Jan97 Magnetic Cloud Event

Polar Arcs 97010 02:00 - 03:00

This period precedes the initial substorm development in the next hour. The oval is contracted and faint with numerous polar arcs visible. Look here for a mosaic of raw image data illustrating the different arc forms available. Here is a mosaic of processed images showing polar arc development. Be sure and see the notes on the characteristics of the UVI images.

Substorm 97010 03:30 - 04:40

Look here for details of all the LBHL images available between 97010/03:34 - 04:42. Be sure and see the notes on the characteristics of the UVI images.

Discussion

The substorm began at 0337 UT at midnight and expanded rapidly poleward and eastward. By 0412UT the intensification had expanded to include all mlt sectors except for the sector between 2100 and 2400LT. This 'gap' becomes more pronounced in the remainder of the images. At 0442 there was a platform motion and there is no UVI image data for that time. POLAR is descending from apogee during this period and the UVI field of view is unable to image the full oval after this period.

A strong dayside intensification near 0900LT was seen on the edge of the UVI field of view at 0442UT.

Substorm 97011 10:00 - 12:00

This is a mosaic of the principal features of the substorm/intensifications seen beginning at 97011/10:27. Look here for details of all the LBHL images available between 97011/10:18 - 11:59. Be sure and see the notes on the characteristics of the UVI images.

Image Times in Mosaic Above (UT)

1027 1045 1058

1119 1144 1159

Discussion

10:27 UT: Substorm begins with intensification premidnight near 2300LT. This period was preceded by low level intensifications in the post-midnight and pre-dusk sectors. The remains of a broad intensification are seen centered at 0300LT. Overall intensity is relatively low.
10:45 UT: The substorm expands poleward and eastward. At 10:45 a second intensification begins near 2100LT. Overall brightness considerably increased.
10:58 UT: The original substorm reactivates on a broad basis while the second intensification is growing. By this time the full nighttime oval is active.
11:19 UT: A poleward bulge agains appears. It is not clear if this is the growth of the second intensification, a reintensification of the original intensification, or a third activation.
11:44 UT: A very intense activation begins near 2300LT. The intensities seen here are some of the brightest seen in this period.
11:59 UT: Last processed image, showing expansion of the 1144 substorm.

Notes on the UVI Images

UVI images have been registered in magnetic coordinates (specifically magnetic apex coordinates) with a resolution in latitude and mlt of 0.5 degrees. The images are smoothed with a median filter 3 pixels wide and lower levels have been clipped for the brighter images. The images have had instrumental background removed but no other processing has been performed. The units are in instrument counts and variations in sensitivity across the detector have not been corrected.

UVI operational modes alternate 18 second and 36 second exposures and the total instrument counts alternate from image to image. However, the images are scaled so the change in exposure is apparent only from the color bar and, perhaps, from increased noise in the image. Note that some mosaic images do not scale the individual image frames. In these images you may see the intensity alternate from frame to frame.

LBHL is the filter most often used for morphological studies since the observed intensity is directly proportional to the incident energy flux.

Questions or comments? / G. A. Germany / University of Alabama in Huntsville / germanyg@cspar.uah.edu