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Electrodynamic influence on the diurnal behaviour of neutral daytime airglow emissions
摘要： The diurnal variations in daytime airglow emission intensity measurements at three wavelengths OI 777.4 nm, OI 630.0 nm, and OI 557.7 nm made from a low-latitude location, Hyderabad (17.5? N, 78.4? E; 8.9? N MLAT) in India have been investigated. The intensity patterns showed both symmetric and asymmetric behaviour in their respective diurnal emission variability with respect to local noon. The asymmetric diurnal behaviour is not expected considering the photochemical nature of the production mechanisms. The reason for this observed asymmetric diurnal behaviour has been found to be predominantly the temporal variation in the equatorial electrodynamics. The plasma that is transported across latitudes due to the action of varying electric field strengths over the magnetic equator in the daytime contributes to the asymmetric diurnal behaviour in the neutral daytime airglow emissions. Independent magnetic and radio measurements support this finding. It is also noted that this asymmetric diurnal behaviour in the neutral emission intensities has a solar cycle dependence with a greater number of days during high solar activity period showing asymmetric diurnal behaviour compared to those during a low solar activity epoch. These intensity variations over a long timescale demonstrate that the daytime neutral optical emissions are extremely sensitive to the changes in the eastward electric field over low and equatorial latitudes.
关键词： Ionosphere (equatorial ionosphere–atmosphere interactions),Atmospheric composition and structure (airglow and aurora)
更新于2025-09-23 15:19:57
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The far-ultraviolet main auroral emission at Jupiter – Part 2: Vertical emission profile
摘要： The aurorae at Jupiter are made up of many different features associated with a variety of generation mechanisms. The main auroral emission, also known as the main oval, is the most prominent of them as it accounts for approximately half of the total power emitted by the aurorae in the ultraviolet range. The energy of the precipitating electrons is a crucial parameter to characterize the processes at play which give rise to these auroral emissions, and the altitude of the emissions directly depends on this energy. Here we make use of far-UV (FUV) images acquired with the Advanced Camera for Surveys on board the Hubble Space Telescope and spectra acquired with the Space Telescope Imaging Spectrograph to measure the vertical profile of the main emissions. The altitude of the brightness peak as seen above the limb is ～ 400 km, which is significantly higher than the 250 km measured in the post-dusk sector by Galileo in the visible domain. However, a detailed analysis of the effect of hydrocarbon absorption, including both simulations and FUV spectral observations, indicates that FUV apparent vertical profiles should be considered with caution, as these observations are not incompatible with an emission peak located at 250 km. The analysis also calls for spectral observations to be carried out with an optimized geometry in order to remove observational ambiguities.
关键词： Atmospheric composition and structure (airglow and aurora),magnetospheric physics (auroral phenomena; current systems)
更新于2025-09-19 17:15:36
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - The Use of Satellite Data in the Copernicus Atmosphere Monitoring Service (Cams)
摘要： The Copernicus Atmosphere Monitoring Service (CAMS) is one of the six thematic services of the European Union's flagship Earth Observation programme Copernicus. CAMS is implemented by the European Centre for Medium-Range Weather Forecasts (ECMWF) together with a network of about 60 entities distributed in 20 European countries: it is thus a truly international and collaborative effort. CAMS delivers operationally a wide range of information products and services on air quality, emissions and surface fluxes, solar radiation and climate forcings. All CAMS atmospheric composition outputs are unrestricted and provided free-of-charge to users worldwide. The CAMS global forecasting system is using ECMWF's Integrated Forecasting System (IFS), which is used successfully for Numerical Weather Prediction and has been extended with modules for atmospheric chemistry, aerosols and greenhouse gases. Over 60 different satellite data streams are assimilated to provide twice daily global atmosphere composition forecasts.
关键词： emissions,atmospheric composition,Copernicus,solar radiation,air quality
更新于2025-09-10 09:29:36
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Retrieving vertical ozone profiles from measurements of global spectral irradiance
摘要： A new method is presented to determine vertical ozone profiles from measurements of spectral global (direct Sun plus upper hemisphere) irradiance in the ultraviolet. The method is similar to the widely used Umkehr technique, which inverts measurements of zenith sky radiance. The procedure was applied to measurements of a high-resolution spectroradiometer installed near the centre of the Greenland ice sheet. Retrieved profiles were validated with balloon-sonde observations and ozone profiles from the space-borne Microwave Limb Sounder (MLS). Depending on altitude, the bias between retrieval results presented in this paper and MLS observations ranges between ?5 and +3 %. The magnitude of this bias is comparable, if not smaller, to values reported in the literature for the standard Dobson Umkehr method. Total ozone columns (TOCs) calculated from the retrieved profiles agree to within 0.7±2.0 % (±1σ) with TOCs measured by the Ozone Monitoring Instrument on board the Aura satellite. The new method is called the “Global-Umkehr” method.
关键词： atmospheric composition,spectral irradiance,ozone profiles,UV monitoring,Umkehr technique
更新于2025-09-09 09:28:46
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Spectral analysis of atmospheric composition: application to surface ozone model-measurement comparisons
摘要： Models of atmospheric composition play an essential role in our scientific understanding of atmospheric processes and in providing policy strategies to deal with societally relevant problems such as climate change, air quality and ecosystem degradation. The fidelity of these models needs to be assessed against observations to ensure that errors in model formulations are found and that model limitations are understood. A range of approaches are necessary for these comparisons. Here, we apply a spectral analysis methodology for this comparison. We use the Lomb-Scargle Periodogram, a method similar to a Fourier transform, but better suited to dealing with the gapped data sets typical of observational data. We apply this methodology to long-term hourly ozone observations and the equivalent model (GEOS-Chem) output. We show that the spectrally transformed observational data shows a distinct power spectrum with regimes indicative of meteorological processes (weather, macroweather) and specific peaks observed at the daily and annual timescales together with corresponding harmonic peaks at half, third etc. of these frequencies. Model output shows corresponding features. A comparison between the amplitude and phase of these peaks introduces a new comparison methodology between model and measurements. We focus on the amplitude and phase of diurnal and seasonal cycles and present observational/model comparisons and discuss model performance. We find large biases notably for the seasonal cycle in the mid-latitude northern hemisphere where the amplitudes are generally overestimated by up to 16 ppb, and phases are too late on the order of 1-5 months. This spectral methodology can be applied to a range of model-measurement applications and is highly suitable for Multimodel Intercomparison Projects (MIPs).
关键词： Lomb-Scargle Periodogram,ozone,spectral analysis,GEOS-Chem,model-measurement comparisons,atmospheric composition
更新于2025-09-04 15:30:14