Auroral Activity on January 6 to 11, 1997


Event Overview

This is one of the ISTP/GGS events we studied. A Coronal Mass Ejection (CME) on January 6 sent disturbances into the solar wind, which eventually caused magnetospheric substorms and impressive auroral displays. There is special event page with much more information than here. Here you'll find images from the POLAR UVI imager and their interpretation, as well as VIS images.

Overview of Available UVI Data

We have analyzed images from January 9, 10 and 11. The orbit of POLAR is such that during the 17 hours of the orbit, we get about 10 hours or so of good viewing geometry per orbit.

Raw Data (January 9, 10 and 11, 1997)

These images are raw images, not calibrated and not transformed into geographic coordinate systems. At the beginning of the sequence, the satellite sees the aurora near the limb of the earth. The motion of the satellite in the images is towards the bottom. In the middle of the sequence (around 16 UT) the satellite looks straight down onto the north pole, and towards the end the aurora is on the limb again. For more images and animations look at the UVI event page.

Summary plots from 9 January with one sample image about every 3 minutes (LBH-long filter)
raw images raw images
07:05-09:04 UT 09:08-11:10 UT

Summary plots from 10 January with one sample image about every 3 minutes (LBH-long filter)
10:01-12:03 UT 12:06-14:06 UT 14:09-16:11 UT
raw images raw images raw images  
16:14-18:20 UT 18:23-20:25 UT 20:29-22:32 UT  

Summary plots from 11 January with one sample image about every 3 minutes (LBH-long filter)
raw images raw images raw images
6:02-8:05 UT 8:08-10:09 UT 10:12-12:11 UT
raw images raw images raw images  
12:14-14:17 UT 14:20-16:26 UT 21:53-23:57 UT  

Energy Flux and Characteristic Energy (January 10, 1997)

Samples of processed images display energy flux and characteristic energy for the period from 10:26 UT to 11:15 UT with one sample every 6 minutes. The data are plotted in geomagnetic coordinates. The outer circle corresponds to 55o geomagnetic latitude. The geographic coordinates are overlaid in light blue. Note that this period is just after the northern hemisphere came into the field of view of the satellite, and only a portion of the aurora is visible from the satellite (compare to the raw images for this period).

We can also compare the derived energy fluxes with local observations from DMSP and NOAA satellite overpasses. These satellites fly at about 800 km altitude over the aurora and measure the electron spectrum along their orbit. We present two examples from January 10 (11:42:53 UT with NOAA, and 12:49:44 with DMSP) where we plotted the locally measured energy flux over the image, using the same color scale. The local measurements cover the part of the satellite track of 120 (NOAA) and 60 second (DMSP) around the image time.

More maps of energy flux on the 10th and on the 11th in the same format as the samples above are also available. These plots show the energy flux from every LBH-long image from the period 10 UT to 23 UT on January 10, 1997. In addition to the overlaid geographic coordinate system, some of the plots also have the locations of Poker Flat Research Range, Alaska, and Sondrestrøm incoherent scatter radar, Greenland, marked.

Before the main auroral activity started, the aurora had a distinct cross polar cap arc. The energy flux in that aurora was very low, as shown in these maps: energy flux 2:09-2:34 UT and energy flux 2:37-3:00 UT.

Hemispheric Power

power plot The energy flux from the UVI images can be integrated over the entire hemisphere to yield the hemispheric power. This quantity gives a good estimate of the intensity of storms and substroms. For January 9 we have analyzed the period from 07:00 to 11:00 UT, with some moderate aurora. The major activity starts on the next day.

power plot The plot shows the hemispheric power for the periods when the aurora was in the field of view of the UVI imager. On Jan 10 between 6:00 and 10:00UT the satellite passed over the southern hemisphere, thus there is a gap in the plot of the total power. Unfortunately (Murphy's law?), the major activity started right in this gap - the strong peak near 11:00UT is only the tail end of the substorm. During the period between 00:00UT and about 10:30UT on the 11th of January, the aurora was very faint, and no hemispheric power has been calculated. A better quality PostScript version of this plot is also available.

Global Modeling

The maps of energy flux and mean energy, as well as the conductances have been combined with other data sources (IS radars, HF radars, magnetometers, low altitude satellites) in the AMIE procedure. Of particular interest of the conclusions from this simulation is the distribution of energy within the geospace environment: Questions like `how much of the available energy went into the ring current, how much into aurora, how much into ionospheric heating' can now be answered.

Solar Wind Simulation

A solar wind model has simulated a shock that originated from the region of the sun where the CME occured (Sun Wei and Syun-Ichi Akasofu) and arrived at the earth 4 days later, consistent with observations.


MAMI ISTP
The "official" GGS Event page for the 6-11 January Event

Other GGS events of interest may be found in
the Catalog of GGS Events

Last updated: 21 April 1997

Questions? Comments? Or would you like to add to this study?
Please send E-mail to Dirk Lummerzheim lumm@gi.alaska.edu