campaign show remarkable agreement with the IFS data. Ten hours earlier, the IFS data show an “X-shaped” pattern in the temperature perturbations emanating from the sheared tropopause fold. Tendencies of the IFS wind components show that these gravity waves are excited by spontaneous emission adjusting the strongly divergent flow when the PFJ impinges the STJ. In situ observations of temperature and wind components at 100 Hz confirm upward propagation of the probed portion of the gravity waves. They furthermore reveal embedded episodes of light-to-moderate CAT, Kelvin Helmholtz waves, and indications for partial wave reflection. Patches of low Richardson numbers in the IFS data coincide with the CAT observations, suggesting that this event was accessible to turbulence forecasting