39 research outputs found
Simultaneous optical, CUTLASS HF radar, and FAST spacecraft observations: signatures of boundary layer processes in the cusp
International audienceIn this paper we discuss counterstreaming electrons, electric field turbulence, HF radar spectral width enhancements, and field-aligned currents in the southward IMF cusp region. Electric field and particle observations from the FAST spacecraft are compared with CUTLASS Finland spectral width enhancements and ground-based optical data from Svalbard during a meridional crossing of the cusp. The observed 630nm rayed arc (Type-1 cusp aurora) is associated with stepped cusp ion signatures. Simultaneous counterstreaming low-energy electrons on open magnetic field lines lead us to propose that such electrons may be an important source for rayed red arcs through pitch angle scattering in collisions with the upper atmosphere. The observed particle precipitation and electric field turbulence are found to be nearly collocated with the equatorward edge of the optical cusp, in a region where CUTLASS Finland also observed enhanced spectral width. The electric field turbulence is observed to extend far poleward of the optical cusp. The broad-band electric field turbulence corresponds to spatial scale lengths down to 5m. Therefore, we suggest that electric field irregularities are directly responsible for the formation of HF radar backscatter targets and may also explain the observed wide spectra. FAST also encountered two narrow highly structured field-aligned current pairs flowing near the edges of cusp ion steps. Key words. Ionosphere (electric fields and currents). Magnetosphere physics (magnetopause, cusp, and boundary layers; auroral phenomena
The effect of energetic electron precipitation on middle mesospheric night-time ozone during and after a moderate geomagnetic storm
Using a ground-based microwave radiometer at Troll Station, Antarctica (72°S, 2.5°E, L = 4.76), we have observed a decrease of 20â70% 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 â79 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
Space Weather impact on the degradation of NOAA POES MEPED proton detectors
The Medium Energy Proton and Electron Detector (MEPED) on board the National
Oceanic and Atmospheric Administration Polar Orbiting Environmental Satellites
(NOAA POES) is known to degrade with time. In recent years a lot of effort has
been put into calibrating the degraded proton detectors. We make use of
previous work and show that the degradation of the detectors can be attributed
to the radiation dose of each individual instrument. However, the effectiveness
of the radiation in degrading the detector is modulated when it is weighted by
the mean index, increasing the degradation rate in periods with
high geomagnetic activity, and decreasing it through periods of low activity.
When taking and the radiation dose into account, we find that the
degradation rate is independent of spacecraft and detector pointing direction.
We have developed a model to estimate the correction factor for all the MEPED
detectors as a function of accumulated corrected flux and the
index. We apply the routine to NOAA POES spacecraft starting with NOAA-15,
including the European satellites MetOp-02 and MetOp-01, and estimate
correction factors
Doppler-shifted auroral H β emission: a comparison between observations and calculations
Two sounding rockets equipped with
photometers and particle detectors have been flown into proton auroras. The
measured altitude dependence of the proton flux is compared with calculations
based upon known energy-range relations for protons in air. Expressions suitable
for numerical calculations of Doppler profiles at arbitrary angles to the
geomagnetic field and at different heights within an aurora are developed.
Profiles due to some typical proton spectra have been calculated and it is shown
that altitude profiles at some wavelengths are more sensitive to the shape of
the proton spectrum than are profiles at other wavelengths. Variations in the Hβ
Doppler profile versus height for several angles with the magnetic field is
studied. Profiles, as generated by the actually measured protons in the energy
range 1 keV to 1 MeV, have been calculated and are compared with direct optical
measurements made by ground and rocket photometers. The rocket photometers took
measurements at different wavelengths within the Doppler profile. The
correspondence between calculations and measurements is generally good. The
total Hβ is calculated and fair agreement with the measured
intensity is found