Qihou Zhou, Arecibo Observatory, zhou@naic.edu
John D. Mathews, Penn State University, JDMathews@psu.edu
Skaggs 2A-305, 1:00-3:00 PM
Tuesday, June 27, 2000
This workshop focuses on recent advances in the studies of meteor
echoes and their impacts on the atmosphere/ionosphere using radar and
optical techniques. Discussion topics include:
Meteoroids are small solid objects that move in the interplanetary space. They are in general smaller than an asteroid and larger than a molecule. The trail of visible light, ionization or particles resulting from meteoroid entering into the atmosphere is referred to as a meteor. Most of the meteoroids intercepting the earth's atmosphere are solar bound and have a velocity between 11 km/s to 72 km/s. Because of its large entry velocity, a typical meteoroid evaporates completely at the altitude range of 80 to 110 km when entering the earth's atmosphere. Those meteoroids surviving the passage through the atmosphere and reaching to the earth's surface are called meteorites. Very small meteoroids that do not evaporate and falls through the atmosphere are called micro-meteorite. Solar bound meteoroids have their origin in comets and asteroids. The spectacular Leonids meteor shower is associated with comet 1866 I (Temple-Tuttle). Leonids have been the most extensively observed meteor shower so far by both radars and lidars and will be discussed at the workshop.
Meteoric Effects on the Atmosphere and Ionosphere
Meteoric ablation is the chief process responsible for the existence of metallic species found in the upper atmosphere. The most abundant metallic atoms in the meteor zone include sodium, iron, magnesium, calcium and lithium. Many of these metals can be directly observed using the resonance lidar technique. The most abundant metallic ions include Fe+, Mg+, Al+, Ca+ and Na+, which are largely responsible for the existence of the nighttime E-region. At high latitudes, meteoric dust are thought to provide the condensation nuclei for the formation of noctilucent clouds. The chemistries involving meteoric metals are fairly complicated. Prof. John Plane will give a review on recent advances on meteoric chemistries. In addition, we will also discuss direct meteoric impact on the atmosphere/ionosphere.
Radar and Optical Observations of Meteors
Other than space-craft observations, ground based meteor observations can be largely classed into radio or optical method. In the radio method, meteor echoes are obtained from the electrons generated through the meteoroid ablation process. Meteoroids themselves are typically too small to produce any detectable signals. Radar echoes from the long-lived ionizations (e.g., > 100 ms) are called trail echoes. More powerful radars also see the ionization that moves with the meteoroid. This type of echoes are referred to as head echoes. Scattering from meteor trails is better understood and this type of echoes have been used to measure atmospheric winds and temperature. On the other hand, there are many unanswered questions regarding head echoes, both in terms of scattering mechanisms and chemistries. Prof. John Mathews will review the meteor scattering mechanisms at the workshop. Radar observations from MF/HF to UHF wavelengths will be reported. Electrodynamics of meteor trail evolution, which may have important implications for interpretation of radar echoes, will also be discussed at the workshop.
The latest addition to the observations of meteors is the lidar technique. This technique has yielded interesting insights into meteoric ablation process, size distribution, relative abundance of different metals etc. There will be presentations on the latest lidar observations at the workshop. In addition, there will also be a video showing the spectacular observations made at the Starfire Range. The stone melting video has been promised to be "cool"!
General References:
Many recent technical papers can be found at the following web site: http://www.naic.edu/~zhou/meteor/meteor_ref.html