Sensitivity of Southern Ocean sea-ice simulations to different atmospheric forcing algorithms

Sea ice is sensitively dependent on the fluxes of energy, mass and momentum between the ocean and the atmosphere, making it worth investigating the modification of these fluxes by the respective boundary layers. Complementary to earlier investigations with a coupled sea-ice-oceanic mixed-layer model for the Southern Ocean, the atmospheric forcing in the present investigation is changed from monthly, observational data to daily, essentially modelled values computed by an operational numerical weather-prediction model. Applying these computations directly as atmospheric surface forcing to the sea-ice-oceanic mixed-layer model yields (in first order) encouraging results, indicating the general reliability of these data. As a supplement to the oceanic mixed-layer model, the fluxes derived from the atmospheric forcing are modified in a first step to include the stability dependency of the atmospheric surface-layer. Compared to the application of usual adjustment practices, this leads to improved results, especially with respect to the ice velocities in divergent ice fields. In the next step, the atmospheric forcing level is raised to the geostrophic level thus incorporating the entire atmospheric boundary layer. While the forcing fields become less dependent on the prescribed boundary conditions of the weather-prediction model, the simulations appear to be reasonable only when the near-surface wind forcing is applied, the overall roughness length is increased and the large-scale stability is reduced. This leads to important implications for coupled atmosphere-sea-ice-ocean models

Meereismodellierung im südlichen Ozean

Das von Hibler (1979) für den Arktischen Ozean entwickelte dynamisch - thermodynamische Meereismodell wurde von Hibler und Ackley (1983) auf das Weddellmeer angewendet. Dieses Modell wurde von Lemke et al. (1990) mit dem ein-dimensionalen ozeani- schen Deckschichtmodell von Lemke (1987) gekoppelt, um den vertikalen ozeanischen Wärmefluß in Abhängigkeit von der Eisbil- dung und nachfolgender Konvektion zu beschreiben. Außerdem führten Owens und Lemke (1990) die Schneehöhe als weitere pro- gnostische Variable im Modell ein. In der vorliegenden Arbeit wird das so modifizierte Weddell- Meereismodell auf die Region des gesamten Südlichen Ozeans er- weitert und im ersten Teil der Arbeit mit klimatologischen Mo- nats- bzw. Jahresmittelwerten angetrieben. Die Ergebnisse des Standardlaufs werden mit Analyseergebnissen aus Satellitendaten, vereinzelten Bodenbeobachtungen bzw. -mes- sungen, und Ergebnissen aus früheren dynamisch-thermo- dynamischen Meereismodellen verglichen. Außerdem werden Sensitivitätsuntersuchungen durchgeführt, um den Einfluß verschiedener physikalischer und numerischer Parameter zu untersuchen. Da die atmosphärischen Klimatologien im Bereich des Südlichen Ozeans je nach Herkunft teilweise erheblich voneinander abweichen, wird zum Vergleich mit alternativen Datensätzen angetrieben. Schließlich wird das Modell mit stochastisch variierenden Windfeldern angetrieben, um dem Effekt täglicher Variabilität nachzugehen. Wegen der hohen Inkonsistenz der verschiedenen atmosphärischen Antriebsfelder und der gleichzeitigen hohen Sensitivität des Modells bezüglich dieser Daten (insb. der Windfelder), wird im zweiten Teil der Arbeit zunächst mit aktuellen, täglichen Analysedaten von numerischen Wettervorhersagemodellen angetrieben, die in Regionen geringer Meß- bzw. Beobachtungsdichte physikalisch konsistenter erscheinen als reine Beobachtungsdatenanalysen, die auf lnterpolationsmethoden basieren. Durch Zurückrechnen der Analyse variablen auf deren ursprüngliches Niveau des Atmosphärenmodells und gleichzeitiger Anwendung einer geeigneten Prandtl-Schicht Formulierung können realistische Ergebnisse erzielt werden, ohne dabei Parameter des Meereismodells auf die neuerliche Art des Antriebs anpassen zu müssen. Um eine Vorbestimmung der Lage der Eisgrenze aufgrund der im Atmosphärenmodell vorgegebenen Randwerte zu vermeiden, wird schließlich der Antrieb auf das geostrophische Niveau angehoben. Dies wird durch eine zusätzliche Kopplung des Meereismodells an das ein-dimensionale atmosphärische Grenzschichtmodell von Koch (1988) realisiert. Dabei wird der Antrieb jeweils dem gleichen klimatologischen bzw. aktuellen Datensatz (s.o.) entnommen, diesmal jedoch vom 850 hpa Niveau. Die Ergebnisse aus diesem Teil der Arbeit werden mit den vorhergehenden verglichen und analysiert. Desweiteren werden wiederum diverse Sensitivitätsstudien durchgeführt und damit gleichzeitig Probleme, die mit dem höheren Antriebsniveau und der eingeschränkten Anwendbarkeit des atmosphärischen Grenzschichtmodells zusammenhängen, diskutiert.I. Zusammenfassung (Abstract) II. Symbol liste A. Symbole B. Indizes III. Einleitung A. Sinn und Ziel B. Vorhergehende Arbeiten C. Übergang (Gliederung) IV. Angewandte Modelle A. Meereismodell B. Deckschichtmodell des Ozeans V. Modellkonfiguration A. Kopplung B. Modellgitter C. Numerik D. Technische Daten VI. Antriebsdaten A. Atmosphäre 1. Klimatologische Daten 2. Aktuelle Daten B. Ozean VII. Verifikationsdaten A. Eis 1. Bodenbeobachtungen 2. Satellitendaten 3. Ergebnisse vorhergehender Modelle B. Grenzschicht VIII. Ergebnisse mit atmosphärischem Antrieb an der Oberfläche A. Atmosphärischer Antrieb mit monatlichen (klimatologischen) Daten (Zyklus 4) 1. Standardexperiment 2. Sensitivitätsuntersuchungen a. Ozeanische Deckschichttiefe konstant b. Vernachlässigung von Schnee c. Erhöhung der Eisfestigkeit d. Verlangsamung des Schließens von Rinnen e. Vernachlässigung der Advektion f. Vernachlässigung der geostrophischen Strömung 3. Alternative Antriebsfelder a. Wind b. Temperatur c. Niederschlag 4. Stochastische Windvariabilität 5. Diskussion B. Atmosphärischer Antrieb mit täglichen (aktuellen) Daten (Zyklus 8) 1. Standardexperiment 2. Sensitivitätsuntersuchungen a. Erhöhung der Eisfestigkeit und der Schubspannung b. Einbeziehung der atmosphärischen Oberflächenschicht 3. Diskussion IV. Schlußfolgerungen aus bisherigen Ergebnissen X. Modellerweiterung A. Grenzschichtmodell der Atmosphäre B. Ankopplung des Grenzschichtmodells C. Antrieb XI. Ergebnisse mit atmosphärischem Antrieb im geostrophischen Niveau A. Atmosphärischer Antrieb mit monatlichen (klimatologischen) Daten (Zyklus 5) B. Atmosphärischer Antrieb mit täglichen (aktuellen) Daten (Zyklus 6) 1. Standardexperiment 2. Sensitivitätsuntersuchungen a. Reduzierung der Modellphysik b. Einfluß des Windfeldes c. Erhöhung der Oberflächenrauhigkeit d. Verhältnis der Schubspannungskoeffizienten e. Einfluß der Winddrehung f . Erhöhung des Auftriebsflusses 3. Diskussion XII. Schlußfolgerungen und Ausblick XIII. Danksagung XIV. Literaturverzeichnis XV. Anhang: Theorie der angewandten Modelle A. Meereismodell 1. Dynamisches Teilmodell 2. Kontinuitätsgleichungen 3. Thermodynamísches Teilmodell B. Deckschichtmodeil des Ozeans 1. Erhaltung von Wärme und Salz 2. Parametrisierung der vertikalen Einmischung 3. Energiebilanz C. Oberflächenschicht der Atmosphäre D. Grenzschichtmodell der Atmosphäre XVI. Abbildunge

Southern Ocean sea-ice simulations forced with operationally derived atmospheric analyses data

As a supplement to an earlier paper on a coupled sea—ice — oceanic mixed-layer [SI — OML] model for the Southern Ocean (Stössel et al.‚ 1990), the atmospheric forcing in this investigation is changed from monthly (climatological) data to daily (instantaneous) values. These data are derived from global analyses from the European Center for Medium Range Weather Forecasts (ECMWF). With these computations applied as surface forcing, results similar to the earlier ones are achieved. Adjustments of the SI-model parameters and/or the coefficients of the bulk formulas can be avoided when the forcing is raised to its originally assigned level, using an appropriate Prandtl—layer parameterization. With this extension, the model results are well comparable with observations based on operationally produced ice charts. A further rise of the atmospheric forcing to the geostrophic level by means of coupling a one—dimensional atmospheric boundary—layer [ABL] model to the SI — OML model, reduces the dependency of the results on the (climatologically) prescribed boundary conditions of the operational numerical weather- prediction [NWP] model. The simulations with this extension, however, appear to be reasonable only when the surface wind pattern is applied, the roughness length over ice and water is increased, and the stability of the ABL over ice is generally reduced

Ocean-sea-ice coupling in a global ocean general circulation model

A global ocean general circulation model has been coupled with a dynamic-thermodynamic sea-ice model. This model has been spun-up in a 1000 year integration using daily atmosphere model data. Main water masses and currents are reproduced as well as the seasonal characteristics of the ice cover of the Northern and Southern Hemispheres. Model results for the Southern Ocean, however, show the ice cover as too thin, and there are large permanent polynyas in the Weddell and Ross Seas. These polynyas are due to a large upward oceanic heat flux caused by haline rejection during the freezing of sea ice. Sensitivity studies were performed to test several ways of treating the sea-surface salinity and the rejected brine. The impact on the ice cover, water-mass characteristics, and ocean circulation are described

Human Cutaneous Dendritic Cells Migrate Through Dermal Lymphatic Vessels in a Skin Organ Culture Model

The capacity to migrate from peripheral tissues, where antigen is encountered, to lymphoid organs, where the primary immune response is initiated, is crucial to the immunogenic function of dendritic cells (DC). The skin is a suitable tissue to study migration. DC were observed to gather in distinct nonrandom arrays (“cords”) in the dermis upon culture of murine whole skin explants. It is assumed that cords represent lymphatic vessels. Using a similar organ culture model with human split-thickness skin explants, we investigated migration pathways in human skin.We made the following observations. 1) Spontaneous emigration of Langerhans cells took place in skin cultured for 1–3 d. Nonrandom distribution patterns of strongly major histocompatibility complex class II-expressing DC (cords) occurred in cultured dermis. A variable, yet high (>50%) percentage of these DC coexpressed the Birbeck granule-associated antigen “Lag” Ultrastructurally, the cells corresponded to mature DC. 2) Electron microscopy proved that the dermal structures harboring the accumulations of DC (i.e., cords) were typical lymph vessels. Moreover, markers for blood endothelia (monoclonal antibody PAL-E, Factor VIII-related antigen) and markers for cords (strong major histocompatibility complex class II expression on nonrandomly arranged, hairy-appearing cells) were expressed in a mutually exclusive pattern. 3) On epidermal sheets we failed to detect gross changes in the levels of expression of adhesion molecules (CD44, CD54/ICAM-1, E-cadherin) on keratinocytes in the course of the culture period.The reactivity of a part of the DC in the dermal cords with Birbeck granule-specific monoclonal antibody “Lag” suggests that the migratory population is composed of both epidermal Langerhans cells and dermal DC. We conclude that this organ culture model may prove helpful in resolving pathways and mechanisms of DC migration

Swiss ichthyosaurs: a review

Switzerland is an ichthyosaur country: it has a rich record of marine reptile fossils, particularly the fish-shaped ichthyosaurs, and the according research. Here, we provide an overview over the 12 or more genera and at least 13 species plus numerous fragmentary remains of ichthyosaurs from the Triassic to the Cretaceous that have been discovered in twelve cantons thus far, of which four species are based on Swiss holotypes. This wealth of ichthyosaur species can be explained by their abundance in the Middle Triassic conservation deposits (Konservat Lagerstätte) of Monte San Giorgio, as well as occasional discoveries in strata of Middle Triassic to Early Cretaceous age. The moderate abundance of outcrops in reasonable conditions in combination with the long history of palaeontological research in Switzerland explains this good fossil record. In addition to this unique overview, we provide more data for further studies and update the knowledge of these taxa

Monte Carlo climate change forecasts with a global coupled ocean-atmosphere model

Four time-dependent greenhouse warming experiments were performed with the same global coupled atmosphere-ocean model, but with each simulation using initial conditions from different ''snapshots'' of the control run climate. The radiative forcing - the increase in equivalent CO2 concentrations from 19852035 specified in the Intergovernmental Panel on Climate Change (IPCC) scenario A - was identical in all four 50-year integrations. This approach to climate change experiments is called the Monte Carlo technique and is analogous to a similar experimental set-up used in the field of extended range weather forecasting. Despite the limitation of a very small sample size, this approach enables the estimation of both a mean response and the ''between-experiment'' variability, information which is not available from a single integration. The use of multiple realizations provides insights into the stability of the response, both spatially, seasonally and in terms of different climate variables. The results indicate that the time evolution of the global mean warming signal is strongly dependent on the initial state of the climate system. While the individual members of the ensemble show considerable variation in the pattern and amplitude of near-surface temperature change after 50 years, the ensemble mean climate change pattern closely resembles that obtained in a 100-year integration performed with the same model. In global mean terms, the climate change signals for near surface temperature, the hydrological. cycle and sea level significantly exceed the variability among the members of the ensemble. Due to the high internal variability of the modelled climate system, the estimated detection time of the global mean temperature change signal is uncertain by at least one decade. While the ensemble mean surface temperature and sea level fields show regionally significant responses to greenhouse-gas forcing, it is not possible to identify a significant response in the precipitation and soil moisture fields, variables which are spatially noisy and characterized by large variability between the individual integrations

Exercise reduces systemic immune inflammation index (SII) in childhood cancer patients

While exercise and physical activity have been suggested to reduce mortality and symptoms in cancer, knowledge on these associations in patients with childhood cancer (CCPs) is sparse. Anti-inflammatory properties of exercise might mediate these beneficial effects. We investigated the influence of exercise on the inflammation markers neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, and systemic-immune-inflammation index (SII) and associations to patient-reported-outcomes in CCPs in a randomized-controlled trial. Results show associations between inflammation markers and patient-reported outcomes. Compared to the control group, SII was significantly reduced following exercise (p=0.036). Anti-inflammatory effects of exercise are also present in CCPs and may underlie exercise-induced benefits on symptoms. Clinical Trial Registration Number: NCT0261202