IMAGE

Page ContentsSection 10
Background
Instrument
Research: Background
Research: Conjugate Substorms
Research: Geocoronal Imaging
Research: Non-conjugate Theta
Research: Reconnection Rate
Publications
Links

 

BackgroundSection 1

The IMAGE mission (Imager for Magnetopause-to-Aurora Global Exploration) is a NASA spacecraft launched in March 2000 into a highly elliptic polar orbit around the Earth. Its highest point (apogeum) is at ~7 Re (Earth radii: 6380 km) above the surface of the Earth and its lowest point (perigeum) at 1000 km.

During its first years IMAGE had its apogeum over the northern hemisphere, but due to precession it will have its apogeum over the southern hemisphere in 2006. IMAGE is a spin-stabilized satellite, with a complete rotation every 120 sesond.

The IMAGE spacecraft is equipped with a suite of cameras to image the aurora (Far-ultra-violet wavelenghts – FUV), the plasmasphere (Extreme-ultrs-violet – EUV), the energetic and cold neutral atoms surrounding the Earth (LENA, MENA, HENA, GEO), and plasma boundaries using radiosonde (RPI).

The main goal of the IMAGE mission is to investigates the response of the Earth’s magnetosphere and iononsophere to changes in the charged particle flux from the Sun (solar wind) and the Sun’s magnetic field (interplanetary magnetic interacting with the Earths own magnetic field.

The main database for the SPG IMAGE project at UoB is the IMAGE Far-Ultra-Violet (FUV) camera system, although data from other IMAGE instruments, other spacecrafts and ground based measurements are also used.

To learn more about the IMAGE mission see: NASA/Goddard IMAGE page

Back to table of contents

 

InstrumentSection 2

IMAGE FUV camera system

  1. The Wideband Imaging Camera (WIC) to image the aurora, mainly produced by electrons, in a broad band for maximum spatial resolution day and night.
  2. The Spectrographic Imager (SI) to image aurora caused by electrons and protons separately. SI has two channels: SI12 at 121.8 nm (i.e.,the Doppler-shifted Lyman alpha and blocks out the bright 121.6 nm emission from the geocorona) images only the proton aurora. SI13 (Oxygen line at 135.6 nm) images electron and proton aurora.WIC and SI image the whole Earth aurora from distances greater than 4 Re from the center of the Earth.
  3.  Geocorona photometers (GEO) to observe the geocorona. The geocorona comes from the cold neutral hydrogen surrounding the Earth, which is lightened up by Solar Lyman alpha (121.6 nm). These measurements can be used to determine the magnetospheric hydrogen content surrounding the Earth.

IMAGE is a spin stabilized satellite and rotates once in 120 s. This enables the GEO photometers to perform a complete 360 degrees measurement during one rotation but the imagers, WIC and SI, have to compensate the apparent motion of the imaged Earth with the Time Delayed Imaging (TDI) technique.

Characteristics of the FUV instruments:

Channel Spectral range Field of view Pixel Spatial res. Temporal res. Sensitivity
(nm) (degrees) (#x#) (deg. and km from apogee) (s) (R)
WIC 140-180 17×17 256×256 0.1 – <100km 120 100
SI12 121.82 * 15×15 128×128 0.15 – 100 km 120 100
SI13 135.6 15×15 128×128 0.15 – 100 km 120 100
GEO 121.6 ** 1×1 1×1 0.33

* blocking out the 121.567 geocorona
** rejecting 130.4 nm

Learn more about the IMAGE FUV: IMAGE FUV.

  • Mende et al.,Far ultraviolet imaging from the IMAGE spacecraft. 1. System design, Space Sci. Rev.,91, 243-270, 2000.
  • Mende et al.,Far ultraviolet imaging from the IMAGE spacecraft. 2. Wideband FUV imaging, Space Sci. Rev.,91, 271-285, 2000.
  • Mende et al.,Far ultraviolet imaging from the IMAGE spacecraft. 3. Spectral imaging of Lyman-alpha and OI 135.6 nm, Space Sci. Rev.,91, 287-318, 2000.

Back to table of contents

 

Research: BackgroundSection 3

  • Conjugate imaging of auroral phenomena
    Aurora generally occurs simultaneously in the northern and southern polar regions at locations that are connected (i.e., conjugated) by closed geomagnetic field lines with footpoints in both hemispheres. Such a connection predicts a symmetric temporal behaviour and spatial location. Simultaneous space-based observations of the same auroral feature in both hemispheres can provide evidence or disprove the expected conjugate behavior. Only twice have scientists had the possibility to study auroral from two spacecrafts that image the aurora in the northern and southern hemisphere at the same time. In the 80s Viking and Dynamic Explorer 1 offered this opportunity and now (2001-2003) the two missions: IMAGE and Polar (POLAR_IMAGE_orbit.jpg).

These unique images have been used to study:

A. Asymmetries of the auroral oval and substorm locations in the conjugate hemispheres.
B. Asymmetries of the dayside reconnection spot, i.e., the footprint of the energy and momentum transfer from the solar wind to the Earth’s upper atmosphere
C. Transpolar arcs or theta aurora. Are they occurring in both hemispheres simultaneously or only in one?

  • The ring current in the magnetosphere and proton precipitation
    Does the intenistity of global proton precipitation follow the increase and decrease of the large current system surrounding the Earth at 2-5 Re, i.e., the ring current.
  • Energy and momentum transport from the Sun (solar wind) to the near Earth system.
    Reconnection rate is a measure of how fast energy and momentum are transferred from the solar wind into the magnetosphere.Combined study using IMAGE from space and EISCAT from Tromsø and Svalbard to study the reconnection rate.
  • Geocoronal imaging and hydrogen density profiles
    The Lyman alpha emission (121.6 nm) from the Sun brighten up the neutral cold hydrogen around the Earth. This is called the geocorona and its brightness depends both on the source (the Sun) and the density of hydrogen around the Earth.Long time series of such data have been used to develop a model of the hydrogen density surrounding the Earth.

Back to table of contents

 

Background: Conjugate SubstormsSection 4

Asymmetries of the auroral oval and substorm locations in the conjugate hemispheres.

While IMAGE imaged the aurora in the northern hemisphere, the Polar satellite with a similar camera imaged the aurora in the southern hemipshere. An auroral substorm is defined as an abrupt brightening of the aurora in a localized spot (substorm onset), that over the next minutes expands both poleward, eastward and westward to become a global phenomenon.

We have identified substorm onset spots and auroral features where we have simultaneous observations by IMAGE and Polar from both hemispheres to look for symmetries/asymmetries in locations of the auroral substorm features.

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 southern hemisphere (Polar VIS Earth camera) is located at 22:30 MLT, i.e., a 1.5 MLT asymmetry.

Based on 13 events we find a systematic asymmetry that is controlled by the interplanetary magnetic field, IMF, clock angle (the orientation of the IMF, viewed from the Sun, relative to the Earth) The asymmetry is consistent with the tension force acting on newly opened (by reconnection on the dayside) field lines as they are draped to the nightside of the Earth and eventually are closed (reconnected) in the magnetotail.

We also identified a possible dipole tilt (the angle of the magnetic dipole axis of the Earth in a fixed Sun-Earth coordinate system) effect which acts 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 field aligned current, FAC, in the winter hemisphere, leading to a larger eastward displacement of the magnetic footpoint in the dark hemisphere.

A comparison with current magnetic field models (Tsyganenko 1996 and 2002) shows that the asymmetry that results from IMF field penetrating the Earths magnetic field has observational support. The models, however, underestimate this effect by an order of magnitude.

  • These results are documented in: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, doi: 10.1029/2003JA010370, 2004.
  • 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.
  • N. Østgaard, S. B. Mende, H. U. Frey, J. B. Sigwarth, A. Aasnes, J. Weygand, Auroral conjugacy studies based on global imaging, J. Atm. Solar-Terres. Phys., doi:10.1016/j.jastp.2006.05.026, 2006.
  • N. Østgaard , S. B. Mende, H. U. Frey, J. B. Sigwarth, A. Aasnes, J. Weygand, Conjugate imaging of substorms Proceedings from the ICS 8 in Banff, Canada, 2006.

Examining the oval location on October 23, 2002, as imaged by IMAGE FUV and Polar VIS Earth camera, its locations in the two hemispheres have revealed an unexpected assymetry:

  • 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 worldwide.

Back to table of contents

 

Research: Geocoronal ImagingSection 5

A model of the hydrogen density surrounding the Earth.

The geocorona is produced when ultra violet emissions at 121.6 nm (Lyman alpha line) from the Sun is resonance scattered by the cold neutral hydrogen surrounding the Earth. 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 surrounding the Earth. By assuming that the medium can be considered to be transparent (optical thin) above 3.5 Re (geocentric distance) and take into account the important mechanisms for loss and gain of these emissions we present mathematical expressions of the neutral hydroge densities at high altitudes.

The hydrogen surrounding the Earth is slightly affected by the Solar radiation pressure and extends to higher altitudes on the Earths nightside. Our expressions are therefore given for different solar zenith angles (i.e., the angle between zenith – straight up – and the direction of the Sun). Such density profiles are needed to analyze the energetic neutral atom imaging data at ring current altitudes and above (HENA and MENA on IMAGE).

The illustration shows how the three GEO photometers view the column density of the hydrogen density.

  • 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.

Back to table of contents

 

Research: Non-conjugate ThetaSection 6

 

When the IMF is strongly northward, auroral polar arcs stretching from the nightside to the dayside can often been seen. Together with the quiet auroral oval the aurora create a feature that looks like the greek letter theta. In 1991 Craven et a. (GRL, 18, 2297, 1991) showed that theta aurora occured simultaneously in the northern and southern hemisphere. We have 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 3 (or 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, IMAGE discovers one-sided theta auroras (2004, 3)

  • 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.

See another case of non-conjugate theta in:

  • N. Østgaard, S. B.Mende, H. U. Frey & J. B. Sigwarth Simultaneous imaging of the reconnection spot in the opposite hemisphere during northward IMF
    Geophys. Res. Lett., Vol 32, L21104, doi:10.1029/2005GL024491, 2005.

Back to table of contents

 

Research: Non-conjugate ThetaSection 6

The ring current in the magnetosphere and the proton precipitation

At 2-4 Re there is a strong electric current around the Earth’s equator. This current increases and decreases in response to the energy transferred from the solar wind into the Earth’s magnetosphere, i.e., the space where the Earth magnetic field is dominating. As protons are not affected strongly by parallel electric fields we expect the proton aurora to be mainly controlled by magnetospheric dynamics. Consequently we think that the proton auroral intensity should follow the increase and decrease of the ring current. We will check this hypothesis.

Back to table of contents

 

Research: Reconnection RateSection 7

Energy and momentum transport from the Sun (solar wind) to the near Earth system.

When the IMF connect with the Earths magnetic field on the dayside in a process called reconnection, the solar wind electric fiels is coupled to the Earths magnetosphere. This process results in efficient transport of solar wind energy to the magnetosphere and increases the magnetospheric plasma convection. This process which is called dayside reconnection is a measure of energy transport in the Solar-Magnetosphere system.

Subsequent reconnection of the lobe magnetic field in the magnetotail transports energy into the closed magnetic field region. Plasma is then transported across the boundary of open-closed field lines in the nightside magnetosphere. This plasma flow is a measure of the efficiency of energy transport inside the magnetosphere and is called the nightside reconnection rate. To estimate this energy transport two quantaties must be defined: 1) The exact location and orientation of the open-closed boundary and 2) The plasma flow across this bounadry.

Global images from the IMAGE FUV system guide us to identify ionospheric signatures of the open-closed field line boundary observed by the two EISCAT radars at Tromso (VHF) and Svalbard (ESR). Continuous radar and optical monitoring of the open-closed field line boundary is used to determine the location, orientation and velocity of the open-closed boundary and the ion flow velocity perpendicular to this boundary.

The magnetotail reconnection electric field is found to be a bursty process that oscillates between between 0 mV/m and 1 mV/m with ~10-15 min periods. These ULF oscillations are mainly caused by the motion of the open-closed boundary. In situ measurements earthward of the reconnection site in the magnetotail by Geotail show similar oscillations in the duskward electric field. We also find that bursts of increased magnetotail reconnection not necessarily have any associated auroral signatures. Finally we find that the reconnection rate correlates poorly with the solar wind electric field. This indicate that the magnetotail reconnection is not directly driven, but is an internal magnetospheric process. Estimates of a coupling efficiency between the solar wind electric field and magnetotail reconnection only seems to be relevant as average on long time scales. The oscillation mode at 1 mHz corresponds to the internal cavity mode with additional lower frequencies, 0.5 and 0.8 mHz, that might be modulated by solar wind pressure variations.

  • 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.

Back to table of contents

 

PublicationsSection 8

  1. N. Østgaard, S. B. Mende, H. U. Frey, J. B. Sigwarth, A. Aasnes, J. Weygand, Auroral conjugacy studies based on global imaging JASTP, special issue from Yosemite 2006, 69, 249-255, 2007.
  2. N. Østgaard , S. B. Mende, H. U. Frey, J. B. Sigwarth, A. Aasnes, J. Weygand, Conjugate imaging of substorms Proceedings from the ICS 8 2006 in Banff, Canada, ISBN 978-0-88953-312-7, 2007.
  3.  N. Østgaard, S. B.Mende, H. U. Frey & J. B. Sigwarth Simultaneous imaging of the reconnection spot in the opposite hemisphere during northward IMF
    Geophys. Res. Lett., Vol 32, L21104, doi:10.1029/2005GL024491, 2005.
  4. A. Kozlovsky, V. Safargaleev, N. Østgaard, T. Turunen, J. Jussila, A Roldugin. On the motion of dayside auroras caused by a solar wind pressure pulse. Ann. Geophys., 23 (2): 509-521 2005.
  5. 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.
  6. 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.
  7. 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.
  8. H.U. Frey , G. Haerendel, S.B. Mende, W. T. Forrester, T.J. Immel, N. Østgaard. Sub-auroral morning proton spots (SAMPS) as a result of plasmapause-ring current interaction, J. Geophys. Res., 109, A10305, 10.1029/2004JA010516, 2004.
  9. 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.
  10. H.U. Frey , N. Østgaard, T.J. Immel, H. Korth, S.B. Mende, Seasonal dependence of localized, High Latitude Dayside Aurora (HiLDA). J. Geophys. Res., Vol. 109, No. A4, A04303, doi: 10.1029/2003JA010293, 2004.
  11. 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.
  12. M. Meurant, J.-C. Gérard, B. Hubert, C. Blockx, N. Østgaard, S.B. Mende. Dynamics of global scale electron and proton precipitation induced by a solar wind pressure pulse. Geophys. Res. Lett., Vol. 30, No. 20, 2032, doi: 10.1029/2003GL018017, 2003.
  13. 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.
  14. H. U. Frey, S. B. Mende, T. J. Immel, S. A. Fuselier, N. Østgaard. Proton aurora in the CUSP during southward IMF. J. Geophys. Res.,108 (A7), 1277 , doi:10.1029/2003JA009861R, 2003.
  15. 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.
  16. T. J. Immel, S. B. Mende, H. U. Frey, N. Østgaard, G. R. Gladstone. Effect of the July 14, 2000 solar flare on Earth’s FUV emissions. J. Geophys. Res., Vol. 108 (A4), 1155, doi:10.1029/2001JA009060, 2003.
  17. H. U. Frey, T. J. Immel, G. Lu, J. Bonnell, S. A. Fuselier, S. B. Mende, B. Hubert, N. Østgaard, G. Le. Properties of localized, high latitude, dayside aurora. J. Geophys. Res., Vol. 108 (A4), 8008, doi:10.1029/2002JA009356, 2003.

Back to table of contents

 

LinksSection 9

Goddard IMAGE
SSL IMAGE FUV

Back to table of contents