The Comprehensive Plasma Instrumentation CPI for the Geotail space craft consists of three plasma analyzers an electrostatic analyzer for hot electrons and ions a complementary electrostatic analyzer for cool plas mas with high bulk speeds such as those found within the solar wind and magnetosheath and an ion composition analyzer for identi cation of ion species such as H He He and O The energy per unit charge E Q ranges for these analyzers are V to kV V to V and V to kV respectively Three dimensional velocity distributions of the ions and electrons are acquired for the rst time in the distant magnetotail and are su ciently accurate to separate E B drifts from eld aligned ows as sociated with currents Among the many speci c scienti c objectives of the plasma observations are the relative importance of ionospheric and solar wind sources searches for plasmoids and ux ropes current sheet acceleration of plasmas and convection and current systems in the magnetotail

This chapter contains sections titled: Introduction Simulation Model Dayside Magnetospheric Boundary Distant Magnetotail Boundary Discussion and Slimmary

We report THEMIS and Geotail observations of prolonged magnetopause (MP) expansions during long-lasting intervals of quasi-radial interplanetary magnetic field (IMF) and nearly constant solar wind dynamic pressure. The expansions were global: the magnetopause was located more than 3 RE and ~7 RE outside its nominal dayside and magnetotail locations, respectively. The expanded states persisted several hours, just as long as the quasi-radial IMF conditions, indicating steady-state situations. For an observed solar wind pressure of ~1.1-1.3 nPa, the new equilibrium subsolar MP position lay at ~14.5 RE, far beyond its expected location. The equilibrium position was affected by geomagnetic activity. The magnetopause expansions result from significant decreases in the total pressure of the high-beta magnetosheath, which we term the low-pressure magnetosheath (LPM) mode. A prominent LPM mode was observed for upstream conditions characterized by IMF cone angles less than 20 ~ 25 grad, high Mach numbers and proton plasma beta<1.3. The minimum value for the total pressure observed by THEMIS in the magnetosheath adjacent to the magnetopause was 0.16 nPa and the fraction of the solar wind pressure applied to the magnetopause was therefore 0.2, extremely small. The equilibrium location of the magnetopause was modulated by a nearly continuous wavy motion over a wide range of time and space scales.

[1] A comparative analysis of the solar wind conditions was performed for extremely disturbed event on 29-31 October 2003. It was found that the ACE and Geotail upstream monitors provided very similar data on the IMF but that plasma measurements in the SOHO CELIAS/MTOF, ACE SWEPAM, IMP 8 MIT, and Geotail CPI experiments are very different. The solar wind velocity was indirectly estimated using the time lag for propagation of such solar wind structures as interplanetary shock, Alfven waves, rotational, and tangential discontinuities from point L1 to the Earth. We found the best correspondence of the estimated velocity was with the ACE SWEPAM data, which displayed very fast (up to 2000 km/s) solar wind, while the IMP 8, Geotail, and SOHO plasma instruments are unable to measure such a fast solar wind stream. Application of the magnetopause models to a data set of numerous geosynchronous magnetopause crossings observed by GOES and LANL satellites enabled estimation of the solar wind dynamic pressure. In general the estimated pressure and density are in agreement with the solar wind plasma parameters provided by the ACE SWEPAM experiment. An estimation of the solar wind density corresponds very well to the electron density restored from the Geotail PWI data. However, during 1600-1800 UT on 29 October, 1700-1800 UT on 30 October, and 0000-0400 UT on 31 October, the estimated solar wind pressure and density are several times larger than provided by the Geotail PWI and ACE SWEPAM. A large helium abundance is considered as a possible reason for the solar wind pressure underestimation in the first case. The understated solar wind density on 30-31 October might be explained by errors in the method for restoring of the plasma data in fast solar wind (>900 km/s) accompanied with intensive fluxes (few tens of particles per cm 2 s sr) of high-energy (>30 MeV) solar energetic protons.

A comparative analysis of the solar wind conditions was performed for extremely disturbed event on 29-31 October 2003. It was found that the ACE and Geotail upstream monitors provided very similar data on the IMF but that plasma measurements in the SOHO CELIAS/MTOF, ACE SWEPAM, IMP 8 MIT, and Geotail CPI experiments are very different. The solar wind velocity was indirectly estimated using the time lag for propagation of such solar wind structures as interplanetary shock, Alfven waves, rotational, and tangential discontinuities from point L1 to the Earth. We found the best correspondence of the estimated velocity was with the ACE SWEPAM data, which displayed very fast (up to 2000 km/s) solar wind, while the IMP 8, Geotail, and SOHO plasma instruments are unable to measure such a fast solar wind stream. Application of the magnetopause models to a data set of numerous geosynchronous magnetopause crossings observed by GOES and LANL satellites enabled estimation of the solar wind dynamic pressure. In general the estimated pressure and density are in agreement with the solar wind plasma parameters provided by the ACE SWEPAM experiment. An estimation of the solar wind density corresponds very well to the electron density restored from the Geotail PWI data. However, during 1600-1800 UT on 29 October, 1700-1800 UT on 30 October, and 0000-0400 UT on 31 October, the estimated solar wind pressure and density are several times larger than provided by the Geotail PWI and ACE SWEPAM. A large helium abundance is considered as a possible reason for the solar wind pressure underestimation in the first case. The understated solar wind density on 30-31 October might be explained by errors in the method for restoring of the plasma data in fast solar wind (>900 km/s) accompanied with intensive fluxes (few tens of particles per cm(2) s sr) of high-energy (>30 MeV) solar energetic protons.

The energetic charged particle, interplanetary magnetic field, and plasma characteristics of the `Bastille Day' shock and ejecta/magnetic cloud events at 1 AU occurring over the days 14–16 July 2000 are described. Profiles of MeV (WIND/LEMT) energetic ions help to organize the overall sequence of events from the solar source to 1 AU. Stressed are analyses of an outstanding magnetic cloud (MC2) starting late on 15 July and its upstream shock about 4 hours earlier in WIND magnetic field and plasma data. Also analyzed is a less certain, but likely, magnetic cloud (MC1) occurring early on 15 July; this was separated from MC2 by its upstream shock and many heliospheric current sheet (HCS) crossings. Other HCS crossings occurred throughout the 3-day period. Overall this dramatic series of interplanetary events caused a large multi-phase magnetic storm with min Dst lower than −300 nT. The very fast solar wind speed (≥ 1100 km s−1) in and around the front of MC2 (for near average densities) was responsible for a very high solar wind ram pressure driving in the front of the magnetosphere to geocentric distances estimated to be as low as ≈ 5 R E, much lower than the geosynchronous orbit radius. This was consistent with magnetic field observations from two GOES satellites which indicated they were in the magnetosheath for extended times. A static force-free field model is used to fit the two magnetic cloud profiles providing estimates of the clouds' physical and geometrical properties. MC2 was much larger than MC1, but their axes were nearly antiparallel, and their magnetic fields had the same left-handed helicity. MC2's axis and its upstream shock normal were very close to being perpendicular to each other, as might be expected if the cloud were driving the shock at the time of observation. The estimated axial magnetic flux carried by MC2 was 52×1020 Mx, which is about 5 times the typical magnetic flux estimated for other magnetic clouds in the WIND data over its first 4 years and is 17 times the flux of MC1. This large flux is due to both the strong axially-directed field of MC2 (46.8 nT on the axis) and the large radius (R 0=0.189 AU) of the flux tube. MC2's average speed is consistent with the expected transit time from a halo-CME to which it is apparently related.

Our aim was to investigate motor activity of the healthy, relatively unprepared colon in the ambulatory state. Twenty-five age- and gender-matched adults had a six-sensor solid-state probe inserted into the proximal transverse colon without sedation. Subjects ambulated freely and ate standard meals. In 528 h of recording, we found a lower ( P < 0.05) area under the curve during the night. Waking induced a threefold increase in motility, whereas meals induced a twofold increase. Women showed less activity ( P < 0.05) in the transverse/descending colon than men. The transverse/descending colon showed more ( P < 0.05) activity than the rectosigmoid colon. Seven patterns were recognized; predominantly, they were simultaneous, propagated, or periodic bursts of 3-cycles/min (cpm) waves. A specialized propagating pressure wave with a high amplitude (>105 mmHg) and a prolonged duration (>14 s) occurred in all subjects (mean 10/day), mostly after waking, after meals, or with defecation. A 3-cpm motor activity was seen in the rectosigmoid region predominantly at night. The colon exhibits a wide spectrum of pressure activity around the clock, with gender and regional differences and circadian rhythm. This comprehensive study provides qualitative and quantitative normative data for colonic manometry.

BACKGROUND:Ingestion of a meal stimulates colonic motility. It is unclear whether the nutrient composition of a meal affects colonic motor response.AIMS:To investigate and compare the effects of a predominantly fat or carbohydrate meal on colonic motility.METHODS:In 18 healthy subjects, ambulatory colonic manometry was performed by placing a six sensor, solid state probe from the mid-transverse colon to the rectum. In a randomised, crossover design, 10 and 27 hours after probe placement, subjects received 4.18 MJ meals containing 60% calories from fat or carbohydrate sources. Preprandial and postprandial pressure activity and motor patterns were evaluated.RESULTS:Both meals induced phasic activity with a greater area under the curve (p<0.03) in the first postprandial hour, compared with the control period. Fat induced motor activity persisted longer (p<0.05) than that of the carbohydrate meal, but the onset of motor response was slower (p<0.001). Although both meals induced more (p<0.001) propagating pressure waves, only the fat meal induced more (p<0.05) simultaneous and retrograde waves. After both meals, 50% of subjects exhibited high amplitude (more than 103 mm Hg), prolonged duration (more than 13 seconds) propagating waves. Both meals induced greater activity (p<0.05) in the transverse/descending colon than in the rectosigmoid colon.CONCLUSIONS:Carbohydrate meals induce colonic motor response, but the effects are short lived when compared with fat meals. The prolonged, segmental, and retrograde phasic activity induced by the fat meal may delay colon transit. Thus meal composition influences colonic motor response.

During the anomalously low density solar wind interval of May 1999, GEOTAIL was in the magnetosheath for ∼37 hours after making an inbound crossing of the expanding bow shock at ∼8 RE upstream of its nominal position. Comparison among data sets obtained from GEOTAIL (magnetosheath), WIND (near upstream‐bow shock), and ACE (far upstream) reveals several unique features: Firstly, during the interval of 1430–1530 UT on 11 May, we observed both in the solar wind and magnetosheath double‐peaked protons with a peak separation of 250–300 km/s, which was close to the local Alfvén velocity during the event. Secondly, we observed extremely strong strahl electrons both in the solar wind and magnetosheath during the interval of 0600–2100 UT on 11 May 1999. We present an overview of the GEOTAIL observations, and discuss their physical significance.

Observations from the Galileo plasma analyzer (PLS) recorded during two near encounters with Europa are reported. The measured ion energy spectra show that the ions near Europa are a mix of thermalized torus plasmas with approximately Maxwellian ion velocity distributions and partially thermalized pickup ions with ring distributions. The measurements are used to determine plasma moments including ion number densities, bulk flow velocities, and ion temperatures. These parameters provide information concerning the interaction that occurs as corotating torus plasmas sweep past this moon. The first encounter on December 19, 1996, took the spacecraft through the wake of the moon with the altitude at closest approach approximately 700 km. The trajectory for the second encounter on February 20, 1997, was on the upstream side of the moon with closest approach at an altitude approximately 600 km. Features of the interaction are found to include (1) deflection of plasma flow away from the moon on the upstream side and into the wake on the downstream side, (2) evidence of boundaries in the near wake that indicate a structured wake, and (3) maximum heavy‐ion densities near closest approach ∼40/cm3 that place a limit on the density of a high‐altitude ionosphere at Europa.

We present Polar plasma wave data during cusp energetic particle (CEP) events at 6–9 RE. These data suggest the presence of coherent electrostatic structures that are highly localized and that have typical velocities on the order of hundreds to thousands of km/s along the ambient magnetic field. Some of the wave signatures are solitary waves and some are wave packets. The Polar wave instrument also provides evidence that some of the bursts of electromagnetic waves (with frequencies of a few hundred Hz and just below the electron cyclotron frequency around 800 Hz to 1–2 kHz) that are observed are cohenrent and propagating both up and down the field lines. Electron cyclotron harmonic (ECH) waves are oftern detected but their duration is usually short (< 1 s). Low Frequency (<1 kHz), broadband, bursty electromagnetic waves are also present. The Polar wave data results are used to obtain a better understanding of the macro/microphysics during a CEP event that takes place on September 11, 1996, by correlating various Polar (∼ 7.0 RE) and Akebono (∼ 1.4 RE) data while both spacecraft are in or near the cusp/cleft region and nearly on the same field line, and magnetometer data from the Canadian Intermagnet and Canopus ground stations, which lie near the base of the magnetic pootprint passing through Polar. Solar wind and magnetic field data from the interplanetary medium and magnetosheath are provided by the Geotail and IMP-8 satellites, respectively. Some of the cusp waves may be indicators of the reconnection process taking place through the cusp, the result of mixing of magnetosheath with magnetospheric plasma, and the consequence of an anisotropic electron population in a depressed magnetic field. The low frequency electromagnetic waves are still under study to determine their role, if any, in the heating and acceleration of the MeV He ions during CEP events.

This paper reports a comparison between Geotail observations of plasmas and magnetic fields at 200 R E in the Earth's magnetotail with results from a time‐dependent, global magnetohydrodynamic (MHD) simulation of the interaction of the solar wind with the magnetosphere. The study focuses on observations from July 7, 1993, during which the Geotail spacecraft crossed the distant tail magnetospheric boundary several times while the interplanetary magnetic field (IMF) was predominantly northward and was marked by slow rotations of its clock angle. Simultaneous IMP 8 observations of solar wind ions and the IMF were used as driving input for the MHD simulation, and the resulting time series were compared directly with those from the Geotail spacecraft. The very good agreement found provided the basis for an investigation of the response of the distant tail associated with the clock angle of the IMF. Results from the simulation show that the stresses imposed by the draping of magnetosheath field lines and the asymmetric removal of magnetic flux tailward of the cusps altered considerably the shape of the distant tail as the solar wind discontinuities convected downstream of Earth. As a result, the cross section of the distant tail was considerably flattened along the direction perpendicular to the IMF clock angle, the direction of the neutral sheet following that of the IMF. The simulation also revealed that the combined action of magnetic reconnection and the slow rotation of the IMF clock angle led to a braiding of the distant tail's magnetic field lines along the axis of the tail, with the plane of the braid lying in the direction of the IMF.