A temporal interpolation method to obtain hourly atmospheric surface pressure tides in Reanalysis 1979–1995

Abstract

Abstract.The diurnal cycle in climatology as revealed in National Centers for Environmental Prediction's Reanalysis 1979-1995 has been studied for global gridded data at 0000, 0600, 1200 and 1800 UT. Climatologies have been prepared for each of the fol time levels separately. There are substantial differences in, for instance, the 00002red 0600 UT climatologies, owing to a diurnal cycle and/or what is referred to commonly as atmospheric tides. The semidiurnal tide is quite strong in the mass fields, but with sampling every 6 hours at the Nyquist frequency, some aspects cannot be studied properly. However, a method of interpolation based on spatial harmonic waves moving at an empirically determined speed can be called upon to make an educated guess about the atmospheric tides at any times in between. This interpolation technique is similar to the one published by Van den Dool and Qin [1996], but the wave speeds are not like the slow Rossby modes but roughly 15 ø westward per hour. We present the global tides in surface pressure thus obtained for every hour of the day for January.

Barometric tides from ECMWF operational analyses

“…Tidal harmonic analyses of hourly barometric measurements, taken at a large number of globally distributed stations, can be spatially interpolated (optimally or otherwise) to yield globally gridded fields. More recently, estimates based on general circulation models (Zwiers and Hamilton, 1986;Madden et al, 1998) and on analyses produced by weather centers (Hsu and Hoskins, 1989; Van den Dool et al, 1997;Ray, 2001) have also been examined. The latter products are of special interest because they are based on "optimal" estimates of the state of the atmosphere arrived at through advanced modeling and data assimilation techniques.…”

“…Comparisons of global barometric tides, derived from the available gridded analyses with the meteorological station data provide a useful test of the analyzed fields and also the interpolation methods (Van den Dool et al, 1997). Ray (2001) examined S 2 (p) in the reanalyses of the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR), as interpolated by Van den Dool et al (1997), and the NASA Goddard Earth Observing System (GEOS-1), for which 3-h fields were available and no interpolation was required.…”

“…Gridded analysis fields have a typical 6-hour sampling interval, however, which leads to S 2 solutions that are standing waves, rather than westward propagating, and with much underestimated amplitudes near longitudes where sampling times happen to coincide with times of the S 2 nodes. Temporal interpolation methods can be used to recover the fully propagating S 2 tide (Van den Dool et al, 1997), but their general usefulness remains to be tested.…”

“…Ray (2001) examined S 2 (p) in the reanalyses of the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR), as interpolated by Van den Dool et al (1997), and the NASA Goddard Earth Observing System (GEOS-1), for which 3-h fields were available and no interpolation was required. Comparisons with data revealed significant inadequacies in the representa-tion of S 2 (p) in both reanalyses (Ray, 2001).…”

“…The solar diurnal and semidiurnal tidal oscillations in surface pressure are extracted from the operational analysis product of the European Centre for Medium Range Weather Forecasting (ECMWF). For the semidiurnal tide this involves a special temporal interpolation, following Van den Dool et al (1997). The resulting tides are compared with a "ground truth" tide data set, a compilation of welldetermined tide estimates deduced from many long time series of station barometer measurements.…”