Comprehensive Observations of GeoSpace Convection and the Aurora
The newly enhanced SuperDARN HF radar network, together with All-Sky and Narrow Field of View Imagers operated as part of the Canadian GeoSpace Monitoring and THEMIS Ground-Based Observatory programs, and the new Resolute Bay AMISR Incoherent Scatter Radar are now capable of observing convection and the aurora with an unprecedented combination of spatio-temporal resolution and geographic extent. These observations extend across orders of magnitude of spatial and temporal scales, and provide contiguous coverage extending from the polar cap to sub-auroral latitudes and across many hours of MLT. We are now in a position to carry out innovative new studies of the convection cycle, how it is related to magnetospheric instabilities, and how it leads to the formation of the aurora. In this talk I will provide an overview of these exciting new observational capabilities, focusing particularly on studies that will be enabled by combining optical and convection measurements in the polar cap and the high-latitude auroral zone.
Diagnosis of Magnetotail Drivers for Ionospheric Electrodynamics Using Networks of Ground-based Magnetometers
One of the most important problems in solar-terrestrial physics concerns understanding the response of the ionosphere to a variety of physical drivers from the magnetotail. In particular, determining the ionospheric response to magnetotail disturbances such as current disruptions and Earthward-directed bursty bulk flows is key to understanding the causal sequence of events during substorms. We present a series of case studies using data from combined networks of magnetometers in the Canadian sector, including those from CARISMA (www.carisma.ca) and the THEMIS ground-based observatory (GBO) network and supporting arrays, to examine the current response in the ionosphere to substorm expansion phase onset. These analyses highlight the importance of extensive magnetometer coverage in order to correctly identify and characterise the initiation and temporal dynamics of substorm-time ionospheric electrodynamics and current systems. We show how magnetometer data can be used to locate and time the onset of substorms using Pi1 data, and further develop a magnetic disturbance diagnostic which may distinguish between tail drivers. We suggest that the structure of the resulting current systems may enable these processes to be distinguished using a new set of local magnetometer derived disturbance indices. We suggest forms for these new ionospheric disturbance indices, as an extension to the traditional AE, AL and AU indices. We show how these diagnostics can provide important input into substorm studies, especially in partnership with in-situ measurements from the THEMIS probes, and contribute towards resolving the causal sequence of energy release in the substorm cycle.
SuperDARN Observations of Ionospheric Effects from the Polar Cap to Middle Latitudes
The Super Dual Auroral Radar Network (SuperDARN) of coherent scatter radars provides measurements of ionospheric electric fields, plasma structuring, acoustic gravity waves, mesospheric winds, and other effects in the coupled magnetosphere - ionosphere - atmosphere system. These measurements are obtained continuously and provide high time resolution over extended spatial scales. The original array of SuperDARN radars was constructed at magnetic latitudes near 60 degrees to optimize the spatial coverage during moderate levels of geomagnetic activity. In recent years there has been a simultaneous expansion of the network to higher and lower latitudes. New radars at middle latitudes have increased the capabilities for SuperDARN to measure ionospheric convection during enhanced levels of geomagnetic activity, such as magnetic storms. In addition, the mid-latitude radars are able to monitor influences in the sub-auroral ionosphere in the vicinity of the plasmapause during quiet times. In this presentation I will provide an overview of how the SuperDARN radars are providing valuable new information about: (1) the expansion of geomagnetic effects from high-latitudes to middle latitudes during magnetic storms; (2) subauroral polarization plasma streams and associated electric fields; and (3) substorm effects at middle latitudes.
Displacement and changes in distribution of Birkeland currents during disturbed conditions relative to nominal activity
Although much is known about the distributions of Birkeland currents and their relationship to ionospheric conductance and convection during periods of nominal activity, relatively little is understood about their expansion and configuration during storm times. This is largely because unlike convection which can be detected remotely via Doppler shifts in HF frequencies and conductance distributions which can be inferred either from coherent radars or auroral emissions, the field aligned currents cannot be sensed remotely but can only be measured in-situ by transiting the currents while measuring the corresponding magnetic field signatures of the currents. Individual satellite observations have provided a wealth of information about Birkeland currents in excellent statistical analyses, but these approaches are less enlightening when applied to storms both because of limited statistics and because the statistical approach may have limited applicability to active conditions. We therefore use the magnetometer data from the Iridium constellation of more than 70 satellites in low altitude, circular, polar orbits to assess the Birkeland currents during active conditions. These data, acquired for scientific use since February 1999, allow determination of the two-dimensional distribution and intensity of Birkeland currents with a few degree resolution in latitude from about one hour of observations. While not short enough to resolve many storm-time dynamics, this time cadence does allow an assessment of some basic features of storm-time currents and their unique character. Specifically, a differential equatorward shift at dusk, dramatic departures from the conventional distributions, and measurement of the time delay and rate of intensification and equatorward displacement. This analysis takes advantage of new data processing techniques developed under NSF's AMPERE project that allow us to use the full horizontal vector for the Birkeland current inversions. The major advances in Birkeland current determination that will be afforded by AMPERE when high-time resolution Iridium data become available and the status of AMPERE are also discussed.
Ionospheric Anomalies in the Polar Cap and at Mid-Latitudes Revealed by Digital Ionosondes and GPS Receivers
Intensification of the magnetosphere-ionosphere coupling during magnetic storms driven by coronal mass ejections (CMEs) or corotating interaction regions (CIRs) lead to extreme disturbances in density and height of ionospheric plasma layers. Dramatic enhancements of the ionospheric density and plasma content (TEC) appear in mid-latitude ionosphere and extend into the polar cap in the form of continuous tongue of ionization and/or isolated plasma patches. These ionospheric anomalies affect propagation of radio waves and microwave GPS signals and can be detected by various ground-based instruments. Using few CIR- and CME- driven geomagnetic storms of the last solar maximum as examples it will be demonstrated how the ionospheric anomalies evolve globally in time and space during the storms. The tomographic 4D inversions of the GPS data acquired by ground network of dual-frequency GPS receivers will be compared with the measurements of plasma drift and density obtained by digital ionosondes which now compose the Canadian High Arctic Ionospheric Network (CHAIN).
PFISR Observations of Ionospheric and Joule Heating During CIRs
During the current extended period of solar minimum conditions the high latitude ionosphere is experiencing recurrent episodes of elevated ion heating in the F-region. These events are correlated with the passage of coronal hole, fast steams by the Earth. Each of these CIR events involves first an enhanced density, slow solar wind followed by a low density, high-speed solar wind interaction with the magnetosphere. The first phase of this interaction lasts about a half-day while the second can span several days. For the past two years, beginning with the start of the International Polar Year (IPY), the Poker Flat Incoherent Scatter Radar (PFISR) has been operating almost continuously. The PFISR mode enables the ionosphere above PFISR to be observed through the E- and F-region as well as multi-beam drift measurements made. The first observation mode provides the ion heating in the F-region while the second provides the electric field in the vicinity of the radar. Each CIR event observed has an ionospheric ion temperature signature that begins with very cold values that rapidly elevate as the first phase of the CIR passage occurs. The ion temperatures, at all local times, then increase by over 100K. In the CIR event additional impulsive heating surges occur. These surges last on the order of hours and increase the ion temperature by many 100's of degrees. This presentation will show how the local electric field Joule heating rates, correlate with these distinct ion heating signature. Frictional heating of the ions over the F-region altitude range will also be presented in an effort to understand how energy deposition into the ionosphere-thermosphere (I-T) system is occurring.
On the Relationship of Joule Heating and NO Radiative Cooling in the Thermosphere
Nitric Oxide (NO) is an important trace constituent in the thermosphere, and it plays an important role in determining the composition and structure of the thermosphere above 100 km. Emissions from the NO molecule are one of the main radiative cooling mechanisms in the thermosphere. Observations from the TIMED SABER instrument have shown that NO emissions at 5.3 mm increase dramatically during geomagnetic storms. This paper examines the relationship between the Joule heating rate and the NO radiative cooling rate, with an aim to obtain an quantitative assessment of global energy balance in the thermosphere. More specifically, we compare in detail the magnetospheric energy input in terms of Joule heating and the thermospheric energy output through radiative cooling for a number of geomagnetic storms. The cross-correlation analysis is carried out to assess the effectiveness of NO "thermostat" effect in regulating the magnetospheric energy input into the thermosphere. Finally, we explore the possibility of using the polar cap index (PCI) as a proxy of thermospheric energetics.