The Global Ultraviolet Imager (GUVI) aboard the NASA TIMED at ∼630 km altitude provides cross-track scanned images of the Earth's ultraviolet airglow and auroral emission in the far ultraviolet (FUV) at wavelengths 115.0 to 180.0 nm. To distinguish different features of RCA, detached auroras in different local time sectors are also used. To unify the terminology, we call these detached auroras the ring current auroras (RCA). As part of our analysis of this event, we ran the Comprehensive Ring Current Model (CRCM). We report here a special auroral event: an IP shock induced dayside, duskside and nightside detached auroras and associated EMIC waves observed by multiple satellites. Analysis of particle and field data on the AMPTEC/CCE satellite in the dayside magnetosphere indicate that enhancements in solar wind pressure can excite EMIC waves driven by an enhancement in the energetic ring current proton flux perpendicular to the magnetic field. Sudden increase in the dynamic pressure of the solar wind can cause an increase in the thermal anisotropy of trapped ring current ions, which enhances the growth rate of EMIC waves. Linear growth rate calculations of EMIC waves also show that the limited latitudinal extent of the transient dayside detached aurora appears to be related to the interaction between hot ring current protons and the cold plasmaspheric ions. demonstrated a good correlation among the duskside proton arcs seen by IMAGE FUV, the ring current hot ions with temperature anisotropy observed by Magnetospheric Plasma Analyzer (MPA) in a geosynchronous orbit and the plasma plumes (dense cold plasma) detected by IMAGE EUV. Enhanced EMIC waves (ground observations) have been observed in association with the duskside proton arcs. Such pitch angle diffusion is thought mainly due to the particle scattering of electromagnetic cyclotron (EMIC) waves. Precipitation of the normally trapped ring current ions is due to pitch angle diffusion of the ions. It is evident that the detached auroras are due to energetic ion precipitation from the ring current. During the recovery phase of magnetic storms, nightside detached auroras and morningside proton spots have been observed. The dayside detached auroras are caused by sudden solar wind dynamic pressure enhancements under northward IMF conditions. The duskside detached arcs could develop from a separation of the duskside oval or when the auroral oval retreats poleward during a north turning of the interplanetary magnetic field (IMF) or when IMF B y rotates from negative to positive. Double dayside detached auroras were also observed by TIME/GUVI. IMAGE FUV SI-12 instruments also observed detached auroras on the dayside. Furthermore, detached arcs are not limited to the duskside. reported that proton precipitation is the major source for detached arcs in the dusk sector. More progress in the study of detached arcs was achieved after the launch of the IMAGE satellite. found that energetic electrons (1 to 10 keV) were the energy source of the detached arcs. Ground radar measurements from Chatanika, Alaska, showed that the detached arcs were about 2 degrees wide in latitude and separated by about 3 degrees from the equatorward edge of the diffuse aurora. using photometer data from the ISIS-2 satellite. Detached auroral arcs or patches at subauroral latitudes in the evening sector were first reported by Moshupi et al. To unify the different terminologies, the detached auroras due to precipitating energetic protons from the ring current are called the ring current auroras. The nightside DA was observed for the first time during a sudden commencement. Compression of the magnetosphere appears to be the driver for both of the DDA and dusk/night DA. Ring current simulations show that ∼10 keV protons with sausage-shaped spatial distribution of high anisotropy in flux and temperature were the particle source for the duskside and nightside DA. GUVI and SSUSI also observed the DA in the duskside and dayside with more details. The DA in the duskside and nightside appeared once the DDA disappeared. This provides direct evidence of the link between the EMIC waves and the DDA. Coincident in situ Polar measurements show that sudden bursts of proton EMIC waves (∼2 min) were associated with the DDA. The SI-12 observations show that the dayside detached aurora (DDA) was located between 60° and 68° Mlat and between 06:00 and 15:00 MLT. The DA were detected by three independent FUV instruments: IMAGE/SI-12, TIMED/GUVI and DMSP/SSUSI. On 21 January 2005, a fast interplanetary (IP) shock compressed the magnetosphere and caused detached auroras (DA) on the dayside, duskside and nightside ionosphere.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |