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Ann. Geophys., 25, 1767-1778, 2007
www.ann-geophys.net/25/1767/2007/
© European Geosciences Union 2007
The quasi-two-day wave studied using the Northern Hemisphere SuperDARN HF radars
S. B. Malinga1,* and J. M. Ruohoniemi2
1School of Physics, University of KwaZulu-Natal, Durban 4000, South Africa
2The Johns Hopkins University Applied Physics Laboratory, Laurel, MD20723, USA
*now at: Hermanus Magnetic Observatory, PO Box 32, Hermanus, 7200, South Africa
Abstract. Data from the Super Dual Radar Network (SuperDARN) radars for 2002 were used
to study the behaviour of the quasi-two-day wave (QTDW) in the Northern
Hemisphere auroral zone. The period of the QTDW is observed to vary in the
range of ~42–56 h, with the most dominant period being ~48 h and
secondary peaks at ~42- and ~52-h. The spectral power shows a
seasonal variation with a peak power (max~70) in summer. The power
shows variations of several days and there is also evidence of changes in
wave strength with longitude. The 42-h and the 48-h components tend to be
strongly correlated in summer. The onset of enhanced wave activity tends to
coincide with the westward acceleration of the zonal mean flow and occurs at
a time of strong southward meridional flow. The most frequent instantaneous
hourly period is in the 40 to 50 h period band, in line with the simultaneous
dominance of the 42-h and the 48-h components. The wave numbers are less
variable and are around −2 to −4 during times of strong wave activity. For a
period of ~48 h, the zonal wave number is about −3 to −4, using a negative
value to indicate westward propagating waves. The 42-h and the 52-h
components cover a wider band in the −4 to 1 range. The wide zonal
wave number spectrum in our results may account for the observed longitudinal
variation in the spectral power of the wave.
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