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The analysis of the global stratospheric meridional circulation, known as the Brewer-Dobson circulation, is an essential part of both experimental and theoretical atmospheric sciences. This large-scale circulation has a crucial influence on the global burden of greenhouse gases and ozone depleting substances throughout the complete atmosphere. This makes it an important factor for the Earth’s radiative budget, which is perceptible at the Earth’s surface despite the remote location of the stratosphere. In the course of climate change it is generally expected that also the Brewer-Dobson circulation undergoes significant changes in structure and strength, although the exact repercussions are still uncertain and thus remain an open scientific question. A general problem for the observational investigation of the dynamical processes in the stratosphere is that residual mean transport cannot be measured directly and hence requires the use of sophisticated proxies. Many studies in the past consider the so-called mean age of air, which is a measure of the average time an air parcel has spent in the stratosphere since passing a certain reference point. While changes in the strength and structure can be detected and visualized using mean age of air, a more thorough distinction between the different involved transport mechanisms of the circulation (residual circulation, mixing) cannot be made. For that, consideration of a full distribution of all relevant transit times through the stratosphere, an age spectrum, is favorable and a powerful tool to analyze the spatial structure as well as possible future changes in detail. Mean age of air and age spectra can be readily derived in atmospheric modeling studies, but an observationally based retrieval is challenging. Mean age of air is usually approximated from measurements of very long-lived trace gas species that act as a dynamical tracer for the stratosphere. The retrieval of age spectra from observations, however, remains an open task for which different methods have been proposed in the past, that often require a combination of strong assumptions and model data explicitly. This is a major issue for a precise and independent investigation of stratospheric dynamics based on measurements. The focus of this cumulative dissertation is on the development process and application of an inversion method to derive stratospheric age spectra from mixing ratios of chemically active substances that combines an applicable and precise ansatz with a minimized amount of necessary model data. Chemically active species have the important benefit that chemistry and transport in the stratosphere are strongly correlated so that the state of depletion of a trace gas can give some information on certain parts of the age spectrum. Considering a sufficient number of distinct trace gases simultaneously, a full approximation of the age spectrum should be possible. The main section of this thesis is split into three parts, which follow the main aspects and key results of the three publications involved (Hauck et al., 2019, 2020; Keber et al., 2020). The newly developed inverse method is based upon the previously established ansatz by Schoeberl et al. (2005), but constrains the shape of the age spectrum by a single parameter inverse Gaussian function. This keeps the balance between applicability and accuracy with a limited amount of measurement data. Additionally, the method introduces a seasonal scaling factor that imposes higher order maxima and minima onto the intrinsically monomodal spectrum based on the seasonal cycle of the tropical upward mass flux to incorporate phases of weaker and stronger transport. A proof of concept of the inverse method is provided using an idealized simulation of the ECHAM/MESSy Atmospheric Chemistry (EMAC) model, where the method is applied to a set of artificial radioactive trace gases with known chemical lifetime. The results imply that the method works properly and retrieves age spectra that match the EMAC reference spectra significantly well on the global and seasonal scale. Only in the lower stratosphere, the performance of the inverse method on the seasonal scale decreases as entrainment into the stratosphere is considered only across the tropical tropopause. Transport across the local extratropical tropopause, however, is a key feature for trace gases in the extratropical lowermost stratosphere so that this entrainment must be included explicitly.
In the second part, the discovered problems are approached to make the inverse method applicable to observations. The formulation of the method is extended to incorporate transport explicitly across the tropical (30° S – 30° N), northern extratropical (30° N – 90° N), and southern extratropical tropopause (30° S – 90° S) each with a single age spectrum that can be inverted independently.
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Background: Point of care devices for performing targeted coagulation substitution in bleeding patients have become increasingly important in recent years. New on the market is the Quantra® from HemoSonics (LC, Charlottesville, VA, US). It uses sonorheometry, a sonic estimation of elasticity via resonance (SEER), a novel ultrasound-based technology that measures viscoelastic properties of whole blood. Several studies have already shown the comparability with devices already established on the market such as the ROTEM® (TEM International GmbH, Munich, Germany).
Objective: In contrast to existing studies, the planned study will be the first prospective interventional study using the new Quantra® system in a cardiac surgical patient cohort. The aim is to investigate the non-inferiority between an already existing coagulation algorithm, based on ROTEM®/Multiplate®, and a new algorithm based on the Quantra®, for the treatment of coagulopathic cardiac surgical patients.
Methods: The study is divided into two phases. In an initial observation phase, whole blood samples of 20 patients will be analyzed using both ROTEM®/Multiplate® and Quantra® obtained at three defined points of time (prior to surgery, after completion of cardiopulmonary bypass, on arrival in the intensive care unit). The obtained threshold values will be used to create an algorithm for hemotherapy. In a second intervention phase, the new algorithm will be tested against an algorithm used routineously for years at our department for non-inferiority.
Results: The main objective of the examination is the cumulative loss of blood within 24 hours after surgery. Statistical calculations based on literature and in-house data suggest that the new algorithm is not inferior if the difference in cumulative blood loss is < 150ml/24 h.
Conclusions: Because of the comparability of the Quantra® sonorheometry system with ROTEM® rotational thromboelastometric measurement methods, the existing hemotherapy treatment algorithm can be adapted to the Quantra device with a proof of non-inferiority. Clinical Trial: International Registered Report Identifier (IRRID): clinicaltrials.gov: NCT03902275