Elimination of seasonal variation from long-term changes of some nutrients in the Baltic Sea

Sisältää myös neljä muuta artikkelia: Lars Grönlund, Juha-Markku Leppänen: Long-term changes in the nutrient reserves and pelagic production in the western Gulf of Finland Guy Hällfors, Åke Niemi: Proposal for standardization of the way of presenting phytoplankton results Juha-Markku Leppänen, Kaisa Kononen, Gerda Behrends, Gesa Hansen: Intercomparison of the measurement of chlorophyll a concentration, primary production capacity, and phyto- and zooplankton abundances during the Baltic Sea Patchiness Experiment (PEX'86) Per Östlund: Plutonium isotope ratios in Baltic Sea sediment

Combining probability distributions of sea level variations and wave run-up to evaluate coastal flooding risks

Tools for estimating probabilities of flooding hazards caused by the simultaneous effect of sea level and waves are needed for the secure planning of densely populated coastal areas that are strongly vulnerable to climate change. In this paper we present a method for combining location-specific probability distributions of three different components: (1) long-term mean sea level change, (2) short-term sea level variations and (3) wind-generated waves. We apply the method at two locations in the Helsinki archipelago to obtain total water level estimates representing the joint effect of the still water level and the wave run-up for the present, 2050 and 2100. The variability of the wave conditions between the study sites leads to a difference in the safe building levels of up to 1&thinsp;m. The rising mean sea level in the Gulf of Finland and the uncertainty related to the associated scenarios contribute notably to the total water levels for the year 2100. A test with theoretical wave run-up distributions illustrates the effect of the relative magnitude of the sea level variations and wave conditions on the total water level. We also discuss our method's applicability to other coastal regions.</p

Land uplift and sea level variability spectrum using fully measured monthly means of tide gauge readings

Sisältää myös seuraavat artikkelit: Robert J. Morris, Åke Niemi, Lauri Niemistö and Eeva-Liisa Poutanen: Sedimentary record of seasonal production and geochemical fluxes in a nearshore coastal embayment in the northern Baltic Sea Hannu Grönvall: Finnish ice servic

Freely decaying weak turbulence for sea surface gravity waves

We study numerically the generation of power laws in the framework of weak turbulence theory for surface gravity waves in deep water. Starting from a random wave field, we let the system evolve numerically according to the nonlinear Euler equations for gravity waves in infinitely deep water. In agreement with the theory of Zakharov and Filonenko, we find the formation of a power spectrum characterized by a power law of the form of $|{\bf k}|^{-2.5}$.Comment: 4 pages, 3 figure

Suomen merentutkimuksen ydinkysymykset - Merentutkimuslaitos suomalaisessa yhteiskunnassa

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SENSIBILIDADE DE ESPECTROS DE ONDAS OCEÂNICAS RECUPERADOS POR RADAR DE ABERTURA SINTÉTICA

SAR (Synthetic Aperture Radar ou Radar de Abertura Sint&#233;tica) &#233; o &#250;nico sensor transportado por sat&#233;lites capaz de medir o espectro direcional de ondas. Sua elevada cobertura espacial e temporal permite caracterizar o estado de mar, especialmente a regi&#227;o de baixa frequ&#234;ncia do espectro de energia, que vem sendo assimilada em modelos num&#233;ricos de previs&#227;o de ondas em diversos centros operacionais espalhados pelo globo. Contudo, a extra&#231;&#227;o do espectro de ondas de uma imagem SAR &#233; um procedimento complexo. Alguns modos de opera&#231;&#227;o n&#227;o permitem o emprego de imagens sequenciais para resolver a ambiguidade direcional de propaga&#231;&#227;o das ondas, o que requer informa&#231;&#245;es adicionais, geralmente obtidas de um modelo de ondas. A depend&#234;ncia destas informa&#231;&#245;es adicionais &#233; investigada aplicando-se a invers&#227;o cl&#225;ssica de Hasselmann a alguns estados de mar te&#243;ricos. Esta abordagem &#233; baseada na transforma&#231;&#227;o anal&#237;tica do espectro direcional de ondas sobre o espectro de imagem SAR correspondente. A solu&#231;&#227;o deste problema inverso &#233; determinada por um algoritmo num&#233;rico que minimiza um funcional n&#227;o linear. Apesar de amplamente utilizado por diversos centros operacionais de previs&#227;o, este m&#233;todo n&#227;o foi extensivamente testado em cen&#225;rios experimentais bem definidos. Os resultados mostram que a depend&#234;ncia investigada &#233; bastante significativa, sobretudo no que diz respeito &#224; dire&#231;&#227;o de propaga&#231;&#227;o das ondas, levantando questionamentos sobre a acur&#225;cia da t&#233;cnica