MAGDAS Project for Space Weather during IHY/ISWI
The Space Environment Research Center (SERC), Kyushu University has deployed the MAGnetic Data
Acqusition System (MAGDAS) at 50 stations along the 210- and 96-degree magnetic meridians (MM) and the
magnetic Dip equator, and several FM-CW radars along the 210-degree MM during the International
Heliophysical Year (IHY) period of 2005-2009 (see http://magdas.serc.kyushu-u.ac.jp/ and
http://magdas2.serc.kyushu-u.ac.jp/). The goal of MAGDAS project is to become the most comprehensive
ground-based monitoring system of the earth's magnetic field. It does not compete with space-based
observation. Rather, this ground-based network complements observation from space. To properly study
solar-terrestrial events, data from both are required.
This project intends to get the MAGDAS network fully operational and provide data for studies on space
weather. By analyzing these new MAGDAS data, we can perform a real-time monitoring and modeling of the
global (e.g. Sq, EEJ) current system and the ambient plasma mass density for understanding the
electromagnetic and plasma environment changes in geospace during helio-magnetospheric storms. In order
to examine the propagation mechanisms of transient disturbances, i.e., sc/si, Pi 2, and DP2, relations of
ionospheric electric and magnetic fields are investigated by analyzing the MAGDAS magnetic data and the
Doppler data of our FM-CW ionospheric radar.
A new EE-index (EDst, EU, and EL) was also proposed by SERC for real-time and long-term geo-space
monitoring. The basic algorithm to obtain EE-index was constructed by Uozumi et al. (2008). EU and EL mainly
represent the range of the EEJ (equatorial electrojet) and CEJ (equatorial counter electrojet) components,
respectively. The baseline levels of EU and EL are obtained by averaging the H-component magnetic variations
observed at the nightside (LT = 18-06) MAGDAS/CPMN (Circum-pan Pacific Magnetometer Network) stations
along the magnetic equator. The baseline value is defined as EDst and its variations are found to be similar to
those of Dst. We examined relationships among the EEJ amplitude, the f10.7 solar radiation flux, the solar
wind parameter, Ap-index and the ionospheric conductivity. We found that the intensity of the EEJ depends on
the 11-years solar activity. The semi-annual EEJ oscillation is caused by changes in the ionosphere dynamo
and not by changes in the ionospheric conductivity. The 14.5-day EEJ oscillation may be caused by waves
inside the atmosphere. The EEJ amplitudes are also controlled by the interplanetary electric field (Ey = - Vsw x
In the present paper, we will present the several scientific results obtained by MAGDAS project, and introduce
a coordinated near-earth satellite and MAGDAS observations for space weather during the International Space
Weather Initiative (ISWI) period of 2010-2012.
SuperMAG: Enabling understanding and monitoring of the global electric current system
SuperMAG is a global collaboration that provides ground magnetic field perturbations from a long list of stations in the same coordinate system, identical time resolution and with a common baseline removal approach. For decades ground based magnetometers have proven to be the workhorse of magnetosphere- ionosphere physics and their importance is indisputable. This unique high quality dataset provides a continuous and nearly global monitoring of the ground magnetic field perturbation. This talk will focus on three topics associated with SuperMAG: 1) Motivation for SuperMAG. 2) Complications associated with global studies utilizing ground based magnetometer data. Focus will be on the automated procedure for determination of the undisturbed daily variations of the magnetic field observed by ground based magnetometers. The technique is validated by the use of data from published quiet days and our automated quiet day curve. The full-width-at-half-max (FWHM) of this difference varies from component to component and it depends on the magnetic latitude. We find that below 60 deg magnetic latitude the RMS error is <10nT. 3) The utilization of the unique near-global and continuous dataset. I illustrated this by showing results from two studies of the spatiotemporal behavior of the global auroral electrojet system. One of classical auroral substorms while the other investigates the response to an abrupt southward turning of the IMF.
Comparison of Ground Magnetometer Array Data with Spacecraft Observations
Few spacecraft are present in near-earth space at any one time. As a consequence it is usually impossible to be certain that the onset of a disturbance seen in space is the beginning of an event or just the time at which the disturbance arrives at the spacecraft. To compensate for this problem large arrays of ground magnetometers and all sky cameras have been deployed over large geographic areas. The assumption is that there are a sufficient number of instruments that the location and time the event begins can be accurately determined, and that this information can be mapped to the equatorial plane of the magnetosphere and associated with the spacecraft observations. Because the instruments are installed and maintained by different institutions numerous problems are encountered in the analysis of the data. These include different formats of the raw and calibrated data; different policies regarding the size of files (granules); the time resolution of data and how they are related to the UTC clock; how missing data are represented; whether missing granules are present in the directory. To deal with these issues we have adopted a policy of transforming all data to the same coordinate system, interpolating the data to a uniform time grid, introducing missing data flags where necessary, creating missing granules with all data except time flagged, and writing these data to a binary flat file. Event data is then read into analysis program for any specific interval by calculating the byte location of the data in the file. This process is much faster than sequential access to text files and greatly simplifies the problem of data buffering across granule boundaries. In this talk we illustrate our approach using data from a number of arrays operated by various institutions during the Themis mission. We will show how Pi 2 pulsations and substorm current wedge perturbations recorded at these different stations can be use to localize a substorm disturbance in time and space.
Travel-time magnetoseismic analysis by ground magnetometer arrays
Travel-time magnetoseismic analysis [Chi and Russell, Geophys. Res. Lett., 32, L18108, 2005] is one of the best examples of heliophysical studies that benefit from simultanenous observations by a network of ground magnetometer arrays. Focusing on the impulses starting from a localized region in the magnetosphere, the travel-time method times the first amplitude peak in magnetic field records, which is associated with the so-called Tamao travel time from the source. The source location, the impulse's start time, and the profile of MHD speeds in the modeled region are then estimated through a data-model fit in a way similar to the practice of terrestrial seismology. Using the observations by magnetometer arrays in North America, we demonstrate how the travel-time method uses sudden impulse signals to estimate the distribution of plasma mass density in the dayside magnetosphere, and we also show how it uses the Pi~2 pulsations to pinpoint the start time and location of substorm onsets in the magnetotail. The available spacecraft observations for the events examined are consistent with the magnetoseismic results, providing support to this new methodology. We conclude by presenting the ongoing investigation on substorm triggering that incorporates the substorm onset time in the magnetotail inferred by the travel-time method and the observations of auroral intensification by satellite or ground-based imagers.
The South American Meridional B-field Array (SAMBA) and opportunities for inter- hemispheric studies
The Antarctic continent, the only landmass in the southern polar region, offers the unique opportunity for observations that geomagnetically range from polar latitudes to well into the inner magnetosphere, thus enabling conjugate observations in a wide range of geomagnetic latitudes. The SAMBA (South American Meridional B-field Array) chain is a meridional chain of 12 magnetometers, 11 of them at L=1.1 to L=2.5 along the coast of Chile and in the Antarctica peninsula, and one auroral station along the same meridian. SAMBA is ideal for low and mid-latitude studies of geophysical events and ULF waves. It is conjugate to the northern hemisphere MEASURE and McMAC chains, offering unique opportunities for inter-hemispheric studies. We use 5 of the SAMBA stations and a number of conjugate stations from the Northern hemisphere to determine the field line resonance (FLR) frequency of closely spaced flux tubes in the inner magnetosphere. Standard inversion techniques are used to derive the equatorial mass density of these flux tubes from the FLRs. From our conjugate pairs we find, surprisingly, that the derived mass density of closely spaced flux tubes, from L=1.6 to L=2.5, drops at a rate that cannot be predicted by any of the existing models or agree with past observations. We also study asymmetries in the power of Pc3 waves. We find that during northern summer solstice the waves are significantly stronger at the northern conjugate point, while during northern winter solstice the wave power is comparable over both conjugate points. Finally, using the SAMBA auroral station, WSD, along with all available southern auroral stations we calculate a southern AE index and its direct conjugate northern AE index and compare both with the standard AE index. We explore under what conditions the north-south asymmetries in the AE calculation are due to the significant gap of auroral stations in the Southern hemisphere and under what conditions the asymmetries have a geophysical source.
A statistical study of the differences between Northern and Southern Hemisphere conjugate AE calculations
The auroral electrojet (AE) index is traditionally calculated from a set of about 10 to 13 ground magnetometer stations located around the typical northern auroral oval location. Similar coverage in the Southern Hemisphere does not exist, so the AE calculation has only been performed using Northern Hemisphere data. A recent study used seven southern auroral region ground magnetometers as well as their conjugate Northern Hemisphere data to calculate conjugate AE indices during the Northern Hemisphere winter (December 2005) using the standard method. The correlation coefficient between the northern and southern AE indices for many of the intervals was above 0.7, but in one interval, it was close to 0. The mean difference between the southern and northern AE indices is largest during southward IMF and for large values of IMF |By| (>5~nT). This is most likely due to the increased activity levels during southward IMF and the greater twisting of the magnetic field lines during strong IMF By. The mean differences between the southern and conjugate northern H component are of the order of ∼35~nT, with the largest differences occurring in the midnight magnetic local time (MLT) sector. Based on these initial results we now conduct a statistical study of nearly 200 intervals during 2006 and 2008 for which data exist for the calculation of both southern and conjugate northern AE indices. We explore the generality of our initial results, and determine whether the North-South asymmetries are the result of the large gap in auroral station coverage in the Southern Hemisphere or have a geophysical source, and in the latter case under what circumstances the asymmetries are most pronounced. We interpret the latter type of asymmetries in terms of seasonal effects, ionospheric effects, and/or MLT dependencies.