Assessment of Uncertainties in Scenario Simulations of Biogeochemical Cycles in the Baltic Sea

Following earlier regional assessment studies, such as the Assessment of Climate Change for the Baltic Sea Basin and the North Sea Region Climate Change Assessment, knowledge acquired from available literature about future scenario simulations of biogeochemical cycles in the Baltic Sea and their uncertainties is assessed. The identification and reduction of uncertainties of scenario simulations are issues for marine management. For instance, it is important to know whether nutrient load abatement will meet its objectives of restored water quality status in future climate or whether additional measures are required. However, uncertainties are large and their sources need to be understood to draw conclusions about the effectiveness of measures. The assessment of sources of uncertainties in projections of biogeochemical cycles based on authors' own expert judgment suggests that the biggest uncertainties are caused by (1) unknown current and future bioavailable nutrient loads from land and atmosphere, (2) the experimental setup (including the spin up strategy), (3) differences between the projections of global and regional climate models, in particular, with respect to the global mean sea level rise and regional water cycle, (4) differing model-specific responses of the simulated biogeochemical cycles to long-term changes in external nutrient loads and climate of the Baltic Sea region, and (5) unknown future greenhouse gas emissions. Regular assessments of the models' skill (or quality compared to observations) for the Baltic Sea region and the spread in scenario simulations (differences among projected changes) as well as improvement of dynamical downscaling methods are recommended.Peer reviewe

Assessment of eutrophication abatement scenarios for the Baltic Sea by multi-model ensemble simulations

Peer reviewe

Testing linear gravity wave theory with simultaneous wind and temperature data from the mesosphere

Linear gravity wave (GW) theory is tested on the basis of simultaneous measurements of horizontal winds from a medium frequency (MF) radar at Juliusruh (54.6°N, 13.4°E) and temperatures from combined Potassium (K) and Rayleigh–Mie–Raman (RMR) lidars at Kühlungsborn (54.1°N, 11.8°E). The applicability of linear GW theory to mesospheric observations is far from obvious given the fact that typically a whole spectrum of waves is observed which may interact non-linearly. Before analyzing our experimental dataset for its fit to expectations from linear GW theory, the chosen methodology is tested with model data from the Kühlungsborn Mechanistic general Circulation Model (KMCM). This model is a mechanistic general circulation model with high spatial resolution such that waves with horizontal wavelengths in excess of are explicitly resolved yielding a semi-realistic wave motion field. This may be considered as a suitable test-bed for defining and optimizing wave analysis approaches. This effort reveals that Stokes parameters analysis of filtered time series of GW-induced wind and temperature fluctuations in comparison to wave amplitudes directly retrieved from the filtered time series allows us to demonstrate the validity of polarization relations based on linear wave theory. Indeed, applying the same methodology to the observations yields similarly conclusive results thus giving evidence for the applicability of linear wave theory to mesospheric observations after appropriate filtering. These investigations are complemented by a comparison of kinetic and potential energy per unit mass for model and measured data. This reveals that the ratio of kinetic and potential energy also roughly follows expectations from linear wave theory

First experimental verification of summertime mesospheric momentum balance based on radar wind measurements at 69°N

Gravity waves (GWs) greatly influence the background state of the middle atmosphere by imposing their momentum on the mean flow upon breaking and by thus driving, e.g., the upper mesospheric summer zonal wind reversal. In this situation momentum is conserved by a balance between the vertical divergence of GW momentum flux (the so-called GW drag) and the Coriolis acceleration of the mean meridional wind. In this study, we present first quantitative mean annual cycles of these two balancing quantities from the medium frequency Doppler radar at the polar site Saura (SMF radar, 69°N, 16°E)

Testing linear gravity wave theory with simultaneous wind and temperature data from the mesosphere

Linear gravity wave (GW) theory is tested on the basis of simultaneous measurements of horizontal winds from a medium frequency (MF) radar at Juliusruh (54.6°N, 13.4°E) and temperatures from combined Potassium (K) and Rayleigh–Mie–Raman (RMR) lidars at Kühlungsborn (54.1°N, 11.8°E). The applicability of linear GW theory to mesospheric observations is far from obvious given the fact that typically a whole spectrum of waves is observed which may interact non-linearly. Before analyzing our experimental dataset for its fit to expectations from linear GW theory, the chosen methodology is tested with model data from the Kühlungsborn Mechanistic general Circulation Model (KMCM). This model is a mechanistic general circulation model with high spatial resolution such that waves with horizontal wavelengths in excess of are explicitly resolved yielding a semi-realistic wave motion field. This may be considered as a suitable test-bed for defining and optimizing wave analysis approaches. This effort reveals that Stokes parameters analysis of filtered time series of GW-induced wind and temperature fluctuations in comparison to wave amplitudes directly retrieved from the filtered time series allows us to demonstrate the validity of polarization relations based on linear wave theory. Indeed, applying the same methodology to the observations yields similarly conclusive results thus giving evidence for the applicability of linear wave theory to mesospheric observations after appropriate filtering. These investigations are complemented by a comparison of kinetic and potential energy per unit mass for model and measured data. This reveals that the ratio of kinetic and potential energy also roughly follows expectations from linear wave theory

River runoff forcing for ocean modeling withinthe Baltic Sea Model Intercomparison Project

The Baltic Sea Model Intercomparison Project (BMIP) aims to study different processes in the Baltic Sea using numerical models from different institutes and groups forced by the same atmospheric and freshwater forcing. In this report a description and an overview about the common freshwater forcing for the period 1961-2018 is given. Originally based on the hydrological model E-HYPE, the BMIP forcing is compiled from the available observations (Neva river), historical reconstruction and hydrological model simulations (hindcast and forecast simulations by the E-HYPE). The final homogenized dataset has daily resolution in freshwater discharge from 91 locations in the Baltic Sea region and is in good agreement with previously available datasets