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Ground-based observations of 11.072 GHz atmospheric ozone (O3) emission have been made using the Ny-Ã…lesund Ozone in the Mesosphere Instrument (NAOMI) at the UK Arctic Research Station (latitude 78°55’0” N, longitude 11°55’59” E), Spitsbergen. Seasonally-averaged O3 vertical profiles in the Arctic polar mesosphere-lower thermosphere region for night-time and twilight conditions in the period 15 August 2017 to 15 March 2020 have been retrieved over the altitude range 62– 98 km. NAOMI measurements are compared with corresponding, overlapping observations by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument. The NAOMI and SABER data are binned according to the SABER instrument 60-day yaw cycles into 3-month ‘winter’ (15 December–15 March), ‘autumn’ (15 August– 15 November), and ‘summer’ (15 April–15 July) periods. The NAOMI observations show the same year-to-year and seasonal variabilities as the SABER 9.6 μm O3 data. The winter night-time (solar zenith angle, SZA = 110°) and twilight (75° = SZA = 110°) NAOMI and SABER 9.6 &#956m O3 volume mixing ratio (VMR) profiles agree to within the measurement uncertainties. However, for autumn twilight conditions the SABER 9.6 µm O3 secondary maximum VMR values are higher than NAOMI over altitudes 88–97 km by 47% and 59% respectively in 2017 and 2018. Comparing the two SABER channels which measure O3 at different wavelengths and use different processing schemes, the 9.6 &#956m O3 autumn twilight VMR data for the three years 2017–19 are higher than the corresponding 1.27 µm measurements with the largest difference (58%) in the 65–95 km altitude range similar to the NAOMI observation. The SABER 9.6 &#956m O3 summer daytime (SZA < 75°) mesospheric O3 VMR is also consistently higher than the 1.27 µm measurement, confirming previously reported differences between the SABER 9.6 µm channel and measurements of mesospheric O3 by other satellite instruments. [ABSTRACT FROM AUTHOR]

We have constructed a coolable spectroscopic cell for characterizing the physical and chemical properties of simulated atmospheric aerosol particles. The cell is designed for experiments in which the refractive indices, freezing temperatures, and the phase and chemical composition of a wide range of aerosol types are measured. The relatively large volume (0.075 [m.sup.3]) of the cell reduces wall--aerosol interactions and allows the aerosol residence time to exceed 2 h. The cell has been optically interfaced to Fourier-transform spectrometers to record broadband infrared, visible, and ultraviolet extinction spectra of aerosol particles and gas-phase components over a range of temperatures (180--300 K). The data generated with the cell have applications in remote sensing, radiative transfer models, heterogeneous atmospheric chemistry, and pollution studies. OCIS codes: 010.0010, 010.1110, 300.0300.

The extinction spectra of aqueous sulfuric acid aerosols fully covering the mid-IR to visible regions from750 to 23,000 cm(super -1) (13.9-0.4 mu m) have been measured in the laboratory with a Fourier-transform spectrometer. Both large and small aerosol particles with compositions of approximately 60-70-wt. % H(sub 2)SO(sub 4) were generated and their spectra recorded at 230 and 294 K. The spectra were fitted to a model incorporating room-temperature refractive-index data and Mie theory calculations to characterize the composition and size distributions of the aerosol samples.

The Ku-band microwave frequencies (10.70–14.25GHz) overlap emissions from ozone (O3) at 11.072 GHz and hydroxyl radical (OH) at 13.441GHz. These important chemical species in the polar middle atmosphere respond strongly to high latitude geomagnetic activity associated with space weather. Atmospheric model calculations predict that energetic electron precipitation (EEP) driven by magnetospheric sub storms produces large changes in polar mesospheric O3 and OH. The EEP typically peaks at geomagnetic latitudes ~65° and evolves rapidly with time longitudinally and over the geomagnetic latitude range 60°–80°. Previous atmospheric modelling studies have shown that during sub storms OH abundance can increase by more than an order of magnitude at 64–84km and mesospheric O3 losses can exceed 50%. In this work, an atmospheric simulation and retrieval study has been performed to determine the requirements for passive microwave radiometers capable of measuring diurnal variations in O3 and OH profiles from high latitude northern hemisphere and Antarctic locations to verify model predictions. We show that, for a 11.072GHz radiometer making 6h spectral measurements with 10kHz frequency resolution and root mean square baseline noise of 1mK, O3 could be profiled over 8×10−4–0.22hPa (~98–58km) with 10–17km height resolution and ~1ppmv uncertainty. For the equivalent 13.441GHz measurements with vertical sensor polarisation, OH could be profiled over 3×10−3–0.29hPa (~90–56km) with 10–17km height resolution and ~3ppbv uncertainty. The proposed observations would be highly applicable to studies of EEP, atmospheric dynamics, planetary scale circulation, chemical transport, and the representation of these processes in polar and global climate models. Such observations would provide a relatively low cost alternative to increasingly sparse satellite measurements of the polar middle atmosphere, extending long-term data records and also providing ground truth calibration data. [ABSTRACT FROM AUTHOR]

The submillimetre is an understudied region of the Earth's atmospheric electromagnetic spectrum. Prior technological gaps and relatively high opacity due to the prevalence of rotational water vapour lines at these wavelengths have slowed progress from a ground-based remote sensing perspective; however, emerging superconducting detector technologies in the fields of astronomy offer the potential to address key atmospheric science challenges with new instrumental methods. A site study, with a focus on the polar regions, is performed to assess theoretical feasibility by simulating the downwelling (zenith angle = 0°) clear-sky submillimetre spectrum from 30 mm (10 GHz) to 150 µm (2000 GHz) at six locations under annual mean, summer, winter, daytime, night-time and low-humidity conditions. Vertical profiles of temperature, pressure and 28 atmospheric gases are constructed by combining radiosonde, meteorological reanalysis and atmospheric chemistry model data. The sensitivity of the simulated spectra to the choice of water vapour continuum model and spectroscopic line database is explored. For the atmospheric trace species hypobromous acid (HOBr), hydrogen bromide (HBr), perhydroxyl radical (HO2) and nitrous oxide (N2O) the emission lines producing the largest change in brightness temperature are identified. Signal strengths, centre frequencies, bandwidths, estimated minimum integration times and maximum receiver noise temperatures are determined for all cases. HOBr, HBr and HO2 produce brightness temperature peaks in the mK to µK range, whereas the N2O peaks are in the K range. The optimal submillimetre remote sensing lines for the four species are shown to vary significantly between location and scenario, strengthening the case for future hyperspectral instruments that measure over a broad wavelength range. The techniques presented here provide a framework that can be applied to additional species of interest and taken forward to simulate retrievals and guide the design of future submillimetre instruments. [ABSTRACT FROM AUTHOR]

This study presents a new ion-neutral chemical model coupled into the Whole Atmosphere Community Climate Model (WACCM). The ionospheric D-region (altitudes ~50-90 km) chemistry is based on the Sodankylä Ion Chemistry (SIC) model, a one-dimensional model containing 307 ion-neutral and ion recombination, 16 photodissociation and 7 photoionization reactions of neutral species, positive and negative ions, and electrons. The SIC mechanism was reduced using the simulation error minimization connectivity method (SEM-CM) to produce a reaction scheme of 181 ion-molecule reactions of 181 ion-molecule reactions of 27 positive and 18 negative ions. This scheme describes the concentration profiles at altitudes between 20 km and 120 km of a set of major neutral species (HNO3, O3, H2O2, NO, NO2, HO2, OH, N2O5/ and ions (O+2, O+4, NO+, NO+ (H2O), O+2 (H2O), H+(H2O), H+(H2O)2, H+(H2O)3, H+(H2O)4, O-3, NO-2, O-, O2, OH-, O-2 (H2O), O-2 (H2O)2, O-4, CO-3, CO-3 (H2O), CO-4, HCO-3, NO-2, NO-3, NO-3 (H2O), NO-3 (H2O)2, NO-3 (HNO3/, NO-3 (HNO3/2, Cl-, ClO-/, which agree with the full SIC mechanism within a 5% tolerance. Four 3-D model simulations were then performed, using the impact of the January 2005 solar proton event (SPE) on D-region HOx and NOx chemistry as a test case of four different model versions: the standard WACCM (no negative ions and a very limited set of positive ions); WACCM-SIC (standard WACCM with the full SIC chemistry of positive and negative ions); WACCM-D (standard WACCM with a heuristic reduction of the SIC chemistry, recently used to examine HNO3 formation following an SPE); and WACCMrSIC (standard WACCM with a reduction of SIC chemistry using the SEM-CM method). The standard WACCM misses the HNO3 enhancement during the SPE, while the full and reduced model versions predict significant NOx, HOx and HNO3 enhancements in the mesosphere during solar proton events. The SEM-CM reduction also identifies the important ion-molecule reactions that affect the partitioning of odd nitrogen (NOx/, odd hydrogen (HOx / and O3 in the stratosphere and mesosphere. [ABSTRACT FROM AUTHOR]

The sub-millimetre is an understudied region of the Earth's atmospheric electromagnetic spectrum. Prior technological gaps and relatively high opacity due to the prevalence of rotational water vapour lines at these wavelengths have slowed progress from a ground-based remote sensing perspective; however, emerging superconducting detector technologies in the fields of astronomy offer the potential to address key atmospheric science challenges with new instrumental methods. A site study, with a focus on the polar regions, is performed to assess theoretical feasibility by simulating the downwelling clear-sky sub-millimetre spectrum from 30 mm (10 GHz) to 150 μm (2000 GHz) at six locations under annual mean, summer, winter, daytime, nighttime and low humidity conditions. Vertical profiles of temperature, pressure and 28 atmospheric gases are constructed by combining radiosonde, meteorological reanalysis, and atmospheric chemistry model data. The sensitivity of the simulated spectra to the choice of water vapour continuum model and spectroscopic line database is explored. For the atmospheric trace species hypobromous acid (HOBr), hydrogen bromide (HBr), perhydroxyl radical (HO2) and nitrous oxide (N2O) the emission lines producing the largest change in brightness temperature are identified. Signal strengths, centre frequencies, bandwidths, estimated minimum integration times and maximum receiver noise temperatures are determined for all cases. HOBr, HBr and HO2 produce brightness temperature peaks in the mK to K range, whereas the N2O peaks are in the K range. The optimal sub-millimetre remote sensing lines for the four species are shown to vary significantly between location and scenario, strengthening the case for future hyperspectral instruments that measure over a broad wavelength range. The techniques presented here provide a framework that can be applied to additional species of interest and taken forward to simulate retrievals and guide the design of future sub-millimetre instruments. [ABSTRACT FROM AUTHOR]

High-resolution infrared spectra of the ν6 fundamental asymmetric axial S–F stretching vibrational mode of 32SF4 have been recorded in absorption at 296 K using a Fourier-transform infrared (FTIR) spectrometer. The band is centred at 729.7 cm−1. In total, 1550 a-type vibration–rotation transitions have been assigned. Analysis of the data has yielded precise spectroscopic constants for the ν6=1 state, as well as revised constants for the ground vibrational state. Other features in the FTIR spectra are attributed to difference-band transitions from excited vibrational levels of the ν4 and ν9 vibrational modes. [Copyright &y& Elsevier]