Using MTP measurements to characterise atmospheric gravity waves in the tropopause region

Atmosphärische Schwerewellen, die nahe am Erdboden angeregt werden, können weit in die Atmosphäre propagieren. Wenn sie brechen, übertragen sie ihre Energie und ihren Impuls an die Hintergrundströmung und treiben damit die globale Zirkulation der mittleren Atmosphäre. Um das Verständnis über die Entstehung und Ausbreitung von Schwerewellen durch die Atmosphäre weiter zu vergrößern, werden u.a. Messkampagnen mit Forschungsflugzeugen durchgeführt, bei denen besonders die Tropopausen-Region im Fokus steht. Diese ist als Barriere für die Ausbreitung von Schwerewellen in größere Höhen bekannt. Mit Hilfe eines passiven Mikrowellenradiometers, dem Microwave Temperature Profiler (MTP), können vom Flugzeug aus Temperaturmessungen sowohl ober- als auch unterhalb der aktuellen Flughöhe gemacht werden. Da atmosphärische Schwerewellen Temperaturschwankungen hervorrufen, bieten die Messungen des MTP eine gute Möglichkeit Schwerewellen direkt messen und charakterisieren zu können. In der folgenden Arbeit wird untersucht, welche Temperaturfluktuationen vom MTP erfasst werden können und wie gut die Eigenschaften von Schwerewellen, wie ihre horizontale und vertikale Wellenzahl und die intrinsische Frequenz, aus den Temperaturdaten des MTP abgeleitet werden können. Hierzu wird eine Kalibrationsmessung im Labor ausgewertet, um die Detektionsgrenze für Temperaturstörungen festlegen zu können. Des Weiteren wird mit Hilfe von Strahlungstransportsimulationen bestimmt, über welchen Bereich der Atmosphäre Informationen in den MTP-Daten enthalten sind. Es wird gezeigt, dass das MTP atmosphärische Temperaturen mit einer Präzision von 0,37 K messen kann, und eine Analyse von Welleneigenschaften für Temperaturfluktuationen von mindestens 1,5 K Amplitude möglich ist. Das MTP kann über einen Bereich von 2-3 km um die Flughöhe Informationen über die potentielle Temperatur, die Stabilität der Schichtung der Luftmassen, sowie dort auftretende Wellen sammeln. Um Schwerewellen charakterisieren zu können, wurde ein neuer Algorithmus zur Auswertung der aus den MTP-Daten abgeleiteten Tempeaturprofilen entwickelt. In dieser Arbeit wird der Algorithmus vorgestellt und seine Kapazitäten in der Erkennung von Wellen-Eigenschaften in MTP-Daten in einer Studie mit synthetischen Daten getestet. Es wird gezeigt, dass die vertikale Wellenlänge und intrinsische Frequenz mit einer Unsicherheit von maximal 30 % bestimmt werden können. Mit Hilfe von MTP-Daten ist es damit möglich, die Bedingungen für Wellen-Ausbreitung innerhalb der Tropopausen-Region zu bewerten. Schließlich wird der neue Algorithmus benutzt, um Messdaten der DEEPWAVEKampagne, die 2014 in Neuseeland stattfand, auszuwerten. Hier zeigt die Auswertung der MTP-Daten, dass auf Flug-Niveau gemessene Impulsflüsse nicht immer bis zur Stratosphäre gelangen. Die Messungen des MTP bieten einen einzigartigen und wichtigen Einblick in die vorherrschenden Bedingungen für Wellenausbreitung durch die Tropopausenregion.Atmospheric gravity waves, which have sources close to the Earth’s surface, can propagate deep into the atmosphere. When these waves break, the energy and momentum they carry is transferred to the background wind. Thus, they drive the global circulation within the middle atmosphere. As one approach to enhance the understanding of the source processes and the propagation of gravity waves through the atmosphere, measurement campaigns with research aircraft have been conducted, which focus on the troposphere region. This region is known to be a barrier for propagation of gravity waves into higher altitudes. With the help of a passive microwave radiometer, the Microwave Temperature Profiler (MTP), measurements of temperature, both, above and below the aircraft can be conducted. As atmospheric gravity waves cause temperature fluctuations, the MTP provides the possibility to directly measure and characterise gravity waves. In the following thesis it will be assessed, which temperature fluctuation signals can be resolved by the MTP instrument and how well characteristics of gravity waves, such as their horizontal and vertical wavenumbers and the intrinsic frequency, can be derived. Calibration measurements in a laboratory will be analysed to define the lower threshold of detectable temperature fluctuation amplitudes. Moreover, radiative transfer calculations will be carried out to investigate which part of the atmosphere the MTP measurements are sensitive to. It will be shown that the MTP is able to measure atmospheric temperatures with a precision of 0:37 K, and that an analysis of wave characteristics is possible from temperature fluctuations with amplitudes of at least 1:5 K. The MTP is sensitive to a vertical altitude region of 2-3 km around the research aircraft, and is able to collect information on the potential temperatures and static stability of the air masses surrounding the aircraft, as well as on gravity waves within this region. To characterise the gravity waves, a new algorithm for further analysis of the temperature profiles derived from MTP measurements has been developed. This algorithm will be described within this thesis and its capabilities of detecting wave characteristics will be tested in a synthetic data study. It will be shown, that the vertical wavelengths and intrinsic frequencies can be derived with a maximum uncertainty of 30 %. Hence, through the use of MTP data, it is possible to assess propagation conditions for gravity waves within the tropopause region. Finally, the algorithm will be used to evaluate measurements from the DEEPWAVE campaign, which took place in New Zealand in 2014. For these data, the analysis shows that momentum fluxes derived from flight-level measurements, do not always reach the stratosphere. The measurements by the MTP instrument provide a unique and important insight to the prevailing conditions of wave propagation through the tropopause region

Using MTP measurements to characterise atmospheric gravity waves in the Tropopause region

Atmosphärische Schwerewellen, die nahe am Erdboden angeregt werden, können weit in die Atmosphäre propagieren. Wenn sie brechen, übertragen sie ihre Energie und ihren Impuls an die Hintergrundströmung und treiben damit die globale Zirkulation der mittleren Atmosphäre. Um das Verständnis über die Entstehung und Ausbreitung von Schwerewellen durch die Atmosphäre weiter zu vergrößern, werden u.a. Messkampagnen mit Forschungsflugzeugen durchgeführt, bei denen besonders die Tropopausen-Region im Fokus steht

39th session of the WCRP Joint Scientific Committee

The thirty-ninth session of the Joint Scientific Committee (JSC-39) of the World Climate Research Programme (WCRP) was held at the Nanjing University of Information Science & Technology (NUIST) in Nanjing, China, from 16 to 20 April 2018

Retrieval of Atmospheric Temperature from Airborne Microwave Radiometer Observations

Atmospheric temperature is a key geophysical parameter associated with fields such as meteorology,climatology, or photochemistry. There exist several techniques to measure temperature profiles. In the case of microwave remote sensing, the vertical temperature profile can be estimated from thermal emission lines of molecular oxygen. The MTP (Microwave Temperature Profiler) instrument is an airborne radiometer developed at the Jet Propulsion Laboratory (JPL), United States. The instrument passively measures natural thermal emission from oxygen lines at 3 frequencies and at a selection of 10viewing angles (from near zenith to near nadir). MTP has participated in hundreds of flights, including on DLR's Falcon and HALO aircraft. These flights have provided data of the vertical temperature distribution from the troposphere to the lower stratosphere with a good temporal and spatial resolution. In this work, we present temperature retrievals based on the Tikhonov regularized nonlinear leastsquares fitting method. In particular, Jacobians (i.e. temperature derivatives) are evaluated by means of automatic differentiation. The retrieval performance from the MTP measurements is analyzed by using synthetic and real data. Besides, the vertical sensitivity of the temperature retrieval is studied by weighting functions characterizing the sensitivity of the transmission at different frequencies with respect to changes of altitude levels

Towards the Temperature Retrieval by Using Airborne Microwave Radiometer Data

Atmospheric temperature is a key geophysical parameter when dealing with the atmosphere in areas such as climatology and meteorology. In general, thermal emissions of molecular lines (e.g. oxygen, carbon dioxide) can be used for the determination of the temperature profile. The superheterodyne radiometer MTP (Microwave Temperature Profiler) passively detects thermal emission from oxygen lines at a selection of frequencies between 55--60 GHz by scanning the atmosphere from near zenith to near nadir in the flight direction. The MTP instrument was designed to observe the vertical temperature distribution over the upper troposphere and lower stratosphere (UTLS) with a good temporal and spatial resolution. The instrument was originally developed at NASA's JPL and has been recently flown on DLR's Falcon and HALO research aircrafts. To estimate the temperature profile from microwave measurements (e.g. provided by MTP), the retrieval algorithm TIRAMISU (Temperature Inversion Algorithm for Microwave Sounding) has been developed at DLR and is currently used to conduct the data processing of the MTP measurements. This study performs the retrievals from the MTP data with a focus on the ML-CIRRUS mission. The corresponding retrieval performance is investigated by associated error characterization and external comparisons with other ground-based and satellite observations. These observations are important to resolve a variety of phenomena in the UTLS region and to potentially improve the temperature spaceborne soundings

Estimating atmospheric temperature profile by an airborne microwave radiometer

As the rising atmospheric issues such as climate change, air pollution, and ozone depletion have extracted extensive attraction worldwide, observing and modeling of atmospheric quantities becomes critical to our understanding of the environment. This work focuses on the performance of an airborne passive microwave radiometer called MTP (Microwave Temperature Profiler). We aim to obtain vertically distributed atmospheric temperature from intensities measured by the instrument in terms of three frequencies and ten viewing angles. A retrieval program TIRAMISU (Temperature InveRsion Algorithm for MIcrowave SoUnding) has been utilized for processing the MTP data. To solve this severely ill-posed inverse problem, an analysis of different ways of constructing the penalty term onto the Tikhonov-type objective function is conducted. This numerical analysis can help us to better understand pros and cons of these regularization methods and to investigate the measurement capabilities of MTP

ACRIDICON–CHUVA Campaign: Studying Tropical Deep Convective Clouds and Precipitation over Amazonia Using the New German Research Aircraft HALO

Between 1 September and 4 October 2014, a combined airborne and ground-based measurement campaign was conducted to study tropical deep convective clouds over the Brazilian Amazon rain forest. The new German research aircraft, High Altitude and Long Range Research Aircraft (HALO), a modified Gulfstream G550, and extensive ground-based instrumentation were deployed in and near Manaus (State of Amazonas). The campaign was part of the German–Brazilian Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON– CHUVA) venture to quantify aerosol–cloud–precipitation interactions and their thermodynamic, dynamic, and radiative effects by in situ and remote sensing measurements over Amazonia. The ACRIDICON–CHUVA field observations were carried out in cooperation with the second intensive operating period of Green Ocean Amazon 2014/15 (GoAmazon2014/5). In this paper we focus on the airborne data measured on HALO, which was equipped with about 30 in situ and remote sensing instruments for meteorological, trace gas, aerosol, cloud, precipitation, and spectral solar radiation measurements

ML-CIRRUS: The Airborne Experiment on Natural Cirrus and Contrail Cirrus with the High-Altitude Long-Range Research Aircraft HALO

The Midlatitude Cirrus experiment (ML-CIRRUS) deployed the High Altitude and Long Range Research Aircraft (HALO) to obtain new insights into nucleation, life cycle, and climate impact of natural cirrus and aircraft-induced contrail cirrus. Direct observations of cirrus properties and their variability are still incomplete, currently limiting our understanding of the clouds’ impact on climate. Also, dynamical effects on clouds and feedbacks are not adequately represented in today’s weather prediction models.Here, we present the rationale, objectives, and selected scientific highlights of ML-CIRRUS using the G-550 aircraft of the German atmospheric science community. The first combined in situ–remote sensing cloud mission with HALO united state-of-the-art cloud probes, a lidar and novel ice residual, aerosol, trace gas, and radiation instrumentation. The aircraft observations were accompanied by remote sensing from satellite and ground and by numerical simulations.In spring 2014, HALO performed 16 flights above Europe with a focus on anthropogenic contrail cirrus and midlatitude cirrus induced by frontal systems including warm conveyor belts and other dynamical regimes (jet streams, mountain waves, and convection). Highlights from ML-CIRRUS include 1) new observations of microphysical and radiative cirrus properties and their variability in meteorological regimes typical for midlatitudes, 2) insights into occurrence of in situ–formed and lifted liquid-origin cirrus, 3) validation of cloud forecasts and satellite products, 4) assessment of contrail predictability, and 5) direct observations of contrail cirrus and their distinction from natural cirrus. Hence, ML-CIRRUS provides a comprehensive dataset on cirrus in the densely populated European midlatitudes with the scope to enhance our understanding of cirrus clouds and their role for climate and weather