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A two-dimensional pole-to-pole numerical model with background solstitial winds has been used to study the global dynamical response of the thermosphere to high-latitude energy inputs associated with a model geomagnetic storm. This model storm has four distinct pulses of heat input over a 12-h period. The thermospheric wave response to the sustained part of the storm heat input consists in the establishment of a global meridional circulation that is initiated in about 3 to 4 hours after storm commencement and never quite reaches steady state in the simulation. The main purpose of this study is to investigate the interaction between the disturbances and the mean meridional flow associated with the storm. It is shown that this interaction can be represented in terms of an induced circulation. This induced circulation is forced by the transient nature of the eddy flux convergences (divergences) of heat and momentum. The equivalent temperature changes due to the induced circulation are one-third to o...

We have carried out numerical simulations of the thermospheric response to the morningside intense diffuse aurora, using a three-dimensional (3-D), nonhydrostatic, composition-dependent, regional-scale, high-resolution numerical model. A diffuse aurora is represented in the model by its equivalent 3-D features of ion drag and joule heating. The diffuse aurora propagates westward within the model grid, which is fixed in the terrestrial frame. Our numerical results show that the neutral atmospheric response to the diffuse aurora is much weaker in a 3-D simulation than in a two-dimensional (2-D) simulation. For example, the predicted zonal flow is weaker by a factor of roughly 2. The fidelity of the 3-D results is supported by a recent study (Brinkman et al., 1995) in which zonal winds predicted from a 2-D model were shown to be larger than observations by a factor of 2. Our numerical results also show that the inertial gravity waves that are generated in the 3-D flow control the energy dissipation and reduce the dynamical response in the source region. These waves propagate in both the north-south and east-west directions. However, the longitudinal propagation rate is relatively small compared to the latitudinal propagation rate. The simulated westward drift of the diffuse aurora creates a distinct displacement of the propagating disturbances, which further reduces the dynamical response in the source region. The study described here underscores the importance of 3-D high-resolution treatments of upper atmospheric physics to analyze and interpret dynamical, compositional, and electrodynamic observations in this region.

A spectral theory is developed for the solar semidiurnal tides in an atmosphere with background zonal winds. According to this theory, the vertical structures of the spectral components of the tide are governed by a set of coupled second-order ordinary differential equations which have to be solved for appropriate lower and upper boundary conditions. The lower boundary condition, in particular, has to be properly formulated to take into account the latitudinal variation of the atmospheric basic-state parameters. While the solutions to the equations have to be obtained by numerical methods, several aspects of their behavior can be revealed by simpler mechanistic models and concepts which are introduced in this first part (Part I) of a two-part report. Discussion of the detailed numerical solutions and of the adequacy of their mechanistic interpretations is given in the companion paper (Part II).

Classical and nonclassical model calculations have been performed for the solar semidiurnal tidal oscillations in the earth's atmosphere, for prescribed basic-state parameters and heating functions appropriate for the solstitial seasons when the nonclassical effects associated with the mean zonal wind are expected to be maximum. It is found that the enrichment of the higher order spectral components characteristic of the nonclassical model is due to the cross-coupling rather than the self-coupling of the spectral components in the model. These cross-coupling effects are shown to be sufficiently well represented by a mode-coupling model described in Section 3 of Part I. As explained in Part I, the effect of cross-coupling may be considered as some kind of indirect forcing. Such indirect forcing, which can be applied either at the lower boundary or inside the medium, is obtained and compared for each spectral component with the direct thermal forcing. It is demonstrated that the actual behavior of ...

Using ground magnetometer data from several stations near the dip equator, the magnetically quiet-time characteristics of the daytime normal electrojet and the morning and afternoon counter-electrojets are established and illustrated. In particular, the solar cycle, seasonal, longitudinal and day-to-day variations of counter-electrojets as well as their dependence on lunar phase are studied. In order to investigate the influence of solar tidal winds in the production of counter-electrojets, the equatorial electric fields generated by such winds through the dynamo mechanism are calculated, using a numerical dynamo simulation model developed earlier at UCLA. From these calculations it is found that westward electric fields responsible for the afternoon counter-electrojets can be produced in the local summer solstice (when these events are most common) by a combination of the solar semidiurnal (2, 2) tide and the diurnal (1, -2) tide. An example from January 1964 is discussed to illustrate that afternoon counter-electrojet events occurring at all longitudes on the same day are likely to be associated with abnormalities in the global Sq or SR current system. It is suggested that the lunar semi-diurnal tide is a more important causative agent for the morning rather than the afternoon counter-electrojets.

Calculations of the semidiurnal atmospheric tide at solstice using improved heating rates are presented. The heating rates for solar absorption by water vapor are based on a global water vapor distribution (Jenne, 1969, 1975; Jenne et al., 1974), the data of McClatchey et al. (1972), and an absorptivity parameterization of Lacis and Hansen (1974); rates for solar absorption by ozone are based on the midlatitude ozone distribution of the U.S. Standard Atmosphere (COESA, 1976) and detailed radiative calculations using the solar fluxes and absorption cross sections of Ackerman (1971) with the Schumann-Runge band cross sections of Kockarts (1971). The heating rates for solstice are quite similar to those reported by Forbes and Garrett (1978) and significantly different from those of Lindzen and Hong (1974), which were used in the previous study of Walterscheid and Venkateswaran (1979b) investigating the influence of mean zonal motion and meridional temperature gradients on the solar semidiurnal tide....

The chemiluminescent reaction responsible for the nightglow in the sodium D lines is embedded in the complex kinetics of an oxygen-hydrogen atmosphere. Various possibilities of identifying this reaction from observational studies are considered. It is suggested that an important clue may be found in the time-variations of the height-integrated glow-intensity.

Ionospheric E-region observations from Boulder (40.0 N, 105.3 W), Grand Bahama (26.6 N, 78.2 W), Mexico City (19.3 N, 99.2 W), Vandenberg (35.6 N, 120.6 W), and Wallops Island (37.9 N, 75.5 W) during the total solar eclipse of 7 March, 1970 are used for reconstructing the distribution of the ionizing XUV radiation over the solar disk. The derived solar image compares reasonably well with the EUV and X-ray pictures of the Sun obtained from rockets.

An attempt is made in this paper to formulate the transport of hydrogen in the earth's upper atmosphere as a Monte Carlo problem. The relevant details of the technique adopted are given. The capability of the technique to provide useful answers to the following questions is demonstrated. How is the flux of hydrogen atoms, possessing enough kinetic energy to escape from the earth's gravitational field, influenced by the fact that the escape takes place not from a particular atmospheric level (the critical level) but from a layer of finite thickness? What is the law of variation of hydrogen density in this finite layer? More specifically, does the hydrogen gas maintain a Maxwellian distribution while diffusing through the layer? If not, how does the distribution change with height inside the layer? The answers obtained are discussed with reference to their statistical validity, and compared with some of the conclusions of earlier investigations.

It is shown that time-structure analysis of geomagnetic crochets can be useful in the ground-based detection of XUV radiation from solar flares. The crochets often manifest a composite structure that consists of a ‘fast’ component presumably produced by EUV radiation (100–1000A) and a ‘slow’ component produced by soft X rays (1–100A). This composite structure is taken into account in the proposed method of analysis for crochet current systems. Some preliminary results are given from the simulation studies of Sq and crochet current systems. These studies are intended to probe into the nature of the atmospheric winds that drive the ionospheric dynamo and that generate both the Sq and crochet currents.

A brief description of the Vaisala radiosonde is given and its general performance-characteristics discussed. Some results of ascents made at Ahmedabad with this type of instrument in the last two years are presented. The question of the diurnal variation of temperature in the upper atmosphere is examined with reference to the serial ascents made in the month of April 1952.

The hydroxyl bands in the glow emanating from the earth's upper atmosphere are chemically excited. The two possible precursor reactions are O3+H→OH*+O2 and O2*+H→OH*+O. Arguments are advanced in this paper to show that the night-time variations of the emission intensifies stimulated by these two reactions might be characteristically different. The relative importance of the reactions can therefore be judged by a systematic observational study of the intensity variations.

The paper describes the techniques developed at Poona for the measurement of electrical potential gradient in the free atmosphere and discusses the results of the observations made over Poona during 1953–1958. The day-to-day and diurnal variations of potential gradient in the troposphere as well as the seasonal variations are discussed. The variation of potential gradient with height follows the theoretical values only during the monsoon months, showing an increase above 300 mb in winter and steady values above 500 mb during summer.

The lower atmospheric wind structure over Ahmedabad has been studied from a detailed. analysis of one complete year's observations. It is found that the local winds introduced by the orographical peculiarities of the surrounding country are (1) the katabatic wind that comes as. a Northeasterly current extending to a depth of about 0'15 to 0,25 km in the months of October to January and (2) the sea breeze that reaches from ,the Gulf of Cambay in the hot months just prior to and after the local monsoon. A seasonal examination of the pilot balloon winds shows that the nature of the diurnal variation of wind is governed mainly by the amount of turbulence in the frictional layer. This variation is confined to about'3000 ft in winter and extends to a greater from the Gulf height in summer. It is also shown how, in the winter months, both the wind and temperature distributions help in the formation of a very stable layer just above 3000 ft limiting the upper reach of surface turbulence.

This paper is an observational study of the equatorial anomaly during a period of declining solar activity. The anomaly is studied at two different longitudes, 75°W and 105°E. Data from both the topside and the bottomside of the F region are used. The topside data were obtained by the satellite Alouette 1. Seasonal and daily variations, longitude dependence, and geomagnetic storm-time distortions of the anomaly are treated.

International audience; In the paper "Saint-Santin Radar Observations of Lower Thermospheric Storms" by C. Mazaudier, R. Bernard and S.V. Venkateswaran (Journal of Geophysical Research 90 (A3), 2885-2895) the name of the third author was inadvertently omitted from the first page. A corrected first page follows

Analysis of 29 days of ionospheric current data obtained by Saint-Santin radar, including both magnetically quiet and disturbed periods, has confirmed the existence of northward currents at all daytime hours. The postulate of field-aligned Van Sabben currents driven by interhemispherical asymmetries seems to be able to account for the anomaly. The desirability of quantitative modeling of the Van Sabben currents on a seasonal or day-to-day basis is highlighted by the Saint-Santin measurements.

This paper develops the linear gradient drift instability theory of middle latitude E/sub S/ -layer irregularities, taking into account the appropriate field geometry and allowing for the fact that, in addition to a predominant perpendicular component, the propagation vector of an irregularity can have a small but significant component parallel to the magnetic field as well. The theory is used to calculate the growth rates and phase and group velocities of the unstable waves as a function of the off-perpendicular propagation angle. Group propagation effects are also considered.