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Simultaneous detection of ionospheric perturbations using mid-latitude all-sky imagers and equatorial C/NOFS measurements C. Sullivan*1, C. Martinis1, R. Macinnis1, W. Burke2, R. Pfaff3, M.Hairston4 1Center for Space Physics, Boston University, 2Institute for Scientific Research, Boston College, 3NASA Goddard Institute for Space Studies, 4Center for Space Sciences, University of Texas- Dallas [email protected] ABSTRACT 2. OBSERVATIONS Data from the Coupled Ion-Neutral Dynamics Investigation (CINDI) and the Vector Electric Field Instrument (VEFI) onboard the Communication/Navigation Outage Forecasting System (C/NOFS) satellite are compared with 630.0 nm airglow data from all-sky imagers located outside the satellite’s orbital path. The comparison is done by mapping the trajectory coordinates along magnetic field lines to the peak emission height of the 630.0 nm airglow. We present a study of medium scale traveling ionospheric disturbances (MSTIDs) and equatorial spread-F (ESF) in the American sector. Coincident variations in in-situ electric field, ion density, and ground-based airglow measurements show similar behavior, an indication that perturbations are occurring along the entire field line and that this type of comparison can provide insight into mid-latitude locations along a field line where no measurements are available. A multi-night analysis of electric field perturbations shows a consistent picture for the presence of bright and dark bands associated with MSTIDs. The potential energy source region is investigated by computing Poynting fluxes. ESF structures observed by magnetically conjugate all-sky imagers can be affected by the South Atlantic Magnetic Anomaly. This study shows the importance of complementing remote sensing with in-situ observations of large scale structures at the equatorial ionosphere. The case study presented for electron density depletions associated with ESF occurred on 25 October 2011 at two magnetically conjugate sites: Arecibo, Puerto Rico, and Mercedes, Argentina. The depletions seen using the all-sky imager in 630.0 nm were then studied using several GPS receivers that measured TEC. After obtaining those data, the rate of change of TEC could be calculated to provide information into phase fluctuations associated with airglow depletions. Data from February 17, 2010 and 27 February 2011 at El Leoncito, Argentina, were good examples of MSTIDs; nights were clear, and the satellite trajectories mapped into the field of view for three consecutive passes on each night. The ground-based images in 630.0 nm at El Leoncito were compared to measured data obtained by the satellite while flying over the American sector. C/NOFS orbits at 400 – 850 km over the equator with an inclination of ± 13 degrees. The VEFI instrument recorded electric and magnetic field intensities, while CINDI recorded densities of O+ and H+. The trajectory of the satellite was then mapped down to the peak emission height for 630.0 nm airglow, ~250 km, in the Northern and Southern hemispheres. Figure 3 is a map of the sites studied with corresponding all-sky imager fields of view. Within the fields of view at Arecibo and Mercedes lie the ± 27 degree geomagnetic latitude lines, indicating the points of magnetic conjugacy. The shaded region represents the C/NOFS trajectory range. Anything measured at 20° mag lat (~1000 km apex height), for example, can be mapped into the fields of view of the imagers. 1. INTRODUCTION The BU Imaging Group uses all-sky imagers to measure 630.0 nm airglow emissions to investigate large-scale ionospheric perturbations at various latitudes. These perturbations can also be studied with data obtained from the equatorial Communication/Navigation Outage Forecasting System (C/NOFS) satellite and GPS satellites. A comparison between the mid-latitude ground-based and satellite data indicates that these perturbations are present along the entire magnetic field line. The perturbations to be studied are equatorial spread-F (ESF) and medium-scale traveling ionospheric disturbances (MSTIDs). Fig. 3: Imagers at Arecibo, Mercedes, and El Leoncito are used for studying the American sector. The dotted lines represent various apex heights to which equatorial events are mapped. Phenomena occurring at ~ 1800 km at the equator can be seen at Arecibo, Mercedes, and El Leoncito because a common magnetic field line lies within their fields of view. Figure 1 is a schematic of the dipolar configuration along a meridian corresponding to the longitude of the imagers. The fields of view of two imagers are shown as well as the ~50 km thick 630.0 nm airglow layer. The region between -1° and 24° mag lat and 400 – 800 km represents the range of satellite trajectories. The orange flux tube connects information from the two imagers at the airglow layer with a particular satellite trajectory. The data are analyzed by mapping along the field line. 3. ANALYSIS Fig. 5: GPS trajectories are plotted over images at Mercedes and Arecibo. The location of the satellite at the time shown is marked with a square. In both instances, the square is on top of a depletion, and the resulting TEC and phase fluctuations measurements agree. One of the goals of comparing the imager data to data collected from GPS satellites was to explain why depletions associated with ESF do not always reach their conjugate point, even if they do in the other site’s field of view. A possible explanation is that even though the images do not show depletions, perhaps due to lack of contrast, the GPS receiver will still measure changes in TEC. One reason changes are not evident in this case is that since 25 October 2011 occurred during a geomagnetic storm, there may have been induced winds opposing the direction of ESF structure development, stopping the depletions from reaching the conjugate point. Figure 6 shows the TEC measurements over Mercedes during two GPS satellite passes. Fig. 8: (Left) Images at three different times with mapped satellite trajectories passing through multiple depletions. (Right) VEFI electric and magnetic field intensities correlating with the optical signatures. Fig. 6: TEC measurements show a clear depletion at 2:16 UT when one of the GPS satellites passes through the structure. Another GPS satellite, passing at the same time, has a trajectory through the Arecibo conjugate point, where depletions cannot be seen. TEC measurements show a continuous decrease, without evidence of depletions. The magnetic field perturbations mimic the changes in the electric field fluctuations. Both data sets were combined to obtain the Poynting flux, Sǁ, that can be used to investigate the direction of energy propagation. It is evident that during the first pass, there is significant energy coming from the Northern hemisphere, while during the third pass, there is no energy transfer. MEDIUM-SCALE TRAVELING IONOSPHERIC DISTURBANCES FEBRUARY 27 2011 This particular case demonstrates changes in electric field intensities as they are related to the presence of bright and dark MSTID bands. Figure 7 shows the concurrence of perturbations in electric field measurements with MSTID bands. This correlation suggests that these disturbances exist throughout the entire magnetic field line (Martinis et al., 2015). EQUATORIAL SPREAD-F Fig. 1: Diagram of the dipolar configuration of the Earth’s magnetic field. Fields of view of Arecibo and El Leoncito imagers are shown at mid-latitudes. Phenomena observed at the equator around 1200 km apex height can be seen at 250 km at mid-latitudes inside the fields of view of the imagers.. ESF structures were prominent at Arecibo and Mercedes on 25 October 2011. The structures extended past Mercedes’ zenith, but were unable to reach the its conjugate point at Arecibo. This night also had concurrent GPS satellite signals piercing through the depletions- an ideal condition for studying TEC changes during an ESF event. Data from magnetically conjugate all-sky imagers and GPS receivers were combined to study ESF. GPS receivers provide information on total electron content (TEC). ESF is characterized by strong decreases in TEC. Data from the receivers are also used to investigate magnetic conjugacy. All-sky imagers and data from C/NOFS are analyzed for MSTID studies. The satellite instruments used are CINDI (Coupled Ion-Neutral Dynamics Investigation) and VEFI (Vector Electric Field Instrument) (de La Beaujardiere et al., 2004). Dark and bright bands are the optical signatures of MSTIDs as measured by all-sky imagers (Martinis et al., 2010). They represent upward and downward motion of the ionosphere. This motion is governed by ambient electric fields; thus, the pattern of MSTIDs is characterized by the direction of the zonal electric field, as summarized in Figure 2, where North is to the top, and East is to the right in each panel. (A) Fig. 9: The Poynting flux for three different times indicating maximum perturbations earlier in the night. Figure 4 displays all-sky images from each site for three times during the night. The depletions at Arecibo clearly reach the conjugate point of Mercedes, but it is evident that the depletions at Mercedes never fully extend down to the Arecibo conjugate point. GPS receiver data were used to examine both the behavior of TEC inside of a depletion, presented in Figure 5, or when the depletion does not extend to the conjugate point, as in Figure 6. ARE (B) Fig. 2: Panel (A) shows the configuration for the generation of dark bands. In panel (B), the zonal electric field is westward, resulting in downward motion, creating bright bands. Magnetic field perturbations were also obtained from VEFI to investigate the energy source of MSTIDs. The rate of energy transfer per unit area of the electromagnetic field, or the Poynting flux, is E X B / μ0. An expression including zonal and meridional components of the fields is shown below (Burke et al., 2015). MER 4. SUMMARY Fig. 7: (Top) Dark and bright MSTID bands are shown in the images at three different times. (Right) Electric field intensities at the same times on 17 February 2010. Perturbations in the zonal electric field measured by VEFI in each of the three satellite passes on 27 February 2011 are shown in Figure 7 (right). Each curve represents the difference between raw values and averaged values. A statistical study covering solstice months at El Leoncito was done to verify the results from Figure 7. Table 1 presents a summary of electric field conditions associated with MSTID bands. In general, a positive (peak) electric field generates dark bands, and a negative (trough) field generates bright bands. FEBRUARY 17 2010 02 : 11 UT Fig. 4: Depletions at Arecibo and Mercedes on 25 October. The conjugate points are represented by black stars. At ~2:10 UT, Arecibo depletions extend past zenith while similar behavior at Mercedes is not observed. Figure 5 shows the all-sky images at Arecibo and Mercedes at ~3:50 UT, with the GPS trajectories superimposed, the TEC data measured by the receiver, and the calculated phase fluctuations. To extend the study beyond electric field patterns related to MSTIDs, the magnetic field intensities, also measured by VEFI, were investigated. Figure 8 reveals the background-subtracted electric field intensities, E - <E>, along with the background-subtracted magnetic field intensities, δB – <δB>, for 17 February 2010. Table 1: Zonal and meridional electric field signs and coincident dark or bright bands observed. Boston University All-Sky Imagers were used in conjunction with C/NOFS and GPS satellites to study ionospheric perturbations associated with ESF and MSTIDs. Comparing images of electron density depletions with GPS receiver data gives insight into magnetic conjugacy, and reasons for the lack thereof. Multiple MSTID bands were compared to the sign of electric field perturbations. Dark (bright) bands were associated with positive (negative) electric field perturbations. February 27, 2011 was a case study with 3 consecutive C/NOFS passes showing the evolution of the electric field perturbations. The magnetic field perturbations were also measured on 17 February 2010, and used to calculate the Poynting flux, or the energy flux density. The result indicates that the energy source of MSTIDs is in the Northern hemisphere. Acknowledgements: C.S. was supported by NSF Aeronomy grant # 1123222. TEC data was obtained from the GPS IGS/SOPAC website. Quick look all-sky images and movies can be accessed from www.buimaging.com. References: Electric Field Ez peak (+) Ez flat Ez trough (-) Em peak (+) Em flat Em trough (-) Bright Bands Dark Bands 0 146 4 4 137 0 3 132 9 7 129 9 Burke, W., W. Burke, C. Martinis, C. Sullivan, L.Gentile, R. Pfaff, C/NOFS observations of electromagnetic coupling between magnetically conjugate MSTID structures, to be submitted , JGR, 2015 de La Beaujardiere, O., and CNOFS Science Definition Team, A mission to forecast scintillations. JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Volume: 66 Issue: 17 Pages: 1573-1591 DOI: 10.1016/j.jastp.2004.07.030 Published: NOV 2004 Martinis, C., J. Baumgardner, J. Wroten, and M. Mendillo (2010), Seasonal dependence of MSTIDs obtained from 630.0 nm airglow imaging at Arecibo, Geophys. Res. Lett., 37, L11103, doi:10.1029/2010GL043569. Martinis, C., R. Macinnis, C. Sullivan, J. Baumgardner, M. Mendillo, R. Pfaff , M. Hairston, Simultaneous detection of ionospheric perturbations using mid-latitude all-sky imagers and equatorial C/NOFS measurements, submitted, JGR, 2015