The variability in the middle atmosphere is driven by a variety of waves covering different spatial and temporal scales. We diagnose the variability in the thermal tides due to changes in the ...background wind by an adaptive spectral filter, which takes the intermittency of tides into account. We apply this diagnostic to temperature observations from daylight-capable lidar at midlatitudes (54∘ N, 12∘ E) as well as to reanalysis data of horizontal winds from Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). These reanalysis data provide additional wind information in the altitude range between 30 and 70 km at the location of the lidar as well as on a global scale. Using the global data gives information on the tidal modes seen at one location. A comparison of the temperature and wind information affirms whether there is a fixed phase relation of the tidal waves in the temperature and the wind data. We found that in general the local tidal signatures are dominated by migrating tidal modes, and the signature is weaker in temperatures than in winds. While the meridional wind tide leads the zonal wind tide by 90∘, the phase relation between the temperature and the wind tide is more complex. At certain altitudes the temperature tide follows the zonal wind tide. This knowledge helps in improving the interpretation of the seasonal variation in tides from different observables, especially when only data from single locations are used. The findings provide additional information about the phase stability of tidal waves, and the results clearly show the importance of a measurement acquisition on a routine basis with high temporal and spatial resolution.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We report on long-term observations of atmospheric parameters in the mesosphere and lower thermosphere (MLT) made over the last 2 decades. Within this study, we show, based on meteor wind ...measurement, the long-term variability of winds, tides, and kinetic energy of planetary and gravity waves. These measurements were done between the years 2002 and 2018 for the high-latitude location of Andenes (69.3∘ N, 16∘ E) and the mid-latitude locations of Juliusruh (54.6∘ N, 13.4∘ E) and Tavistock (43.3∘ N, 80.8∘ W). While the climatologies for each location show a similar pattern, the locations differ strongly with respect to the altitude and season of several parameters. Our results show annual wind tendencies for Andenes which are toward the south and to the west, with changes of up to 3 m s−1 per decade, while the mid-latitude locations show smaller opposite tendencies to negligible changes. The diurnal tides show nearly no significant long-term changes, while changes for the semidiurnal tides differ regarding altitude. Andenes shows only during winter a tidal weakening above 90 km, while for the Canadian Meteor Orbit Radar (CMOR) an enhancement of the semidiurnal tides during the winter and a weakening during fall occur. Furthermore, the kinetic energy for planetary waves showed strong peak values during winters which also featured the occurrence of sudden stratospheric warming. The influence of the 11-year solar cycle on the winds and tides is presented. The amplitudes of the mean winds exhibit a significant amplitude response for the zonal component below 82 km during summer and from November to December between 84 and 95 km at Andenes and CMOR. The semidiurnal tides (SDTs) show a clear 11-year response at all locations, from October to November.
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Recent studies have shown that day-to-day variability of the migrating semidiurnal solar (SW2) tide within the mesosphere and lower thermosphere (MLT) is a key driver of anomalies in the ...thermosphere–ionosphere system. Here, we study the variability in both the amplitude and phase of SW2 using meteor radar wind and lidar temperature observations at altitudes of 75–110 km as well as wind and temperature output from the Navy Global Environmental Model – High Altitude (NAVGEM-HA), a high-altitude meteorological analysis system. Application of a new adaptive spectral filter technique to both local radar wind observations and global NAVGEM-HA analyses offers an important cross-validation of both data sets and makes it possible to distinguish between migrating and non-migrating tidal components, which is difficult using local measurements alone. Comparisons of NAVGEM-HA, meteor radar and lidar observations over a 12-month period show that the meteorological analyses consistently reproduce the seasonal as well as day-to-day variability in mean winds, mean temperatures and SW2 features from the ground-based observations. This study also examines in detail the day-to-day variability in SW2 during two sudden stratospheric warming, events that have been implicated in producing ionospheric anomalies. During this period, both meteor radar and NAVGEM-HA winds show a significant phase shift and amplitude modulation, but no signs of coupling to the lunar tide as previous studies have suggested. Overall, these findings demonstrate the benefit of combining global high-altitude meteorological analyses with ground-based observations of the MLT region to better understand the tidal variability in the atmosphere.
•First quasi continuous meteor head echo measurements for a period of over two years are presented.•The observed sporadic meteors are compared to the prediction of a meteor input function (MIF).•Only ...40% of the observed meteors were detected within the full width half maximum of the specific sporadic meteor sources.
We present the first quasi continuous meteor head echo measurements obtained during a period of over two years using the Middle Atmosphere ALOMAR Radar System (MAARSY). The measurements yield information on the altitude, trajectory, vector velocity, radar cross section, deceleration and dynamical mass of every single event. The large statistical amount of nearly one million meteor head detections provide an excellent overview of the elevation, altitude, velocity and daily count rate distributions during different times of the year at polar latitudes. Only 40% of the meteors were detected within the full width half maximum of the specific sporadic meteor sources. Our observation of the sporadic meteors are compared to the observations with other radar systems and a meteor input function (MIF). The best way to compare different radar systems is by comparing the radar cross section (RCS), which is the main detection criterion for each system. In this study we aim to compare our observations with a MIF, which provides information only about the meteoroid mass. Thus, we are using a statistical approach for the elevation and velocity dependent visibility and a specific mass selection. The predicted absolute count rates from the MIF are in a good agreement with the observation when it is assumed that the radar system is only sensitive to meteoroids with masses higher than one microgram. The analysis of the dynamic masses seems to be consistent with this assumption since the count rate of events with smaller masses are low and decrease even more by using events with relatively small errors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This study combines 8 years of middle atmospheric wind data observed at 52°N latitude from two radars in different longitudinal sectors to investigate solar tides. The power spectral density of ...horizontal winds exhibits a −3 power law within the frequency range 2.0 < f < 7.0 cpd (equivalent to periods 3.6 − 12.0 hr). Particularly noteworthy are the 4.8‐ and 4‐hr tides, exhibiting signal‐to‐noise ratios ranging between 13 and 16 dB, surpassing the 0.01 significance level. This challenges their previous oversight in literature, possibly due to inadequacies in prevailing noise models. Cross‐spectra between longitudinal sectors emphasize the dominance of sun‐synchronous components in the six lowest‐frequency tides. Composite spectra indicate that tidal enhancements during SSWs resemble regular seasonal variations. Intriguingly, year‐to‐year spectral variations suggest that these enhancements are more influenced by seasonal dynamics than by SSW, contrasting with established literature. These findings underscore the need to reevaluate tidal harmonics and consider appropriate noise models in future studies.
Plain Language Summary
Tides are ubiquitous in celestial systems, influencing celestial objects diversely when one orbits another. Extensive studies have explored the tidal effects on processes such as planetary habitability, climate fluctuations, meteorological patterns, geophysical activities, geological hazards, heat and mass circulation, and certain biological behaviors. However, most existing literature focuses on the lowest‐frequency tidal harmonics, with limited attention given to higher‐frequency ones. In the Earth's atmosphere, the exact count of solar tidal harmonics remains uncertain, and an ongoing debate persists regarding the existence of higher‐frequency harmonics, arising potentially from difficulties in distinguishing them from sporadic regional buoyancy waves. Here, we provide evidence for the statistically significant existence of the first six orders of tidal harmonics, extracted from 8 years of middle atmospheric wind observations. Spectral coherence between two distinct longitudinal sectors signifies that the six harmonics primarily correspond to sun‐synchronous tides synchronized with the Sun. The presence of higher‐frequency tides suggests that tidal effects are characterized by greater complexity than currently understood.
Key Points
Wind spectrum reveals 6 tidal harmonics significantly higher than background noise with −3 frequency power law
Coherence between two longitudinal sectors reveals that the harmonics are synchronized with the Sun
Winter tidal enhancements seem to be influenced by seasonal factors rather than SSW, presenting a contrast to existing literature
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Mean vertical velocity measurements obtained from radars at polar latitudes
using polar mesosphere summer echoes (PMSEs) as an inert tracer have been
considered to be non-representative of the mean ...vertical winds over the last
couple of decades. We used PMSEs observed with the Middle Atmosphere Alomar
Radar System (MAARSY) over Andøya, Norway (69.30∘ N,
16.04∘ E), during summers of 2016 and 2017 to derive mean vertical
winds in the upper mesosphere. The 3-D vector wind components (zonal,
meridional and vertical) are based on a Doppler beam swinging experiment
using five beam directions (one vertical and four oblique). The 3-D wind
components are computed using a recently developed wind retrieval technique.
The method includes full non-linear error propagation, spatial and temporal
regularisation, and beam pointing corrections and angular pointing
uncertainties. Measurement uncertainties are used as weights to obtain
seasonal weighted averages and characterise seasonal mean vertical
velocities. Weighted average values of vertical velocities reveal a weak
upward behaviour at altitudes ∼84–87 km after eliminating the
influence of the speed of falling ice. At the same time, a sharp decrease
(increase) in the mean vertical velocities at the lower (upper) edges of the
summer mean altitude profile, which are attributed to the sampling issues of
the PMSE due to disappearance of the target corresponding to the certain
regions of motions and temperatures, prevails. Thus the mean vertical
velocities can be biased downwards at the lower edge, and the mean vertical
velocities can be biased upwards at the upper edge, while at the main central
region the obtained mean vertical velocities are consistent with expected
upward values of mean vertical winds after considering ice particle
sedimentation.
This article addresses the further development of the ground-based temperature radiometer TEMPERA, which measures atmospheric microwave radiation in one linear polarization in order to retrieve ...temperature profiles up to an altitude of 50 km (Stähli et al. , 2013). The latest innovation is a new polarimetric receiver, which allows observing the atmosphere simultaneously in left- and right-circular polarization. In combination with an adapted inversion method, the fully polarimetric analysis can improve the accuracy and extends the vertical upper limit of retrieved temperature profiles. Comparisons between single polarization and fully polarimetric retrievals with simulated atmospheric spectra are presented, and the influence of the Earth's magnetic field is analyzed. In addition, we propose a simple calibration method for fully polarimetric radiometers and present first atmospheric spectra measured with the new TEMPERA-C instrument.
Long-term and continuous observations of mesospheric–lower thermospheric winds
are rare, but they are important to investigate climatological changes at
these altitudes on timescales of several ...years, covering a solar cycle and
longer. Such long time series are a natural heritage of the mesosphere–lower
thermosphere climate, and they are valuable to compare climate models or long-term runs of general circulation models (GCMs). Here we present a
climatological comparison of wind observations from six meteor radars at two
conjugate latitudes to validate the corresponding mean winds and atmospheric
diurnal and semidiurnal tides from three GCMs, namely the Ground-to-Topside Model
of Atmosphere and Ionosphere for Aeronomy (GAIA), the Whole Atmosphere Community
Climate Model Extension (Specified Dynamics) (WACCM-X(SD)), and the Upper
Atmosphere ICOsahedral Non-hydrostatic (UA-ICON) model. Our results indicate
that there are interhemispheric differences in the seasonal characteristics of
the diurnal and semidiurnal tide. There are also some differences in the mean
wind climatologies of the models and the observations. Our results indicate
that GAIA shows reasonable agreement with the meteor radar observations
during the winter season, whereas WACCM-X(SD) shows better agreement with
the radars for the hemispheric zonal summer wind reversal, which is more
consistent with the meteor radar observations. The free-running UA-ICON tends
to show similar winds and tides compared to WACCM-X(SD).
Middle atmospheric ozone, water vapour and zonal and meridional wind profiles have been measured with the two ground-based microwave radiometers GROMOS-C and MIAWARA-C.
The instruments have been ...located at the Arctic research base AWIPEV at Ny-Ålesund, Svalbard (79∘ N, 12∘ E), since September 2015. GROMOS-C measures ozone spectra in the four cardinal directions with an elevation angle of 22∘.
This means that the probed air masses at an altitude of 3 hPa (37 km) have a horizontal distance of 92 km to Ny-Ålesund. We retrieve four separate ozone profiles along the lines of sight and calculate daily mean horizontal ozone gradients which allow us to investigate the small-scale spatial variability of ozone above Ny-Ålesund.
We present the evolution of the ozone gradients at Ny-Ålesund during winter 2018/2019, when a major sudden stratospheric warming (SSW) took place with the central date at 2 January, and link it to the planetary wave activity.
We further analyse the SSW and discuss our ozone and water vapour measurements in a global context.
At 3 hPa we find a distinct seasonal variation of the ozone gradients.
The strong polar vortex during October and March results in a decreasing ozone volume mixing ratio towards the pole. In November the amplitudes of the planetary waves grow until they break in the end of December and an SSW takes place.
From November until February ozone increases towards higher latitudes and the magnitude of the ozone gradients is smaller than in October and March. We attribute this to the planetary wave activity of wave numbers 1 and 2 which enabled meridional transport. The MERRA-2 reanalysis and the SD-WACCM model are able to capture the small-scale ozone variability and its seasonal changes.
Upper mesospheric winds observed by the Svalbard specular meteor radar (16.01°E,78.16°N) are analyzed to study the tidal variabilities during the 2009 sudden stratospheric warming (SSW). We report a ...textbook case of nonlinear interactions between planetary waves (PWs) and the SW2 tide (SWm denotes semidiurnal westward propagating tidal mode with zonal wave number m). The Lomb‐Scargle algorithm, bispectrum, wavelet spectra, and Manley‐Rowe relations are combined to explore the frequency match, phase coherence, energy budget, and wave number relations among the interacting waves and their temporal evolution. Our results suggest that (1) 5, 10, 16 day PW normal modes interact with SW2 generating significant sidebands (S2Ss) at frequencies lower and higher than SW2, known as SW1 and SW3 enhancements, respectively; (2) SW2 is the main energy supplier for both SW1 and SW3, hence shrinks in the interactions; (3) whereas the PWs export relatively negligible energy to SW3 but accept energy from SW2 in generating SW1, therefore, the PWs is not subject to the interactions but controlled by external dynamics, which might in turn act as a key in switching on/off the SW1 and SW3 interactions independently; (4) the SW1 enhancement could be explained as a byproduct of the planetary wave amplification by stimulated tidal decay (PASTIDE); (5) PASTIDE contributes energy to the secondary PW in the late SSW stage reported in previous studies; and (6) one SW1 component associated with the 16 day PW is very close to the semidiurnal lunar mode in frequency, which might contaminate the estimation of the lunar tidal amplification in previous studies.
Plain Language Summary
Nonlinear interaction is a prototypical behavior of waves, as fundamental as Doppler shift, interference, and diffraction. Nonlinear interactions between atmospheric planetary scale waves have been reported in numerous studies. In the current work, we apply for the first time Manley‐Rowe relations to determine the energy flow in the atmospheric interactions and roles of the interacting waves. Particularly, we report and analyze a textbook case of nonlinear interactions between planetary waves (PWs) and the migrating solar semidiurnal tide. Our analysis suggests that the secondary waves, well known as zonal wave 1 and wave 3 enhancements, are fed on the energy mainly from the tide. Although the energy flow through PWs is relatively negligible, our investigations suggest that the energy budget of PWs might act as a key in turning on/off the interactions. When PWs accept energy in the interaction, the wave 1 is generated, whereas when PWs export energy, the wave 3 is generated. In the combined case, PWs could accept energy from the tide and meanwhile export energy to wave 3, generating both wave 1 and wave 3. The energy transport from the tide to PWs in generating wave 1 might supply the secondary PW in the late sudden stratospheric warming stage reported in previous studies.
Key Points
A textbook case of nonlinear interactions between planetary waves and SW2 tide results in asynchronous SW1 and SW3
Manley‐Rowe relations explain the energy flow topology and the roles of interacting waves; SW1 is accompanied by secondary PW
SW1 contaminates the estimation of M2 amplification; we suggest tentative scenarios for interpreting the SW1/SW3 asynchrony
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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