Browsing by Author "Tanskanen, Eija"

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  • Auringon koronan aukot ja niiden vaikutus aurinkotuulen nopeuteen
    (2018-04-24) Opas, Mikael
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Aurinkotuulen Alfvénin aallot ja niiden ominaisuudet
    (2018-05-04) Immonen, Sampo
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Auroral substorm observations since 1914: latitudinal distribution and energetics
    (2019-10-21) Jaakonaho, Iina
     Sähkötekniikan korkeakoulu | Master's thesis
    The Earth is in a constant interaction with the solar wind. This interaction varies over different time scales, depending on the conditions of the Sun and the near-Earth space. The solar wind energy convection and dissipation in the Earth’s magnetosphere and ionosphere give rise to disturbances in the geomagnetic field, collectively called geomagnetic activity. Auroral substorm, a common phenomenon in the northern and southern auroral region, is one of the main forms of geomagnetic activity. Understanding the substorm variability over time and at different locations improves the capability to predict the activity and prepare for it. This master's thesis examined the long-term and seasonal substorm variation and latitudinal distribution in the northern auroral region, with the focus on the ionospheric energy dissipation. Substorms were identified with an automated search algorithm from ground-based magnetometer measurements in Fennoscandia and Svalbard. The latitudinal analysis covered years 1993-2018, and the centennial activity at Sodankylä was examined during 1914-2015. The interannual and annual substorm trends were found to vary over the latitude range, with the largest overall energy dissipation observed at the Sørøya station (70.5N) and the most frequent substorm activity at the Bear Island station (74.5N). The longest substorms, on average, were observed at Kevo (69.7N) and the strongest at Sodankylä (67.4N) and Muonio (68.0N). In the centennial analysis of the Sodankylä observations, substorms were found to occur most frequently during the declining phase of the solar cycles. It was concluded that the observation latitude may make a significant difference in ground-based substorm research, and thus sufficient latitudinal coverage should be considered.
  • Avaruussääinstrumentit ja mittausalustat
    (2013-08-30) Peitso, Pyry
     Sähkötekniikan korkeakoulu | Master's thesis
    Avaruussää on Maapallon lähiavaruuden ilmiö. Sillä on useita ilmenemismuotoja, joista tunnetuin on revontulet. Avaruussää aiheuttaa haittaa kriittisille infrastruktuureille, kuten satelliiteille ja sähköverkoille. Tämän diplomityön tarkoituksena on tutkia nykyisiä avaruussääinstrumenttejä sekä mittausjärjestelmiä ja kartoittaa niiden toimintakyky sekä heikkouksia. Magnetometri-, ionosfääri, aurinkotuuli- ja Aurinkoinstrumentaatiolle ja järjestelmille suoritetaan kattava analyysi. Lopputulokset osoittavat että nykyiset instrumentit kykenevät mittaamaan kaikkia avaruussäähän liittyviä ilmiöitä. Magnetometrimittausten peitto revontuliovaalilla ei ole riittävä tarkkaan avaruussäätutkimukseen, sillä magneettikenttää ei kyetä mittaamaan merellä. Ionosfäärimittauksilla on samanlaisia ongelmia maantieteellisen peiton kanssa ja niistä on saatavilla lyhyempiä aikasarjoja. Aurinko- ja aurinkotuulimittaukset ovat keskittyneet pienelle määrälle satelliitteja jotka ovat kalliita ja hankalia korvata. Lopputuloksina suositellaan CubeSat-satelliittien kyytiin asennettavien magnetometrien testausta, vedenalaisten magnetometrien käyttöönottoa sekä parannuksia ionosfäärin ja magnetosfäärin mittauspeitossa. Kykyä suorittaa jatkuvia Aurinko- ja aurinkotuulimittauksia avaruuteen sijoitetuilla järjestelmillä pitäisi myös ylläpitää.
  • Avaruussäämittasalkku - yksinkertaisia mittalaitteita opetukseen
    (2016-12-13) Jaakonaho, Iina
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Coulomb drag propulsion experiments of ESTCube-2 and FORESAIL-1
    (2020-12) Iakubivskyi, Iaroslav; Janhunen, Pekka; Praks, Jaan; Allik, Viljo; Bussov, Kadri; Clayhills, Bruce; Dalbins, Janis; Eenmäe, Tõnis; Ehrpais, Hendrik; Envall, Jouni; Haslam, Sean; Ilbis, Erik; Jovanovic, Nemanja; Kilpua, Emilia; Kivastik, Joosep; Laks, Jürgen; Laufer, Philipp; Merisalu, Maido; Meskanen, Matias; Märk, Robert; Nath, Ankit; Niemelä, Petri; Noorma, Mart; Mughal, Muhammad Rizwan; Nyman, Samuli; Pajusalu, Mihkel; Palmroth, Minna; Paul, Aditya Savio; Peltola, Tatu; Plans, Mathias; Polkko, Jouni; Islam, Quazi Saimoon; Reinart, Anu; Riwanto, Bagus; Sammelselg, Väino; Sate, Janis; Sünter, Indrek; Tajmar, Martin; Tanskanen, Eija; Teras, Hans; Toivanen, Petri; Vainio, Rami; Väänänen, Mika; Slavinskis, Andris
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    This paper presents two technology experiments – the plasma brake for deorbiting and the electric solar wind sail for interplanetary propulsion – on board the ESTCube-2 and FORESAIL-1 satellites. Since both technologies employ the Coulomb interaction between a charged tether and a plasma flow, they are commonly referred to as Coulomb drag propulsion. The plasma brake operates in the ionosphere, where a negatively charged tether deorbits a satellite. The electric sail operates in the solar wind, where a positively charged tether propels a spacecraft, while an electron emitter removes trapped electrons. Both satellites will be launched in low Earth orbit carrying nearly identical Coulomb drag propulsion experiments, with the main difference being that ESTCube-2 has an electron emitter and it can operate in the positive mode. While solar-wind sailing is not possible in low Earth orbit, ESTCube-2 will space-qualify the components necessary for future electric sail experiments in its authentic environment. The plasma brake can be used on a range of satellite mass classes and orbits. On nanosatellites, the plasma brake is an enabler of deorbiting – a 300-m-long tether fits within half a cubesat unit, and, when charged with -1 kV, can deorbit a 4.5-kg satellite from between a 700- and 500-km altitude in approximately 9–13 months. This paper provides the design and detailed analysis of low-Earth-orbit experiments, as well as the overall mission design of ESTCube-2 and FORESAIL-1.
  • CubeSatien luotettavuuden nostaminen HALT-testauksella
    (2021-12-08) Keskinen, Sami
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Differences in the solar cycle variability of simple and complex active regions during 1996-2018
    (2019-09-04) Nikbakhsh, Shabnam; Tanskanen, Eija; Käpylä, Maarit; Hackman, T.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Aims. Our aim is to examine the solar cycle variability of magnetically simple and complex active region. Methods. We studied simple (alpha and beta) and complex (beta gamma and beta gamma delta) active regions based on the Mount Wilson magnetic classification by applying our newly developed daily approach. We analyzed the daily number of the simple active regions (SARs) and compared that to the abundance of the complex active regions (CARs) over the entire solar cycle 23 and cycle 24 until December 2018. Results. We show that CARs evolve differently over the solar cycle from SARs. The time evolution of SARs and CARs on different hemispheres also shows differences, even though on average their latitudinal distributions are shown to be similar. The time evolution of SARs closely follows that of the sunspot number, and their maximum abundance was observed to occur during the early maximum phase, while that of the CARs was seen roughly two years later. We furthermore found that the peak of CARs was reached before the latitudinal width of the activity band starts to decease. Conclusion. Our results suggest that the active region formation process is a competition between the large-scale dynamo (LSD) and the small-scale dynamo (SSD) near the surface, the former varying cyclically and the latter being independent of the solar cycle. During solar maximum, LSD is dominant, giving a preference to SARs, while during the declining phase the relative role of SSD increases. Therefore, a preference for CARs is seen due to the influence of the SSD on the emerging flux.
  • Electrical design of an auroral photometer for nanosatellite applications
    (2024-03-11) Miettinen, Santeri
     Sähkötekniikan korkeakoulu | Master's thesis
    With the increasing popularity of cubesatellites and nanosatellites, the cost of launching space-based instruments has drastically decreased. This encourages small institutes and corporations to design and develop their own scientific instruments for space applications. This has been one of the driving factors for the Sodankylä Geophysical Observatory (SGO), which is developing its own CubeSat program to help grow the scale of the scientific observations of the observatory. This thesis designs, develops, and electrically tests a prototype of an auroral photometer for nanosatellite applications. The proposed photometer is designed to fly onboard LappiSat-1, the first satellite developed by SGO. The photometer demonstrates the ability to detect auroral emissions by using avalanche photodiodes (APDs) instead of traditionally used photomultiplier tubes. The reverse voltage of the APD is controlled by a microcontroller unit (MCU) to keep the internal gain of the photodiode stable in a temperature-varying environment. The photocurrents produced by the APDs are converted to voltage using a variable-gain transimpedance amplifier. The data is collected using an analog to digital converter and is saved to onboard memory by the MCU. Communication between the satellite platform and the other LappiSat-1 payloads is implemented using a CAN bus.
  • Geomagneettinen aktiivisuus eteläisellä ovaalilla: alimyrskyt ja vuodenaikaisvaihtelu
    (2018-04-24) Luomanen, Juhana
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Low Cost and IoT Magnetometer for Underwater Applications
    (2020-12-14) Castrejon Suarez del Real, Ingrid
     Sähkötekniikan korkeakoulu | Master's thesis
    Magnetometers are essential tools in our understanding of Solar-Terrestrial interactions. Solar activity, such as solar storms or solar energetic particles (SEP), may damage our infrastructure and lead to energy and communications blackouts, potentially generating a huge economic burden. With the help of magnetometers we can analyse changes in the Earth’s magnetic field, and, thus, mitigate the negative effects of space weather. Although we have sophisticated instruments to measure the Earth’s magnetic field we are still limited by the amount of area we can cover. Commercially available scientific magnetometers are expensive, hence, making it challenging to deploy large numbers of them throughout the globe. In addition, maintaining them requires time, effort, knowledge, and money. Furthermore, accessing the data is not always straightforward. Having a broad coverage of magnetic instruments around the globe may help us understand not only solar-terrestrial interactions, but it may also help us understand the Earth’s inner core, animal migration behaviour, or other unknowns such as the influence of the solar cycle variation on the Earth’s climate, or the polarity flip of the Earth’s magnetic field. This will consequently help us prevent and mitigate the effects of natural disaster. This thesis aims to develop a breadboard prototype of a high-quality, low-cost, and easily replicable magnetometer for underwater applications that provides real-time data access in order to facilitate worldwide deployment of magnetic instruments and help achieve global coverage of magnetic field observations. The prototype includes three low-cost single-core fluxgate magnetic sensors in conjunction with six low-pass-filters and a 24-bit analog-to-digital converter, and an Arduino board as a microcontroller. It allows real-time data access through the use of a cellular network and an IoT (Internet of Things) analytics platform, and it aims to enable underwater capability by tracking the magnetometer movements in the water and by further applying a coordinate frame transformation. The observations show that while a resolution smaller than 0.1 nT is possible, higher quality sensors, such as ring-core fluxgate sensors, are needed if increased accuracy and precision are desirable. The simulation results show that the algorithm implemented for correcting the difference in orientation of the instrument with re- spect to the Earth’s frame of reference, would accurately correct the measured field while moving underwater. These results demonstrate that a low-cost high-quality instrument with real-time data transmission is possible, thus, facilitating global deployment of magnetometers, and as a result, the increase of world coverage of magnetic observations.
  • Magnetic environment in the Arctic: recovery of historical magnetic recordings from Scandinavian SMA network
    (2019-08-19) Kärhä, Otto
     Sähkötekniikan korkeakoulu | Master's thesis
    The Earth has a magnetic field that protects it from particles that mainly come from the Sun. Changes in the properties of solar wind and the response of the magnetosphere to these changes form the geomagnetic activity on the Earth. This activity occurs mainly as magnetic storms and substorms. A major magnetic storm can break down electricity distribution and communication satellites. The only way to learn to understand the magnetic field and its phenomena is to measure the changes in it. Fluctuations in the magnetic field have been measured for over a hundred years. In the 1960s, researchers presented the idea that magnetometer stations could be installed in a dense chain in a north-south direction. The concept of the Alaskan meridian chain was introduced in 1968. This chain proved the presence of the Auroral Oval. But the problem with the meridian chain is that it cannot be used to completely study phenomena that move in an east-west direction. The International Magnetospheric Study (IMS) took place from 1977 to 1979. The aim was to study the magnetosphere everywhere in the Earth at the same time. The Scandinavian Magnetometer Array (SMA), where a dense magnetometer chain was placed in the northern part of Scandinavia, was part of the IMS. This chain extended both in north-south as well as east-west directions. The SMA-instruments contained a camera with 35mm film and three wire-suspended magnets. The movement of the magnets were recorded optically on the film. In order to utilize the optical data recorded on the film, it must be digitized. Regarding local and precise magnetic disturbances, the current digitized results are generally one hour-periods. The main goal of this thesis is to track down and digitize the strongest magnetic storm in 1977 that lasted for several days. The results are compared with the data of the permanent magnetometer station located in Abisko. When the magnitude of the magnetic storm is determined as the lowest Disturbance Storm Time (Dst) index peak value, the digitized storm is the 4th largest during the IMS and the 6th largest during the available SMA data.
  • Solar Cycle Occurrence of Alfvénic Fluctuations and Related Geo-Efficiency
    (2017) Tanskanen, Eija; Snekvik, K.; Slavin, J. A.; Pérez-Suárez, D.; Viljanen, A.; Goldstein, M. L.; Käpylä, M.J.; Hynönen, Reko; Häkkinen, L. V. T.; Mursula, K.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We examine solar wind intervals with Alfvénic fluctuations (ALFs) in 1995–2011. The annual number, the total annual duration, and the average length of ALFs vary over the solar cycle, having a maximum in 2003 and a minimum in 2009. ALFs are most frequent in the declining phase of solar cycle, when the number of high-speed streams at the Earth's vicinity is increased. There is a rapid transition after the maximum of solar cycle 23 from ALFs being mainly embedded in slow solar wind (<400 km/s) until 2002 to ALFs being dominantly in fast solar wind (>600 km/s) since 2003. Cross helicity increased by 30% from 2002 to 2003 and maximized typically 4–6 h before solar wind speed maximum. Cross helicity remained elevated for several days for highly Alfvénic non-ICME streams, but only for a few hours for ICMEs. The number of substorms increased by about 40% from 2002 to 2003, and the annual number of substorms closely follows the annual cross helicity. This further emphasizes the role of Alfvénic fluctuations in modulating substorm activity. The predictability of substorm frequency and size would be greatly improved by monitoring solar wind Alfvénic fluctuations in addition to the mean values of the important solar wind parameters.
  • Solar Radio Brightenings and Dimmings from 37 GHz Ra- dio Maps Since 1996
    (2020-06-15) Jha, Tapolina
     Sähkötekniikan korkeakoulu | Master's thesis
    Solar radio observations have been recorded over the last few decades and it has become crucial to automate the image processing and feature detection pipeline. Metsähovi Radio Observatory has recorded solar radio observations for nearly 40 years. Such a long span of solar radio dataset is quite a rare and will produce unique information on the solar radio disturbances when analysed thoroughly with modern artificial intelligence methods. In this thesis, an end-to-end process has been developed which includes clas- sification, processing and analysis of the solar radio maps observed at 37 GHz from January 1996 to December 2018. We generated solar radio maps out of the raw observations, detected different solar bright or quiet features, com- pared the features with other solar datasets and finally produced long term quantitative and morphology analysis of the detected features. Analysis with different available methods for interpolation, thresholding, clustering gave a better idea about the dataset itself as well as about the effectiveness of the processing techniques. Supervised classification for removal of cloud affected observations helped improving the algorithms. Active regions and coronal mass ejections were found to be easily detectable around the limb in Metsähovi observations. Radio brightenings were observed not only at same locations as active regions, but in addition, at high latitudes. Enhanced brightness in the polar region confirmed the earlier claims about polar cap brightening in mm-wavelength observations. The complex magnetic regions were found to produce the most intense radio brightenings.
  • Study of Magnetic Complexity of Solar Active Regions from 1996 to 2017
    (2018) Nikbakhsh, Shabnam; Tanskanen, Eija; Hackman, Thomas; Käpylä, Maarit
     Abstract
    Solar Active Regions (ARs) are areas on the photosphere where the sun'smagnetic field is especially strong. Major manifestations of the solar magnetic activity, such as flares and Coronal Mass Ejections (CMEs), are associated with ARs. The Mount Wilson Classification groups ARsaccording to their magnetic structures from the less complex, Alphaclass, to the more complex one, Beta-Gamma-Delta class. In this study,we investigated the Mount Wilson magnetic classification and latitudedata of 4760 ARs from January 1996 to December 2017. We showed that theabundance of Simple ARs (SARs) follows very closely the sunspot number.In addition, we found that in both cycle 23 and 24, the abundance ofSARs peaks during the sunspot maximum. On the other hand, the abundanceof Complex ARs (CARs) reaches its maximum value two years after solarmaximum in both cycles. We also studied the latitudinal distributionsof the different magnetic complexity classes, and found out that,independent of the complexity type, the northern and southerndistributions are the same. Furthermore, we investigated the earlierclaim of the time lag in between SARs and CARs being due to thebutterfly wing widths getting narrower as the cycle progresses, forcingthe rising flux tubes to get more packed and the resulting activeregions more complex. The maximum of CARs, however, was clearly seen tooccur before the linear decrease of the wing widths took place, makingthis scenario unlikely.