Conveners:
Josh Semeter (joshua.semeter@sri.com),
Craig Heinselman, Phil Erickson
2004 Monday 28 June 0400-0600 PM
The goal of the workshop was to identify and discuss current research initiatives in the field of Polar Aeronomy, with an emphasis on how the upcoming deployment of the Advanced Modular Incoherent Scatter Radar (AMISR) at Poker Flat, Alaska, and Resolute Bay, Canada, can advance these topics. The AMISR project constitutes a decisive long term commitment by NSF to CEDAR science. Each AMISR deployment will serve as the centerpiece of an upper atmospheric facility (UAF), embodying collaborative optical and radar instrumentation from a diverse set of investigators. As such, the use of AMISR with other diagnostics constituted a thematic focus of the workshop. The workshop consisted of a series of speakers each representing a particular scientific theme. Background information on AMISR and its capabilities were given in the preceding tutorial talk by Craig Heinselman (http://cedarweb.hao.ucar.edu/workshop/tutorials/2004/heinselman04.pdf).
The workshop was introduced by AMISR PI John Kelly (SRI). Kelly stressed that community involvement is critical to the success of the AMISR project. The community also includes international researchers. Canadian involvement is particularly important for a successful program at Resolute Bay.
The first science topic concerned the formation of thin layers in the ionospheric E-region, represented by Craig Heinselman (SRI). As an example, Heinselman presented measurements of a sporadic E layer collected using the Sondrestrom ISR. The measurements showed the bifurcation of an advecting sporadic E structure. The evolution of such structures cannot be adequately characterized from these data because of the time required to obtain the measurements. He noted that the cause of the horizontal tilt in the layer is also not well understood. Local interactions among sporadic E layers, auroral ionization (measured using optics and radar), and sporadic neutral atom structures (detected with lidars) have been proposed, but concrete observational evidence is still lacking. The AMISR facility will be able to remove much of the spatial/temporal ambiguities limiting observational studies of thin layers.
Phil Erickson (MIT-Haystack) then discussed large scale magnetosphere-ionosphere coupling, primarily in the sub-auroral region. He focused on UHF coherent backscatter as a means of estimating E-field strength in the auroral electrojets and sub-auroral polarization streams (SAPS). In one particular storm event (October 30, 2003), he noted that the poleward edge of a SAPS was observed in Sondrestrom elevation scans, high-lighting the utility of AMISR to fill in the global perspective of SAPS morphology and evolution. Another unique strength of AMISR is its versatility in configuration. Phil proposed that a configuration involving multiple smaller radars could be used in an interferometric mode to estimate electric field strength over small scales.
Collaborations between AMISR and both SuperDARN and PolarDARN were discussed by Bill Bristow (Univ. of Alaska). He noted that combined measurements of the convection velocity field with these complementary diagnostics will allow us to better understand ionospheric variability at multiple scales, and its influence on magnetosphere-ionosphere coupling. For example, it is still not known how fast the convection pattern responds to magnetospheric forcing, or how large the scale-dependent variability within the convection pattern is.
The topic of Polar Mesospheric Summer Echoes (PMSEs) was discussed by Mike Kelly (Cornell). Phased array ISR will allow for an improved characterization of the spatial structure of PMSEs. Kelly noted, however, that backscatter signal strength has a strong k-vector dependence, and argued that it will likely require a full AMISR face to detect PMSEs with reasonable SNR.
Roger Smith discussed AMISR contributions to the study of neutral wind effects on the dissipation of electromagnetic energy from the magnetosphere (on behalf of Mark Conde, both at Univ. of Alaska). He presented evidence from the HEX and JOULE rocket cakpaigns showing large gradients in zonal wind in the vicinity of auroral precipitation. Such neutral wind dynamics can have a significant effect on electrodynamic coupling to the magnetospheric source. Smith also highlighted general contributions that AMISR will make as a supporting diagnostic for Poker Flat rocket experiments.
Eric Donovan (Univ. of Calgary) discussed potential collaborative science between AMISR and the THEMIS satellite mission. As part of the THEMIS mission, a network of ground-based auroral cameras is being constructed and deployed across central Canada, providing a global-scale composite image of the auroral zone. Donovan argued that in order to optimally support THEMIS, at least one of the two Resolute Bay AMISR faces should be pointed southward into the Canadian camera array. Among the science topics that would be facilitated by such a configuration is the correlation of specific auroral forms with the transport of magnetic flux across open/closed field line boundary.
Josh Semeter (SRI) discussed the use of conjugate measurements by AMISR and space-borne sensors in the study of small-scale MI coupling. He noted that electrons accelerated by interactions with Alfven waves near the polar cap boundary produce a particularly high degree of structure in the ionosphere, leading to some of the largest conductivity gradients at any latitude. Because of the intense filamentary currents carried by Alfven waves, these conductivity gradients can lead to polarization electric fields which, in turn, affect MI coupling via feedback. In addition to providing high resolution measurements of ionospheric structure, AMISR will be able to track and characterize small scale variability in electric field patterns around active auroral forms.
Although this set of topics does not constitute a comprehensive review of activity in polar aeronomy that will be addressed with AMISR, the results of the workshop set the stage for a more focused discussion anticipated at the 2004 joint GEM/CEDAR workshop. By that time, deployment and testing of the Poker flat AMISR face will have been completed. The two AMISR faces at Resolute Bay will be in place in 2006.