ALBERT

Description: This study mainly focuses on the validation of total column (TC) ozone data derived from the Ozone Mapping and Profiler Suite (OMPS) on board the NASA's Suomi National Polar-orbiting Partnership satellite (NPP). OMPS is an advanced suite of three hyperspectral instruments that maps global ozone on a daily basis and extends the more than 30 yr total ozone and ozone profile records. The algorithm used to derive OMPS TC ozone is adapted from the heritage of Total Ozone Mapping Spectrometer (TOMS) Version 7 algorithm but with a number of enhancements. Validation is primarily performed through comparisons with an ensemble of 74 global distributed Brewer and Dobson spectrophotometers measurements. Linear regression performs fair agreement between OMPS TC ozone and ground-based TC ozone measurements with root mean square error (RMSE) around of 3% (10 DU). Comparison shows that OMPS TC ozone estimates 0.21% higher than Brewer measurements average, with station-to-station standard deviation of 3.14%. As comparing with Dobson measurements, OMPS TC ozone averages 0.86% higher than the station average with standard deviation of 3.05%. The relative differences between OMPS and ground TC ozone were analysed varying with latitude and time as well as viewing geometry respectively. Comparisons show relative differences within 2% over most of latitude and viewing conditions. Only comparing with Brewer measurements did it show an OMPS TC ozone dependent error, large negative bias was observed as OMPS TC ozone below 220 DU and positive bias shown above 460 DU.

Description: Compared to the recently improved understanding of nightside diffuse aurora, the mechanism(s) responsible for dayside diffuse aurora remains poorly understood. While dayside chorus has been thought as a potential major contributor to dayside diffuse auroral precipitation, quantitative analyses of the role of chorus wave scattering have not been carefully performed. In this study we investigate a dayside diffuse auroral intensification event observed by the Chinese Arctic Yellow River Station (YRS) all-sky imagers (ASI) on 7 January 2005 and capture a substantial increase in diffuse auroral intensity at the 557.7 nm wavelength that occurred over almost the entire ASI field-of-view near 09:24 UT, i.e., ~12:24 MLT. Computation of bounce-averaged resonant scattering rates by dayside chorus emissions using realistic magnetic field models demonstrates that dayside chorus scattering can produce intense precipitation losses of plasma sheet electrons on timescales of hours (even approaching the strong diffusion limit) over a broad range of both energy and pitch angle, specifically, from ~1 keV to 50 keV with equatorial pitch angles from the loss cone to up to ~85° depending on electron energy. Subsequent estimate of loss cone filling index indicates that the loss cone can be substantially filled, due to dayside chorus driven pitch angle scattering, at a rate of ≥0.8 for electrons from ~500 eV to 50 keV that exactly covers the precipitating electrons for the excitation of green-line diffuse aurora. Estimate of electron precipitation flux at different energy levels, based on loss cone filling index profile and typical dayside electron distribution observed by THEMIS spacecraft under similar conditions, gives a total precipitation electron energy flux of the order of 0.1 erg cm−2 s−1 with ~1 keV characteristic energy (especially when using T01s), which can be very likely to cause intense green-line diffuse aurora activity on the dayside. Therefore, dayside chorus scattering in the realistic magnetic field can greatly contribute to the YRS ASI observed intensification of dayside green-line aurora. Besides wave induced scattering and changes in the ambient magnetic field, variations in associated electron flux can also contribute to enhanced diffuse aurora emissions, the possibility of which we cannot exactly rule out due to lack of simultaneous observations of magnetospheric particles. Since the geomagnetic activity level was rather low during the period of interest, it is reasonable to infer that changes in the associated electron flux in the magnetosphere should be small, and consequently its contribution to the observed enhanced diffuse auroral activity should be small as well. Our results support the scenario that dayside chorus could play a major role in the production of dayside diffuse aurora, and also demonstrate that changes in magnetospheric magnetic field should be considered to reasonably interpret observations of dayside diffuse aurora.