Cesar Valladares, Boston College, cesar@dl5000.bc.edu
Jan Sojka, Utah State University, fasajka@sojka.cass.usu.edu
Skaggs GC-402, 1:00-3:00 and 4:00-6:00 PM with GIFT
Thursday, June 29, 2000
The HLPS group is one of the founding groups of CEDAR. The initial areas of interest were to investigate the formation, lifetime and decay of large-scale polar cap patches and their reconfiguration into auroral blobs, and to study the electrodynamics of sun-aligned arcs and their coupling to the magnetosphere. Since the beginning, strong emphasis was stressed not only on acquired experimental data from several different techniques, but also on performing precise modeling of selected events based on the observations. Since the initiation of the HLPS group we have conducted over 10 campaigns using incoherent scatter radars, coherent radars, scintillation receivers, imagers, digisondes, instrumentation on-board satellites, magnetometers, Fabry-Perot interferometers, and GPS receivers. We have also convened 3 dedicated Workshops at Peaceful Valley. The main achievements of the HLPS group are well described in two special issues of Radio Science.
One of the accomplishments during the last 6 years has been to identify five different mechanisms that can play an active role in the formation of polar cap arcs. These mechanisms are: the switching of the IMF By component, north-to-south reversals of Bz, large plasma jets located near the polar cap boundary, passage of traveling convection vortices, and cusp precipitation. In January 1999 we carried out a campaign, first to determine whether these mechanisms operate individually or jointly. The second goal of the 1999 campaign was to define metrics that could be applied on data collected by instruments that operate routinely in order to evaluate the statistics and importance of each of the five patch formation mechanisms. Some of the metrics which we selected were the electric field and its latitudinal and longitudinal variation, the shape and size of the polar cap patches, density gradients, the magnitude of the structuring, and the patch repetition frequency. Other important parameters are the polar cap flow, the three components of the IMF, ionospheric currents and the solar flux.
In the study of Sun-aligned arcs, we are now able to simulate the electrodynamics of single and multiple polar cap arcs using a magnetosphere-ionosphere coupled model. This model is driven by realistic magnitudes of electric fields, conductivities and currents. We also understand the relation between the By component of the IMF and the dawn-dusk motion of the Sun-aligned arcs. An advance has also been reported about the regions to which the polar cap arcs map to. In the next few years we should be able to take advantage of the numerous imagers and radars already located within the polar cap and the Polar satellite that is able to view the whole polar cap. One of the tasks for the next years will be to investigate the behavior of the Sun-aligned arcs from he time they are formed until their decay. This also implies the need to study how the electrodynamics evolves in time and varies as a function of the arc intensity, alignment, and dawn-dusk motion, and how this electrodynamics adjust itself to temporal changes of the ‘global’ polar cap convection.
Other areas of interest at the present time are:
A partial list of the presenters is given below.
Jan Sojka - Introduction
Cesar Valladares - Results from the January 1999 campaign
Santi Basu - Plans for the January 2001 campaign
Parvez Guzdar - 3D structuring on polar cap arcs
Lie Zhu - Ionosphere-magnetosphere coupling within sun-aligned arcs