East, Sally Anne; (1993) The investigation of noctilucent clouds and other mesospheric phenomena using ground-based instrumentation and rockets. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The optical and dynamical properties of the summer phenomena known as Noctilucent Clouds (NLC) have been studied globally since the early 1960s. These clouds only occur naturally in the Earth's mesosphere, and are presently studied using remote sensing from rockets, and satellites in addition to ground-based observations. Direct evidence of the topology, and structure of an aerosol layer, such as a NLC can be achieved using non-imaging photodiode/photometers housed on a rocket payload. The APL designed photometers utilize the spin of the rocket payload, therefore scanning the entire sky laterally, and producing a two- dimensional image of the aerosol layer traversed during the upleg and downleg flights. The APL photodiode/photometers were flown during the MAED (Middle Atmospheric ElectroDynamics) and NLC-91 (NoctiLucent Clouds 1991) summer rocket campaigns respectively. These multinational rocket campaigns were coordinated with ground-based and satellite observations. The resultant APL data provides a complementary data source to be compared and contrasted with other rocket experiments flown during the absence/presence of NLC and/or PMSE (Polar Mesospheric Summer Echoes). A Bomem Michelson Interferometer (MI) was stationed in Sweden during the summer rocket campaign, NLC-91 provided measurements of the hydroxyl (3,1) band emission from a layer positioned ~87 km. The presented data were kindly provided by the Space Dynamics Laboratory, Utah State University; analyzed and interpreted by the author. The data gave a measure of the upper mesospheric conditions during the presence and absence of NLC during the rocket campaign. The interpretation of the raw data gave an indication of stratospheric filtering of upward propagating waves whose diminution could produce the upward forcing that may be involved in the NLC formation processes. Intensity and rotational temperature profiles deduced during the absence/presence of NLC gave clear results of small- and large-scale waves, and possible correlation between the hydroxyl intensity, and mesopausal temperature. A ground-based Imaging Fabry-Perot Interferometer (IFPI) stationed at the Bear Lake Observatory (BLO), Utah, (41.93°N, 111.42°W) has been operated, since 1989, to study the behaviour of the mesospheric winds at mid-latitudes deduced from the measurements of intensity, and wind speeds of the 8430 Å hydroxyl (6,2) band. The results presented have been studied during the summer periods from this site. This IFPI has provided an opportunity of observing this weak infra-red emission line, and provides a continuous monitoring of the mesopause region throughout the year. A comparison of characteristics on a night by night basis of hydroxyl intensity variations, and wind speed structure, and variations from the mid-latitude IFPI (BLO) with intensity fluctuations indicated by the Bomem MI as being associated with the absence/presence of NLC at summer high latitudes.

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