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Vial/Forbes Lunar Semidiurnal Tides


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Description of Instrument/Model

These are model lunar semidiurnal tides calculated in the Earth's atmosphere. The lunar day is 24 hr 50.47 min. The phases vary between 0.00 and 12.00 hours in lunar time, where 0 lunar time refers to the time of lower transit. This is when the moon is 180 degrees opposite one's position on Earth, and is entirely analogous to solar local time. The calculations were done for each month, where the day assumed was the 15th of each month. The results are independent of solar cycle, so the year is arbitrary. The year 1993 was chosen because this was the year that the model runs were made. The semidiurnal amplitudes and phases of the eastward neutral wind, the northward neutral wind, the neutral temperature, and the geopotential are given for 12 altitudes between about 78 and 102 km. The altitudes are slightly for each month. The original results were southward winds, so the phases were shifted by 6 hours to make them northward. The maximum amplitudes are just below 20 m/s for the winds, about 6 degrees K for the temperature, and nearly 2500 m2/s2 in geopotential. Some temperature amplitudes are shown as 0 near the pole but with some phase. This is the result of truncating amplitudes less than 0.005 K.

The summary plots show the amplitudes of the semidiurnal lunar tides in the eastward wind, the northward wind, the neutral temperature, and the geopotential.


Vial F. and J. M. Forbes, Monthly simulations of the lunar semidiurnal tide, J. Atmos. Terr. Phys., 56, 1591-1607, 1994.

Summary Plots for the Vial/Forbes Semidiurnal Lunar Tides

Older semidiurnal solar tides

Newer semidiurnal solar tides

-Revised 19 May 2000 by Barbara Emery