Thermosphere Ionosphere Mesosphere Energetics Dynamics Research Articles

Observational Evidence for the Influence of Diurnal Tide in Driving Winds in the Polar Upper Mesosphere and Lower Thermosphere

AbstractThe meteor radar wind observations over Esrange (67.9°N, 21.10°E) and Rothera (67.5°S, 68.1°W), located respectively in the northern and southern polar latitudes show seasonal variation in the upper mesosphere and lower thermosphere (UMLT) winds with strong westward flow in the zonal wind and equatorward flow in the meridional wind during April‐September over Esrange and October‐February over Rothera. The semi‐diurnal tide shows larger amplitudes over Esrange than over Rothera. However, the diurnal tide (DT) shows comparable amplitudes in both stations. The DT amplitude decreases with height over both stations. Significant correlations between the DT amplitude and mean zonal wind (−0.74 for Esrange and −0.54 and −0.77 for Rothera) indicate the possible role of DT in driving the westward winds. The space‐time spectral analysis of the temperature obtained from the radiance observations of the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on board the TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite reveals the summer maximum of migrating diurnal tide of zonal wavenumber 1 (DW1) over both 60°N and 60°S, indicating that the DT is mostly composed of DW1. These results suggest that the westward winds in the polar UMLT region are largely driven by the westward momentum contributed by the DW1 tide due to its interaction with the background wind.

Critical Dynamics in Stratospheric Potential Energy Variations Prior to Significant (M > 6.7) Earthquakes

Lithosphere–atmosphere–ionosphere coupling (LAIC) is studied through various physical or chemical quantities, obtained from different sources, which are observables of the involved complex processes. LAIC has been proposed to be achieved through three major channels: the chemical, the acoustic, and the electromagnetic. Accumulated evidence supporting the acoustic channel hypothesis has been published, while atmospheric gravity waves (AGWs) play a key role in LAIC as the leading mechanism for the transmission of energy from the lower atmosphere to the stratosphere and mesosphere, associated with atmospheric disturbances observed prior to strong earthquakes (EQs). The seismogenic AGW is the result of temperature disturbances, usually studied through stratospheric potential energy (EP). In this work, we examined 11 cases of significant EQs (M > 6.7) that occurred during the last 10 years at different geographic areas by analyzing the temperature profile at the wider location of each one of the examined EQs. The “Sounding of the Atmosphere using Broadband Emission Radiometry” (SABER) instrument, part of the “Thermosphere Ionosphere Mesosphere Energetics Dynamics” (TIMED) satellite, data were employed to compute the potential energy (EP) of the AGW. Using the temperature profile, we first calculated EP and determined the altitudes’ range for which prominent pre-seismic disturbances were observed. Subsequently, the EP time series at specific altitudes, within the determined “disturbed” range, were for the first time analyzed using the criticality analysis method termed the “natural time” (NT) method in order to find any evidence of an approach to a critical state (during a phase transition from a symmetric phase to a low symmetry phase) prior to the EQ occurrence. Our results show criticality indications in the fluctuation of EP a few days (1 to 15 days) prior to the examined EQs, except from one case. In our study, we also examined all of the temperature-related extreme phenomena that have occurred near the examined geographic areas, in order to take into account any possible non-seismic influence on the obtained results.

Diurnal Response of the Thermospheric radiative cooling to March 16–21, 2015 Geomagnetic Storm

It is well known that huge amount of energy is deposited into the high latitude thermosphere region during geomagnetic storm events. The energy deposition increases the thermospheric temperature by hundreds of degree kelvin. The radiative cooling by Nitric Oxide (NO) at 5.3 μm and CO2 at 15 μm emissions, being dominant coolants in the thermosphere, play important roles in regulating the thermospheric temperature during geomagnetic storm period. We utilized the NO 5.3 μm and CO2 15 μm radiative emissions, as observed by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) onboard NASA’s TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite, to investigate the diurnal response of thermospheric cooling to March 16–21, 2015 storm. We also used the atomic oxygen density and temperature from the TIMED-SABER satellite to explore their correlations with the cooling flux. It is observed that the CO2 and NO cooling emissions respond differently to the March 16–21, 2015 storm during day and night. Both the NO (about five times) and CO2 (about 70%) emission show strong enhancement during storm period. A stronger enhancement and a quicker recovery is observed in the NO 5.3 μm emission. Although the CO2 emission shows lesser enhancement than the NO emission, it lasts longer than the later. The CO2 emission takes about 5–6 days to return to its pre-onset value. The response of the NO 5.3 μm emission is short-term and lasts for about 3–4 days before returning to the pre-onset value. The NO and CO2 emission exhibit strong positive correlation with the storm’s intensity both during day and night suggesting that more intense is the storm more energy exits the thermosphere.

Solar Radiation and Climate Experiment (SORCE) X-Ray Photometer System (XPS): Final Data-Processing Algorithms

The X-ray Photometer System (XPS) is one of four instruments onboard NASA’s Solar Radiation and Climate Experiment (SORCE) mission. The SORCE spacecraft operated from 2003 to 2020 to provide key climate-monitoring measurements of total solar irradiance (TSI) and solar spectral irradiance (SSI). The XPS is a set of photometers to measure the solar X-ray ultraviolet (XUV) irradiance shortward of 34 nm and the bright hydrogen emission at 121.6 nm. Each photometer has a spectral bandpass of about 7 nm, and the XPS measurements have an accuracy of about 20%. The updates for the final data-processing algorithms for the XPS solar-irradiance data products are described. These processing updates include improvements for the instrumental corrections for background signal, visible-light signal, and degradation trending. Validation of these updates is primarily with measurements from a very similar XPS instrument onboard NASA’s Thermosphere-Ionosphere-Mesosphere-Energetics-Dynamics (TIMED) mission. In addition, the XPS Level 4 spectral model has been improved with new reference spectra derived with recent XUV observations from NASA’s Solar Dynamics Observatory (SDO) and Miniature X-ray Solar Spectrometer (MinXSS) cubesat.

Short- and long-term stationary planetary wave variability in the middle atmosphere in contemporaneous satellite and reanalysis data

Short- and long-term variabilities of stationary planetary waves (SPW) in the middle atmosphere are investigated from temperatures obtained from two satellites (Formosa Satellite-3/Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED)) and a reanalysis dataset (ERA-Interim). COSMIC data analysis with a smaller window size enables investigation of short-term variabilities and wavelet analysis shows the presence of 30 to 120 days oscillations in the stratosphere during different years and are attributed to wave-mean flow interactions. This result in observational data is seen only due to the use of COSMIC data and its unique sampling pattern that enabled the extraction of short-term variability. Additionally, annual and quasi-biennial features are also observed. SABER analysis also shows similar long-term variations. The annual variation in both datasets shows linearly increasing spectral power indicating that the stratosphere is increasingly becoming chaotic and irregular and the dynamics are becoming stronger and expanding equatorward. Vertically upward propagation of SPW1 and SPW2 into the mesosphere is hindered during Sudden Stratospheric Warmings (SSW) due to the prevalent westward winds and smaller mesospheric amplitudes are observed. During no SSW years, larger SPW1 and SPW2 amplitudes are seen in the mesosphere. A positive correlation is observed between COSMIC SPW amplitudes and gravity wave (GW) potential energy (Ep) while the longitudes of maximum amplitudes are out of phase.

Mesospheric Nitric Oxide Transport in WACCM

AbstractEnergetic particle precipitation (EPP) causes ionization of the main constituents of the Earth's atmosphere which leads to the production of nitric oxide (NO) throughout the polar mesosphere and lower thermosphere (MLT). Due to the long lifetime of NO during winter, it can also be transported deeper into the atmosphere by the mesospheric residual circulation (the indirect EEP effect). This study investigates the mesospheric indirect NO response to EEP using Whole Atmosphere Community Climate Model (WACCM) version 6. In comparison to observations from the instrument Solar Occultation For Ice Experiment (SOFIE) on the AIM (Aeronomy of Ice in the Mesosphere) satellite, a wintertime underestimation is found in the modeled mesospheric NO amount. WACCM's temperature profile is found to be vertically shifted compared to observations by SOFIE and by The Sounding of the Atmosphere using Broadband Emission Radiometry instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite (SABER). The discrepancies in NO are therefore attributed to the model's ability to simulate the dynamics responsible for the indirect EEP effect. The drivers of this transport are investigated by sensitivity runs of WACCM's gravity wave forcing. Changing the amplitude of the non‐orographic gravity waves and the Prandtl number improves the modeled vertical distribution of NO and temperature in the MLT region.

Comparison of ICON/MIGHTI and TIMED/TIDI Neutral Wind Measurements in the Lower Thermosphere.

This study cross-compares ICON/MIGHTI and Thermosphere, Ionosphere, Mesosphere Energetics & Dynamics (TIMED)/TIMED Doppler Interferometer (TIDI) MLT region neutral winds from middle Northern Hemisphere to low Southern Hemisphere latitudes. We utilized MIGHTI level-2.2 (v4) and TIDI level-3 (v11) neutral winds from January 2020 to November 2020 and found their conjunctions using a space-time window of LST ± 15 min, latitude ± 4°, and longitude ± 4° around each TIDI wind measurement. Due to the nature of their orbital geometry, frequent conjunctions occurred between MIGHTI and TIDI. These conjunctions are spread in longitudes and they occur at approximately fixed LSTs and latitudes, which allows us to compare their observed diurnal variability. MIGHTI and TIDI wind observations agree well (except on the TIDI coldside during forward flight) and show similar large amplitude longitudinal variations that can reach more than 100 m/s. MIGHTI and TIDI zonal and meridional winds show moderate correlations of 0.60 and 0.55, respectively. The slopes of regression fits for zonal and meridional winds are 0.92 and 0.91, respectively. The root mean square differences in zonal and meridional winds are 56 and 66 m/s, respectively. We found that TIDI coldside measurements in forward flight show a systematic bias and this behavior is repetitive as the instrument pointing direction is changed by the periodic TIMED yaw maneuver. The nature of this systematic bias suggests that the TIDI zero-wind references (at least for the coldside telescopes) need revision. This investigation can provide guidance toward improving the TIDI data analysis. In addition, the results of this study act as a validation of MIGHTI MLT winds.

Dynamical Coupling Between the Low‐Latitude Lower Thermosphere and Ionosphere via the Nonmigrating Diurnal Tide as Revealed by Concurrent Satellite Observations and Numerical Modeling

AbstractThe diurnal eastward‐propagating tide with zonal wavenumber 3 (DE3) is an important tidal component due to its ability to effectively couple the ionosphere‐thermosphere with the tropical troposphere. In this work, we present the first results of a prominent zonal wavenumber‐4 (WN4) structure in the low‐latitude ionosphere observed by the Scintillation Observations and Response of The Ionosphere to Electrodynamics (SORTIE) CubeSat mission during May 27–June 5, 2020. Least squares analyses of concurrent in situ ion number density measurements from the SORTIE and the Ionospheric Connection Explorer satellites near 420 and 590 km show this pronounced WN4 to be driven by DE3. Thermosphere Ionosphere Mesosphere Energetics Dynamics Sounding of the Atmosphere using Broad band Emission Radiometry temperatures and Specified‐Dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension output demonstrate that the ionospheric WN4 structure is driven by DE3 propagating from the lower thermosphere.

Spatial variability in long-term temperature trends in the middle atmosphere from SABER/TIMED observations

Temperatures obtained from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite during the period from 2003 to 2019 are analysed to obtain trends in the region from 50°S to 50°N using the method of Empirical Mode Decomposition (EMD). This method is used to remove long-term oscillations from the data to accurately estimate the linear trends. The novelty of the current study is in dividing the entire study region into sub-regions of 5° latitude and 10° longitude to investigate the associated longitudinal variability. The study shows that the global middle atmosphere, including the global mesopause and stratopause, is cooling as a whole. In the stratosphere and lower mesosphere the observed trends are −0.5 K/decade and in the upper mesosphere, the trends increase to −1.0 K/decade. Mesopause temperatures in Southern Hemisphere and stratopause temperatures in Northern Hemisphere are showing stronger cooling trends in comparison to the other hemisphere. Over tropical and subtropical regions, Southern Hemisphere mesopause is showing a stronger cooling trend over Indian Ocean and Asian region while the cooling trends are symmetric around the equator over Pacific and Atlantic Oceans. Two important results obtained in the present study are as follows: (1) A warming trend, reaching 2.5 K/decade, is observed around 77 km over the Equator and adjoining tropical latitudes, which is attributed to processes leading to the mesospheric semi-annual oscillation (MSAO). (2) Anomalous cooling is observed in the stratopause region over the Southern Indian Ocean (SIO) longitudes. Temperature trends are large and negative ranging from −1 to −2 K/decade over SIO while the trends over the Southern Pacific Ocean (SPO) and the Southern Atlantic Ocean (SAO) lying in the same latitudinal band are small and positive, reaching values of 1 K/decade. It is envisaged that the recent accelerated warming of the SIO is probably responsible for the cooling of the stratopause region above.

Local-time, seasonal and solar cycle variation of Nitric Oxide radiative emission over Indian longitude sector

• Localtime,seasonal & solar cycle variations of NO emission are studied over Indian longitude. • Maximum volume emission rate(VER), dobule the nighttime mean, is observed at 13 LT. • Peak altitude of NOVER descends downward by 18 km from midnight to noon. • Peak VER & intensity show a winter maximum and a summer minimum. We study the local-time, seasonal and solar cycle variations of Nitric Oxide (NO) infrared radiative emission, as observed by Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the NASA’s Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite, over Indian longitude sector. It covers nineteen (January 2002-December 2020) years of NO radiative emission data in the altitude region of 100–155 km. The NO volume emission rate (VER) shows a strong local-time variation with maximum and minimum, respectively, during local-noon and local-midnight. The peak altitude of NO VER decreases by about 18 km from the midnight to the lowest altitude of 117 km at noon. The mean NO VER also undergoes a significant change between the day and night. The mean daytime NO VER is more than double the night-time counterpart. The seasonal variation of peak NO VER shows a maximum during the month of December and a minimum during March. The peak altitude is maximum during September and minimum during June unlike the peak NO VER. The lowest peak altitude, maximum VER and maximum intensity are observed during winter. The relative change in NO VER between the winter and the summer seasons, peaks around 116 km, increases with altitude above 108 km. The long-term trend of NO VER/intensity shows a clear solar cycle variation with higher values during the higher solar activity periods. The NO intensity exhibits a strong correlation with sunspot number (SSN), F10.7 solar index and Lyman- α during both 23rd and 24th solar cycles, although the peak VER does not coincide with the peak SSN.

On the unusually bright and frequent noctilucent clouds in summer 2019 above Northern Germany

Noctilucent Clouds (NLC) and Mesospheric Summer Echoes (MSE) are ice-related phenomena that occur occasionally in the mid-latitude summer mesopause region and more frequently in the polar regions. We observe both phenomena above our site at Kühlungsborn (Germany, 54.1°N, 11.8°E) by lidar and radar since 1997 and 1998, respectively. The NLC season 2019 turned out to be record-breaking with respect to different parameters. We observed the brightest NLC (backscatter coefficient at 532 nm of βmax≈54⋅10−10m-1sr-1 ), the longest continuous NLC (~11 h) and the largest occurrence rates in June (~20%). The seasonally averaged NLC height was found 600 m lower in altitude in 2019 compared to our long-term record. Consistent with the NLC data, radar observations of MSE showed unusually long-lasting echoes and a higher occurrence rate in June 2019. In contrast to our initial expectations, this increase of ice abundance in 2019 was not related to a generally stronger advection from higher latitudes. Mean winds observed by a nearby meteor radar were essentially weaker than in previous years, even though the winds were still typically southward during NLC. Instead, we found unusually low mean temperatures below 83 km altitude (and down to 75 km) being the main reason for these extraordinary observations. Furthermore, water vapor concentrations were slightly enhanced in June 2019. Low temperatures and enhanced water vapor may be caused by stronger upwelling in the upper mesosphere. However, there is no vertical wind data available. Low solar activity was also a factor that promoted these good NLC conditions. Overall, we judge this a singular event and not as an indicator for climate change. Temperature data in the mesopause region and below are taken from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on NASA's Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite as well as Earth Observing System (EOS) Microwave Limb Sounder (MLS) onboard NASA's Aura satellite.

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.

Variability of the Brunt–Väisälä frequency at the OH<sup>∗</sup>-airglow layer height at low and midlatitudes

Abstract. Airglow spectrometers, as they are operated within the Network for the Detection of Mesospheric Change (NDMC; https://ndmc.dlr.de, last access: 1 November 2020), for example, allow the derivation of rotational temperatures which are equivalent to the kinetic temperature, local thermodynamic equilibrium provided. Temperature variations at the height of the airglow layer are, amongst others, caused by gravity waves. However, airglow spectrometers do not deliver vertically resolved temperature information. This is an obstacle for the calculation of the density of gravity wave potential energy from these measurements. As Wüst et al. (2016) showed, the density of wave potential energy can be estimated from data of OH∗-airglow spectrometers if co-located TIMED-SABER (Thermosphere Ionosphere Mesosphere Energetics Dynamics, Sounding of the Atmosphere using Broadband Emission Radiometry) measurements are available, since they allow the calculation of the Brunt–Väisälä frequency. If co-located measurements are not available, a climatology of the Brunt–Väisälä frequency is an alternative. Based on 17 years of TIMED-SABER temperature data (2002–2018), such a climatology is provided here for the OH∗-airglow layer height and for a latitudinal longitudinal grid of 10∘×20∘ at midlatitudes and low latitudes. Additionally, climatologies of height and thickness of the OH∗-airglow layer are calculated.

Determination of the “Wave Turbopause” Using a Numerical Differentiation Method

AbstractThis paper proposes a new algorithm to determine the wave turbopause based on numerical differentiation using temperature data collected from the Sounding of the Atmosphere using Broadband Emission Radiometry onboard the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite. The vertical gradient profile of the temperature standard deviation, which serves as a proxy of wave activity, is obtained based on Tikhonov regularization. In the vicinity of the altitude of wave turbopause, wave damping is much reduced, and upward wave propagation occurs with little damping effect. The corresponding vertical gradient profile should reach a maximum with values that are no longer negative. Thus, we determine the wave turbopause as the unique maximum that is the first after the last change in the derivative value from negative to positive. The wave turbopause altitudes determined by this new method agree well with those of previous studies, especially regarding the behavior of the monthly variation. The error of the wave turbopause altitude derived from this new method is 1.9 km, which is much improved from the error of 3.3 km estimated by the previous method. Additionally, latitudinal variations of the wave turbopause altitude for different seasons and their monthly variations for 0°, 30°N, and 70°N latitudes during 2016–2018 are presented. Similar to the mesopause, the wave turbopause also exhibits a two‐level structure with a summer minimum at high latitudes.

Investigation of vertical wavenumber spectra during sudden stratospheric warming (SSW) events over the Indian region

ABSTRACTThe vertical wavenumber (VWN) characteristics during sudden stratospheric warming (SSW) events (2003–2016) is investigated for the first time using temperature observation of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on-board Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite (for the altitude range of 20–70 km) and ERA-Interim reanalysis data (for the altitudes of 0.1–20 km). Highly negative VWN spectral slope value (approximately) of −4.82 (at 25° N, 77° E) and −4.41 (at 35° N, 77° E) at 40–50 km altitude is observed during the 2013 SSW event, a sort of which is not perceived in any other SSW events (2003–2016). The combined effect of planetary waves (PWs) with wavenumber 1 and 2 during 2013 SSW may be responsible for such distinctive observation near the peak temperature altitude. This study elicits the importance of polar vortex portraying that lower latitudes are affected if only the vortex splits and presents the first of its kind VWN characteristics during SSW events.

Derivation of gravity wave intrinsic parameters and vertical wavelength using a single scanning OH(3-1) airglow spectrometer

Abstract. For the first time, we present an approach to derive zonal, meridional, and vertical wavelengths as well as periods of gravity waves based on only one OH* spectrometer, addressing one vibrational-rotational transition. Knowledge of these parameters is a precondition for the calculation of further information, such as the wave group velocity vector. OH(3-1) spectrometer measurements allow the analysis of gravity wave ground-based periods but spatial information cannot necessarily be deduced. We use a scanning spectrometer and harmonic analysis to derive horizontal wavelengths at the mesopause altitude above Oberpfaffenhofen (48.09∘ N, 11.28∘ E), Germany for 22 nights in 2015. Based on the approximation of the dispersion relation for gravity waves of low and medium frequencies and additional horizontal wind information, we calculate vertical wavelengths. The mesopause wind measurements nearest to Oberpfaffenhofen are conducted at Collm (51.30∘ N, 13.02∘ E), Germany, ca. 380 km northeast of Oberpfaffenhofen, by a meteor radar. In order to compare our results, vertical temperature profiles of TIMED-SABER (thermosphere ionosphere mesosphere energetics dynamics, sounding of the atmosphere using broadband emission radiometry) overpasses are analysed with respect to the dominating vertical wavelength.

Mesopause region temperature variability and its trend in southern Brazil

Abstract. Nowadays, the study of the upper atmosphere is increasing, mostly because of the need to understand the patterns of Earth's atmosphere. Since studies on global warming have become very important for the development of new technologies, understanding all regions of the atmosphere becomes an unavoidable task. In this paper, we aim to analyze the temperature variability and its trend in the mesosphere and lower thermosphere (MLT) region during a period of 12 years (from 2003 to 2014). For this purpose, three different heights, i.e., 85, 90 and 95 km, were focused on in order to investigate the upper atmosphere, and a geographic region different to other studies was chosen, in the southern region of Brazil, centered in the city of Santa Maria, RS (29∘41′02′′ S; 53∘48′25′′ W). In order to reach the objectives of this work, temperature data from the SABER instrument (Sounding of the Atmosphere using Broadband Emission Radiometry), aboard NASA's Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite, were used. Finally, two cases were studied related to distinct grids of latitude/longitude used to obtain the mean temperature profiles. The first case considered a grid of 20∘ × 20∘ lat/long, centered in Santa Maria, RS, Brazil. In the second case, the region was reduced to a size of 15∘ × 15∘ in order to compare the results and discuss the two cases in terms of differences or similarities in temperature trends. Observations show that the size of the geographical area used for the average temperature profiles can influence the results of variability and trend of the temperature. In addition, reducing the time duration of analyses from 24 to 12 h a day also influences the trend significantly. For the smaller geographical region (15∘ × 15∘) and the 12 h daily time window (09:00–21:00 UT) it was found that the main contributions for the temperature variability at the three heights were the annual and semi-annual cycles and the solar flux influence. A smaller trend (−0.02 ± 0.16 % decade−1) was found at 90 km height and small positive trends (0.58 ± 0.26 % and 0.41 ± 0.19 % decade−1) were found at altitudes of 85 and 95 km, respectively.. Keywords. Atmospheric composition and structure (middle atmosphere – composition and chemistry; pressure, density, and temperature) – meteorology and atmospheric dynamics (climatology)

Long-term trends in stratospheric ozone, temperature, and water vapor over the Indian region

Abstract. We have investigated the long-term trends in and variabilities of stratospheric ozone, water vapor and temperature over the Indian monsoon region using the long-term data constructed from multi-satellite (Upper Atmosphere Research Satellite (UARS MLS and HALOE, 1993–2005), Aura Microwave Limb Sounder (MLS, 2004–2015), Sounding of the Atmosphere using Broadband Emission Radiometry (SABER, 2002–2015) on board TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics)) observations covering the period 1993–2015. We have selected two locations, namely, Trivandrum (8.4∘ N, 76.9∘ E) and New Delhi (28∘ N, 77∘ E), covering northern and southern parts of the Indian region. We also used observations from another station, Gadanki (13.5∘ N, 79.2∘ E), for comparison. A decreasing trend in ozone associated with NOx chemistry in the tropical middle stratosphere is found, and the trend turned to positive in the upper stratosphere. Temperature shows a cooling trend in the stratosphere, with a maximum around 37 km over Trivandrum (−1.71 ± 0.49 K decade−1) and New Delhi (−1.15 ± 0.55 K decade−1). The observed cooling trend in the stratosphere over Trivandrum and New Delhi is consistent with Gadanki lidar observations during 1998–2011. The water vapor shows a decreasing trend in the lower stratosphere and an increasing trend in the middle and upper stratosphere. A good correlation between N2O and O3 is found in the middle stratosphere (∼ 10 hPa) and poor correlation in the lower stratosphere. There is not much regional difference in the water vapor and temperature trends. However, upper stratospheric ozone trends over Trivandrum and New Delhi are different. The trend analysis carried out by varying the initial year has shown significant changes in the estimated trend. Keywords. Atmospheric composition and structure (middle atmosphere – composition and chemistry; troposphere – composition and chemistry) – meteorology and atmospheric dynamics (climatology)

Temporal Variability of Atomic Hydrogen From the Mesopause to the Upper Thermosphere

AbstractWe investigate atomic hydrogen (H) variability from the mesopause to the upper thermosphere, on time scales of solar cycle, seasonal, and diurnal, using measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite, and simulations by the National Center for Atmospheric Research Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X). In the mesopause region (85 to 95 km), the seasonal and solar cycle variations of H simulated by WACCM‐X are consistent with those from SABER observations: H density is higher in summer than in winter, and slightly higher at solar minimum than at solar maximum. However, mesopause region H density from the Mass‐Spectrometer‐Incoherent‐Scatter (National Research Laboratory Mass‐Spectrometer‐Incoherent‐Scatter 00 (NRLMSISE‐00)) empirical model has reversed seasonal variation compared to WACCM‐X and SABER. From the mesopause to the upper thermosphere, H density simulated by WACCM‐X switches its solar cycle variation twice, and seasonal dependence once, and these changes of solar cycle and seasonal variability occur in the lower thermosphere (~95 to 130 km), whereas H from NRLMSISE‐00 does not change solar cycle and seasonal dependence from the mesopause through the thermosphere. In the upper thermosphere (above 150 km), H density simulated by WACCM‐X is higher at solar minimum than at solar maximum, higher in winter than in summer, and also higher during nighttime than daytime. The amplitudes of these variations are on the order of factors of ~10, ~2, and ~2, respectively. This is consistent with NRLMSISE‐00.

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.