NOAA
The NOAA Polar Orbiting Environmental Satellite (POES) orbits the Earth in a high-inclination (polar), sun-synchronous orbit at about 800 km altitude. The particle observations on the NOAA satellites give essential information about sources (substorm and convection injection) and loss processes (charge exhange and wave/particle interaction) of energetic charged particles in the magnetosphere and their interaction with the atmosphere.
Background
Instruments
Research
Publications
The Total Energy Detector (TED)
The Total Energy Detector (TED) monitors the energy fluxes carried into the atmosphere by electrons and positive ions over the energy range between 50 and 20,000 eV. Particles of these energies are stopped by the atmosphere of the Earth at altitudes above 100 km, producing aurora. The instrument design utilizes cylindrical, curved-plate electrostatic analyzers to select (by impressing a variable voltage between the analyzer plates) the species and energy of those particles that are permitted to reach the detector.
The Medium Energy Proton and Electron Detector (MEPED)
In addition to the Total Energy Detector (TED) that provides the data used to determine auroral activity, the Medium Energy Proton and Electron Detector (MEPED) monitors the intensities of charged particle radiation at higher energies extending up to cosmic rays.
The Electron Telescope
The electron telescope is a 25 mm2 silicon solid state detector positioned behind a series of metal apertures that define a 15° (half-angle) cone where charged particles from space may reach the detector. Two identical electron telescopes are included. One, termed the 0° electron detector, is mounted on the 3-axis stabilized NOAA spacecraft to view outward along the Earth-center-to-satellite vector. The second electron telescope, called the 90° detector, is mounted to view in a direction approximately perpendicular to the 0° detector. The pair of electron telescopes provide 3 integral channels of energetic electron data: >30 keV
>100 keV
>300 keV
The Proton Telescope
The proton telescope design is identical to the electron telescope, with two exceptions. The first is that a strong magnetic field is imposed across the aperture structure to prevent electrons from reaching the silicon solid-state detector. The second is that there is no nickel foil covering the detector, so very low energy protons are allowed to enter the detector. Electronic analysis of the pulses produced by the energy lost by protons in the solid state detector identify protons within six energy ranges:
30 – 80 keV
80 – 250 keV
250 – 800 keV
800 – 2500 keV
2500 – 6900 keV
>6900 keV.
The Omnidirectional Proton Detectors.
In order to monitor the intensities of still higher energy protons that arrive at the Earth because of solar energetic particle events, four additional silicon solid state detectors are included. Each of these four detectors contains a 50 mm2 area by 3 mm thick solid state detector mounted beneath a near-hemispherical (120° full angle) shell- shaped metal absorber. The material and thickness of the absorber determines the minimum energy that a proton needs to reach the detector and be counted. On the NOAA satellites earlier than NOAA15 these detectors can also be used to detect relativistic electrons above 1.5 MeV.
HILDCAA Events
The Earth’s magnetic field at the equator, as monitored by the Dst index, can stay below its quiet day value for days. This can happen after storms resulting in a very slow recovery of the Dst index, or it can happen in the absence of a storm. Such “anomalous” behavior of the Dst recovery is observed during times showing continuous auroral activity called High Intensity Long Duration Continuous AE Activity — HILDCAA
The Dst is mostly attributed to the ring current (RC), but it also depends on other current systems in the magnetosphere such as magnetopause, tail and auroral currents . The ion injection into the RC is sufficient to account for the reduced Dst index during HILDCAAs. It is determined that the HILDCAA events are associated with a low level injection of protons into the outer portion of the RC above L equal 4. The HILDCAA events are thus not due to plasma sheet current intensifications or earthward motion of this current. The prolonged low-level ion injection is associated with fluctuations in the solar wind magnetic field. These fluctuations can be described as an Alfve?n wave, where the varying Bz component causes intermittent reconnection, intermittent substorm activity, and sporadic injection of plasma sheet energy into the outer portion of the RC prolonging its final decay to quiet day values, or when occurring without a storm, depresses the Dst to a more or less constant value lasting for days. This continuous auroral activity is the signature of HILDCAAs. It has been shown that direct particle injection into the RC to a large extent can account for the RC depression during HILDCAAs. The duration of the Bz negative phases are not long enough to drive a magnetic storm.
M. I. Sandanger, F. Søraas, K. Aarsnes, K. Oksavik, D. S. Evans and M. S. Greer, Proton injections into the ring current associated with Bz variations during HILDCAA events. The Inner Magnetosphere: Physics and Modeling, edited by Tuija I. Pulkkinen, Nikolai A. Tsyganenko, and Reiner H. W. Friedel, Geophysical Monograpgh 155, 249-256, AGU, Washington DC, 2005.
F. Søraas, K. Aarsnes, K. Oksavik, M. I. Sandanger, D. S. Evans, and M. S. Greer, Evidence for particle injection as the cause of Dst reduction during HILDCAA events. Journal of Atmospheric and Solar-Terrestrial Physics, 66, 177-186, 2004.
F. Søraas, K. Aarsnes, K. Oksavik, and D. S. Evans, Ring current intensity estimated from low altitude proton observations, Journal of Geophysical Research, 107(A7), doi:10.1029/2001JA000123, 2002.
Relativistic electrons
During some storms relativistic electrons appear in the magnetosphere in the L range 3 to 7. The drift orbits to these electrons are within the region of the RC-protons. The area with anisotropy in the 30 – 80 keV protons matches the area with loss of relativistic electrons. This is a strong indicator that the relativistic electrons are scattered into the atmospheric loss cone by electromagnetic ion cyclotron waves generated from unstable protons. This loss of relativistic electrons occur at all local times, but is most pronounced at the evening/prenoon sector.. Our findings are in accord with the theory thatsuggested that ion cyclotron waves generated by the unstable proton population can precipitate relativistic electrons in the above 1MeV range.
Ring Current –growth and decay
Stormy weather in the near-Earth environment is mostly caused by large solar eruptions, which eject clouds of charged particles at high speeds into interplanetary space. Depending on the type of the solar disturbance, the speed of the plasma flow, the associated interplanetary field structure, and the state of the magnetosphere, the storm signatures in the near-Earth environment can be highly variable. Geomagnetic disturbances are manifested by increased auroral ionospheric currents at high and mid-latitudes and by enhancements in the ring current at lower latitudes.
The main physical cause for the ground magnetic perturbations at low latitudes, Dst, is the variability of the ring current (RC) composed of energetic ions encircling the Earth at altitudes of several Earth radii. There have been many suggestions on how the RC particles are injected. Are they injected by successive substorm expansions? Is the collapse of the tail-like field to a more dipolar configuration during the expansion phase the basic mechanism for this process, or are the injection caused by the global convection driven by dayside reconnection.
The decay/recovery phase of the RC is not completely understood. In larger storms there is usually a fast initial decay, attributed to a collapse of the tail current and/or a fast decay of oxygen ions through charge exchange, and/or large-scale convection losses in the main phase of the storm. After this abrupt reduction in the RC, the decay is more gradual depending on charge exchange of the RC ions with the geocorona and wave-particle interaction at or near the plasmapause forcing the RC ions into the loss cone. These processes result in an average decay time of the RC at about 7 to 10 hours. The initial asymmetric and the symmetric recovery phases of the ring current can be followed in local time by looking at the Storm Time Equatorial Belt (STEB) development
The NOAA satellites provide a tool for monitoring many of these injection and loss processes:
F. Søraas, K. Aarsnes, K. Oksavik, and D. S. Evans, Ring current intensity estimated from low altitude proton observations, Journal of Geophysical Research, 107(A7), doi:10.1029/2001JA000123, 2002.
F. Søraas, K. Aarsnes, D. V. Carlsen, K. Oksavik and D. S. Evans, Ring current behavior as revealed by energetic proton precipitation. The Inner Magnetosphere: Physics and Modeling, edited by Tuija I. Pulkkinen, Nikolai A. Tsyganenko, and Reiner H. W. Friedel, Geophysical Monograph 155, 237-248, AGU, Washington DC, 2005.
Søraas, F., K. Aarsnes, J.Å. Lundblad and D.S. Evans, Enhanced pitch angle scattering of protons at mid-latitudes during geomagnetic storms, Phys.Chem. Earth (C) 24,1-3, 287-292,1999.
STEB: The Storm Time Equatorial Belt
The STEB is created when hot ring current ions charge exchange with cold atoms from the geocorona and produce an energetic neutral atom (ENA). The ENA move in all directions and a part of them will travel towards the earth where they can be detected by the NOAA satellites in a belt around the earth’s magnetic equator.
F. Søraas, K. Oksavik, K. Aarsnes, D. S. Evans, and M. S. Greer, Storm time equatorial belt – an ‘image’ of ring current behavior, Geophysical Research Letters, 30(2) 10.1029/2002GL015636, 2003.
M. Sørbø, F. Søraas, K. Aarsnes, K. Oksavik and D. S. Evans (2006),Latitude distribution of vertically precipitating energetic neutral atoms observed at low altitudes, Geophys. Res. Lett., 33, L06108, doi:10.1029/2005GL025240
Søraas, and M. Sørbø, Low altitude observations of ENA from the ring current and from the proton oval, J. Atm. Solar-Terr. Phys., in press.
M. Daae, P. Espy, H. Nesse Tyssøy, D. Newnham, J. Stadsnes, and F. Søraas, The effect of energetic electron precipitation on middle mesospheric night-time ozone during and after a moderate geomagnetic storm, Geophys. Res. Lett., 39, L21811, doi:10.1029/2012GL053787, 2012.
Nesse Tyssøy, J. Stadsnes, M. Sørbø, C. J. Mertens, and D. S. Evans, Changes in upper mesospheric and lower thermospheric temperatures caused by energetic particle precipitation, J. Geophys. Res., 115, A10323, doi:10.1029/2010JA015427, 2010.
M. E. Usanova, I. R. Mann, Z. C. Kale, I. J. Rae, R. D. Sydora, M. Sandanger, F. Søraas, K.-H. Glassmeier, K.-H. Fornacon, H. Matsui, P. A. Puhl-Quinn, A. Masson, X. Vallieres, Conjugate ground and multisatellite observations of compression-related EMIC Pc1 waves and associated proton precipitation, J. Geophys. Res., 115, A07208, doi:10.1029/2009JA014935, 2010.
J. Pollock, A. Isaksson, J.-M. Jahn, F. Søraas, M. Sørbø, Remote global-scale observations of intense low-altitude ENA emissions during the Halloween geomagnetic storm of 2003, Geophys. Res. Lett., 36, L19101, doi:10.1029/2009GL038853, 2009.
M.I. Sandanger, F. Søraas, M. Sørbø, K. Aarsnes, K. Oksavik, D.S. Evans, Relativistic electron losses related to EMIC waves during CIR and CME storms, J. Atm. Solar-Terr. Phys., Vol. 71, 1126-1144, 2009.
M. Sørbø, F. Søraas, M. I. Sandanger, D. S. Evans, Ring current behaviour during corotating interaction region and high speed stream events, J. Atm. Solar-Terr. Phys., Vol. 71, 1103-1125, 2009.
Sandanger, F. Søraas, K. Aarsnes, K. Oksavik, and D. S. Evans, Loss of relativistic electrons: Evidence for pitch angle scattering by electromagnetic ion cyclotron waves excited by unstable ring current protons, J. Geophys. Res., doi:10.1029/2006JA012138, 2007
T. Tsurutani, W. D. Gonzalez, A. L. C. Gonzalez, F. L. Guarnieri, N. Gopalswamy, M. Grande, Y. Kamide, Y. Kasahara, G. Lu, I. Mann, R. McPherron, F. Soraas, V. Vasyliunas, Corotating solar wind streams and recurrent geomagnetic activity: A review, J. Geophys. Res., 111, A07S01, doi:10.1029/2005JA011273, 2006.
F. L. Guarnieri, B. T. Tsurutani, W. D. Gonzalez, A. L. C. Gonzalez, M. Grande, F. Soraas, E. Echer, ICME and CIR storms with particular emphases on HILDCAA events.ILWS WORKSHOP 2006, GOA, FEBRUARY 19-20, 2006.
F. Søraas, M. Sørbø, K. Aarsnes and D. S. Evans, Ring current behavior inferred from ground magnetic and space observations, Geophysical Monograph Volume 167, AGU, Washington DC,
M. Sørbø, F. Søraas, K. Aarsnes, K. Oksavik, D. S. Evans, Latitude distribution of vertically precipitating energetic neutral atoms observed at low altitudes, Geophys. Res. Lett., 33, L06108, doi:10.1029/2005GL025240, 2006.
Asikainen, K. Mursula, R. Kerttula, R. Friedel, D. Baker, F. Søraas, J.F. Fennell and B. Blake Global View of energetic Particles During a major Magnetic Storm. The Inner Magnetosphere: Physics and Modeling, edited by Tuija I. Pulkkinen, Nikolai A. Tsyganenko, and Reiner H. W. Friedel, Geophysical Monograpgh 155, AGU, Washington DC, 2005.
M. I. Sandanger, F. Søraas, K. Aarsnes, K. Oksavik, D. S. Evans and M. S. Greer, Proton injections into the ring current associated with Bz variations during HILDCAA events. The Inner Magnetosphere: Physics and Modeling, edited by Tuija I. Pulkkinen, Nikolai A. Tsyganenko, and Reiner H. W. Friedel, Geophysical Monograpgh 155, 249-256, AGU, Washington DC, 2005.
F. Søraas, K. Aarsnes, D. V. Carlsen, K. Oksavik and D. S. Evans, Ring current behavior as revealed by energetic proton precipitation. The Inner Magnetosphere: Physics and Modeling, edited by Tuija I. Pulkkinen, Nikolai A. Tsyganenko, and Reiner H. W. Friedel, Geophysical Monograpgh 155, 237-248, AGU, Washington DC, 2005.
Oksavik, F. Søraas, J. Moen, R. Pfaff, J. A. Davies, and M. Lester, Simultaneous optical, CUTLASS HF radar, and FAST spacecraft observations: Signatures of boundary layer processes in the cusp. Annales Geophysicae, 22 (2), 511-525, 2004.
F. Søraas, K. Aarsnes, K. Oksavik, M. I. Sandanger, D. S. Evans, and M. S. Greer, Evidence for particle injection as the cause of Dst reduction during HILDCAA events. Journal of Atmospheric and Solar-Terrestrial Physics, 66, 177-186, 2004.
E. Milan, M. Lester, S. W. H. Cowley, K. Oksavik, M. Brittnacher, R. A. Greenwald, G. Sofko, J.-P. Villain, Variation in polar cap area during two substorm cycles, Ann. Geophys., 21 (5), 1121-1140, 2003.
F. Søraas, K. Oksavik, K. Aarsnes, D. S. Evans, and M. S. Greer, Storm time equatorial belt – an ‘image’ of ring current behavior, Geophysical Research Letters, 30(2) 10.1029/2002GL015636, 2003.
Søraas, K. Aarsnes, K. Oksavik, D. S. Evans, Ring current intensity estimated from low-altitude proton observations, J. Geophys. Res., 107(A7), 1149, doi:10.1029/2001JA000123, 2002.
Moen, J. A. Holtet, A. Pedersen, B. Lybekk, K. R. Svenes, K. Oksavik, W. F. Denig, E. Lucek, F. Søraas, and M. Andre, Cluster boundary layer measurements and optical observations at magnetically conjugate sites, Annales Geophysicae, Vol 19, page 1655 – 1668, 2001.
