| dc.description.abstract | This thesis comprises analytical and experimental investigations of the mesosphere, specifically the altitude region 50–90 km.
The analytical work consists of correlation analyses of mesospheric temperature data from rocket soundings at three Western Hemisphere stations—Wallops Island, Port Churchill, and Point Barrow—during the period 1956–1972, and at Thumba in 1970–1971.
The analysis with the solar index at the Western Hemisphere stations shows a heating effect, consistently observed in the night-time auroral mesosphere at Port Churchill and Point Barrow, attributed to energetic solar particle precipitation. The effect is stronger in winter than in summer.
Longer-term heating effects attributable to solar activity-induced changes in upper atmospheric circulation are also observed.
The analysis with the geomagnetic index shows similar long-term heating effects.
A mesospheric heating effect due to Joule heating by the auroral electrojet, with the effect propagating downwards into the mesosphere, and stronger at auroral latitudes, is observed. Again, the effect is stronger in winter and decreases at mid-latitudes.
At Thumba, analysis with solar indices shows:
A heating effect attributable to enhancements in solar 2000–3000 Å ultraviolet fluxes.
No significant effect with the 1–8 Å and 8–20 Å solar indices.
A heating effect possibly due to a heat source in the auroral thermosphere, with the disturbance propagating towards the equator.
Analysis with the equatorial electrojet intensity index over Thumba shows no significant effects due to the equatorial electrojet.
Harmonic analysis of annual, semi-annual, and other sub-annual mesospheric temperature variations at Thumba shows results generally similar to those obtained by other workers.
The experimental work includes passive inflatable falling-sphere experiments and tests of ground instrumentation for rocket-grenade experiments. Preliminary results from five falling-sphere experiments at Thumba are presented.
An important result brought out in these analyses is that solar and geomagnetic activity effects are observed in the mesosphere. The techniques developed in these analyses can also be used to study direct as well as propagating effects occurring in the lower atmosphere. | |
