Neutral Thermosphere Research Articles

Atmospheric response to heating within a stable auroral red arc

We assume the electron conduction hypothesis for the stable auroral red arc. That is, energy conducted in the electron gas from the magnetosphere atong the geomagnetic field lines into the ionosphere heats the ambient F-region electrons. These, in turn, excite the ( 1D) term of atomic oxygen by electron impact giving rise to the λ6300 emission characteristic of the arc. A two-dimensional model of a red arc is constructed using solutions of the one-dimensional electron heat-conduction equation so that the calculated two-dimensional λ6300 volume emission-rate contours model the contours determined from photometric observations. The resulting electron temperature, λ6300 volume emission-rate, and neutral heating-rate contours are obtained for the arc model. More than 99 per cent of the energy conducted from the magnetosphere is transferred to the neutral gas in the ionosphere through elastic and inelastic collisions of the electrons and ions with the neutrals. A two-dimensional steady-state dynamic model of the neutral thermosphere incorporating thermal conduction, viscosity, and ion drag is used to calculate the temperature perturbation and circulation pattern within the arc region. The pressure forces originating from the red-arc heating drive a thermal cell with upward motion in the red-arc region and a stow subsidence over a much greater area outside the arc. The adiabatic warming and cooling by these motions significantly reduce the neutral temperature increase within the red arc compared to the increase obtained in the absence of motions, but the warming and cooling enlarge the horizontal scale of the region of temperature increase.

Latitudinal variations in the neutral atmospheric density

In-situ atmospheric density measurements from the Explorer 32 density gages for the time period May through October 1966 reveal latitudinal density structure in the neutral thermosphere during geomagnetically undisturbed times. For altitudes between 300 and 700 km the summer northern latitude densities are greater than the equatorial densities. For latitudes greater than 55°N, the northern latitude to equatorial latitude density ratio is smallest during the day (near 1.3) and increases at night to values greater than 2. Large (>3) high-latitude to equatorial density ratios are observed near or in the auroral zone. These large ratios are observed even on geomagnetically quiet days. These results suggest that auroral zone and high latitude heating is a permanent feature of the summer thermosphere.

Composition and temperature of the neutral tropic lower thermosphere

A diurnal pair of upper atmosphere composition payloads was launched near 9°30′ south latitude aboard Nike-Apache rockets on March 11, 1965. Higher O/O2 ratios were obtained in the daytime than at night, and the values were approximately equal to those obtained at Wallops Island. The data indicated the existence of atomic nitrogen in the order of 1 to 2% of the molecular species, but the extent of possible instrumental and observational errors precludes a firm conclusion in this respect. Argon-nitrogen turbopause levels of 101 and 103 km were deduced from the daytime and nighttime data, respectively. No conclusive dependence on time or location was noted in these results or those of other flights. Contrary to expectations, the indicated daytime exospheric temperature of 600°K was lower than the nighttime (1100°K).

Direct in situ measurements of wave propagation in the neutral thermosphere

Atmospheric density variation measurements by density gages on Explorer 32 satellite confirm wave propagation in neutral thermosphere as free internal gravity waves

Midlatitude neutral thermosphere density and temperature measurements

Midlatitude neutral thermosphere density and temperature measurements, noting effect of atomic oxygen adsorption by instruments