Sporadic meteor sources as observed by the Jicamarca high-power large-aperture VHF radar
Introduction
Since the early 1940's specular meteor radars (referred to as SMR hereafter) have been the main source of meteor observations entering the Earth's atmosphere (e.g., Jones and Brown, 1993, Galligan and Baggaley, 2005; and references therein). These systems use wavelengths between 3 and 15 m, on few occasions systems with larger wavelengths have been used (e.g., Steel and Elford, 1987). The combined results from these systems gathered over many years of observations have allowed the identification of the currently well accepted six sources of sporadic meteors, i.e., North Apex (NA), South Apex (SA), Helion, Anti-Helion (AH), North Toroidal (NT), and South Toroidal (ST) (e.g., Jones and Brown, 1993, Taylor and Elford, 1998, Galligan and Baggaley, 2005).
In this work we present for the first time the sources of sporadic meteors as inferred from the meteor-head echoes detected by the Jicamarca High-Power Large-Aperture Radar (HPLAR). This type of radar (e.g., ALTAIR, Arecibo, EISCAT, Jicamarca, Millstone Hill, MU, and Sondrestorm) has been used for meteor-head studies since mid 1990's originally motivated by predictions of several returns of the Leonids meteor showers (e.g., Janches et al., 2000b, Close et al., 2002, Sato et al., 2000, Chau and Woodman, 2004). The radar frequencies from these radars start around 50 MHz (at Jicamarca and MU) and go as high as 1.29 GHz (at Sondrestorm). These radars are mainly sensitive to the plasma surrounding the meteoroid as it enters the Earth's atmosphere (between 70 and 140 km). Faster geocentric meteoroids will ionize at higher altitude and will have more chance to be observed by the HPLARs (e.g., Janches and ReVelle, 2005). More details on the scattering mechanism of meteor-head echoes are given by Close et al. (2004) and Mathews (2004).
We first present the experimental setup and meteor parameters either directly measured or derived. The expected statistical errors for some derived parameters are presented in Appendix A. In Section 3 we show the meteor sources as seen by the Jicamarca radar and the speed and initial altitude distributions of selected meteors sources, including the not well defined Antapex (or Apex prograde) source. Finally results are interpreted and discussed, special emphasis is given to the comparison with results obtained by SMRs.
Section snippets
Experimental setup and meteor parameters
Meteor-head observations have been performed using the large Jicamarca array () for transmission and at least three quarter sections for reception (). The same linear polarization (north–east) has been used in both modes. The antennas were phased to point on-axis (1.46° from zenith towards the south–west). Complex voltages (raw data) from at least three quarters were recorded. Note that we only need the information from three non-collinear antennas in order to locate the
Meteor sources
Before determining the radiant, i.e., where meteors are coming from (derived from the meteor vector velocities), we have performed Earth zenith attraction and Earth rotation corrections, to get the undisturbed meteor velocity with respect to the Earth (instantaneous) inertial frame of reference (also called geocentric velocities in the literature). This correction is mainly important for meteors with slow geocentric velocities (the Earth's escape velocity is ). Note that we have not
Speed and initial altitude distributions
Now that we have identified different meteor populations, we could proceed to present statistics for any meteor parameter or pair of parameters. However in this work we only present the speed and initial altitude distributions of selected sources. In Fig. 5 we show the geocentric (in black) and heliocentric (in red) speed distributions for the following meteor sources: (a) All retrograde Apex sources, (b) narrow SA, (c) Antapex (Apex-prograde), (d) AH, (e) ST, and (f) extra-solar. Although not
Discussion
As shown in previous works (e.g., Janches et al., 2003, Close et al., 2002, Chau and Woodman, 2004), the HPLARs provide meteor measurements with very high accuracy in velocity, initial altitude, and deceleration, among other parameters. Using interferometry, Jicamarca's results show that the location (inferred from the velocities) of the meteors on a modified (non-inertial) ecliptic coordinate system are also excellent, being able to observe pretty much all the known sporadic meteors sources
Concluding remarks
Using the Jicamarca (11.95° S, 76.87° W, 1° dip angle) high-power large-aperture radar (HPLAR), we have detected 170,000 meteor heads in less than 90 h of observations spread in 14 days, between November 2001 and February 2006. From these observations 91% are of from the Solar System and the remaining appear to be extra-solar.
The solar meteors are mainly clustered in six main sources, i.e., South and North Apex, Helion, Anti-Helion, and South and North Toroidal. These sources have been
Acknowledgements
We thank P. Brown, D. Holdsworth, D. Janches, and M. Oppenheim for their comments, suggestions, and encouragement during different stages of this work. The Jicamarca Radio Observatory is a facility of the Instituto Geofísico del Perú and is operated with support from the NSF Cooperative Agreement ATM-0432565 through Cornell University.
References (24)
- et al.
A technique for calculating meteor plasma density and meteoroid mass from radar head echo scattering
Icarus
(2004) Novel applications of MST radars in meteor studies
J. Atmos. Sol. Terr. Phys.
(2001)Theory of equatorial electrojet plasma waves: New developments and current status
J. Atmos. Sol. Terr. Phys.
(1985)- et al.
Determination of the meteoroid velocity distribution at the Earth using high-gain radar
Icarus
(2004) - et al.
Observed diurnal and seasonal behavior of the micrometeor flux using the Arecibo and Jicamarca radars
J. Atmos. Sol. Terr. Phys.
(2005) - et al.
Doppler studies of near-Antapex UHF radar micrometeors
Icarus
(2000) - et al.
Micrometeor observations using the Arecibo 430 MHz radar. I. Determination of ballistic parameter from measured Doppler velocity and deceleration results
Icarus
(2000) Radio science issues surrounding HF/VHF/UHF radar meteor studies
J. Atmos. Sol. Terr. Phys.
(2004)- et al.
Radar interferometric imaging studies of long-duration meteor echoes observed at Jicamarca
J. Geophys. Res.
(1994) - et al.
Observations of meteor-head echoes using the Jicamarca 50 MHz radar in interferometer mode
Atmos. Chem. Phys.
(2004)
Characterization of Leonid meteor head echo data collected using the VHF–UHF advanced research projects agency long-range tracking and instrumentation radar (ALTAIR)
Radio Sci.
The orbital distribution of radar-detected meteoroids of the Solar System dust cloud
Mon. Not. R. Astron. Soc.
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2015, IcarusCitation Excerpt :However the asymmetry also originates in part from a heterogeneous distribution of particle orbits. Studies of the sporadic meteors (that is, those meteors distinct from meteor showers) show concentrations of meteoroid orbits towards the direction of the Earth’s motion around the Sun (e.g. Stohl, 1986; Brown and Jones, 1995; Chau et al., 2007; Campbell-Brown, 2008) and many others). When displayed in a co-moving reference frame centered on the apex of the Earth’s way, a number of concentrations of impinging orbits are discerned.