No description available.

No description available.

No description available.

Abstract The Cassini/Huygens mission is a collaborative mission of NASA and ESA to study the Saturnian system. Cassini Plasma Spectrometer (CAPS)is one of the scientific investigations onboard the Cassini orbiter. It consists of three separate spectrometers: Electron Spectrometer (ELS), Ion Mass Spectrometer (IMS) and Ion Beam Spectrometer (IBS). The University of Oulu has a co-investigator status in the CAPS project, and been mainly involved in simulating the structure and scientific performance of the IBS instrument. IBS is a high resolution hemispherical electrostatic analyser aimed to study the solar wind ions. This thesis contains an Introduction and five original papers. Papers I–III contain a detailed description of the simulation process of the IBS instrument and related results. In Paper I the manufacturing tolerances were calculated in order to verify that the high resolution requirements can be achieved using available manufacturing processes. In Paper II the simulations have been further developed and the instrument properties have been studied in more detail. In Paper III the simulation model is used to help the analysis and interpretation of the laboratory calibrations of the IBS flight model. Papers IV and V study the long-term fluctuations in solar wind and interplanetary magnetic field in the period range of 1–2 years (so called mid-term quasi periodicities, MTQP), using the wavelet transformation method to produce dynamic power spectra. In paper IV the MTQP structure in solar wind speed at 1 AU was studied using the longest available series of geomagnetic activity. It was shown that the long-term occurrence MTQP fluctuations roughly follows the long-term solar activity, suggesting that MTQP fluctuations are closely connected with the solar dynamo activity. Moreover, it was also noted that MTQP activity may offer a possibility for a precursory signal which could be used to predict significant changes in long-term solar activity. While Paper IV presents the temporally longest study of MTQP fluctuations, Paper V gives the spatially widest treatment of the same phenomenon. Paper V studies MTQP fluctuations in solar wind and interplanetary magnetic field measured by four probes in the outer heliosphere. It is shown that two MTQP fluctuations of different periods (1.3 and 1.7 years)co existed during solar cycle 22, while during solar cycle 21 only the 1.7-year band existed. This suggests that the solar dynamo acts differently during even and odd cycles. It is also shown that the two MTQP fluctuations during solar cycle 22 are organized latitudinally. While the 1.3-year periodicity originates from equatorial regions, the 1.7-year fluctuations arise at mid-latitudes. / Original papers Original papers are not included in the electronic version of the dissertation. Vilppola, J. H., Keisala, J. T., Tanskanen, P. J., & Huomo, H. (1993). Optimization of hemispherical electrostatic analyzer manufacturing with respect to resolution requirements. Review of Scientific Instruments, 64(8), 2190–2194. https://doi.org/10.1063/1.1143958 Vilppola, J. H., Tanskanen, P. J., Huomo, H., & Barraclough, B. L. (1996). Simulations of the response function of a plasma ion beam spectrometer for the Cassini mission to Saturn. Review of Scientific Instruments, 67(4), 1494–1501. https://doi.org/10.1063/1.1146881 Vilppola, J. H., Tanskanen, P. J., Barraclough, B. L., & McComas, D. J. (2001). Comparison between simulations and calibrations of a high resolution electrostatic analyzer. Review of Scientific Instruments, 72(9), 3662–3669. https://doi.org/10.1063/1.1392337 Mursula, K., Zieger, B., & Vilppola, J. H. (2003). Mid-term quasi-periodicities in geomagnetic activity during last 15 solar cycles: Connection to solar dynamo strength. Solar Physics, 212(1), 201–207. https://doi.org/10.1023/a:1022980029618 Mursula, K., & Vilppola, J. H. (2004). Fluctuations of the Solar Dynamo Observed in the Solar Wind and Interplanetary Magnetic Field at 1 AU and in the Outer Heliosphere. Solar Physics, 221(2), 337–349. https://doi.org/10.1023/b:sola.0000035053.17913.26

The Interplanetary Magnetic Field (IMF) has a controlling effect on the Magnetosphere and Ionosphere. The objective in this work is to investigate the probable effects of IMF on Ionospheric and Geomagnetic response. To fulfill the objective the concept of an event has been created based on the polarity reversals and rate of change of the interplanetary magnetic field components, Bz and By. Superposed Epoch Method (SPE) was employed with the three event definitions, which are based on IMF Bz southward turnings ranging from 6 to 11 nT in order to quantify the effects of IMF By and Bz. For the first event only IMF Bz turnings were taken into account while for the remaining, positive and negative polarity for IMF By were added. Results showed that the increase in the magnitude of IMF Bz turnings increased the drop of F layer critical frequency, f0F2. The drop was almost linear with the increase in magnitude of polarity reversals. Reversals with a positive IMF By has resulted in the continuation of geomagnetic activity more than 4 days, that is to say, the energy, that has penetrated as a consequence of reversal with a positive By polarity, was stored in outer Magnetosphere,whereas, with a negative IMF By the energy was consumed in a small time scale. At the second step of the work, although conclusions about geomagnetic activity could be done, as a consequence of data gaps for f0F2 in addition to having low numbers of events, characterization of f0F2 due to constant IMF By polarity could not be accomplished. Thus, a modeling attempt for the characterization of the response due to polarity reversals of IMF components with the Genetic Programming was carried out. Four models were constructed for different polarity reversal cases and they were used as the components of one general unique model. The model is designed in such a way that given 3 consecutive value of f0F2, IMF By and IMF Bz, the model can forecast one hour ahead value of f0F2. The overall model, GETY-IYON was successful at a normalized error of 7.3%.

As the solar wind reaches Mercury it interacts with the planet’s magnetic field slowing down, forming a bow shock in front of the planet and diverting the flow around it. Along with the solar wind comes the interplanetary magnetic field, an extension of the sun’s magnetic field. The interaction between the bow shock and the interplanetary magnetic field impacts the behaviour of the plasma both up- and downstream of the bow shock. An important factor is the angle between the normal to the bow shock surface and the interplanetary magnetic field, θBN. The angle can be divided into two categories: quasi-parallel for when θBN < 45° and quasi-perpendicular for θBN > 45°. It is expected for a quasi-parallel configuration to have stronger fluctuations in both the solar wind upstream of the bow shock and in the magnetosheath downstream caused by reflected particles backstreaming into the solar wind. Quasi-perpendicular configurations are expected to have less fluctuations in both regions due to fewer solar wind particles being reflected back. In this thesis this connection is investigated at the bow shock at Mercury using magnetic field data from the MESSENGER mission. By looking at the data when the spacecraft travels through the thin bow shock the local θBN angle can be calculated. The fluctuation level is then calculated as the standard deviation of the magnetic field in a 30 second period upstream and downstream of the crossing. The results found are unexpected as the correlation between θBN and the fluctuation levels are weaker and more uniformly distributed than expected compared to similar studies conducted at Earth using the Cluster satellites. This is most likely due to the smaller spatial scale of the Hermean system: the structures perpendicular to the interplanetary magnetic field of upstream activity, such as SLAMS, cover a greater proportion of the bow shock than at Earth allowing them to extend over into neighbouring regions of different θBN values, giving a more uniform distribution of the fluctuation levels. / När solvinden når Merkurius växelverkar den med planetens magnetfält och solvinden saktas ned och avledes till att flöda kring planeten. Då solvinden decelereras formas en chock framför planeten, bogchocken. Tillsammans med solvinden kommer det interplanetära magnetfältet, som är en förlängning av solens magnetfält. Växelverkan mellan bogchocken och det interplanetära magnetfältet påverkar plasmat både upp- och nedströms från bogchocken. En viktigt faktor är vinkeln mellan normalen till bogchocken och det interplanetära magnetfältet, θBN . Bogchocken kan delas in i två kategorier: kvasi-parallell då θBN < 45° och kvasi-vinkelrät då θBN > 45°. Vid kvasi-parallella förhållanden förväntas starkare fluktuationer i magnetfältet både uppströms i solvinden och nedströms i magnetskiktet, orsakat av reflekterade partiklar som färdas in i den inkommande solvinden. Kvasi-vinkelräta förhållanden förväntas ha mindre fluktuationer då färre partiklar reflekteras. I den här uppsatsen undersöks kopplingen vid Merkurius bogchock med data från rymdsonden MESSENGER. Genom att använda data då rymdsonden färdas igenom den tunna bogchocken kan det lokala värdet på θBN uträknas. Fluktuationsnivåerna räknas ut som standardavvikelsen av magnetfältet under en 30 sekundersperiod uppströms och nedströms från korsningen. Resultaten är ej som förväntade då kopplingen mellan θBN och fluktuationsnivån är mycket svagare och jämnt fördelade än förväntat, baserat på resultat från jorden från Cluster-satelliterna. Den mest troliga förklaringen är att Merkurius och dess bogchock är mindre än jordens: de strukturerna som är vinkelräta till det interplanetära magnetfältet hos uppströmsfenomen, t.ex SLAMS, täcker då en större proportion av bogchocken än vid jorden vilket tillåter dem att sträcka sig in i närliggande regioner med annorlunda θBN värden, vilket ger en mer jämn utbredning av fluktuationsnivåerna.