NOTES ON "METEOR OBSERVATIONS FROM ISRAEL" BY DR. NOAH BROSCH
"We observed the 1998 and 1999 Leonid meteor shower with phased-array radar systems operating in the L-band from Israel. We discovered that the radar meteors exhibit a two-peaked height distribution. One population corresponds to that of the regular optical meteors and peaks at ~120 km. The newly discovered population forms a wide distribution centered at ~240 km with a long tail to high altitudes. We propose that this population consists essentially of H2O-ice bodies ejected from the nucleus of P55/Tempel-Tuttle comet along with the "regular" meteoroids. The high-velocity interaction between the fluffy-ice cometary chunks and the thermosphere ions causes sputtering and the subsequent disruption of the ice chunk, while producing the detected radar return. Supporting evidence for our finding is the newly-identified long tail of the meteor distribution at high altitudes, identified in intensified-video observations of the Leonids. The analogy with the water-ice mini-comets proposed by Frank and collaborators is emphasized and observational tests of the suggestion of H2O-ice meteoroids are proposed."
COMMENTS AND NOTES
Dr. Brosch et. al., in their just-published paper, briefly describe their work using Israeli military radar. The system used phased-array installations operating in the L-band (~1 GHz). A single active phased-array was used in 1998, and two were used in 1999.
As soon as Dr. Brosch and his team gave a brief summary of their results at the 1999 Leonids MAC Workshop, the results were strongly disputed. A summary of the reasons for this dispute can be found on the SKiYMET notes page. (Be sure to follow the links there to the various SKiYMET radar pages to learn more about their system, however).
Because the radar used for the experiments was Israeli military radar, no details about it could be given. Thus it seems impossible to be sure exactly how the data was obtained.
Dr. Brosch, in his article, says that all of the objections have been studied and none are valid - that they have ruled out range-doubling, artifacts caused by sidelobe reception, etc. And to the fact that no other radar detected meteors at the ~240 km height, it is admitted by Wayne Hocking of Mardoc Inc, operators of the SKiYMET radar system, that their system (and probably most others) were not looking for these super-high meteors and, in fact, most of the radar systems were incapable of detecting them. There were also a few visual reports, using intensified cameras aboard the MAC aircraft, of high-burning Leonid meteors, I believe; but not nearly as many as seeming found by the Israeli team.
So why did the Leonids storms produce returns at this height while other showers have not? His theory, as I understand it, is that the Leonid meteoroids contain a lorge amount of water ice. This water ice is physically sputtered off the particle by collisions with the atoms and molecules in the high atmosphere. (The ablation that produces the trains we are used to can occur only lower in the atmosphere). This ice can survive only a very few perihelion passages. Thus, we need several things to make this happen: a comet that contains a large amount of water ice; an orbit that allows the ejected particles to be concentrated into discrete dust trails by a resonance with one of the major planets; and the earth must cross one of these dust trails while it is still relatively young in terms of perihelion passages. Dr Brosch and his team propose several experiments these next two years to search for the presence of this water.
There is one strange bit of evidence missing. Using backscatter-radar at an L-band frequency, it would appear that these ~240 km meteors would have produced enough ionization to have enabled some very long-distance MS contacts. In fact, Dr. Brosch recently requested information on this. A message was placed on one of the primary MS reflectors used heavily by the Europeans, with the request to relay it on, asking about contacts or reception reports over extra-long distances during the Leonids storms. There were no replies. A search was made of the E-mail reports posted following the 1998 and 1999 Leonid showers, and again no reports of this type were found. With the concentration of stations available in Europe, the apparent number of good operators actually on during the peak times, and the fact that many are very well equipped, this seems very curious.
The formal publication of this article (delayed because of clearance problems, apparently) will no doubt stir up yet more controversy. The theory seems plausable. Much hinges, however, on the actual collection of the data - information which they will not be allowed to share.
The 2001 and 2002 Leonid showers are predicted to bring storms to some part(s) of the world (though this is not as certain as had been though just a short time ago). No doubt every VHF operator who can possibly operate will be on the air at those times. Dr. Brosch has requested data on any contacts or reception reports from the previous years beyond the normal maximum range. No doubt he would like information on any made during the showers of 2001 and 2002. If you work (or hear) anyone greater than ~5700 km, please report it. And report all details. If this ~240 km ionization is real, what other group than the Amateur Radio VHF MS operators is better able to study and exploit it?