Mesospheric Inversion Layers

Atmospheric gravity wave (AGW) characteristics were examined using Rayleigh lidar data collected over a period spanning 11 years above Logan, UT (41.7 • N, 111.8 • W), over an altitude range of 45-90 km. Variations of the relative density perturbations obtained with 3-km vertical resolution and 10-min temporal resolution are used to identify the presence of monochromatic gravity wave features throughout the mesosphere. The measured vertical wavelengths λ z ranged over 6-19 km with 12-14 km the most prevalent and the measured wave period τ ranged over 2-8 h with 5-6 h the most prevalent. The values of λ z , τ and mean wind velocity u were used to infer vertical phase velocities c z , horizontal wavelengths λ x , horizontal phase velocities c x and horizontal distances to the source region x. There appears to be a clear seasonal dependence in c z , τ, c x , λ x , and x but not in λ z . The c z values maximize in summer, τ and x maximize in winter whereas c x and λ x , maximize in winter and summer but minimize in spring and autumn. The values of x ranged over 1300-5000 km for waves at 60 km and ~2000-7500 km for waves at 90 km. The source of these AGWs is, thus, far away. Furthermore, for one of these monochromatic waves to exist all night or appear to extend over 45-90 km, it has to originate from a very extended region and persist for a long time.

The day-today measurements of the daytime intensities of hydroxyl (OH) Meinel (8-3) band airglow emissions at 731.6 and 740.2 nm carried out from the equatorial station Thiruvananthapuram (8.5 • N, 76.5 • E, 0.5 • dip) during the period of January-March 2001 have been investigated. This investigation provides evidence for the presence of a long period (≈16 days) wave modulating these intensities at the mesopause altitudes. Simultaneous radar measurements of zonal wind at ∼87 km, i.e. mesopause from Tirunelveli (8.7 • N, 77.8 • E, 0.33 • dip), a location nearby, also reveal the presence of these long period oscillations. The daytime airglow and zonal wind undergo changes simultaneously. Similar modulations are seen in the solar 10.7 cm flux also preceding dayglow and wind variabilities by 4-5 days. It is inferred in the present case that the changes in the solar flux are the cause of the generation of this long period wave in the atmosphere below the mesosphere. The oscillations in the measured dayglow intensities in the mesopause region and the winds at ∼87 km are resulting from the modulation caused by this wave in this region after a delay of 4-5 days.

Objective: It is theoretically observed that atmospheric gravity waves play a key role in vertical coupling during the Mesosphere Temperature Inversion (MTI). Therefore, the present paper describes the observational evidence for vertical coupling between the stratosphere and mesosphere through the short-period gravity waves (GWs), during the Mesosphere Temperature Inversion (MTI) over a tropical region, Gadanki (13.5 o N, 79.2 o E), India. Method: The combined observations of Mesosphere-Stratosphere-Troposphere (MST) Radar and Rayleigh LIDAR located at Gadanki is utilized to study the vertical coupling. We used a unique experimental design from the two ground-based instruments that scan the lower and middle atmosphere simultaneously during the observational campaign. This kind of combined instruments are very sparsely located on the same site to make the observations unique to understand the vertical coupling processes of GWs. Result: The vertical flux of the horizontal momentum of GWs of periods in the range 20 min. to 2h is investigated in the mesosphere using the MST Radar winds. The emphasis is made on the variability of zonal and meridional momentum fluxes in the mesosphere and possible reasons for the variability of fluxes during MTI. It is observed that raise in momentum fluxes of ~7 m 2 / s 2 in the eastward flux and ~10 m 2 /s 2 in southward flux at mesospheric altitudes during the MTI. Conclusion: The gravity wave (GW) analysis using the LIDAR temperature profiles indicate the connection between GW breaking at mesosphere altitudes and temperature inversion and thus the turbulence caused mesospheric echoes. The study suggests the prospect of coupling between stratosphere and mesosphere during the MTI.

The low-latitude middle atmospheric gravity wave characteristics are presented using 310 nights of Rayleigh lidar observations made at Gadanki (13.5 • N, 79.2 • E) over the period from March 1998 to December 2002. The gravity wave characteristics are presented in terms of vertical wave number and frequency spectra, along with the estimated potential energy for the four seasons, namely, spring, summer, autumn and winter. The computed wave number spectra for both the stratosphere and the mesosphere are found to differ significantly from a saturated model predicted spectrum. The spectra were found to be shallower at lower wave numbers and steeper at higher wave numbers with transition at ∼8.85×10 −4 cy/m. The computed frequency spectra seem to follow the model plot with a power law index of-5/3 above a frequency of ∼2×10 −4 Hz. The estimated potential energy per unit mass increases gradually up to ∼60 km and then rather rapidly above this height to reach values of the order of 200 J/kg at ∼70 km.

Measurements of turbulence and waves were made as part of the Mesosphere‐Lower Thermosphere Turbulence Experiment (MTeX) on the night of 25–26 January 2015 at Poker Flat Research Range, Chatanika, Alaska (65°N, 147°W). Rocket‐borne ionization gauge measurements revealed turbulence in the 70‐ to 88‐km altitude region with energy dissipation rates between 0.1 and 24 mW/kg with an average value of 2.6 mW/kg. The eddy diffusion coefficient varied between 0.3 and 134 m2/s with an average value of 10 m2/s. Turbulence was detected around mesospheric inversion layers (MILs) in both the topside and bottomside of the MILs. These low levels of turbulence were measured after a minor sudden stratospheric warming when the circulation continued to be disturbed by planetary waves and winds remained weak in the stratosphere and mesosphere. Ground‐based lidar measurements characterized the ensemble of inertia‐gravity waves and monochromatic gravity waves. The ensemble of inertia‐gravity waves had a s...

Objective: It is theoretically observed that atmospheric gravity waves play a key role in vertical coupling during the Mesosphere Temperature Inversion (MTI). Therefore, the present paper describes the observational evidence for vertical coupling between the stratosphere and mesosphere through the short-period gravity waves (GWs), during the Mesosphere Temperature Inversion (MTI) over a tropical region, Gadanki (13.5 o N, 79.2 o E), India. Method: The combined observations of Mesosphere-Stratosphere-Troposphere (MST) Radar and Rayleigh LIDAR located at Gadanki is utilized to study the vertical coupling. We used a unique experimental design from the two ground-based instruments that scan the lower and middle atmosphere simultaneously during the observational campaign. This kind of combined instruments are very sparsely located on the same site to make the observations unique to understand the vertical coupling processes of GWs. Result: The vertical flux of the horizontal momentum of GWs of periods in the range 20 min. to 2h is investigated in the mesosphere using the MST Radar winds. The emphasis is made on the variability of zonal and meridional momentum fluxes in the mesosphere and possible reasons for the variability of fluxes during MTI. It is observed that raise in momentum fluxes of ~7 m 2 / s 2 in the eastward flux and ~10 m 2 /s 2 in southward flux at mesospheric altitudes during the MTI. Conclusion: The gravity wave (GW) analysis using the LIDAR temperature profiles indicate the connection between GW breaking at mesosphere altitudes and temperature inversion and thus the turbulence caused mesospheric echoes. The study suggests the prospect of coupling between stratosphere and mesosphere during the MTI.

We report the first characterization of potential energy densities and vertical wave number spectra of Antarctic gravity waves (GWs) from 35 to 105 km, derived from Fe lidar temperature measurements at McMurdo (77.8°S, 166.7°E) in 2011-2013 winters. For GWs with periods of 2-10 h, the potential energy density per unit volume (E pv) decreases by 2 orders of magnitude from 35 to 105 km, while that per unit mass (E pm) increases from several to hundreds of J/kg. E pm increases with a mean scale height of~10.4 km in the Rayleigh region (35-65 km) and of~13.2 km in the Fe region (81-105 km), and of particular interest is the inferred severe dissipation in between (65-81 km). Overall, the vertical evolutions of E pv and E pm indicate considerable wave energy loss from the stratosphere to the lower thermosphere. The vertical wave number spectra exhibit power law forms for vertical wavelengths λ z <~10 km. The mean spectral slope in the spectral range of 2-10 km is about À2.55 and À2.26 in the Rayleigh and Fe regions with standard deviations of 0.36 and 0.38, respectively. Large variations in the power spectral densities (PSDs) are seen for λ z > 10 km in 35-60 km. PSDs increase by 1 order of magnitude from the stratosphere to the lower thermosphere. Using higher temporal resolution data to include 0.5-2 h waves increase E pm by~25-45% and increase PSDs of 2-5 km waves by a factor of 2 and of >10 km waves by less than 50%. LU ET AL.

We analyzed the C-structures in the mesospheric metal layers. We used two datasets: one from a narrow band Sodium (Na) Density and Temperature LIDAR and the other from a high-resolution dual band Na and Potassium (K) LIDAR, both operated at São José dos Campos, Brazil (23° S, 46° W). We also investigated the Es layer occurrence and wind shear influences forming these structures. We found three C-type events over 82 analyzed nights in the first data set. They all showed lower temperatures inside C-structures compared to the borders. The squared Brunt-Väissälä frequency analyses showed positive values in the region of C-structures. In two out of three cases, dynamical instability was present (Ri &lt; 0.25). We compared these results with the nine simultaneous C-type events identified in the 185 nights from the second data set. They showed height and time simultaneity correspondence as observed in the Na and K layers. Our results showed a low correlation between Es occurrence and C-str...

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This work reports the analysis of the local-time variations of daytime CO 2 in the Upper Mesosphere and Lower Thermosphere region as observed by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. Results show that daytime SABER CO 2 in the upper mesosphere between latitudes 30°S and 50°N is lower in the morning than in the afternoon. The same was found in the lower thermosphere but between latitudes 50°S and 50°N. The opposite was found in the upper mesosphere between 50°S and 30°S. These results are compared to simulations of CO 2 by the Whole Atmosphere Community Climate Model-eXtended. It was found that the local-time variations of Whole Atmosphere Community Climate Model-eXtended CO 2 are weaker than SABER CO 2. Model diagnostics indicated that these local-time variations in the model are driven primarily (secondarily) by strong vertical (meridional) gradients in Upper Mesosphere and Lower Thermosphere CO 2 volume mixing ratios and strong local-time variations in vertical (meridional) winds. This work concludes that SABER CO 2 shows significant local-time variations that are not well simulated by Whole Atmosphere Community Climate Model-eXtended, and we suggest that this is likely because of weaker tidal forcing in the model.

The day-today measurements of the daytime intensities of hydroxyl (OH) Meinel (8-3) band airglow emissions at 731.6 and 740.2 nm carried out from the equatorial station Thiruvananthapuram (8.5 • N, 76.5 • E, 0.5 • dip) during the period of January-March 2001 have been investigated. This investigation provides evidence for the presence of a long period (≈16 days) wave modulating these intensities at the mesopause altitudes. Simultaneous radar measurements of zonal wind at ∼87 km, i.e. mesopause from Tirunelveli (8.7 • N, 77.8 • E, 0.33 • dip), a location nearby, also reveal the presence of these long period oscillations. The daytime airglow and zonal wind undergo changes simultaneously. Similar modulations are seen in the solar 10.7 cm flux also preceding dayglow and wind variabilities by 4-5 days. It is inferred in the present case that the changes in the solar flux are the cause of the generation of this long period wave in the atmosphere below the mesosphere. The oscillations in the measured dayglow intensities in the mesopause region and the winds at ∼87 km are resulting from the modulation caused by this wave in this region after a delay of 4-5 days.

We report the first characterization of potential energy densities and vertical wave number spectra of Antarctic gravity waves (GWs) from 35 to 105 km, derived from Fe lidar temperature measurements at McMurdo (77.8°S, 166.7°E) in 2011-2013 winters. For GWs with periods of 2-10 h, the potential energy density per unit volume (E pv) decreases by 2 orders of magnitude from 35 to 105 km, while that per unit mass (E pm) increases from several to hundreds of J/kg. E pm increases with a mean scale height of~10.4 km in the Rayleigh region (35-65 km) and of~13.2 km in the Fe region (81-105 km), and of particular interest is the inferred severe dissipation in between (65-81 km). Overall, the vertical evolutions of E pv and E pm indicate considerable wave energy loss from the stratosphere to the lower thermosphere. The vertical wave number spectra exhibit power law forms for vertical wavelengths λ z <~10 km. The mean spectral slope in the spectral range of 2-10 km is about À2.55 and À2.26 in the Rayleigh and Fe regions with standard deviations of 0.36 and 0.38, respectively. Large variations in the power spectral densities (PSDs) are seen for λ z > 10 km in 35-60 km. PSDs increase by 1 order of magnitude from the stratosphere to the lower thermosphere. Using higher temporal resolution data to include 0.5-2 h waves increase E pm by~25-45% and increase PSDs of 2-5 km waves by a factor of 2 and of >10 km waves by less than 50%. LU ET AL.

Three nights of simultaneous Rayleigh lidar temperature measurements over Gadanki (13.5 • N, 79.2 • E) and medium frequency (MF) radar wind measurements over Tirunelveli (8.7 • N, 77.8 • E) have been analyzed to illustrate the possible effects due to tidal-gravity wave interactions on upper mesospheric inversion layers. The occurrence of tidal gravity wave interaction is investigated using MF radar wind measurements in the altitude region 86-90 km. Of the three nights, it is found that tidal gravity wave interaction occurred in two nights. In the third night, diurnal tidal amplitude is found to be significantly larger. As suggested in Sica et al. (2007), mesospheric temperature inversion seems to be a signature of wave saturation in the mesosphere, since the temperature inversion occurs at heights, when the lapse rate is less than half the dry adiabatic lapse rate.

We study the occurrence characteristics of mesospheric inversion layers (MILs) in the 60–105 km altitude region over the low-latitude Indian sector. We note that lower inversions in the mesospheric temperatures occur in the 70–75 km altitude regions while the upper inversions occur in 90–95 km altitude regions. The mesopause altitude is mostly noted to be ~ 98 km with the night-time mesopause (particularly in the year 2002) showing a small peak in the mesopause occurrence at ~ 75 km altitude. We note higher occurrence rate of MILs during high solar activity year compared to low solar activity year. It is also observed that night time MILs show a systematic seasonal variability, with higher occurrence of single and double temperature inversions during equinoxes.

One of the atmospheric constituents that can be retrieved from observations by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite is atomic oxygen in the upper mesosphere. Atomic oxygen can be determined during both day and night using two different techniques that both rely on ozone chemistry. The O concentrations retrieved from SABER data are higher by a factor of 2-5 compared to concentrations determined from other measurements and techniques and compiled in current empirical models. This paper presents variability of atomic oxygen with a focus on the diurnal cycle in low latitudes and the seasonal cycle of daily mean atomic oxygen globally. The results show a large diurnal variation, ranging from a factor of 2 to more than a factor of 10, of atomic oxygen near the equator. The relative magnitude varies with season (larger near the equinoxes) and with altitude (largest near 85 km). Vertical transport by the migrating diurnal tide explains the observed variation. The semiannual variation in tidal amplitude affects the seasonal variation of daily average atomic oxygen, which likely indicates that there is irreversible transport by the tides. At high latitudes, the atomic oxygen variation is characterized by wintertime maxima over the altitude range 80-95 km and summertime maxima above. The wintertime peaks are associated with the downwelling from the mean circulation and are particularly strong in late winter of 2004, 2006, and 2009, responding to the unusual dynamical situations in those years.

The response of the middle atmosphere temperature to short term solar UV radiation related to the 27day period of the sun has been studied by Rayleigh Lidar at mid-latitude in the height range 30-90 km. Among the 9 sequences, each of 3 to 4 months duration, which corresponds to clear solar signature, two types of behavior have been found' either the temperature response is positively correlated with the solar UV flux in the whole height range, or the response reverses abruptly from positive to negative within the height interval 40-60 km. It is important to notice that this second type of behavior is observed as well in summer or in winter, i.e. even in the absence of planetary wave activity, but has only been seen during the Westward phase of the QBO. If such a change of the temperature is confirmed to be solar induced, this response to change in the UV flux is clearly different from the one we observed for the 1 !-year solar cycle. Therefore the 27-day signature of atmospheric structure should not be used as a proxy for the 11-year variation.

The mesospheric nightglow in the infrared region corresponds to the emission lines photochemically produced by OH radicals, O 2 and atomic oxygen. We develop a model with the intention to reproduce the climatology of the OH nightglow and perform comparisons with observational data. 25 species and more than 80 reactions are used describing most of the atmospheric chemical processes but also the photolysis of a few molecules. The different excited vibrational levels of OH are taken into consideration, as well as the excited state of O 2 . A broad wavelength range with various widths allows an accurate expression of the photolysis coefficients. The first step is to validate a 0D photochemical model with most of the kinetic reactions updated. Sensitivity tests are performed to appreciate the importance of specific reactions. We also observe the nightglow response to density variations. A spectrum of the OH nightglow is developed using the concentrations calculated and is exploited to es...

The response of the middle atmosphere temperature to short term solar UV radiation related to the 27day period of the sun has been studied by Rayleigh Lidar at mid-latitude in the height range 30-90 km. Among the 9 sequences, each of 3 to 4 months duration, which corresponds to clear solar signature, two types of behavior have been found' either the temperature response is positively correlated with the solar UV flux in the whole height range, or the response reverses abruptly from positive to negative within the height interval 40-60 km. It is important to notice that this second type of behavior is observed as well in summer or in winter, i.e. even in the absence of planetary wave activity, but has only been seen during the Westward phase of the QBO. If such a change of the temperature is confirmed to be solar induced, this response to change in the UV flux is clearly different from the one we observed for the 1 !-year solar cycle. Therefore the 27-day signature of atmospheric structure should not be used as a proxy for the 11-year variation.

The capabilities of the continuous wavelet transform (CWT) and the multiresolution analysis (MRA) are presented in this work to measure vertical gravity wave characteristics. Wave properties are extracted from the ®rst data set of Rayleigh lidar obtained between heights of 30 km and 60 km over La Reunion Island (21°S, 55°E) during the Austral winter in 1994 under subtropical conditions. The altitudewavelength representations deduced from these methods provide information on the time and spatial evolution of the wave parameters of the observed dominant modes in vertical pro®les such as the vertical wavelengths, the vertical phase speeds, the amplitudes of temperature perturbations and the distribution of wave energy. The spectra derived from measurements show the presence of localized quasi-monochromatic structures with vertical wavelengths <10 km. Three methods based on the wavelet techniques show evidence of a downward phase progression. A ®rst climatology of the dominant modes observed during the Austral winter period reveals a dominant night activity of 2 or 3 quasi-monochromatic structures with vertical wavelengths between 1±2 km from the stratopause, 3±4 km and 6±10 km observed between heights of 30 km and 60 km. In addition, it reveals a dominant activity of modes with a vertical phase speed of)0.3 m/s and observed periods peaking at 3±4 h and 9 h. The characteristics of averaged vertical wavelengths appear to be similar to those observed during winter in the southern equatorial region and in the Northern Hemisphere at mid-latitudes.

An advanced meteor radar, viz, Sri Venkateswara University (SVU) meteor radar (SVU MR)operating at 35.25 MHz, was installed at Sri Venkateswara University (SVU), Tirupati (13.63°N, 79.4°E), India, inAugust 2013 for continuous observations of horizontal winds in the mesosphere and lower thermosphere(MLT). This manuscript describes the purpose of the meteor radar, system configuration, measurementtechniques, its data products, and operating parameters, as well as a comparison of measured mean windsin the MLT with contemporary radars over the Indian region. It is installed close to the Gadanki (13.5°N,79.2°E) mesosphere-stratosphere-troposphere (MST) radar tofill the region between 85 and 100 km wherethis radar does not measure winds. The present radarprovides additional information due to its highmeteor detection rate, which results in accurate wind information from 70 to 110 km. As afirst step, wemade a comparison of SVU MR-derived horizontal winds in the MLT region with those measured by similarand different (MST and MF radars) techniques over the Indian region, as well as model (horizontal windmodel 2007) data sets. The comparison showed an exquisite agreement between the overlapping altitudes(82–98 km) of different radars. Zonal winds compared very well, as did the meridional winds. The observeddiscrepancies and limitations in the wind measurement are discussed in the light of different measuringtechniques and the effects of small-scale processes like gravity waves. This new radar is expected to play animportant role in our understanding of the vertical and lateral coupling of different regions of the atmosphere that will be possible when measurements from nearby locations are combined.

Mesospheric inversion layers (MILs) are a useful diagnostic to simultaneously investigate middle atmosphere radiation, chemistry, and dynamics in high-top general circulation models. Climatologies of long-lived extratropical winter MILs observed by the Microwave Limb Sounder (MLS) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instruments are compared to MILs in the Whole Atmosphere Community Climate Model (WACCM). In general, MIL location, amplitude, and thickness statistics in WACCM are in good agreement with the observations, though WACCM middle- and high-latitude winter MILs occur 30%–50% more often than in MLS and SABER. This work suggests that planetary wave-driven MILs may form as high as 90 km. In the winter, MILs display a wave-1 pattern in both hemispheres, forming most often over the region where the climatological winter stratospheric anticyclones occur. These MILs are driven by the decay of vertically propagating planetary waves...

We investigate the role of convective processes in triggering middle atmospheric gravity waves with the help of simultaneous measurements of middle atmospheric temperature variability from two tropical stations, Gadanki (13.5 o N, 79.2 o E) and Arecibo (18.3 o N, 66.7 o W). Our data reveal that some of the wave periods are similar at both locations indicating the source regions of waves to be similar at both the stations. However, the potential energies of short period gravity waves are found to be significantly higher over Gadanki compared to that at Arecibo. The most striking observation is that background wind conditions were similar and convective processes occurred very close to Gadanki compared to Arecibo. In the view absence of other wave sources during the period of observations, we suggest the strength as well as the distance of convective cells from the location of the observations is responsible for the observed differences in gravity wave spectrum and energies.

A Rayleigh-scatter lidar operated from Utah State University (41.7°N, 111.8°W) for a period spanning 11 years ― 1993 through 2004. Of the 900 nights observed, data on 150 extended to 90 km or above. They were the ones used in these studies related to atmospheric gravity waves (AGWs) between 45 and 90 km. This is the first study of AGWs with an extensive data set that spans the whole mesosphere. Using the temperature and temperature gradient profiles, we produced a climatology of the Brunt-Väisälä (buoyancy) angular frequency squared, N2 (rad/s)2. The minimum and maximum values of N2 vary between 2.2×10-4 (rad/s)2 and 9.0×10-4 (rad/s)2. The corresponding buoyancy periods vary between 7.0 and 3.5 minutes. While for long averages the atmosphere above Logan, Utah, is convectively stable, all-night and hourly profiles showed periods of convective instability (i.e., negative N2). The N2 values were often significantly different from values derived from the NRL-MSISe00 model atmosphere bec...

On the night of December 3rd, 2004 (UT day 338), we observed a significant acceleration of horizontal wind near 100 km between 0900 and 0915 UT accompanied by a temperature cooling at the same altitude and warming below it. The Lomb spectrum analysis of the raw dataset revealed that a gravity wave with 1.5 hr period was significant between 0500 and 0900 UT, but blurred after 0900 UT, suggesting the transfer of wave energy and momentum from wave field to mean flow. Most likely, this observed phenomenon is due to the breaking of an upward propagating gravity wave with an apparent period of $1.5 hr. Using linear saturation theory and assuming a monochromatic wave packet, we estimated the characteristics of breaking gravity wave, eddy diffusion coefficient, and a simple relation between Prandtl number and turbulence localization measure when the wave is breaking, from the experimentally determined heating rate, horizontal wind acceleration, and background temperature and winds.

This paper deals with the variability of optically measured daytime OH temperatures during two different solar activity epochs, over Trivandrum (8.5 • N, 76.5 • E), a tropical station in India. The data used for the present study span the period of February-March, during the solar maximum year of 2001 and solar minimum year of 2005. The mean daytime temperature (180±5 K) during the 2001 study period was found to be lower than the mean temperature (195±9 K) of the 2005 study period by ∼15 K. However, apart from this noticeable shift in mean temperature level, the variabilities in the temperature of both years were strikingly similar. Moreover, the wave periodicities present during these periods were also quite similar. Possible reasons for these observations were investigated in the context of the various forcings that control the energetics of the equatorial mesopause region. The observations presented in this study are unique and reveal a number of newer aspects of the energetics of the tropical mesopause.

The Stratospheric Ozone Monitoring Radiometer (SOMORA) is continuously operated in Switzerland and measures ozone volume mixing ratio q O 3 in the stratosphere and lower mesosphere with a time resolution of about 30 min. Temporal variances S (wave period band 1-3 h) of daytime and nighttime ozone are studied at an altitude of 55 km from October 1, 2000 to May 1, 2001. Gravity waves are assumed as cause of the observed short-time fluctuations of q O 3. Strong negative and positive correlations are found between the dynamic state of the stratosphere (represented by time series of ERA-40 reanalyses) and SOMORA's S and q O 3 series of lower mesospheric ozone. Oscillations with periods of 5-30 days are present in the S and q O 3 series.

The various occurrence characteristics of day and night tropical (10°N-15°N, 60°E-90°E) mesospheric inversion layers (MILs) are studied by using TIMED Sounding of the Atmosphere using Broadband Emission Radiometry satellite data products of kinetic temperature; volume mixing ratios of O, H, and O 3 ; volume emission rates of O 2 (1 Δ) and OH (1.6 μm channel), and chemical heating rates due to seven dominant exothermic reactions among H, O, O 2 , O 3 , OH, HO 2 , and CO 2 cooling rates for the year 2011. Although both dynamics and chemistry play important roles, the present study mainly focuses on the chemical processes involved in the formation of day and night MILs. It is found that the upper level height of daytime (nighttime) MIL descends (ascends) from~88 km (~80 km) in winter to~72 km (~90 km) in summer. The day and night inversion amplitudes are correlated with total chemical heating rates and CO 2 cooling rates, and they show semi annual variation with larger (smaller) values during equinoxes (solstices). The daytime (nighttime) inversion layers are predominantly due to the exothermic reaction, R 5 : O + O + M → O 2 + M and R 6 : O + O 2 + M → O 3 + M (R 3 : H + O 3 → OH + O 2). In addition, the CO 2 causes large cooling at the top and small heating at the bottom levels of both day and night MILs. In the absence of dynamical effects, the chemical heating and CO 2 cooling jointly contribute for the occurrence of day and night MILs. H, O, O 2 , O 3 , OH, and HO 2 that enhances the background temperature in the MLT region [Mlynczak and

The natural variability in the terrestrial mesosphere needs to be known to correctly quantify global change. The response of the thermal structure to solar activity variations is an important factor. Some of the earlier studies highly overestimated the mesospheric solar response. Modeling of the mesospheric temperature response to solar activity has evolved in recent years, and measurement techniques as well as the amount of data have improved. Recent investigations revealed much smaller solar signatures and in some cases revealed no significant solar signal at all. However, not much effort has been made to synthesize the results available so far. This article presents an overview of the energy budget of the mesosphere and lower thermosphere and an up-to-date status of solar response in temperature structure based on recently available observational data. An objective evaluation of the data sets is attempted, and important factors of uncertainty are discussed.

We investigate the role of convective processes in triggering middle atmospheric gravity waves with the help of simultaneous measurements of middle atmospheric temperature variability from two tropical stations, Gadanki (13.5 o N, 79.2 o E) and Arecibo (18.3 o N, 66.7 o W). Our data reveal that some of the wave periods are similar at both locations indicating the source regions of waves to be similar at both the stations. However, the potential energies of short period gravity waves are found to be significantly higher over Gadanki compared to that at Arecibo. The most striking observation is that background wind conditions were similar and convective processes occurred very close to Gadanki compared to Arecibo. In the view absence of other wave sources during the period of observations, we suggest the strength as well as the distance of convective cells from the location of the observations is responsible for the observed differences in gravity wave spectrum and energies.

We summarize two years of Mesosphere Lower Thermosphere Photometer (MLTP) operation of mesospheric OH and O 2 emission monitoring. The deduced mesospheric OH and O 2 temperatures show large variability. Nightly temperature variations over Gadanki (13.5°N, 79.2°E) are dominated by the short period wave features, while tidal amplitudes are relatively small. Our measurements are the first to report a long period seasonal variation at two upper mesospheric altitudes simultaneously over the Indian sector. Our observations reveal the presence of a dominant semi-annual oscillation ($6 months periodicity) together with a shorter period ($2.5 months periodicity) oscillation in both OH and O 2 data.

The Na density variations in the E region have been studied over the past few decades. Although considerable progress in understanding and in modeling the metal layer observations has been made, Na density features above 100 km have yet to be explained. Various studies have linked them to the Na + variations, a major reservoir for Na in E region. But the lack of comprehensive modeling investigations and of wind and temperature observations prevents further understanding on this important ion-neutral coupling topic. In this study, we conduct a numerical simulation on the summer time Na density behavior in the midlatitude E region, where both the ion density and the neutral atmosphere are modulated by tidal and gravity waves. Simulation results show good agreement with Na lidar measurements and reveal that atmospheric waves can transport Na upward to generate Na layers and variations in E region considerably. The vertical wind component of the large amplitude tidal wave can extend the Na layer above 120 km into the thermosphere. The simulation also demonstrates that the modulation of large amplitude gravity (GW) wave can generate small-scale sporadic Na layers (Na s) in the E region. Finally, eddy diffusion enhancement in the GW saturation process can significantly alter the Na s spatial and temporal structures. Plain Language Summary This new model reveals that the mysterious variations of metal Na layer near the boundary of Earth neutral atmosphere are closely related to the disturbances near the surface of the earth within the troposphere.

A coordinated investigation of the gravity wave breaking and the A coordinated investigation of the gravity wave breaking and the associated dynamical instability by a Na lidar and an Advanced associated dynamical instability by a Na lidar and an Advanced Mesosphere Temperature Mapper over Logan, UT (41.7°N, Mesosphere Temperature Mapper over Logan, UT (41.7°N, A coordinated investigation of the gravity wave breaking and the associated dynamical instability by a Na lidar and an Advanced Mesosphere Temperature Mapper over Logan, UT (41.7°N, 111.8°W

A mesospheric model of the airglow emission is developed to recover the night variations observed at ground level. The model is based on a 1D vertical photochemical model, including the photodissociation and heating processes. The spectral radiation is calculated at high altitude and propagated through the atmosphere to the ground. We also include short scale vertical dynamic such as turbulences and the molecular diffusion. Simulations reveal realistic emissions when compared with space observations. In addition, we estimate the impact of changes associated with parameterized atmospheric tides. The comparison with observations is performed over high altitude and ground level. We confront the model outputs at high altitude with satellite observations (SABER and GOMOS) and the simulations propagated at ground level are compared to local measurements campaigns performed in France and India. Biases between observed and simulated radiances and volume emission rates are suspected to be du...

The low-latitude middle atmospheric gravity wave characteristics are presented using 310 nights of Rayleigh lidar observations made at Gadanki (13.5 • N, 79.2 • E) over the period from March 1998 to December 2002. The gravity wave characteristics are presented in terms of vertical wave number and frequency spectra, along with the estimated potential energy for the four seasons, namely, spring, summer, autumn and winter. The computed wave number spectra for both the stratosphere and the mesosphere are found to differ significantly from a saturated model predicted spectrum. The spectra were found to be shallower at lower wave numbers and steeper at higher wave numbers with transition at ∼8.85×10 −4 cy/m. The computed frequency spectra seem to follow the model plot with a power law index of-5/3 above a frequency of ∼2×10 −4 Hz. The estimated potential energy per unit mass increases gradually up to ∼60 km and then rather rapidly above this height to reach values of the order of 200 J/kg at ∼70 km.

Observations of the quasi-2-day planetary wave over a period of two years with the medium frequency (MF) radar operated at Tirunelveli (8:7 • N; 77:8 • E), India, are presented. The observational aspects of the characteristics of the wave over the low latitude station and its possible interaction with the mean wind and the diurnal tide are studied in detail. The amplitude of the 2-day wave has been observed to be larger in winter than in summer with noticeable inter-annual variability. The period of the wave varied between 46 and 53 h with a dependence on season. The vertical wavelength during large-amplitude wave bursts has been observed to be in the range of 35-70 km. The clear anti-correlation between the diurnal tide and the quasi-2-day wave occurrences and the presence of the 16-h wave provide indications for their interaction, which might have extracted energy from the primary diurnal tide. The changes in the mean wind during the passage of the quasi-2-day wave re ect the importance of the wave in determining the mesospheric momentum budget.

Objective: It is theoretically observed that atmospheric gravity waves play a key role in vertical coupling during the Mesosphere Temperature Inversion (MTI). Therefore, the present paper describes the observational evidence for vertical coupling between the stratosphere and mesosphere through the short-period gravity waves (GWs), during the Mesosphere Temperature Inversion (MTI) over a tropical region, Gadanki (13.5 o N, 79.2 o E), India. Method: The combined observations of Mesosphere-Stratosphere-Troposphere (MST) Radar and Rayleigh LIDAR located at Gadanki is utilized to study the vertical coupling. We used a unique experimental design from the two ground-based instruments that scan the lower and middle atmosphere simultaneously during the observational campaign. This kind of combined instruments are very sparsely located on the same site to make the observations unique to understand the vertical coupling processes of GWs. Result: The vertical flux of the horizontal momentum of GWs of periods in the range 20 min. to 2h is investigated in the meso-sphere using the MST Radar winds. The emphasis is made on the variability of zonal and meridional momentum fluxes in the mesosphere and possible reasons for the variability of fluxes during MTI. It is observed that raise in momentum fluxes of ~7 m 2 / s 2 in the eastward flux and ~10 m 2 /s 2 in southward flux at mesospheric altitudes during the MTI. Conclusion: The gravity wave (GW) analysis using the LIDAR temperature profiles indicate the connection between GW breaking at mesosphere altitudes and temperature inversion and thus the turbulence caused mesospheric echoes. The study suggests the prospect of coupling between stratosphere and mesosphere during the MTI.

In the present study, long-term trends in the diurnal tide in the troposphere and stratosphere over a tropical station Gadanki (13.5°N, 79.2°E) are investigated using ERA-Interim wind and temperature products available since 1979. Suitability of the ERA-Interim data for the present study is ascertained using simultaneous radiosonde and MST radar observations over Gadanki and good consistency was found between the two. In general, diurnal tide amplitudes are found to increase from troposphere to stratosphere, as expected. Amplitude of the diurnal tide shows a long-term linear increasing trend, which becomes prominent in the stratosphere. Interestingly, convection over Gadanki also exhibits an increasing trend suggesting that they are related. Role of solar cycle on the diurnal tide is investigated by separating the tidal amplitudes during minimum and maximum of solar cycles 21, 22 and 23. Significantly higher amplitudes in the recent extended solar minimum are noticed though no consistent relation is found between solar activity and tides, in general. These results are discussed in the light of role of convection on the generation of the diurnal tide and their propagation to the higher altitudes, coupling lower and middle atmospheres. Special emphasis is made on the observed large amplitudes of the diurnal tide in the extended solar minimum while relating the observed changes to the background circulation.

The various occurrence characteristics of day and night tropical (10°N-15°N, 60°E-90°E) mesospheric inversion layers (MILs) are studied using TIMED-SABER (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics-Sounding of the Atmosphere using Broadband Emission Radiometry) satellite data products of kinetic temperature, volume mixing ratios of O, H, and O 3 , volume emission rates of O 2 (1 Δ) and OH (1.6μm channel), chemical heating rates due to seven dominant exothermic reactions among H, O, O 2 , O 3 , OH, HO 2 , and CO 2 cooling rates for the year 2011. Although both dynamics and chemistry play important roles, the present study mainly focuses on the chemical processes involved in the formation of day and night MILs. It is found that the upper level height of daytime (nighttime) MIL descends (ascends) from ~88 km (~80 km) in winter to ~72 km (~90 km) in summer. The day and night inversion amplitudes are correlated with total chemical heating rates and CO 2 cooling rates and they show semi annual variation with larger (smaller) values during equinoxes (solstices). The daytime (nighttime) inversion layers are predominantly due to the exothermic reaction, R 5 : O+O+M→O 2 +M and R 6 : O+O 2 +M→O 3 +M (R 3 : H+O 3 →OH+O 2). In addition, the CO 2 causes large cooling at the top and small heating at the bottom levels of both day and night MILs. In the absence of dynamical effects, the chemical heating and CO 2 cooling jointly contribute for the occurrence of day and night MILs.

Temperature profiles between 30 and 65 km have been obtained in São José dos Campos, Brazil (23° S, 46° W) with a lidar operated at 589 nm since 1993. The long-term knowledge of this temperature profile has allowed us to know its average climatology as well as the nighttime evolution. During the period of late September-early October, 2002 we observed profiles which differ considerably from the average for the same period in other years. Specially, a profile obtained on the night of October 2, 2002 called our attention by presenting an unusual stratospheric inversion layer with a decrease of 8-10 K between 38 and 42 km. Subsequent analysis showed that this period coincided with an unprecedented major southern hemisphere stratospheric warming at high latitude. Analysis of additional SABER temperature data showed that inversion layers at the same altitude extends to a wide area at low latitude.

In this study we show examples of very special shapes in the height-time evolution of the sodium layers measured by lidar installed at São José dos Campos (23°, 46°w), Brazil. We selected two nights during the period from 1996 to 1999, in order to analyze the morphology of the Na layer and its relation with gravity wave perturbations. In some cases the Na layer becomes narrower and then broadens whereas in others, the sodium layers bifurcate. Since the linear layer response is not always adequate to describe gravity wave sodium layer interactions (by linear response, it is meant that the layer density perturbations have the same temporal and spatial frequencies as the gravity wave), nonlinear components of the layer density response must be considered in interpreting sodium lidar data. In this work, these observed morphologies are presented and discussed under linear and nonlinear layer density response.

Simultaneous observations of the middle atmosphere and lower thermosphere by Na Wind/Temperature (W/T) and Rayleigh/Raman lidar and other ground-based measurements were conducted the night of October 21, during the ALOHA-93 campaign. Rayleigh/Raman lidar measurements provide density from 25 to 90 km and temperature from 25 to 85 km. From the same location, Na W/T lidar measurements were also obtained between ~ 83 and 103 km. The combined data provides continuous temperature from 25 to 103 km. Strong perturbations which may be associated with the diurnal tide are observed in the temperature and wind profiles.

1] Atomic oxygen (O) is a fundamental component in chemical aeronomy of Earth's mesosphere and lower thermosphere region extending from approximately 50 km to over 100 km in altitude. Atomic oxygen is notoriously difficult to measure, especially with remote sensing techniques from orbiting satellite sensors. It is typically inferred from measurements of the ozone concentration in the day or from measurements of the Meinel band emission of the hydroxyl radical (OH) at night. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite measures OH emission and ozone for the purpose of determining the O-atom concentration. In this paper, we present the algorithms used in the derivation of day and night atomic oxygen from these measurements. We find excellent consistency between the day and night O-atom concentrations from daily to annual time scales. We also examine in detail the collisional relaxation of the highly vibrationally excited OH molecule at night measured by SABER. Large rate coefficients for collisional removal of vibrationally excited OH molecules by atomic oxygen are consistent with the SABER observations if the deactivation of OH(9) proceeds solely by collisional quenching. An uncertainty analysis of the derived atomic oxygen is also given. Uncertainty in the rate coefficient for recombination of O and molecular oxygen is shown to be the largest source of uncertainty in the derivation of atomic oxygen day or night. Citation: Mlynczak, M. G., et al. (2013), Atomic oxygen in the mesosphere and lower thermosphere derived from SABER: Algorithm theoretical basis and measurement uncertainty,

LIDAR (LIght Detection And Ranging) is an optical remote sensing technique which can
be used to probe middle atmosphere (stratosphere & mesosphere) from where RADAR (RAdio
Detection And Ranging) system fails to get scattering. The Mie and Rayleigh lidar system
installed at National Atmospheric Research Laboratory (NARL), Gadanki (13.5°N, 79.2°E) has
been operating at 532 nm green laser with increased energy of ~600 mJ/pulse and pulse repletion
frequency of 50 Hz since 2007. From the Rayleigh lidar observations, vertical profiles of
atmospheric density and temperature can be obtained above ~25-30 km (where the aerosols are
almost negligible) at high spatial and temporal resolutions. The temperature profiles often show
mesospheric inversion layers (MILs), the causative mechanisms of which are yet to be
understood. In the present study, the improved performance of the lidar system is demonstrated
by showing the height profile of temperature and its error obtained with the high power laser
(~12 W per pulse) on 20 January 2007 when compared to the same obtained using the low power
laser (~5 W per pulse) on 05 February 2007 over Gadanki. The temperature errors observed at
~80 km are ~3.5 K, ~18 K with high and low power lasers respectively. A large MIL has been
observed on 20 January 2007 above ~78 km with amplitude of ~31 K from the lidar temperature
operated with high power laser. The dominant gravity wave (GW) period and vertical
wavelengths are found to be T~66 min and λz~6.4 km in the inversion region. The wave
saturation ratio and eddy diffusion coefficient due to the GW breaking are calculated and it is
found that the wave gets saturated at ~84-85 km and the eddy diffusion coefficient increases
from ~25 m2/sec above the inversion region (~83 km). This result suggests that the occurrence of
this large MIL event is probably due to gravity wave breaking.

The seasonal and diurnal variations of temperature, intensity and winds within the mesopause region have been obtained, over a 22 month period, by analysing ground-based Fabry-Perot observations of the hydroxyl (OH) (62) Meinel band emission at 843.0 mn. Tidal variations are revealed clearly in the monthly-averaged hourly-mean temperature data. The diurnal variations of hydroxyl temperature and intensity are usually out-of-phase, while for other emissions, e.g. 02, the temperature and intensity variations are normally in-phase. The amplitudes of the tidal variations in temperature and intensity are generally larger in winter than in summer. Throughout most seasons, the zonal and meridional winds also show pronounced tidal variations, although the largest tidal amplitudes of the winds occur in late summer and autumn

The method of obtaining absolute temperature estimates by measuring the ambipolar diffusion coefficient with meteor radars in the mesopause region is basically well known. However, there is still a need to refine and adjust the background temperature gradient model which is necessary to calculate the temperature values. Therefore, a detailed comparison with independent temperature measurements is necessary to evaluate the performance of the method and to obtain more information about the temperature gradient. Recent studies provide some evidence that the impact of the gradient model on temperature estimates affects the absolute temperatures, but that it is of minor importance for wave analysis. This paper focuses on a detailed evaluation of the meteor radar temperatures by comparing them with SABER satellite and OH-emission mesopause region temperatures. The seasonal variation of the observed temperatures is well reproduced by the COMMA general circulation model.