Dynamic features of successive upwelling events in the Baltic Sea - a numerical case study

Coastal upwelling often reveals itself during the thermal stratification season as an abrupt sea surface temperature (SST) drop. Its intensity depends not only on the magnitude of an upwelling-favourable wind impulse but also on the temperature stratification of the water column during the initial stage of the event. When a "chain" of upwelling events is taking place, one event may play a part in forming the initial stratification for the next one; consequently, SST may drop significantly even with a reduced wind impulse. Two upwelling events were simulated on the Polish coast in August 1996 using a three-dimensional, baroclinic prognostic model. The model results proved to be in good agreement with in situ observations and satellite data. Comparison of the simulated upwelling events show that the first one required a wind impulse of 28000 kg m-1 s-1 to reach its mature, full form, whereas an impulse of only 7500 kg m-1 s-1 was sufficient to bring about a significant drop in SST at the end of the second event. In practical applications like operational modelling, the initial stratification conditions prior to an upwelling event should be described with care in order to be able to simulate the coming event with very good accuracy

Upwelling events, coastal offshore exchange, links to biogeochemical processes - Highlights from the Baltic Sea Sciences Congress at Rostock University, Germany, 19-22 March 2007

The Baltic Sea Science Congress was held at Rostock University, Germany, from 19 to 22 March 2007. In the session entitled"Upwelling events, coastal offshore exchange, links to biogeochemical processes" 20 presentations were given,including 7 talks and 13 posters related to the theme of the session.This paper summarises new findings of the upwelling-related studies reported in the session. It deals with investigationsbased on the use of in situ and remote sensing measurements as well as numerical modelling tools. The biogeochemicalimplications of upwelling are also discussed.Our knowledge of the fine structure and dynamic considerations of upwelling has increased in recent decades with the advent ofhigh-resolution modern measurement techniques and modelling studies. The forcing and the overall structure, duration and intensity ofupwelling events are understood quite well. However, the quantification of related transports and the contribution to the overall mixingof upwelling requires further research. Furthermore, our knowledge of the links between upwelling and biogeochemical processes is stillincomplete. Numerical modelling has advanced to the extent that horizontal resolutions of c. 0.5 nautical miles can now be applied,which allows the complete spectrum of meso-scale features to be described. Even the development of filaments can be describedrealistically in comparison with high-resolution satellite data.But the effect of upwelling at a basin scale and possible changes under changing climatic conditions remain open questions

N D0-branes and antibranes in the background independent string field theory

In this paper we extend our previous work hep-th/0102063 to the case D0-brane+antibrane system.Comment: 20 page

Modelling of the circulation, water exchange and water age properties of the Gulf of Bothnia

To estimate the mean circulation, water exchange and water age in the Gulf of Bothnia a ten-year simulation using a three-dimensional numerical model was carried out. The results confirmed the early findings byWitting (1912) and Palm´en (1930) that a mean cyclonic circulation takes place both in the Bothnian Sea and in the Bothnian Bay. However, the modelling results showed clearly that there exist meso-scale circulation features including coastal ‘jets’, not reported in the Witting-Palm´en results. The simulated mean currents were also higher than those found earlier, while the persistency of this circulation is typically between 20 and 60%, which is similar to the earlier results. There is a large difference between the various model-based water-exchange estimates: these are strictly dependent on the time-averaging used. Water age proved to reflect properties of the mean circulation system, and the highest water age (of around 7.4 years) was found in the central part of the Bothnian Bay. The water age was found to be rather high also in the entire Gulf of Bothnia, which provides evidence of the rather slow water exchange between the Gulf and the Baltic Sea. This leads to the conclusion that, from the physical point of view, the Gulf of Bothnia is vulnerable to eutrophication

Main upwelling regions in the Baltic Sea — a statistical analysis based on three-dimensional modelling

In the Baltic Sea upwelling is an important process, especially in the coastal areas, causing vertical mixing and displacement of the water body. During thermal stratification, when the surface layer of the water is depleted of nutrients, upwelling plays a key role in replenishing the euphotic zone with the nutritional components necessary for biological productivity. Up to now, only a few comprehensive investigations have been carried out to study the locations of the main upwelling areas in the Baltic and how commonly these upwellings take place. Here, three-dimensional high-resolution modelling is used as a tool to statistically estimate an index reflecting the persistency of upwellings (downwellings) in various parts of the Baltic. This estimate is made for the summer season over the ten-year period from 1979 to 1988. The new idea in this paper is to use the persistency (stability) of the vertical velocity to define an upwelling index, instead of calculating the frequency of upwelling on the basis of changes in the sea-surface temperature, as is usually done. The model results were compared with measurements of surface temperature and salinity in the Gulf of Finland in 1988, where several strong upwelling cases were observed. The fit between the model results and measurements was found to be good. The upwelling indexes were compared with corresponding upwelling frequencies in the Swedish coastal area based on an analysis of long-term sea-surface temperature measurements. The results, based on these two different approaches, correspond well with each other. Consequently, we can expect that the three-dimensional model can be used to good effect as a tool to describe the overall statistics of the main upwelling areas in the Baltic. The results of the ten-year simulation show that coastal-type upwellings (downwellings) dominate, with values of the index as high as 30%–50% (–30% to –50%), being typically between 10% and 30% (–10% to –30%). The width scale of upwellings (perpendicular to the coast) is typically only 5–20 km. The length scale is somewhat more variable, being typically between 30 and 150 km (alongshore)

A method for determination of energy center of a solitary pulse

A new method is suggested for estimating the energy center of a solitary pulse. The method permits to diminish the estimate variance as compared to the same characteristic of the center-of-gravity method. The method is based on a recursive procedure of calculation of cylindrical convolution, which facilitates the implementation

Mean circulation and water exchange in the Gulf of Finland — a study based on three-dimensional modelling

A three-dimensional baroclinic prognostic model has been applied to study the mean circulation and its persistency as well as the water exchange in the Gulf of Finland. A five-year simulation for 1987–1992 was carried out using a nested grid approach, where a high-resolution sub-model of the Gulf of Finland was forced at the open boundary by a larger-scale Baltic Sea model. Realistic meteorological forcing for the period under study was used. The overall results of the investigation showed that the mean circulation pattern was complex with numerous meso-scale eddies, although a cyclonic mean circulation generally is discernible. The mean surface circulation of the Gulf was found to take place in the form of a strong outflow adjacent to the Finnish coast compensated for by an inflow at the Estonian coast, a circulation which is highly dependent on depth. The outflow on the northern side of the Gulf proved to be a distinct feature with a persistency ranging between 50% and 80%. The water exchange between the Gulf and the Baltic Proper appears to be stronger than previously estimated. It was found that ordinary budget estimates of water exchange (based on calculating the amount of in- and out-flowing water) do not give much relevant information concerning the Baltic Sea Proper–Gulf water exchange since these straightforward estimates do not reflect the internal dynamics of the Gulf of Finland