The 16-day wave in the Arctic and Antarctic mesosphere and lower thermosphere

Abstract

Abstract. The 16-day planetary wave in the polar mesosphere and lower thermosphere has been investigated using meteor radars at Esrange (68 • N, 21 • E) in the Arctic and Rothera (68 • S, 68 • W) in the Antarctic. The measurements span the 10-year interval from October 1999 to July 2009 and the 5-year interval February 2005 to July 2009, respectively. The height range covered is about 80-100 km. In both polar regions the wave is seen to occur in intermittent bursts, where wave amplitudes typically reach a maximum of about 15 m s −1 , and never more than about 20 m s −1 . Horizontal wind variance within a wave-period range of 12 to 20 days is used as a proxy for the activity of the 16-day wave. Wave activity is strong for 3 to 4 months in winter, where it is present across the entire height range observed and monthly wave variance reaches about 65 m 2 s −2 . Some weak and intermittent activity is observed throughout the other seasons including summer. However, there is a high degree of inter-annual variability and in some individual years wave activity is almost absent. The data are used to construct a representative climatology for the Arctic and Antarctic. The seasonal cycle of the 16-day wave is found to be very similar in both polar regions. The 16-day wave has slightly greater amplitudes in the zonal component of the winds than in the meridional. Mesospheric temperatures measured by the radars were used to further investigate the 16-day wave. The temperatures reveal a clear signature of the 16-day wave. Temperature amplitudes are generally only a few Kelvin but occasional bursts of up to 10 K have been observed. Observations of the wave in summer are sometimes consistent with the suggestion of ducting from the winter hemisphere.

Aura MLS observations of the westward-propagating <i>s</i>=1, 16-day planetary wave in the stratosphere, mesosphere and lower thermosphere

“…This range of periods has also been used in the majority of studies of the 16-day wave, (e.g. Forbes et al, 1995;Miyoshi, 1999;Luo et al, 2002a;Jiang et al, 2005;Lima et al, 2006;Day and Mitchell, 2010). Our results should thus be directly comparable with these other studies.…”

“…∼4 K in the Southern Hemisphere. The tendency for wave amplitudes to decrease at heights above ∼80 km was also reported in the radar studies of the polar MLT 16-day wave by Day and Mitchell (2010).…”

“…Williams and Avery, 1992;Luo et al, 2002b;Hibbins et al, 2009;Day and Mitchell, 2010). These studies have also revealed a winter-time maximum in wave amplitudes and a weaker secondary maximum in summer.…”

“…Ground based studies include e.g. Williams and Avery (1992); Espy and Witt (1996); Jacobi (1998); Mitchell et al (1999);Luo et al (2000Luo et al ( , 2002a; Hibbins et al (2009);Day and Mitchell (2010). Only some of these studies measured temperatures, including Espy and Witt (1996) and Espy et al (1997) who used a Michelson interferometer to measure OH rotational temperatures near the mesopause over Stockholm (60 • N).…”

“…The wave has been reported to have wind amplitudes of up to about ∼15 m s −1 and temperature amplitudes reaching ∼10 K in the MLT (e.g. Williams and Avery, 1992;Forbes et al, 1995;Day and Mitchell, 2010).…”