Middle Atmospheric Thermal Structure Research Articles

Long-term variabilities in thermal structure, CO2 concentration and associated cooling rates in the Earth's middle atmosphere: Observations and model simulations

Enhanced anthropogenic activities in the recent decades are ensuing in the large-scale accumulation of carbon dioxide (CO2) concentration in the Earth's atmosphere. CO2 in the atmosphere induces warming in the troposphere and cooling in the middle atmosphere. A systematic analysis of the middle atmospheric thermal structure and its variability at decadal scale is need of the hour to perceive the consequences of increased anthropogenic activity in totality. In this regard, long-term variations of temperature, CO2 concentration and associated cooling rates in the middle and upper atmosphere (30–110 km) are investigated using Sounding of Atmosphere by Broadband Emission Radiometry (SABER) on board Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) satellite observations during 2002–2021 and Specified Dynamics-Whole Atmosphere Community Climate Model (SD-WACCM) simulations during 2002–2017 over 50 N–50 S latitudes. The results show that CO2 concentration measured by SABER is significantly underestimated by the WACCM simulations, especially above 90 km altitude. In order to find the long-term trends in each variable, Multivariate Linear Regression (MLR) technique is employed to the residual data obtained after removing seasonal variations. SABER observations show decreasing trend in temperature with a rate of 0.5–2.5 K/decade and an increase in CO2 vmr of 16–18 ppmv/decade. The effect of Solar Cycle, QBO and ENSO on each of the variables is also investigated. The significance of the present study lies in evaluating the SD-WACCM simulations of long-term variabilities in the thermal structure, CO2 vmr and associated cooling rates using two decades of observations.

A study of the middle atmospheric thermal structure over western India: Satellite data and comparisons with models

Long term variations of the middle atmospheric thermal structure in the upper stratosphere and lower mesosphere (20–90km) have been studied over Ahmedabad (23.1°N, 72.3°E, 55m amsl), India using SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) onboard TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics) observations during year 2002 to year 2014. For the same period, three different atmospheric models show over-estimation of temperature (∼10K) near the stratopause and in the upper mesosphere, and a signature of under-estimation is seen above mesopause when compared against SABER measured temperature profiles. Estimation of monthly temperature anomalies reveals a semiannual and ter-annual oscillation moving downward from the mesosphere to the stratosphere during January to December. Moreover, Lomb Scargle periodogram (LSP) and Wavelet transform techniques are employed to characterize the semi-annual, annual and quasi-biennial oscillations to diagnose the wave dynamics in the stratosphere-mesosphere system. Results suggested that semi-annual, annual and quasi-biennial oscillations are exist in stratosphere, whereas, semi-annual and annual oscillations are observed in mesosphere. In lower mesosphere, LSP analyses revealed conspicuous absence of annual oscillations in altitude range of ∼55–65km, and semi-annual oscillations are not existing in 35–45km. Four monthly oscillations are also reported in the altitude range of about 45–65km. The temporal localization of oscillations using wavelet analysis shows strong annual oscillation during year 2004–2006 and 2009–2011.

Investigations of the middle atmospheric thermal structure and oscillations over sub-tropical regions in the Northern and Southern Hemispheres

The temperature retrieved from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) onboard Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite during January 2002 to September 2015 are used in this study to delineate the differences of middle atmospheric thermal structure in the Northern Hemisphere (NH) and Southern Hemisphere (SH). Two stations namely Mt. Abu (24.59°N, 72.70°E) in NH and Reunion Island (21.11°S, 55.53°E) in SH are chosen over sub-tropical regions. Temperature climatology from SABER observations suggests that stratopause is warmer, and upper mesosphere is cooler in NH as compared to SH. Three atmospheric models are used to understand the monthly thermal structure differences for different altitudes. Moreover, semi-annual, annual and quasi-biennial oscillations are studied using Lomb Scargle Periodogram and Wavelet transform techniques. Over NH, summer and winter season are warmer (~4 K) and cooler (~3 K) respectively in stratosphere as compared to SH. It is important to note here that Mt. Abu temperature is warmer (~9 K) than Reunion Island in winter but in summer season Mt. Abu temperature is cooler in upper mesosphere and above mesosphere NH shows warming. Results show that annual oscillations are dominated in both hemisphere as compared to semi-annual and quasi-biennial oscillations. In upper mesosphere, strength of annual oscillations is substantial in NH, while semi-annual oscillations are stronger in SH. Wavelet analyses found that annual oscillations are significant in NH near mesopause, while semi-annual oscillations are strengthening in SH.

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Earth's middle atmospheric thermal structure is unique, and having imprints of various physical and chemical processes taking place in the Earth's atmosphere. Nd-YAG laser based Rayleigh lidars are operational at Mt. Abu (24.5°N, 72.7°E) and at Gadanki (13.5°N, 79.2°E) to study the middle atmospheric temperature structure in the altitude region of 30–75 km. Temperature profiles are derived using Rayleigh lidar measured neutral density profiles. Nightly mean temperature profiles, during 1997–2001, are utilized to obtain average temperature profile for each month over Mt. Abu. Lidar observed temperatures are compared with the temperatures observed by Halogen Occultation Experiment (HALOE), on-board Upper Atmospheric Research Satellite (UARS), the CIRA-86 and MSISE-90. Observed temperature profiles are in qualitative agreement with CIRA-86 and MSISE-90 model below 50 km, and the agreement is better during winter months. Quantitatively there are significant differences noted, up to 10 K, above 50 km. The temperature profiles are also compared with the equatorial model for the Indian region, based on rocket and balloon measurements. Significant day to day variability is found, which is as high as ±10 K at ∼70 km. The mean values of the stratopause height and temperature are found to be 48 km and 271 K, respectively. Seasonal variation shows equinoctial and summer maxima below 55 km, whereas above 70 km winter maximum with equinoctial minima are present. Comparative study of thermal structure with Gadanki, a tropical station, revealed significant differences in the thermal structure over tropical and sub-tropical locations.

Lidar observations of the middle atmospheric thermal structure over north China and comparisons with TIMED/SABER

According to the observational data for over 120 nights of the Rayleigh lidar located in Beijing, China (40.5°N, 116.2°E), the middle atmospheric thermal structure (35–85km) over North China was obtained. Lidar observation results show good agreements with SABER temperature data sets, which justify that both the two instruments are reliable. Lidar results show significant difference with the NRLMSISE-00 empirical model and lidar temperatures are usually colder than the model data during the observational time, which may be due to the associations of high level of solar activity, greenhouse gases and the frequent haze weather in North China. To characterize the seasonal variations of the atmospheric temperature structure over Beijing, the amplitude and phase profiles of the annual, semi-annual and 3-month sinusoidal oscillations were extracted by multi-parameter sinusoidal regression. A stratospheric temperature enhancement (STE) event and a long-term mesospheric temperature inversion layer (MIL) are observed in the early winter of 2012/2013. The observed STE event could be due to the enhancement of planetary wave (k=1) activity while the long-term MIL could be due to gravity wave-planetary wave interactions in the masopause region.

The impact of a realistic vertical dust distribution on the simulation of the Martian General Circulation

AbstractLimb‐scanning observations with the Mars Climate Sounder and Thermal Emission Spectrometer (TES) have identified discrete layers of enhanced dust opacity well above the boundary layer and a mean vertical structure of dust opacity very different from the expectation of well‐mixed dust in the lowest 1–2 scale heights. To assess the impact of this vertical dust opacity profile on atmospheric properties, we developed a TES limb‐scan observation‐based three‐dimensional and time‐evolving dust climatology for use in forcing general circulation models (GCMs). We use this to force the MarsWRF GCM and compare with simulations that use a well‐mixed (Conrath‐ν) vertical dust profile and Mars Climate Database version 4 (MCD) horizontal distribution dust opacity forcing function. We find that simulated temperatures using the TES‐derived forcing yield a 1.18 standard deviation closer match to TES temperature retrievals than a MarsWRF simulation using MCD forcing. The climatological forcing yields significant changes to many large‐scale features of the simulated atmosphere. Notably the high‐latitude westerly jet speeds are 10–20 m/s higher, polar warming collar temperatures are 20–30 K warmer near northern winter solstice and tilted more strongly poleward, the middle and lower atmospheric meridional circulations are partially decoupled, the migrating diurnal tide exhibits destructive interference and is weakened by 50% outside of equinox, and the southern hemisphere wave number 1 stationary wave is strengthened by up to 4 K (45%). We find the vertical dust distribution is an important factor for Martian lower and middle atmospheric thermal structure and circulation that cannot be neglected in analysis and simulation of the Martian atmosphere.

Observations of a middle atmosphere thermal structure over Durban using a ground-based Rayleigh LIDAR and satellite data

Studying the middle atmospheric thermal structure over southern Africa is an important activity to improve the understanding of atmospheric dynamics of this region. Observations of a middle atmosphere thermal structure over Durban, South Africa (29.9°S, 31.0°E) using the Durban Rayleigh Light Detection and Ranging (LIDAR) data collected over 277 nights from April 1999 to July 2004, including closest overpasses of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and Halogen Occultation Experiments (HALOE) satellites, are presented in this paper. There seems to be good agreement between the LIDAR and satellite observations. During autumn and winter, the temperatures measured by the LIDAR in the height region between 40 km and 55 km were 5 K to 12 K higher than those measured by the satellites. The data from the LIDAR instrument and the SABER and HALOE satellites exhibited the presence of an annual oscillation in the stratosphere, whereas in the mesosphere, semi-annual oscillations dominated the annual oscillation at some levels. The stratopause was observed in the height range of ~40 km - 55 km by all the instruments, with the stratopause temperatures measured as 260 K - 270 K by the LIDAR, 250 K - 260 K by the SABER and 250 K - 270 K by the HALOE. Data from the SABER and HALOE satellites indicated almost the same thermal structure for the middle atmosphere over Durban.

Middle atmospheric thermal structure over sub-tropical and tropical Indian locations using Rayleigh lidar

Earth's middle atmospheric thermal structure is unique, and having imprints of various physical and chemical processes taking place in the Earth's atmosphere. Nd-YAG laser based Rayleigh lidars are operational at Mt. Abu (24.5°N, 72.7°E) and at Gadanki (13.5°N, 79.2°E) to study the middle atmospheric temperature structure in the altitude region of 30–75km. Temperature profiles are derived using Rayleigh lidar measured neutral density profiles. Nightly mean temperature profiles, during 1997–2001, are utilized to obtain average temperature profile for each month over Mt. Abu. Lidar observed temperatures are compared with the temperatures observed by Halogen Occultation Experiment (HALOE), on-board Upper Atmospheric Research Satellite (UARS), the CIRA-86 and MSISE-90. Observed temperature profiles are in qualitative agreement with CIRA-86 and MSISE-90 model below 50km, and the agreement is better during winter months. Quantitatively there are significant differences noted, up to 10K, above 50km. The temperature profiles are also compared with the equatorial model for the Indian region, based on rocket and balloon measurements. Significant day to day variability is found, which is as high as ±10K at ∼70km. The mean values of the stratopause height and temperature are found to be 48km and 271K, respectively. Seasonal variation shows equinoctial and summer maxima below 55km, whereas above 70km winter maximum with equinoctial minima are present. Comparative study of thermal structure with Gadanki, a tropical station, revealed significant differences in the thermal structure over tropical and sub-tropical locations.

On the role of dust storms in triggering atmospheric gravity waves observed in the middle atmosphere

Abstract. Lower atmospheric perturbations often produce measurable effects in the middle and upper atmosphere. The present study demonstrates the response of the middle atmospheric thermal structure to the significant enhancement of the lower atmospheric heating effect caused by dust storms observed over the Thar Desert, India. Our study from multi-satellite observations of two dust storm events that occurred on 3 and 8 May 2007 suggests that dust storm events produce substantial changes in the lower atmospheric temperatures as hot spots which can become sources for gravity waves observed in the middle atmosphere.

Middle atmospheric thermal structure obtained from Rayleigh lidar and TIMED/SABER observations: A comparative study

A novel measurement of seasonal variability of the middle atmospheric thermal structure has been carried out by comparing ground‐based lidar and space‐based TIMED/SABER observations from a low‐latitude station, Gadanki (13.5°N, 79.2°E), India. Lidar temperature has been cross‐verified by retrieving from Cooperative Institute for Research in the Atmosphere's (CIRA) CIRA‐86 model and SABER observation density and pressure values independently. Observed results are also compared with CIRA‐86 model data. Model data show significant difference with observed ones. Observed results match nicely among themselves throughout the year, which further validates the SABER data at low latitude with an average deviation of ∼2 K in 35–75 km altitude range with respect to the Rayleigh lidar. Seasonal pattern of adiabatic lapse rate all over the altitude range reveals a statically stable atmosphere during the observation period. Stratopause temperature shows semiannual oscillation (SAO) in seasonal pattern of variation, which matches with previous observations from low‐latitude stations.

A comprehensive study on middle atmospheric thermal structure over a tropic and sub-tropic stations

The general characteristics of middle atmospheric thermal structure have been studied by making use of the Rayleigh lidar data collected over the period of about four years (1998–2001). Here, the data has been used from two different stations in the Indian sub-continent in tropics (Gadanki; 13.5°N, 79.2°E) and in sub-tropics (Mt. Abu; 24.5°N, 72.7°E). The observed monthly mean temperature profiles are compared with different model atmospheres (CIRA-86 and MSISE-90). We observed, the mean temperature profiles have closer agreement with MSISE-90 than CIRA-86. The temperature profiles measured by lidar and HALOE satellite overpass nearby lidar site are generally in agreement with each other. The systematic and statistical errors in deriving temperature are found to be uniform for both the stations, as ∼1 K at 50 km, ∼3 K at 60 km and ∼10 K at 70 km. The special features of mesospheric temperature inversion (MTI) and double stratopause structure (DBS) are also addressed for both the stations.

Lidar observations of the middle atmospheric thermal tides and comparison with the High Resolution Doppler Imager and Global Scale Wave Model: 2. October observations at Mauna Loa (19.5°N)

Using more than 145 hours of nighttime lidar measurements obtained during October 3–16, 1996, and October 2–11, 1997, the tidal signature in the middle atmospheric thermal structure (15–95 km) at Mauna Loa, Hawaii (19.5°N), was investigated. The daytime High Resolution Doppler Imager (HRDI) temperatures taken in September and October 1993–1997 and zonally averaged at the same latitude were also used. The daytime HRDI and nighttime lidar temperature differences from their respective daytime and nighttime averages were compared to the equivalent differences predicted by the Global Scale Wave Model (GSWM) at the same latitude. Some consistent local solar time (LST)‐related structures were observed in both HRDI and lidar data, suggesting the presence of important migrating tidal components. In particular, a warm period was clearly identified, propagating downward from 105 km at 0800 LST to 65 km at 0000 LST and surrounded by two colder periods above and below. These warm/cold periods were predicted to occur 2 to 3 hours later by GSWM compared to the HRDI observations. Other LST‐related structures were observed by lidar between 30‐ and 80‐km altitude, in particular, a colder early night, warmer midnight, and colder late night around ∼70 km, suggesting a significant semidiurnal component at this altitude. As previously observed, the amplitudes predicted by GSWM were much smaller than those observed by lidar and HRDI. A new analysis “constrained wave adjustment” method described in a companion paper [Leblanc et al., this issue] was used to estimate the diurnal and semidiurnal components from the nighttime‐only lidar data. The main point of disagreement between the lidar observations and GSWM predictions occurred between 60 and 85 km. A large semidiurnal component was observed by lidar, leading to early and late cold night and warm midnight, while no such large semidiurnal component was predicted by GSWM, leading to an apparent warm early night at 60 km and an apparent cold midnight at 80 km and above. It appears that the tidal structure observed by lidar is more representative of that predicted by GSWM at 24°N, suggesting a latitudinal shift between theory and observation. It is not clear whether this shift is related to an indetermination of the tidal source and/or propagation or if the observed differences are simply due to oscillations related to local/regional local solar time obscuring the global tidal signature.

Lidar observations of the middle atmospheric thermal tides and comparison with the High Resolution Doppler Imager and Global‐Scale Wave Model: 1. Methodology and winter observations at Table Mountain (34.4°N)

The tidal signature in the middle atmospheric thermal structure was investigated using more than 140 hours of nighttime lidar measurements at Table Mountain (34.4°N) during January 1997 and February 1998. The lidar profiles (30–85 km) revealed the presence of persistent mesospheric temperature inversions around 65‐ to 70‐km altitude with a clear local solar time (LST) dependence. Daytime temperature profiles (65–105 km) obtained by the High Resolution Doppler Imager (HRDI) on board the Upper Atmosphere Research Satellite (UARS) in January and February from 1994 to 1997 and zonally averaged at the latitude of the Table Mountain Facility (TMF) were considered together with the lidar results. The daytime HRDI and nighttime lidar temperature differences from their respective daytime and nighttime averages were compared to the equivalent differences predicted by the Global Scale Wave Model (GSWM). A remarkable consistency was observed between the lidar and the HRDI upper mesospheric thermal structure, with a continuous downward propagation of warm temperatures from 100 km at 1000 LST to 75 km at 2000 LST and 65–70 km at 0300–0500 LST, surrounded above and below by colder temperatures. This structure was predicted by GSWM but with a 2‐ to 4‐hour delay and a weaker amplitude. On the lower side of this structure (i.e., 65–70 km) a thin layer, characterized by early night cold temperatures and late night warm temperatures, was identified as the result of the downward propagation of the temperature inversions. Using a new analysis technique, which we have named “constrained wave adjustment” for convenience in future reference, and assuming that the observed temperature variability was entirely driven by tides, some estimations of the diurnal and semidiurnal phases and amplitudes were made from the lidar measurements between 40‐ and 85‐km altitude. Although it does not allow a complete and accurate extraction of the tidal components, this new method appeared to work well for the present TMF study. The estimated diurnal amplitude exhibited a minimum at 63 km with a fast phase transition, characteristic of the transition between the upper stratospheric trapped modes (phase at 1800 LST) and the upward propagating modes. This transition layer was predicted by GSWM to be at 5‐km lower altitude. This altitude shift was present throughout the middle mesosphere. Immediately above the transition layer, the very fast growing diurnal amplitude between 65 and 72 km was followed by a substantial decrease and by the emergence of the semidiurnal component, resulting in the formation of the mesospheric temperature inversion layers. However, the amplitude of the inversions remained large compared to the theoretical tidal predictions and a different formation mechanism should possibly be considered. Recent modeling studies have shown that gravity wave breaking can be significantly affected by the tidal background winds and some preferential wave breaking times could emerge that are dependent on the phase of the diurnal tide and the characteristics of the dissipating waves. This “LST filtering” could result in LST‐dependent temperature inversion layers similar to those observed by lidar. The new analysis technique presented in this paper was also applied to study the temperature tidal oscillations at Mauna Loa Observatory (19.5°N). The results are presented in a companion paper [Leblanc et al., this issue].

Modelling the climatic response to solar variability

The Sun, the primary energy source driving the climate system, is known to vary in time both in total irradiance and in spectral composition in the ultraviolet. According to solar interior evolution models, the solar luminosity has increased steadily by 25-30% over the past 4 x 109years. Periodic variations are also suspected with characteristic timescales of 11 or 22 years, 80-90 years and possibly longer periods. The ultraviolet radiation below 300 nm also exhibits significant changes over the 27-day solar rotation period as well as the 11-year solar cycle. Variations in the solar constant are expected to produce both direct and indirect (feedback) perturbations in the global surface temperature. A hierarchy of zero- to three-dimensional models have been used to study the complex couplings involved by such effects. The response of a zonally averaged model to possible total irradiance changes associated with the Gleissberg cycle is investigated and compared with measurements of the sea-surface temperature made since 1860. Changes in the solar ultraviolet irradiance modulate the amount and distribution of atmospheric ozone, which is predicted to change by several percent in the stratosphere. These perturbations directly affect the middle atmospheric thermal structure, but may also generate indirect effects that could possibly account for some short-term geophysical signatures of solar activity. The cycle-modulated energetic particle interaction with the middle atmosphere is also a possible source of global climatic perturbations.