Messung individueller Risikoeinstellungen

Es werden verschiedene Methoden zur Messung der Risikoeinstellung einzelner Individuen vorgestellt und kritisch diskutiert. Berücksichtigt werden unter anderem Selbsteinschätzungen und experimentell orientierte Verfahren. Die Zusammenstellung wendet sich insbesondere an Wissenschaftler und Praktiker, die nach anwendbaren Verfahren zur Risikoeinstellungsmessung suchen

The Nature of Eddy Kinetic Energy in the Labrador Sea: Different Types of Mesoscale Eddies, their Temporal Variability and Impact on Deep Convection

Oceanic eddies are an important component in preconditioning the central Labrador Sea (LS) for deep convection and in restratifying the convected water. This study investigates the different sources and impacts of Eddy Kinetic Energy (EKE) and its temporal variability in the LS with the help of a 52-year long hindcast simulation of a 1/20° ocean model. Irminger Rings (IR) are generated in the West Greenland Current (WGC) between 60 and 62°N, mainly affect preconditioning and limit the northward extent of the convection area. The IR exhibit a seasonal cycle and decadal variations linked to the WGC strength, varying with the circulation of the subpolar gyre. The mean and temporal variations of IR generation can be attributed to changes in deep ocean baroclinic and upper ocean barotropic instabilities at comparable magnitudes. The main source of EKE and restratification in the central LS are Convective Eddies (CE). They are generated by baroclinic instabilities near the bottom of the mixed layer during and after convection. The CE have a mid-depth core and reflect the hydrographic properties of the convected water mass with a distinct minimum in potential vorticity. Their seasonal to decadal variability is tightly connected to the local atmospheric forcing and the associated air-sea heat fluxes. A third class of eddies in the LS are the Boundary Current Eddies shed from the Labrador Current (LC). Since they are mostly confined to the vicinity of the LC, these eddies appear to exert only minor influence on preconditioning and restratification

The Nature and Variability of Eddy Kinetic Energy in an Ocean General Circulation Model With a Focus on the South Pacific Subtropical Gyre and the Labrador Sea

This thesis focuses on the nature of oceanic Eddy Kinetic Energy (EKE), its generation and temporal variability. An Ocean General Circulation Model (OGCM) based on the NEMO code builds the foundation for these investigations. For a first case study, several simulations of a 1/4° configuration are used to investigate the temporal variability of EKE in the South Pacific Subtropical Countercurrent (STCC). Decadal changes in wind stress curl associated with the Interdecadal Pacific Oscillation (IPO) lead to up- and downwelling in the STCC, influencing the meridional density gradient and thereby STCC strength, baroclinic instability and the resulting EKE. An additional 30 to 40% of the local density anomalies can be explained by long baroclinic Rossby waves propagating into the region, modulating the decadal signal of the IPO’s influence in the STCC on interannual time scales. In a second case study, the model’s horizontal resolution is regionally increased to 1/20° in the North Atlantic to investigate different types of mesoscale eddies in the Labrador Sea. On decadal time scales, the temporal variability of EKE in the LS is driven by the large-scale atmospheric circulation. In the case of Convective Eddies (CE), local winter heat loss leads to deep convection, a baroclinically unstable rim-current is established along the edge of the convection area and generates EKE at mid-depth. The variations of EKE associated with the surface intensified Irminger Rings (IR) and Boundary Current Eddies are driven by the large-scale changes of the currents of the subpolar gyre. While IR play a vital role in stratifying large parts of the LS and thus suppressing deep convection, CE are the major driver of rapid restratification during and after deep convection

VLBI and GPS-based Time-Transfer Using CONT08 Data

One important prerequisite for geodetic Very Long Baseline Interferometry (VLBI) is the use of frequency standards with excellent short term stability. This makes VLBI stations, which are often co-located with Global Navigation Satellite System (GNSS) receiving stations, interesting for studies of time- and frequency-transfer techniques. We present an assessment of VLBI time-transfer based on the data of the two week long consecutive IVS CONT08 VLBI campaign by using GPS Carrier Phase (GPSCP). CONT08 was a 15 day long campaign in August 2008 that involved eleven VLBI stations on five continents. For CONT08 we estimated the worst case VLBI frequency link stability between the stations of Onsala and Wettzell to 1e-15 at one day. Comparisons with GPSCP confirm the VLBI results. We also identify time-transfer related challenges of the VLBI technique as used today

Temporal Variability of Oceanic Eddy Kinetic Energy: A High Resolution Model Analysis

Mesoscale variability of velocities is an important part of the global ocean circulation, as it contains more kinetic energy than the mean flow over most of the ocean. Understanding its generation, dissipation and modulation processes therefore is crucial to better understand ocean circulation in general. In this thesis, a global 1/12◦ ocean model (ORCA12) is used to study the distribution of mean surface Eddy Kinetic Energy (EKE), its seasonal cycle and possible driving mechanisms, averaged over 26 years (1981-2007). For the calculation of EKE, the deviations from yearly mean horizontal velocities u, v are found to be best suitable. The model is then evaluated using EKE derived from satellite altimetry (AVISO). The total EKE from the model, including geostrophic parts, realistically reproduces the observed geostrophic mean EKE and its seasonal cycle. Seasonal cycles of surface EKE in the subtropical gyres, including most of the Western Boundary Currents (WBCs), peak in the summer months in both hemispheres. The mean EKE and amplitudes of the annual cycle are generally larger in the Pacific, compared to the Atlantic. The seasonal variations of EKE in the WBCs are driven by dissipation processes at the sea surface, namely the wind stress and thermal interactions with the atmosphere in winter. Only in the core regions of the currents other processes play a role as the surface EKE there peaks in winter/spring, not consistent with the dissipation hypothesis. The balance of dissipation and generation terms in the strong, chaotic WBCs, however, varies from year to year. In the subtropical gyres’ interior, dissipation is not solely responsible for the annual cycle. Instead, the vertical shear of near-surface horizontal velocities is found to peak in summer, in phase with the EKE. This seasonal cycle of the shear can be observed down to ∼ 150m depth, depending on the region. Inspections of profiles of horizontal velocity and EKE reveal the vertical shear to be associated with the velocity differences between the Mixed Layer and the interior ocean, possibly leading to instabilities which locally generate surface intensified EKE, largest in summer. Therefore, the seasonal cycle of near-surface vertical shear of horizontal velocities seems to be responsible for the seasonal variations of surface EKE, although the general source of EKE in the subtropical gyres remains unclear

Decadal variability of Eddy Kinetic Energy in the South Pacific Subtropical Countercurrent in an Ocean General Circulation Model

The Eddy Kinetic Energy (EKE) associated with the Subtropical Countercurrent (STCC) in the western subtropical South Pacific is known to exhibit substantial seasonal and decadal variability. Using an eddy-permitting ocean general circulation model, which is able to reproduce the observed, salient features of the seasonal cycles of shear, stratification, baroclinic production and the associated EKE, we investigate the decadal changes of EKE. We show that the STCC region exhibits, uniquely among the subtropical gyres of the world’s oceans, significant, atmospherically forced, decadal EKE variability. The decadal variations are driven by changing vertical shear between the STCC in the upper 300 m and the South Equatorial Current below, predominantly caused by variations in STCC strength associated with a changing meridional density gradient. In the 1970s, an increased meridional density gradient results in EKE twice as large as in later decades in the model. Utilizing sensitivity experiments, decadal variations in the wind field are shown to be the essential driver. Local wind stress curl anomalies associated with the Interdecadal Pacific Oscillation (IPO) lead to up- and downwelling of the thermocline, inducing strengthening or weakening of the STCC and the associated EKE. Additionally, remote wind stress curl anomalies in the eastern subtropical South Pacific, which are not related to the IPO, generate density anomalies that propagate westward as Rossby waves and can account for up to 30–40 % of the density anomalies in the investigated region