Cluster observation of few-hour-scale evolution of structured plasma in the inner magnetosphere

Abstract

Using Cluster Ion Spectrometry (CIS) data from the spacecraft-4 perigee traversals during the 2001–2006 period (nearly 500 traversals after removing those that are highly contaminated by radiation belt particles), we statistically examined the local time distribution of structured trapped ions at sub- to few-keV range as well as inbound–outbound differences of these ion signatures in intensities and energy–latitude dispersion directions. Since the Cluster orbit during this period was almost constant and approximately north–south symmetric at nearly constant local time near the perigee, inbound–outbound differences are attributed to temporal developments in a 1–2 h timescale. Three types of structured ions at sub- to few keV range that are commonly found in the inner magnetosphere are examined: <br><br> &ndash; Energy–latitude dispersed structured ions at less than a few keV, <br> &ndash; Short-lived dispersionless ion stripes at wide energy range extending 0.1–10 keV, <br> &ndash; Short-lived low-energy ion bursts at less than a few hundred eV. <br><br> The statistics revealed that the wedge-like dispersed ions are most often observed in the dawn sector (60% of traversals), and a large portion of them show significant enhancement during the traversals at all local times. The short-lived ion stripes are predominantly found near midnight, where most stripes are significantly enhanced during the traversals and are associated with substorm activities with geomagnetic AL < &minus;300 nT. The low-energy bursts are observed at all local times and under all geomagnetic conditions, with moderate peak of the occurrence rate in the afternoon sector. A large portion of them again show significant enhancement or decay during the traversals

Circulation of Heavy Ions and Their Dynamical Effects in the Magnetosphere: Recent Observations and Models

“…In the sub-keV range, the low-latitude source may be also important. A recent study by Yamauchi et al (2013) reviewed the variety of ion signatures observed in the sub-keV range. One common feature is a "wedge-like" dispersion signature.…”

“…However, the drift signatures were often mixed with new upflowing ions, indicating that low latitude upflow (an interval from the low-altitude ionosphere to the plasmasphere) is also a source (Giang et al 2009). Short bursts of low energy (<100 eV) field aligned ions is another indication of low latitude outflow Yamauchi et al (2013).…”

Ion drift simulation of sudden appearance of sub-keV structured ions in the inner magnetosphere

“…Trapped hot ions at an energy range of 0.05-5 keV in the inner magnetosphere have complicated morphologies and mirror altitudes at different longitude, geomagnetic conditions, and L values (McIlwain, 1974;Quinn and McIlwain, 1979;Ejiri et al, 1980;Fennell et al, 1981;Sauvaud et al, 1981;Newell and Meng, 1986;Ebihara et al, 2001Ebihara et al, , 2004Yamauchi et al, 1996Yamauchi et al, , 2013. These trapped hot ions in the inner magnetosphere bounce between the Northern Hemisphere and the Southern Hemisphere with short bounce periods of only about 11 min for 100 eV protons and 4 min for 1 keV protons at L = 4 (see, e.g., Quinn and McIlwain, 1979).…”

“…Using this feature, Yamauchi et al (2013) statistically examined the temporal evolution of three types of structured ions that are commonly found at sub-to few keV range in the inner magnetosphere using inbound-outbound differences in the proton data taken by the Cluster Ion Spectrometry (CIS) COmposition DIstribution Function (CODIF) instrument (Rème et al, 2001). Cluster orbits of perigee traversals in the inner magnetosphere during the 2001-2006 period are nearly symmetric about the equatorial plane along nearly the same longitude, with less than 1-2 h local time (LT) difference between the inbound and the outbound passes.…”

“…Cluster orbits of perigee traversals in the inner magnetosphere during the 2001-2006 period are nearly symmetric about the equatorial plane along nearly the same longitude, with less than 1-2 h local time (LT) difference between the inbound and the outbound passes. The symmetry with respect to the equatorial plane for both the orbit and the motion of trapped ions allowed Yamauchi et al (2013) to interpret the inbound-outbound differences in the latitudinal profile of the 0.1-1 keV ion population as temporal changes by, for example, ion energization, transport, or loss, with a timescale of the order of an hour.…”