C. Kruschwitz

Observations of Persistent Leonid Meteor Trails 2. Photometry and Numerical Modeling

During the 1998 Leonid meteor shower, multi-instrument observations of persistent meteor trains were made from the Starfire Optical Range on Kirtland Air Force Base, New Mexico, and from a secondary site in nearby Placitas, New Mexico. The University of Illinois Na resonance lidar measured the Na density and temperature in the trains, while various cameras captured images and videos of the trains, some of which were observed to persist for more than 30 min. The Na density measurements allow the contribution of Na airglow to the observed train luminescence to be quantified for the first time. To do this, persistent train luminescence is numerically modeled. Cylindrical symmetry is assumed, and observed values of the Na density, temperature, and diffusivity are used. It is found that the expected Na luminosity is consistent with narrowband CCD all-sky camera observations, but that these emissions can contribute only a small fraction of the total light observed in a 0.5–1 μ bandwidth. Other potential luminosity sources are examined, in particular, light resulting from the possible excitation of monoxides of meteoric metals (particularly FeO) and O2(b1∑g+) during reactions between atmospheric oxygen species and meteoric metals. It is found that the total luminosity of these combined processes falls somewhat short of explaining the observed brightness, and thus additional luminosity sources still are needed. In addition, the brightness distribution, the so-called hollow cylinder effect, remains unexplained.

Meteor trail advection observed during the 1998 Leonid Shower

Sodium resonance lidar observations of meteor trails are reported from the 1998 Leonid shower experiment at the Starfire Optical Range, Kirtland Air Force Base, NM (35.0° N, 106.5° W). The lidar was operating in a spatially scanning mode that allowed tracking for up to one half-hour. Three trails are presented here whose motion allowed inference of radial as well as vector wind components and apparent diffusivities. The winds are derived independently using the narrow linewidth sodium (Na) resonance Doppler lidar technique and are compared with the tracking results.

First observations of long‐lived meteor trains with resonance lidar and other optical instruments

In November 1998 the earth passed through a maximum in the cometary material responsible for the yearlyLeonids meteorshower. Themeteorstormeventpro- duced numerous examples of long-lived chemiluminescent trails|visible to the naked eye|over New Mexico, where a major observation campaign was centered. One trail was detected for over an hour with a CCD camera employing a narrow sodiumlter, and many others were observed for over ten minutes each. For the rst time, sodium densi- ties in such trails were measured while also being imaged in sodium light. Wehaveveried onesource of long-lived light emissions|a sodium-catalyzed reaction involving ozone| but it is far too weak to explain the visibility of such trails. Inaddition,wepresentanewexplanationforthecylindrical shell appearance long reported for chemiluminescent trails and show that ozone depletion by chemical processes is a possible explanation for this phenomenon.

The excitation of the Na airglow from Coqui Dos rocket and ground‐based observations

On February 20 1998 two rockets were launched from Puerto Rico as part of the Coqui Dos campaign. Data from on-board photometers and ground-based data from a Na lidar and an airglow imager allowed an estimate to be made, using both the TIME-GCM and MSIS models, of the branching coefficient α for the Na airglow emission. Assuming the hydrogen density is within the range predicted by the two models the data are consistent with α being less than 0.05. This value is well below a recent theoretical estimate of 0.67 and also below the nominally accepted value of 0.1 derived from previous aeronomic data.

Meteor trail advection and dispersion; Preliminary lidar observations

Sodium resonance lidar observations of meteor ablation trails at the Arecibo Observatory (18.30°N, 66.75°W) are presented. Of particular interest is the event of 23 March 1998, during the Coqui II sounding rocket campaign. On this date, the lidar was operating with two beams probing different volumes of the sodium layer separated zonally by 15.7±0.8 km. A single meteor trail was observed near 89 km altitude in both lidar field-of-views with a 310±50 s temporal displacement. This observational separation suggested a westward zonal wind of 50±10 m/s, while trail dispersion yielded an upper bound for the total diffusion coefficient of 2.6±0.5 m²/s which is consistent with dispersion seen in other trails. The data supports the need for future observation with systems specialized for meteor detection.

A new explanation of persistent double meteor trains

[1] Persistent meteor trains, studied for more than a century, remain somewhat mysterious [Newton, 1869; Trowbridge, 1907; Chapman, 1955; Hapgood, 1980]. The Leonids meteor showers of recent years afforded opportunities to apply new research technologies, including lidars and sophisticated cameras. Here we explore a particularly curious but common feature: double trains. Since the traditional hollow cylinder explanation has been shown to be untenable, we suggest a new explanation, arguing that one train is due to gaseous vapor train emissions behind the meteor while the other is due to heterogeneous chemistry associated with recoagulated dust. In this model the separation is caused by gravitational sedimentation of dust particles, an idea supported by rocket-based observations of recoagulated dust behind a meteor, by rocket-based observations of enhanced sodium emissions in a dust layer, by rocket observations of a dusty trail, and by recent theoretical estimates of chemical reactions on dust.