Upper atmospheric response to transient heating

Abstract

The response of the upper atmosphere to various forms of time‐dependent heating is calculated by use of approximate analytic solutions of the heat conduction equation. Time lags of maximum temperature and density behind peak heating are distinctly different and, for short‐duration heating events, are strongly altitude dependent. The time and space characteristics of a one‐dimensional heat source that produces a density change consistent with the observed drag on satellites during a geomagnetic disturbance are identified. The desired model for polar substorm heating maximizes in the 140‐ to 160‐km altitude region with an average duration of 4 to 5 hours. The relationship between the amount of heat injected per unit column during a disturbance of maximum geomagnetic index ap is q ∝ (ap)1/2. This simple relationship suggests a common heating mechanism that is present at all levels of activity.

On the dynamic response of the thermosphere at low altitudes to geomagnetic disturbances

“…Since all eleven satellites examined had perigees in a relatively narrow height band, Jacobs treated the data collectively to yield a time delay of 0.23-day (least-squares) by which the atmosphere's response appeared to lag behind the geomagnetic variations. It is the purpose of this paper to point out that the method employed by Jacobs in deriving his lag value includes a built-in delay, which if not properly interpreted, can give rise to some erroneous conclusions, as for example, in Thomas and Ching [1969]. This paper also extends Jacobs' analysis and presents an improved relationship for modeling the observed density changes at low altitudes.…”

“…As a result, there is a great deal of disagreement as to the intensity of the heating, as well as to the time delay of the atmosphere's response behind the magnetic variations reflected in the Kp (or ap) indices. Thus, various authors [Jacobs, 1967;Jacchia and Slowey, 1964;1967;Roemet, 1966] have independently reported finding time lags in the observed density fluctuations of the order of •-day; in a recent theoretical investigation, Thomas and Ching [1969] have found, for different heat sources, time lags that varied between 0 and «-day and that were strongly dependent upon altitude.…”

Density Perturbations in the Upper Atmosphere Caused by the Dissipation of Solar Wind Energy

“…The latter is made responsible for upwelling of air rich in molecular nitrogen and large-scale horizontal transport of air rich in atomic oxygen Conclude that the composition changes they observe cannot be explained entirely by a temperature increase but must also involve perturbations of the homopause region Duncan (1969) Suggests that during magnetic storms, upwelling of air rich in molecular species occurs at high and middle latitudes. At the same time, air rich in atomic oxygen is transported by large-scale wind circulation towards lower latitudes Thomas and Ching (1969) Calculate upper atmospheric temperature and density response to transient heating using a one-dimensional, time dependent, analytical heat conduction model Volland (1969) Uses linearized analytical one-dimensional model to determine the geomagnetic activity effect caused by various types of heat sources Chandra and Herman (1969), , A self-consistent one-dimensional numerical model of the thermosphere and ionosphere is used to simulate density and composition changes caused by perturbations of the turbopause region Cole (1971) Speculates that Joule heating at polar latitudes causes uplifting and mixing of air; and that these mixing effects are transported to lower latitudes by large convection cells Volland and Mayr (1971) Present the first three-dimensional time dependent model of the geomagnetic activity effect. It is based on the linearized set of balance equations, a system transfer function (STF) approach, and an expansion into spherical harmonics and Fourier components.…”

Theoretical models of ionospheric storms

“…Response of the atmospheric density lags the changes of Kp with a delay time of about 6 hr, with a little longer delay at low latitudes . Thomas and Ching (1969) have shown that time lags of maximum density and temperature after the peak of heating are different and are altitude dependent. May and Miller (1971) have suggested that the atmospheric density changes are correlated more with Dst field of geomagnetic disturbances than Kp.…”