TRESPASS FALL 1997 SCHEDULE

ISTP Observations of Sun-Earth Connection Events.

During the first 6 months of 1997, the satellites and ground facilities of the International Solar Terrestrial Physics (ISTP) "Observatory" have tracked four solar eurptions all the way from the Sun, through interplanetary space, to the Earth's magnetic environment, causing there, violent disturbances and spectacular auroral displays. These four events occurred in January, February, April and May.

In this talk an overview will be given of the ISTP mission and how each element was used to track the January event. This will include solar observations, in-situ interplanetary measurements, and the magnetospheric, ionospheric, and, ground response. Finally, the January event will be compared with the other three large solar-storm events of this year.

More information about these events is available on the World Wide Web at http://www-istp.gsfc.nasa.gov/.

Interhemispheric Analysis of Geomagnetic Disturbances that Occurred Deep in the Polar Caps.

Geomagnetic data obtained in 1995-1996, from the newly deployed digital magnetometers at four Antarctic Sites (Vostok, Lomsomolskay, Sude, adn Minry) and the U.S. Automatic Geophysical Observatories (AGO) was studied in conjunction with with the Greenland magnetometer data. Some magnetometer sites in Greenland and Antarctica are magnetically conjugate by means of the IGRF model. However, these sites are located deep in the geomagnetic polar caps, and therefore, the corresponding geomagnetic field lines can map either far into the magnetospheric tail or can be open to the solar wind during most of the day. We search for ground-based signatures of "apparent conjugacy" deep within the polar caps, especially for conditions when the substorm-like disturbances occur over Greenland and Antarctica simultaneously. We found that in this case the field-aligned currents develop in both polar caps due to a global reduction of the interplanetary electric field imparted to the magneosphere from the solar wind.

The Interplanetary Causes of Intense and Super Intense Magnetic Storms an Magnetic "Quiet" Throughout the Solar Cycle.

The interplanetary causes of intense (Dst less than -100 nt) magnetic storms will be reviewed. Great (Dst less than -250 nT) and super intense (Dst less that -400 nT) are far rarer, and possible interplanetary mechanisms will be discussed. High Intensity Long Duration Continuous AE Activity (HILDCAA) events occur during the declining and minimum phases of the solar cycle. These subsorm events are caused by IMF Alfvenic (Bz) fluctuations that are intrinsic to high-speed streams emanating from solar coronal holes. High latitude geomagnetic activity due to the Alfven waves can be higher during this phase of the solar cycle than during solar maximum. A specific "viscous interaction" mechanism will be discussed using Polar plasma wave data. Wave-particle interactions at the magnetopause and in the low latitude boundary layer (LLBL) are thought to provide sufficient crossfield diffusion to form the LLBL at Earth and Jupiter. Pitch angle scatter by the waves may lead to the dayside aurora.

Magnetic Field Signatures of Dayside Reconnection at 30 Re in the Magnetotail.

IMP 8 spacecraft provides a complete cross-sectional coverage of the magnetotail and nearby magnetosheath at x= -30Re to determine the global geometry of magnetospheric system and its response to different IMF directions. Sorted by IMF direction, vector maps of the magnetic field in the cross-sectional plane expose the asymmetries in the field line tilting, current sheet rotation, distribution of IMF associated fields and their localization in the magnetotail, and rotation of the magnetic field draping around the magnetopause and the degree of this rotation with different IMF direction in the magnetosheath. These asymmetric geometrical changes concentrate along the magnetotail's flands and reveal the openness of the magnetotail geometry. Particularly, the non-uniform localization of the IMF penetration indicate the open regions evidently reflects the global features of the dayside merging. This talk will emphasize on the global magnetic field signatures seen in the vector and contour maps which are ultimately linked to the dayside merging. We will compare the results from MRC-global MHD model which gives strikingly similar features. Initial results from LANL plasma instrument on IMP 8 will be presented for the first time, in the context of the magnetic field results.

The View of the Solar Corona from SOHO/LASCO.

The NASA/ESA spacecraft SOHO carrying the LASCO coronagraph package is the fifth orbiting white light coronagraph, which measures the column electron density. The LASCO field of view ranges from 1.1 to 32 solar radii, both closer to and further from the sun than has been available to previous instruments. The wider field of view combined with lower levels of stray light and more sensitive detectors is providing a new view of both evolutionary and transient processes in the corona. The sun is continually ejecting material in discrete bursts along pre-existing streamers. These ejecta have a speed profile that mimics the theoretical predictions of the slow solar wind. It isn't clear if the ejecta are simply the low end of the distribution of CME`s or are some new phenomena such as the result of an upwelling magnetic field that is observed to expand outward throught the field of the inner coronagraph. CMEs, large expulsions of plasma, have been observed in their initial stages, close to the solar surface. The properties of the CMEs appear to be similar to those in earlier epochs, but several characteristics occur more frequently: occurrence rate, acceleration and disconnection. Halo CMEs, in which the material is detected moving toward (or away from) the Earth, are being well observed, and are providing a clear indication of the solar precursor to major geomagnetic storms.

New Perspectives on the Solar Wind.

Recent observations from the coronal instruments on the Solar and Heliospheric Observatory (SOHO), launched in December 1995, have provided new perspectives on our understanding of the source regions of the fast and slow solar wind. Some of the most outstanding results from the ultraviolet Coronagraph Spectrometer (UVCS) on SOHO will be presented. The implications of these observations for our understanding of the physical processes responsible for the acceleration of the solar wind will be discussed.

Transient Flows in the Magnetospheric Cusp: MACCS and POLAR Observations

Most pictures of high latitude convection flows are either average patterns or take some time to create, which hide rapid variations in the flow. However we know from spacecraft observations that solar wind/magnetosphere coupling is a very unsteady process, giving rise to flux transfer events (FTE's) and other short lived features. Local observations made in the inonosphere also show short lived features that are presumably a response to solar wind changes. In this talk, I will show how we are using magnetometer arrays (in particular the MACCS array and neighboring magnetometers) to image ionospheric convection at a high time resolution (seconds). I will focus on one particular event for which the POLAR spacecraft was in the cusp and on a field line that mapped down close to one of the MACCS observatories to illustrate how rapidly flows change in response to IMF changes, and the power of combining detailed in situ spacecraft measurements with ground based data that can probide that global context.

Annual and Semiannual variations in the F2-Layer

Studies of the critical frequency of F2 (or peak electron density Nmf2] extend over many decades. It is well known that summer/winter variations of quiet-day noon NmF2 are prevalent in some parts of the world, semiannual variations in others. Possible explanations are considered.

Studies using the UCL/Sheffield/NOAA-SEL Coupled Thermosphere-Ionosphere Model show that composition changes, arising from the global thermospheric circulation, can broadly explain the observed distribution of noon NmF2 at midlatitudes.

Energetic Neutral Atom [ENA] observations in and near a proton auroral arc measured with a rocket-borne instrument.

A rocket equipped with solid state detectors sensitive to ions/portons and ENA with energies above 20 keV was launched into the Poleward Leap phase of the auroral substorm. The rocket reached an altitude of 454 km, that is into the region of intense charge exchange for precipitating ions. At low altitudes the pitch angle distribution of the precipitating particles was observed symmetric with respect to the magnetic field line. At higher altitudes this changed, however. The particle flux did not exhibit symmetry around the magnetic field as would be expected for a charged particle beam. This asymmetry and the fact that it only occurs at high altitudes is interpreted to indicate the detection of ENA, most likely hydrogen in our case. The measured flux will consist of a charged component which is symmetric with respect to the magnetic field line and a neutral component which is not controlled by the magnetic field and appears to arrive from a specific azimuthal direction. From the measurements of ENA it is possible to get an estimate of the proton precipitation surrounding the rocket. The flux of ENA will be strongest in the direction coming from the most intense region of proton precipitation, which appears to be at the south of the rocket. the rocket measurements are compared with calculations of the spreading of a proton beam in the upper atmosphere.

Recent Monte Carlo calculations of the proton transport in the upper atmosphere will be reported on. These calculations indicate that about 10% of the incoming protons leave the upper atmosphere as ENA and could thus significantly contribute to the Earth's ENA albedo.

Observations of Planetary Aurora

While people have observed the Earth's northern lights throughout recorded history, it is only since the turn of the century that there has been siinificant understanding of the physics by which the impressive auroral displays are produced. Ground-based and satellite data have revealed the basic nature of the Earth's aurora, yet debate continues today on the details of the energy generation mechanism(s) and the regions in the Earth's magnetic field where these operate. Over the past 20 years we have gained new insight into the general nature of planetary aurora through measurements of the auroras on all 4 giant plants, with by far the most energetic (and best-observed) aurora on Jupiter. Jupiter's aurora are 100-1000 times more energetic than the Earth's, the input energy likely dominates the global dynamics of Jupiter's upper atmosphere, and there is a unique interaction with Io which produces a persistent localized auroral emission at Io's magnetic footprint in Jupiter's atmosphere. This last feature is similar to mass accretion from a companion star onto a white dwarf star in "AM her" binary systems. This talk will present an overview of observations and the physics of planetary aurora, concentrating on the auroras at the Earthand the giant planets.

Thermospheric Oxygen-Hot, Cold, Dissociated, and Ionized.

This talk is geared to the majority of CSP students who do not study the thermosphere. It is a synopsis of work done during a sabbatical year at NCAR. That effort centered on establishing the incoherent scatter radar techniques as a means to monitor the density of the upper atmosphere, which we need since the last satellite to do so died in 1981. Ionospheric measurements with the radar combined with a theory of ionosphere-atmosphere interaction gave different results, however, and so something was wrong with a theory (asn experimentalist's viewpoint). The disagreement could be resolved if sufficient "hot" oxygen should exist near the exobase, numbering 1-2% of the "cold" oxygen density, in which case hot O would vie with the classical electron gas as the main heat source for the ions near the exobase. This work is a tale of how a well-laid plan of inquiry immediately took a sharp and unexpected turn, and of how when two ways of determining something give different results, we may be about to learn something new.

The Magnetospheric Response to the CME Passage of January 10-11, 1997, as Observed at Geosynchronous Orbit.

The response of the magnetosphere to the passage of the January 10-11, 1997 CME is described from the vantage point of geosynchronous orbit. Salient aspects of the observed response include 1) the global compression of the magnetosphere, including plasma sheet density enhancements, geosynchronous magnetopause crossings, and a temporary relativistic electron flux enhancement, 2) strongly stretched magnetotail field, with attendant substorm activity, 3) enhanced magnetospheric convection, leading to plasmaspheric erosion and dayside drainage, 4) no detectable superdense plasma sheet, and 5) propagating plasma-sheet density fronts.

Solar mass Ejections and Recent Geoactivity

CME's are an important aspect of coronal and interplanetary dynamics. They cause large geomagnetic stroms and can drive transient interplanetary shocks, which are a key source of energetic particles. However, our knowledge of the origins and early development of CME's at the Sun is limited. CME's are most frequently associated with erupting prominences and long-enduring X-ray arcades, but sometimes with little or no observed surface activity. I will review some of the well-determined coronal properties of CME's and what we know about their source regions, including some recent studies using Yohkoh, SOHO and radio data. One set of exciting, new observations is of halo CME's, which had been rarely observed in coronal graphs before the SOHO mission. However, since late 1996, the LASCO coronagraphs have observed about a dozen halo-type CME's. Such CME's suggest the launch of a geoeffective disturbance toward Earth. Indeed, 7 of 9 halo CME's observed between December 1996 and May 1997 were associated with magnetic clouds and geomagnetic storms at Earth

Storms in Jupiter's Inner Magnetosphere

Numerous (greater than 50) example of energy-time dispersed charged particle signatures of dynamic. longitudinally confined, hot plasma injections have been observed in Jupiter's inner magnetosphere by the Energetic charged P article (EPD)instrument on the Galileo spacecraft (ion and electron energies greater than20 keV measured). These injections , analogous in some respects to injections observed at Earth during "magnetospheric substorms", ahve been observed between~6.3 and ~23 RJ, and they appear to occur uniformly in System III longitude. Wehave now discovered that these injection events may also organize themselves in time in a fashion analogous to the wee-known "magnetic storms" that occur in the Earth's magneotsphere. during on period when the Ganlileo spacecraft was inbound near ` 13 RJ, the magnetosphere was observed iby EPD to become suddenly very disturbed following the transition time. Time dispersion analysis show t that all of these dynamic events were generated at absolute times that matched or followed the time of the quiet/disturbed transition. It is unknown whether the physical caouses of these dynamic events at Jupiter have any relationship to the causes of similar dynamic events that occur within Earth's magnetosphere.

Dayside/Nightside Coupling at Substorm Onset

The magnetospheric substorm is a global phenomenon. However most emphasis has been placed on studying the geotail and nightside to understand how the substorm expansion phase is initiated. This emphasis is reasonable given that energy is stored in the tail and then release. However, correlations between substorm onset and changes on the dayside have been noted in the past. We further examine these correlations by making use of simultaneous observations made approximately 12 hours apart in local time in North America and Siberia. The times of substorm onsets are determined with an array of magnetometers and rapid-run all-sky video cameras located near Tixie making use of the usual signatures: auroral breakups, Pi 2 pulsations, and magnetic bays. Simultaneous signatures on the dayside at cusp latitudes are monitored using the MACCS array of magnetometers in northern Canada. We report on signatures near the cusp relating to substorm onset, in particular changes in ULF wave activity, wave bursts, and sudden changes in ionospheric currents and flows.