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1.
The thermal response of the Earth's ionospheric plasma is calculated for various suddenly applied electron and ion heat sources. The time-dependent coupled electron and ion energy equations are solved by a semi-automatic computational scheme that employs Newton's method for coupled vector systems of non-linear parabolic (second order) partial differential equations in one spatial dimension. First, the electron and composite ion energy equations along a geomagnetic field line are solved with respect to a variety of ionospheric heat sources that include: thermal conduction in the daytime ionosphere; heating by electric fields acting perpendicular to the geomagnetic field line; and heating within a stable auroral red are (SAR-arc). The energy equations are then extended to resolve differential temperature profiles, first for two separate ion species (H+, O+) and then for four separate ion species (H+, He+, N+, O+) in addition to the electron temperature. The electron and individual ion temperatures are calculated for conditions within a night-time SAR-arc excited by heat flowing from the magnetosphere into the ionosphere, and also for typical midlatitude daytime ionospheric conditions. It is shown that in the lower ionosphere all ion species have the same temperature; however, in the topside ionosphere above about 400 km, ion species can display differential temperatures depending upon the balance between thermal conduction, heating by collision with electrons, cooling by collisions with the neutrals, and energy transfer by inter-ion collisions. Both the time evolution and steady-state distribution of such ion temperature differentials are discussed.The results show that below 300km both the electrons and ions respond rapidly (<30s) to variations in direct thermal forcing. Above 600 km the electrons and ions display quite different times to reach steady state, depending on the electron density: when the electron density is low the electrons reach steady state temperatures in 30 s, but typically require 700 s when the density is high; the ions, on the other hand, reach steady state in 700 s when the density is high, and 1500–2500 s when the density is low. Between 300 and 600 km, a variety of thermal structures can exist, depending upon the electron density and the type of thermal forcing; however steady state is generally reached in 200–1000 s. 相似文献
2.
Midlatitude F-region neutral winds and temperatures determined from Fabry-Perot interferometer measurements of the doppler shifts and widths of nightglow 630.0 nm line profiles are presented for the priority regular world day 14 August 1980. They exhibit, in many respects, the observed behavior for other summer, geomagnetically quiet nights at solar maximum. The neutral temperature decreases from 1500°K after sunset (21 h LT) to a minimum of ˜ 1200°K before dawn (05 h LT), except to the north of the observatory. The zonal winds are eastward at sunset at 50 m/sec, decrease to zero at 02 h LT and are westward just before dawn. The meridional winds are zero just after sunset and reach a maximum equatorward value of 50–70 m/sec at local midnight but do not decrease as predicted; instead, they remain at roughly these values towards dawn. The NCAR thermospheric general circulation model (TGCM) is used to predict the global upper atmospheric temperature and circulation patterns for this world day. The model predictions agree with the measured neutral temperatures and exhibit qualitative similarities to the measured neutral winds. It is concluded that inclusion in the model of ion drift at midlatitudes should improve the agreement with observations. 相似文献
3.
Using 3 years of high-quality temperature measurements (2002–2004) recorded from Maui, HI (20.8°N), we have investigated the characteristics of mesospheric seasonal oscillations at low-latitudes. Measurements of the near-infrared OH (6,2) and O2 (0,1) nightglow emission layers (centered at 87 and 94 km) independently reveal a distinct semi-annual oscillation (SAO) and annual oscillation (AO) with amplitudes of 3.8 and 2.0 K, respectively. An observed asymmetry in the seasonal variation of the nocturnal mean, previously reported by Taylor et al. [2005. Characterization of the semi-annual-oscillation in mesospheric temperatures at low-latitudes. Advances in Space Research 35, doi:10.1016/j.asr.2005.05.111] from this site is shown to be due to a superposed AO of amplitude 50% of the SAO signature. Detailed investigations of the local-time variation of the SAO amplitude and phase combined with TIME-GCM simulations of the seasonal variation of the diurnal tide strongly suggest a large local-time dependence of the amplitude (but not phase) of the observed SAO. These data indicate that the true mean temperature SAO amplitude could be as high as 7 K at this latitude. 相似文献
4.
During the evening of 9 April and the morning of 10 April 1969, the twilight zenith intensity of the atomic oxygen red line OI(3P-1D) at 6300 Å was measured at the Blue Hill Observatory (42°N, 17°W). At the same time incoherent scatter radar data were being obtained at the Millstone Hill radar site 50 km distant. We have used a diurnal model of the mid-latitude F-region to calculate the ionospheric structure over Millstone Hill conditions similar to 9–10 April 1969. The measured electron temperature, ion temperature, and electron density at 800 km are used as boundary conditions for the model calculations. The diurnal variation of neutral composition and temperature were obtained from the OGO-6 empirical model and the neutral winds were derived from a semiempirical three-dimensional dynamic model of the neutral thermosphere. The solar EUV flux was adjusted to yield reasonable agreement between the calculated and observed ionospheric properties.This paper presents the results of these model computations and calculations of the red line intensity. The 6300 Å emission includes contributions from photoelectron excitation, dissociative recombination, Schumann-Runge photodissociation and thermal electron impact. The variations of these four components for morning and evening twilight between 90–120° solar zenith angles, and their relative contributions to the total 6300 Å emission line intensity, are presented and the total is compared to the observations. For this particular day the Schumann-Runge photodissociation component, calculated using the solar fluxes tabulated by Ackermann (1970), is the dominant component of the morning twilight 6300 Å emission. During evening twilight it is necessary to utilize a lower O2 density than for the morning twilight in order to bring the calculated and observed 6300 Å emission rates into agreement. The implication that there may be a diurnal variation in the O2 density at the base of the thermosphere is discussed in the light of available experimental data and current theoretical ideas. 相似文献
5.
Rolando R. Garcia Susan Solomon Raymond G. Roble David W. Rusch 《Planetary and Space Science》1984,32(4):411-423
A two-dimensional numerical model with coupled photochemistry and dynamics has been used to investigate the response of the middle atmosphere (16–116 km) to changes in solar activity over the 11-year solar cycle. Model inputs that vary with solar cycle include solar radiation, cosmic ray and auroral ionization rates and the flux of NOx at the model's upper boundary.In this study, the results of model runs for solar cycle minimum and maximum conditions are compared. In the stratosphere, using currently accepted estimates of changes in solar radiation at wavelengths longer than 180 nm, only small responses in ozone, temperature and zonal winds are obtained. On the other hand, changes at shorter wavelengths, and the effects of particle precipitation, lead to large variations in the abundances of trace species in the thermosphere and upper mesosphere. In particular, very large abundances of NOx are produced above 90 km by auroral particle precipitation. Considerable amounts of NOx are transported subsequently to the stratosphere by the global mean meridional circulation. It is shown that this excess NOx can lead to significant decreases in ozone concentrations at high latitudes and that it may explain observations of nitrate deposition in Antarctic snow. 相似文献
6.
This paper presents results from the TIME-GCM-CCM3 thermosphere–ionosphere–lower atmosphere flux-coupled model, and investigates how well the model simulates known F2-layer day/night and seasonal behaviour and patterns of day-to-day variability at seven ionosonde stations. Of the many possible contributors to F2-layer variability, the present work includes only the influence of ‘meteorological’ disturbances transmitted from lower levels in the atmosphere, solar and geomagnetic conditions being held at constant levels throughout a model year.In comparison to ionosonde data, TIME-GCM-CCM3 models the peak electron density (NmF2) quite well, except for overemphasizing the daytime summer/winter anomaly in both hemispheres and seriously underestimating night NmF2 in summer. The peak height hmF2 is satisfactorily modelled by day, except that the model does not reproduce its observed semiannual variation. Nighttime values of hmF2 are much too low, thus causing low model values of night NmF2. Comparison of the variations of NmF2 and the neutral [O/N2] ratio supports the idea that both annual and semiannual variations of F2-layer electron density are largely caused by changes of neutral composition, which in turn are driven by the global thermospheric circulation.Finally, the paper describes and discusses the characteristics of the F2-layer response to the imposed ‘meteorological’ disturbances. The ionospheric response is evaluated as the standard deviations of five ionospheric parameters for each station within 11-day blocks of data. At any one station, the patterns of variability show some coherence between different parameters, such as peak electron density and the neutral atomic/molecular ratio. Coherence between stations is found only between the closest pairs, some 2500 km apart, which is presumably related to the scale size of the ‘meteorological’ disturbances. The F2-layer day-to-day variability appears to be related more to variations in winds than to variations of thermospheric composition. 相似文献
7.
R.G. Roble R.E. Dickinson E.C. Ridley B.A. Emery P.B. Hays T.L. Killeen N.W. Spencer 《Planetary and Space Science》1983,31(12):1479-1499
The neutral gas temperature and circulation of the thermosphere are calculated for December solstice conditions near solar cycle maximum using NCAR's thermospheric general circulation model (TGCM). High-latitude heat and momentum sources significantly alter the basic solar-driven circulation during solstice. At F-region heights, the increased ion density in the summer hemisphere results in a larger ion drag momentum source for the neutral gas than in the winter hemisphere. As a result there are larger wind velocities and a greater tendency for the neutral gas to follow the magnetospheric convection pattern in the summer hemisphere than in the winter hemisphere. There is about three times more Joule heating in the summer than the winter hemisphere for moderate levels of geomagnetic activity due to the greater electrical conductivity in the summer E-region ionosphere.
The results of several TGCM runs are used to show that at F-region heights it is possible to linearly combine the solar-driven and high-latitude driven solutions to obtain the total temperature structure and circulation to within 10–20%. In the lower thermosphere, however, non-linear terms cause significant departures and a linear superposition of fields is not valid.
The F-region winds at high latitudes calculated by the TGCM are also compared to the meridional wind derived from measurements by the Fabry-Perot Interferometer (FPI) and the zonal wind derived from measurements by the Wind and Temperature Spectrometer (WATS) instruments onboard the Dynamics Explorer (DE−2) satellite for a summer and a winter day. For both examples, the observed and modeled wind patterns are in qualitative agreement, indicating a dominant control of high latitude winds by ion drag. The magnitude of the calculated winds (400–500 m s−1) for the assumed 60 kV cross-tail potential, however, is smaller than that of the measured winds (500–800 m s−1). This suggests the need for an increased ion drag momentum source in the model calculations due to enhanced electron densities, higher ion drift velocities, or some combination that needs to be further denned from the DE−2 satellite measurements. 相似文献
8.
The solar extreme ultraviolet (e.u.v.) flux and solar ultraviolet (u.v.) flux in the Schumann-Runge continuum region have been measured by spectrometers on board the Atmosphere Explorer satellites from about 1974 to 1981. The solar flux spectra measured on 23 April 1974 (a day the Atmosphere Explorer satellite reference spectrum was obtained), 13–28 July 1976 (a period of spotless conditions near solar cycle minimum), and 19 February 1979 (a day near solar cycle maximum) are used to examine the global mean temperature structure of the thermosphere above 120 km. The results show that for solar cycle minimum the calculated global mean exospheric temperature is in agreement with empirical model predictions, indicating that the energy absorbed by the thermosphere is balanced by downward molecular thermal conduction. For solar cycle maximum the energy absorbed by the thermosphere is not balanced by downward thermal conduction but agreement between the calculated and observed temperature is obtained with the inclusion of 5.3μm radiational cooling by nitric oxide. Model calculations of the minor neutral constituents in the thermosphere show that about three times more nitric oxide is produced during solar cycle maximum than solar cycle minimum conditions. The results suggest that nitric oxide cooling is small during solar cycle minimum, because of low nitric oxide densities and low thermospheric temperatures, but it becomes significantly larger during solar cycle maximum, when nitric oxide densities and thermospheric temperatures are larger.23 April 1974 was a moderately disturbed day and the results of the global mean temperature calculation indicate that it is necessary to consider a high latitude heat source associated with the geomagnetic activity to obtain agreement between the calculated and observed global mean temperature structure. 相似文献
9.
A three-dimensional, semi-empirical dynamic model of the neutral thermosphere is used to examine the effect of the displaced geomagnetic and geographic poles on the daily variation of neutral gas motion. The global-scale pressure distribution to drive the neutral gas motion is derived from the empirical model of Jacchia (1965). The ionization distribution is obtained from the Pennsylvania State M.K 1 model ionosphere using the first few longitudinal Fourier coefficients of the ionization distribution. The calculations were made at various latitudes at equinox and solstice and for various values of solar activity. The results show that the calculated neutral winds for the case where the geomagnetic and geographic poles are coincident differ at most only a few per cent from the winds calculated assuming the poles displaced. With the poles coincident, longitude and local time are interchangeable, and one dimension in any dynamic model of the thermosphere may be eliminated. 相似文献
10.
A time-dependent two-dimensional numerical model of the minor neutral constituents of the thermosphere NO, N(2D), and N(4S) is used to examine the effects of winds in transporting these constituents from their production region in auroral arcs. The calculations show that thermospheric winds flowing through regions of enhanced local auroral production produce downwind plumes of enhanced minor neutral constituent densities and that the densities depend upon the wind velocity. Below about 200 km N(2D) is in photochemical equilibrium and is not transported. Above 200 km N(2D) is transported by the wind and since quenching of N(2D) by O is small and the radiational lifetime is long, a downwind plume of emission at 5200 Å develops from the particle source region. We present data from a rocket flight in the vicinity of the magnetospheric cusp and data from the Atmosphere Explorer-D (AE-D) satellite that both show enhanced 5200 Å emission rates in a general downwind direction from a region of direct particle precipitation. The general wind speed and direction are obtained from predictions made by the NCAR thermospheric general circulation model. The results suggest that transport of N(2D) by the wind system is more important than the convection of O+ ions by electric fields in causing the enhanced 5200 Å emission rate in regions outside but in the vicinity of direct particle precipitation. 相似文献