Six Meter CME Generated Back Scatter Prediction.

By Chip Angle, N6CA 11.13.00

We have been observing the many solar data pages on the internet and have come up with a pretty interesting and somewhat predictable back scatter path to South America and the far south eastern Caribbean. This part of the world is difficult to work on six meters from southern California. This same type of opening should be present in many other areas of the world.

A full halo Coronal Mass Ejection (CME) is an explosive eruption on the sun that is headed directly at the earth. These CMEs and many other events are seen by the SOHO satellite. The "full halo" is observed as an ever increasing ring or halo as it approaches the earth. The CMEs can generate solar winds at speeds of 1 to 2 million miles per hour. The SOHO spacecraft, which is about 1 million miles from earth is located at one of the earth-sun libration points (equal gravity balance point). When a CME is observed by SOHO it usually takes about 70 hours for the CME generated solar wind to arrive at earth however, one recent CME got here in 31 hours. Movies of these CMEs are available at the SOHO web site listed below.

The ACE satellite measures solar wind plus many other sun parameters and is also positioned at the earth-sun libration point. The solar wind arrival at the ACE satellite usually registers a very rapid increase in solar wind velocity. The solar wind then takes about an hour to reach earth's polar regions. If the CME is intense enough there will be an increase in the Aurora at both poles of the earth and many times it will produce visible Aurora at far southern latitudes.

This CME-solar wind arrival usually means the estimated planetary K index will also rise. If the K index is large enough (multiple 7s or 8s) we may have very good back scatter from northern South America beacons into the southwest United States. These beacons will then peak much further south than the direct beam heading. In the case of the Venezuelan YV4AB/b beacon, the normal beam heading from Southern California is about 100 degrees. When these CME enhanced events occur, the YV4AB/b beacon can best heard much further south at a beam heading of 140 to 150 degrees. This is the back scatter path. We have observed this phenomenon three times so far this year.

Logic says if you can hear northern South America on back scatter then you should be able to hear south eastern Caribbean stations as well. Sure enough, when the expected October 5th 2000 CME hit us, the YV4AB/b beacon was heard on back scatter. A quick phone call to Mike J87AB in St. Vincent resulted in several back scatter contacts and provided a new and rare country to many six meter Dxers. This same CME resulted in the longest and loudest V73 Kwajalien opening I have ever heard. We now keep an eye out for these CMEs on a regular basis. A planetary K index of multiple sevens (7) or greater seem to be required for this particular path to form.

The April 6th CME event was very large, multiple 8s for the planetary K resulted in early morning (1630Z) propagation to Argentina and Uruguay and was the strongest and longest YV4AB/b and PY0FF/b opening I have ever observed.

It appears to be a predictable form of six meter propagation to the Caribbean and northern South America from the southwestern US. Of course The CMEs must also occur at the key times of the year, spring and fall and at the solar cycle maximum. This backscatter path is but one of the many effects of the CMEs we get at the solar maximum. There are undoubtedly many more of them. It's just one more little piece of the six meter puzzle.

SOHO web site is at:

ACE web site is at:

Planetary K index at:

Special thanks to N6XQ, K6ODV and W6CPL for their contributions to this effort.

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