Large increase of the midlatitude ionospheric electron density in response to a magnetic

storm

Chaosong Huang, J. C. Foster, L. P. Goncharenko,

P. J. Erickson, and W. Rideout

Haystack Observatory

Massachusetts Institute of Technology

Presented in the CEDAR Workshop

Santa Fe, New Mexico, June 27 – July 2, 2004

The 2004 ISR World Day M-I Coupling Campaign was conducted during March 29 – April 3. It was very quiet during March 29 - April 2. A magnetic storm started to occur at 1418 UT on April 3 and reached a minimum Dst of -149 nT at 0042 UT on April 4.

The Millstone Hill radar was operated from 12 UT on March 29 to 02 UT on April 4 and detected a significant increase (> 100%) of the ionospheric F-region electron density on April 3 over the quiet time values. The increase of the electron density occurred within several hours after the storm sudden commencement (SSC).

Unfortunately, other radars were turned off around 12 UT on April 3, shortly before the SSC and missed the storm.

A magnetic storm started to occur at 1418 UT on April 3, 2003.The vertical line indicates the sudden storm commencement (SSC).

The F-peak electron density becomes very high after the SSC. ________________________________________________________

Electron density and temperature at 330-km altitude over Millstone Hill.Ne and Te after SSC on April 3 are much higher than quiet-time values.

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The electron density over the F-region after the SSC on April 3 is much higher than the quiet-time values.

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The electron temperature over the F-region after the SSC on April 3 is much lower than the quiet-time values.

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Eastward electric field and southward neutral wind after the SSC may move the F layer to higher altitudes and increase the electron density.

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The increases of the F-peak height and electron density after the SSCin local afternoon over North America.

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The increases of the F-peak height and electron density after the SSCin local evening over Europe.

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Total electron content derived from the Millstone Hill radar measurement.TEC over the F-region after the SSC is ~2 times the quiet time values.

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Summary

A magnetic storm started to occur at 1418 UT on April 3, 2004. Within several hours of the SSC, the F-region electron density over Millstone Hill in local afternoon sector was increased by a factor of 2-3, compared with the electron density on the preceding quiet days, and the F-region electron temperature was reduced by 800-1500 K. Total electron content (TEC) showed the same increase as the electron density.

It is generally believed that an increase of the F-region electron density after a SSC is a positive storm effect. If this is the case, the electron density increase is the consequence of a lifted F layer by equatorward atmospheric disturbances. However, the meridian neutral wind derived from the radar data was only weakly southward during the period of interest. An important science question is what mechanism causes the great increase of 2-3 times in the F-region electron density.