Douglas G. Torr

Use of FUV auroral emissions as diagnostic indicators

In an earlier study we modeled selected FUV auroral emissions (O I (1356 A), N2 Lyman-Birge-Hopfield (LBH) (1464 A), and LBH (1838 A)) to examine the sensitivity of these emissions and their ratios to likely changes in the neutral atmosphere. In this paper we extend that study to examine the dependence of these same emissions and their ratios on the shape of the energy distribution of the auroral electrons. In particular, we wish to determine whether changes in energy spectra might interfere with our determination of the characteristic energy. Modeled column-integrated emissions show relatively small (<30%) dependences on the shape and width of the incident energy spectrum, provided the average energy and total energy flux of the energy distribution are held constant. Long-wavelength FUV emissions, which are relatively unaffected by O2 absorption losses, exhibit virtually no dependence on the shape of the incident energy distribution. Changes in ratios of FUV short- to long-wavelength emissions as a function of characteristic energy are much larger than those due to changes in energy distribution. As a result, the determination of characteristic energy using these emission ratios is relatively unambiguous. We also examine the relative intensities of the aurora and the dayglow for various conditions. The intensities of modeled FUV auroral emissions relative to the dayglow emissions are presented as a function of solar zenith angle and incident energy flux. Under certain conditions (energy flux ≤ 1 erg cm−2 s−1 and solar zenith angle ≤50°) the dayglow will be the limiting factor in the detection of weak auroras.

F 2 peak electron density at Millstone Hill and Hobart: Comparison of theory and measurement at solar maximum

This paper compares the observed behavior of the F2 layer of the ionosphere at Millstone Hill and Hobart with calculations from the field line interhemispheric plasma (FLIP) model for solar maximum, solstice conditions in 1990. During the study period the daily F10.7 index varied by more than a factor of 2 (123 to 280), but the 81-day mean F10.7 (F10.7A) was almost constant near 190. Calculations were performed with and without the effects of vibrationally excited N2 (N2*) which affects the loss rate of atomic oxygen ions. In the case without N2* there is generally good agreement between the model and measurement for the daytime, peak density of the F region (NmF2). Both the model and the measurement show a strong seasonal anomaly with the winter noon densities a factor of 3 to 4 greater than the summer noon densities at Millstone Hill and a factor of 2 greater at Hobart. The seasonal anomaly in the model is caused by changes in the neutral composition as given by the mass spectrometer and incoherent scatter (MSIS) 86 neutral density model. There is generally little or no increase in the observed noon NmF2 as a function of daily F10.7 except at Millstone Hill in winter. In May-July, where the measured NmF2 shows least dependence on daily F10.7, there is excellent agreement between the model and data. The modeled NmF2 is about 30% less than the measured values at Millstone Hill at the December solstice, but both model and data increase with increasing daily F10.7 index. At Hobart, on the other hand, the model densities are greater than or comparable to the measured densities for the December solstice. This suggests that the differences between model and data are not due to the incorrect solar EUV flux. The effect of including N2* is to worsen the agreement between model and data at Millstone Hill by reducing the summer densities from good agreement to 40% below the data. In winter the N2* effects are much smaller, and the densities are reduced by only 10%. While N2* worsens the model-data comparison at Millstone Hill, it does bring the model seasonal density ratio into better agreement with the data and also improves the agreement at Hobart. Although the 1990 daytime ionosphere can be well modeled without N2*, it may still be important for high levels of solar and magnetic activity. There is a very close relationship between the height at which peak density occurs hmF2 variation and the NmF2 variation with F10.7 in summer at Millstone Hill. In contrast to the generally good agreement between model and data at noon, the model badly underestimates the density at night at Millstone Hill at all seasons. At Hobart the model reproduces the nighttime density variations well in both winter and summer. The international reference ionosphere (IRI) model generally provides a good representation of the average behavior of noon NmF2 and hmF2 but because the data show a lot of day-to-day variability, there are often large differences. The FLIP model is able to reproduce this variability when hmF2 is specified. The IRI model peak densities are better than the FLIP densities at night, but the IRI model does not represent the Millstone Hill summer data very well at night in 1990.

Ionospheric effects of the March 1990 Magnetic Storm: Comparison of theory and measurement

This paper presents a comparison of the measured and modeled ionospheric response to magnetic storms at Millstone Hill and Arecibo during March 16-23, 1990. Magnetic activity was low until midday UT on day 18 when Kp reached 6, days 19 and 20 were quiet, but a large storm occurred around midnight UT on day 20 (Kp=7) and it was moderately disturbed (Kp=4) for the remainder of the study period. At Millstone Hill, the daytime peak electron density (NmF2) showed only a modest 30% decrease in response to the first storm and recovered to prestorm values before the onset of the second storm. The model reproduces the daytime peak electron density well for this period. However, the severe storm on March 20 caused a factor of 4 depletion in electron density, while the model densities were not greatly affected. The inclusion of vibrationally excited nitrogen (N2*) in the model was unable to account for the observed large electron density depletions afterward March 20. The storm did not appear to affect the overall magnitude of the electron density at Arecibo very much, but did cause unusual wavelike structure in the peak density and peak height following the storm. The model reproduces the daytime NmF2 very well for Arecibo, but after sunset the model densities decay too rapidly. This study indicates that successful modeling of severe ionospheric storms will require better definition of the storm time inputs, especially of the neutral atmosphere.

Vacuum ultraviolet thin films. 1: Optical constants of BaF 2 , CaF 2 , LaF 3 , MgF 2 , Al 2 O 3 , HfO 2 , and SiO 2 thin films

The optical constants of MgF(2) (bulk) and BaF(2), CaF(2), LaF(3), MgF(2), Al(2)O(3), HfO(2), and SiO(2) films deposited on MgF(2) substrates are determined from photometric measurements through an iteration process of matching calculated and measured values of the reflectance and transmittance in the 120-230-nm vacuum ultraviolet wavelength region. The potential use of the listed fluorides and oxides as vacuum ultraviolet coating materials is discussed in part 2 of this paper.

The neutral thermosphere at Arecibo during geomagnetic storms

Over the past five years, simultaneous incoherent scatter and optical observations have been obtained at Arecibo, Puerto Rico, during two major geomagnetic storms. The first storm we examine occurred during the World Day campaign of 12–16 January 1988, where on 14 January 1988, Kp values greater than 7 were recorded. An ion-energy balance calculation shows that atomic oxygen densities at a fixed height on 14 January 1988 were about twice as large as they were on the quiet days in this period. Simultaneous radar and Fabry-Perot interferometer observations were used to infer nighttime O densities on 14–15 January 1988 that were about twice as large as on adjacent quiet nights. On this night, unusually high westward ion velocities were observed at Arecibo. The Fabry-Perot measurements show that the normal eastward flow of the neutral wind was reversed on this night. The second storm we examine occurred on the night of 13–14 July 1985, when Kp values reached only 4+, but the ionosphere and thermosphere responded in a similar manner as they did in January 1988. On the nights of both 13–14 July 1985 and 14–15 January 1988, the electron densities observed at Arecibo were significantly higher than they were on nearby geomagnetically quiet nights. These results indicate that major storm effects in thermospheric winds and composition propagate to low latitudes and have a pronounced effect on the ionospheric structure over Arecibo.

New Sources for the Hot Oxygen Geocorona

This paper investigates new sources of thermospheric non thermal (hot) oxygen due to exothermic reactions involving numerous minor (ion and neutral) and metastable species. Numerical calculations are performed for low latitude, daytime, winter conditions, with moderately high solar activity and low magnetic activity. Under these conditions we find that the quenching of metastable species are a significant source of hot oxygen, with kinetic energy production rates a factor of ten higher than those due to previously considered O2+ and NO+ dissociative recombination reactions. Some of the most significant new sources of hot oxygen are reactions involving quenching of O+(²D), O(¹D), N(²D), O+(²P) and vibrationally excited N2 by atomic oxygen.

New Sources for the Hot Oxygen Geocorona: Solar Cycle, Seasonal, Latitudinal, and Diurnal Variations

This paper demonstrates the variability of thermospheric sources of hot oxygen atoms. Numerical calculations were performed for day and night, high and low solar activity, summer and winter, and low- and middle-latitude conditions. Under most conditions, reactions involving metastable species are more important hot O sources than previously considered dissociative recombination of O 2 + and NO + . All the hot O sources are an order of magnitude lower at midnight than at noon. At night, dissociative recombination of O 2 + and NO + are the most important sources. Quenching of vibrationally excited N 2 (N 2 * ) by O is the most important metastable source at night. Above 300 km, hot O sources increase by an order of magnitude between solar minimum and solar maximum. For a given level of solar activity, the high-altitude total production rate of hot O kinetic energy is greater during winter than during summer, indicating a dominance of cooler hot O sources during summer. The N 2 * source dominates at low altitudes. At high altitudes it is almost negligible at solar minimum, but increases to become the dominant source at solar maximum. Atomic oxygen quenching of N( 2 D) is a large source at solar minimum and is still important at solar maximum. Overall, seasonal variations are small compared to solar cycle, diurnal and latitudinal variations. While quenching of metastable species is more important at midlatitudes than at low latitudes, there is little latitudinal variation in hot O production due to dissociative recombination of NO + and O 2 + .

Gravitoelectric-electric coupling via superconductivity

Recently we demonstrated theoretically that the carriers of quantized angular momentum in superconductors are not the Cooper pairs but the lattice ions, which must execute coherent localized motion consistent with the phenomenon of superconductivity. We demonstrate here that in the presence of an external magnetic field, the free superelectron and bound ion currents largely cancel providing a self-consistent microscopic and macroscopic interpretation of near-zero magnetic permeability inside superconductors. The neutral mass currents, however, do not cancel, because of the monopolar gravitational charge. It is shown that the coherent alignment of lattice ion spins will generate a detectable gravitomagnetic field, and in the presence of a time-dependent applied magnetic vector potential field, a detectable gravitoelectric field.

On the inversion of O+(²D-²P) 7320 Å twilight airglow observations: A method for recovering both the ionization frequency and the thermospheric oxygen atom densities

In this paper we demonstrate that it is possible to invert twilight observations of the O+(²D -²P)-7320 A airglow emission to obtain information about both the thermospheric atomic oxygen densities and the unattenuated O+(²P) ionization frequency. The efficacy of the proposed approach, which relies upon making twilight observations in more than one viewing direction, is illustrated using a synthetic data set and an inversion algorithm based on a simple photochemical model. The results of this study show that day-to-day variations in the thermospheric oxygen atom densities may be monitored from the ground without requiring complementary measurements of the solar EUV flux. The study also shows that twilight observations may be used to monitor variations in the solar flux components that are responsible for O+(²P) production and EUV heating of the upper thermosphere.

Finslerian structures: The Cartan–Clifton method of the moving frame

A theory of Finslerian structures is presented using an unpublished method of Clifton. It consists of using Cartan’s moving frame method with fields of special bases, and the Cartan calculus of tensor‐valued forms with nonredundant coordinates on sphere bundles (which are the base spaces of the Finsler bundles). The formulation only requires a modicum of new concepts and does not involve Lagrangians at any fundamental level, including the definitions of metrics and connections. Finslerian connections on Riemannian (and even flat) metrics are discussed. The invariant forms of the sphere bundle of Minkowski space are obtained. The possibility of describing equations of motion through autoparallels, rather than extremals, is illustrated.