Spatial and temporal variations of the atmospheric sodium layer observed with a steerable laser radar
LASER radar observations of resonance scattering from atmospheric sodium during the night have, on occasions, shown evidence of short term changes in the height distribution1–3. It has been suggested that these changes arise from the movement of a horizontally structured sodium layer, but the measurements have all been limited to the vertical direction, and have provided no direct evidence of a horizontal variation. Evidence of horizontal structure at mesospheric heights has been provided by observations of hydroxyl emissions in the airglow, both from the ground4 and from an aircraft5,6. In addition, the observed fluctuations of intensities and infrared rotational temperatures of the hydroxyl bands have been associated with the passage of atmospheric gravity waves7,8. We report here observations intended to examine the short term and small scale horizontal variations of the sodium layer which might also be associated with such waves.
Infrared Photography of OH Airglow Structures
INFRARED airglow emission is bright, patchy and erratic1,2. The primary source of this emission was identified by Meinel3 as rotation-vibration bands of the OH molecule. These and subsequent studies4–6 did not delineate the true morphology of the infrared night sky because large fields of view (∼20 deg2) were used and only point by point measurements taken. Accurate mapping of the night sky requires a small field of view to resolve the smallest structures and a rapid scanning rate to “freeze” any time variations in the luminosity.
Noctilucent clouds: A steady‐state model
A simple model of a noctilucent cloud is developed leading to requirements for a steady-state cloud. The sizes achieved by particles falling through a supersaturated layer and the mass budget of the cloud are considered. The necessity of an updraught to explain the persistence of the clouds is discussed.