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Due to the precession of the Polar spacecraft long time series of imaging data from the
southern hemisphere are obtained from imagers on board Polar. At the same time IMAGE FUV provide
images from the northern hemisphere. We have identified 6 substorms where we have observations
from both hemispheres. The figure to the right shows the substorm onset on September 13, 2001,
where the onset location in the northern hemisphere (IMAGE/FUV WIC) is at 21 MLT, while the
onset in the southren hemisphere (Polar VIS Earth camera) is located at 22:30 MLT. The duskward
displacement (1.5 hours) of the southern substorm onset is attributed to the IMF influence on
the magnetotails configuration. The tension force on interconnected (open) field lines
associated with a positive IMF By component will twist the magnetotail, explaining the
observed displacement of substorm onset locations.
[pdf] N. Østgaard, S. B. Mende , H. U. Frey , T. J. Immel, L. A. Frank, J. B. Sigwarth, T. J. Stubbs. Interplanetary magnetic field control of the location of substorm onset and auroral features in the conjugate hemispheres. J. Geophys. Res., Vol. 109, No. A7, A07204, 10.1029/2003JA010370, 2004.
After extending the dataset to 15 substorm auroral features we were able to identify a possible dipole tilt affect which act as a secondary controlling factor (after the IMF clock angle) of the asymmetric location of auroral features during substorms. Our result can be explained by a stronger FAC in the winter hemisphere, leading to a larger eastward displacement of the magnetic footpoint in the dark hemisphere. A comparison with durrent magnetic field models (T96 and T02) shows that the implementation of a penetrating field (i.e., the IMF) has observational support. The model, however, underestimate thios effect by an order of magnitude.
[pdf] N. Østgaard, N. A. Tsyganenko, S. B. Mende , H. U. Frey , T. J. Immel, M. Fillingim, L. A. Frank, J. B. Sigwarth. Observations and model predictions of substorm auroral asymmetries in the conjugate hemispheres. Geophys. Res. Lett., 32, 5, L05111, doi:10.1029/2004GL022166, 2005.
Examning the oval location on October 23, 2002, as imaged by IMAGE FUV and Polar VIS Earth camera, the oval locations in the two hemispheres have revealed an unexpected assymetry.
[pdf] T. J. Stubbs , R. R. Vondrak and N. Østgaard, J. B. Sigwarth and L. A. Frank. Simultaneous observations of the auroral oval in both hemispheres under varying conditions. Geophys. Res. Lett., Vol 32, L03103, doi:10.1029/2004GL021199, 2005.
This study was released by NASA and received a lot of attention in the scientific community world wide.
We have also identified two events where a theta aurora is observed in one hemisphere, but not
in the other. On November 5 (figure to the right), the theta was observed strong and clear in
the northern hemisphere (IMAGE/FUV - 135.6 nm). Although the VIS Earth camera images (130.4 nm)
were contaminated by energetic protons, it is clear that the images from the southern
hemisphere do not show any theta aurora. These observations were confirmed by DMSP passes in
the two hemispheres. Theta aurora is associated with northward IMF and 4 cell plasma convection
patterns. We attribute the non-conjugate occurance of theta aurora to the IMF Bx control of the
different rates of lobe reconnection in the two hemispheres, which is the driver of the plasma
convection and shear flows,
producing the electric fieds that causes the theta aurora.
This study is featured as one of the IMAGE discoveries
[pdf] N. Østgaard, S. B. Mende, H. U. Frey, L. A. Frank , J. B. Sigwarth., Observations of non-conjugate theta aurora. Geophys. Res. Lett., Vol. 30, No. 21, 2125, doi: 10.1029/2003GL017914, 2003.
[pdf] N. Østgaard, J. Moen, S. B. Mende, H. U. Frey, T. J. Immel, P. Gallop, K. Oksavik, M. Fujimoto. Estimates of magnetotail reconnection rate based on IMAGE FUV and EISCAT measurements Ann. Geophys. (Eleventh International EISCAT Workshop), 23 (1), 123-134, 2005.
The geocorona is produced when solar Lyman alpha (121.6 nm) radiation is resonance scattered by
exospheric neutral hydrogen. We have shown that measurements of Lyman alpha from the IMAGE-FUV/GEO
instrument can be used to give us information about the hydrogen density surounding the Earth. By
assuming that the medium can be considered to be optical thin above 3.5 Re (geocentric distance) and
taking into account the attenuation of solar Lyman alpha to the nightside, contribution from the inner
geocorona, the phase dependent scattering cross section etc. we give empirical derived expressions for
the hydrogen densities at high altitudes as a function of solar zenith angles. Such density profiles
are needed to analyze the energetic neutral atom imaging data at ring current altitudes and above
(HENA and MENA on IMAGE).
[pdf] N. Østgaard, S. B. Mende, H. U. Frey, G. R. Gladstone, H. Lauche. Neutral hydrogen density profiles derived from geocoronal imaging. J. Geophys. Res., Vol. 108, No. A7, 1300, doi:10.1029/2002JA009749, 2003.
N. Østgaard and E. Tanksanen, Energetics of isolated and stormtime
substorms. Disturbances in Geospace:
The Storm-Substorm Relationship, Geophysical Monograph 142, doi: 10.1029/142GM14, 2003.
[pdf] N. Østgaard, G. A. Germany, J Stadsnes, R. R. Vondrak, Energy analysis of substorms based on remote sensing techniques, solar wind measurements and geomagnetic indices. J. Geophys. Res., Vol. 107, NO. A9, 1233, doi: 10.1029/2001JA002002, 2002.
Energy deposition from electron precipitation as a function of geomagnetic indices: We have also examined how the hemispherical energy deposition (0.1-100 keV) relates to the geomagnetic indices AL and AE and presented simple expressions that can be used when global imaging is not availbale.
Electron precipitation and ionospheric conductances: In collaboration with the group at the University of Bergen, Norway, the same dataset have been used to show the importance of the energetic tail of the electron distribution for ionospheric parameters as Hall conductance and large scale electric fields.
Plans: Ultimately, our goal is to develop a model that gives the typical electron energy spectra as function of time, magnetic local time and magnetic latitude during substorms. Ionospheric parameters as Hall and Pedersen conductance and the ratio of the two will be part of such a study as well. This should be a highly valuable tool for modelling the MI coupling. Another goal is to estimate the relative energy contribution from electrons and protons during substorms.
N. Østgaard, J. Stadsnes, J. Bjordal, G. A. Germany, R. R. Vondrak, G. K. Parks, S. A Cummer, D. L.
Chenette, J. G. Pronko, Auroral electron distributions derived from combined UV and X-ray emissions. J.
Geophys. Res., Vol.106, 26,081 - 26,090, 2001.
[pdf] N. Østgaard, R. R. Vondrak, J. W. Gjerloev, G. A. Germany, A relation between the energy deposition by electron precipitation and geomagnetic indices during substorms. J. Geophys. Res., Vol. 107, NO. A9, 1233, doi: 10.1029/2001JA002003, 2002.
[pdf] A. Aksnes, J Stadsnes, J. Bjordal, N. Østgaard, R. R. Vondrak, D. L. Detrick, T. J. Rosenberg, G. A. Germany and D. Chenette. Instantaneous ionosphericglobal conductance maps during an isolated substorm. Ann. Geophysicae, 20, 1181, 2002.
[pdf] A. Aksnes, J Stadsnes, G. Lu, N. Østgaard, R. R. Vondrak, D. L. Detrick, T. J. Rosenberg, G. A. Germany and M. Schulz. Effects of energetic electrons on the electrondynamics in the ionosphere Ann. Geophys., 2, 475 - 496, 2004.
N. Østgaard, J. Stadsnes, J. Bjordal, R. R. Vondrak, S. A Cummer, D. L. Chenette, M. Schulz and J. G.
Pronko, Cause of the localized maximum of X-ray emission in the morning sector: A comparison with electron
measurements. J. Geophys. Res., Vol. 105, No A9, p. 20,869 - 20,885, 2000.
[pdf] N. Østgaard, J. Stadsnes, J. Bjordal, R. R. Vondrak, S. A Cummer, D. L. Chenette, M. Schulz, G. K. Parks, M. J. Brittnacher, D. L. McKenzie and J. G. Pronko, Global X-ray emission during an isolated substorm - A case study. J. Atmos. Solar-Terr. Phys., Vol. 62 (10), p. 889 - 900, 2000.
[pdf] N. Østgaard, J. Stadsnes, J. Bjordal, R. R. Vondrak, S. A Cummer, D. L. Chenette, G. K. Parks, M. J. Brittnacher and D. L. McKenzie, Global Scale Electron Precipitation Features seen in UV and X-rays During Substorms. J. Geophys. Res., Vol. 104, p. 10,191 - 10,204, 1999.
[pdf] N. Østgaard, D. L. Detrick, T. J. Rosenberg, R. R. Vondrak, H. U. Frey, S. B. Mende, S. E. Håland, J Stadsnes, High-latitude dayside energetic precipitation and IMF BZ rotations. J. Geophys. Res., Vol. 108 (A4), 8013, doi:10.1029/2002JA009350, 2003.
S. B. Mende, C. W. Carlson, H. U. Frey, L. M. Peticolas, N. Østgaard.
FAST and IMAGE-FUV observations of a Substorm onset.
J. Geophys. Res., Vol. 108, (A9), 1344, doi:10.1029/2002JA009787, 2003.
[pdf] J. A. Slavin, D. H. Fairfield, R. P. Lepping, M. Hesse, A. Ieda, E. Tanskanen, N. Østgaard, T. Mukai, T. Nagai, H. J. Singer and P. R. Sutcliffe, Simultaneous observations of earthward flow bursts and plasmoid ejection during magnetospheric substorms. J. Geophys. Res.,Vol. 107, NO. A7, 10.1029/2000JA003501, 2002.
[pdf] S. Håland, N. Østgaard, J. Bjordal, J.Stadsnes, S. Ullaland, G. D. Reeves, D. L. Chenette, B. Wilken, T. Yamamoto, T. Doke, G. K. Parks and M. J. Brittnacher, Magnetospheric and Ionospheric Response to a Substorm: Geotail HEP-LD and Polar PIXIE Observations, J. Geophys. Res., Vol. 104, No. A12, p. 28,459. 1999.
[pdf] N. Østgaard, J. Stadsnes, K. Aarsnes, F. Søraas, Karl Måseide, M. Smith and J.Sharber, Simultaneous Measurements of X-rays and Electrons During a Pulsating Aurora. Ann. Geophysicae, 16, 148 - 160, 1998.