Blar i Registrations from Cristin på forfatter "Ohma, Anders"
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Background removal from global auroral images: Data driven dayglow modelling
Ohma, Anders; Madelaire, Michael; Laundal, Karl Magnus; Reistad, Jone Peter; Hatch, Spencer Mark; Gasparini, Sara; Walker, Simon (Journal article; Peer reviewed, 2023)Global images of auroras obtained by cameras on spacecraft are a key tool for studying the near-Earth environment. However, the cameras are sensitive not only to auroral emissions produced by precipitating particles, but ... -
Dependence of the global dayside reconnection rate on interplanetary magnetic field By and the earth’s dipole tilt
Reistad, Jone Peter; Holappa, Lauri; Ohma, Anders; Gabrielse, Christine; Sur, Dibyendu; Asikainen, Timo; DeJong, Anna (Journal article; Peer reviewed, 2022)In the recent years, significant attention has been given to the combined effect of Interplanetary Magnetic Field (IMF) duskward component (By) and dipole tilt on the global magnetosphere-ionosphere system response. Numerous ... -
Evolution of IMF By induced asymmetries during substorms: Superposed epoch analysis at geosynchronous orbit
Ohma, Anders; Laundal, Karl Magnus; Reistad, Jone Peter; Østgaard, Nikolai (Journal article; Peer reviewed, 2022)The By component of the magnetic field inside the magnetosphere is positively correlated with the By component of the Interplanetary Magnetic Field (IMF). This leads to asymmetries in aurora, plasma convection and electric ... -
Evolution of IMF By Induced Asymmetries: The Role of Tail Reconnection
Ohma, Anders; Østgaard, Nikolai; Laundal, Karl Magnus; Reistad, Jone Peter; Hatch, Spencer Mark; Tenfjord, Paul Arne Riksheim (Journal article; Peer reviewed, 2021)North-south asymmetries arise in the magnetosphere-ionosphere system when a significant east-west (By) component is present in the interplanetary magnetic field (IMF). During such conditions, a By component with the same ... -
Geomagnetic Response to Rapid Increases in Solar Wind Dynamic Pressure: Event Detection and Large Scale Response
Madelaire, Michael; Laundal, Karl Magnus; Reistad, Jone Peter; Hatch, Spencer Mark; Ohma, Anders; Haaland, Stein Egil (Journal article; Peer reviewed, 2022)Discontinuities in the solar wind trigger a variety of processes in the magnetosphere-ionosphere system. A rapid increase in solar wind dynamic pressure causes compression of the magnetosphere. This manifests itself as a ... -
Local Mapping of Polar Ionospheric Electrodynamics
Laundal, Karl Magnus; Reistad, Jone Peter; Hatch, Spencer Mark; Madelaire, Michael; Walker, Simon; Hovland, Amalie Øie; Ohma, Anders; Merkin, V.G.; Sorathia, K.A. (Journal article; Peer reviewed, 2022)An accurate description of the state of the ionosphere is crucial for understanding the physics of Earth's coupling to space, including many potentially hazardous space weather phenomena. To support this effort, ground ... -
The Lompe code: A Python toolbox for ionospheric data analysis
Hovland, Amalie Øie; Laundal, Karl Magnus; Reistad, Jone Peter; Hatch, Spencer Mark; Walker, Simon; Madelaire, Michael; Ohma, Anders (Journal article; Peer reviewed, 2022)A recent paper by Laundal et al. (2022c) presented a new technique to combine all available measurements of polar ionospheric electrodynamics; magnetic field measurements from ground and space, ionospheric convection data ... -
The Magnitude of IMF By Influences the Magnetotail Response to Solar Wind Forcing
Holappa, Lauri; Reistad, Jone Peter; Ohma, Anders; Gabrielse, Christine; Sur, Dibyendu (Journal article; Peer reviewed, 2021)The dynamics of substorms are known to be dominated by the North-South (Bz) component of the Interplanetary Magnetic Field (IMF), which is the most important driver of the dayside reconnection. Even though the dawn-dusk ... -
Modulation of Magnetospheric Substorm Frequency: Dipole Tilt and IMF By Effects
Ohma, Anders; Reistad, Jone Peter; Hatch, Spencer Mark (Journal article; Peer reviewed, 2021)Substorm activity is heavily influenced by the Interplanetary Magnetic Field (IMF) Bz component and magnetospheric substorms occur most frequently when Bz is strongly negative. The substorm occurrence rate is also affected ... -
Observations of Asymmetric Lobe Convection for Weak and Strong Tail Activity
Ohma, Anders; Østgaard, Nikolai; Reistad, Jone Peter; Tenfjord, Paul; Laundal, Karl Magnus; Moretto, Therese; Haaland, Stein; Krcelic, Patrik; Milan, Stephen Eric (Journal article; Peer reviewed, 2019)In this study we use high‐quality convection data from the Electron Drift Instrument on board Cluster to investigate how near‐Earth tail activity affects the average convection pattern in the magnetotail lobes when the ... -
Quantifying the Lobe Reconnection Rate During Dominant IMF By Periods and Different Dipole Tilt Orientations
Reistad, Jone Peter; Laundal, Karl Magnus; Østgaard, Nikolai; Ohma, Anders; Burrell, Angeline G.; Hatch, Spencer Mark; Håland, Stein Egil; Thomas, Evan G. (Journal article; Peer reviewed, 2021)Lobe reconnection is usually thought to play an important role in geospace dynamics only when the Interplanetary Magnetic Field (IMF) is mainly northward. This is because the most common and unambiguous signature of lobe ... -
The relationship between interhemispheric asymmetries in polar ionospheric convection and the magnetic field line footpoint displacement field
Laundal, Karl Magnus; Madelaire, Michael; Ohma, Anders; Reistad, Jone Peter; Hatch, Spencer Mark (Journal article; Peer reviewed, 2022)Polar electrodynamics is largely controlled by solar wind and magnetospheric forcing. Different conditions can make plasma convection and magnetic field disturbances asymmetric between hemispheres. So far, these asymmetries ... -
Seasonal and hemispheric asymmetries of F‐region polar cap plasma density: Swarm and CHAMP observations
Hatch, Spencer Mark; Haaland, Stein; Laundal, Karl Magnus; Moretto, Therese; Yau, Andrew; Bjoland, Lindis Merete; Reistad, Jone Peter; Ohma, Anders; Oksavik, Kjellmar (Journal article; Peer reviewed, 2020)One of the primary mechanisms of loss of Earth's atmosphere is the persistent “cold” ( urn:x-wiley:jgra:media:jgra56068:jgra56068-math-0001 20 eV) ion outflow that has been observed in the magnetospheric lobes over large ... -
Spatial Resolution in Inverse Problems: The EZIE Satellite Mission
Madelaire, Michael; Laundal, Karl Magnus; Gjerloev, J.; Hatch, Spencer Mark; Reistad, Jone Peter; Vanhamäki, H.; Waters, Colin; Ohma, Anders; Mesquita, Rafael L. A.; Merkin, Viacheslav (Journal article; Peer reviewed, 2023)Inverse modeling has become one of the primary methods for studying ionospheric electrodynamics, especially when using magnetic field measurements from below the ionosphere. We present a method for quantifying the spatial ... -
Statistical Temporal Variations in the Auroral Electrojet Estimated With Ground Magnetometers in Fennoscandia
Walker, Simon; Laundal, Karl Magnus; Reistad, Jone Peter; Ohma, Anders; Hatch, Spencer Mark (Journal article; Peer reviewed, 2023)We present the implementation of an improved technique to coherently model the high-latitude ionospheric equivalent current. Using a fixed selection of 20 ground magnetometers in Fennoscandia, we present a method based on ... -
Substorm Impact on Dayside Ionospheric Currents
Elhawary, Reham Zakaria Ahmed Mohamed; Laundal, Karl Magnus; Reistad, Jone Peter; Madelaire, Michael; Ohma, Anders (Journal article; Peer reviewed, 2023)Ionospheric dayside dynamics is strongly controlled by the interaction between the Interplanetary Magnetic Field (IMF) and the Earth's magnetic field near the dayside magnetopause, while nightside ionospheric dynamics ... -
Transient high latitude geomagnetic response to rapid increases in solar wind dynamic pressure
Madelaire, Michael; Laundal, Karl Magnus; Reistad, Jone Peter; Hatch, Spencer Mark; Ohma, Anders (Journal article; Peer reviewed, 2022-08-16)Rapid changes in solar wind dynamic pressure can produce a transient geomagnetic response in the high latitude ionosphere. In this study we carry out a superposed epoch analysis of the geomagnetic response based on 2,058 ...