THEMIS Observations of Double-onset Substorms and Their Association with IMF Variations
On 16 July 2008, two pairs of Pi2 pulsation bursts occurred successively and simultaneously at the ground- based observatory system for the THEMIS mission. The keogram at CHBG (L=3.90, corrected geomagnetic longitude 23.0) showed auroral activations at each Pi2 onset. The ground-based magnetometers and geosynchronous orbit sensed magnetic perturbations like the one affected by the formation of the substorm current wedge. The horizontal magnetic variation vectors, consisting of H and D components, had the vortex patterns like the ones induced by the upward and downward field-aligned currents during substorm times. These observations display two recurrent occurrences of double-onset substorms. Meanwhile the THEMIS-B probe at ~ XGSM 25 Re observed two same variation trends of the interplanetary magnetic field (IMF) with a low clock angle as those in the upstream region shifted to ~1 AU just in front of Earth¡¦s magnetopause. The mapping of ground Pi2 onsets to the IMF observations shows that they appear under two variation cycles of north-to-south and then north. Same as previous missions reported, this event manifests that double-onset substorms are externally triggered in association with the IMF variations.
A field line resonance investigation of two-dimensional profile of magnetospheric density observed by multiple magnetometer networks
One of the modern and popular uses of ground magnetometer data is to identify field line resonance frequencies through cross-phase or cross-amplitude analysis and infer the equatorial mass density in the magnetosphere. Most studies on this topic to date focus on the observations along a specific meridian, and, as the Earth rotates, the observations constantly advance in local time. This study presents the field line resonance analysis using data gathered by a number of magnetometer networks in North America, such as McMAC, Falcon, IGPP-LANL, THEMIS, CARISMA, AUTUMN, and Alaskan stations. The observations provide two-dimensional snapshots of the equatorial mass density over a range of L-values and local hours. We will show the spatiotemporal features of density structure observed by the combined two-dimensional magnetometer network and how they are compared with the results obtained by observations along a single meridian.
Two magnetospheric response modes to interplanetary shock impacts
The normal magnetospheric response to an interplanetary shock is a global compression of the magnetosphere that produces a global increase in the equatorial H component magnetic field. The magnetospheric compression is accompanied by an intensification of the magnetopause currents and their simultaneous movement closer to the Earth. Another, more rare and more complex interaction occurs when the increase in solar wind dynamic pressure associated with the shock is simultaneous with a northward turning of the IMF. In this case, in addition to the magnetospheric compression, the global structure of the outer magnetosphere reconfigures to change the pattern of magnetospheric plasma convection. A characteristic observation during such an atypical response is that the low-latitude ground increase in the H-component is seen only on the night side. Only a small, or sometimes negative, change in H is observed on the day side. We suggest an explanation of these phenomena based upon different time delays of the magnetopause and tail current systems following the shock impact. In response to the northward turning of the IMF, a change in convection on the closed field region begins about 30 minutes following the development of the 4-cell convection system in the open field line region. The development of the reverse convection cells is, in part, supported by a special transition FAC system. A calculation of the magnetic effects due to the total FAC including the transition current system shows good agreement with ground magnetometer measurements.
Statistical Study of ULF Pc 1-2 Wave Propagation Characteristics in the High Latitude Ionospheric Waveguide
It is well-documented that the ionospheric cavity bounded by the E and F2 layers acts as a waveguide for geomagnetic pulsations. Using data from a five-station search-coil magnetometer array in the Antarctic (ordered poleward: Halley Bay, AGO P2, South Pole, AGO P1, AGO P5), a study is made of ULF Pc 1-2 geomagnetic pulsations in the 0.1-1.0 Hz range to examine their spectral wave power attenuation during propagation through the ionospheric waveguide. Here we present results from a statistical study of over 100 events showing that Pc 1-2 geomagnetic pulsations exhibit well-defined poleward ducting behavior in the ionospheric waveguide as well as significant spectral power loss during poleward propagation, which suggests that Pc 1-2 waves are injected into the lower latitude ionosphere and guided through the ducting layer. Through the use of spectrograms and wave power attenuation plots, we show both qualitatively and quantitatively how these behaviors are affected by specific ionospheric conditions connected to the timing of the event with regard to magnetic local time. It is also examined in a statistical way how wave spectral power attenuation is related to sunlit conditions, which are thought to contribute to the ionospheric conductivity.
The CANMOS Magnetometer System and its Space Weather Applications
The Canadian Magnetic Observatory Network (CANMOS) is composed of 13 observatories spread across
Canada. It also includes a magnetic calibration facility that provides calibration of professional and military
grade magnetic compasses and other specialized equipment. CANMOS is used by the Canadian Space
Weather Forecast Service to provide forecasts of geomagnetic activity and warnings of geomagnetic storms.
By working with industry, forecasts are developed of how geomagnetic storms may affect their systems.
netPICOmag: from Design to Network Implementation
netPICOmag is the successful conclusion of a design effort involving networking based on Rabbit microcontrollers, PIC microcontrollers, and pulsed magnetometer sensors. GPS timing allows both timestamping of data and the precision counting of the number of pulses produced by the sensor heads in one second. Power over Ethernet, use of DHCP, and broadcast of UDP packets mean a very simple local installation, with one wire leading to a relatively small integrated sensor package which is vertically placed in the ground. Although we continue to make improvements, including through investigating new sensor types, we regard the design as mature and well tested. Here we focus on the need for yet denser magnetometer networks, technological applications which become practical using sensitive yet inexpensive magnetometers, and deployment methods for large numbers of sensors. With careful calibration, netPICOmags overlap with research grade magnetometers. Without it, they still sensitively detect magnetic variations and can be used for an education or outreach program. Due to their low cost, such an application allows many students to be directly involved in gathering data that can be very relevant to them personally when they witness auroras.
AUTUMN/STEP and POLARIS EHB: Spanning Canada With Research Magnetometers
AUTUMN (Athabasca University THEMIS UCLA Magnetometer Network) was emplaced in 2005, originally as a
subauroral network in the province of Alberta. With the help of the University of Saskatchewan and Berkeley, a
magnetometer at Inuvik, NWT was added in 2006. A magnetometer was installed at Fort Vermilion, Alberta in
2007, and the AUTUMN Edmonton magnetometer was moved to La Ronge, Saskatchewan in 2008. AUTUMN
thus now has several auroral zone stations. The STEP (Solar-Terrestrial Environment Program) chain
originated in the 1980s. Several of its stations are still operating, some with both fluxgates and induction coils.
Many have been upgraded to use the internet, and all now feature GPS timing and 1s cadence (fluxgates). In
2007, a cooperative approach between NRCan, universities, and the POLARIS infrastructure for Earth Science
project brought about magnetometers on the east coast of Hudson Bay (EHB), with good spacing and
placement in the auroral and subauroral zones. We will describe how the above research magnetometers
complement the observatory instruments of the NRCan CANMOS array to facilitate space physics
investigations on a continental scale. We also describe the challenges facing a large magnetometer array
composed of diverse instruments, and run with little funding. AUTUMN's latest stratagem for wide
magnetometer deployment with minimal effort or cost has been the development of the $500 netPICOmag,
described elsewhere. Finally, we describe how to obtain data, and give examples of studies done using it.