Upper Atmosphere Research Satellite Research Articles

Development of WACCM With the Non‐Hydrostatic MPAS‐A Dynamical Core

AbstractThe non‐hydrostatic Model for Prediction Across Scales‐Atmosphere (MPAS‐A) dynamical core has recently been adapted for the Specified Chemistry Whole Atmosphere Community Climate Model (SC‐WACCM). In this study, the mean zonal wind and temperature climatology from SC‐WACCM/MPAS‐A is compared with the results from SC‐WACCM using the finite volume and spectral element dynamical cores, as well as the zonal wind and temperature climatology of Upper Atmosphere Research Satellite mission and SABER. The simulations have been performed at horizontal resolutions of ∼100 km. Generally a good agreement is seen between the results from the three dynamical cores, which verifies that the new dynamical core is working with WACCM.

Estimating the impact of the 1991 Pinatubo eruption on mesospheric temperature by analyzing HALOE (UARS) temperature data

Abstract. The Mt. Pinatubo eruption in 1991 had a severe impact on the Earth system, with a well-documented warming of the tropical lower stratosphere and a general cooling of the surface. This study focuses on the impact of this event on the mesosphere by analyzing solar occultation temperature data from the Halogen Occultation Experiment (HALOE) instrument on the Upper Atmosphere Research Satellite (UARS). Previous analyses of lidar temperature data found positive temperature anomalies of up to 12.9 K in the upper mesosphere that peaked in 1993 and were attributed to the Pinatubo eruption. Fitting the HALOE data according to a previously published method indicates a maximum warming of the mesosphere region of 4.1 ± 1.4 K and does not confirm significantly higher values reported for that lidar time series. An alternative fit is proposed that assumes a more rapid response of the mesosphere to the volcanic event and approximates the signature of the Pinatubo with an exponential decay function having an e-folding time of 6 months. It suggests a maximum warming of 5.4 ± 3.0 K, if the mesospheric perturbation is assumed to reach its peak 4 months after the eruption. We conclude that the HALOE time series probably captures the decay of a Pinatubo-induced mesospheric warming at the beginning of its measurement period.

ML-TOMCAT: machine-learning-based satellite-corrected global stratospheric ozone profile data set from a chemical transport model

Abstract. High-quality stratospheric ozone profile data sets are a key requirement for accurate quantification and attribution of long-term ozone changes. Satellite instruments provide stratospheric ozone profile measurements over typical mission durations of 5–15 years. Various methodologies have then been applied to merge and homogenise the different satellite data in order to create long-term observation-based ozone profile data sets with minimal data gaps. However, individual satellite instruments use different measurement methods, sampling patterns and retrieval algorithms which complicate the merging of these different data sets. In contrast, atmospheric chemical models can produce chemically consistent long-term ozone simulations based on specified changes in external forcings, but they are subject to the deficiencies associated with incomplete understanding of complex atmospheric processes and uncertain photochemical parameters. Here, we use chemically self-consistent output from the TOMCAT 3-D chemical transport model (CTM) and a random-forest (RF) ensemble learning method to create a merged 42-year (1979–2020) stratospheric ozone profile data set (ML-TOMCAT V1.0). The underlying CTM simulation was forced by meteorological reanalyses, specified trends in long-lived source gases, solar flux and aerosol variations. The RF is trained using the Stratospheric Water and OzOne Satellite Homogenized (SWOOSH) data set over the time periods of the Microwave Limb Sounder (MLS) from the Upper Atmosphere Research Satellite (UARS) (1991–1998) and Aura (2005–2016) missions. We find that ML-TOMCAT shows excellent agreement with available independent satellite-based data sets which use pressure as a vertical coordinate (e.g. GOZCARDS, SWOOSH for non-MLS periods) but weaker agreement with the data sets which are altitude-based (e.g. SAGE-CCI-OMPS, SCIAMACHY-OMPS). We find that at almost all stratospheric levels ML-TOMCAT ozone concentrations are well within uncertainties of the observational data sets. The ML-TOMCAT (V1.0) data set is ideally suited for the evaluation of chemical model ozone profiles from the tropopause to 0.1 hPa and is freely available via https://doi.org/10.5281/zenodo.5651194 (Dhomse et al., 2021).

SuperDARN, WINDII and WACCM-X neutral and ion winds observed at high latitudes during geomagnetic disturbances

In 2018 a band of strong westward zonal wind (400–600 m s−1) was found in both daytime polar thermospheres, at 65° – 70° geographic latitude. It was imbedded in the eastward zonal wind background and because of its narrow longitudinal structure was called a “wind wall”. The observations were made with the Wind Imaging Interferometer (WINDII) on the NASA Upper Atmosphere Research Satellite (UARS), through Doppler wavelength shifts of the O(1S) atomic oxygen dayglow emission at 557.7 nm. This wind wall was not always present, but when it was it always occurred at the same geographic longitude, around 300°E in the northern hemisphere and 150°E in the southern hemisphere. A subsequent study showed that these wind walls occurred during times of enhanced geomagnetic disturbance, indicated by the ap index, and that the wind fields corresponded closely with those predicted by the WACCM-X model. Additional information on the wind wall and its temporal behavior could be provided by simultaneous observations from a ground-based instrument, located at the appropriate latitude and longitude. It proved possible to obtain a few WINDII observations made early in the UARS mission coincident with a Super Dual Auroral Radar Network (SuperDARN) station, and the results of these comparisons, together with data provided by the WACCM-X model are presented and discussed. The comparison showed that for significant geomagnetic disturbances the neutral wind/plasma drift reversals occurred at the same longitude and the same Universal Time.

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.

An Improved Lyman‐Alpha Composite

AbstractThe hydrogen Lyman‐alpha (Lyman α) line at 121.56 nm is the strongest solar vacuum ultraviolet emission line. Especially because of the impacts on planetary atmospheres, long‐term data sets of Lyman α are important for understanding solar and atmospheric processes. A revised composite data set of daily Lyman α values beginning in 1947 is constructed using measurements of Lyman α from Atmospheric Explorer E, Solar Mesospheric Explorer, Upper Atmosphere Research Satellite, and Solar Radiation and Climate Experiment. Gaps are filled using proxy models based on the Magnesium II index and the 10.7‐ and 30‐cm solar radio fluxes (F10.7 and F30).

Long‐Term Trends in the Low‐Latitude Middle Atmosphere Temperature and Winds: Observations and WACCM‐X Model Simulations

AbstractIn recent years, the middle atmosphere has evoked great scientific interest as long‐term changes can be clearly captured owing to the large perturbation amplitudes at these altitudes. In the present study, more than 25 years of the data are used to investigate the long‐term trends in the middle atmosphere by suitably combining the observations from different techniques (Rocketsonde, High‐Resolution Doppler Imager (HRDI)/Upper Atmosphere Research Satellite (UARS), Halogen Occultation Experiment (HALOE)/UARS, Sounding of the Atmosphere using Broadband Emission Radiometry (SABER)/Thermosphere Ionosphere Mesosphere Energetic Dynamics (TIMED), and Mesosphere‐stratosphere‐troposphere (MST) radar) from Indian region. As different instruments/techniques are used and the time periods are not the same, extreme care has been taken while merging various data sets to obtain meaningful long‐term trends. To understand the observed long‐term trends, Whole Atmosphere Community Climate Model–eXtended model simulations for the Indian low‐latitude regions are also used. A significant cooling trend of ~−1.7 ± 0.5 K/decade between 30 and 80 km is noticed. Large decreasing trend (~5 m/s/decade) in the eastward winds is noticed which is significant between 70 and 80 km only changing from strong eastward wind in 1970s to weak westward wind in recent decade. No significant trends are observed in the meridional wind. These observations are well captured by the Whole Atmosphere Community Climate Model–eXtended model simulations while considering changes in concentrations of greenhouse gases including carbon dioxide (CO2), methane (CH4), water vapor (H2O), and chlorofluorocarbon species that cause depletion of stratospheric ozone (O3). Thus, it is prudent to conclude that long‐term decreasing trends in the zonal winds and cooling trends in the temperature in the middle atmosphere are caused to a large extent by greenhouse gases suggesting the role of anthropogenic changes in the dynamics of the middle atmosphere.

WINDII Observations and WACCM‐X Simulations of High‐Latitude Winds Under Different Solar Radio Flux and Geomagnetic Disturbance Conditions

AbstractThermospheric zonal winds at altitudes of 140 to 250 km are shown to reverse from eastward to strong westward between 100° and 200° in geographic longitude and 60°S to 70°S latitude in the Southern Hemisphere. The reversal also occurs at the same latitude in the Northern Hemisphere, but from 200° to 340° longitude. The phenomenon has been previously described as a “wind wall.” Observations by the Wind Imaging Interferometer (WINDII) on the National Aeronautics and Space Administration's Upper Atmosphere Research Satellite (UARS) and simulations by the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) are utilized to explore the characteristics of what has been called a wind wall. In order to study the dependence on solar radio flux and geomagnetic activity, the relationships of the maximum zonal wind and F10.7 (the solar radio flux at 10.7 cm) and ap indices are investigated. The results show that WINDII observations and WACCM‐X simulations agree well in describing this wind signature. Moreover, the appearance of the wind wall is found to have a strong dependence on the solar radio flux and geomagnetic activity. In addition, WINDII winds have a stronger response to geomagnetic activity than WACCM‐X winds.

High‐Latitude Observations of a Localized Wind Wall and Its Coupling to the Lower Thermosphere

AbstractReversals in the thermospheric zonal winds at altitudes of 140 to 250 km from eastward to westward have been found at southern geographic latitudes between 60° and 70°. These are confined to a narrow region between 100° and 200° in longitude with zonal velocities regularly of −400 m/s, sometimes reaching −600 m/s, so sharply defined that the authors describe it as a “wind wall.” The observations were made by the Wind Imaging Interferometer on National Aeronautics and Space Administration's Upper Atmosphere Research Satellite, and they occur as the field of view crosses the high polar cap wind field. The wind reversals at the wall boundaries create a convergence on the west side of the wall and a divergence on the east side that potentially generate vertical flows, consistent with observed perturbations in the O(1S) emission rate. They are present about one half of the time in local summer and autumn.

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)

Longitudinal and seasonal variations of O(1D) nightglow emission maxima at southern midlatitudes

The Wind Imaging Interferometer (WINDII) experiment on the Upper Atmosphere Research Satellite (UARS) offers a global view of the O(1D) airglow emission rates and neutral winds over the entire altitude range from 190 to 300 km, and provides a unique means for drawing a self-consistent picture of the state of the nighttime upper thermosphere at southern mid-latitudes and by proxy–the ionosphere. The focus of the current study is an investigation of the global seasonal, local time, altitude and longitudinal variability of O(1D) nightglow at southern mid-latitudes (20°S–40°S) employing multi-year observations of O(1D) airglow VERs and neutral winds over the same altitude range and by the same instrument. The results reported here are from four austral seasons, two summers (December solstice, 1992–1993 and 1994–1995), and two equinoxes (March and September 1992). A clear midnight O(1D) VER enhancement is observed at high solar activity during austral summer solstice and equinox (DJF, 1992–1993, and SON, 1992) and at low solar activity during summer (DJF, 1994–1995). The midnight VER enhancement was followed by a wave 4 signature developing after local midnight during all seasons considered particularly during high solar activity summer solstice and spring equinox. The analysis also revealed a complex global O(1D) nightglow VER field, which independently of season exhibited vast regions of very low O(1D) VER (1–4 photons cm−3s−1) in the pre-midnight period at 200°E–300°E longitude throughout the entire latitude range of 5°S–40°S. Particularly noticeable was a region of very low VERs observed poleward of 25°S throughout the local night independent of local time and seasons, over the longitude range from 340°E to 100°E–120°E, which was co-located with the midlatitude ionospheric trough. Another persistent signature observed was an enhancement at 100°E–200°E, at latitudes south of 25°S–30°S, which corresponds to a wave 1 or is a part of a wave 2 signature, likely the result of transport of plasma associated with the Weddell Sea Anomaly. The most prominent result revealed by the study is the role of the wave 4 and wave 1 in the coupling of the lower atmosphere and the thermosphere/ionosphere.

Impacts of Mt Pinatubo volcanic aerosol on the tropical stratosphere in chemistry–climate model simulations using CCMI and CMIP6 stratospheric aerosol data

Abstract. To simulate the impacts of volcanic eruptions on the stratosphere, chemistry–climate models that do not include an online aerosol module require temporally and spatially resolved aerosol size parameters for heterogeneous chemistry and aerosol radiative properties as a function of wavelength. For phase 1 of the Chemistry-Climate Model Initiative (CCMI-1) and, later, for phase 6 of the Coupled Model Intercomparison Project (CMIP6) two such stratospheric aerosol data sets were compiled, whose functional capability and representativeness are compared here. For CCMI-1, the SAGE-4λ data set was compiled, which hinges on the measurements at four wavelengths of the SAGE (Stratospheric Aerosol and Gas Experiment) II satellite instrument and uses ground-based lidar measurements for gap-filling immediately after the 1991 Mt Pinatubo eruption, when the stratosphere was too optically opaque for SAGE II. For CMIP6, the new SAGE-3λ data set was compiled, which excludes the least reliable SAGE II wavelength and uses measurements from CLAES (Cryogenic Limb Array Etalon Spectrometer) on UARS, the Upper Atmosphere Research Satellite, for gap-filling following the Mt Pinatubo eruption instead of ground-based lidars. Here, we performed SOCOLv3 (Solar Climate Ozone Links version 3) chemistry–climate model simulations of the recent past (1986–2005) to investigate the impact of the Mt Pinatubo eruption in 1991 on stratospheric temperature and ozone and how this response differs depending on which aerosol data set is applied. The use of SAGE-4λ results in heating and ozone loss being overestimated in the tropical lower stratosphere compared to observations in the post-eruption period by approximately 3 K and 0.2 ppmv, respectively. However, less heating occurs in the model simulations based on SAGE-3λ, because the improved gap-filling procedures after the eruption lead to less aerosol loading in the tropical lower stratosphere. As a result, simulated tropical temperature anomalies in the model simulations based on SAGE-3λ for CMIP6 are in excellent agreement with MERRA and ERA-Interim reanalyses in the post-eruption period. Less heating in the simulations with SAGE-3λ means that the rate of tropical upwelling does not strengthen as much as it does in the simulations with SAGE-4λ, which limits dynamical uplift of ozone and therefore provides more time for ozone to accumulate in tropical mid-stratospheric air. Ozone loss following the Mt Pinatubo eruption is overestimated by up to 0.1 ppmv in the model simulations based on SAGE-3λ, which is a better agreement with observations than in the simulations based on SAGE-4λ. Overall, the CMIP6 stratospheric aerosol data set, SAGE-3λ, allows SOCOLv3 to more accurately simulate the post-Pinatubo eruption period.

Multi-decadal records of stratospheric composition and their relationship to stratospheric circulation change

Abstract. Constituent evolution for 1990–2015 simulated using the Global Modeling Initiative chemistry and transport model driven by meteorological fields from the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) is compared with three sources of observations: ground-based column measurements of HNO3 and HCl from two stations in the Network for the Detection of Atmospheric Composition Change (NDACC, ∼ 1990–ongoing), profiles of CH4 from the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS, 1992–2005), and profiles of N2O from the Microwave Limb Sounder on the Earth Observing System satellite Aura (2005–ongoing). The differences between observed and simulated values are shown to be time dependent, with better agreement after ∼ 2000 compared with the prior decade. Furthermore, the differences between observed and simulated HNO3 and HCl columns are shown to be correlated with each other, suggesting that issues with the simulated transport and mixing cause the differences during the 1990s and that these issues are less important during the later years. Because the simulated fields are related to mean age in the lower stratosphere, we use these comparisons to evaluate the time dependence of mean age. The ongoing NDACC column observations provide critical information necessary to substantiate trends in mean age obtained using fields from MERRA-2 or any other reanalysis products.

WINDII airglow observations of wave superposition and the possible association with historical “bright nights”

AbstractLongitudinal variations of airglow emission rate are prominent in all midlatitude nighttime O(1S) lower thermospheric data obtained with the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS). The pattern generally appears as a combination of zonal waves 1, 2, 3, and 4 whose phases propagate at different rates. Sudden localized enhancements of 2 to 4 days duration are sometimes evident, reaching vertically integrated emission rates of 400 R, a factor of 10 higher than minimum values for the same day. These are found to occur when the four wave components come into the same phase at one longitude. It is shown that these highly localized longitudinal maxima are consistent with the historical phenomena known as “bright nights” in which the surroundings of human dark night observers were seen to be illuminated by this enhanced airglow.

Study of Stratospheric Sudden Warming (SSW) over the tropical and subtropical regions of India using Rayleigh lidar

ABSTRACTThe Stratospheric Sudden Warming (SSW) is one of the most spectacular phenomena in the atmosphere and has impacts on the Earth’s lower, middle, and upper atmospheres. In this study, two major SSW episodes associated with vortex displacement and vortex splitting that occurred in the years 1998 and 1999, respectively, are investigated for the first time over Mt. Abu using lidar observations. Analyses show that ground-based lidar and satellite observations from the Halogen occultation experiment (HALOE) on board the upper atmospheric research satellite (UARS) can capture the effect of SSW events. Lidar measurements are able to capture SSW warming and its decay very accurately. The impact of SSW is further investigated in the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim-reanalysed potential vorticity. Moreover, a detailed study has been presented to understand the latitudinal variation of SSW warming and the associated mesospheric cooling over the Indian region. The results showed that warming is higher over the northern Indian region (35° N, 77° E) compared with the southern Indian region (5° N, 77° E).

WINDII observations of thermospheric O(1D) nightglow emission rates, temperature, and wind: 1. The northern hemisphere midnight temperature maximum and the wave 4

AbstractThe midnight temperature maximum (MTM) is a large‐scale neutral temperature anomaly with a wide‐ranging effect on the nighttime thermospheric dynamics at low latitudes. The focus of the current study is an investigation of the extent of the MTM to northern midlatitudes (20°N–40°N), employing multiyear observations of O(1D) airglow volume emission rates (VERs), Doppler temperatures (DoT), and neutral winds over the altitude range of 190–300 km by the Wind Imaging Interferometer (WINDII) experiment on board the Upper Atmosphere Research Satellite. The MTM dependence on longitude, season, local time, and altitude was examined. Midnight maxima were observed both in the O(1D) VER and DoT with peaks at ~24 local time (LT) during winter solstice, 22 LT for fall equinox, and 2 LT for spring equinox. The peak in the DoTs was marked with strong southward meridional winds (e.g., ~100–150 m s−1). Latitude/longitude maps of the VER and DoT revealed wave 4 signatures most persistently seen around local midnight, with very little variation in phase, while the amplitude of the individual peaks varied with time. The observed perturbations in the O(1D) VER and temperature were out of phase with respect to longitude. Two of the peaks at ~100°E and 260°E–300°E were almost stationary, while the other two peaks varied in strength over the period of observation. A common feature was that one of the wave 4 peaks was always over the American sector; it was constant with local time, and the meridional wind was southward only over the same region.

WINDII on UARS in the context of SCISAT and Odin

The fundamental elements of the atmosphere are its energy input, composition, temperature and dynamics. Of these the dynamics have had the least observational investigation because of the difficulty of the measurement of winds through optical remote sensing. This article reviews one approach to this topic, the application of the Doppler Michelson Interferometer, focusing on one particular instrument, the Wind Imaging Interferometer (WINDII) flown on NASA׳s Upper Atmosphere Research Satellite (UARS) from 1991 to 2003. With this concept, the wind is measured through the phase shifts of a single fringe from a Michelson interferometer set to an appropriately large optical path difference, determined by phase stepping over that fringe. This configuration allows the implementation of field-widening, allowing the measurements to be made over a wide field, providing wind images extending from roughly 80km to 300km altitude. The Doppler target is the day and night airglow of the upper atmosphere, whose emission rates provide valuable information about the composition of the atmosphere and whose wavelength shifts provide the Doppler information. The primary result, not fully predicted, was the observation of the influence of the dynamics on the composition of the atmosphere. This review provides a minimal instrumentation description, but adequate references, and concentrates on the larger picture of how these data contribute to understanding the interactions of composition, temperature and dynamics, in the context of the SCISAT and Odin measurements. Some new results presented indicate future directions, yet to be explored in full.

Investigations of mesospheric temperature inversions over sub-tropical location using lidar and satellites measurements

Characteristics of Mesospheric Temperature Inversions (MTIs) are studied using ~290 nights of Rayleigh Lidar data collected over Mt. Abu (24.5°N, 72.7°E) during the period of 1997 to 2004 for the first time from an Indian sub-tropical location. Three MTI events have been investigated and statistical analysis has also been performed. A strong MTI event, with amplitude of about 30K, at altitudes between 60 and 70km was observed on 30 December 2003. It was accompanied by strongly perturbed mesospheric zonal winds as observed by TIMED Doppler Interferometer (TIDI) onboard Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED). Two MTI episodes during March and December 2000 have been investigated, which showed that MTI can persist for few days and its amplitude varies gradually. Ozone observed by Halogen Occultation Experiment (HALOE) onboard Upper Atmospheric Research Satellite (UARS) also showed significantly higher variability during strong MTI events. A statistical analysis of MTI occurrence and their characteristics have been done using Lidar data (1997–2004), HALOE on board UARS (1997–2004) and SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) on board TIMED (2002–2004). The frequency of occurrence of MTIs is maximum during winter and minimum during summer and average magnitude of MTIs is ~20K with prominent seasonal variability. SABER and Lidar observed occurrence statistics is showing very similar pattern and SABER is able to capture stronger MTIs (~50K). The average bottom height of MTIs from Lidar is having strong seasonality (lower height during winter) in contrast to satellites observed heights of MTIs.

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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.

Global OZone Chemistry And Related trace gas Data records for the Stratosphere (GOZCARDS): methodology and sample results with a focus on HCl, H<sub>2</sub>O, and O<sub>3</sub>

Abstract. We describe the publicly available data from the Global OZone Chemistry And Related trace gas Data records for the Stratosphere (GOZCARDS) project and provide some results, with a focus on hydrogen chloride (HCl), water vapor (H2O), and ozone (O3). This data set is a global long-term stratospheric Earth system data record, consisting of monthly zonal mean time series starting as early as 1979. The data records are based on high-quality measurements from several NASA satellite instruments and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on SCISAT. We examine consistency aspects between the various data sets. To merge ozone records, the time series are debiased relative to SAGE II (Stratospheric Aerosol and Gas Experiments) values by calculating average offsets versus SAGE II during measurement overlap periods, whereas for other species the merging derives from an averaging procedure during overlap periods. The GOZCARDS files contain mixing ratios on a common pressure–latitude grid, as well as standard errors and other diagnostics; we also present estimates of systematic uncertainties in the merged products. Monthly mean temperatures for GOZCARDS were also produced, based directly on data from the Modern-Era Retrospective analysis for Research and Applications. The GOZCARDS HCl merged product comes from the Halogen Occultation Experiment (HALOE), ACE-FTS and lower-stratospheric Aura Microwave Limb Sounder (MLS) data. After a rapid rise in upper-stratospheric HCl in the early 1990s, the rate of decrease in this region for 1997–2010 was between 0.4 and 0.7 % yr−1. On 6–8-year timescales, the rate of decrease peaked in 2004–2005 at about 1 % yr−1, and it has since levelled off, at ~ 0.5 % yr−1. With a delay of 6–7 years, these changes roughly follow total surface chlorine, whose behavior versus time arises from inhomogeneous changes in the source gases. Since the late 1990s, HCl decreases in the lower stratosphere have occurred with pronounced latitudinal variability at rates sometimes exceeding 1–2 % yr−1. Recent short-term tendencies of lower-stratospheric and column HCl vary substantially, with increases from 2005 to 2010 for northern midlatitudes and deep tropics, but decreases (increases) after 2011 at northern (southern) midlatitudes. For H2O, the GOZCARDS product covers both stratosphere and mesosphere, and the same instruments as for HCl are used, along with Upper Atmosphere Research Satellite (UARS) MLS stratospheric H2O data (1991–1993). We display seasonal to decadal-type variability in H2O from 22 years of data. In the upper mesosphere, the anticorrelation between H2O and solar flux is now clearly visible over two full solar cycles. Lower-stratospheric tropical H2O has exhibited two periods of increasing values, followed by fairly sharp drops (the well-documented 2000–2001 decrease and a recent drop in 2011–2013). Tropical decadal variability peaks just above the tropopause. Between 1991 and 2013, both in the tropics and on a near-global basis, H2O has decreased by ~ 5–10 % in the lower stratosphere, but about a 10 % increase is observed in the upper stratosphere and lower mesosphere. However, such tendencies may not represent longer-term trends. For ozone, we used SAGE I, SAGE II, HALOE, UARS and Aura MLS, and ACE-FTS data to produce a merged record from late 1979 onward, using SAGE II as the primary reference. Unlike the 2 to 3 % increase in near-global column ozone after the late 1990s reported by some, GOZCARDS stratospheric column O3 values do not show a recent upturn of more than 0.5 to 1 %; long-term interannual column ozone variations from GOZCARDS are generally in very good agreement with interannual changes in merged total column ozone (Version 8.6) data from SBUV instruments. A brief mention is also made of other currently available, commonly formatted GOZCARDS satellite data records for stratospheric composition, namely those for N2O and HNO3.