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U index(Also called U figure.) The difference between consecutive daily mean values of the horizontal component of the geomagnetic field. Each value is derived from a 48-hour interval covering two GMT days and is assigned to the second day of the pair. The monthly U index, the mean of the daily values, is the most frequently used. See u index.
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u indexThe value  where U is the U index, A the magnetic co-latitude, and B the angle between the magnetic meridian and the horizontal component of the magnetic intensity. The annual and longer-period mean values of the u index exhibit one of the strongest solar-terrestrial relationships known.
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ubacThe shady (usually poleward, or north in the Northern Hemisphere) side of a mountain. The term originated and is most often used in reference to mountains in the Alps. It is characterized by a lower timber line and snow line than the sunny side (the adret).
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