It looks like fog — but it isn’t. The air blurs and bites. It crunches between the teeth, stings the eyes, and carries off blossoms barely opened. A strange, foreign smell of fine dust. Spirals of light debris twirl and waltz. Trees flail under a wind that doesn’t belong here.The Arabian desert has arrived — uninvited — in the second season, supposedly the mildest of the four, at least according to our schoolbooks, already contradicted by climate change. This yellow sky, these wild shifts in temperature, are the breath of the Rebe' al-Khali — the Empty Quarter — which, on the fiftieth day of spring, sends a gust from its distant dunes to sweep across our shores.Khamsin, Arabic for “fifty.” Farther north, its twin rises from Africa’s great voids — the sirocco, or chergui, slow and humid, heavy and oppressive. Its melancholic veil...