Brent W. Grime

A study of the role of ion-molecule chemistry in the formation of sporadic sodium layers

Over two campaigns in 1998 and 1999, multiple sporadic sodium events were observed by the Arecibo Observatory sodium density lidar while simultaneously monitoring the plasma density using the incoherent scatter radar. In this paper, we test the theoretical explanation proposed by Cox and Plane (1998) where Na + in a plasma layer is neutralized via an ion–molecule mechanism to form a sporadic sodium layer. A particular challenge is to interpret observations made in a Eulerian frame of observation where the spatial and temporal characteristics of events cannot easily be separated. The reaction scheme in the original mechanism is modi=ed to include the reactions NaO + +N2 → Na + ·N2 +O and NaO + +O2 → Na + +O3, following the results of theoretical quantum calculations. Six unique case studies of sporadic sodium layers are presented here, and excellent agreement between simulation and observations was obtained for =ve of them. c � 2002 Published by Elsevier Science Ltd.

20 W of continuous-wave sodium D2 resonance radiation from sum-frequency generation with injection-locked lasers

A 20-W all-solid-state continuous-wave single-frequency source tuned to the sodium D2a line at 589.159 nm has been developed for adaptive optical systems. This source is based on sum-frequency mixing two injection-locked Nd:YAG lasers in lithium triborate in a doubly resonant external cavity. Injection locking the Nd:YAG lasers not only ensures single-frequency operation but also allows the use of a single rf local oscillator for Pound-Drever-Hall locking both the injection-slave and the sum-frequency cavities. We observe power-conversion efficiencies in excess of 55% and a linearly polarized diffraction-limited output tunable across the sodium D2 line (589.156 to 589.160 nm) with no change in output power and with high amplitude and pointing stability.

Simultaneous atomic and ion layer enhancements observed in the mesopause region over Arecibo during the Coqui II Sounding Rocket Campaign

The NASA Coqui II sounding rocket campaign in Puerto Rico provided the opportunity to obtain a large number of lidar and incoherent scatter radar observations of atomic sodium and ion layers in the upper mesosphere and lower thermosphere. Sodium layer enhancements, coupled with ion layers, were frequently observed in the range of 90–105 km altitude. We found that above 97 km all of the enhanced Na layers were observed to have an associated ion layer, and below that altitude some Na enhancements could occur in their absence. Finally, we show one extraordinary case of a sporadic Na layer that grew to near its peak concentration before the associated ion layer appeared at its altitude.

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.

Observations of persistent Leonid meteor trails: 1. Advection of the “Diamond Ring”

From a single image of a persistent trail left by a −1.5 magnitude Leonid meteor on November 17, 1998, the relative winds between 92.5 and 98 km altitude are derived, where the altitudes are determined by a sodium lidar. These are converted to true winds 82 sec after the appearance of the meteor by fixing the winds at 98 km to match the results of following the trail with the lidar for twelve minutes. The image and winds reveal a fine example of the effects of a gravity wave having a vertical wavelenth of 5.50 ± 0.02 km, a horizontal wavelength of 2650 ± 60 km, an intrinsic period of 19.5 ± 0.4 hours, and an observed period of 8.6 ± 0.1 hours. Effects of the gravity wave are still present in the wind field 70 min later.

Joint observations of sodium enhancements and field-aligned ionospheric irregularities

Resonance Lidar observations of neutral sodium and VHF coherent scatter radar observations of field-aligned 3-meter irregularities were obtained during the Coqui II rocket campaign in Puerto Rico. The Lidar, a facility instrument at the Arecibo Observatory (18.3°N, 66.8°W), and the University of Illinois Radar, located near Salinas on the south of the island, both monitored volumes near where the uplegs of the nominal rocket trajectories intersected the E-region. The Observatorys Incoherent Scatter Radar was also used to characterize the plasma layers. Preliminary investigation of the data sets has shown a potential correspondence between VHF backscatter from plasma layers and a new class of characteristic enhancements in the neutral sodium.

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.

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.

20 Watt CW All-Solid-State 589-nm Sodium Beacon Excitation Source Based on Doubly Resonant Sum-Frequency Generation in LBO

A doubly resonant sum-frequency ring containing an LBO crystal, pumped by 1064 nm and 1319 nm continuous-wave Nd:YAG injection-locked ring lasers, produced a 20 W diffraction-limited, single-frequency, 589-nm beam. A 12 W circularly polarized beam produced a 7.2-magnitude guidestar.