Bearing in mind the limited width of the ITCZ in the area of AF447's demise, and given the considerable range (air to air) for a high altitude loitering Zephyr drone, it should be possible to keep the drone out of any nasty weather's harm's way (see below). For polar duty, the "out of season" lack of insolation could well be a downing discrepancy for any solar-powered winged beastie. So for high latitude on station polar radio-relay duties, a helium-filled solar-powered (and -thrusted) blimp may prove to be a better solution. This one
see link is capable of months on blimp-station at 60,000ft. Its solar panels can be on its sides.
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The ITCZ is a region of light winds, which lends it the name the doldrums. The convergence of the Southeast and Northeast Trade Winds, within the doldrums, creates a zone of Cumulus clouds and attendant shower activity. Cumulus clouds often build up to great heights. Aircraft reports have estimated tops of Cumulonimbus to be as high as 12,000 m. The ITCZ varies from 20 miles to as much as 300 miles in width, and typically has an undulating conformation.
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Seasonal Meandering of the ITCZ. We are interested in the ITCZ because, under certain circumstances, tropical depressions on the ITCZ intensify to hurricanes. It may seem puzzling that the ITCZ can produce cyclones, when the Coriolis force is at its weakest near the equator. The answer to this puzzle lies in the fact that the ITCZ is not stationary on the equator, but migrates north and south with the seasons. The ITCZ moves north during the high-sun season of the Northern Hemisphere, and south during the high-sun season in the Southern Hemisphere. These movements are not perfectly symmetrical above and below the equator, because of the influence of land masses, among other factors.
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from this link