Nonmigrating tidal variability in the SABER/TIMED mesospheric ozone
2014; American Geophysical Union; Volume: 41; Issue: 11 Linguagem: Inglês
10.1002/2014gl059844
ISSN1944-8007
AutoresD. Pancheva, P. Mukhtarov, Anne K. Smith,
Tópico(s)Solar and Space Plasma Dynamics
ResumoGeophysical Research LettersVolume 41, Issue 11 p. 4059-4067 Research LetterFree Access Nonmigrating tidal variability in the SABER/TIMED mesospheric ozone D. Pancheva, Corresponding Author D. Pancheva National Institute of Geophysics, Geodesy and Geography, Bulgarian Academy of Sciences, Sofia, Bulgaria Correspondence to: D. Pancheva, [email protected]Search for more papers by this authorP. Mukhtarov, P. Mukhtarov National Institute of Geophysics, Geodesy and Geography, Bulgarian Academy of Sciences, Sofia, BulgariaSearch for more papers by this authorA. K. Smith, A. K. Smith Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USASearch for more papers by this author D. Pancheva, Corresponding Author D. Pancheva National Institute of Geophysics, Geodesy and Geography, Bulgarian Academy of Sciences, Sofia, Bulgaria Correspondence to: D. Pancheva, [email protected]Search for more papers by this authorP. Mukhtarov, P. Mukhtarov National Institute of Geophysics, Geodesy and Geography, Bulgarian Academy of Sciences, Sofia, BulgariaSearch for more papers by this authorA. K. Smith, A. K. Smith Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USASearch for more papers by this author First published: 16 May 2014 https://doi.org/10.1002/2014GL059844Citations: 7AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Abstract This paper presents for the first time evidence showing nonmigrating tidal variations in the mesospheric ozone (O3) derived from the Sounding of the Atmosphere using Broadband Emission Radiometry/Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (SABER/TIMED) for a full 11 year period, 2002–2012. The O3 tidal fields are extracted from the data by the same method as the temperature tides have been derived. The spatial distribution and seasonal variability of the three strongest nonmigrating O3 tidal variabilities, i.e., SW3, DW2, and DE3, are shown. They demonstrate repeatable presence each year. These O3 tidal variations have large amplitudes at the seasons and latitudes for which the respective temperature (T) tides amplify, i.e., near the equator and during the equinoxes. The phases of the T and O3 tidal signatures are out of phase above 95 km. This phase relationship no longer holds for tidal perturbations below about 90 km. The O3 SW3 and DW2 tidal variations have similar interannual variabilities that appear to follow El Niño–Southern Oscillation variability. The O3 DE3 tidal field, however, has a clear biyearly interannual variability as the biyearly maxima correlate with the westerly phase of the quasi-biennial oscillation in tropical stratospheric winds but only up to 2008. Key Points Evidence of nonmigrating tidal variations of mesospheric O3 is presented The strongest nonmigrating O3 tidal variations are SW3, DW2, and DE3 Phases of T and O3 tidal signatures are out of phase above 95 km 1 Introduction Understanding the global spatial distribution and temporal variability of mesospheric ozone provides important information on the photochemistry, dynamics, and energetics of the Earth's middle atmosphere. It is known that ozone is an effective absorber of ultraviolet radiation and reacts exothermically with several species including atomic oxygen and hydrogen [Mlynczak and Solomon, 1993]. In this way knowledge of ozone improves understanding of the energy balance in the mesosphere and lower thermosphere (MLT) region. Ozone density is affected by atmospheric motions, and so ozone can be used also as a tracer of the MLT dynamics [Marsh et al., 2002]. The presence of a maximum in ozone density and mixing ratio in the upper mesosphere and lower thermosphere (MLT) region has been known for several decades. It is known as the secondary ozone maximum in comparison with the original ozone maximum in the stratosphere. The set of chemical reactions producing and destroying ozone (O3) is fairly simple. From the photochemistry there is a single production term for O3, which is the three-body associative reaction between molecular oxygen (O2) and atomic oxygen (O). There are several kinetic reactions and one photolytic reaction that destroy O3. The kinetic reactions that play a significant role in the vicinity of the second ozone maximum are those of O3 with O and with atomic hydrogen (H). The photochemical reactions of ozone with hydrogen and oxygen species cause significant reduction in the odd oxygen (O and O3) concentration from the stratopause to the mesopause [Bates and Nicolet, 1950]. Near the mesopause, however, the photolysis of O2 in the Schumann-Runge bands produces large amounts of odd oxygen, which produces an ozone maximum despite the loss due to chemical reactions involving hydrogen. Smith and Marsh [2005] by using the three-dimensional ROSE dynamical-chemical model found that the secondary ozone layer is formed in the vicinity of the O density maximum. The low temperatures in the mesopause are very important for defining the magnitude of the O3 maximum because they accelerate the formation of ozone and inhibit the loss. The locations of both the mesopause and the O density maximum contribute to defining the altitude of the O3 layer. Smith and Marsh [2005] also found that the magnitude of the nighttime O3 maximum is sensitive to the eddy and molecular diffusion rates primarily through the influence of these processes on the H concentration. While eddy diffusion acts to decrease O3 by bringing water (the source of H) up from below the molecular diffusion acts to increase it by moving H upward out of the MLT region. It is known that O3 variability in the upper mesosphere is dominated by its diurnal cycle which changes between low density during daytime and high density during nighttime. The photolytic destruction rate is extremely fast (from a few seconds to a few minutes) for O3, which is optically thin in the upper mesosphere. The nighttime chemical lifetime is about an order of magnitude longer, i.e., about 30 min at ~100 km [Smith et al., 2011]. Although photochemical considerations alone explain the dominant diurnal cycle of O3, the contributions from the large-amplitude atmospheric tides in the MLT region cannot be ignored. At low latitudes the temperature amplitudes of the monthly mean migrating diurnal tide can reach up to ~25–27 K [Mukhtarov et al., 2009], and they show clear semiannual variability with equinoctial amplifications. These temperature variations significantly affect the O3 variability through the temperature dependence of O3 chemical reactions. Additionally, the number density on a pressure surface which also affects the O3 mixing ratio [Smith et al., 2008, 2011] increases with decreasing temperature according to the ideal gas law. Since the lifetime of O3 in the MLT is short during both day and night, direct transport of O3 by atmospheric tides can be ignored. The lifetime of O, however, is long; above 85 km height it changes from weeks to months. Smith et al. [2010] found that the diurnal cycle of O in the upper mesosphere is driven by the diurnal tide. Near the equator, where the tidal vertical winds are largest, the O transport in the vertical direction can be substantial. The magnitude of the O changes due to the tidal transport can exceed an order of magnitude in the period near the vernal equinox when the amplitude of the migrating diurnal tide is the largest. As the O3 distribution is closely tied up to that of O, then this tidal transport will impact significantly the low-latitude O3 variability as well. Recent studies based on the observations made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) satellite have provided new insight into physical processes that control the variability of the secondary O3 maximum. Smith et al. [2008] reported on high O3 mixing ratios in the nighttime mesopause, even over 20 ppmv (parts per million by volume), observed in SABER O3 measurements. The highest O3 mixing ratios are clustered near the equator during equinoxes. They used a simplified model of the migrating diurnal tide to demonstrate that the high nighttime O3 values are observed in exactly the place and time at which the diurnal tide is the largest. These high mixing ratios are a result of upward air motion, which cools the air adiabatically and also brings low concentrations of O and H from below. Full daytime and nighttime local time coverage of O3 measurements facilitates studying the tidal variability of the MLT O3 maximum. The O3 variabilities due to migrating tides are masked by the large photochemically driven day-night differences. However, such variabilities can be investigated by looking only at the daytime data. This has been done by Marsh et al. [2002], using full daytime O3 measurements from the High Resolution Doppler Imager in the altitude range between 70 and 95 km, and Dikty et al. [2010], using daytime SABER temperature and O3 measurements. Both studies attributed the increase of the afternoon O3 in the upper mesosphere to photochemical effects driven by the migrating diurnal tide. Air that is rich in O is believed to be pumped down from the lower thermosphere and to form O3 by the associative reaction between O2 and O. The two impacts of tidal motion on O3 discussed here are out of phase. Higher temperatures, which lead to lower O3, are in phase with higher O, which leads to higher O3. The relationship between the O3 and temperature tidal perturbations will vary, depending primarily on the strength of the vertical transport of O. During the past decade, significant progress has been made in elucidating and delineating the MLT response to nonmigrating tides from the lower atmosphere [Oberheide and Forbes, 2008]. This is due to the satellite missions that provide continuously and globally distributed measurements of the different atmospheric parameters. The basic aim of the present communication is to search for possible nonmigrating tidal variability of the MLT O3 seen in the SABER measurements. In this case the full daytime and nighttime O3 data can be used because the nonmigrating tides depend on the universal time (UT). 2 Observations and Method for Data Analysis The TIMED satellite was launched on 7 December 2001, and the SABER instrument began making observations in January 2002. The SABER instrument [Russell et al., 1999] views the Earth's limb to the side of the orbital plane (~74° inclination). Ozone emissions in the 9.6 µm bands are used to retrieve the mixing ratios corresponding to the line-of-sight tangent point. The emission of the strong 9.6 µm bands provides a method for observing O3 both daytime and nighttime as the origin of this emission is thermal in nature. The 9.6 µm bands depart from local thermodynamic equilibrium (LTE) in the MLT. The SABER v. 1.07 ozone 9.6 µm retrieval incorporates a detailed non-LTE model originally developed by Mlynczak and Drayson [1990a, 1990b] and updated with collisional rates from Martin-Torres [1999]. The non-LTE retrieval of O3 from the 9.6 µm emission requires knowledge of the O profiles; in SABER v. 1.07 they are taken from the US Naval Research Laboratory- Mass Spectrometer and Incoherent Scatter Radar model [Picone et al., 2002]. The SABER O3 measurements are made over the globe from lower stratosphere to lower thermosphere (20–110 km). The scanning direction of the SABER instrument is perpendicular to the flight direction of TIMED. Once approximately every 60–65 days the TIMED satellite performs a yaw maneuver reversing the scanning direction of SABER by 180°. This measuring geometry limits the latitude coverage from 83°S to 52°N and from 52°S to 83°N during alternate periods. Continuous measurements are available only in the latitude range of ±52°. Using both ascending and descending orbital modes, it takes 60 days for SABER to sample the data over the full 24 h of local times. The SABER v. 1.07 O3 data were downloaded from the web site http://saber.gats-inc.com/. In this study we also use temperature data available from SABER. The O3 data from 2002 to 2012 (full 11 years) are used to study the temporal variability and global spatial structure of the O3 variations that show coherent behavior consistent with nonmigrating tides. The data were averaged into 5 km altitude and 10° latitude bins, and each bin was independently fit. We work in UT; for each altitude (from 20 to 110 km at each 5 km) and latitude (from 50°S to 50°N at each 10°), the data were arranged in a matrix with 24 columns in longitude (a step of 15°) and a number of rows equal to the length of the entire period (2002–2012) in hours. Before the O3 data analysis was performed, the data were preprocessed by removing outliers and apparently erroneous profiles. The used for this purpose criterion is 3 (three) standard deviations. The data analysis method for calculating the climatological O3 tidal characteristics is carried out in two steps: first, the daily characteristics of the waves for each year are derived and second, the monthly mean wave characteristics are calculated by vector averaging of the daily wave parameters for each calendar month. The climatology of the wave characteristics during the entire 11 year period is estimated by vector averaging of the monthly mean wave characteristics for each month of the year. The method for deriving the daily characteristics of the atmospheric waves from the SABER O3 data is the same as that for the SABER temperatures and is described in detail by Pancheva et al. [2009]. In order to extract the waves from the SABER O3 data (i.e., to determine their amplitudes and phases) at a given latitude and altitude, we perform a linear two-dimensional (time-longitude) least squares fitting for the mean O3, the first three tidal periods (diurnal, semidiurnal, and terdiurnal tides) with zonal wave numbers up to 3, and the first four modes of the stationary planetary waves (SPW), i.e., SPWs with zonal wave numbers 1, 2, 3, and 4. All these components are extracted simultaneously from the O3 data. Because it takes SABER 60 days to sample 24 h in local time by combining ascending and descending data together, the length of the sliding window used for performing the least squares fitting procedure is 60 days. Then the 60 day window is moved through the time series with steps of 1 day in order to obtain the daily values of the wave characteristics. The derived O3 tidal amplitudes are measured in ppmv. 3 Nonmigrating O3 Variability The climatological features of the waves seen in the SABER O3 data are investigated using the distribution of the monthly mean tidal amplitudes and phases in time and space (latitude and altitude). The results of data analysis cover the interval between February 2002 and December 2012. Throughout the remainder of this paper we utilize the notation DWm and DEm to denote a westward or eastward propagating diurnal tide, respectively, with zonal wave number m. For semidiurnal and terdiurnal tides, S and T replace D, respectively. The stationary planetary waves (SPW) with zonal wave number m are expressed as SPWm. In this study we will present the features of only those nonmigrating O3 tidal variations whose peak amplitudes are at least 10% of the largest mean (zonal and time average) O3 or diurnal amplitude (due to the diurnal cycle of photochemistry and the DW1 tidal impact). The analysis of the SABER O3 data revealed that the diurnal O3 amplitudes are slightly larger than the mean O3; their climatological (2002–2012) monthly mean peak values are, respectively, 10.7 and 10.6 ppmv. Hence, only O3 changes with climatological amplitudes around and larger than 1 ppmv will be studied here. The careful consideration of all nonmigrating O3 variabilities for each year indicated that there are three nonmigrating O3 tidal variations whose seasonally repeating peak amplitudes are larger than 10% of the respective O3 mean/diurnal changes. These are SW3, DW2, and DE3 O3 changes. All these O3 tidal fields amplify around the equator. Figure 1 shows examples of these nonmigrating variabilities extracted from the SABER O3 measured mixing ratios over the equator. Figure 1 (top) shows the SW3 tide in 2011; its peak amplitude is ~21% of the largest mean O3 (~10.4 ppmv) in the same year. The DW2 tide in 2005 is shown in Figure 1 (middle); its peak amplitude is ~16% of the largest mean O3 (~11.6 ppmv). Figure 1 (bottom) shows the DE3 tide in 2004; its peak amplitude is ~11% of the largest mean O3 (~12 ppmv). While the SW3 and DW2 tidal variations amplify around 95 km altitude, the DE3 one has maximum slightly higher, at ~100 km altitude. The SW3 and DW2 tidal fields reveal equinoctial amplifications although the September–October amplifications are significantly stronger than those in March–April; the largest DE3 tide is also seen in September–October. Similar seasonal cycles in the DE3 temperature and wind tides were reported by Pancheva et al. [2010] and Wu et al. [2008], respectively. Figure 1Open in figure viewerPowerPoint Examples of the nonmigrating tidal variations extracted from the SABER ozone measurements as follows: (top) SW3 in 2011, (middle) DW2 in 2005, and (bottom) DE3 in 2004. The interannual variability of these three nonmigrating O3 tides will be presented as the multiyear (2002–2012) monthly mean averaged amplitudes over the equator. It has been already mentioned that the O3 SW3 and DW2 tidal variations demonstrate some differences in the altitude distribution and seasonal variability with respect to the DE3 one. The careful inspection of their multiyear monthly mean amplitudes reveals again some similarity between the interannual variability of the O3 SW3 and DW2 which is different from that of the O3 DE3. Due to this, their interannual variabilities will be considered separately. Figure 2a presents the monthly mean amplitudes of the O3 SW3 (upper plot) and DW2 (bottom plot) shown in blue at the level where both tides have the largest amplitudes, i.e., at 95 km and over the equator. The semiannual pattern with maxima in equinoxes is well evident for both tides at each year. Usually, the September–October maximum is larger than that in March–April with an exception in 2009 when the March–April maximum is larger than that in September–October. Both tides show similar interannual variability with September–October amplifications in 2002 (particularly SW3), 2005, 2007, and 2011. Smith et al. [2010] found that below 85–90 km height O3 responds most strongly to the large O variations while above 90–95 km O3 responds more strongly to the temperature. Hence, at 95 km we expect the variability in O3 tidal amplitude to correlate with the respective temperature (T) tidal amplitude variability. The latter are shown in Figure 2a with red. The figure shows not only similar seasonal variabilities but also some similarity in the interannual variabilities between the O3 and T tides. The correlation coefficients calculated between O3 and T tidal amplitudes for the considered interval of time are, respectively, 0.68 and 0.62 for DW2 and SW3 tidal variations; both coefficients are above 95% confidence level. Figure 2Open in figure viewerPowerPoint (a) Monthly mean amplitudes of the (upper plot) O3 SW3 and (bottom plot) DW2 shown in blue and the respective T tides (in red) over the equator at h = 95 km. (b) Monthly Niño 3.4 index data. (c) The same as Figure 2a but for the O3 and T DE3 tide at h = 100 km. (d) Monthly zonal wind over Singapore. Positive wind means westerly and negative wind means easterly. Figure 2c presents the monthly mean amplitudes of the O3 and T DE3, shown in blue and red, respectively, at h = 100 km (where the O3 DE3 has maximum) and over the equator. Both tidal fields have very similar seasonal behavior; however, while the T DE3 reveals broad maximum between August and October, the O3 DE3 has the largest amplitude in October. Hence, the O3 DE3 tidal field reveals a delay of 1–2 months with the respect to the T DE3 tide in most of the years. According to the interannual variability the O3 DE3 tide shows clear biyearly variability of the October maximum; it amplifies during 2002, 2004, 2006, 2008, 2010, and 2012. The T DE3 tide also shows such variability but only up to 2008. It is now generally accepted that the nonmigrating tides partly arise from zonally asymmetric thermal forcing, as for example, the release of latent heat from deep convective clouds. Interannual variations in the tropical deep convection are mostly related to the El Niño–Southern Oscillation (ENSO), which shifts the magnitude and position of convection. The stratospheric quasi-biennial oscillation (QBO) also significantly affects the tropical troposphere. Variability in ENSO and the QBO may affect the interannual behavior of the T and O3 nonmigrating tides. The Niño 3.4 index (http://www.esrl.noaa.gov/psd/data/correlation/nina34.data) has traditionally been used as a measure of ENSO strength in the tropical Pacific, while the monthly mean zonal wind at Singapore as a QBO index. The interannual variability of the O3 DE3 tide reveals clear biyearly behavior suggesting a possible impact of the stratospheric QBO. Figure 2d presents the monthly zonal wind at Singapore in the altitude range ~16–33 km (http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo/). It is well evident that while the T DE3 (Figure 2c, red) amplifies when the zonal mean wind has westerly (eastward) phase at ~30 hPa (around 24 km altitude) during almost the entire year for the O3 DE3 tide (Figure 2c, blue) such relationship is valid only up to 2008. After 2008 the biyearly variability of the O3 DE3 tide might be affected also by ENSO and possibly other tropospheric patterns; the signals from these potential forcing processes cannot, however, be separated with this fairly short record. Figure 2b shows monthly Niño 3.4 index of ENSO variability during 2002–2012. A careful comparison between the Niño 3.4 index and the T and O3 SW3 and DW2 temporal variability (Figure 2a) indicates an opposite relationship between them; i.e., usually the T and particularly O3 tidal amplifications are seen when the Niño 3.4 index tends to be minimum. All large minimums of the Niño 3.4 index seen in 2005/2006, 2007/2008, 2008/2009, 2010/2011, and 2011/2012 are accompanied by T and O3 SW3 and DW2 amplifications; 2002 is, however, an exception of this relationship. The low Niño 3.4 index means La Niña conditions, which includes stronger than average convective activity over the Indonesia area. Perhaps, there is something in this activity that preferentially excites these westward propagating nonmigrating tides. As already mentioned, the climatology of the O3 nonmigrating tides is studied by estimating the mean wave characteristics for each month of the year. Figure 3 (left) shows the climatological (average for 2002–2012) altitude structures of the nonmigrating O3 tides: SW3 (Figure 3, top), DW2 (Figure 3, middle), and DE3 (Figure 3, bottom). Figure 3 (right) shows the climatological latitude structures of the same nonmigrating O3 tides; the tides are presented at those altitudes where they have the largest amplitudes: 95 km for the SW3 and DW2 tides and 100 km for the DE3 tide. All three nonmigrating tides reveal main amplifications in October; there are secondary amplifications in February–March for the SW3 and DW2 tides and in March–April for the DE3 tide. These amplifications for all three tides are near or at the equator, but the SW3 and DW2 tides have slight equinoctial amplifications at middle latitudes as well. Figure 3Open in figure viewerPowerPoint Climatological (2002–2012) (left) altitude and (right) latitude structures of the nonmigrating (top) SW3, (middle) DW2, and (bottom) DE3 tidal variations extracted from the SABER ozone measurements. Figures 1-3 presented the altitude and latitude structures of the nonmigrating O3 tidal amplitudes. The tidal phase structures can be illustrated better in an altitude-longitude frame. Figure 4 (left) shows the altitude-longitude structures of the climatological (average 2002–2012) monthly mean nonmigrating O3 tidal variabilities in October over the equator at 00 UT; the SW3 tidal field is shown in Figure 4 (top), while those of the DW2 and DE3 can be seen in the Figure 4 (middle and bottom), respectively. The white line marks the zero-level variability. The plots reveal that the phase of the O3 tidal variations moves downward with time for the westward (SW3 and DW2) and eastward (DE3) tidal fields. Two different vertical phase structures can be distinguished for the westward propagating O3 SW3 and DW2 tidal variations: a very low vertical phase shift below the tidal O3 maximum at ~95 km altitude and rapidly decreasing O3 SW3 and DW2 tidal variations above ~95 km with more rapid phase shift than that below ~95 km. The eastward propagating O3 DE3 tidal field has a phase structure that is similar both below and above its maximum at ~100 km. The altitude range where the considered nonmigrating O3 tidal variations have detectable amplitudes is between ~80 and 105 km. Figure 4Open in figure viewerPowerPoint Average (2002–2012) altitude-longitude cross sections of the (left) nonmigrating ozone and (right) temperature variabilities in October over the equator at 00 UT are shown; the following tidal variabilities can be seen: (top) SW3, (middle) DW2, and (bottom) DE3; the white line marks the zero-level variability. The nonmigrating O3 tidal structures indicate the impact of the respective nonmigrating tides that amplify in the MLT region. It has been already mentioned that the O3 variability is closely related to the temperature variability through the effect on the chemical rate coefficients and atmospheric density [Smith and Marsh, 2005]. Figure 4 (right) is the same as Figure 4 (left) but for the SABER T nonmigrating tidal variabilities. A careful comparison of each pair of nonmigrating tidal variabilities, i.e., in O3 and T at a give height, reveals the well-known negative correlation between the O3 and T. There is, however, an important shift in the phase difference between the O3 and temperature tides. The phase slopes of the O3 tides are similar to those of the respective T tides only above ~95 km height. In other words, the O3 and T tides are out of phase at altitudes above 95 km; the relative phase shifts rapidly below this altitude. For the DW2 tide, which has substantial amplitude below 90 km, the O3 and temperature tides are close to being in phase at 85 km. The phase relationship between the O3 and T tidal variations below and above 95 km is defined by the two main processes that produce the tidal modulation of O3 density: one is inducing variation of temperature by tides which change the chemical reaction rates and atmospheric density and another is change the profile of atomic oxygen through transport. There is a transition level between these two competing processes. Xu et al. [2010] studied the modulation of OH airglow by tides and found that this level is at ~94.5 km. The OH airglow emission rate is positively correlated with temperature below 94 km and negatively correlated above (Figure 3 in the above mentioned paper). 4 Discussion This communication presents for the first time evidence showing nonmigrating tidal variations in the mesospheric O3. For this purpose the daytime and nighttime SABER O3 measurements for a full 11 year period, 2002–2012, were analyzed. This study presents the spatial distribution and seasonal variability of only those nonmigrating O3 tidal fields whose amplitudes are at least 10% of either the mean O3 or the largest diurnal O3 variability. It was found that such O3 tidal variations are SW3, DW2, and DE3. All these O3 tidal fields demonstrated repeatable presence each year. The O3 SW3, DW2, and DE3 tidal signatures have large amplitudes at the seasons and latitudes for which the respective T nonmigrating tides amplify, i.e., near the equator and during the equinoxes. The O3 tidal variations show significantly larger amplitudes in September–October than in March–April. Analysis (not shown) indicates that the amplitudes of the T SW3, DW2, and DE3 tides in the altitude range 90–100 km also are significantly larger in northern autumn than in spring. The magnitude of the ozone response is expected to be mainly associated with the respective T amplitude at the same level plus variations due to a strong chemical amplification centered around 95 km. This seems to be consistent with the monthly variations of each individual tide but does not explain the differences in amplitude among the different tides. The O3 SW3 and DW2 tides have largest amplitudes at altitude of ~95 km, i.e., where the mesospheric O3 maximum is located, while the O3 DE3 tide amplifies at a higher level, ~100 km, where the mesospheric O3 is decreasing. This difference in the amplification level partly explains why the O3 DE3 response is weaker than those of O3 SW3 and DW2 nevertheless that the T DE3 is significantly larger than the T SW3 and DW2 tides. Additionally, the amplitude of vertical velocity may also vary between the different tides, which could contribute to the apparent discrepancy between the magnitude of the T tide and its O3 response. Only numerical simulations with a dynamical-chemical model would be able to shed some light on the factors which determine the altitude and magnitude of the O3 response to the considered T nonmigrating tides. The multiyear (2002–2012) monthly mean O3 tidal amplitudes, presented in Figures 2a (SW3 and DW2) and 2c (DE3), demonstrated clear interannual variability. The O3 SW3 and DW2 tides revealed similar variabilities with significant amplifications predominantly in years when the Niño 3.4 index of ENSO tends to be minimum. This suggests that the La Niña conditions may preferentially excite these westward propagating nonmigrating tides. The O3 DE3 tide, however, revealed clear biyearly interannual variability. It indicated a correlation with the westerly (eastward) phase of the QBO in tropical stratospheric winds but only up to 2008. The biyearly variability of the O3 DE3 tidal field might also be affected by ENSO and possibly other tropospheric patterns (such as the tropospheric biennial oscillation and Pacific decadal oscillation); these multiyear signals, however, cannot be separated using this fairly short record. Comparison of the phase of the T and O3 tidal signatures (Figure 4) shows an out of phase relationship above 95 km. Such a phase relationship is expected where the time scale for O3 photochemistry is short compared to the time scale for T changes due to the tides and the perturbations to O due to tidal transport are relatively weak. This relationship no longer holds for tidal perturbations below about 90 km; there the very large vertical gradients of background O lead to the opposite relationship. Positive T perturbations are associated with downward motion and therefore downward transport of O. Where this becomes the dominant process affecting O3, then there will be a rapid phase shift in the vertical between O3 perturbations out of phase with T (above about 95 km) to those in phase with T (below 85 km). This change in the important processes driving the O3 response to nonmigrating tides could explain the shift in the vertical structure, seen most clearly for the DW2 and SW3 tides in Figure 4. In conclusion we note that this study for the first time shows the response of the mesospheric O3 to nonmigrating tides from the lower atmosphere. It is worth mentioning that the analysis of the SABER O3 data revealed also the regular presence of the SPW4 O3 variability. The knowledge for the spatial distribution and temporal variability of the mesospheric O3 is important because O3 is an effective absorber of the ultraviolet radiation and reacts exothermically with several species including O and H. Therefore, the O3 variability will alter the heating rate and temperature in the MLT region. Acknowledgments We are grateful to the SABER team for the access to the data on http://saber.gats-inc.com. This work was supported by the European Office of Aerospace Research and Development (EOARD), Air Force Office of Scientific Research, Air Force Material Command, USAF, under grant FA8655-12-1-2057. The National Center for Atmospheric Research is sponsored by the National Science Foundation. We thank the anonymous reviewers for their insightful comments on the original manuscript. The Editor thanks two anonymous reviewers for their assistance in evaluating this paper. References Bates, D. R., and M. 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