Spatio-temporal development of large-scale auroral electrojet currents relative to substorm onsets

During auroral substorms, the electric currents flowing in the ionosphere change rapidly, and a large amount of energy is dissipated in the auroral ionosphere. An important part of the auroral current system is the auroral electrojets whose profiles can be estimated from magnetic field measurements from low-earth orbit satellites. In this paper, we combine electrojet data derived from the Swarm satellite mission of the European Space Agency with the substorm database derived from the SuperMAG ground magnetometer network data. We organize the electrojet data in relation to the location and time of the onset and obtain statistics for the development of the integrated current and latitudinal location for the auroral electrojets relative to the onset. The major features of the behaviour of the westward electrojet are found to be in accordance with earlier studies of field-aligned currents and ground magnetometer observations of substorm temporal statistics. In addition, we show that, after the onset, the latitudinal location of the maximum of the westward electrojet determined from Swarm satellite data is mostly located close to the SuperMAG onset latitude in the local time sector of the onset regardless of where the onset happens. We also show that the SuperMAG onset corresponds to a strengthening of the order of 100 kA in the amplitude of the median of the westward integrated current in the Swarm data from 15 min before to 15 min after the onset.Peer reviewe

Reconstruction of precipitating electrons and three-dimensional structure of a pulsating auroral patch from monochromatic auroral images obtained from multiple observation points

In recent years, aurora observation networks using high-sensitivity cameras have been developed in the polar regions. These networks allow dimmer auroras, such as pulsating auroras (PsAs), to be observed with a high signal-to-noise ratio. We reconstructed the horizontal distribution of precipitating electrons using computed tomography with monochromatic PsA images obtained from three observation points. The three-dimensional distribution of the volume emission rate (VER) of the PsA was also reconstructed. The characteristic energy of the reconstructed precipitating electron flux ranged from 6 to 23 keV, and the peak altitude of the reconstructed VER ranged from 90 to 104 km. We evaluated the results using a model aurora and compared the model’s electron density with the observed one. The electron density was reconstructed correctly to some extent, even after a decrease in PsA intensity. These results suggest that the horizontal distribution of precipitating electrons associated with PsAs can be effectively reconstructed from ground-based optical observations

Auroral imaging with combined Suomi 100 nanosatellite and ground-based observations: A case study

Auroras can be regarded as the most fascinating manifestation of space weather and they are continuously observed by ground-based and, nowadays more and more, also by space-based measurements. Investigations of auroras and geospace comprise the main research goals of the Suomi 100 nanosatellite, the first Finnish space research satellite, which has been measuring the Earth's ionosphere since its launch on Dec. 3, 2018. In this work, we present a case study where the satellite's camera observations of an aurora over Northern Europe are combined with ground-based observations of the same event. The analyzed image is, to the authors' best knowledge, the first auroral image ever taken by a cubesat. Our data analysis shows that a satellite vantage point provides complementary, novel information of such phenomena. The 3D auroral location reconstruction of the analyzed auroral event demonstrates how information from a 2D image can be used to provide location information of auroras under study. The location modelling also suggests that the Earth's limb direction, which was the case in the analyzed image, is an ideal direction to observe faint auroras. Although imaging on a small satellite has some large disadvantages compared with ground-based imaging (the camera cannot be repaired, a fast moving spinning satellite), the data analysis and modelling demonstrate how even a small 1-Unit (size: 10 cm x 10 cm x 10 cm) CubeSat and its camera, build using cheap commercial off-the-shelf components, can open new possibilities for auroral research, especially, when its measurements are combined with ground-based observations.Comment: Accepted manuscript 34 pages, 17 figure

Multi-instrument observations of large-scale atmospheric gravity waves/traveling ionospheric disturbances associated with enhanced auroral activity over Svalbard

This study reports on observations of large-scale atmospheric gravity waves/traveling ionospheric disturbances (AGWs/TIDs) using Global Positioning System (GPS) total electron content (TEC) and Fabry–Perot Interferometer’s (FPI’s) intensity of oxygen red line emission at 630 nm measurements over Svalbard on the night of 6 January 2014. TEC large-scale TIDs have primary periods ranging between 29 and 65 min and propagate at a mean horizontal velocity of ~749–761 m/s with azimuth of ~345–347° (which corresponds to poleward propagation direction). On the other hand, FPI large-scale AGWs have larger periods of ~42–142 min. These large-scale AGWs/TIDs were linked to enhanced auroral activity identified from co-located all-sky camera and IMAGE magnetometers. Similar periods, speed and poleward propagation were found for the all-sky camera (~60–97 min and ~823 m/s) and the IMAGE magnetometers (~32–53 min and ~708 m/s) observations. Joule heating or/and particle precipitation as a result of auroral energy injection were identified as likely generation mechanisms for these disturbances. © 2018 COSPAR. Published by Elsevier Ltd. All rights reserved

Multi-instrument observations of large-scale atmospheric gravity waves/traveling ionospheric disturbances associated with enhanced auroral activity over Svalbard

This study reports on observations of large-scale atmospheric gravity waves/traveling ionospheric disturbances (AGWs/TIDs) using Global Positioning System (GPS) total electron content (TEC) and Fabry-Perot Interferometer’s (FPI’s) intensity of oxygen red line emission at 630 nm measurements over Svalbard on the night of 6 January 2014. TEC large-scale TIDs have primary periods ranging between 29 and 65 minutes and propagate at a mean horizontal velocity of ∼749–761 m/s with azimuth of ∼345°–347° (which corresponds to poleward propagation direction). On the other hand, FPI large-scale AGWs have larger periods of ∼42–142 minutes. These large-scale AGWs/TIDs were linked to enhanced auroral activity identified from co-located all-sky camera and IMAGE magnetometers. Similar periods, speed and poleward propagation were found for the all-sky camera (∼60–97 minutes and ∼823 m/s) and the IMAGE magnetometers (∼32–53 minutes and ∼708 m/s) observations. Joule heating or/and particle precipitation as a result of auroral energy injection were identified as likely generation mechanisms for these disturbances

Äärimmäiset avaruussäämyrksyt, niiden vaikutukset ja varautuminen

Tässä hankkeessa kerättiin tietoa äärimmäisen voimakkaiden avaruussää-myrskyjen vaikutuksista erilaisiin teknisiin järjestelmiin. Selvitykseen osallistuivat Ilmatieteen laitos, Helsingin yliopisto (HY, Avaruusfysiikan tutkimus) ja Change in Momentum -yritys. Raportissa esitellään laajasta kirjallisuustutkimuksesta kerättyä tietoa voimakkaista myrskyistä ja tietokonesimulaatioiden tuloksia. Raportin loppuosassa käsitellään avaruussäämyrskyihin liittyviä suoria ja välillisiä yhteiskunnallisia riskejä, kuvataan verrokkimaiden kansallisten riskiarvioiden tuloksia jaesitellään varautumisharjoituksiin soveltuva äärimmäisen avaruusmyrskyn skenaario. Kirjallisuustutkimuksessa kiinnitettiin erityistä huomiota avaruus-säämyrskyjen aiheuttamiin ongelmiin sähkönjakelujärjestelmissä niiden laajojen kerrannaisvaikutusten vuoksi. Nopeat vaihtelut Maan magneetti-kentässä synnyttävät jakelujärjestelmiin haitallisia geomagneettisesti indusoituneita (GI) virtoja. Äärimmäisten myrskyjen aikaan saattaa esiintyä jopa kolme kertaa suurempia magneettikentän aikaderivaattoja Euroopassa mitattuihin arvoihin verrattuna. Haittavaikutuksille altis alue ulottuu Keski- ja Etelä-Eurooppaan asti. Meidän tulee siis varautua myrskyjen aiheuttamiin välillisiin vaikutuksiin esim. kansainvälisten toimitusketjujen ongelmien seurauksena, vaikka Suomen sähkönjakelujärjestelmän GI-virtojen sietokyvyn tiedetään olevan hyvä. Koska geomagneettisia myrskyjä riittävän tarkasti kuvaavat aikasarjat ovat verrattain lyhyitä (<150 vuotta), tilastollisissa arvioissa esiintymistodennäköisyyksille esiintyy vielä paljon vaihtelua. Kirjallisuudessa annetut arviot yleisesti vertailukohteena käytetyn vuoden 1859 Carrington-myrskyn kaltaisen ääritapahtuman todennäköisyy-delle seuraavan 10 vuoden sisällä vaihtelevat välillä 0,5–20 %. Hankkeessa testattiin ensimmäistä kertaa Helsingin yliopiston Vlasiator-simulaatiota avaruussäämyrskyjen mallinnuksessa erityisesti satelliittien toimintaympäristöön liittyen. Suurteholaskentaa vaativa Vlasiator on maailman ainoa mallinnustyökalu, joka kattaa koko lähiavaruuden ja kuvaa tarkasti avaruusplasman ionien vaikutuksen myrskyjen kehittymiseen. Simulaatiot osoittivat, että äärimmäisten myrskyjen aikaan geostationaariset ja navigointi-satelliitit menettävät ajoittain magnetosfäärin antaman suojan Auringon hiukkaspurkauksia vastaan. Geostationaaristen satelliittien hiukkasmittausten perusteella HY:n tutkijat arvioivat myös, että korkeaenergiaisten elektronien vuot saattavat olla äärimmäisissä tilanteissa 1–3 kertaluokkaa suuremmat kuin aiempien myrskyjen aikana mitatut satelliittiteknologialle ongelmia aiheuttaneet vuot. Tässä hankkeessa vuosina 2021–2022 tehtyjä Vlasiatorajoja ja muuta tutkimustyötä tarkennetaan ja laajennetaan Suomen Akatemian rahoittamassa “Preparing for the most extreme space weather” -hankeessa vuosina 2020–2023.In this project, information about extreme space weather storms and their impacts on different technological systems was collected by Finnish Meteorological Institute, University of Helsinki (UoH, Space Physics Research), and Change in Momentum company. The report presents findings from a wide literature study addressing strong space weather storms and results from computer simulations. Latter part of the report discusses direct and indirect societal risks due to extreme storms, describes national risk assessments of some reference countries, and presents a storm scenario that can be used in tabletop exercises. The literature study focused on storm impacts on power transmission as they imply indirect effects in several other systems of high societal importance. Rapid variations in Earth’s magnetic field drive harmful Geomagnetically Induced Currents (GIC) into power networks. During extreme storms the time derivatives of geomagnetic field can be even 3 times larger than measured values in Europe. The impacted area covers also Mid- and South-European latitudes. Although Finland’s power transmission system in known to be resilient against GIC, we should be prepared to tackle indirect GIC-impacts that may appear e.g. as breaks in critical supply chains. Statistical estimates for the occurrence rates of extreme storms show large variability, because time series of accurate enough magnetic field measurements are relatively short (<150 years). Literature suggests that the occurrence probability for a storm of similar intensity as the famous Carrington extreme storm in 1859 to happen in forthcoming 10 years is in the range of 0,5–20%. The Vlasiator high performance computing code of UoH was tested for the first time in simulations of extreme space weather activity in this project. Simulation results were analysed with the focus on satellites’ plasma environment. Vlasiator is the only modelling tool in the world that can handle near-Earth plasma processes globally and describe accurately the crucial ion physics contribution to storm evolution. Simulation results show that geostationary and navigation satellites can occasionally loose the protection by Earth’s magnetosphere against hostile solar particle bursts during extreme activity. Furthermore, statistical analysis of geostationationary particle data by the UoH team suggests that fluxes of high energy electrons can be 1–3 orders of magnitude larger than the fluxes which have caused problems for satellites during previous storms. Vlasiator-simulations and other research conducted in this project (2021–2022) will be continued and expanded in the project “Preparing for the most extreme space weather” funded by the Academy of Finland (2020–2023)

Radar—CubeSat Transionospheric HF Propagation Observations: Suomi 100 Satellite and EISCAT HF Facility

Radio waves provide a useful diagnostic tool to investigate the properties of the ionosphere because the ionosphere affects the transmission and properties of high frequency (HF) electromagnetic waves. We have conducted a transionospheric HF-propagation research campaign with a nanosatellite on a low-Earth polar orbit and the EISCAT HF transmitter facility in Tromsø, Norway, in December 2020. In the active measurement, the EISCAT HF facility transmitted sinusoidal 7.953 MHz signal which was received with the High frEquency rAdio spectRomEteR (HEARER) onboard 1 Unit (size: 10 × 10 × 10 cm) Suomi 100 space weather nanosatellite. Data analysis showed that the EISCAT HF signal was detected with the satellite's radio spectrometer when the satellite was the closest to the heater along its orbit. Part of the observed variations seen in the signal was identified to be related to the heater's antenna pattern and to the transmitted pulse shapes. Other observed variations can be related to the spatial and temporal variations of the ionosphere and its different responses to the used transmission frequencies and to the transmitted O- and X-wave modes. Some trends in the observed signal may also be associated to changes in the properties of ionospheric plasma resulting from the heater's electromagnetic wave energy. This paper is, to authors' best knowledge, the first observation of this kind of “self-absorption” measured from the transionospheric signal path from a powerful radio source on the ground to the satellite-borne receiver

Forecasting auroras from regional and global magnetic field measurements

We use the connection between auroral sightings and rapid geomagnetic field variations in a concept for a Regional Auroral Forecast (RAF) service. The service is based on statistical relationships between near-real-time alerts issued by the NOAA Space Weather Prediction Center and magnetic time derivative (dB / dt) values measured by five MIRACLE magnetometer stations located in Finland at auroral and sub-auroral latitudes. Our database contains NOAA alerts and dB / dt observations from the years 2002-2012. These data are used to create a set of conditional probabilities, which tell the service user when the probability of seeing auroras exceeds the average conditions in Fennoscandia during the coming 0-12 h. Favourable conditions for auroral displays are associated with ground magnetic field time derivative values (dB / dt) exceeding certain latitude-dependent threshold values. Our statistical analyses reveal that the probabilities of recording dB / dt exceeding the thresholds stay below 50% after NOAA alerts on X-ray bursts or on energetic particle flux enhancements. Therefore, those alerts are not very useful for auroral forecasts if we want to keep the number of false alarms low. However, NOAA alerts on global geomagnetic storms (characterized with K-p values > 4) enable probability estimates of > 50% with lead times of 3-12 h. RAF forecasts thus rely heavily on the well-known fact that bright auroras appear during geomagnetic storms. The additional new piece of information which RAF brings to the previous picture is the knowledge on typical storm durations at different latitudes. For example, the service users south of the Arctic Circle will learn that after a NOAA ALTK06 issuance in night, auroral spotting should be done within 12 h after the alert, while at higher latitudes conditions can remain favourable during the next night.Peer reviewe

3D structure of discrete arcs obtained by auroral computed tomography analysis

The Tenth Symposium on Polar Science/Ordinary sessions: [OS] Space and upper atmospheric sciences, Wed. 4 Dec. /Entrance Hall (1st floor) at National Institute of Polar Research (NIPR