SM44A-01 INVITED
Interplanetary Discontinuities: What They Are and What Effects They Have on the Magnetosphere?
The nature of several fundamental interplanetary discontinuities (tangential (TD),rotational (RD)and fast and intermediate shocks) will be briefly reviewed. The effects of these structures and their impingement on the magnetosphere will be explored. Some, but not all of the possible effects are: substorm triggering, magnetospheric compression/inflation, initiation of storm recovery phases, and dayside auroras. Examples of each will be shown and the physical processes involved will be discussed.
SM44A-02
Magnetospheric and Ionospheric Response to the Interplanetary Shocks
The Cluster spacecraft and ground-based Digisonde network observed on November 7, 2004 a strong interplanetary shock interaction with Earth's magnetosphere which initiated a strong magnetic storm with Dst = -373 nT. When this interplanetary shock encountered the Earth system, the Cluster fleet were traveling in the inner magnetosphere region (L shell = 4.2) at almost exactly the Cluster's perigee (around 0900 MLT). This event provides an excellent opportunity to study the geospace response to a powerful interplanetary shock. The angle between the sun-Earth line and the normal direction of the shock front is only 3.0 degree indicating that the shock hit the geospace at ~12LT (local time) initially. It is found that energetic particle fluxes are enhanced strongly and the shock related ionospheric phenomena have obvious longitudinal and latitudinal distribution. The interplanetary shock has a significant influence on the dayside mid-high latitude stations, e.g. Millstone Hill, Wallops Island, etc. whereas the stations at the night sector do not seem to respond to the interplanetary shock immediately.
SM44A-03 INVITED
Aspects of Magnetopause/Magnetosphere Response to Interplanetary Discontinuites, and Features of Magnetopause Kelvin-Helmholtz Waves.
We review some recent work on (i) the response of the magnetosphere to impinging interplanetary discontinuities, and (ii) the excitation of surface waves of Kelvin-Helmholtz (KH) origin at the magnetopause. The work will be concerned with strongly northward-pointing IMF. Data from various spacecraft are discussed and KH activity is analyzed using compressible, linearized MHD theory. In one example, the products of sudden and large--amplitude pressure changes interacting with the bow shock are studied by two-spacecraft observations in the near flanks. We show that the wave in the boundary layer propagates down the tail faster than the pressure front in the magnetosheath, resulting in motions and distortions of the magnetopause boundary which precede the arrival of the magnetosheath front. We then discuss an example of KH waves observed at the flankside magnetopause during passage of the rear end of a magnetic cloud. We argue that these waves are generated remotely at the dayside. The magnetopause KH waves are monitored from the magnetosheath where they appear as an envelope modulation of the magnetosonic waves. A drift to lower frequencies (longer wavelengths) in the spectral power of the KH activity is attributed to a decrease in the IMF clock angle. Finally, we discuss features of the two-stage magnetopause/magnetosphere response elicited by a joint solar wind tangential discontinuity/vortex sheet followed by an interval of northward IMF. This work is supported by NASA grant NNX08AD11G, NASA Cluster grant to UNH, and by Argentine CONICET grant PIP 5291/05.
SM44A-04 INVITED
Effective solar wind structures for large flux enhancement of the outer radiation belt
Forecasting when and how often relativistic electrons largely increase at geosynchronous (GEO) orbit is one of the most important issues of the space weather research. Here we show our recent effort to understand the effective solar wind structures associated with the large flux enhancement at GEO. From superposed epoch analyses of last 10 year data set, it is found that the high-speed solar wind associated with coronal hole stream is more effective for the large flux enhancement on average than the high-speed solar wind associated with coronal mass ejections. The large flux enhancement depends not only on the solar wind speed but also on the sector polarity and seasons, i.e., the large flux enhancement tends to occur when the sector polarity meets so-called spring-toward fall-away (STFA) rule. The results showed that intermittent southward interplanetary magnetic field (IMF) embedded within high speed coronal hole stream is essential for a large flux enhancement of the outer belt. A case study for coronal hole stream events showed that continuous hot and sub-relativistic electron injections and enhancement of chorus waves occur when the sector polarity meets the STFA rule, associated with the intermittent southward IMF. These electron injections and wave enhancement are essential for non-adiabatic acceleration of relativistic electrons. Besides these large flux enhancement events, it is important to understand when and how the extremely large flux enhancement takes place at GEO. We show the importance of gdouble inflationh mechanism that the rarefaction of the solar wind and subsequent magnetosphere inflation play an important role for the extreme events possibly via the diminished drift loss at dayside magnetopause.
SM44A-05
ICME-Magnetosphere-Ionosphere Interaction in Storm of November 6, 2001
ICME-magnetosphere-ionosphere interaction pays an important role in the energy and particle transfer in the solar wind-magnetosphere-ionosphere system. This talk presents a study of such an event on 6 November, 2001. A halo CME was observed by LASCO/SOHO at 1635 UT on 4 November 2001. About 33 hours later at 0153 UT on 6 November, the ICME and associated front shock arrived at the Earth orbit and caused a strong geomagnetic storm with Dst < −280nT, associated with a moderate ionospheric positive storm and 100 km uplift of the F-layer. Prior to the shock impact on the magnetopause, the Cluster four spacecraft were located in the duskside near-Earth tail close to the equator. Afterwards the spacecraft are meandering back and forth between the ICME and the magnetopause boundary layer. POLAR satellite was located near the inner boundary of the duskside plasma sheet. At 0154 UT the magnetosphere was greatly compressed, the Cluster spacecraft then moved out of the magnetosphere and stayed in the ICME until 0227 UT. During the crossing of the magnetopause, an O+ beam of 30 km/s mainly in the -Cx direction is observed. The number density of O+ reaches ~32/cm3, about three times larger than that of protons. The energy of O+ ions is ranged around a few keV to a couple of tens of keV. While in the ICME adjacent to the magnetopause, the bulk velocity of the O+ beam reduces to ~13 km/s, kinetic energy of ions is below 10-20 keV, with a peak pitch angle about 90o. During the same time period Polar in the inner plasma sheet observes a rapid increase of the O+ number flux with peak energy around 430 eV. FAST satellite below 2000 km altitude on the duskside of 19-21h MLT also sees an up-flowing O+ coics. It is also interesting to note that the left-hand polarized kinetic Alfven waves are excited near the magnetospheric boundary. The resonances between the kinetic Alfven waves and the beam particles lead to the pitch angle diffusion of resonant ions, forming a pick- up distribution of beam particles (Xiao et al., 2006). The relevant dynamical processes in the ICME- magnetosphere-ionosphere interaction are discussed.
SM44A-06
Transport of Transient Solar Wind Particles in Earth's Cusps
Where does the solar wind enter the Earth's magnetosphere? We report first observations of transient solar wind particles produced by solar disturbances (CMEs, for example) in the Earth's mid-altitude cusps (~5 RE) with densities nearly equal to those in the magnetosheath. The nearly equal density observed at mid- altitude cusps compared to those in the magnetosheath suggests the particles may be free streaming along B. An estimate of the number of particles entering the cusp for a one-hour transient using a typical RExRE cusp area yields ~1030 particles. An important question not answered by observations is what fraction remains in the magnetosphere or mirrors back to the magneto sheath. Modeling could tell us if any of these particles directly contribute to the ring current. The transient ions are moving parallel to the magnetic field (B) toward Earth and often coexist with ionospheric particles that are flowing out. Phase space distributions show a mixture of hot and cold electrons and multiple ion species including energetic O+ and ionospheric cold O+ beams accompanied by electromagnetic and broadband electrostatic emissions and Bernstein mode waves. These observations are not explained by any existing models and would require inductive effects induced by the solar wind interaction with the magnetosphere.
SM44A-07
Energetic and Dynamic Response of the Magnetosphere and Ionosphere to Solar Wind Dynamic Pressure Impulse
We present a case study of magnetospheric and ionospheric response to the sudden enhancement of solar wind dynamic pressure on 21-22 January 2005. The event was triggered by a fast-moving interplanetary shock at a speed exceeding 900 km/s, which was followed by an interplanetary coronal mass ejection (ICME). In the sheath region between the shock front and the trailing ICME, the solar wind dynamic pressure was highly elevated with a peak value around 80 nPa, and the IMF Bz oscillated between north and south. While the minimum value of the Dst index was about -100 nT, the solar wind dynamic pressure corrected Dst value reached -160 nT. Multi-instrument observations from the low-altitude ionosphere including ground based and low-earth orbiting satellites from NOAA, along with measurements at geosynchronous orbit, are used to assess the global energy partitioning in response to solar wind dynamic pressure impulse. In addition, numerical simulations from the Ring- current Atmosphere interaction Model (RAM) are carried out to shed light on the underling physical processes that may be responsible for the unusually large energy injection into the ring current. We also show the intercomparison between the RAM simulations and the IMAGE-ENA images of the ring current energy content during the event.
SM44A-08
Geospace magnetic field responses to interplanetary shocks
We perform a statistical survey of geospace magnetic field responses, including the geosynchronous magnetic field and the sudden impulses on the ground, to interplanetary shocks (IP shocks) between 1998 and 2005. The magnitudes of the geosynchronous magnetic field (dBz) responses to IP shocks peak near the noon meridian, however the the dependence of the relative amplitude of the responses is much weaker. Negative responses (where dBz is negative) were sometimes observed in the nightside of the magnetosphere even though the IP shocks always cause increases in the solar wind dynamic pressure, a new phenomenon not widely reported in the literature. For a moderately-compressed magnetosphere, the amplitude of the geosynchronous response dBz could be determined by the average value of the background local magnetic field. As the magnitude of the upstream solar wind dynamic pressure increases, the rate of response increases correspondingly. The dBz around the subsolar region is mainly determined by the the change of the square root of the solar wind dynamic pressure across the corresponding IP shock, while the amplitude of sudden impulses correlates better with this parameter when the magnetosphere is less compressed. The dBz at the geosynchronous orbit near local noon and the amplitude of sudden impulses (dSYM-H) on the ground are highly correlated.