Five-day planetary waves in the middle atmosphere from Odin satellite data and ground-based instruments in Northern Hemisphere summer 2003, 2004, 2005 and 2007

摘要

A number of studies have shown that 5-day planetary waves modulatenoctilucent clouds and the closely related Polar Mesosphere Summer Echoes(PMSE) at the summer mesopause. Summer stratospheric winds should inhibitwave propagation through the stratosphere and, although some numericalmodels (Geisler and Dickinson, 1976) do show a possibility for upward wavepropagation, it has also been suggested that the upward propagation may inpractice be confined to the winter hemisphere with horizontal propagation ofthe wave from the winter to the summer hemisphere at mesosphere heightscausing the effects observed at the summer mesopause. It has further beenproposed (Garcia et al., 2005) that 5-day planetary waves observed in thesummer mesosphere could be excited in-situ by baroclinic instability in theupper mesosphere. In this study, we first extract and analyze 5-dayplanetary wave characteristics on a global scale in the middle atmosphere(up to 54 km in temperature, and up to 68 km in ozone concentration) usingmeasurements by the Odin satellite for selected days during northernhemisphere summer from 2003, 2004, 2005 and 2007. Second, we show that 5-daytemperature fluctuations consistent with westward-traveling 5-day waves arepresent at the summer mesopause, using local ground-based meteor-radarobservations. Finally we examine whether any of three possible sources ofthe detected temperature fluctuations at the summer mesopause can beexcluded: upward propagation from the stratosphere in the summer-hemisphere,horizontal propagation from the winter-hemisphere or in-situ excitation as aresult of the baroclinic instability. We find that in one case, far fromsolstice, the baroclinic instability is unlikely to be involved. In onefurther case, close to solstice, upward propagation in the same hemisphereseems to be ruled out. In all other cases, all or any of the three proposedmechanisms are consistent with the observations.