Nonmigrating Tides Research Articles

Longitude Structure of Wavenumber 4 of the Ionosphere After Midnight Based on the OI135.6 nm Night Airglow Using FY‐3D Ionospheric Photometer

AbstractIn this study, based on the OI135.6 nm night airglow data of the FY‐3D Ionospheric Photometer (IPM) during the 2018–2021 geomagnetically quiet period, the global wavenumber 4 longitudinal structure of the equatorial ionization anomaly (EIA) at 2:00 local time was discovered, and the component of the wavenumber 4 was extracted from these structures. Compared with the OI135.6 nm night airglow data of the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) F18 during 2011–2014, there were significant differences in the variation pattern of the relative amplitude of the two versus solar activity and the seasonal variation in the proportion of the component of the wavenumber 4. Based on the neutral wind speed observation results of the Michelson Interferometer for Global High‐Resolution Thermospheric Imaging on board the Ionospheric Connection Explorer (ICON) from 2020 to 2021, the longitudinal structures of the 4 ionospheric waves after midnight are related to the cross‐equatorial meridional wind. We believe that the wavenumber 4 longitudinal structures after midnight originate from the semidiurnal eastward‐propagating with zonal wavenumber 2 (SE2) nonmigrating tide in the cross‐equatorial neutral wind rather than the diurnal eastward‐propagating with zonal wavenumber 3 (DE3) nonmigrating tide in from the zonal wind, which modulates the daytime wavenumber 4 longitudinal structures.

On the importance of middle-atmosphere observations on ionospheric dynamics using WACCM-X and SAMI3

Abstract. Recent advances in atmospheric observations and modeling have enabled the investigation of thermosphere–ionosphere interactions as a whole-atmosphere problem. This study examines how dynamical variability in the middle atmosphere (MA) affects intra-day changes in the thermosphere and ionosphere. Specifically, this study investigates ionosphere–thermosphere interactions during different time periods of January 2013 using the Specified Dynamics Whole Atmosphere Community Climate Model, eXtended version (SD-WACCM-X), coupled to the Naval Research Laboratory (NRL) ionosphere of the Sami3 is Another Model of the Ionosphere (SAMI3) model. To represent the weather of the day, the coupled thermosphere–ionosphere system is nudged below 90 km toward the atmospheric specifications provided by the Navy Global Environmental Model for High-Altitude (NAVGEM-HA). Hindcast simulations during January 2013 are carried out with the full dataset of observations normally assimilated by NAVGEM-HA and with a degraded dataset where observations above 40 km are not assimilated. Ionospheric regions with statistically significant changes are identified using key ionospheric properties, including the electron density, peak electron density, and height of the peak electron density. Ionospheric changes show a spatial structure that illustrates the impact of two different types of coupling between the thermosphere and the ionosphere: variability induced by wind-dynamo coupling through electric conductivity and ion-neutral interactions in the upper thermosphere. The two simulations presented in this study show that changing the state of the MA affects ionosphere–thermosphere coupling through changes in the behavior and amplitude of non-migrating tides, resulting in improved key ionospheric specifications.

Climatology of the Nonmigrating Tides Based on Long-Term SABER/TIMED Measurements and Their Impact on the Longitudinal Structures Observed in the Ionosphere

This paper presents climatological features of the longitudinal structures WN4, WN3, and WN2 and their drivers observed in the lower thermospheric temperatures and in the ionospheric TEC. For this purpose, two long-term data sets are utilized: the satellite SABER/TIMED temperature measurements, and the global TEC maps generated with the NASA JPL for the interval of 2002–2022. As the main drivers of the longitudinal structures are mainly nonmigrating tides, this study first investigates the climatology of those nonmigrating tides, which are the main contributors of the considered longitudinal structures; these are nonmigrating diurnal DE3, DE2, and DW2, and semidiurnal SW4 and SE2 tides. The climatology of WN4, WN3, and WN2 structures in the lower thermosphere reveals that WN4 is the strongest one with a magnitude of ~20 K observed at 10° S in August, followed by WN2 with ~13.9 K at 10° S in February, and the weakest is WN3 with ~12.4 K observed over the equator in July. In the ionosphere, WN3 is the strongest structure with a magnitude of 5.9 TECU located at −30° modip latitude in October, followed by WN2 with 5.4 TECU at 30 modip in March, and the last is WN4 with 3.7 TECU at −30 modip in August. Both the climatology of the WSA and the features of its drivers are investigated as well.

Semidiurnal nonmigrating tides in low-latitude lower thermospheric NO: A climatology based on 20 years of Odin/SMR measurements

The Sub-Millimetre Radiometer (SMR) on board the Odin satellite provides almost 20 years of nitric oxide (NO) measurements in the mesosphere and lower thermosphere (MLT) at equatorial crossing local solar times (LSTs) of 6AM and 6PM. In this study, we use Odin/SMR observations to estimate how lower thermospheric NO mixing ratios at low latitudes are affected by solar nonmigrating tides. Most of the previous studies based on satellite data have focused on the signatures of diurnal tides in the MLT and above, while we concentrate here on nonmigrating semidiurnal tides. To study the contribution of these tides to NO mixing ratio variations, we average pairs of NO measurements along ascending and descending orbital tracks at 107 km altitude over latitudes between −40°and +40°. We consider monthly climatologies of these pair-averages and analyse residuals with respect to their zonal mean. In this way, it is possible to study the effect of nonmigrating even-numbered tidal components, albeit there is a non-tidal component arising largely from quasi-stationary planetary waves. Spectral wave amplitudes are extracted using a Fourier transform as function of (apparent) zonal wavenumber with a focus around −30°, −20°and 30°latitudes. From our analysis, it appears that the semidiurnal (apparent) zonal wavenumber 4 arising from the SW6 and SE2 tides is dominant close to the equator (e.g., at −20°), except during some boreal summer months (June, July, August). On the other hand, wave-1 plays a more prominent role at subtropical latitudes, especially in the southern hemisphere, where it surpasses wave-4 during 7 months (March and May-to-October) at −30°. There is little observational evidence to date documenting the presence of the semidiurnal nonmigrating tides in NO in the low-latitude MLT. Our results hence provide one of the first evidences of the climatological signature of these tides in NO, in an altitude range that remains poorly observed.

Spatial and temporal correlations of thermospheric zonal winds from GOCE satellite observations

Winds in the thermosphere play an important role in the transport of momentum and energy in the upper atmosphere and affect the composition, dynamics and morphology of the ionospheric plasma. Although the general morphology of the winds is well understood, we are only starting to understand its variability. During the last decade it has become inherently clear that in addition to solar forcing of the thermosphere, the lower atmosphere also is an important driver of thermospheric variability. Therefore, an understanding of thermospheric variability and its spatial and temporal correlations is critical for an improved understanding of the coupled ionosphere-thermosphere system and the coupling to the lower atmosphere. The Gravity Field and Steady-State Ocean Explorer (GOCE) provided zonal winds near dawn and dusk at an altitude of around 260 km from November 2009 to October 2013. We have used GOCE zonal wind observations from low- to mid-latitudes obtained during geomagnetically quiet times to investigate spatial and temporal correlations in the zonal winds near dawn and dusk. Latitudinal correlations were calculated for the GOCE zonal winds for December solstice separately for each year from 2009 to 2012 and their year-to-year variation was established. Correlations between hemispheric conjugate points were found at mid latitudes during the latter years. Latitudinal correlations for December solstice 2009 and June solstice 2010 were compared and the correlation length was found to be consistently larger in the winter hemisphere during dawn and in the summer hemisphere during dusk. Zonal wind longitudinal/temporal correlations were also determined for December 2009 and 2011 and for June 2010 and found to be periodic in longitude/time. The temporal evolution of the temporal/longitudinal correlations were found to gradually decrease over the course of several days. The maxima in the correlation coefficients were always located in the winter hemisphere during dawn and in the summer hemisphere during dusk. During dawn, the largest contributors to the temporal/longitudinal correlations were found to be nonmigrating tides, whereas during dusk, additional waves appear to play important roles.

Detection of Migrating and Non-Migrating Atmospheric Tides Derived from ERA5 Temperature Meteorological Analyses

To better extract the tides represented in the European meteorological analysis ERA5, an analysis of the histograms of the diurnal and semi-diurnal modes as a function of longitudes was performed. This analysis revealed that modes with different characteristics appeared regionally along a single longitude. Retrieved migrating tides were compared with a tidal model showing global agreement below 60 km and twice the amplitude in meteorological analyses at mid-latitude. Non-migrating tidal modes have been identified along the tropical band. They logically appear above the convective zones, probably due to water vapor excess. Their characteristics are different from migrating components. This preliminary study has shown that it is necessary to develop additional observations allowing for more frequent sampling to retrieve migrating and non-migrating tides that can only be achieved with satellite constellations from space.

Wavenumber-4 Structure in COSMIC-2 Observations: Vertical Plane Perspective

High-rate radio occultation (RO) in COSMIC-2 (FORMOSAT7) enables us to investigate the finer details of the ionosphere owing to the measurements being made at a significantly high spatiotemporal resolution, which was unthinkable a decade ago. In the vertical plane, local-time ionospheric wavenumber-4 (WN4) structures display tilted phase-fronts over the equatorial ionization anomaly (EIA) belt. The longitudinal extent of a tilted WN4 phase-front approximates the zonal wavelength of nonmigrating DE3 tide in the local-time frame of reference, i.e., ~900. The WN4-filtered (residual) component indicates a greater tilt (when visible), with a larger longitudinal extent of a wavenumber structure in the vertical plane. The WN4 structure over the EIA crest region is found to be out of phase (in phase) with respect to that over the EIA trough region during daytime (nighttime), which also depended on the altitude under consideration. Intriguingly, above 400 km, the WN4 structures in the EIA crest and trough regions are seen to be in phase with each other at all local times. The phenomenon of the “longitudinal co-location” of WN4 over the EIA crest and trough regions at altitudes above ~400 km at all local times remains unexplained. Results also highlight that the formation of WN4 is governed by a complex interplay of direct forcing of nonmigrating tides and the zonal electric field whose characteristics within the EIA belt vary drastically with latitude and altitude under consideration.

Short-Term Variability of Non-Migrating Diurnal Tides in the Stratosphere from CMAM30, ERA-Interim, and FORMOSAT-3/COSMIC

The variability of non-migrating tides in the stratosphere is investigated using temperature data from Canadian Middle Atmosphere Model (CMAM30), ERA-interim reanalysis and Formosa Satellite-3 and Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) from 2006 to 2010 using a ±10-day window. CMAM30 and ERA results show that the amplitudes of non-migrating tides, DS0 and DW2, are negligible in the mid and high-latitude stratosphere, and the results from satellite datasets are significantly affected by aliasing in this region, in spite of using a smaller window size for analysis (±10 days). Significant short term variability ranging from 30 to 100 days is observed in DS0 and DW2 over the equatorial and tropical latitudes. These tides are seen as two prominent bands around the equator with DS0 maximising during boreal summers and DW2 maximising during boreal winters. These variabilities are compared with the variability in amplitude of the stationary planetary wave with wavenumber one (SPW1) in the high-latitude stratosphere using the continuous wavelet transform (CWT). It is found that during boreal winters, the variability of SPW1 at 10 hPa over 65° N is similar to that of DS0 and DW2 over the equator at 0.0007 hPa. This provides evidence that SPW1 from the high-altitude stratosphere moving upward and equator-ward could be interacting with the migrating diurnal tide and generating the non-migrating tides in the equatorial mesosphere and lower thermosphere (MLT). The variabilities, however, are not comparable during summers, with SPW1 being absent in the Northern Hemisphere. It is thus concluded that non-linear interactions could be a source of non-migrating tidal variability in the equatorial MLT region during boreal winters, but during summers, the tidal variabilities have other sources in the lower atmosphere. The anti-symmetric nature of the vertical global structures indicates that these tides could be the result of global atmospheric oscillations proposed by the classical tidal theory.

Validation of equatorial electrojet derived from Swarm observations using ground based magnetometers

This paper presents the analysis of the Equatorial electrojet (EEJS) and Counter equatorial electrojet (CEJS) at quiet times (Kp⩽3) deduced from the absolute scalar magnetometers (ASM) of the Swarm satellites. The EEJS and CEJS were compared with their corresponding values, EEJG and CEJG respectively, from ground magnetometers in the South American, West African, and Asian sectors during the years 2014–2018. The results show that EEJS highly correlated with EEJG, over South American, West African and Asian sectors with correlation coefficients of 0.91, 0.77 and 0.92 respectively. CEJS with CEJG also showed a reasonably good correlation of 0.78, 0.98 and 0.83 over South American, West African and Asian sectors respectively. For the first time, the Swarm observations of CEJ and EEJ are validated against CEJ and EEJ from ground magnetometers, over South America, West Africa and Asia. Both the occurrence rates of CEJS and CEJG show similar diurnal and seasonal trends, with the highest occurrence rates in the morning (7:00–9:00 LT) and evening (15:00–19:00 LT) times and the lowest occurrence rates around noon (11:00 to 12:00 LT) time. The seasonal occurrence rates of CEJS and CEJG were high in the solstice months and the lowest rates were during equinox months for all the sectors. The longitudinal variability of CEJS and CEJG show highest occurrence rates in the West African sector and the lowest occurrence rates in the Asian sector. This longitudinal variability of CEJS and CEJG occurrence rates were attributed to the effect of the non-migrating tides, migrating tides and stationary planetary waves. The annual occurrence rates of CEJS and CEJG seemed anti-correlated with F10.7.

Tidal Structures in the Mesosphere and Lower Thermosphere and Their Solar Cycle Variations

We studied the correlations between the migrating and non-migrating tides and solar cycle in the mesosphere and lower thermosphere (MLT) regions between 60° S and 60° N, which are in LAT-LON Earth coordinates, by analyzing the simulation datasets from the thermosphere and ionosphere extension of the Whole Atmosphere Community Climate Model (WACCM-X). A least squares fitting method was utilized to obtain the daily mean migrating tides and non-migrating tides. The Pearson linear correlation coefficient was used to analyze the correlations between tides and solar activity. Our analysis shows that the negative correlations between tides and solar activity are mostly impacted by the first symmetrical structure of the tidal modes for both migrating and non-migrating components. The coefficient of molecular thermal conductivity for the first symmetrical structure is small at low solar flux, so the tides dissipate more slowly when the F10.7 cm radio flux level is low. Thus, the amplitudes of tidal variations under a solar minimum condition are larger than those under a solar maximum condition. The correlation between tides and solar activity could also be influenced by some other factors, such as geomagnetic activity and the density of carbon dioxide CO2 on Earth. The tidal variations can be influenced by westward background wind, which grows stronger as geomagnetic activity rises. Further, dissipation of the tides decreases because the heat conduction and molecular viscosity are weakened in the cooling thermosphere caused by increasing CO2, which results in larger tidal amplitudes under the solar maximum condition. It is found that the correlations between tides and solar cycle vary at different altitudes and latitudes. The negative correlations are most possibly influenced by the first symmetrical structure of tidal variations and may also be impacted by geomagnetic activity. The positive correlations are impacted by the density of CO2.

Evaluation for effects of variable Martian upper atmosphere on ionospheric peak electron density based on the MGS RO observation

The Martian ionospheric peak is dominated by photochemical processes at dayside. Its primary variations can be well described by the Chapman theory; nevertheless, deviation still exists between observation and the theory. Some factors may be responsible for that deviation, in which the variable upper atmosphere is an important one. Ionospheric radio occultation (RO) measurement can be used to investigate the effect of the upper atmosphere on the Martian ionosphere, since concurrent variations of the ionospheric peak and the neutral scale height (Hn) can be estimated from RO electron density profiles. In this study, Hn was estimated from the Mars Global Surveyor (MGS) RO observation to quantitatively evaluate the effect of the upper atmosphere on the variability of the peak electron density of the M2 layer (NmM2). That effect manifests in the abilities of solar zenith angle functions for describing NmM2 variability and in the NmM2 deviation from the Chapman theory. Compared with the Chapman function, the simple cosine function is sufficiently accurate for describing dayside NmM2 variation owing to the cold Martian upper atmosphere that consists of heavier molecules, which weakens the spherical effect of planetary atmosphere. Hn variations, especially the longitudinal variation associated with non-migrating tides, are important factors responsible for the NmM2 deviation from the Chapman theory. Statistically, they can cause ∼1.4% average deviation for the condition of the MGS RO measurement. An effective modification method based on available Hn was correspondingly suggested to promote the accuracy of NmM2 estimation based on the Chapman theory. It is notable that Hn variations do not show evident contribution to NmM2 deviation from the Chapman theory in the southern hemisphere, where the stronger crustal magnetic fields likely have dominant contribution to the NmM2 deviation as compared with Hn variations.

Using Principal Component Analysis of Satellite and Ground Magnetic Data to Model the Equatorial Electrojet and Derive Its Tidal Composition

AbstractThe intensity of the equatorial electrojet (EEJ) shows temporal and spatial variability that is not yet fully understood nor accurately modeled. Atmospheric solar tides are among the main drivers of this variability but determining different tidal components and their respective time series is challenging. It requires good temporal and spatial coverage with observations, which, previously could only be achieved by accumulating data over many years. Here, we propose a new technique for modeling the EEJ based on principal component analysis (PCA) of a hybrid ground‐satellite geomagnetic data set. The proposed PCA‐based model (PCEEJ) represents the observed EEJ better than the climatological EEJM‐2 model, especially when there is good local time separation among the satellites involved. The amplitudes of various solar tidal modes are determined from PCEEJ based tidal equation fitting. This allows to evaluate interannual and intraannual changes of solar tidal signatures in the EEJ. On average, the obtained time series of migrating and nonmigrating tides agree with the average climatology available from earlier work. A comparison of tidal signatures in the EEJ with tides derived from neutral atmosphere temperature observations show a remarkable correlation for nonmigrating tides such as DE3, DE2, DE4, and SW4. The results indicate that it is possible to obtain a meaningful EEJ spectrum related to solar tides for a relatively short time interval of 70 days.

The Global Monsoon Convective System as Reflected in Upper Atmosphere Gravity Waves

AbstractThe concept of a global monsoon system collectively comprising 6 tropical regions is applied to Outgoing Longwave Radiation (OLR) as a proxy for convectively generated gravity waves (GWs), leading to the global monsoon convective system (GMCS). The six tropical regions are North and South Africa, Central and South America, and the South Asia‐Pacific and Malay Archipelago/Australia‐Pacific regions. The extended GMCS is considered in terms of gravity wave momentum fluxes (GWMFs) at 30, 50, 70, and 90 km altitude during the summer season in both hemispheres between December 2016, and August 2020. The GWMFs are inferred from TIMED/SABER temperature measurements. Intermonthly, interseasonal, and interannual variations in monthly mean GWMFs are interpreted in terms of OLR as a proxy for the spatial‐temporal variability of GW sources, and in terms of MERRA2 zonal winds that quantify the influences of changes in background propagation conditions. It is found that temporal variations in GWMFs associated with the GMCS as a whole are not highly correlated with OLR, but at 30, 50, and 70 km are quantitatively linked to Doppler‐shifting effects by local winds, wind filtering at 15 km altitude, and “instrument filtering.” These effects are also compared and examined in the context of GW variances at 50 km in Southern Hemisphere summer measured by the CIPS instrument on the AIM satellite, which measures a different part of the GW spectrum. The SABER GWMF response at 90 km is irregular and variable, but sometimes consists of 3‐ and 4‐peaked structures in longitude that may reflect nonmigrating tide influences on GW propagation conditions.

Analysis of migrating and non-migrating tides of the Extended Unified Model in the mesosphere and lower thermosphere

Abstract. Atmospheric tides play a key role in coupling the lower, middle, and upper atmosphere/ionosphere. The tides reach large amplitudes in the mesosphere and lower thermosphere (MLT), where they can have significant fluxes of energy and momentum, and so strongly influence the coupling and dynamics. The tides must therefore be accurately represented in general circulation models (GCMs) that seek to model the coupling of atmospheric layers and impacts on the ionosphere. The tides consist of both migrating (sun-following) and non-migrating (not sun-following) components, both of which have important influences on the atmosphere. The Extended Unified Model (ExUM) is a recently developed version of the Met Office's GCM (the Unified Model) which has been extended to include the MLT. Here, we present the first in-depth analysis of migrating and non-migrating components in the ExUM. We show that the ExUM produces both non-migrating and migrating tides in the MLT of significant amplitude across a rich spectrum of spatial and temporal components. The dominant non-migrating components in the MLT are found to be DE3, DW2, and DW3 in the diurnal tide and S0, SW1, and SW3 in the semidiurnal tide. These components in the model can have monthly mean amplitudes at a height of 95 km as large as 35 m s−1/10 K. All the non-migrating components exhibit a strong seasonal variability in amplitude, and a significant short-term variability is evident. Both the migrating and non-migrating components exhibit notable variation with latitude. For example, the temperature and wind diurnal tides maximise at low latitudes and the semidiurnal tides include maxima at high latitudes. A comparison against published satellite and ground-based observations shows generally good agreement in latitudinal tidal structure, with more differences in seasonal tidal structure. Our results demonstrate the capability of the ExUM for modelling atmospheric migrating and non-migrating tides, and this lays the foundation for its future development into a whole atmosphere model. To this end, we make specific recommendations on further developments which would improve the capability of the model.

Signature of a mesospheric bore in 557.7 nm airglow emission using all-sky imager at Hanle (32.7oN, 78.9oE)

A prominent signature of dark bore front in the mesospheric O( 1 S) airglow emission is observed on a night in the late winter at Hanle (32.7 o N, 78.9 o E) located in the western Himalaya. The leading front was followed by a series of evident trailing waves and the event lasts for more than two hours. The characteristic features of the bore indicate it to be linear undular type. Instantaneous temperature profile shows presence of stable region through formation of thermal duct in the upper mesosphere possibly supported by chemistry and/or dynamics. With time, the bore fronts became faint in presence of ripples as they reached other side of imager field of view (FOV). During the initial period around 3–4 waves h −1 appear to enter the imager FOV. The observed average phase speed, period and horizontal wavelength are found to be 40 m/s, 12 min and 29 km, respectively. The bore fronts exhibit a clockwise rotation at a rate of around 5° h −1 . The front edge perpendicular to the direction of propagation shows small-amplitude undulation indicating nonuniform duct structure. The tropospheric meteorological conditions may indicate plausible contribution from jet stream, weather front (linked with the Himalayan orography), and nonmigrating tides to excite and sustain the mesospheric bore event although further investigations in this direction are being sought to understand the actual underlying physical processes.

Concurrent effects of Martian topography on the thermosphere and ionosphere at high northern latitudes

Martian topography modulated non-migrating tides play important roles in the upper atmosphere and thus in the ionosphere through their coupling, especially in their longitude variations. In this study, the neutral scale height (Hn) and ionospheric peak electron density (NmM2) and height (hmM2) retrieved from the MGS radio occultation measurements were used to investigate the coupling between the Martian thermosphere and ionosphere under the forcing of topography modulated tides by investigating their concurrent longitude variations. A segment of the measurements with fixed local time was selected to analyze the relationships between the longitude variations of the parameters in detail. Longitude variations of the thermosphere and ionosphere are significant though topographic fluctuations are not very prominent at high northern latitudes. Longitude fluctuations of Hn and NmM2 are nearly in anti-phase and percentage fluctuation amplitudes of Hn are nearly twice as large as those of NmM2, which indicate the non-migrating tide forced coupling between the ionosphere and thermosphere conforms to the Chapman theory, and suggests longitude variation of NmM2 can be used as a quantitative indicator for that of the thermal structure in the lower thermosphere. Longitude variation phases of Hn and hmM2 are also discrepant. That is due to tide vertical propagation since Hn and hmM2 depend on the atmospheric thermal structures at different height levels. The thermosphere and ionosphere show longitude variations due to the topography; however, they are dominated by inconsistent longitude components. This implies discrepant exciting and propagating efficiencies of various topography modulated tides.Graphical

Intercomparison of middle atmospheric meteorological analyses for the Northern Hemisphere winter 2009–2010

Abstract. Detailed meteorological analyses based on observations extending through the middle atmosphere (∼ 15 to 100 km altitude) can provide key information to whole atmosphere modeling systems regarding the physical mechanisms linking day-to-day changes in ionospheric electron density to meteorological variability near the Earth's surface. However, the extent to which independent middle atmosphere analyses differ in their representation of wave-induced coupling to the ionosphere is unclear. To begin to address this issue, we present the first intercomparison among four such analyses, JAGUAR-DAS, MERRA-2, NAVGEM-HA, and WACCMX+DART, focusing on the Northern Hemisphere (NH) 2009–2010 winter, which includes a major sudden stratospheric warming (SSW). This intercomparison examines the altitude, latitude, and time dependences of zonal mean zonal winds and temperatures among these four analyses over the 1 December 2009 to 31 March 2010 period, as well as latitude and altitude dependences of monthly mean amplitudes of the diurnal and semidiurnal migrating solar tides, the eastward-propagating diurnal zonal wave number 3 nonmigrating tide, and traveling planetary waves associated with the quasi-5 d and quasi-2 d Rossby modes. Our results show generally good agreement among the four analyses up to the stratopause (∼ 50 km altitude). Large discrepancies begin to emerge in the mesosphere and lower thermosphere owing to (1) differences in the types of satellite data assimilated by each system and (2) differences in the details of the global atmospheric models used by each analysis system. The results of this intercomparison provide initial estimates of uncertainty in analyses commonly used to constrain middle atmospheric meteorological variability in whole atmosphere model simulations.

Longitudinal Structure in the Altitude of the Sporadic E Observed by COSMIC in Low-Latitudes

The longitudinal structure in the altitude of the Sporadic E (Es) was investigated for the first time based on the S4 index provided by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) in low latitudes. The longitudinal structure is identified as a symmetrically located wavenumber-4 (WN4) pattern within 30°S–30°N. The WN4 occurs primarily during the daytime at the June solstice and equinoxes, with the largest amplitude at the September equinox and the smallest one at the March equinox. It moves eastward with a speed of ~90°/day. The strongest WN4 appears within 10–20°N and 5–15°S in the Northern and Southern hemispheres, respectively. At the June solstice and the September equinox, the WN4 is stronger in the Northern hemisphere than in the Southern hemisphere, while the situation is reversed at the March equinox. The altitude distribution of the convergence null in the diurnal eastward non-migrating tide with zonal wavenumber-3 (DE3) for the zonal wind is similar to that of the WN4. This and other similar features, such as the seasonal variation, eastward speed, and the symmetrical locations, support the dominant role of the DE3 tide for the formation of the WN4 structure.

Thermal structure of Mars’ middle and upper atmospheres: Understanding the impacts of dynamics and solar forcing

We report six years of observations of dayside temperatures of the middle and upper atmospheres of Mars made by the Imaging Ultraviolet Spectrograph instrument aboard the MAVEN spacecraft. Thermospheric temperatures show strong long-term variability associated with Martian season and solar cycle. Temperatures from both the Martian thermosphere and mesosphere show strong short-term variability indicating coupling from the lower atmosphere. The observed local time effect is strong in both upper and middle atmosphere temperatures. The thermosphere tends to be colder in the morning compared to the evening when temperatures are higher. Middle atmospheric temperatures show cooling during the dawn and dusk hours. Our analysis shows strong tidal activity during aphelion, whereas non-migrating tides are suppressed during perihelion, possibly due to increased dust activity. Observations during the deep minimum of solar cycle 24 reveal that thermospheric temperatures are highly variable with respect to local time if solar forcing, Mars–Sun distance, and spatial effects are removed.

First results from the retrieved column O/N2 ratio from the Ionospheric Connection Explorer (ICON): Evidence of the impacts of nonmigrating tides.

In near-Earth space, variations in thermospheric composition have important implications for thermosphere-ionosphere coupling. The ratio of O to N2 is often measured using far-UV airglow observations. Taking such airglow observations from space, looking below the Earth's limb allows for the total column of O and N2 in the ionosphere to be determined. While these observations have enabled many previous studies, determining the impact of non-migrating tides on thermospheric composition has proved difficult, owing to a small contamination of the signal by recombination of ionospheric O+. New ICON observations of far UV are presented here, and their general characteristics are shown. Using these, along with other observations and a global circulation model we show that during the morning hours and at latitudes away from the peak of the equatorial ionospheric anomaly, the impact of non-migrating tides on thermospheric composition can be observed. During March - April 2020, the column O/N2 ratio was seen to vary by 3 - 4 % of the zonal mean. By comparing the amplitude of the variation observed with that in the model, both the utility of these observations and a pathway to enable future studies is shown.