New optical experiments for studying equatorial irregularities
Jonathan J. Makela1, John W. Meriwether2, Ethan S. Miller1, Shaun J. Armstrong1
A new narrowfield imaging system, the Portable Ionospheric Camera and Small Scale Observatory (PICASSO), was installed at the Cerro Tololo Inter-American Observatory (geographic: 30.17 S, 289.19 E; geomagnetic 16.72 S, 0.42 E) near La Sarena, Chile in August 2006. The imaging system, pointed towards the northern horizon, obtains high-resolution images of the ionosphere through the observation of the 630.0- and 777.4-nm emissions and provides excellent data on the spatio-temporal development of equatorial plasma bubbles (EPBs) associated with equatorial spread-F. The wide field-of-view in the longitudinal direction of approximately 2000 km at F-layer altitudes allows the simultaneous observation of multiple EPBs as they drift through the field of view, from which we can deduce the inter-bubble spacing which should be related to the underlying seeding mechanism. In addition, we present examples on how the images obtained from the southern hemisphere can be used with corollary instruments in the conjugate hemisphere to deduce additional properties of equatorial irregularities, such as the altitude of the scattering layer.
Another new experiment is being set up in the African sector as part of the International Heliospherical Year (IHY). The Remote Equatorial Nighttime Observatory of Ionospheric Regions (RENOIR) consists of two different types of optical instruments, a wide-angle version of the PICASSO imaging system installed in Chile, and two miniaturized Fabry-Perot Interferometers (MiniME). The wide-field imaging system will be used to characterize the two-dimensional (latitude vs longitude) structure of the depletions. This will be done by measuring the natural emissions occurring in the ionosphere at wavelengths of 630.0 and 777.4 nm. The two FPI systems will be used to measure the background thermospheric neutral winds and the neutral temperature. From the FPI data, we will be able to deduce what, if any, control neutral dynamics have on the development of these irregularities. Two systems are included so we can field them at sites separated by several hundreds of kilometers in order to study wind gradients and gravity waves known to be present in the thermosphere. The instruments will enable studying thermosphere-ionosphere coupling during the passage of EPBs as well as the effects of the background neutral wind field on the development of EPBs. We present results from the two MiniME systems during their pre-deployment testing phase and discuss the technique developed for analyzing the multiple orders obtained from the MiniMEs.