A level of temperatures at which exhaust trails must occur even if the ambient air is completely dry. This flight level is determined with the help of a chart called a tephigram. A tephigram is an aerological map on which temperatures and potential temperatures are marked along x and Y-axes, respectively and are used to ascertain the stability of atmosphere. The chart is prepared by a meteorologist. DRYTRA is expressed as flight level. See also tephigram.
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