HOT METEOR SHOWER PREDICTED...

[NW7US]

The following is a digest of material I have written in various columns in CQ VHF magazine, CQ Magazine, and elsewhere.

(copyright, 2003, Tomas Hood)

The Fall Meteor Shower Season

One of the largest yearly meteor showers occurs during November. Appearing to radiate out of the constellation of Leo on the night and morning of November 17-18, the Leonids are known to create intense meteor bursts. Since the source of the Leonids, the Tempel-Tuttle comet, passed closest to the sun in February of 1998, the years following were expected to produce very strong displays. The greatest display since 1998 was the peak of 3,700 per hour in 1999. Every year since has been significantly less spectacular. However, a few forecasters think that we still might have a meteor storm with an hourly rate of thousands, sometime in the next several years. If this year is more typical of the last few, we'll see a rate of several hundred per hour. The visuals might only be 10 to 20 per hour, but when we are talking about meteor scatter radio propagation, we count the smallest meteor-formed plasma clouds that will support VHF radio signals.

There is a prediction this year that the Earth will pass through the fifteenth revolution of the Tempel-Tuttle comet on November 13, five days earlier than the normal Leonids shower. According to Esko Lyytinen and Tom van Flandern < http://leonid.arc.nasa.gov/1998.html >, their prediction calls for a possible peak of up to 250 visual meteors per hour. Recently, Jeremie Vaubaillon of the Institut de Mecanique Celeste et de Calcul des Ephemerides, France, confirmed Esko's calculations. Based on these calculations, the normal Leonids shower could produce a ZHR of up to 50 per hour. The ZHR (Zero Hourly Rate) refers to the expected number of meteors that will be seen in an hour under ideal conditions such as a moonless sky without any interfering artificial illumination. For those who are interested in working meteor scatter propagation, the ZHR helps us gauge the general level of activity of a shower. A far greater number of non-visual meteor bursts will occur that will support propagation of VHF signals.

The best time to work meteor scatter off the Leonids is around 11:30 PM, local time, in the Northern Hemisphere. Alaska and the Pacific Northwest could be the best area to work the first, November 13, peak. For the normal peak, at 0150 UTC, November 18, the best location will be the eastern side of North America.

Working Meteor Scatter

Meteors are particles (debris from a passing comet) ranging in size from a spec of dust to a small pebble, and some move slowly while some move fast. When you view a meteor, you typically see a streak that persists for a little while after the meteor vanishes. This "streak" is called the "train" and is basically a trail of glowing plasma left in the wake of the meteor. The Leonids are fast meteors and they leave a high number of long trains. They enter Earth's atmosphere traveling at speeds of over 158,000 miles per hour. Besides being fast, the Leonids usually contain a large number of very bright meteors. The trains of these bright meteors can last from several seconds to several minutes.

Meteor scatter propagation is a mode where radio signals are refracted off of these trains of ionized plasma. The ionized trail is produced by vaporization of the meteor. Meteors no larger than a pea can produce ionized trails up to twelve miles in length in the "E" Layer of the Ionosphere. Because of the height of these plasma trains, the range of a meteor scatter contact is between 500 and 1300 miles. The frequencies that are best refracted are between 30 and 100 MHz. However, with the development of new software and techniques, frequencies up to 440 MHz have been used to make successful radio contacts off of these meteor trains. On the lower frequencies, like on six meters, contacts may last from mere seconds to well over a minute. The lower the frequency, the longer the specific "opening" made by a single meteor train. A meteor train that supports a sixty-second refraction on six meters might only support a one-second refraction for a two-meter signal. Special high-speed methods are used on these higher frequencies to take advantage of the limited available time.

A great introduction by Shelby, W8WN, on working meteor scatter is found at < http://www.amt.org/Meteor_Scatter/shelbys_welcome.htm >. OZ1RH wrote " Working DX on a Dead 50MHz Band Using Meteor Scatter," a great working guide < http://www.uksmg.org/deadband.htm >. W4VHF has also created a good starting guide at < http://www.amt.org/Meteor_Scatter/letstalk-w4vhf.htm >. Links to various groups, resources, and software is found at < http://www.amt.org/Meteor_Scatter/default.htm >.

The next big meteor shower, after November's Leonids, is the yearly Geminids, December 6 to 19 with a possible ZHR of 60, peaking on December 14 at 1510 UTC. After this one comes the Quadrantids, December 28 to January 7 with a ZHR of about 50, peaking on January 4 at 0450 UTC. There are many smaller showers during the fall meteor shower season. Check out < http://comets.amsmeteors.org/meteors/calendar.html > for a good look at what is in store.

(copyright, 2003, Tomas Hood. All rights reserved.)