Change search
Refine search result
1 - 26 of 26
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Baumann, Carsten
    et al.
    McCloskey, Aoife E.
    Timing of the solar wind propagation delay between L1 and Earth based on machine learning2021In: Journal of Space Weather and Space Climate, E-ISSN 2115-7251, Vol. 11, no 41Article in journal (Refereed)
    Abstract [en]

    Erroneous GNSS positioning, failures in spacecraft operations and power outages due to geomagnetically induced currents are severe threats originating from space weather. Knowing the potential impacts on modern society in advance is key for many end-user applications. This covers not only the timing of severe geomagnetic storms but also predictions of substorm onsets at polar latitudes. In this study, we aim at contributing to the timing problem of space weather impacts and propose a new method to predict the solar wind propagation delay between Lagrangian point L1 and the Earth based on machine learning, specifically decision tree models. The propagation delay is measured from the identification of interplanetary discontinuities detected by the advanced composition explorer (ACE) and their subsequent sudden commencements in the magnetosphere recorded by ground-based magnetometers. A database of the propagation delay has been constructed on this principle including 380 interplanetary shocks with data ranging from 1998 to 2018. The feature set of the machine learning approach consists of six features, namely the three components of each the solar wind speed and position of ACE around L1. The performance assessment of the machine learning model is examined based on of 10-fold cross-validation. The machine learning results are compared to physics-based models, i.e., the flat propagation delay and the more sophisticated method based on the normal vector of solar wind discontinuities (vector delay). After hyperparameter optimization, the trained gradient boosting (GB) model is the best machine learning model among the tested ones. The GB model achieves an RMSE of 4.5 min concerning the measured solar wind propagation delay and also outperforms the physical flat and vector delay models by 50% and 15% respectively. To increase the confidence in the predictions of the trained GB model, we perform a performance validation, provide drop-column feature importance and analyze the feature impact on the model output with Shapley values. The major advantage of the machine learning approach is its simplicity when it comes to its application. After training, values for the solar wind speed and spacecraft position from only one datapoint have to be fed into the algorithm for a good prediction.

  • 2. Blagoveshchenskaya, N. F.
    Perturbing the high-latitude upper ionosphere (F region) with powerful HF radio waves: A 25-year collaboration with EISCAT2020In: Radio Science Bulletin, ISSN 1024-4530, Vol. 2020, no 373, p. 40-55Article in journal (Refereed)
    Abstract [en]

    We present a brief review of experimental investigations concerning the perturbation of the high-latitude upper ionosphere (F region) by powerful HF radio waves (pump waves), carried out by the team from the Arctic and Antarctic Research Institute (AARI) during a 25-year collaboration with the European Incoherent Scatter (EISCAT) Scientific Association. Three types of HF pumping experiments were carried out by the Russian team at EISCAT. The first type of experiments was related to the modification of the ionosphere-magnetosphere coupling by HF pumping into the nightside ionosphere auroral E and F regions. The second type of experiments was concerned with investigations of geophysical phenomena by using the EISCAT HF heating facility and multi-instrument diagnostics. Most of the experiments were closely related to radio science and nonlinear plasma experiments (a third type of experiment). The main attention was paid to the investigation of artificial ionospheric turbulence in the upper ionosphere (F region) induced by the extraordinary (X-mode) HF pump waves. A great number of X-mode experiments, carried out by the Russian team at EISCAT, clearly demonstrated for the first time that an X-polarized HF pump wave was able to produce various HF-induced phenomena in the high-latitude ionospheric F region, which could be even much stronger than the O-mode effects. We found for the first time that the powerful X-mode HF radio waves, injected into the high-latitude ionospheric F2 layer towards the magnetic zenith, were capable of generating artificial field-aligned irregularities, radio-induced optical emissions in the red (630 nm) and green (557.7 nm) lines, strong electron acceleration leading to Ne enhancements, ion-acoustic and Langmuir electrostatic waves, and spectral components in the narrowband stimulated electromagnetic emission observed at a large distance from the HF heater. The features and behavior of the X-mode effects were analyzed and compared with the O-mode effects.

  • 3. Cai, L.
    et al.
    Oyama, S.
    Aikio, A.
    Vanhamäki, H.
    Virtanen, I.
    Fabry-Perot Interferometer Observations of Thermospheric Horizontal Winds During Magnetospheric Substorms2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 5, p. 3709-3728Article in journal (Refereed)
    Abstract [en]

    The high-latitude ionosphere-thermosphere system is strongly affected by the magnetospheric energy input during magnetospheric substorms. In this study, we investigate the response of the upper thermospheric winds to four substorm events by using the Fabry-Perot interferometer at Troms?, Norway, the International Monitor for Auroral Geomagnetic Effects magnetometers, the EISCAT radar, and an all-sky camera. The upper thermospheric winds had distinct responses to substorm phases. During the growth phase, westward acceleration of the wind was observed in the premidnight sector within the eastward electrojet region. We suggest that the westward acceleration of the neutral wind is caused by the ion drag force associated with the large-scale westward plasma convection within the eastward electrojet. During the expansion phase, the zonal wind had a prompt response to the intensification of the westward electrojet (WEJ) overhead Troms?. The zonal wind was accelerated eastward, which is likely to be associated with the eastward plasma convection within the substorm current wedge. During the expansion and recovery phases, the meridional wind was frequently accelerated to the southward direction, when the majority of the substorm WEJ current was located on the poleward side of Troms?. We suggest that this meridional wind acceleration is related to a pressure gradient produced by Joule heating within the substorm WEJ region. In addition, strong atmospheric gravity waves during the expansion and the recovery phases were observed.

  • 4. Heino, Erkka
    et al.
    Partamies, Noora
    Observational Validation of Cutoff Models as Boundaries of Solar Proton Event Impact Area2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 7, article id e2020JA027935Article in journal (Refereed)
    Abstract [en]

    High energy protons accelerated during solar proton events (SPEs) can access the Earth's middle atmosphere at high and middle latitudes causing large-scale ionization and chemical changes. In this study, we have compared the performance of two cutoff latitude models that predict the limit of the SPE impact area in the atmosphere during 73 SPEs from 1997 to 2010. We use observations from 13 riometer stations and the D Region Absorption Prediction (DRAP) model to test the performance of the two cutoff latitude models by Dmitriev et al. (2010, https://doi.org/10.1029/2010JA015380) and Nesse Tyss?y and Stadsnes (2015, https://doi.org/10.1002/2014JA020508). We find similar performance from the two cutoff latitude models with respect to observations, but the Dmitriev et al. (2010, https://doi.org/10.1029/2010JA015380) model performs slightly better when observations are contrasted with the DRAP model results. The better performing model is also continuous with magnetic local time and particle energy, making it more suited for future use in climate model proton forcing. SPE forcing is currently included in climate models with a single static cutoff latitude limit at 60° geomagnetic latitude. In reality, the area that the solar protons can access is not static but varies with particle rigidity and geomagnetic conditions. We estimate that the SPE impact area is overestimated 90% of the time by this single static cutoff limit and the average overestimation of the impact area is about 15?25% for protons with energies <32?MeV.

  • 5. Heino, Erkka
    et al.
    Verronen, Pekka T.
    Kero, Antti
    Kalakoski, Niilo
    Partamies, Noora
    Cosmic Noise Absorption During Solar Proton Events in WACCM-D and Riometer Observations2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 2, p. 1361-1376Article in journal (Refereed)
    Abstract [en]

    Solar proton events (SPEs) cause large‐scale ionization in the middle atmosphere leading to ozone loss and changes in the energy budget of the middle atmosphere. The accurate implementation of SPEs and other particle ionization sources in climate models is necessary to understand the role of energetic particle precipitation in climate variability. We use riometer observations from 16 riometer stations and the Whole Atmosphere Community Climate Model with added D region ion chemistry (WACCM‐D) to study the spatial and temporal extent of cosmic noise absorption (CNA) during 62 SPEs from 2000 to 2005. We also present a correction method for the nonlinear response of observed CNA during intense absorption events. We find that WACCM‐D can reproduce the observed CNA well with some need for future improvement and testing of the used energetic particle precipitation forcing. The average absolute difference between the model and the observations is found to be less than 0.5 dB poleward of about 66° geomagnetic latitude, and increasing with decreasing latitude to about 1 dB equatorward of about 66° geomagnetic latitude. The differences are largest during twilight conditions where the modeled changes in CNA are more abrupt compared to observations. An overestimation of about 1° to 3° geomagnetic latitude in the extent of the CNA is observed due to the fixed proton cutoff latitude in the model. An unexplained underestimation of CNA by the model during sunlit conditions is observed at stations within the polar cap during 18 of the studied events.

  • 6. Kleimenova, N. G.
    et al.
    Manninen, J.
    Gromova, L. I.
    Gromov, S. V.
    Turunen, T.
    Bursts of Auroral-Hiss VLF Emissions on the Earth’s Surface at L ~ 5.5 and Geomagnetic Disturbances2019In: Geomagnetism and Aeronomy, ISSN 0016-7932, E-ISSN 1555-645X, Vol. 59, no 3, p. 272-280Article in journal (Refereed)
    Abstract [en]

    We have studied the geomagnetic conditions during the occurrence of auroral-hiss VLF emissions on the Earth’s surface in the form of noise bursts at frequencies above 5–6 kHz. The study is based on an analysis of auroral-hiss observations at auroral latitudes in northern Finland at Kannuslehto station (KAN, L ~ 5.5) during the winter campaigns of 2013–2018. It is shown that auroral-hiss bursts are most often observed in the interval of 20–01 MLT under low geomagnetic activity (Kp < 3). It has been found that the bursts are typical for the growth phase of a magnetospheric substorm; the bursts cease abruptly at the onset of the substorm (the break-up of auroras), which is apparently due to a drastic increase in the absorption of VLF waves in the ionosphere. The bursts are often accompanied by the generation of geomagnetic Pi2 pulsations. VLF observations have shown that auroral-hiss bursts are not observed on the Earth’s surface in the main phase of magnetic storms; however, they are typical of the recovery phase. It has been found from model data that, during the occurrence of auroral hiss, KAN station is usually projected to the near-equatorial region of the auroral oval or to the zone of diffuse precipitation of more energetic electrons, i.e., to lower latitudes than the typical position of visible auroras during that time.

  • 7. Kozlovsky, A.
    et al.
    Shalimov, S.
    Oyama, S.
    Hosokawa, K.
    Lester, M.
    Ogawa, Y.
    Hall, C.
    Ground Echoes Observed by the Meteor Radar and High-Speed Auroral Observations in the Substorm Growth Phase2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 11, p. 9278-9292Article in journal (Refereed)
    Abstract [en]

    Abstract Multi-instrument observations by a meteor radar (MR), auroral cameras, ionosondes, and ground magnetometers were made in Northern Europe at auroral latitudes (between 64° and 72° corrected geomagnetic latitude) at 22?24 magnetic local time in the substorm growth phase. The southward drifting growth phase auroral arc was associated with enhanced electron density up to 2?1012 m-3 (corresponding to a plasma frequency, foEs of about 13 MHz) at about 110-km altitude. Such an enhanced E layer electron density caused bending toward the ground of the MR radio waves transmitted at a frequency, fr, of 36.9 MHz and at low elevation (el. < 25°), such that the radar received ground echoes characterized by a near-zero Doppler shift. The amplitude of the echoes was modulated at a frequency of a few hertz, and a similar modulation was found in the auroral luminosity at 427.8 nm near the location of the bending of MR radio waves. The modulation was due to irregular (random) fluctuations of auroral precipitation. Although such a few-hertz variation of the auroral precipitation cannot produce more than 1% modulation of the ionospheric electron density, even such a small modulation can lead to 50% modulation of the MR ground scatter provided foEs ≈ fr sin (el.). The ionosonde and MR data provide evidence that this condition was satisfied in the present case. Due to a high-frequency (>2 Hz) amplitude modulation of the ground scatter, the MR erroneously accepts such signals as echoes from meteor trails.

  • 8. Kvammen, A.
    et al.
    Gustavsson, B.
    Sergienko, T.
    Brändström, U.
    Rietveld, M.
    Rexer, T.
    Vierinen, J.
    The 3-D Distribution of Artificial Aurora Induced by HF Radio Waves in the Ionosphere2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 4, p. 2992-3006Article in journal (Refereed)
    Abstract [en]

    We present 3-D excitation rate estimates of artificial aurora in the ionospheric F layer, induced by high-frequency radio waves from the European Incoherent Scatter heating facility. Simultaneous imaging of the artificial aurora was done with four separate Auroral Large Imaging System stations, permitting tomography-like 3-D auroral reconstruction of the enhanced atomic oxygen emissions at 6,300, 5,577, and 8,446 Å. Inspection of the 3-D reconstructions suggests that the distribution of energized electrons is less extended in altitude than predicted by transport calculations of electrons accelerated to 2?100 eV. A possible reason for this discrepancy is that high-frequency pumping might induce an anisotropic distribution of energized electrons.

  • 9. Mandrikova, O. V.
    et al.
    Rodomanskaya, A. I.
    Mandrikova, B. S.
    Application of the New Wavelet-Decomposition Method for the Analysis of Geomagnetic Data and Cosmic Ray Variations2021In: Geomagnetism and Aeronomy, ISSN 0016-7932, E-ISSN 1555-645X, Vol. 61, no 4, p. 492-507Article in journal (Refereed)
    Abstract [en]

    The potential use of the wavelet-decomposition method developed by the authors for the analysis of geomagnetic data and cosmic ray variations is studied. With the use of adaptive threshold functions, the method allows the isolation of nonstationary, short-period (from 1 × 10–3 Hz and greater) variations in the data and the estimation of their parameters. Data from a network of ground-based magnetometers (www.inrtermagnet.org) and neutron monitors (http://cosray.unibe.ch/) were used in the work. The advantages of the method are shown on the example of magnetic storms on July 9 and September 27, 2017; the effectiveness of the method for the detection of low-amplitude anomalous variations in heterogeneous data has been proven experimentally. The dynamics of variations in the geomagnetic field at meridionally located stations and in the auroral zone is considered in detail; patterns of the occurrence and propagation of geomagnetic disturbances preceding and accompanying the intervals of magnetic storms are obtained. The application of the method made it possible to detect clearly and estimate weak short-term increases in geomagnetic activity observed against the background of increased cosmic ray intensity preceding the onset of magnetic storms. It is noted that the identified geomagnetic disturbances occurred synchronously at stations from high latitudes to the equator and correlated with the periods of southward turns of the IMF Bz component and increased auroral activity. During these intervals, cosmic rays exhibited low-amplitude Forbush effects, which were detected with this method.

  • 10. Marshalko, Elena
    et al.
    Kruglyakov, Mikhail
    Kuvshinov, Alexey
    Juusola, Liisa
    Kwagala, Norah Kaggwa
    Sokolova, Elena
    Pilipenko, Vyacheslav
    Comparing Three Approaches to the Inducing Source Setting for the Ground Electromagnetic Field Modeling due to Space Weather Events2021In: Space Weather: The International Journal of Research and Application, E-ISSN 1542-7390, Vol. 19, no 2, article id e2020SW002657Article in journal (Refereed)
    Abstract [en]

    Ground-based technological systems, such as power grids, can be affected by geomagnetically induced currents (GIC) during geomagnetic storms and magnetospheric substorms. This motivates the necessity to numerically simulate and, ultimately, forecast GIC. The prerequisite for the GIC modeling in the region of interest is the simulation of the ground geoelectric field (GEF) in the same region. The modeling of the GEF in its turn requires spatiotemporal specification of the source which generates the GEF, as well as an adequate regional model of the Earth?s electrical conductivity. In this paper, we compare results of the GEF (and ground magnetic field) simulations using three different source models. Two models represent the source as a laterally varying sheet current flowing above the Earth. The first model is constructed using the results of a physics-based 3-D magnetohydrodynamic (MHD) simulation of near-Earth space, the second one uses ground-based magnetometers? data and the Spherical Elementary Current Systems (SECS) method. The third model is based on a ?plane wave? approximation which assumes that the source is locally laterally uniform. Fennoscandia is chosen as a study region and the simulations are performed for the September 7?8, 2017 geomagnetic storm. We conclude that ground magnetic field perturbations are reproduced more accurately using the source constructed via the SECS method compared to the source obtained on the basis of MHD simulation outputs. We also show that the difference between the GEF modeled using laterally nonuniform source and plane wave approximation is substantial in Fennoscandia.

  • 11. Marshalko, Elena
    et al.
    Kruglyakov, Mikhail
    Kuvshinov, Alexey
    Viljanen, Ari
    Three-Dimensional Modeling of the Ground Electric Field in Fennoscandia During the Halloween Geomagnetic Storm2023In: Space Weather: The International Journal of Research and Application, E-ISSN 1542-7390, Vol. 21, no 9Article in journal (Refereed)
    Abstract [en]

    In this study, we perform three-dimensional (3-D) ground electric field (GEF) modeling in Fennoscandia for three days of the Halloween geomagnetic storm (29–31 October 2003) using magnetic field data from the International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network and a 3-D conductivity model of the region. To explore the influence of the inducing source model on 3-D GEF simulations, we consider three different approaches to source approximation. Within the first two approaches, the source varies laterally, whereas in the third method, the GEF is calculated by implementing the time-domain realization of the magnetotelluric intersite impedance method. We then compare GEF-based geomagnetically induced current (GIC) with observations at the Mäntsälä natural gas pipeline recording point. We conclude that a high correlation between modeled and recorded GIC is observed for all considered approaches. The highest correlation is achieved when performing a 3-D GEF simulation using a “conductivity-based” laterally nonuniform inducing source. Our results also highlight the strong dependence of the GEF on the earth's conductivity distribution.

  • 12. McKay, D.
    et al.
    Paavilainen, T.
    Gustavsson, B.
    Kvammen, A.
    Partamies, N.
    Lumikot: Fast Auroral Transients During the Growth Phase of Substorms2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 13, p. 7214-7221Article in journal (Refereed)
    Abstract [en]

    The development of a magnetospheric substorm may be classified into three phases: growth, expansion, and recovery. The growth phase is important as it includes processes that lead to the expansion. In a recent growth-phase study, a type of fast discrete auroral transient phenomena?referred to as Lumikot?were observed. The Lumikot are several kilometers across and move in the high-energy precipitation region, parallel to the main growth-phase arc, with both east-west and west-east directions of travel during the same event. Their apparent transverse movement and quasi-stable intensity make them distinct from cooccurring optical pulsating aurorae. Comparison to other studies show that they occur in the cosmic noise absorption region and it is likely that the Lumikot are colocated with high-energy particle populations on the boundary between the outer radiation belt and the plasmasheet.

  • 13.
    Nuntiyakul, W.
    et al.
    Chiang Mai Univ, Fac Sci, Dept Phys & Mat Sci, Chiang Mai, Thailand; Chiang Mai Univ, Fac Sci, Res Ctr Phys & Astron, Chiang Mai, Thailand; Natl Astron Res Inst Thailand NARIT, Chiang Mai, Thailand.
    Mangeard, P-S
    Univ Delaware, Dept Phys & Astron, Bartol Res Inst, Newark, DE 19716 USA.
    Ruffolo, D.
    Natl Astron Res Inst Thailand NARIT, Chiang Mai, Thailand; Mahidol Univ, Fac Sci, Dept Phys, Bangkok, Thailand.
    Evenson, P.
    Univ Delaware, Dept Phys & Astron, Bartol Res Inst, Newark, DE 19716 USA.
    Bieber, J. W.
    Univ Delaware, Dept Phys & Astron, Bartol Res Inst, Newark, DE 19716 USA.
    Clem, J.
    Univ Delaware, Dept Phys & Astron, Bartol Res Inst, Newark, DE 19716 USA.
    Hallgren, Allan
    Uppsala universitet, Högenergifysik.
    Madsen, J.
    Univ Wisconsin, Wisconsin IceCube Particle Astrophys Ctr, Madison, WI USA.
    Pyle, R.
    Pyle Consulting Grp Inc, St Charles, IL USA.
    Sáiz, A.
    Mahidol Univ, Fac Sci, Dept Phys, Bangkok, Thailand.
    Tilav, S.
    Univ Delaware, Dept Phys & Astron, Bartol Res Inst, Newark, DE 19716 USA.
    Direct Determination of a Bare Neutron Counter Yield Function2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 4, article id e2019JA027304Article in journal (Refereed)
    Abstract [en]

    Ground-based neutron counters are a standard tool for detecting atmospheric showers from GeV range primary cosmic rays of either solar or galactic origin. Bare neutron counters, a type of lead-free neutron monitor, function much like standard neutron monitors but have different yield functions primarily because they are more sensitive to neutrons of lower energy. When operated together with standard monitors, the different yield functions allow estimates to be made of the energy spectrum of galactic or solar particles. In 2010 a new array of 12 bare neutron detectors was installed at the South Pole to operate together with the neutron monitor there. Prior to installation, two of the detectors were operated on a ship that traveled from Sweden to Antarctica and back from November 2009 to April 2010. The purpose of this latitude survey was to use Earth's magnetic field as a spectrometer, blocking cosmic rays below the local cutoff rigidity (momentum per unit charge), from which we determined the response function versus rigidity of these bare counters. By comparing that measured response function to direct measurements of the cosmic ray spectrum taken by the PAMELA spacecraft, we were able to make a direct determination of the yield function for these detectors.

  • 14. Ogurtsov, M.
    et al.
    Veretenenko, S. V.
    Helama, S.
    Jalkanen, R.
    Lindholm, M.
    Assessing the signals of the Hale solar cycle in temperature proxy records from Northern Fennoscandia2020In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 66, no 9, p. 2113-2121Article in journal (Refereed)
    Abstract [en]

    Eight proxy records of Northern Fennoscandian summer temperature variability were analyzed for the CE 1700–2000 period. Stable and statistically significant correlation between the summer temperature reconstructions and a quasi 22-year Hale solar cycle was found to be present through the entire study period. The revealed solar–climatic link is a result of the effect of a weak solar cycle signal on a climatic system having internal bi-decadal variability. Precise physical mechanisms to explain this link are far from clear but galactic cosmic ray flux appears a probable physical agent to mediate the solar effect to the lower troposphere. No evidence of a link between Northern Fennoscandian temperature and quasi 20-year planetary-tidal cycle was found.

  • 15. Ohtani, S.
    et al.
    Gjerloev, J. W.
    Johnsen, M. G.
    Yamauchi, M.
    Brändström, U.
    Lewis, A. M.
    Solar Illumination Dependence of the Auroral Electrojet Intensity: Interplay Between the Solar Zenith Angle and Dipole Tilt2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 8, p. 6636-6653Article in journal (Refereed)
    Abstract [en]

    The present study investigates the dependence of the local auroral electrojet (AEJ) intensity on solar illumination by statistically examining northward geomagnetic disturbances in the auroral zone in terms of the solar zenith angle χ. It is found that on the dayside, both westward and eastward electrojets (WEJ and EEJ) are more intense for smaller χ, suggesting that the solar extreme ultraviolet‐induced conductance is the dominant factor for the AEJ intensity. On the nightside, in contrast, the χ dependence of the AEJ intensity, if sorted solely by the magnetic local time, apparently depends on the station longitude and hemisphere. However, if additionally sorted by the dipole tilt angle ψ, a consistent pattern emerges. That is, although χ and ψ are correlated, the solar zenith angle and dipole tilt angle have physically different effects on the AEJ intensity. The nightside AEJ, especially the WEJ, tends to be more intense for smaller |ψ|. Moreover, whereas the WEJ is statistically more intense when the ionosphere is dark, the EEJ is more intense when it is sunlit. The preference of the WEJ for the dark ionosphere prevails widely in magnetic local time from premidnight to dawn, and therefore, it cannot be attributed to the previously proposed processes of the preferred monoenergetic or broadband auroral precipitation in the dark ionosphere. Instead, it may be explained, at least morphologically, in terms of the conductance enhancement due to the diffuse auroral precipitation, which is also prevalent from premidnight to dawn and is more intense in the dark hemisphere.

  • 16. Oyama, S.
    et al.
    Shinbori, A.
    Ogawa, Y.
    Kellinsalmi, M.
    Raita, T.
    Aikio, A.
    Vanhamäki, H.
    Shiokawa, K.
    Virtanen, I.
    Cai, L.
    Workayehu, A. B.
    Pedersen, M.
    Kauristie, K.
    Tsuda, T. T.
    Kozelov, B.
    Demekhov, A.
    Yahnin, A.
    Tsuchiya, F.
    Kumamoto, A.
    Kasahara, Y.
    Matsuoka, A.
    Shoji, M.
    Teramoto, M.
    Lester, M.
    An Ephemeral Red Arc Appeared at 68° MLat at a Pseudo Breakup During Geomagnetically Quiet Conditions2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 10, article id e2020JA028468Article in journal (Refereed)
    Abstract [en]

    Various subauroral optical features have been studied by analyzing data collected during periods of geomagnetic disturbances. Most events have been typically found at geomagnetic latitudes of 45?60°. In this study, however, we present a red arc event found at geomagnetic 68° north (L ≈ 7.1) in the Scandinavian sector during a period of geomagnetically quiet conditions within a short intermission between two high-speed solar wind events. The red arc appeared to coincide with a pseudo breakup at geomagnetic 71?72°N and a rapid equatorward expansion of the polar cap. However, the red arc disappeared in approximately 7 min. Simultaneous measurements with the Swarm A/C satellites indicated the appearance of the red arc at the ionospheric trough minimum and a conspicuous enhancement of the electron temperature, suggesting the generation of the arc by heat flux. Since there are meaningful differences in the red arc features from already-known subauroral optical features such as the stable auroral red (SAR) arc, we considered that the red arc is a new phenomenon. We suggest that the ephemeral red arc may represent the moment of SAR arc birth associated with substorm particle injection, which is generally masked by bright dynamic aurorae.

  • 17. Parhomov, V. A.
    et al.
    Eselevich, V. G.
    Eselevich, M. V.
    Dmitriev, A. V.
    Suvorova, A. V.
    Khomutov, S. Y.
    Tsegmed, B.
    Tero, R.
    Magnetospheric response to the interaction with the sporadic solar wind diamagnetic structure2021In: Solar-Terrestrial Physics, ISSN 2500-0535, Vol. 7, p. 11-28Article in journal (Refereed)
    Abstract [en]

    We report the results of a study on the movement of the solar wind diamagnetic structure (DS), which is a sequence of smaller-scale microDS being part of the May 18, 2013 coronal mass ejection, from a source on the Sun to Earth’s surface. DS determined from the high negative correlation coefficient (r=–0.9) between the IMF modulus (B) and the SW density (N) on the ACE and Wind satellites at the L1 point, on the THB and THC satellites (r=–0.9) in near-Earth orbit, and on the THA satellite inside the magnetosphere is carried by the solar wind from the Sun to Earth’s orbit, while maintaining its fine internal structure. Having a large size in the radial direction (≈763 Rᴇ, where Rᴇ is the Earth radius), DS flows around the magnetosphere. At the same time, microDS of size ≤13 Rᴇ passes through the bow shock and magnetopause as a magnetized plasmoid in which the ion concentration increases from 10 cm⁻³ to 90 cm⁻³, and the velocity decreases as it moves toward the magnetotail. When a microDS passes through the magnetopause, a pulsed electric field of ~400 mV/m is generated with subsequent oscillations with a period of T~200 s and an amplitude of ~50 mV/m. The electric field accelerates charged particles of the radiation belt and produces modulated fluxes of protons in an energy range 95–575 keV on the day side and electrons in 40–475 keV and protons in 95–575 keV on the night side. In the duskside magnetosphere (19–23 MLT), the substorm activation is observed in geomagnetic pulsations and auroras, but without a magnetic negative bay. In the post-midnight sector (01–05 MLT), a sawtooth substorm occurs without the growth phase and breakup with deep modulation of the ionospheric current and auroral absorption. The duration of all phenomena in the magnetosphere and on Earth is determined by the period of interaction between DS and the magnetosphere (~4 hrs). To interpret the regularities of the magnetospheric response to the interaction with DS, we consider alternative models of the impulsive passage of DS from SW to the magnetosphere and the classical model of reconnection of IMF and the geomagnetic field.

  • 18. Partamies, N.
    et al.
    Tesema, F.
    Bland, E.
    Heino, E.
    Nesse Tyssøy, H.
    Kallelid, E.
    Electron precipitation characteristics during isolated, compound, and multi-night substorm events2021In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 39, no 1, p. 69-83Article in journal (Refereed)
    Abstract [en]

    A set of 24 isolated, 46 compound, and 36 multi-night substorm events from the years 2008–2013 have been analysed in this study. Isolated substorm events are defined as single expansion–recovery phase pairs, compound substorms consist of multiple phase pairs, and multi-night substorm events refer to recurring substorm activity on consecutive nights. Approximately 200 nights of substorm activity observed over Fennoscandian Lapland have been analysed for their magnetic disturbance magnitude and the level of cosmic radio noise absorption. Substorm events were automatically detected from the local electrojet index data and visually categorized.

    We show that isolated substorms have limited lifetimes and spatial extents as compared to the other substorm types. The average intensity (both in absorption and ground-magnetic deflection) of compound and multi-night substorm events is similar. For multi-night substorm events, the first night is rarely associated with the strongest absorption. Instead, the high-energy electron population needed to cause the strongest absorption builds up over 1–2 additional nights of substorm activity. The non-linear relationship between the absorption and the magnetic deflection at high- and low-activity conditions is also discussed. We further collect in situ particle spectra for expansion and recovery phases to construct median precipitation fluxes at energies from 30 eV up to about 800 keV. In the expansion phases the bulk of the spectra show a local maximum flux in the range of a few keV to 10 keV, while in the recovery phases higher fluxes are seen in the range of tens of keV to hundreds of keV. These findings are discussed in the light of earlier observations of substorm precipitation and their atmospheric effects.

  • 19. Smith, Andrew W.
    et al.
    Forsyth, Colin
    Rae, Jonathan
    Rodger, Craig J.
    Freeman, Mervyn P.
    The Impact of Sudden Commencements on Ground Magnetic Field Variability: Immediate and Delayed Consequences2021In: Space Weather: The International Journal of Research and Application, E-ISSN 1542-7390, Vol. 19, no 7Article in journal (Refereed)
    Abstract [en]

    We examine how Sudden Commencements (SCs) and Storm Sudden Commencements (SSCs) influence the occurrence of high rates of change of the magnetic field (R) as a function of geomagnetic latitude. These rapid, high amplitude variations in the ground-level geomagnetic field pose a significant risk to ground infrastructure, such as power networks, as the drivers of geomagnetically induced currents. We find that rates of change of ?30 nT min?1 at near-equatorial stations are up to 700 times more likely in an SC than in any random interval. This factor decreases with geomagnetic latitude such that rates of change around 30 nT min?1 are only up to 10 times more likely by 65°. At equatorial latitudes we find that 25% of all R in excess of 50 nT min?1 occurs during SCs. This percentage also decreases with geomagnetic latitude, reaching ≤1% by 55°. However, the time period from the SC to 3 days afterward accounts for ≥90% of geomagnetic field fluctuations over 50 nT min?1, up to ?60° latitude. Above 60°, other phenomena such as isolated substorms account for the majority of large R. Furthermore, the elevated rates of change observed during and after SCs are solely due to those classified as SSCs. These results show that SSCs are the predominant risk events for large R at mid and low latitudes, but that the risk from the SC itself decreases with latitude.

  • 20. Stauning, Peter
    Using PC indices to predict violent GIC events threatening power grids2020In: Journal of Space Weather and Space Climate, E-ISSN 2115-7251, Vol. 10Article in journal (Refereed)
    Abstract [en]

    The aim of the present contribution is to investigate the timing relations between enhancements in the Polar Cap (PC) indices and power grid disturbances related to geomagnetically induced currents (GIC). The polar cap indices, PCN (North) and PCS (South), are based on measurements of geomagnetic variations in the central polar caps. These variations are strongly related to the transpolar convection of plasma and magnetic fields driven by the solar wind. During cases of enhanced merging processes at the front of the magnetosphere and subsequent tailward convection of plasma and embedded magnetic fields, the magnetospheric tail configuration may accumulate excess energy, which upon release may cause violent substorm activity. Earlier reports have disclosed remarkably lengthy intervals, ranging up to several hours, of elevated PC index values preceding GIC-related power grid disruptions. The present investigation has shown that the delays of typically 3–4 h between increases in the PC indices and GIC-related power grid disturbances are related to displacements of the substorm processes responsible for strong GIC events to subauroral latitudes where vulnerable power grids reside. The results have shown that PC index values remaining above an “alert level” of 10 mV/m through more than 1 h indicate a high risk for violent GIC events that may threaten power grids and other vulnerable technical systems. These results support the application of real-time PC indices in space weather monitoring and forecast services.

  • 21. Tesema, Fasil
    et al.
    Partamies, Noora
    Tyssøy, H. Nesse
    Kero, Antti
    Smith-Johnsen, C.
    Observations of Electron Precipitation During Pulsating Aurora and Its Chemical Impact2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 6, article id e2019JA027713Article in journal (Refereed)
    Abstract [en]

    Pulsating auroras (PsAs) are low-intensity diffuse aurora, which switch on and off with a quasiperiodic oscillation period from a few seconds to ?10 s. They are predominantly observed after magnetic midnight, during the recovery phase of substorms and at the equatorward boundary of the auroral oval. PsAs are caused by precipitating energetic electrons, which span a wide range of energies between tens and hundreds of keV. Such energetic PsA electrons will deposit their energy at mesospheric altitudes and induce atmospheric chemical changes. To examine the effects of energetic PsA electrons on the atmosphere, we first collect electron flux and energy measurements from low-latitude spacecraft to construct a typical energy spectrum of precipitating electrons during PsA. Among the 840 PsA events identified using ground-based auroral all-sky camera (ASC) network over the Fennoscandian region, 253 events were observed by DMSP, POES, and FAST spacecraft over the common field of view of five ASCs. The combined measurements from these spacecraft enable us to obtain an energy spectrum consisting of nonrelativistic and relativistic (30 eV to 1,000 keV) electrons during PsA. The median spectrum was found to be in good agreement with earlier estimates of the PsA spectra. We then use the Sodankylä Ion-neutral Chemistry (SIC) model to assess the chemical effect of PsA electrons. The observed extreme and median spectra of PsA produce a significant depletion in the mesospheric odd oxygen concentration up to 78%.

  • 22. Vokhmyanin, M.
    et al.
    Apatenkov, S.
    Gordeev, E.
    Andreeva, V.
    Partamies, N.
    Kauristie, K.
    Juusola, L.
    Statistics on Omega Band Properties and Related Geomagnetic Variations2021In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 126, no 7Article in journal (Refereed)
    Abstract [en]

    Using the list of the omega structures based on the Magnetometers-Ionospheric Radars-All-sky Cameras Large Experiment network (Partamies et al., 2017, https://doi.org/10.5194/angeo-35-1069-2017), we obtained a number of important statistical characteristics describing the surface magnetic field. Based on 438 events, typical magnetic variations associated with the passage of the single omega were obtained. The typical variation, obtained using superposed epoch analysis, is associated with a local bending of the westward electrojet and statistically confirms the distribution of equivalent ionospheric currents obtained in earlier observations of single omegas. It was found that during low and moderate geomagnetic activity, the appearance of the omega structures in the dark morning magnetic local time (MLT) sector results in two times higher than average dB/dt on the ground surface. Also, the velocity, direction of movement, and area of omega structures were calculated. It is shown that faster and bigger omegas produce larger time derivatives of the ground magnetic field. Furthermore, we demonstrate that in the 03?08 MLT sector, superposed magnetic variations for the arbitrary events of very high time derivatives |dB/dt| > 10 nT/s, reveal magnetic signatures similar to omegas. Our findings, together with the results described by Apatenkov et al. (2020, https://doi.org/10.1029/2019gl086677), emphasize the important role of omega structures in the formation of large geomagnetically induced currents.

  • 23. Warden, L. J.
    et al.
    Waters, C. L.
    Sciffer, M. D.
    Hull, A. J.
    On the Estimation of the Ratio of ULF Wave Electric Fields in Space and the Magnetic Fields at the Ground2021In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 126, no 7Article in journal (Refereed)
    Abstract [en]

    Three new methods for estimating a ratio of the ultralow frequency (ULF; 1?100 mHz) wave equatorial electric field amplitude in the Earth's magnetosphere to ground magnetic field amplitudes for field line resonances (FLR) are described. These methods use ratios of the time series extrema, ratios of the envelope waveform and the ratio of the spectral amplitude at the FLR frequency. These methods were applied to four ULF resonance intervals; three detected by the Van Allen Probe A spacecraft and one detected by the POLAR spacecraft. The intervals were conjoined with the CARISMA and IMAGE ground magnetometer arrays. The spectral ratio results for the Van Allen Probe intervals were approximately twice to three times the ratios estimated from the two time series based methods. The POLAR interval showed similar values across all three methods. The differences are attributed to broadband frequency signals that modify the time series amplitudes, while the spectral method avoids these off-resonant frequencies. Based on the results of this study, a spectral based method for calculating the ratio at the FLR frequency is best.

  • 24. Wawrzaszek, Anna
    et al.
    Gil, Agnieszka
    Modzelewska, Renata
    Tsurutani, Bruce T.
    Wawrzaszek, Roman
    Analysis of Large Geomagnetically Induced Currents During the 7–8 September 2017 Storm: Geoelectric Field Mapping2023In: Space Weather: The International Journal of Research and Application, E-ISSN 1542-7390, Vol. 21, no 3Article in journal (Refereed)
    Abstract [en]

    High temporal and high spatial resolution geoelectric field models of two Mäntsälä, Finnish pipeline geomagnetically induced current (GIC) intervals that occurred within the 7?8 September 2017 geomagnetic storm have been made. The geomagnetic measurements with 10 s sampling rate of 28 IMAGE ground magnetometers distributed over the north Europe (from 52.07° to 69.76° latitude) are the bases for the study. A GeoElectric Dynamic Mapping (GEDMap) code was developed for this task. GEDMap considers 4 different methods of interpolation and allows a grid of 0.05° (lat.) ? 0.2° (lon.) spatial scale resolution. The geoelectric field dynamic mapping output gives both spatial and temporal variations of the magnitude and direction of fields. The GEDMap results show very rapid and strong variability of geoelectric field and the extremely localized peak enhancements. The magnitude of geoelectric fields over Mäntsälä at the time of the two GIC peaks were 279.7 and 336.9 mV/km. The comparison of the GIC measurements in Mäntsälä and our modeling results show very good agreement with a correlation coefficient higher than 0.8. It is found that the auroral electrojet geoelectric field has very rapid changes in both magnitude and orientation causing the GICs. It is also shown that the electrojet is not simply oriented in the east-west direction. It is possible that even higher time resolution base magnetometer data of 1 s will yield even more structure, so this will be our next effort.

  • 25. Wharton, S. J.
    et al.
    Wright, D. M.
    Yeoman, T. K.
    James, M. K.
    Sandhu, J. K.
    The Variation of Resonating Magnetospheric Field Lines With Changing Geomagnetic and Solar Wind Conditions2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 7, p. 5353-5375Article in journal (Refereed)
    Abstract [en]

    Standing ultralow frequency waves redistribute energy and momentum around the Earth's magnetosphere. The eigenfrequencies of these standing waves can be measured by applying the cross-phase technique to ground magnetometer data. To make a detection, the flux tubes in the vicinity of the magnetometers must all be driven at their local eigenfrequencies by a source with a sufficient frequency width. Therefore, successful measurement of the local eigenfrequencies indicates that a broadband source is exciting the flux tubes. We have analyzed 10 years of magnetometer data with an automated cross-phase algorithm and used correlations with the OMNI data set to understand under what conditions broadband excitation occurs and how the conditions affect the eigenfrequency values. This is the largest such survey of its kind to date. We found that lower eigenfrequencies at higher latitudes (L>5) and higher eigenfrequencies at lower latitudes (L<4) were excited under different conditions. It was also possible to directly compare the first and third harmonics at midlatitudes. The lower eigenfrequencies were excited during more disturbed conditions, and we suggest that these harmonics are driven by solar wind pressure pulses or the Kelvin-Helmholtz instability at the magnetopause. The higher eigenfrequencies were excited when the magnetosphere was relatively quiet, and we suggest that the cause was waves generated upstream of the Earth's bow shock. The eigenfrequencies were observed to decrease in the middle magnetosphere during disturbed intervals. This is because the intensification of the ring current weakens the magnetic field. Variations in magnetic local time and latitude were also investigated.

  • 26. Yadav, Sneha
    et al.
    Shiokawa, K.
    Oyama, S.
    Otsuka, Y.
    Multievent Analysis of Oscillatory Motion of Medium-Scale Traveling Ionospheric Disturbances Observed by a 630-nm Airglow Imager Over Tromsø2020In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 125, no 3, article id e2019JA027598Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive investigation on the propagation characteristics of duskside medium-scale traveling ionospheric disturbances (MSTIDs) using 630.0-nm airglow emissions over Troms? (69.6°N, 19.2°E; magnetic latitude: 66.7°N). The unique points of our observation are (1) duskside MSTIDs primarily exhibited eastward motion under quiet conditions but turned to the westward direction associated with geomagnetic disturbances, (2) the westward moving MSTIDs again turned to the eastward direction when the geomagnetic disturbance ceased, (3) the turning of MSTIDs to the westward direction was invariably associated with an increase of the northward component of the magnetic field observed by the local ground-based magnetometers and with the equatorward expansion of the auroral oval, and (4) the Super Dual Auroral Radar Network convection maps revealed that the location of Troms? was inside (outside) the duskside convection cell during the time of appearance of westward (eastward) moving MSTIDs. The average eastward and westward velocities of MSTIDs were ~25?80 and ~40?140 m/s, respectively. The Doppler shift measurement of the 630-nm airglow by a Fabry-Perot interferometer at Troms? showed that northeastward winds were predominant during the appearance of eastward moving MSTIDs. These experimental evidences suggest that the oscillatory motion of MSTIDs over high latitudes is driven by the convection electric field. The MSTIDs tend to move eastward under geomagnetically quiet conditions but show westward motion under the influence of convection electric field associated with auroral activities in the duskside of two-cell convection pattern.

1 - 26 of 26
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf