Abstract. This paper presents mesospheric carbon monoxide (CO) data acquired by the ground-based microwave radiometer of the British Antarctic Survey (BAS radiometer) stationed at Troll station in Antarctica (72° S, 2.5° E, 1270 m a.s.l.). The dataset covers the period from February 2008 to January 2010, however, due to very low CO concentrations below approximately 80 km altitude in summer, profiles are only presented during the Antarctic winter. CO is measured for approximately 2 h each day and profiles are retrieved approximately every half hour. The retrieved profiles, covering the pressure range from 1 to 0.01 hPa (approximately 48 to 80 km), are compared to measurements from Microwave Limb Sounder on the Aura satellite (Aura/MLS) and Whole Atmosphere Community Climate Model with Specified Dynamics (SD-WACCM). This intercomparison reveals a low bias of 0.5 to 1 ppmv at 0.1 hPa (approximately 64 km) and 2.5 to 3.5 ppmv at 0.01 hPa (approximately 80 km) of the BAS microwave radiometer compared to both reference datasets. One explanation for this low bias could be the known high bias of MLS which is on the same order of magnitude. The ground based radiometer shows high and significant correlation (coefficients higher than 0.9/0.7 compared to MLS/SD-WACCM) at all altitudes compared with both reference datasets. The dataset can be accessed under http://dx.doi.org/10/mhq.

It has been difficult to establish a definitive causal link between radiation belt electron dropouts and solar wind dynamic pressure, due to adiabatic effects and observations limited to a single location in space at one time. Here we reconstruct the radial profiles of radiation belt electron phase space density (PSD) for the entire year of 2002 (solar maximum), based on a combination of the VERB radial diffusion model and data assimilation of the sparse observations from six satellites including GEO1989, GEO1990, LANL‐97A, LANL‐01A, GPSns33, and POLAR, to perform a statistical analysis of the potential relationship between electron PSD dropout and solar wind dynamic pressure variation. We capture 59 electron PSD dropout events, 81% associated with solar wind dynamic pressure sudden jumps (i.e., pulses) or modest increase, consistent with the results of Shprits et al. (2012) for the period of 1990–1991. With the continuous availability of high quality solar wind data in 2002, we further identify 41 pressure pulses and determine that 68% of them are associated with electron PSD dropouts. We also identify 49 pressure enhancements, 41% of which are associated with electron PSD dropouts. Our results support that gradual or sharp enhancements in solar wind dynamic pressure can play an important role in producing electron PSD dropouts, owing to inward intrusion of the magnetopause that enhances the loss to the magnetopause and outward radial diffusion. But we conclusively demonstrate that solar wind dynamic pressure pulses and enhancements are neither a necessary nor a sufficient condition for the formation of electron PSD dropouts, which suggests that some other mechanism(s), which remains mysterious, is required to explain electron PSD dropout occurrences without pressure pulse or modest pressure increase. For the first time, we also perform a quantitative comparison of conjunctions between electron PSD reanalysis results and satellite PSD data, which indicates a tolerable and reasonable error in assimilated PSD within a factor of 5. Differences in assimilated PSD and satellite PSD have a potential for use to evaluate the ignored processes in the physical model and to estimate the errors associated with satellite measurements.

Instruments Data Provenance & Structure

Using a ground‐based microwave radiometer at Troll Station, Antarctica (72°S, 2.5°E,L = 4.76), we have observed a decrease of 20–70% in the mesospheric ozone, coincident with increased nitric oxide, between 60 km and 75 km altitude associated with energetic electron precipitation (E > 30 keV) during a moderate geomagnetic storm (minimum Dst of −79 nT) in late July 2009. NOAA satellite data were used to identify the precipitating particles and to characterize their energy, spatial distribution and temporal variation over Antarctica during this isolated storm. Both the ozone decrease and nitric oxide increase initiate with the onset of the storm, and persist for several days after the precipitation ends, descending in the downward flow of the polar vortex. These combined data present a unique case study of the temporal and spatial morphology of chemical changes induced by electron precipitation during moderate geomagnetic storms, indicating that these commonplace events can cause significant effects on the middle mesospheric ozone distribution.

The dynamics of the radiation belt Phase Space Density (PSD) is analyzed using measurements from four spacecraft taken during two hundred days in 1990 and 1991. In situ measurements from CRRES, Akebono, GPS, and GEO and a realistic model of the magnetic field are used to infer values of PSD. The inferred values of PSD are assimilated into a radial diffusion model by means of Kalman filtering to produce a reanalysis of the relativistic electron PSD during this time interval. The statistical analysis shows that the plasmapause location is well correlated with the location of the peak of PSD. Positive innovation outside of the plasmasphere shows that local acceleration is present in the trough region. The peak of PSD and the local source, as inferred from the innovation, are displaced inward during times of increased geomagnetic activity. Analysis of non‐adiabatic dropouts in PSD shows that the dropouts often coincide with sudden increases in the solar wind dynamic pressure. Approximately 73% of the dropouts can be associated with the simultaneous sudden jumps (>7 nPa over several hours) in the solar wind dynamic pressure, approximately 15% could be associated with small jumps or gradual increases in solar wind dynamic pressure, and the remaining 12%, which consists of only 3 events, occurred during relatively steady solar wind dynamic pressure.

Data assimilation is becoming an increasingly important tool for understanding the near Earth hazardous radiation environments. Reanalysis of the radiation belts can be used to identify the electron acceleration mechanism and distinguish local acceleration from radial diffusion. However, for any practical applications we need to determine how reliable is reanalysis, and how significant is the dependence of the results on the assumptions of the code and choice of boundary conditions. We present the sensitivity of reanalysis of the radiation belt electron phase space density (PSD) to the assumed location of the outer boundary, using the VERB code and a Kalman filter. We analyze the sensitivity of reanalysis to changes in the electron-loss throughout the domain, and the sensitivity to the assumed boundary condition and its effect on the innovation vector. All the simulations presented in this study for all assumed loss models and boundary conditions, show that peaks in the phase space density of relativistic electrons build up between 4.5 and 6RE during relativistic electron flux enhancements in the outer radiation belt. This clearly shows that peaks build up in the heart of the electron radiation belt independent of the assumptions in the model, and that local acceleration is operating there. The work here is also an important step toward performing reanalysis using observations from current and future missions.

We present reanalysis of radiation belt electron phase space density using the VERB code and a Kalman filter at higher L than previously used. Simulations show that when setting up the boundary at L = 10, the heart of the outer radiation belt is negligibly affected for most of the time. We analyze the sensitivity of the reanalysis to changes in the electron-loss throughout the domain. In addition we examine the merits of including a boundary between trapped an un-trapped electrons. We show that reanalysis can reproduce phase space density and the dynamics in the heart of the outer radiation belt in a similar way for different electron losses. Furthermore, peaks in the outer radiation belt are seen in all the simulations presented in this study, supporting the idea that peaks develop in the heart of the radiation belt as a consequence of local acceleration processes.