CEDAR: ALOHA/ANLC-93; Airglow Imaging Studies

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This proposal involves the study of atmospheric airglow and noctilucent clouds (ANLCs) with a wide field imager from the NCAR Electra aircraft for the ALOHA/ANLC-93 campaign. The imager will provide correlative data to the campaign which includes lidar, radar, and spectroscopic information from the Upper Mesosphere- Lower Thermosphere region. The basic campaign objectives are to locate and study the geophysical conditions associated with ANLCs, gravity wave dynamics, and sporadic Na layers. In addition to providing an observational contribution to these team goals, a specific study of the horizontal attributes of gravity waves resolved from these data will be performed and compared to an existing data set which was taken over a 7 month period in 1991-92 at Bear Lake, UT with the same instrument that is proposed here. Lockheed has developed and successfully demonstrated in several ground based campaigns, a sensitive, bare CCD imager capable of measuring OH, O2, Na, and OI nightglows with high signal to noise ratios. In particular, OH imaging using broad band techniques (7500-9300 >), have produced 50:1 S:N with 60 s exposures using .35o pixels (>.5 km resolution overhead) with all- sky optics. With this sensitivity, airglow intensity amplitudes on the order of a few percent have been observed. The array is a 1024 X 1024 (15.4mm X 15.4mm) which is >4x larger than the commercially available arrays used in aeronomical studies to date. The system uses commercial electronics (including a computer) which are rugged and stable for the aircraft environment. Coordination has been made with NCAR to install an all-sky dome on the aircraft to accommodate the all-sky field. Aircraft pitch and roll stability have been investigated to suggest that, for typical flight conditions, angular resolutions of >.5o over 30 seconds can be achieved. The wide field camera will be used to (1) document irregularities in the OH airglow layer which are caused by atmospheric gravity waves and tides affecting the layer for flight segments where the Solar Elevation Angle (SEA)-10o (which is the condition for most flight paths for the campaign); (2) image solar scattered illumination of noctilucent clouds where -6oSEA-8o for the ANLC phase; and (3) image the Na 'sodium flash' at SEA>-6.5o in support of the study of sporadic Na layers. Observations (2) and (3) are feasible on the two planned flights north into the polar cap. With the OH imagery, the horizontal wavelength, intensity amplitude, apparent horizontal phase velocity, and spatial extent (up to 500 km radius of the aircraft), will be studied in objective (1). Spectral density analysis will be performed on imagery to resolve the horizontal gravity wave information. In the ANLC campaign,m observations of the clouds will be attempted to provide information of ANLC's location. From Na 'flash' imagery, the Na density will be inverted from the image. For a very specific location (i.e. SEA>-6.5o) the Na column density will be derived from the image for an assumed constant solar illumination of the layer.