A TEMPORAL INTERPOLATION METHOD TO OBTAIN HOURLY ATMOSPHERIC SURFACE PRESSURE TIDES IN REANALYSIS 1979-1995

The diurnal cycle in climatology as revealed in National Centers for E nvironmental Prediction's Reanalysis 1979-1995 has been studied for gl obal gridded data at 0000, 0600, 1200 and 1800 UT. Climatologies have been prepared for each of the four time levels separately. There are s ubstantial differences in, for instance, the 0000(2) and 0600 UT clima tologies, owing to a diurnal cycle and/or what is referred to commonly as atmospheric tides. The semidiurnal tide is quite strong in the mas s fields, but with sampling every 6 hours at the Nyquist frequency, so me aspects cannot be studied properly. However, a method of interpolat ion based on spatial harmonic waves moving at an empirically determine d speed can be called upon to make an educated guess about the atmosph eric tides at any times in between. This interpolation technique is si milar to the one published by Van den Dool and Qin [1996], but the wav e speeds are not like the slow Rossby modes but roughly 15 degrees wes tward per hour. We present the global tides in surface pressure thus o btained for every hour of the day for January.