Equatorial spread F-related airglow depletions at Arecibo and conjugate observations

We present evidence of the incursion into the Caribbean region of airglow depletions associated with the equatorial Rayleigh-Taylor instability. Data from the Boston University all-sky imager located at Arecibo, Puerto Rico (18.3 degrees N, 66.7 degrees W, 28 degrees N magnetic latitude), have been used to identify several nights with 630.0 nm airglow patterns that are typical signatures of equatorial spread F and distinctly different from the more common `airglow bands'' frequently observed there. Two case studies (2 November 2002 and 26 February 2003) show the occurrence of simultaneous airglow depletions observed with another all-sky imager located at El Leoncito, Argentina (31.8 degrees S, 69.3 degrees W, 18 degrees S magnetic latitude), relatively close to the Arecibo conjugate point. Supporting information is obtained from Defense Meteorological Satellite Program, ROCSAT-1, and GPS data, all of them showing the presence of strong ionospheric irregularities collocated with the airglow depletions. Mapping the circular field of view from Arecibo into the Southern Hemisphere reveals a distorted pattern due to the differences in the magnetic field characteristics in both hemispheres. This adds an interesting spatial complexity to the formulation of conjugate point observing programs in the Latin American longitude sector.