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Ann. Geophys., 20, 679-690, 2002
www.ann-geophys.net/20/679/2002/
© European Geosciences Union 2002
MF radar observations of mean winds and tides over Poker Flat, Alaska (65.1° N, 147.5° W)
P. Kishore1, S. P. Namboothiri1, K. Igarashi1, Y. Murayama1, and B. J. Watkins2
1Communications Research Laboratory, Tokyo, Japan
2Geophysical Institute, Univ. of Alaska, Fairbanks, Alaska, USA
Correspondence to: S. P. Namboothiri
(nambooth@crl.go.jp)
Abstract. MF radar wind
measurements in the mesosphere and lower thermosphere over Poker Flat, Alaska
(65.1° N, 147.5° W) are used to study the features of mean winds and solar
tides. Continuous observation with the newly installed radar is in progress and
in the present study we have analyzed a database of the first 27 months
(October 1998–December 2000) of observation. The observed mean wind
climatology has been compared with previous measurements and the latest
empirical model values (HWM93 model). Similarly, the tidal characteristics are
described and compared with the Global Scale Wave Model (GSWM00).
The mean wind characteristics observed are fairly consistent
with previous wind measurements by the Poker Flat MST radar. The main feature
of the zonal circulation is the annual variation with summer westward flow and
winter eastward flow. The annual mean zonal wind has a west-ward motion at
altitudes below 90 km. The annual mean meridional circulation has mainly
southward motion at 70–100 km. There is very good agreement between the radar
zonal winds and the HWM93 model winds. Comparison of the meridional winds shows
some discrepancy. Analysis of two years of data indicated that the year-to-year
consistency is preserved in the mean circulation in the mesosphere.
Tidal characteristics observed are also consistent with
previous measurements. Semidiurnal tides have the largest amplitudes in summer
while the weakest amplitude is observed during the winter months. The vertical
wavelength is longer during the summer season compared to the winter season.
Comparison with the GSWM00 produces mixed results. There is reasonable
agreement between the observed and modeled phases. Diurnal tide amplitudes are
comparable in magnitude with that of the semidiurnal tide. Seasonal variation
is less evident in the amplitudes. Comparison of the observed tidal parameters
with the GSWM00 reveals some agreement and discrepancies.
Key words. Meteorology and
atmospheric dynamics (climatology; middle atmosphere dynamics; waves and tides)
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