Report series in Geophysics


Recent Submissions

  • Järvinen, Onni (Helsingin yliopisto, 2013)
  • Kitaigorodskii, Sergey (2013)
    Report series in Geophysics 72
    The several conclusions of similarity theory for wind driven waves are discussed together with experimental data being revisited by the author (Kitaigorodskii, 1983, 1998). First of them is so-called wind speed scaling, often being used in literature on wind waves as Kitaigorodskii scaling. It is stressed that existing data cannot be served for rejection of concept of fully developed (mature) wind waves. Second of them is the derivation of so-called law omega–4 (Kitaigorodskii, 1962, 1983) for replacement of Phillips law (Phillips, 1958). The main question related to this problem is about existence of the transition from direct cascade regime to wind wave breaking dissipation scales. It is established "a bridge" between description of wave spectra used in Kitaigorodskii (1962) and weakly nonlinear theory of waves. This was the third question discussed here.
  • Uusikivi, Jari (Helsingin yliopisto, 2013)
    Sea ice has been recognized as one of the key elements of polar and sub-polar seas, including Baltic Sea. The existence of sea ice cover and its properties have influence to many aspects of marine biology, climate and seafaring. This thesis is concentrated on describing physical and optical properties of landfast ice, and also pack ice, in the Baltic Sea. The aim of the thesis is to use measurements to study the interactions between optical and physical properties of sea ice and how these can affect the biology in sea ice. Decade long observations of ice properties were used to construct a statistical model of properties of landfast ice. Temperature was found to be the most important factor determining ice thickness and contribution of snow ice to the ice thickness was determined by the amount of winter time precipitation. Stratigraphy of ice and growth history had influence to the vertical distribution of organisms in the ice cover as snow ice layers and columnar ice layers were found to favor different types of organisms. Thickness of meteoric ice layer, including snow ice and superimposed ice, controlled the albedo of ice cover when no snow cover was on the ice. Based on the observations of fast ice conditions and albedo, the effects of snow thickness and meteoric ice thickness to the albedo of sea ice were formulated as albedo parameterization equations. The optical properties of sea ice with spectral resolution were studied on the landfast sea ice. Emphasis in these studies was given to optical properties in the ultraviolet and visible wavelengths. Organic matter, dissolved and particulate, was the most important factor determining the ultraviolet properties of sea ice cover. The optical properties in the ultraviolet were also actively modified by the living organisms in the ice cover by producing mycosporine like amino acids (MAAs) in relatively high amounts. MAAs are a family of photoprotective compounds that absorb UV radiation efficiently. At the visible part of spectrum the ice by itself and the thickness of meteoric ice layer were the most important determinants. Salinity and the initial salt entrapment during ice growth in the Baltic Sea were measured to be less than in the oceans with equal ice growth rates. The turbulent fluxes of heat and salinity under the landfast sea ice were measured to be small.
  • Koistinen, Esa (2007)
    Report series in Geophysics 54
  • Oikkonen, Annu (2008)
    Report series in Geophysics 56
  • Leppäranta, Matti (2009)
    Report series in Geophysics 61
  • Mäkiranta, Eeva (2009)
    Report series in Geophysics 58
  • Rasmus, Kai; Granberg, Harry; Kanto, Kimmo; Kärkäs, Eija; Lavoie, C.; Leppäranta, Matti (2003)
    The project ’Seasonal Snow in Antarctica’ was set up to measure the physical properties of Antarctic snow cover in 1999-2001. The present document is the project data report. An introduction is given of the project, descriptions of the experiments are made, and the data obtained by the scientists in the different working groups during the two expeditions to Antarctica are described
  • Leppäranta, Matti (1998)
  • Leppäranta, Matti (1998)
  • Järvinen, Onni; Leppäranta, Matti; Vehviläinen, Juho (University of Helsinki, Division of Geophysics and Astronomy, 2012)
    Report series in Geophysics No 71
    Field programme on the surface layer of the ice sheet in the Dronning Maud Land, Antarctica has been performed in 2009-2011. The objectives were to examine the annual accumulation and sublimation history, snow melting, chemistry of snow impurities, and life history of supraglacial and epiglacial lakes in blue ice regions. Fieldwork was done during FINNARP 2009 and 2010 expeditions. The sites were at the Finnish research station Aboa (73 02.5'S, 013 24.4'W), a snow line from Rampen at the edge of the ice shelf pass Aboa to the station Svea, and blue ice at Basen and neighboring nunataks. Snow measurements were made using classical snow pit method, ice and snow sampling, and with automatic observation stations (surface radiation balance, penetration of sunlight into snow and ice, and temperature within the surface layer of snow and ice). Life history, physics, and ecological state of lakes were mapped. This document is the data report including a brief project introduction, descriptions of the experiments, and the data obtained.
  • Raiskila, Selen (Helsingin yliopisto, 2013)
    Meteorite impact cratering has played a key role in Earth's geological past and has left a dramatic effect on biological and geological records forming large volumes of igneous rocks and important mineral deposits. By studying terrestrial impact craters we can have valuable information of impact generated changes in rocks and minerals. Integrated geophysical study in this dissertation combines different methods to distinguish the meteorite impact related features from features caused by endogenic processes. Optical microscopy provides diagnostic evidence of shock produced deformations in minerals.Shocked and un-shocked rocks have contrasts in petrophysical properties, which cause anomalies to regional magnetic and gravity fields over meteorite impact structures.Magnetic minerals may re-magnetize during impact and thus provide information of the past geomagnetic field and the ancient paleoposition of impact site. This dissertation focuses to the Finnish impact structure, Keurusselkä, which was discovered in 2003. The structure is situated in central Finland (62°08 N, 24°37 E) within the Central Finland Granitoid Complex, which formed 1890 1860 million years ago during the Svecofennian orogeny. Keurusselkä is deeply eroded remain of a complex crater, named after the Lake Keurusselkä, which is the dominant present day feature of the crater area. For this study rock and drill core samples were collected from Keurusselkä region. The samples were chosen according to a sampling strategy, where samples were taken in and outside the impact region to investigate the impact related features and their radial distance from the centre of the impact. The main focus was to prove or disprove the impact origin of Keurusselkä. First indication of impact was shatter cones, which are conical features in rocks formed by an impact shock and pressure. Shatter cones were found in a circular area interpreted as the central uplift of the original crater. In this dissertation petrographic analysis of thin sections was done to find evidence of deformational features in minerals. Diagnostic evidence for Keurusselkä was achieved when planar deformation features(PDFs) were found from quartz grains in shatter cones indicating impact pressures up to 20 GPa. Samples from 3 shallow drillings in southwest part of the Keurusselkä structure were also studied. Impact like monomictic breccia was found from one of the drill cores. Petrographic analysis revealed clay minerals (illite, smectite-group), which most likely have altered from impact glass. Magnetic minerals were obtained for paleomagnetic purposes, i.e. to examine the ancient position and drift of Baltica. Paleomagnetic directions obtained from shatter cones indicate re-magnetization. The virtual geomagnetic pole implies that the impact event took place ~1120 million years ago during the formation of Rodinia supercontinent. Petrophysical properties (density, susceptibility) of rocks were measured for differences between shocked and un-shocked rocks. The exposed bedrock in Keurusselkä was noticed to be fractured and damaged, which causes anomalies to the regional magnetic and gravity field. The geophysical signals were modelled along two profiles using measured physical properties of Keurusselkä rocks. The highly magnetized centre of the structure forms an eroded circular central uplift with diameter of 6 km. Based on the gravity minimum around the structure an area of ~16 km in diameter and depth of ~1200 meters was modelled to explain the observed anomalies. The original size of the crater is estimated to be 24-27 km in diameter.
  • Bućko, Michał (Helsingin yliopisto, 2012)
  • Airo, Meri-Liisa; Kiuru, Risto (University of Helsinki, Division of Geophysics and Astronomy, 2012)
    Report series in Geophysics No 68