Abstract
Abstract. In an earlier paper (Manson et al., 1999a) tidal data (1990–1997) from six Medium Frequency Radars (MFR) were compared with the Global Scale Wave Model (GSWM, original 1995 version). The radars are located between the equator and high northern latitudes: Christmas Island (2° N), Hawaii (22° N), Urbana (40° N), London (43° N), Saskatoon (52° N) and Tromsø (70° N). Common harmonic analysis was applied, to ensure consistency of amplitudes and phases in the 75–95 km height range. For the diurnal tide, seasonal agreements between observations and model were excellent while for the semi-diurnal tide the seasonal transitions between clear solstitial states were less well captured by the model. Here the data set is increased by the addition of two locations in the Pacific-North American sector: Yamagawa 31° N, and Wakkanai 45° N. The GSWM model has undergone two additional developments (1998, 2000) to include an improved gravity wave (GW) stress parameterization, background winds from UARS systems and monthly tidal forcing for better characterization of seasonal change. The other model, the Canadian Middle Atmosphere Model (CMAM) which is a General Circulation Model, provides internally generated forcing (due to ozone and water vapour) for the tides. The two GSWM versions show distinct differences, with the 2000 version being either closer to, or further away from, the observations than the original 1995 version. CMAM provides results dependent upon the GW parameterization scheme inserted, but one of the schemes provides very useful tides, especially for the semi-diurnal component.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)
Highlights
The study of atmospheric tides in the middle atmosphere (MA) is important for a variety of reasons
The following brief description gives the highlights of amplitudes, and phases for the solar semi-diurnal and diur- GSWM2000 in so far as it differs from the other model nal tides for 7 Medium Frequency Radars (MFR) locations
It should be noted that very thorough comparisons exist between winds and tides measured by the MFR and other ground based systems: MWR (Meteor Wind Radar) and MFR radars at 40◦ N (Hocking and Thayaparan, 1997); MFR and Fabry-Perot Interferometers (“green line” and hydroxyl) at 52◦ N (Manson et al, 1996; Meek et al, 1997); and MFR, EISCAT (European Incoherent Scatter) and VHF radars (Manson et al, 1992) at 70◦ N
Summary
The study of atmospheric tides in the middle atmosphere (MA) is important for a variety of reasons. Tidal structures in the MA are extremely complex, so that successful modelling requires the understanding of a wide range of atmospheric phenomena, including radiational, chemical and dynamical These include the distribution of ozone and water vapour in height, season and planetary location; the background winds and mean temperatures; molecular and eddy diffusivity; and gravity wave stress and Newtonian cooling effects. The following brief description gives the highlights of amplitudes, and phases for the solar semi-diurnal and diur- GSWM2000 in so far as it differs from the other model nal tides for 7 MFR locations These were compared with used, GSWM (originated in 1995). It will be interesting here to compare solstices (Hagan et al, 1999) The latter are very close to the CMAM tides with a larger MFR data set
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