"Are there really two layers in the atmosphere where the meteoroids burn up? Puzzling Israeli radar data could indicate that one class of dust particles decays at 250 km and the other at 120 km altitude, but the result remains controversal."
No information has been released yet, although it is supposed to be included in a future journal. If true, this is very surprising; why has it not been reported previously? A number of people doubt the validity of this report. Until we have further information, you may wish to read and ponder the following comments. And be sure to explore the various Web sites, linked from this page and from the bottom of the Hot News Page.

The following is a note, somewhat edited, from Prof. Wayne Hocking of Mardoc Inc, concerning the radar data of the 1999 Leonids:

"The results from the SKiYMET radars are shown at http://www.members.home.net/leonidsbyradar/home.htm (well worth exploring all of their pages).
Our radars saw a peak at around 90 km (normal for radars) and a second one at around 105-110 km. We did not see one at over 200 km, but (we did not) look. (Emphasis mine).

"However, I will say this. The report from Brosch et al used a phased array radar, and, as far as I can tell, was used by personnel who were not overly experienced in using phased array radars for meteor studies. Phased array radars suffer from the fact that if they are phased too far from their "optimum" direction of beam-pointing, they produce serious grating lobes. They are generally designed to be able to be "steered" to different directions by phasing - but only in a limited range of angles - say within +/- 20 degrees of the normal bore direction. Further sterring must be done mechanically. If they are asked to steer further using phasing, grating lobes can arise. Thus (a) signal is received from angles at which the operator is unaware .. generally low to the horizon.
If the operator assumes that the signals are coming down the main beam, but it is really coming down a grating lobe, then errors in the height determination can ocur - easily by a factor of 2 too high. My first guess is that the Israeli radar was detecting two groups of meteors - one down the main beam, and one through a grating lobe. I tried to get information about spacing of the elements in the phased array, but it was not forthcoming... this would have helped me resolve whether grating lobes were an issue.

"At this stage my comments are speculative, since I was not able to talk to the personnel involved, and when I did question those whom I could I was simply brushed off with comments along the lines of "we have considered everything". But having worked with phased array radars for many years, I believe the possibility is a real one."

---- Wayne Hocking (Mardoc, Inc)

Several other comments have been received from others in attendance at the April conference concerning the Israeli radar report, two of which are copied below:

"I recently had some contacts with Dr. Brosch. He wrote:
' ... Some of the latter results will appear in the special EM&P issue. For the time being, the radar results have not yet been released for publication, although we have good hopes this will happen sooner....'"
---Sirko

"I've been at the Leonid MAC Workshop in Tel Aviv in April and heard Noah Brosch giving the talk. As Sirko remarked, a report will appear in the conference proceedings to be published in Earth Moon Planets. There's a small snake hidden: I want to add, that perhaps not all technical details you'd perhaps like to hear will be made public: when these were asked on the conference, like power and detection characteristics of the used radar etc., the answer was that these are classified data. They used a radar of the Israeli military.... :-)"
--- Marco Langbroek

Early summary of the 1999 Leonids findings (and questions), including the controversial Israeli radar report, on Daniel Fisher's page, Story 2 Item 3. Good summary, shows how much we still don't know!
(And other links from the bottom of the "Hot News" page, below).

Other reports from the 1999 Leonids MAC Workshop - this Web site still being updated.

The SKiYMET radar summary (URL above) and the graphs and charts from the various world-wide sites linked from the SKiYMET Web site show the 1999 Leonid storm and also the heights of the meteors detected. They use much lower frequencies than are of primary interest to us, but which are good choices for meteor detection. They show most of the Leonids at about 90-100 km, with some up to about 120 km - see the information from the various sites for details. (This is somewhat higher than average for most meteors, as would be expected due to the high velocity of the Leonid shower). They do not show anything higher than about 120 km. However, as is stated, they were not looking for extremely high reflections. In fact, the sites were not capable of detecting Leonids above about 130 km.
The Israeli report apparently is being prepared at this time for publication in a special issue of Earth Moon & Planets, which I do not have access to. (Help, someone?) Because of the fact that military radar was used and because of the extra security concerns over there, there may not be enough systems data in the article to make a determination if their observations were real or if they were only artifacts of off-bore antenna lobes. The required censorship may also make peer review for publication difficult.
My personal feeling now is that this result was most likely only an artifact of the radar system. However, according to the messages received by others from the Israeli group, they do not think so. How can we find out what is true? Are 1900 mile (3000 km) contacts possible using the Leonids? We still don't know. Hopefully, some other groups will attempt high-altitude detection during the next 3 showers. (After 2002, the Leonids should become only a minor shower again until the next 33-year period rolls around).
However, some over-1600-mile (2600 km) MS 144-MHz contacts, if completed, might provide some further information. At best they would be very difficult. Anyone with full power, a large array and a good location crazy enough to try in November?

These comments are taken primarily from the report on the April MAC Conference by Daniel Fischer (Story 2 Item 3). It is suggested that you also read his report. Hopefully we will soon have additional information as more data is released.

"How real is the fine structure in the ZHR profile of the peak? There was considerable debate about the reality of several peaks of the meteor rate before and after the main peak."
All reports from that part of the world show a very strong, very sharp peak, only about 5 minutes from the time predicted by Asher et al. In addition, several reports showed brief, additional "spikes" superimposed on the main peak.
The reality of these extra small peaks is disputed by some (e.g., Peter Jenniskens), but strongly defended by others.
What does this mean to us? For at least 10 years, Amateurs have been reporting sudden enhancements on the Perseids, and more recently the Leonids. These were usually brief (~5 to 10 minutes or so), possibly limited in geographical area. (The geographical limitations could also involve the height of the radiant above the horizon and several other factors, so care must be taken here). Also, for a number of years, several experienced visual observers have reported the same thing - a sudden, brief enhancement at their location which was not seen by other experienced observers several hundred miles away.
Amateur Radio Operators began regularly reporting these controversial small enhancements during the strong Perseid displays about 10 years ago, not knowing that some visual observers had reported the same type of thing in earlier showers. At that time, those reports were generally disregarded as being false or simply statistical variations. Those who had experienced a number of these enhancements felt that they were real - that there really were small "filaments" of debris in the larger cloud of particles. When the earth's orbit intersected one of these small "filaments", a small area would see an enhancement for a few minutes.
Now we have the dust-trail theory and the first successful predictions made using it (but made possible by the 5:14 resonance of the Leonids). Could these small enhancements have also hung together inside the larger cloud of particles? And what about other showers, such as the Perseids, where this has been experienced on a number of occasions, but which do not have a known resonance that would tend to keep some particles bunched together? Even if these enhancements are real, is there a physical explanation for them, or is it only a random variation?
The answers are not known yet. But it was, to a great extent, the continued reports (with exact times) by Hams that caused a few of those in the field of meteor studies to take another look at the actual distribution of meteors in the shower.
Our schedules, being in a specific direction at a specific time (and frequency) and thus constrained by the geometry of the arriving trains, does not lend itself to providing any accurate information here. Any enhancement is as likely to be due to the changing geometry and the "effectivity" of the shower as it is to an actual increase in meteors. However, random operating, with many stations congregating on the calling frequency from a large area, has been the method by which these "spikes" have been detected. Unfortunately, most of us are primarily interested in making as many random contacts as possible, especially if new states or grids are available. We log these, but don't log what else we are hearing! Yet it takes only a few seconds to jot down calls (and grids), with an occasional time reference. A note in the notebook of the time every 10 minutes would be sufficient. Then, if a sudden enhancement is noted, the approximate time it began and ended should also be noted, along with comments about it (and your antenna heading at the time). Reports of this type are certainly not definitive, and one or two such reports do not give enough information to be of any value. But a number of reports like this can be used to determine whether or not something actually happened. Again, they would not be definitive; but they can then cue researchers to look more closely at other, perhaps overlooked, data!
Let's keep some records during the showers!

"You see 7 times as many meteors from the air than from the ground!"
"Discovered" during the MAC flights, this seems to be true. From perhaps 35,000 feet, you can look through a much larger volume of the atmosphere, especially near the horizon.
So what? We can't take a fully-equipped station aloft to operate meteor scatter.
True. But some might have access to mountain tops.
Back in the 1960's, a particular Amateur reported a number of receptions of signals out to about 1600 miles (2600 km), and on two or three occasions, greatly beyond this distance. Many, probably most, did not believe these reports. This Amateur has been a Silent Key for a number of years, so first-hand information is no longer available. (And I have been unable to locate some of my old notes on this subject for a promised article).
However, I personally (W8WN) heard one of the things reported. And I heard exactly what was reported, which had some details that would not have been known without an actual reception. (The distances for me were normal MS distances).
This does not prove that the operator actually did hear some or any of the things he said he did. It should be noted, though, that he was a very good operator with a state of the art station. Also, he operated from the top of a 10,000 foot (3300 meter) mountain, with an eastern horizon over 150 miles away.
Are super-distances possible, either by multiple-hop, very high meteors, or a very good location combined with exceptional meteors? This is a very controversial subject. There are few, if any, operators currently able to operate with a full-power station from a high mountain top, and many of us simply do not even have a good take-off angle for the "normal" MS distances. Here is another question that still needs research.

"What can we learn from the radio emission of meteor?"
Observers in both Israel and New Mexico reported hearing electrophonic sounds from meteors during the 1999 Leonids shower. These "sounds" have been reported for hundreds of years (as have sounds associated with the aurora). It is generally believed that they are associated with VLF electromagnetic emissons, tho the mechanism of both the generation of the emissions and the detection of them by the human ear as sounds is unknown.
During the 1999 Leonids, an array of radio antennas normally used for lightning research was deployed, and it recorded up to 18,000 VLF radio signals per hour during the storm. Many signals were received when there were no visual meteors seen.
A number of Hams are now "Lofers," experimenting on the tiny VLF band that has been made available. Others like to listen to "whistlers" and other "'sferics" generated by the antipodal reflection of static crashes. Is this another area of research that would be especially suited for us?
For more information, see the GEFS homepage. Other electrophonic sound data is found on several visual and radio astronomy pages.

"This year's activity will be a decisive test whether there will really be more storms in 2001 and 2002, and should thus be monitored well."
Asher again stated at the conference that all reasonable cometary dust ejection models make Leonid storms in 2001 and 2002 all but inevitable. Perhaps a ZHR of 6000or more those years?
2000 is not expected by most to produce a storm. But less data is available for 2000 than for predictions for 2001 and 2002. This year's observations will be critical for fine-tuning the predictions for the next two years. (See the suggestions for this year's operating plans on the Hot News page).

Return to the W8WN meteor scatter "Hot News" page. (More Leonid info and links there).