Planetary wave seasonality from meteor wind measurements at 7.4° S and 22.7° S

摘要

In this study we have used wind observation data from the mesosphere and lowerthermosphere (MLT) region, obtained from meteor radar measurements in SãoJoão do Cariri (7.4° S, 36.5° W) from July 2004 toDecember 2008 and in Cachoeira Paulista (22.7° S,45.0° W) from January 2002 to July 2006 and from September 2007 toNovember 2008. From the spectral analysis it was possible to identify thepresence of planetary-scale oscillations in the hourly winds for the twolatitudes and to study their transient character, which allowed elaborationof a climatology of planetary oscillation signatures. Planetary waves withperiods near 2-days, 6–7 days, and 16 days were focussed on in this study. Thequasi-2-day waves in the meteoric winds showed a seasonal cycle, with intenseamplitudes occurring after the austral summer solstice and extending untilthe end of the season. The vertical wavelengths of the 2-day wave overCachoeira Paulista were larger than those at São João do Cariri. Apossible modulation of the quasi-2-day wave amplitudes by the quasi-biennial oscillation (QBO) has beenobserved only at São João do Cariri. The 6–7 day oscillationspresented more intense amplitudes during August–November but were presentwith lower amplitudes during March–April at both sites. The 6–7 day verticalwavelengths over São João do Cariri were larger than at CachoeiraPaulista. The 6–7 day amplitudes exhibited intra-seasonal and annualbehavior, however, there was no clear evidence of QBO modulation. The 16-dayoscillations showed a seasonal cycle at São João do Cariri, withamplifications from austral spring to mid-summer and weaker amplitudes fromautumn until early winter, however, there was no clear seasonality over CachoeiraPaulista. The 16-day vertical wavelengths have assumed values of λ ~ 45–85 km over both sites. 16-day wave amplitudes at the two sitesshowed different long-term behaviors.