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Compact and lightweight sensors with a high-frequency resolution are required for the passive observation of atmospheric water and oxygen emission lines at a reduced cost and power consumption. A molecular assessment high-resolution observation spectrometer (MAHOS) is developed as a compact, low power, digital fast Fourier transform spectrometer to be installed on a microsatellite. MAHOS has a compact design with dimensions of 0.154 × 0.125 × 0.040 m3 and mass of 0.7 kg. It uses only a few materials including a field programmable gate array (FPGA) module with a lightweight aluminum alloy box. The highly stable spectrometer exhibits a sampling speed of 2.6624 GS/s and 16,384 frequency channels. The stability of the spectrometer is longer than 1200 s within the 1 GHz bandwidth. Thermal dissipation is achieved through a heat conductive gel filled in the gap between the most heat generating component, the FPGA and the aluminum alloy case. Results of a finite element analysis indicate that the design stiff and stable enough to survive in the launch environment. Thermal analysis indicates the durability of the system during operation. Even in space where heat dissipation is not possible, self-heating temperatures are not a problem for the FPGA. In the future, the performance of the spectrometer will be verified by conducting environmental tests.

Satellite data records of stratospheric water vapour have been compared to balloon-borne frost point hygrometer (FP) profiles that are coincident in space and time. The satellite data records of 15 different instruments cover water vapour data available from January 2000 through December 2016. The hygrometer data are from 27 stations all over the world in the same period. For the comparison, real or constructed averaging kernels have been applied to the hygrometer profiles to adjust them to the measurement characteristics of the satellite instruments. For bias evaluation, we have compared satellite profiles averaged over the available temporal coverage to the means of coincident FP profiles for individual stations. For drift determinations, we analyzed timeseries of relative differences between spatiotemporally coincident satellite and hygrometer profiles at individual stations. In a synopsis we have also calculated the mean biases and drifts (and their respective uncertainties) for each satellite record over all applicable hygrometer stations in three altitude ranges (10–30 hPa, 30–100 hPa, and 100 hPa to tropopause). Most of the satellite data have biases < 10 % and average drifts < 1 % yr−1 in at least one of the respective altitude ranges. Virtually all biases are significant in the sense that their uncertainty range in terms of twice the standard error of the mean does not include zero. Statistically significant drifts (95 % confidence) are detected for 35 % of the ~1200 timeseries of relative differences between satellites and hygrometers.

In this study, an on-board calibration hot load (CHL) unit was developed for a terahertz sensing system (THzSens) receiver at 480 GHz to observe the emission lines of water and oxygen in the atmosphere. The compact CHL unit can be mounted on a microsatellite. We propose an accurate calibration method and a unit compact in design. We conducted experiments in order to obtain the best possible return loss value below the required −60 dB for calibration. The CHL unit uses two specular reflection absorber (SRA) plates and a radar absorbing material (RAM) as the absorber termination. The absorbers are assembled in a lightweight case made of carbon-fiber-reinforced plastics. The SRAs are placed at the Brewster angle with respect to the incident radiation to minimize reflection, which was found experimentally at 480 GHz. The CHL design is expected to have less than −78 dB reflection loss including SRA back scattering at 480 GHz. The return loss as a function of frequency for this design is below −60 dB, meeting the design requirements. Further, a compact prototype CHL was manufactured based on the proposed quasi-optical design. The new CHL for 480 GHz is 1/10 in the volume of the previous SMILES CHL for 650 GHz. The manufactured CHL prototype will be evaluated as a calibrator using the transmitter/receiver setup used in this study.

Nineteen limb-viewing data sets (occultation, passive thermal, and UV scattering) and two nadir upper tropospheric humidity (UTH) data sets are intercompared and also compared to frost-point hygrometer balloon sondes. The upper troposphere considered here covers the pressure range from 300–100 hPa. UTH is a challenging measurement, because concentrations vary between 2–1000 ppmv (parts per million by volume), with sharp changes in vertical gradients near the tropopause. Cloudiness in this region also makes the measurement challenging. The atmospheric temperature is also highly variable ranging from 180–250 K. The assessment of satellite-measured UTH is based on coincident comparisons with balloon frost-point hygrometer sondes, multi-month mapped comparisons, zonal mean time series comparisons, and coincident satellite-to-satellite comparisons. While the satellite fields show similar features in maps and time series, quantitatively they can differ by a factor of 2 in concentration, with strong dependencies on the amount of UTH. Additionally, time-lag response-corrected Vaisala RS92 radiosondes are compared to satellites and the frost-point hygrometer measurements. In summary, most satellite data sets reviewed here show on average ∼30 % agreement amongst themselves and frost-point data but with an additional ∼30 % variability about the mean bias. The Vaisala RS92 sonde, even with a time-lag correction, shows poor behavior for pressures less than 200 hPa.

We present a multiyear time series of column abundances of carbon monoxide (CO), hydrogen cyanide (HCN), and ethane (C2H6) measured using Fourier-transform infrared (FTIR) spectrometers at 10 sites affiliated with the Network for the Detection of Atmospheric Composition Change (NDACC). Six are high-latitude sites: Eureka, Ny-Ålesund, Thule, Kiruna, Poker Flat, and St. Petersburg, and four are midlatitude sites: Zugspitze, Jungfraujoch, Toronto, and Rikubetsu. For each site, the interannual trends and seasonal variabilities of the CO time series are accounted for, allowing background column amounts to be determined. Enhancements above the seasonal background were used to identify possible wildfire pollution events. Since the abundance of each trace gas emitted in a wildfire event is specific to the type of vegetation burned and the burning phase, correlations of CO to the long-lived wildfire tracers HCN and C2H6 allow for further confirmation of the detection of wildfire pollution. A GEOS-Chem tagged CO simulation with Global Fire Assimilation System (GFASv1.2) biomass burning emissions was used to determine the source attribution of CO concentrations at each site from 2003 to 2018. For each detected wildfire pollution event, FLEXPART back-trajectory simulations were performed to determine the transport times of the smoke plume. Accounting for the loss of each species during transport, the enhancement ratios of HCN and C2H6 with respect to CO were converted to emission ratios. We report mean emission ratios with respect to CO for HCN and C2H6 of 0.0047 and 0.0092, respectively, with a standard deviation of 0.0014 and 0.0046, respectively, determined from 23 boreal North American wildfire events. Similarly, we report mean emission ratios for HCN and C2H6 of 0.0049 and 0.0100, respectively, with a standard deviation of 0.0025 and 0.0042, respectively, determined from 39 boreal Asian wildfire events. The agreement of our emission ratios with literature values illustrates the capability of ground-based FTIR measurements to quantify biomass burning emissions. We provide a comprehensive dataset that quantifies HCN and C2H6 emission ratios from 62 wildfire pollution events. Our dataset provides novel emission ratio estimates, which are sparsely available in the published literature, particularly for boreal Asian sources.

Air quality on our planet has been changing in particular since the industrial revolution (1750s) because of anthropogenic emissions. It is becoming increasingly important to realize air cleanliness, since clean air is as valuable a resource as clean water. A global standard for quantifying the level of air cleanliness is swiftly required, and we defined a novel concept, namely the Clean aIr Index (CII). The CII is a simple index defined by the normalization of the amount of a set of individual air pollutants. A CII value of 1 indicates completely clean air (no air pollutants), and 0 indicates the presence of air pollutants that meet the numerical environmental criteria for the normalization. In this time, the air pollutants used in the CII were taken from the Air Quality Guidelines (AQG) set by the World Health Organization (WHO), namely O3, particulate matters, NO2, and SO2. We chose Japan as a study area to evaluate CII because of the following reasons: (i) accurate validation data, as the in situ observation sites of the Atmospheric Environmental Regional Observation System (AEROS) provide highly accurate values of air pollutant amounts, and (ii) fixed numerical criteria from the Japanese Environmental Quality Standards (JEQS) as directed by the Ministry of the Environment (MOE) of Japan. We quantified air cleanliness in terms of the CII for the all 1896 municipalities in Japan and used data from Seoul and Beijing to evaluate Japanese air cleanliness. The amount of each air pollutant was calculated using a model that combined the Weather Research and Forecasting (WRF) and Community Multiscale Air Quality (CMAQ) models for 1 April 2014 to 31 March 2017. The CII values calculated by the WRF–CMAQ model and the AEROS measurements showed good agreement. The mean of the correlation coefficient for the CII values of 498 municipalities where the AEROS measurements operated was 0.66±0.05, which was higher than that of the Air Quality Index (AQI) of 0.57±0.06. The CII values averaged for the study period were 0.67, 0.52, and 0.24 in Tokyo, Seoul, and Beijing, respectively; thus, the air in Tokyo was 1.5 and 2.3 times cleaner, i.e., lower amounts of air pollutants, than the air in Seoul and Beijing, respectively. The average CII value for the all Japanese municipalities was 0.72 over the study period. The extremely clean air, CII ≈0.90, occurred in the southern remote islands of Tokyo and to the west of the Pacific coast, i.e., Kochi, Mie, and Wakayama prefectures during summer, with the transport of clean air from the ocean. We presented the top 100 clean air cities in Japan as one example of an application of CII in society. We confirmed that the CII enabled the quantitative evaluation of air cleanliness. The CII can be useful and valuable in various scenarios such as encouraging sightseeing and migration, investment and insurance business, and city planning. The CII is a simple and fair index that can be applied to all nations.

Acetonitrile (CH3CN) is a volatile organic compound (VOC) and a potential tracer of biomass burning. We evaluated the capability of using observations derived from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the International Space Station (ISS) to measure CH3CN profiles. The error in a CH3CN vertical profile from the Level-2 research (L2r) product version 3.0.0 was estimated by theoretical error analysis and also compared with other instrumental measurements. We estimated the systematic and random errors to be ∼5.8 ppt (7.8 %) and 25 ppt (60 %), respectively, for a single observation at 15.7 hPa in the tropics, where the CH3CN measurements are enhanced. The major source of systematic error was the pressure-broadening coefficient, and its contribution to the total systematic error was approximately 60 % in the middle stratosphere (15.7–4.8 hPa). The random error decreased to less than 40 % after averaging 10 profiles in the pressure range of 28.8–1.6 hPa. The total error due to uncertainties in other molecular spectroscopic parameters (2.8 ppt) was comparable to that of CH3CN spectroscopic parameters. We compared the SMILES CH3CN profiles with those of the microwave limb sounder (MLS) on the Aura satellite (version 4.2). The SMILES CH3CN values were consistent with those from MLS within the standard deviation (1σ) of the MLS observations. The difference between the SMILES and MLS CH3CN profiles increased with altitude and was within 20–35 ppt (20 %–260 %) at 15.7–1.6 hPa. We observed discrepancies of 5–10 ppt (10 %–30 %) between the SMILES CH3CN profiles observed by different spectrometers, and hence, we do not recommend merging SMILES CH3CN profiles derived from different spectrometers. We found that the SMILES CH3CN volume mixing ratio (VMR) in the upper stratosphere has a seasonal maximum in February.

Nineteen limb viewing (occultation and passive thermal) and two nadir humidity data sets are intercompared and also compared to frostpoint hygrometer balloon sondes. The upper troposphere considered here covers the pressure range from 300–100 hPa. Water vapor in this region is a challenging measurement because concentrations vary between 2–1000 parts per million volume with sharp changes in vertical gradients near the tropopause. The atmospheric temperature is also highly variable ranging from 180–250 K. The assessment of satellite measured humidity is based on coincident comparisons with frostpoint hygrometer sondes, multi month mapped comparisons, zonal mean time series comparisons and coincident satellite to satellite comparisons. While the satellite fields show similar features in maps and time series, quantitatively, they can differ by a factor of two in concentration, with strong dependencies on the amount of H2O. Additionally, time-lag response corrected Vaisala-RS92 radiosondes are compared to satellites and the frostpoint hygrometer measurements. In summary, most satellite data sets reviewed here show on average ~30 % agreement amongst themselves and frostpoint data but with an additional ~30 % variability about the mean. The Vaisala-RS92 sonde even with a time-lag correction shows poor behavior for pressure less than 200 hPa.

In this study, we compare the diurnal variation in stratospheric ozone of the MACC (Monitoring Atmospheric Composition and Climate) reanalysis, ECMWF Reanalysis Interim (ERA-Interim), and the free-running WACCM (Whole Atmosphere Community Climate Model). The diurnal variation of stratospheric ozone results from photochemical and dynamical processes depending on altitude, latitude, and season. MACC reanalysis and WACCM use similar chemistry modules and calculate a similar diurnal cycle in ozone when it is caused by a photochemical variation. The results of the two model systems are confirmed by observations of the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) experiment and three selected sites of the Network for Detection of Atmospheric Composition Change (NDACC) at Mauna Loa, Hawaii (tropics), Bern, Switzerland (midlatitudes), and Ny-Ålesund, Svalbard (high latitudes). On the other hand, the ozone product of ERA-Interim shows considerably less diurnal variation due to photochemical variations. The global maxima of diurnal variation occur at high latitudes in summer, e.g., near the Arctic NDACC site at Ny-Ålesund, Svalbard. The local OZORAM radiometer observes this effect in good agreement with MACC reanalysis and WACCM. The sensed diurnal variation at Ny-Ålesund is up to 8% (0.4 ppmv) due to photochemical variations in summer and negligible during the dynamically dominated winter. However, when dynamics play a major role for the diurnal ozone variation as in the lower stratosphere (100–20 hPa), the reanalysis models ERA-Interim and MACC which assimilate data from radiosondes and satellites outperform the free-running WACCM. Such a domain is the Antarctic polar winter where a surprising novel feature of diurnal variation is indicated by MACC reanalysis and ERA-Interim at the edge of the polar vortex. This effect accounts for up to 8% (0.4 ppmv) in both model systems. In summary, MACC reanalysis provides a global description of the diurnal variation of stratospheric ozone caused by dynamics and photochemical variations. This is of high interest for ozone trend analysis and other research which is based on merged satellite data or measurements at different local time.

Hydrogen chloride (HCl) is the most abundant (more than 95 %) among inorganic chlorine compounds Cly in the stratosphere. The HCl molecule has been observed to obtain long-term quantitative estimations of total budget of the stratospheric anthropogenic chlorine compounds. In this study, we provided HCl vertical profiles at altitudes of 16–100 km using the superconducting submillimeter-wave limb-emission sounder (SMILES) from space. We used the SMILES Level-2 research product version 3.0.0. The period of the SMILES HCl observation was from October 12, 2009 to April 21, 2010, and the latitude coverage was 40S–65N. The average HCl vertical profile showed an increase with altitude up to the stratopause (~ 45 km), approximately constant values between the stratopause and the upper mesosphere (~ 80 km), and a decrease from the mesopause to the lower thermosphere (~ 100 km). This behavior was observed in the all latitude regions, and reproduced by the SD-WACCM model. We compared the SMILES HCl vertical profiles in the stratosphere and lower mesosphere with HCl profiles from MLS on the Aura satellite, as well as from ACE-FTS on SCISAT and from TELIS (balloon-borne). The TELIS observations were performed using the superconductive limb emission technique, as used by SMILES. The globally averaged vertical HCl profiles of SMILES well agreed with those of MLS and ACE-FTS within 0.25 and 0.2 ppbv between 20 and 40 km, respectively. The SMILES HCl concentration was smaller than those of MLS and ACE/FTS as the altitude increased from 40 km, and the difference was approximately 0.4–0.5 ppbv at 50–60 km. The difference between SMILES and TELIS HCl observations was about 0.3 ppbv in the polar winter region between 20 and 34 km, except near 26 km. SMILES HCl error sources that may cause discrepancies with the other observations are investigated by a theoretical error analysis. We calculated errors caused by the uncertainties of spectroscopic parameters, instrument functions, and atmospheric temperature profiles. The jacobian for the temperature explains the negative bias of the SMILES HCl concentration at 50–60 km. The HCl vertical profile from the middle troposphere to the lower thermosphere is reported for the first time from SMILES observations; the data quality is quantified by comparisons with other measurements and via theoretical error analysis.

Atomic oxygen is a key oxidant for greenhouse gases such as H2O, CH4, and N2O whose amounts are currently increasing in the stratosphere. Ozone photolysis is a major source of atomic oxygen generation. We found, for the first time, that the ozone photolysis of 48O3 and 18O16O16O generated a sharp diurnal variation of δ18OOO in the middle stratosphere (37 km), in contrast to the temporal variation of 48O3. The average isotopic enrichment δ18OOO derived from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) observation was higher during daytime (16.2 ± 3.3%) than at night (13.7 ± 3.6%). Isotopic fractionation effects were simulated for both ozone formation reaction and ozone photolysis with the ozone photolysis contribution estimated to be 80% of the daytime δ18OOO enhancement. Significant solar radiation dependence was observed in the isotopic fractionation of ozone photolysis derived from the SMILES observation and theoretical calculations. These results show that δ18O can be a powerful tool to investigate oxidant chemistry.

Spectrum width and intensity of ozone (O3) observed in the MLT region behaves quite differently than in the stratosphere for submillimeter-wave limb emission spectroscopic observation. For example, O3 spectra in the stratosphere are stronger during the day than at night. Conversely, spectra in the MLT region at night are stronger than those occurring during the day due to diurnal variations in O3 behavior. These opposing behaviors cause problems, including oscillations and inaccuracies particularly for O3 vertical profiles in the MLT region retrieved with an application of one retrieval procedure for the entire vertical range (stratosphere to thermosphere). Recently, we developed an optimal retrieval method for O3 in the MLT region for spectra, observed by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) instrument on the International Space Station. Optimizations were performed for frequency window range, retrieval vertical range, vertical grids, and a priori information for O3 and temperature. Precision and accuracy were evaluated by error analysis and comparisons with previous products. The random error was estimated to be about 5% and 35% in the mesosphere and lower thermosphere, respectively, for nighttime O3 profiles in the MLT region. The total systematic error was about 6% in the MLT region. Certain improvements for both random noise (from 50% to 35%) and systematic error (from 10% to 6%) were obtained. We succeeded in revealing the positive correlation between O3 and ClO at nighttime in the upper mesosphere using the optimized O3 profiles; furthermore, its chemical mechanism was explained quantitatively.

We present a multi-year time series of column abundances of carbon monoxide (CO), hydrogen cyanide (HCN), and ethane (C2H6) measured using Fourier transform infrared (FTIR) spectrometers at ten sites affiliated with the Network for Detection of Atmospheric Composition Change (NDACC). Six are high-latitude sites: Eureka, Ny-Alesund, Thule, Kiruna, Poker Flat, and St. Petersburg , and four are mid-latitude sites: Zugspitze, Jungfraujoch, Toronto, and Rikubetsu. For each site, the inter-annual trends and seasonal variabilities of the CO time series are accounted for, allowing ambient concentrations to be determined. Enhancements above ambient levels were used to identify possible wildfire pollution events. Since the abundance of each trace gas emitted in a wildfire event is specific to the type of vegetation burned and the burning phase, correlations of CO to the long-lived wildfire tracers HCN and C2H6 allow for further confirmation of the detection of wildfire pollution, while complementary measurements of aerosol optical depth from nearby AERONET sites confirm the presence of wildfire smoke. A GEOS-Chem tagged CO simulation with Global Fire Assimilation System (GFAS) biomass burning emissions was used to determine the source attribution of CO concentrations at each site from 2003–2018. The influence of the various wildfire sources is found to differ between sites while North American and Asian boreal wildfires fires were found to be the greatest contributors to episodic CO enhancements in the summertime at all sites.

Remote sensing of atmospheric state variables typically relies on the inverse solution of the radiative transfer equation. An adequately characterized retrieval provides information on the uncertainties of the estimated state variables as well as on how any constraint or a priori assumption affects the estimate. Reported characterization data should be intercomparable between different instruments, empirically validatable, grid-independent, usable without detailed knowledge of the instrument or retrieval technique, traceable and still have reasonable data volume. The latter may force one to work with representative rather than individual characterization data. Many errors derive from approximations and simplifications used in real-world retrieval schemes, which are reviewed in this paper, along with related error estimation schemes. The main sources of uncertainty are measurement noise, calibration errors, simplifications and idealizations in the radiative transfer model and retrieval scheme, auxiliary data errors, and uncertainties in atmospheric or instrumental parameters. Some of these errors affect the result in a random way, while others chiefly cause a bias or are of mixed character. Beyond this, it is of utmost importance to know the influence of any constraint and prior information on the solution. While different instruments or retrieval schemes may require different error estimation schemes, we provide a list of recommendations which should help to unify retrieval error reporting. © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License

Acetonitrile (CH3CN) is one of the volatile organic compounds (VOC) and a potential tracer of biomass burning. We evaluated the capability of using observations derived from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the International Space Station (ISS) to measure CH3CN profiles. The error in a CH3CN vertical profile from the Level-2 research (L2r) product version 3.0.0 was estimated by both theoretical error analysis and compared with other instrumental measurements. We estimated the systematic and random errors to be ~5.8 ppt (7.8 %) and 25 ppt (60 %) for a single observation at 15.7 hPa, respectively, in the Tropics, where the CH3CN measurements are enhanced. The major source of systematic error was a pressure broadening, and its contribution to the total systematic error was approximately 60 % in the middle stratosphere (15.7–4.8 hPa). The random error decreased to less than 40 % after averaging 10 profiles in the pressure range of 28.8–1.6 hPa. The total error due to uncertainties in other molecular spectroscopic parameters was comparable (2.8 ppt) to those of CH3CN spectroscopic parameters. We compared the SMILES CH3CN profiles with those of the Microwave Limb Sounder (MLS) on the Aura satellite (version 4.2). The SMILES CH3CN values were consistent with those from MLS within the standard deviation (1 σ) of the MLS observations. The difference between the SMILES and MLS CH3CN profiles increased with altitude and was within 20–35 ppt (20–260 %) at 15.7–1.6 hPa. We observed discrepancies of 5–10 ppt (10–30 %) between the SMILES CH3CN profiles observed by different spectrometers, so we do not recommend merging SMILES CH3CN profiles derived from the different spectrometers. We found that SMILES CH3CN VMR in the upper stratosphere has a seasonal maximum in February, which is consistent with the fact that biomass burning events are highest from December–March.

Himawari-8, a next-generation geostationary meteorological satellite, was successfully launched by the Japanese Meteorological Agency (JMA) on 7 October 2014 and has been in official operation since 7 July 2015. The Advanced Himawari Imager (AHI) onboard Himawari-8 has 16 channels from 0.47 to 13.3 μm and performs full-disk observations every 10 min. This study describes AHI aerosol optical property (AOP) retrieval based on a multi-channel algorithm using three visible and one near-infrared channels (470, 510, 640, and 860 nm). AOPs were retrieved by obtaining the visible surface reflectance using shortwave infrared (SWIR) data along with normalized difference vegetation index shortwave infrared (NDVISWIR) categories and the minimum reflectance method (MRM). Estimated surface reflectance from SWIR (ESR) tends to be overestimated in urban and cropland areas. Thus, the visible surface reflectance was improved by considering urbanization effects. Ocean surface reflectance is obtained using MRM, while it is from the Cox and Munk method in ESR with the consideration of chlorophyll-a concentration. Based on validation with ground-based sun-photometer measurements from Aerosol Robotic Network (AERONET) data, the error pattern tends to the opposition between MRMver (using MRM reflectance) AOD and ESRver (Using ESR reflectance) AOD over land. To estimate optimal AOD products, two methods were used to merge the data. The final aerosol products and the two surface reflectances were merged, which resulted in higher accuracy AOD values than those retrieved by either individual method. All four AODs shown in this study show accurate diurnal variation compared with AERONET, but the optimum AOD changes depending on observation time.

This paper describes the algorithms of the level-2 research (L2r) processing chain developed for the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES). The chain has been developed in parallel to the operational chain for conducting researches on calibration and retrieval algorithms. L2r chain products are available to the scientific community. The objective of version 2 is the retrieval of the vertical distribution of trace gases in the altitude range of 18–90 km. A theoretical error analysis is conducted to estimate the retrieval feasibility of key parameters of the processing: line-of-sight elevation tangent altitudes (or angles), temperature and ozone profiles. While pointing information is often retrieved from molecular oxygen lines, there is no oxygen line in the SMILES spectra, so the strong ozone line at 625.371 GHz has been chosen. The pointing parameters and the ozone profiles are retrieved from the line wings which are measured with high signal to noise ratio, whereas the temperature profile is retrieved from the optically thick line center. The main systematic component of the retrieval error was found to be the neglect of the non-linearity of the radiometric gain in the calibration procedure. This causes a temperature retrieval error of 5–10 K. Because of these large temperature errors, it is not possible to construct a reliable hydrostatic pressure profile. However, as a consequence of the retrieval of pointing parameters, pressure induced errors are significantly reduced if the retrieved trace gas profiles are represented on pressure levels instead of geometric altitude levels. Further, various setups of trace gas retrievals have been tested. The error analysis for the retrieved HOCl profile demonstrates that best results for inverting weak lines can be obtained by using narrow spectral windows.

Open access. © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License., Time series of stratospheric and lower mesospheric water vapour using 33 data sets from 15 different satellite instruments were compared in the framework of the second SPARC (Stratosphere-troposphere Processes And their Role in Climate) water vapour assessment (WAVAS-II). This comparison aimed to provide a comprehensive overview of the typical uncertainties in the observational database that can be considered in the future in observational and modelling studies, e.g addressing stratospheric water vapour trends. The time series comparisons are presented for the three latitude bands, the Antarctic (80°-70°S), the tropics (15°S-15°N) and the Northern Hemisphere mid-latitudes (50°-60°N) at four different altitudes (0.1, 3, 10 and 80hPa) covering the stratosphere and lower mesosphere. The combined temporal coverage of observations from the 15 satellite instruments allowed the consideration of the time period 1986-2014. In addition to the qualitative comparison of the time series, the agreement of the data sets is assessed quantitatively in the form of the spread (i.e. the difference between the maximum and minimum volume mixing ratios among the data sets), the (Pearson) correlation coefficient and the drift (i.e. linear changes of the difference between time series over time). Generally, good agreement between the time series was found in the middle stratosphere while larger differences were found in the lower mesosphere and near the tropopause. Concerning the latitude bands, the largest differences were found in the Antarctic while the best agreement was found for the tropics. From our assessment we find that most data sets can be considered in future observational and modelling studies, e.g. addressing stratospheric and lower mesospheric water vapour variability and trends, if data set specific characteristics (e.g. drift) and restrictions (e.g. temporal and spatial coverage) are taken into account. © Author(s) 2018., The Atmospheric Chemistry Experiment (ACE), also known as SCISAT, is a Canadian-led mission mainly supported by the Canadian Space Agency and the Natural Sciences and Engineering Research Council of Canada. We would like to thank the European Space Agency (ESA) for making the MIPAS level-1b data set available. MLS data were obtained from the NASA Goddard Earth Sciences and Information Center. Work at the Jet Propulsion Laboratory, California Institute of Technology, was done under contract with the National Aeronautics and Space Administration. SCIAMACHY spectral data have been provided by ESA. The work on the SCIAMACHY water vapour data products has been funded by DLR (German Aerospace Center) and the University of Bremen. The SCIAMACHY limb water vapour data set v3.01 is a result of the DFG (German Research Council) Research Unit "Stratospheric Change and its Role for Climate Prediction" (SHARP) and the ESA SPIN (ESA SPARC Initiative) project and were partly calculated using resources of the German HLRN (High-Performance Computer Center North). We would like to thank Mark Hervig for providing the SOFIE data and Takafumi Sugita for providing the ILAS-II data. We acknowledge the HALOE science team and the many members of the HALOE project for producing and characterising the high-quality HALOE data set. Further, we would like to thank Ellis Remsberg for valuable comments on the manuscript. Stefan Lossow was funded by the SHARP project under contract STI 210/9-2. We want to express our gratitude to SPARC and WCRP (World Climate Research Programme) for their guidance, sponsorship and support of the WAVAS-II programme. We acknowledge support by Deutsche Forschungsgemeinschaft and Open Access Publishing Fund of Karlsruhe Institute of Technology.

We are planning a mission to Mars using a micro-satellite to carry a sub-millimeter sensor to orbit and have performed a feasibility study to determine what we can measure and to what success. The sensor will measure atmospheric molecular oxygen, water, ozone, and hydrogen peroxide to retrieve their volume mixing ratios and change over time. The sensor will also retrieve the temperature field, the wind field, and the magnetic field at various levels of success. The expected measurement errors for molecular oxygen is below 100 ppmv in limb view below 50 km, with 20 ppmv for near surface measurements. For water in limb-view, the retrieval errors are below 1 ppmv with a detection limit of a few tens of ppbv. For ozone the limits are at 2 ppbv, and for hydrogen peroxide the retrieval limits are in the range of 1 ppbv. In nadir-viewing geometry, the expected errors in the column are worse but not by much since we can keep integrating the signal from the same area for a long time, though the vertical resolution clearly suffers.

Ozone is known to have large oxygen isotopic enrichments of about 10% in the middle stratosphere; however, there have been no reports of ozone isotopic enrichments above the middle stratosphere. We derived an enrichment δ18OOO in the stratosphere and the lower mesosphere from observations of the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) onboard the International Space Station (ISS) using a retrieval algorithm optimized for the isotopic ratio. The retrieval algorithm includes (i) an a priori covariance matrix constrained by oxygen isotopic ratios in ozone, (ii) an optimization of spectral windows for ozone isotopomers and isotopologues, and (iii) common tangent height information for all windows. The δ18OOO by averaging the SMILES measurements at the latitude range of 20 to 40° N from February to March in 2010 with solar zenith angle < 80° was 13% (at 32 km) with the systematic error of about 5%. SMILES and past measurements were in good agreement, with δ18OOO increasing with altitude between 30 and 40 km. The vertical profile of δ18OOO obtained in this study showed an increase and a decrease with altitude in the stratosphere and mesosphere, respectively. The δ18OOO peak, 18%, is found at the stratopause. The δ18OOO has a positive correlation with temperature in the range of 220–255 K, indicating that temperature can be a dominant factor to control the vertical profile of δ18OOO in the stratosphere and mesosphere. This is the first report of the observation of δ18OOO over a wide altitude range extending from the stratosphere to the mesosphere (28–57 km).

Diurnal variations of ClO, HO2, and HOCl were simultaneously observed by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) between 12 October 2009 and 21 April 2010. These were the first global observations of the diurnal variation of HOCl in the upper atmosphere. A major reaction for the production of HOCl is ClO + HO2 → HOCl + O2 (Reaction (R1)) in extra-polar regions. A model study suggested that in the mesosphere, this is the only reaction influencing the amount of HOCl during the night. The evaluation of the pure reaction period, when only Reaction (R1) occurred in the Cly chemical system, was performed by checking the consistency of the HOCl production rate with the ClO loss rate from SMILES observation data. It turned out that the SMILES data at the pressure level of 0.28 hPa (about 58 km) in the autumn mid-latitude region (20–40°, February–April 2010) during night (between modified local time 18:30 and 04:00) were suitable for the estimation of the rate constant, k1. The rate constant obtained from SMILES observations was k1(245 K) = (7.75 ± 0.25) × 10−12 cm3 molecule−1 s−1. This result is consistent with results from a laboratory experiment and ab initio calculations for similar low-pressure conditions.

We present a method for characterizing the magnetic anomalies from the crustal fields in the lower atmosphere of Mars that requires two perpendicular linear polarization measurements of the Zeeman ...

We observed ozone (O3) in the vertical region between 250 and 0.0005 hPa (~ 12–96 km) using the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the Japanese Experiment Module (JEM) of the International Space Station (ISS) between 12 October 2009 and 21 April 2010. The new 4 K superconducting heterodyne receiver technology of SMILES allowed us to obtain a one order of magnitude better signal-to-noise ratio for the O3 line observation compared to past spaceborne microwave instruments. The non-sun-synchronous orbit of the ISS allowed us to observe O3 at various local times. We assessed the quality of the vertical profiles of O3 in the 100–0.001 hPa (~ 16–90 km) region for the SMILES NICT Level 2 product version 2.1.5. The evaluation is based on four components: error analysis; internal comparisons of observations targeting three different instrumental setups for the same O3 625.371 GHz transition; internal comparisons of two different retrieval algorithms; and external comparisons for various local times with ozonesonde, satellite and balloon observations (ENVISAT/MIPAS, SCISAT/ACE-FTS, Odin/OSIRIS, Odin/SMR, Aura/MLS, TELIS). SMILES O3 data have an estimated absolute accuracy of better than 0.3 ppmv (3%) with a vertical resolution of 3–4 km over the 60 to 8 hPa range. The random error for a single measurement is better than the estimated systematic error, being less than 1, 2, and 7%, in the 40–1, 80–0.1, and 100–0.004 hPa pressure regions, respectively. SMILES O3 abundance was 10–20% lower than all other satellite measurements at 8–0.1 hPa due to an error arising from uncertainties of the tangent point information and the gain calibration for the intensity of the spectrum. SMILES O3 from observation frequency Band-B had better accuracy than that from Band-A. A two month period is required to accumulate measurements covering 24 h in local time of O3 profile. However such a dataset can also contain variation due to dynamical, seasonal, and latitudinal effects.

The diurnal variation of HOCl and the related species ClO, HO2 and HCl measured by satellites has been compared with the results of a one-dimensional photochemical model. The study compares the data from various limb-viewing instruments with model simulations from the middle stratosphere to the lower mesosphere. Data from three sub-millimetre instruments and two infrared spectrometers are used, namely from the Sub-Millimetre Radiometer (SMR) on board Odin, the Microwave Limb Sounder (MLS) on board Aura, the Superconducting Submillimeter-wave Limb-Emission Sounder (SMILES) on the International Space Station, the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board ENVISAT, and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on board SCISAT. Inter-comparison of the measurements from instruments on sun-synchronous satellites (SMR, MLS, MIPAS) and measurements from solar occultation instruments (ACE-FTS) is challenging since the measurements correspond to different solar zenith angles (or local times). However, using a model which covers all solar zenith angles and data from the SMILES instrument which measured at all local times over a period of several months provides the possibility to verify the model and to indirectly compare the diurnally variable species. The satellite data were averaged for latitudes of 20° S to 20° N for the SMILES observation period from November 2009 to April 2010 and were compared at three altitudes: 35, 45 and 55 km. Besides presenting the SMILES data, the study also shows a first comparison of the latest MLS data (version 3.3) of HOCl, ClO, and HO2 with other satellite observations, as well as a first evaluation of HO2 observations made by Odin/SMR. The MISU-1D model has been carefully initialised and run for conditions and locations of the observations. The diurnal cycle features for the species investigated here are generally well reproduced by the model. The satellite observations and the model agree well in terms of absolute mixing ratios. The differences between the day and night values of the model are in good agreement with the observations although the amplitude of the HO2 diurnal variation is 10–20% lower in the model than in the observations. In particular, the data offered the opportunity to study the reaction ClO+HO2 → HOCl+O2 in the lower mesosphere at 55 km. At this altitude the HOCl night-time variation depends only on this reaction. The result of this analysis points towards a value of the rate constant within the range of the JPL 2006 recommendation and the upper uncertainty limit of the JPL 2011 recommendation at 55 km.

Although the links between stratospheric dynamics, climate and weather have been demonstrated, direct observations of stratospheric winds are lacking, in particular at altitudes above 30 km. We report observations of winds between 8 and 0.01 hPa (~35–80 km) from October 2009 to April 2010 by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the International Space Station. The altitude range covers the region between 35–60 km where previous space-borne wind instruments show a lack of sensitivity. Both zonal and meridional wind components were obtained, though not simultaneously, in the latitude range from 30° S to 55° N and with a single profile precision of 7–9 m s–1 between 8 and 0.6 hPa and better than 20 m s–1 at altitudes above. The vertical resolution is 5–7 km except in the upper part of the retrieval range (10 km at 0.01 hPa). In the region between 1–0.05 hPa, an absolute value of the mean difference < 2 m s–1 is found between SMILES profiles retrieved from different spectroscopic lines and instrumental settings. Good agreement (absolute value of the mean difference of ~2 m s–1) is also found with the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis in most of the stratosphere except for the zonal winds over the equator (difference > 5 m s−1). In the mesosphere, SMILES and ECMWF zonal winds exhibit large differences (> 20 m s–1), especially in the tropics. We illustrate our results by showing daily and monthly zonal wind variations, namely the semi-annual oscillation in the tropics and reversals of the flow direction between 50–55° N during sudden stratospheric warmings. The daily comparison with ECMWF winds reveals that in the beginning of February, a significantly stronger zonal westward flow is measured in the tropics at 2 hPa compared to the flow computed in the analysis (difference of ~20 m s–1). The results show that the comparison between SMILES and ECMWF winds is not only relevant for the quality assessment of the new SMILES winds, but it also provides insights on the quality of the ECMWF winds themselves. Although the instrument was not specifically designed for measuring winds, the results demonstrate that space-borne sub-mm wave radiometers have the potential to provide good quality data for improving the stratospheric winds in atmospheric models.

Earth observation has the potential to make significant contributions to policy and society, as we discussed in Chap. 1 of this book.

A Mars-orbiting sub-millimeter sensor can be used to retrieve the magnetic field at low altitudes over large areas of significant planetary crustal magnetism of the surface of Mars from measurements of circularly polarized radiation emitted by the 368 GHz ground-state molecular oxygen absorption line. We design a full retrieval system for one example orbit to show the expected accuracies on the magnetic field components that one realization of such a Mars satellite mission could achieve. For one set of measurements around a tangent profile, we find that the two horizontal components of the magnetic field can be measured at about 200 nT error with a vertical resolution of around 4 km from 6 up to 70 km in tangent altitude. The error is similar regardless of the true strength of the magnetic field, and it can be reduced by repeated measurements over the same area. The method and some of its potential pitfalls are described and discussed.

Peak stratospheric chlorofluorocarbon (CFC) and other ozone depleting substance (ODS) concentrations were reached in the mid- to late 1990s. Detection and attribution of the expected recovery of the stratospheric ozone layer in an atmosphere with reduced ODSs as well as efforts to understand the evolution of stratospheric ozone in the presence of increasing greenhouse gases are key current research topics. These require a critical examination of the ozone changes with an accurate knowledge of the spatial (geographical and vertical) and temporal ozone response. For such an examination, it is vital that the quality of the measurements used be as high as possible and measurement uncertainties well quantified. In preparation for the 2014 United Nations Environment Programme (UNEP)/World Meteorological Organization (WMO) Scientific Assessment of Ozone Depletion, the SPARC/IO3C/IGACO-O3/NDACC (SI2N) Initiative was designed to study and document changes in the global ozone profile distribution. This requires assessing long-term ozone profile data sets in regards to measurement stability and uncertainty characteristics. The ultimate goal is to establish suitability for estimating long-term ozone trends to contribute to ozone recovery studies. Some of the data sets have been improved as part of this initiative with updated versions now available. This summary presents an overview of stratospheric ozone profile measurement data sets (ground and satellite based) available for ozone recovery studies. Here we document measurement techniques, spatial and temporal coverage, vertical resolution, native units and measurement uncertainties. In addition, the latest data versions are briefly described (including data version updates as well as detailing multiple retrievals when available for a given satellite instrument). Archive location information for each data set is also given.

International audience; The disjunct eddy covariance (DEC) method is an interesting alternative to the conventional eddy covariance (EC) method because it allows the estimation of turbulent fluxes of species for which fast sensors are not available. We have developed and validated a new disjunct sampling system (called MEDEE). This system is built with chemically inert materials. Air samples are taken quickly and alternately in two cylindrical reservoirs, the internal pressures of which are regulated by a moving piston. The MEDEE system was designed to be operated either on the ground or aboard an aircraft. It is also compatible with most analysers since it transfers the air samples at a regulated pressure. To validate the system, DEC and EC measurements of CO 2 and latent heat fluxes were performed concurrently during a field campaign. EC fluxes were first compared to simulated DEC (SDEC) fluxes and then to actual DEC fluxes. Both the simulated and actual DEC fluxes showed a good agreement with EC fluxes in terms of correlation. The determination coefficients (R 2) were 0.93 and 0.91 for DEC and SDEC latent heat fluxes, respectively. For DEC and SDEC CO 2 fluxes R 2 was 0.69 in both cases. The conditions of low fluxes experienced during the campaign impaired the comparison of the different techniques especially for CO 2 flux measurements. Linear regression analysis showed an 14 % underestimation of DEC fluxes for both CO 2 and latent heat compared to EC fluxes. A first field campaign, focusing on biogenic volatile organic compound (BVOC) emissions, was carried out to measure isoprene fluxes above a downy oak (Quercus Pubescens) forest in the southeast of France. The measured standard emission rate was in the lower range of reported values in earlier studies. Further analysis will be conducted through ground-based and airborne campaigns in the coming years.

To investigate the feasibility of new satellite observations, including air quality (AQ) observations from geostationary (GEO) orbit, it is essential to link the measurement precision ( e ) with sensor specifications in advance. The present study attempts to formulate the linkage between e and specifications of a UV/visible sensor (signal-to-noise ratio (SNR), full width at half maximum (FWHM) of the slit function, and sampling ratio (SR)) on a GEO satellite. A sophisticated radiative transfer model (JACOSPAR) is used to calculate synthetic radiance spectra that would be measured by a UV/visible sensor observing the atmosphere over Tokyo (35.7°N, 139.7°E) from GEO orbit at 120°E longitude. The spectra, modified according to given sensor specifications, are analyzed by the differential optical absorption spectroscopy technique to estimate the e for slant column densities of O 3 and NO 2 . We find clear relationships: for example, the e of the O 3 slant column density (molecules cm −2 ) and SNR at 330 nm are linked by the equation log( e ) = −1.06 · log(SNR) + 20.71 in the UV region, and the e of the NO 2 slant column density and SNR at 450 nm are linked by log( e ) = −0.98 · log(SNR) + 18.00, at a FWHM = 0.6 nm (for the Gaussian slit function) and SR = 4. The relationships are mostly independent of other specifications (e.g., horizontal and temporal resolutions), as they affect e primarily through SNR, providing constraints in determining the optimal SNR (and alternatively FWHM and SR) for similar UV/visible sensors dedicated for AQ studies.

Time series of total column abundances of hydrogen chloride (HCl), chlorine nitrate (ClONO2), and hydrogen fluoride (HF) were determined from ground-based Fourier transform infrared (FTIR) spectra recorded at 17 sites belonging to the Network for the Detection of Atmospheric Composition Change (NDACC) and located between 80.05° N and 77.82° S. By providing such a near-global overview on ground-based measurements of the two major stratospheric chlorine reservoir species, HCl and ClONO2, the present study is able to confirm the decrease of the atmospheric inorganic chlorine abundance during the last few years. This decrease is expected following the 1987 Montreal Protocol and its amendments and adjustments, where restrictions and a subsequent phase-out of the prominent anthropogenic chlorine source gases (solvents, chlorofluorocarbons) were agreed upon to enable a stabilisation and recovery of the stratospheric ozone layer. The atmospheric fluorine content is expected to be influenced by the Montreal Protocol, too, because most of the banned anthropogenic gases also represent important fluorine sources. But many of the substitutes to the banned gases also contain fluorine so that the HF total column abundance is expected to have continued to increase during the last few years. The measurements are compared with calculations from five different models: the two-dimensional Bremen model, the two chemistry-transport models KASIMA and SLIMCAT, and the two chemistry-climate models EMAC and SOCOL. Thereby, the ability of the models to reproduce the absolute total column amounts, the seasonal cycles, and the temporal evolution found in the FTIR measurements is investigated and inter-compared. This is especially interesting because the models have different architectures. The overall agreement between the measurements and models for the total column abundances and the seasonal cycles is good. Linear trends of HCl, ClONO2, and HF are calculated from both measurement and model time series data, with a focus on the time range 2000–2009. This period is chosen because from most of the measurement sites taking part in this study, data are available during these years. The precision of the trends is estimated with the bootstrap resampling method. The sensitivity of the trend results with respect to the fitting function, the time of year chosen and time series length is investigated, as well as a bias due to the irregular sampling of the measurements. The measurements and model results investigated here agree qualitatively on a decrease of the chlorine species by around 1% yr−1. The models simulate an increase of HF of around 1% yr−1. This also agrees well with most of the measurements, but some of the FTIR series in the Northern Hemisphere show a stabilisation or even a decrease in the last few years. In general, for all three gases, the measured trends vary more strongly with latitude and hemisphere than the modelled trends. Relative to the FTIR measurements, the models tend to underestimate the decreasing chlorine trends and to overestimate the fluorine increase in the Northern Hemisphere. At most sites, the models simulate a stronger decrease of ClONO2 than of HCl. In the FTIR measurements, this difference between the trends of HCl and ClONO2 depends strongly on latitude, especially in the Northern Hemisphere.

This article presents our implementation of a non-LTE solver in spherical symmetry for molecular rotational transition in static or expanding atmospheres. The new open-source code relies on the Gauss–Seidel Accelerated Lambda Iteration methodology that provides a rapid and accurate convergence of the non-LTE problems, which is now routinely used in astrophysical and planetary research. The non-LTE code is interfaced with the widely used package, the Atmospheric Radiative Transfer Simulator (ARTS), to facilitate spectral line simulations for various viewing geometries. In this paper we describe the numerical implementation, provide the first validation results for the populations against two other non-LTE codes, and then discuss the possible application. The quantitative comparisons are performed using an established ortho-water non-LTE model applied to cases of optical thick and thin conditions of Ganymede’s atmosphere. The differences in populations expressed as excitation temperatures show very good agreement in both cases. Finally, we also apply this model to a sample of data from the Microwave Instrument for the Rosetta Orbiter (MIRO) instrument. The new non-LTE package is demonstrated to be fast and accurate, and we hope that it will be a useful addition to the planetary community. In addition, being open source and part of the ARTS, it will be further improved and developed.

This paper presents extensive validation analyses of ozone observations from the Atmospheric Chemistry Experiment (ACE) satellite instruments: the ACE Fourier Transform Spectrometer (ACE-FTS) and the Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (ACE-MAESTRO) instrument. The ACE satellite instruments operate in the mid-infrared and ultraviolet-visible-near-infrared spectral regions using the solar occultation technique. In order to continue the long-standing record of solar occultation measurements from space, a detailed quality assessment is required to evaluate the ACE data and validate their use for scientific purposes. Here we compare the latest ozone data products from ACE-FTS and ACE-MAESTRO with coincident observations from satellite-borne, airborne, balloon-borne and ground-based instruments, by analysing volume mixing ratio profiles and partial column densities. The ACE-FTS version 2.2 Ozone Update product reports more ozone than most correlative measurements from the upper troposphere to the lower mesosphere. At altitude levels from 16 to 44 km, the mean differences range generally between 0 and +10% with a slight but systematic positive bias (typically +5%). At higher altitudes (45-60 km), the ACE-FTS ozone amounts are significantly larger than those of the comparison instruments by up to ~40% (typically +20%). For the ACE-MAESTRO version 1.2 ozone data product, agreement within ±10% (generally better than ±5%) is found between 18 and 40 km for the sunrise and sunset measurements. At higher altitudes (45-55 km), systematic biases of opposite sign are found between the ACE-MAESTRO sunrise and sunset observations. While ozone amounts derived from the ACE-MAESTRO sunrise occultation data are often smaller than the coincident observations (by as much as -10%), the sunset occultation profiles for ACE-MAESTRO show results that are qualitatively similar to ACE-FTS and indicate a large positive bias (+10 to +30%) in this altitude range. In contrast, there is no significant difference in bias found for the ACE-FTS sunrise and sunset measurements. These systematic effects in the ozone profiles retrieved from the measurements of ACE-FTS and ACE-MAESTRO are being investigated. This work shows that the ACE instruments provide reliable, high quality measurements from the tropopause to the upper stratosphere and can be used with confidence in this vertical domain

The Atmospheric Chemistry Experiment (ACE) satellite was launched on 12 August 2003. Its two instruments measure vertical profiles of over 30 atmospheric trace gases by analyzing solar occultation spectra in the ultraviolet/visible and infrared wavelength regions. The reservoir gases HNO3, ClONO2, and N2O5 are three of the key species provided by the primary instrument, the ACE Fourier Transform Spectrometer (ACE-FTS). This paper describes the ACE-FTS version 2.2 data products, including the N2O5 update, for the three species and presents validation comparisons with available observations. We have compared volume mixing ratio (VMR) profiles of HNO3, ClONO2, and N2O5 with measurements by other satellite instruments (SMR, MLS, MIPAS), aircraft measurements (ASUR), and single balloon-flights (SPIRALE, FIRS-2). Partial columns of HNO3 and ClONO2 were also compared with measurements by ground-based Fourier Transform Infrared (FTIR) spectrometers. Overall the quality of the ACE-FTS v2.2 HNO3 VMR profiles is good from 18 to 35 km. For the statistical satellite comparisons, the mean absolute differences are generally within ±1 ppbv ±20%) from 18 to 35 km. For MIPAS and MLS comparisons only, mean relative differences lie within±10% between 10 and 36 km. ACE-FTS HNO3 partial columns (~15–30 km) show a slight negative bias of −1.3% relative to the ground-based FTIRs at latitudes ranging from 77.8° S–76.5° N. Good agreement between ACE-FTS ClONO2 and MIPAS, using the Institut für Meteorologie und Klimaforschung and Instituto de Astrofísica de Andalucía (IMK-IAA) data processor is seen. Mean absolute differences are typically within ±0.01 ppbv between 16 and 27 km and less than +0.09 ppbv between 27 and 34 km. The ClONO2 partial column comparisons show varying degrees of agreement, depending on the location and the quality of the FTIR measurements. Good agreement was found for the comparisons with the midlatitude Jungfraujoch partial columns for which the mean relative difference is 4.7%. ACE-FTS N2O5 has a low bias relative to MIPAS IMK-IAA, reaching −0.25 ppbv at the altitude of the N2O5 maximum (around 30 km). Mean absolute differences at lower altitudes (16–27 km) are typically −0.05 ppbv for MIPAS nighttime and ±0.02 ppbv for MIPAS daytime measurements.

We estimate the concentration changes, caused by streamer discharge in sprites, of ozone and related minor species as odd nitrogen (NOx) and hydrogen (HOx) families in the upper stratosphere and mesosphere. The streamer has an intense electric field and high electron density at its head, where a large number of chemically-radical ions and atoms are produced through electron impact on neutral molecules. After its propagation, densities of minor species can be perturbed through ion-neutral chemical reactions initiated by the relaxation of these radical products. We evaluate the production rates of ions and atoms using an electron kinetics model and by assuming that the electric field and electron density are in the head region. We calculate the density variations mainly for NOx, Ox, and HOx species using a one-dimensional model of the neutral and ion composition of the middle atmosphere, including the effect of the sprite streamer. Results at the nighttime condition show that the densities of NO, O3, H, and OH increase suddenly through reactions triggered by the first atomic nitrogen and oxygen product, and electrons just after streamer initiation. It is shown that NO and NO2 still remain for 1 h by a certain order of increase with their source-sink balance, predominantly around 60 km; for other species, increases in O3, OH, HO2, and H2O2 still remain in the range of 40–70 km. From this affirmative result of long-time behavior previously not presented, we emphasize that sprites would have the power to impact local chemistry at night. We also discuss the consistency with previous theoretical and observational studies, along with future suggestions.

The ACE-FTS (Atmospheric Chemistry Experiment – Fourier Transform Spectrometer) solar occultation instrument that was launched onboard the Canadian SCISAT-1 satellite in August 2003 is measuring vertical profiles from the upper troposphere to the lower mesosphere for a large number of atmospheric constituents. Methane is one of the key species. The version v2.2 data of the ACE-FTS CH4 data have been compared to correlative satellite, balloon-borne and ground-based Fourier transform infrared remote sensing data to assess their quality. The comparison results indicate that the accuracy of the data is within 10% in the upper troposphere – lower stratosphere, and within 25% in the middle and higher stratosphere up to the lower mesosphere (

It is important to obtain the year-to-year trend of stratospheric minor species in the context of global changes. An important example is the trend in global ozone depletion. The purpose of this paper is to report the accuracy and precision of measurements of stratospheric chemical species that are made at our Poker Flat site in Alaska (65° N, 147° W). Since 1999, minor atmospheric molecules have been observed using a Fourier-Transform solar-absorption infrared Spectrometer (FTS) at Poker Flat. Vertical profiles of the abundances of ozone, HNO3, HCl, and HF for the period from 2001 to 2003 were retrieved from FTS spectra using Rodgers' formulation of the Optimal Estimation Method (OEM). The accuracy and precision of the retrievals were estimated by formal error analysis. Errors for the total column were estimated to be 5.3%, 3.4%, 5.9%, and 5.3% for ozone, HNO3, HCl, and HF, respectively. The ozone vertical profiles were in good agreement with profiles derived from collocated ozonesonde measurements that were smoothed with averaging kernel functions that had been obtained with the retrieval procedure used in the analysis of spectra from the ground-based FTS (gb-FTS). The O3, HCl, and HF columns that were retrieved from the FTS measurements were consistent with Earth Probe/Total Ozone Mapping Spectrometer (TOMS) and HALogen Occultation Experiment (HALOE) data over Alaska within the error limits of all the respective datasets. This is the first report from the Poker Flat FTS observation site on a number of stratospheric gas profiles including a comprehensive error analysis.

Radio astronomical data of C6H- observed with the Nobeyama 45 m and IRAM 30 m telescopes have been analyzed by the local thermodynamic equilibrium approximation to give the column density of (6.1-8.0) × 1012 cm-2 and the excitation temperature of 32 ± 3 K, with an assumed source size of 30'' ± 3''. The abundance of C6H- was estimated to be 8.6% of C6H. The observed line shapes of C6H - and C6H indicate that the distribution of C 6H- is more present in the inner region than C6H. The production mechanism of C6H- is discussed.

The ortho-to-para nuclear spin ratio of cyclopropenylidene (cyclic C3H2) in TMC-1 cores was investigated using the 45 m radio telescope at Nobeyama Radio Observatory. We have observed four ortho lines (J = 212-101, 312-303, 321-312, and 330-321) and four para lines (J = 202-111, 211-202, 220-211, and 322-313) of cyclic C3H2 in six cores in TMC-1. A statistical equilibrium analysis of the observed intensities revealed apparent correlation between the ortho-to-para ratio of cyclic C3H2 and chemical evolution of the molecular cloud; the ortho-to-para ratio in younger cores is less than 2, while that in older cores is close to the statistical ratio of 3. A simple chemical model calculation indicates that the correlation is ascribed to the conservation of nuclear spin angular momenta in chemical reactions relevant to the production, destruction, and reproduction of cyclic C3H2. Since cyclic C3H2 has been observed in a variety of sources, the ortho-to-para ratio of cyclic C3H2 may be a useful probe of chemical evolution of molecular clouds.