Abstract.A number of studies have shown that 5-day planetary waves modulate noctilucent clouds and the closely related Polar Mesosphere Summer Echoes (PMSE) at the summer mesopause. Summer stratospheric winds should inhibit wave propagation through the stratosphere and, although some numerical models (Geisler and Dickinson, 1976) do show a possibility for upward wave propagation, it has also been suggested that the upward propagation may in practice be confined to the winter hemisphere with horizontal propagation of the wave from the winter to the summer hemisphere at mesosphere heights causing the effects observed at the summer mesopause. It has further been proposed (Garcia et al., 2005) that 5-day planetary waves observed in the summer mesosphere could be excited in-situ by baroclinic instability in the upper mesosphere. In this study, we first extract and analyze 5-day planetary wave characteristics on a global scale in the middle atmosphere (up to 54 km in temperature, and up to 68 km in ozone concentration) using measurements by the Odin satellite for selected days during northern hemisphere summer from 2003, 2004, 2005 and 2007. Second, we show that 5-day temperature fluctuations consistent with westward-traveling 5-day waves are present at the summer mesopause, using local ground-based meteor-radar observations. Finally we examine whether any of three possible sources of the detected temperature fluctuations at the summer mesopause can be excluded: upward propagation from the stratosphere in the summer-hemisphere, horizontal propagation from the winter-hemisphere or in-situ excitation as a result of the baroclinic instability. We find that in one case, far from solstice, the baroclinic instability is unlikely to be involved. In one further case, close to solstice, upward propCorrespondence to: A. Belova (allab@irf.se) agation in the same hemisphere seems to be ruled out. In all other cases, all or any of the three proposed mechanisms are consistent with the observations.
Abstract. Temperature and ozone data from the submillimetre radiometer (SMR) installed aboard the Odin satellite have been examined to study the relationship between temperature and ozone concentration in the lower and upper stratosphere in winter time. The retrieved ozone and temperature profiles have been considered between the range of 24-46 km during the Northern Hemisphere (NH) winter of December 2002 to March 2003 and January to March 2005. A comparison between the ozone mixing ratio and temperature fields has been made for the zonal means, wavenumber one variations and 5-day planetary waves. The amplitude values in temperature variations are ∼5 K in the wavenumber one and 0.5-1 K in the 5-day wave. In ozone mixing ratio, the amplitudes reach ∼0.5 ppmv in the wavenumber one and 0.05-0.1 ppmv in the 5-day wave.Several stratospheric warming events were observed during the NH winters of 2002/2003 and early 2005. Along with these warming events, amplification of the amplitude has been detected in wavenumber one (up to 30 K in temperature and 1.25 ppmv in ozone) and partly in the 5-day perturbation (up to 2 K in temperature and 0.2 ppmv in ozone).In general, the results show the expected in-phase behavior between the temperature and ozone fields in the lower stratosphere due to dynamic effects, and an out-of-phase pattern in the upper stratosphere, which is expected as a result of photochemical effects. However, these relationships are not valid for zonal means and wavenumber one components when the wave amplitudes are changing dramatically during the strongest stratospheric warming event (at the end of December 2002/beginning of January 2003). Also, for several shorter intervals, the 5-day perturbations in ozone and temperature are not well-correlated at lower heights, particularly when conditions change rapidly. Good agreement between the temperature fields from Odin and ECMWF data is found at middle latitude where, in general, the 5-day perturbations from the two data sets coincide in both phase and amplitude throughout the examined interval. Analysis of the wavenumber one and the 5-day wave perturbations in temperature and ozone fields from Odin and from Aura demonstrates that, for the largest part of the examined period, quite similar characteristics are found in the spatial and temporal domain, with slightly larger amplitude values seen by Aura. Hence, the comparison between the Odin data, sampled each third day, and daily data from Aura and the ECMWF shows that the Odin data are sufficiently reliable to estimate the properties of the 5-day oscillations, at least for the locations and time intervals with strong wave activity.
The sub-millimetre radiometer (SMR) on board the Odin satellite measures signatures of ozone in two bands centred at 501.8 and 544.6 GHz. From the measurements, ozone volume mixing ratio profiles in the stratosphere and lower mesosphere are retrieved using the Optimal Estimation Method. In this paper, the ozone profiles measured by Odin-SMR (level-2 data ver. 2.1 and 2.0, respectively) are compared to measurements taken by ground-based millimetre wave radiometers in the Arctic; at Kiruna, Sweden; in the mid-latitudes on the Zugspitze, Germany; and in the tropics at Mérida, Venezuela. The Kiruna Microwave Radiometer (KIMRA) covers the frequency range 195-224 GHz, and the Millimeter Wave Radiometer MIRA 2, which was operated on the Zugspitze and at Mérida, measures in the frequency band 268-281 GHz. From the measurements, ozone profiles in the vertical range between approximately 15-65 km were retrieved using the Optimal Estimation Method. Since the ground-based measurements have a lower vertical resolution than those of Odin the latter were degraded using the averaging kernels of the ground-based retrievals. The comparison of the resulting profiles to the ground-based data enables the identification of biases in the Odin measurements and their possible latitudinal variation. In general, a good agreement between satellite and ground-based measurements for the 501.8 GHz band was found in the stratosphere except for a negative bias in the Odin data of about 10-15% in the tropical measurements. The Odin measurements taken at 544.9 GHz yielded systematically 20-30% lower ozone mixing ratios in the middle stratosphere than the ground-based measurements at all sites.
The signature of five-day planetary waves in ozone and temperature data from the advanced sub-millimeter radiometer aboard the Odin satellite is examined. The period January-March 2005 and heights from 24-56 km are used. We find highest wave amplitudes in both temperature and ozone in the winter hemisphere at 60 • N-70 • N. The relative phases between ozone and temperature perturbations show the expected antiphase behaviour in the photochemistrydominated region at about 40 km altitude. We compare the global planetary wave properties from Odin with five-day perturbations in ozone measured by the millimeter wave radiometer in Kiruna (KIMRA, 67 • 50 N, 20 • 24 E). In the early part of the comparison interval (January-February) at 40 km, we find good correlation between the two in terms of both phase and amplitude of the perturbations. In the latter part of the comparison interval (March) where mean ozone levels are higher, the amplitudes of the ozone five-day perturbations over Kiruna are much higher than the wave amplitudes found using Odin. We conclude that five-day variations in ozone due to planetary waves can be detected by KIMRA in some circumstances, but that other sources of variability dominate at other heights and times.Résumé : Nous étudions la signature d'ondes planétaires de 5 jours sur les données d'ozone et de température enregistrées par le radiomètre sous-millimétrique (SMR) embarqué à bord du satellite Odin. Nous utilisons la période entre janvier et mars 2005 à des altitudes de 24 à 56 km. Nous trouvons les ondes de plus grande amplitude pour la température et l'ozone dans l'hémisphère d'hiver entre 60 • N et 70 • N. Les phases relatives entre les perturbations d'ozone et de température montrent l'opposition de phase attendue dans la région dominée par la photochimie autour de 40 d'altitude. Nous comparons les propriétés ondulatoires planétaires obtenues des données de Odin avec les perturbations d'ozone telles que mesurées sur 5 jours par le radiomètre millimétrique Kiruna (KIMRA, 67 • 50 N, 20 • 24 E. Dans la première partie de la comparaison (janvier-février) à 40 km, nous trouvons une excellente corrélation entre les deux pour la phase et l'amplitude des perturbations. Dans la dernière partie de la comparaison (mars), lorsque les niveaux moyens d'ozone sont plus élevés, les amplitudes des perturbations sur 5 jours de l'ozone sont beaucoup plus grandes à Kiruna que celles observées par Odin. Nous en concluons que les variations d'ozone sur 5 jours dues aux ondes planétaires peuvent être détectées par KIMRA en certaines circonstances, mais que d'autres sources de variation dominent à d'autres altitudes et d'autres temps.[Traduit par la Rédaction]
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