Transcript Fig. 4 - cedar

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