Sounding Of The Atmosphere Using Broadband Emission Radiometry Temperature Research Articles

Global Middle-Atmosphere Response to Winter Stratospheric Variability in SABER and MLS Mean Temperature

Abstract Satellite observations of middle-atmosphere temperature are used to investigate the short-term global response to planetary wave activity in the winter stratosphere. The focus is on the relation between variations in the winter and summer hemispheres. The analysis uses observations from Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics (TIMED) Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) for 2002–21 and Aura Microwave Limb Sounder (MLS) for 2004–21, and reanalysis temperatures and winds from MERRA-2 for 2002–21. We calculate temporal correlations of the Eliassen–Palm flux divergence in the winter stratosphere with global temperature. Results show a robust perturbation extending to midlatitudes of the Southern Hemisphere (SH) stratosphere during Northern Hemisphere (NH) winter. An increase in wave forcing is followed by a decrease in temperatures over the depth of the stratosphere in the SH, peaking at a lag of 3 days. Summer mesospheric temperature perturbations of the opposite sign are seen in many winters. Comparable signals in the NH summer middle-atmosphere are present during some SH winters but are weaker and less consistent than those in the SH during NH winter. A diagnostic evaluation of the patterns of correlation, the mesospheric zonal winds, and the stability criteria suggests that the temperature perturbations in the midlatitude summer mesosphere are more closely associated with the summer stratosphere directly below than with the wave activity in the winter stratosphere. This suggests that the interhemispheric coupling in the stratosphere is driving or contributing to the coupling between the winter stratosphere and the summer mesosphere that has been reported in several investigations. Significance Statement There are many instances in which one part of the atmosphere is found to regularly respond to perturbations occurring in a distant region. In this study, we use observations to investigate one such pattern: temperature changes at high altitude (60–100 km) in the summer that follow dynamical changes near the winter pole at 40–60 km. Such analysis is useful to understand which physical processes contribute to the global connectivity and variability of the atmosphere.

Trends in the Airglow Temperatures in the MLT Region—Part 3: Ground-Based and SABER Measurements

Ground-based temperature measurements at Svalbard, Wuppertal, and Hohenpeissenberg were analyzed to obtain F10.7, Ap index, and Dst index trends. The trends were then compared to those obtained from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature measurements at the same locations. Trend analysis was carried out for overlapped time periods, full range of available data, and the CO2-detrended full range of available data. The Svalbard meteor radar (SABER) temperature showed a weak (moderate) correlation with F10.7 and a moderate (weak) correlation with Ap and Dst indices. The trends in the Wuppertal OH* temperature compare well with the SABER temperature when a full range of data is used in the analysis. Both temperatures had a similar F10.7 trend with the same level of correlation coefficient. The F10.7 trend in the Hohenpeissenberg OH* temperature compared well with that obtained by SABER, but the former displayed a weak correlation. The Hohenpeissenberg data displayed a very weak correlation with Ap and Dst indices. Our study clearly shows that a longer dataset would better capture trends in temperature, as was evidenced by the results of Wuppertal data. The CO2-detrended temperatures overall showed slightly larger trend values with a slightly better correlation.

A case study of a thermally ducted undular mesospheric bore accompanied by ripples over the western Himalayan region

An undular mesospheric bore event has been recorded over the western Himalayan region in O(1S) 557.7 nm airglow images on a clear and moonless night of 02 October 2018 using a multi-wavelength all-sky imager at Hanle, Leh Ladakh, India (32.77°N, 78.97°E). The bore has a prominent leading dark front followed by trailing waves and it propagates with a mean observed phase velocity of ~31 ± 5 m/s. It also shows a small-scale undulation and clockwise rotation in its phase front. In order to understand the evolution of the bore, vertical temperature profiles from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard TIMED satellite and HWM14 wind maps are used. SABER temperature shows a mesospheric inversion layer prior to the occurrence of the bore event which acted as a thermal duct layer to guide the propagation of the bore. The analyses also suggest that inhomogeneity in the duct depth at different parts of the bore’s horizontal extension could lead the small-scale undulations in the bore phase fronts. The same can also be responsible for the rotation of the bore. Additionally, the peak separation of the bore’s trailing waves suggests that large-scale gravity wave interaction with pre-existing thermal duct could be the potential source for the generation of the undular bore at mesospheric height. Furthermore, the present results indicate that neutral instabilities and weakening duct layer in the path of the bore propagation might have accelerated the faster dissipation of the bore’s energy and consequently suppress its long-distance horizontal propagation.

Effects of Latitude-Dependent Gravity Wave Source Variations on the Middle and Upper Atmosphere

Atmospheric gravity waves (GWs) are generated in the lower atmosphere by various weather phenomena. They propagate upward, carry energy and momentum to higher altitudes, and appreciably influence the general circulation upon depositing them in the middle and upper atmosphere. We use a three-dimensional first-principle general circulation model (GCM) with implemented nonlinear whole atmosphere GW parameterization to study the global climatology of wave activity and produced effects at altitudes up to the upper thermosphere. The numerical experiments were guided by the GW momentum fluxes and temperature variances as measured in 2010 by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument onboard NASA’s TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite. This includes the latitudinal dependence and magnitude of GW activity in the lower stratosphere for the boreal summer season. The modeling results were compared to the SABER temperature and total absolute momentum flux and Upper Atmosphere Research Satellite (UARS) data in the mesosphere and lower thermosphere. Simulations suggest that, in order to reproduce the observed circulation and wave activity in the middle atmosphere, GW fluxes that are smaller than observed fluxes have to be used at the source level in the lower atmosphere. This is because observations contain a broader spectrum of GWs, while parameterizations capture only a portion relevant to the middle and upper atmosphere dynamics. Accounting for the latitudinal variations of the source appreciably improves simulations.

Trends in the Airglow Temperatures in the MLT Region—Part 2: SABER Observations and Comparisons to Model Simulations

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature measurements at low latitudes from 89 km to 97 km were used to derive the F10.7 and Ap index trends, and the trends were compared to model simulations. The annual mean nonzonal (e.g., at the model simulation location at 18° N, 290° E) SABER temperature showed a good-to-moderate correlation with F10.7, with a trend of 4.5–5.3 K/100 SFU, and a moderate-to-weak correlation with the Ap index, with a trend of 0.1–0.3 K/nT. The annual mean zonal mean SABER temperature was found to be highly correlated with the F10.7, with a similar trend, and moderately correlated with the Ap index, with a trend in a similar range. The correlation with the Ap index was significantly improved with a slightly larger trend when the zonal mean temperature was fitted with a 1-year backward shift in the Ap index. The F10.7 (Ap index) trends in the simulated O2 and the O(1S) temperature were smaller (larger) than those in the annual mean nonzonal mean SABER temperature. The trends from the simulations were better compared to those in the annual mean zonal mean temperature. The comparisons were even better when compared to the trend results obtained from fitting with a backward shift in the Ap index.

Gravity-wave-perturbed wind shears derived from SABER temperature observations

Abstract. Large wind shears around the mesopause region play an important role in atmospheric neutral dynamics and ionospheric electrodynamics. Based on previous observations using sounding rockets, lidars, radars, and model simulations, large shears are mainly attributed to gravity waves (GWs) and modulated by tides (Liu, 2017). Based on the dispersion and polarization relations of linear GWs and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature data from 2002 to 2019, a method of deriving GW-perturbed wind shears is proposed. The zonal-mean GW-perturbed shears have peaks (13–17 ms−1 km−1) at around the mesopause region, i.e., at z = 90–100 km at most latitudes and at z = 80–90 km around the cold summer mesopause. This latitude–height pattern is robust over the 18 years and agrees with model simulations. The magnitudes of the GW-perturbed shears exhibit year-to-year variations and agree with the lidar and sounding rocket observations in a climatological sense but are 60 %–70 % of the model results in the zonal-mean sense. The GW-perturbed shears are hemispherically asymmetric and have strong annual oscillation (AO) at around 80 km (above 92 km) at the northern (southern) middle and high latitudes. At middle to high latitudes, the peaks of AO shift from winter to summer and then to winter again with increasing height. However, these GW-perturbed shears may be overestimated because the GW propagation direction cannot be resolved by the method and may be underestimated due to the observational filter, sampling distance, and cutoff criterion of the vertical wavelength of GWs.

Intercomparison and evaluation of ground- and satellite-based stratospheric ozone and temperature profiles above Observatoire de Haute-Provence during the Lidar Validation NDACC Experiment (LAVANDE)

Abstract. A two-part intercomparison campaign was conducted at Observatoire de Haute-Provence (OHP) for the validation of lidar ozone and temperature profiles using the mobile NASA Stratospheric Ozone Lidar (NASA STROZ), satellite overpasses from the Microwave Limb Sounder (MLS), the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), meteorological radiosondes launched from Nîmes, and locally launched ozonesondes. All the data were submitted and compared “blind”, before the group could see results from the other instruments. There was good agreement between all ozone measurements between 20 and 40 km, with differences of generally less than 5 % throughout this region. Below 20 km, SABER and MLS measured significantly more ozone than the lidars or ozonesondes. Temperatures for all lidars were in good agreement between 30 and 60 km, with differences on the order of ±1 to 3 K. Below 30 km, the OHP lidar operating at 532 nm has a significant cool bias due to contamination by aerosols. Systematic, altitude-varying bias up to ±5 K compared to the lidars was found for MLS at many altitudes. SABER temperature profiles are generally closer to the lidar profiles, with up 3 K negative bias near 50 km. Total uncertainty estimates for ozone and temperature appear to be realistic for nearly all systems. However, it does seem that the very low estimated uncertainties of lidars between 30 and 50 km, between 0.1 and 1 K, are not achieved during Lidar Validation Network for the Detection of Atmospheric Composition Change (NDACC) Experiment (LAVANDE). These estimates might have to be increased to 1 to 2 K.

A Comparison of Einstein A Coefficients for OH Rotational Temperature Measurements Using a Large Astronomical Data Set

The Einstein A coefficients are considered to be a significant source of uncertainty in the measurement of OH rotational temperatures. Using simultaneous ground and spaced-based observations of OH emission, five sets of Einstein A coefficients were examined for their impact upon rotational temperature calculations. The ground-based observations are taken from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) instrument which is a high resolution, r = λ / Δ λ ≥ 20 , 000 , spectrograph operating in the H-band from approximately 1.5 to 1.7 μ m. APOGEE collected over one-hundred-and-fifty-thousand spectra of the night sky over a period from June 2011 to June 2013. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite has made simultaneous atmospheric measurements with the APOGEE spectrograph. SABER observes the OH volume emission rate (VER) around 1.6 μ m, providing measurements coincident with those of the OH emission in the APOGEE sky spectra. Four of the five sets of Einstein A coefficients tested yielded statistically identical mean rotational temperatures of approximately 195 K for the OH ( 4 − 2 ) transition. The Einstein A coefficients were found to have a significant impact upon the measured OH ( v ′ = 4 ) vibrational populations with some sets of coefficients yielding populations over 50% greater. Simultaneous SABER observations were used to determine which set of Einstein A coefficients best reflected atmospheric temperatures, and four of the five tested coefficients yielded nearly identical results. The difference between OH rotational temperatures and SABER temperatures was on average 1 K.

Variation of Small‐Scale Gravity Wave Activity in the Ionosphere During the Major Sudden Stratospheric Warming Event of 2009

AbstractThe present study investigates the effect of the major sudden stratospheric warming (SSW) event of 2009, on the small‐scale gravity wave (GW) activity in the ionosphere. Small‐scale fluctuations with time periods within the range of 10–90 min observed in Global Positioning System total electron content (TEC) data have been used as a proxy for GW activity in the ionosphere. TEC data from five longitudinally separated Global Positioning System stations located around 60∘N latitude have been utilized for this purpose. In the initial phase of the major warming, when the stratospheric conditions are similar to a minor warming during which the mean zonal flow starts to weaken, the ionopsheric GW activity tends to increase. However, during the peak phase of the SSW, as the zonal mean wind starts to reverse its direction, and after the peak warming, as the winds remain weak, conditions are less favorable for upward propagation of a spectrum of GWs, and thus the ionospheric GW activity is reduced, as seen from the behavior of the small‐scale TEC fluctuations during the latter period of the SSW. Similar reduction in GW activity is also observed in the middle atmosphere (65–100 km) as seen from GWs derived from SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) temperature profiles. The reductions in GW activity is more prominent during local daytime as compared to nighttime period. The reduction in GW activity shows a longitudinal variation with some locations showing relatively more reduction in the GW activity as compared to others.

Quasi-90-day oscillation observed in the MLT region at low latitudes from the Kunming meteor radar and SABER

Observations of a quasi-90-day oscillation in the mesosphere and lower thermosphere (MLT) region from April 2011 to December 2014 are presented in this study. There is clear evidence of a quasi-90-day oscillation in temperatures obtained from the Kunming meteor radar (25.6°N, 103.8°E) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), as well as in wind observed by the Kunming meteor radar. The quasi-90-day oscillation appears to be a prominent feature in the temperatures and meridional wind tides and presents quite regular cycles that occur approximately twice per year. The amplitudes and phases of the quasi-90-day oscillation in the SABER temperature show a feature similar to that of upward-propagated diurnal tides, which have a vertical wavelength of ~20 km above 70 km. In the lower atmosphere, a similar 90-day variability is presented in the surface latent heat flux and correlates with the temperature in the MLT region. Similar to the quasi-90-day oscillation in temperature, a 90-day variability of ozone (O3) is also present in the MLT region and is considered to be driven by a similar variability in the upwardly-propagated diurnal tides generated in the lower atmosphere. Moreover, the 90-day variability in the absorption of ultraviolet (UV) radiation by daytime O3 in the MLT region is an in situ source of the quasi-90-day oscillation in the MLT temperature.

Variations of global gravity waves derived from 14 years of SABER temperature observations

AbstractThe global gravity wave (GW) potential energy (PE) per unit mass is derived from SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) temperature profiles over the past 14 years (2002–2015). Since the SABER data cover longer than one solar cycle, multivariate linear regression is applied to calculate the trend (means linear trend from 2002 to 2015) of global GW PE and the responses of global GW PE to solar activity, to QBO (quasi‐biennial oscillation) and to ENSO (El Niño–Southern Oscillation). We find a significant positive trend of GW PE at around 50°N during July from 2002 to 2015, in agreement with ground‐based radar observations at a similar latitude but from 1990 to 2010. Both the monthly and the deseasonalized trends of GW PE are significant near 50°S. Specifically, the deseasonalized trend of GW PE has a positive peak of 12–15% per decade at 40°S–50°S and below 60 km, which suggests that eddy diffusion is increasing in some places. A significant positive trend of GW PE near 50°S could be due to the strengthening of the polar stratospheric jets, as documented from Modern Era Retrospective‐analysis for Research and Applications wind data. The response of GW PE to solar activity is negative in the lower and middle latitudes. The response of GW PE to QBO (as indicated by 30 hPa zonal winds over the equator) is negative in the tropical upper stratosphere and extends to higher latitudes at higher altitudes. The response of GW PE to ENSO (as indicated by the Multivariate ENSO Index) is positive in the tropical upper stratosphere.

Daily estimates of the migrating tide and zonal mean temperature in the mesosphere and lower thermosphere derived from SABER data

AbstractSatellites provide a global view of the structure in the fields that they measure. In the mesosphere and lower thermosphere, the dominant features in these fields at low zonal wave number are contained in the zonal mean, quasi‐stationary planetary waves, and tide components. Due to the nature of the satellite sampling pattern, stationary, diurnal, and semidiurnal components are aliased and spectral methods are typically unable to separate the aliased waves over short time periods. This paper presents a data processing scheme that is able to recover the daily structure of these waves and the zonal mean state. The method is validated by using simulated data constructed from a mechanistic model, and then applied to Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature measurements. The migrating diurnal tide extracted from SABER temperatures for 2009 has a seasonal variability with peak amplitude (20 K at 95 km) in February and March and minimum amplitude (less than 5 K at 95 km) in early June and early December. Higher frequency variability includes a change in vertical structure and amplitude during the major stratospheric warming in January. The migrating semidiurnal tide extracted from SABER has variability on a monthly time scale during January through March, minimum amplitude in April, and largest steady amplitudes from May through September. Modeling experiments were performed that show that much of the variability on seasonal time scales in the migrating tides is due to changes in the mean flow structure and the superposition of the tidal responses to water vapor heating in the troposphere and ozone heating in the stratosphere and lower mesosphere.

Mesospheric temperatures estimated from the meteor radar observations at Mohe, China

AbstractIn this work, we report the estimation of mesospheric temperatures at 90 km height from the observations of the VHF all‐sky meteor radar operated at Mohe (53.5°N, 122.3°E), China, since August 2011. The kinetic temperature profiles retrieved from the observations of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on board the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics satellite are processed to provide the temperature (TSABER) and temperature gradient (dT/dh) at 90 km height. Based on the SABER temperature profile data an empirical dT/dh model is developed for the Mohe latitude. First, we derive the temperatures from the meteor decay times (Tmeteor) and the Mohe dT/dh model gives prior information of temperature gradients. Second, the full width at half maximum (FWHM) of the meteor height profiles is calculated and further used to deduce the temperatures (TFWHM) based on the strong linear relationship between FWHM and TSABER. The temperatures at 90 km deduced from the decay times (Tmeteor) and from the meteor height distributions (TFWHM) at Mohe are validated/calibrated with TSABER. The temperatures present a considerable annual variation, being maximum in winter and minimum in summer. Harmonic analyses reveal that the temperatures have an annual variation consistent with TSABER. Our work suggests that FWHM has a good performance in routine estimation of the temperatures. It should be pointed out that the slope of FWHM as a function of TSABER is 10.1 at Mohe, which is different from that of 15.71 at King Sejong (62.2°S, 58.8°E) station.

Properties of the Long-Term Oscillations in the Middle Atmosphere Based on Observations from TIMED/SABER Instrument and FPI over Kelan

The properties of the long-term oscillations in the middle atmosphere have been investigated using the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature data and Fabry–Perot interferometer (FPI) data. Results for SABER temperature show that the semiannual oscillation (SAO) has three amplitude maxima at altitudes of 45, 75, and 85 km, respectively, and shows prominent seasonal asymmetries there. The SAOs in the upper mesosphere (75 km) are out of phase with those in the mesopause (85 km) in the tropical regions, which can generate an enhancement of 11 K on average at each equinox, contributing to the lower mesospheric inversion layer (MIL). It is shown that stronger enhancement can be found at the spring equinox than at the autumn equinox. The triennial oscillation (TO) is significant in the tropical region. The spectral peak of the TO is probably a sub-peak of the quasi-biennial oscillation (QBO) and is due to modulation of QBO. In addition, there may be potential interaction of the TO with SAO at 85 km at the equator. The relation between ENSO and TO has also been discussed. The ENSO signal may modulate the amplitude of the TO, mainly in the lower stratosphere. The annual oscillation (AO) and SAO are analyzed over Kelan by FPI data. Generally, the amplitudes of FPI wind are smaller than those of the Horizontal Wind Model (HWM07). The comparison between FPI and TIMED Doppler Interferometer (TIDI) winds shows relatively large discrepancy. This may be due to the tidal aliasing in the nighttime results derived from the FPI data. Results also show that the algorithm to derive FPI temperature needs improvements.

Low‐latitude gravity wave variances in the mesosphere and lower thermosphere derived from SABER temperature observation and compared with model simulation of waves generated by deep tropical convection

AbstractA portion of waves generated by deep convection have scales and amplitudes large enough to be detected by spaceborne instruments. We have analyzed temperature data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite for subtidal‐scale fluctuations. Filtering was applied both vertically and horizontally to extract wave variances. We have analyzed the altitude region between 70 and 130 km and focus on the variances at equatorial latitudes for the altitude region between 70 and 120 km as a function of season, local time intervals, geographical location, and altitude. We find significant variances where convection is particularly prolific (Intertropical Convergence Zone) and at altitudes where wave trapping is known to be favored (e.g., the lower thermospheric duct). The locations of significant variances persist from year to year. Standard deviations of a few tens of kelvins are found. We have also performed simulations of the response to deep tropical convection with a time‐dependent, high‐resolution fully compressible dynamical model. Our simulations give wave amplitudes that agree reasonably well with the observed amplitudes and show layering that is consistent with the observations. Our main finding is that significant variations seen in TIMED/SABER temperature data have a convective wave source and are concentrated in layers where thermal ducts occur.

On the latitudinal distribution of mesospheric temperatures during sudden stratospheric warming events

AbstractMesospheric rotational temperatures from O2(0‐1) and OH(6‐2) band nightglow emissions that originate from 94 and 87 km altitudes, respectively, were obtained from a low‐latitude location, Mount Abu (24.6°N, 72.8°E), in India using a high spectral resolution grating spectrograph, which showed significant enhancements during the major sudden stratospheric warming (SSW) event of January 2013. To investigate the relationship of these enhancements in the context of SSW occurrences, a detailed study was carried out for 11 SSW events that occurred during 2004–2013 using SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) data. In addition to SABER, Optical Spectrograph and Infrared Imaging System and Solar Occultation For Ice Experiment mesospheric temperatures were also used which showed similar latitudinal behavior as obtained by SABER. The longitudinal mean mesospheric temperatures at different latitudes of Northern and Southern Hemispheres have been derived. It is found that during SSW events the well‐known mesospheric cooling over the Northern Hemispheric high latitudes turns to heating over midlatitudes and then reverts to cooling closer to equatorial regions. This trend continues into the Southern Hemisphere as well. These variations in the mesospheric temperatures at different latitudes have been characterized based on northern hemispheric stratospheric temperature enhancements at high latitudes during SSW periods. In comparison with the COSPAR International Reference Atmosphere‐86‐derived temperatures, the SABER temperatures show an increase/decrease in Southern/Northern Hemisphere. Such a characterization in mesospheric temperatures with respect to latitudes reveals a hitherto unknown intriguing nature of the latitudinal coupling in the mesosphere that gets set up during the SSW events.

A superposed epoch study of the effects of solar wind stream interface events on the upper mesospheric and lower thermospheric temperature

The response of mesosphere and lower thermosphere (MLT) temperature to energetic particle precipitation over the Earth’s polar regions is not uniform due to complex phenomena within the MLT environment. Nevertheless, the modification of MLT temperatures may require an event-based study to be better observed. This work examines the influence of precipitation, triggered by solar wind stream interfaces (SI) event from 2002 to 2007, on polar MLT temperature. We first test the relationship between the ionospheric absorption measured by the SANAE IV (South African National Antarctic Expedition IV) riometer and the layer of energetic particle precipitation from POES (Polar Orbiting Environmental Satellites). The combined particle measurements from POES 15, 16, 17 and 18 were obtained close in time to the pass of the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) temperature retrieval. Here, a superposed epoch technique is described and implemented to obtain average temperature profiles during SI-triggered particle precipitation. The superposed epoch average shows no significant temperature decrease below 100 km prior to the onset of SI-triggered precipitation, whereas a clear superposed average temperature decrease is observed at 95 km after the SI impact. A case study of SI event also yields similar observations. Results indicate that cooling effects due to the production of mesospheric odd hydrogen might be major contributors to temperature decrease under compressed solar wind stream.

Atomic hydrogen in the mesopause region derived from SABER: Algorithm theoretical basis, measurement uncertainty, and results

Atomic hydrogen (H) is a fundamental component in the photochemistry and energy balance of the terrestrial mesopause region (80–100 km). H is generated primarily by photolysis of water vapor and participates in a highly exothermic reaction with ozone. This reaction is a significant source of heat in the mesopause region and also creates highly vibrationally excited hydroxyl (OH) from which the Meinel band radiative emission features originate. Concentrations (cm−3) and volume mixing ratios of H are derived from observations of infrared emission from the OH (υ = 9 + 8, Δυ = 2) vibration-rotation bands near 2.0 µm made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. The algorithms for deriving day and night H are described herein. Day and night concentrations exhibit excellent agreement between 87 and 95 km. SABER H results also exhibit good agreement with observations from the Solar Mesosphere Explorer made nearly 30 years ago. An apparent inverse dependence on the solar cycle is observed in the SABER H concentrations, with the H increasing as solar activity decreases. This increase is shown to be primarily due to the temperature dependence of various reaction rate coefficients for H photochemistry. The SABER H data, coupled with SABER atomic oxygen, ozone, and temperature, enable tests of mesospheric photochemistry and energetics in atmospheric models, studies of formation of polar mesospheric clouds, and studies of atmospheric evolution via escape of hydrogen. These data and studies are made possible by the wide range of parameters measured simultaneously by the SABER instrument.

Global structure and seasonal variability of the migrating terdiurnal tide in the mesosphere and lower thermosphere

The morphology of the migrating terdiurnal tide with zonal wavenumber 3 (TW3) in the mesosphere and lower thermosphere (MLT) is revealed using the TIMED satellite datasets from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and the TIMED Doppler Interferometer (TIDI) instruments from 2002 to 2009, as well as the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM). The annual mean structures of the TW3 from the TIME-GCM clearly resemble the first real symmetric (3,3) Hough mode. The TW3 temperature and zonal wind components have three peaks at midlatitudes and near the equator, while the TW3 meridional wind components show four peaks at mid and low latitudes. These features are consistent with those resolved in SABER temperature and TIDI zonal wind above ~95km. TW3 components in the TIME-GCM are stronger during winter and spring months at midlatitudes, which is in agreement with previous ground-based radar measurements. On the other hand, TW3 components of temperature, zonal and meridional winds from SABER and TIDI display different seasonal variations at different altitudes and latitudes. The results presented in this paper will provide an observational basis for further modeling study of terdiurnal tide impacts on the thermosphere and ionosphere.

TIMED/SABER observations of lower mesospheric inversion layers at low and middle latitudes

We present the global distribution, seasonal, and interannual variations of the lower mesospheric inversion layers (MILs) using SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) temperature data. We show that both the characteristics and the formation mechanisms of large spatiotemporal‐scale lower MILs are latitude dependent. At low latitudes, the monthly zonal mean amplitude of the lower MILs exhibits a semi‐annual cycle and reaches a maximum of ∼40 K in spring and a secondary maximum of ∼30 K in autumn. On the equator, the semi‐annual oscillations in the background and diurnal‐migrating‐tide temperatures could contribute more than 12 and 25 K, respectively, suggesting they are the key causes of large spatiotemporal‐scale lower MILs at low latitudes. At middle latitudes, the monthly zonal mean amplitude of the lower MILs exhibits an annual cycle with its maximum in the range 24–33 K in winter. In addition, their longitudinal distribution and daily variation in winter are closely correlated with the transient structure of a composite wave composed of stationary and westward‐propagating quasi‐16‐day planetary waves with zonal wave number 1. The correlation coefficient between the lower MILs and the composite wave can sometimes reach unity. The composite planetary wave could contribute temperature enhancements of at least 15–20 K to the lower MILs. Thus, we believe that the transient structure of planetary waves is also an important cause of the large spatiotemporal‐scale lower MILs in winter at middle latitudes, in addition to previously proposed mechanisms.