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AFRL-AFOSR-VA-TR-2016-0262 


Irregularties and Forecast Studies of Equatorial 
Spread 


David Hysell 
CORNELL UNIVERSITY 
373 PINE TREE RD 
ITHACA, NY 14850-2820 


07/25/2016 
Final Report 


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Irregularties and Forecast Studies of Equatorial Spread 

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David Hysell 

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14. ABSTRACT 

Progress Simula ting equatorial spread F (ESF) in pursuit of a space-weatherfo recast capability is 
summarized. ESF is the main manifestation ofspace weatheratlow magnetic latitudes in the ionosphere 
and is responsible for disrupting communication, navigation, imaging, and surveillance systems important 
to the AirForce and otherfederal agencies. 

A 3D numerical simulation ofthe plasma instabilities responsible forESF written atComell hasbeen 
developed and upgraded underthisaward. Plasma numberdensity, electric field, and neutral wind data 
necessary fordriving the simulation have been collected in campaignsatthe J icamarca Radio Observatory 
conducted approximately semi-annually. The simulation code is initialized and forced using campaign 
data. Simulation results, specific ally the plasma depletions and plumes characteristic of ESF, are compared 
with coherent scatter radar imagery of ESF irregula ritiesmade a tj icamarca. Such imagery is directly 
comparable to the 3D simulation products, offering a prediction-assessment strategy that is uniquely 
conducive to closure. In multiple campaign studies, the simulation wasable to recoverthe ionospheric 
dynamicsthatunfolded in nature including the occurrence ornon-occurrence of ESF 

15. SUB| ECTTERMS 

ionosphere irregularity, ionosphere modeling, equatorial spread F,forecasting,C/NOFS 


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Final Report: Irregularties and Forecast Studies of 
Equatorial Spread F Grant/Contract Number: 

FA9550-12-1-0462 


D. L. Hysell 

Earth and Atmospheric Sciences 
Cornell University 

July 13, 2016 


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Abstract 


Progress simulating equatorial spread F (ESF) in pursuit of a space-weather forecast capability 
is summarized. ESF is the main manifestation of space weather at low magnetic latitudes in the 
ionosphere and is responsible for disrupting communication, navigation, imaging, and surveillance 
systems important to the Air Force and other federal agencies. 

A 3D numerical simulation of the plasma instabilities responsible for ESF written at Cornell 
has been developed and upgraded under this award. Plasma number density, electric field, and 
neutral wind data necessary for driving the simulation have been collected in campaigns at the 
Jicamarca Radio Observatory conducted approximately semi-annually. The simulation code is ini¬ 
tialized and forced using campaign data. Simulation results, specifically the plasma depletions and 
plumes characteristic of ESF, are compared with coherent scatter radar imagery of ESF irregu¬ 
larities made at Jicamarca. Such imagery is directly comparable to the 3D simulation products, 
offering a prediction-assessment strategy that is uniquely conducive to closure. In multiple cam¬ 
paign studies, the simulation was able to recover the ionospheric dynamics that unfolded in nature 
including the occurrence or non-occurrence of ESF. The positive results indicate that the important 
processes underlying ESF have been taken into consideration in the modeling. Most importantly, 
the simulation has produced no “false alarms,” meaning that no necessary conditions for ESF are 
being overlooked. 

Sometimes, the numerical simulations fail to predict ESF depletions. We suspect that the cause 
of the depletions lies outside the immediate field of view of Jicamarca and outside the scope of our 
simulations. We have therefore built, programmed, and fielded a new kind of multistatic, software- 
defined HF radar/sounder/beacon system for observing the ionosphere regionally. The system uses 
HF signals to probe the ionosphere along multiple ground-to-ground ray paths. Complete knowledge 
of the state of the F region ionosphere would permit us to predict the main characteristics of the 
received HF signals (range and group delay, arrival bearing, amplitude, and polarization). Our 
objective has been to go the other way and to infer the regional ionospheric state from the totality 
of the beacon data. The ionospheric specification thus rendered should reveal the presence of 
nascent irregularities in the ionosphere that could precondition or “seed” it for ESF events. Such 
irregularities would constitute “sufficient conditions” for ESF not accounted for in our simulation 
studies. 

Our beacon network now includes four stations - one transmitting station at Ancon, two re¬ 
ceiving stations at Jicamarca, and one receiving station at Huancayo, Peru. The stations utilize 
two frequencies, doubling the number of ray paths otherwise available and increasing the span of 
altitudes being probed. Data from a campaign conducted in August of 2015 have been processed 
using a new, end-to-end inversion method. The method is able to reproduce the ionosphere which 
would give rise to the HF propagation paths observed while being minimally structured. While the 
method is computationally expensive, it is scalable and stable. The first results from the beacon 
network and the data inversion are presented. 


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Introduction 


Under this award, we studied the aeronomy of the equatorial ionosphere under conditions known 
historically as “equatorial spread F” (ESF). ESF is space-weather phenomenon occurring mainly 
after sunset and characterized by towering plumes of depleted plasma that are striking to observe. 
ESF generates plasma density irregularities with relative amplitudes approaching 100% of back¬ 
ground with scale sizes ranging from centimeters to hundreds of kilometers. ESF disrupts radio 
communication, navigation, and imaging systems including space-based synthetic aperture radars 
and over-the-horizon radars and therefore poses a hazard (see reviews by Woodman [2009] and 
Kelley et al. [2011]). We study ionospheric instability to mitigate the hazard. 

Unlike ionospheric substorms in the auroral zone, ESF does not require solar storms and is 
not limited to periods of high geomagnetic activity. Spread F occurs frequently in the equatorial 
zone, more often than not in some seasons, and its impact varies with the season and solar cycle 
along with the level of geomagnetic activity. The instabilities responsible for ESF are variants 
of simple E x B instability and derive their free energy from the unstable stratification of the 
ionosphere after sunset. Despite this, ESF has proven to be difficult to predict. This is because its 
fundamental drivers, the background zonal ionospheric electric field and the thermospheric winds, 
are themselves highly variable. Paradoxically, the only time when ESF can be predicted reliably is 
during geomagnetically active periods when the background electric fields and winds have somewhat 
predictable storm-time responses. 

The predominant circulation pattern in the postsunset equatorial ionosphere is vortex flow in 
the region where the zonal conductivity gradient from the evening terminator meets the vertical 
conductivity gradient in the steep postsunset bottomside density profile (e.g. Haerendel et al. [1992]; 
Kudeki and Bhattacharyya [1999]; Eccles et al. [1999]). Attendant with the vortex is vertical shear 
in the horizontal plasma flow [Kudeki et al, 1981; Tsunoda et al., 1981], and attendant with the 
shear is vertical current. While vertical current had not previously been considered in ESF studies, 
Hysell and Kudeki [2004] showed that it actually contributes substantially to ionospheric instability, 
reducing the e-folding time of growing irregularities and accounting for the preferred horizontal scale 
sizes seen on ESF morphology. In addition, instabilities driven by vertical currents can account for 
precursor “bottom-type” layers which are nearly ubiquitous in the postsunset equatorial ionosphere 
and inhabit the valley region where instabilities driven by zonal currents should not function. 

Under our award from AFOSR, we have been testing whether the balance of the physics control¬ 
ling the stability of the postsunset equatorial ionosphere and the onset of ESF was well understood 
in view of the new ideas about shear flow and vertical currents. Our research has had four phases. 
In the first, we developed a three-dimensional numerical simulation of the equatorial ionosphere 
capable of reproducing both realistic background ionospheric flows and fast-growing irregularities. 
The emphasis was on reproducing vertical currents and their effects. In the second, we developed 
an experimental mode at the Jicamarca Radio Observatory capable of observing the most impor¬ 
tant drivers of ESF at once while also being able to observe its effects. Jicamarca makes direct 
observations of vector plasma drifts, and three Fabry-Perot interferometers have recently become 
available for measuring horizontal thermospheric winds which help drive the evening vortex. Third, 
we conducted a number of campaigns at Jicamarca. We used the resulting data to both initialize 
and force the numerical simulation and then investigated whether the predictions it makes on given 
nights are accurate. 


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In the final phase of the project, we added a new experimental capability. We designed, 
programmed, and deployed a network of HF beacons. The beacons employ software-defined 
transceivers and function as next-generation multistatic HF sounders. By employing PRN coding 
and other innovations, the sounders can measure phase and group delay, amplitude, polarization, 
and arrival angles of the signals reflected from the ionosphere. The sounders operate at very low 
power levels and are inexpensive to purchase, deploy, and operate. The network now includes a 
transmitting station in Ancon, Peru, and receiving stations at Jicamarca (2) and Huancayo (1). 

The HF beacon network probes the bottomside F region ionosphere in the region around Jica¬ 
marca, providing information about plasma density irregularities well outside the radar’s field of 
view (that might eventually drift into the field of view). The advantage of the beacon network is 
that it can monitor a large volume of space for extended periods of time at low cost and with only 
minimal human intervention, infrastructure, and impact. The disadvantage is that the observables 
are related to the ionospheric state in a complicated way. Like GPS signals, the beacon signals 
represent path-integrated quantities. Unlike GPS, the paths in this case are not straight lines 
and are unknown a priori. Furthermore, the HF beacon observables depend on parameters other 
than the plasma number density (the magnetic field and the electron-neutral collision frequency 
notably) and in a complicated way. Inverting the beacon data is challenging, but the computational 
resources required are now in place. 

The software required to invert the beacon data and reconstitute a model ionosphere on their 
basis is nontrivial, to say the least, The problem is underdetermined and poorly conditioned (po¬ 
tentially unstable). We developed an algorithm for this purpose that is practical if computationally 
expensive. The algorithm employs raytracing to solve for rays emanating from a beacon transmitter 
as an initial value problem. The raytracing code is the inner iterative loop of the algorithm. The 
middle iterative loop is a shooting algorithm that assures that the rays launched from transmitting 
stations are received at receiving stations, thus turning the problem into a boundary value problem. 
The observables (group delay, phase delay, amplitude, bearing on reception) for every ray between 
every station pair at every HF frequency is thus predicted for a candidate model ionosphere. 

In the outer loop of the algorithm, the parameters that describe the model ionosphere are 
updated so as to make the predicted and observed observable match. This is an optimization 
problem which we solve using a damped Levenberg Marquardt method. Damping is required to 
stabilize the results. Other data sources including electron density profiles from Jicamarca and 
elsewhere can easily be incorporated in the inversion. The model itself is parametrized using a 3- 
parameter Chapman function to describe vertical variations in electron number density and bicubic 
B-splines to describe horizontal variations. In all, our model ionosphere is parametrized in terms 
of 675 coefficients (an adjustable number). Empirical models are used to describe the background 
neutral atmosphere, ionospheric composition, and geomagnetic field. These quantities are necessary 
for calculating the complex wave index of refraction along the ray paths. 

The algorithm was demonstrated using campaign data from August, 2015. 


Accomplishments 

The main accomplishments of our project during its first year are itemized below: 
i> Multiple ESF campaigns have been conducted at Jicamarca. The list of campaigns now reads 


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as: 


Dec. 17-21, 2012 (JV e , T e , Ti, vj_ profiles + radar RTI) 

Apr. 11-16, 2013 (added FPI winds) 

Sep. 16 - Oct. 3, 2013 (added wide-field imaging) 

May 5-9, 2014 (added 2 HF stations) 

Nov. 24 - 28, 2014 
Dec. 15 - 22, 2014 
Feb. 9 - 15, 2015 
Mar. 23 - 27, 2015 

Aug. 25 - 28, 2015 (added 3rd HF station) 

Dec. 9 -13, 2015 

Data from all of the campaigns prior to Dec. 2015 have been reduced and analyzed. The most 
recent campaign data are undergoing analysis. 

t> The Cornell ionospheric simulation code was upgraded in a number of respects, including the 
addition of hydrogen ions and allowances for the effects of ion inertia. The code was modified 
so as to be able to ingest data (in the form of initial conditions and drivers) from the Jicamarca 
ISR along with regional Fabry-Perot interferometers in Peru, 
o A new observing mode was developed at Jicamarca for this project. Throughout its history, 
Jicamarca was used to observe ionospheric plasma density, temperature and composition or 
vertical and east-west drift profiles, but not both. The new mode subdivides the antenna 
array and incorporates time-division multiplexing to allow multiple observing modes to be run 
concurrently. Additionally, radar imaging of coherent scatter from ESF irregularities can be 
measured simultaneously. The new mode was employed in the AFOSR observing campaigns, 
o The code was initialized and driven using data from the aforementioned campaigns. Our goal 
was to determine whether or not the simulation code produced the same results as nature given 
the same initial conditions and forcing. To a considerable degree, they did. We regard this as a 
significant achievement which we endeavored to document in the published literature. The result 
implies that the aeronomy of the postsunset equatorial ionosphere is sufficiently well understood 
for forecasting (to the extent the drivers, the electric fields and winds, can be forecast). That 
the simulation code produced no false alarms (predictions of topside irregularities where none 
were observed) implies that there is no hidden necessary conditions for ESF being overlooked. 
i> That the simulation results included some missed detections (observations of topside ESF plumes 
where none were predicted) suggests that there could be hidden sufficient conditions for ESF 
to occur. To test whether disturbances propagating into the region from outside are causing 
irregularities where none are expected, an HF beacon network for regional monitoring was 
developed. 

o The HF beacon network was deployed and is now functioning. A signal chain for acquiring data, 
processing, and ingesting them into a regional ionospheric model based in statistical inverse 
theory has also been completed. 

i> The aforementioned work has been performed by the PI, Hysell, graduate students at Cornell, 
colleagues at Jicamarca, and with the help of Juha Vierinen, a former Jicamarca summer scholar 


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now employed at MIT Haystack Observatory. Results from our work has been presented at 
CEDAR workshops, at the ISEA meeting in Ethiopia, and at the recent Multistatic Meteor 
Radar workshop at IAP in Germany. 

> Four papers describing our work have been published: 

o Hysell, D. L., R. Jafari, M. A. Milla, and J. W. Meriwether (2014), Data-driven numerical 
simulations of equatorial spread F in the Peruvian sector, J. Geophys. Res. Space Physics, 
119, 38153827, doi:10.1002/2014JA019889. 

o Hysell, D. L., M. A. Milla, L. Condori, and J. W. Meriwether (2014), Data-driven numer¬ 
ical simulations of equatorial spread F in the Peruvian sector: 2. Autumnal equinox, J. 
Geophys. Res. Space Physics, 119, 69816993, doi:10.1002/2014JA020345. 
o Hysell, D. L., M. A. Milla, L. Condori, and J. Vierinen (2015), Data-driven numerical 
simulations of equatorial spread F in the Peruvian sector 3: Solstice, J. Geophys. Res. 
Space Physics, 120, 10,809201310,822, doi:10.1002/2015JA021877. 
o Hysell, D. L., M. A. Milla, and J. Vierinen (2016), A multistatic HF beacon net¬ 
work for ionospheric specification in the Peruvian sector, Radio Sci., 51, 3922013401, 
doi: 10.1002/2016RS005951. 

Narrative 

Here, we show one of the many examples of model/data congruity arising from this study. The 
publication record gives a more complete accounting of model/data comparisons and their impli¬ 
cations. 

Fig. 1 shows observations made at Jicamarca during June-solstice conditions which are generally 
unfavorable for ESF. We were fortunate to have captured even one active ESF event in late April. 
This time, a bottom-type scattering layer appeared at 0010 UT (1910 LT) followed by the passages 
of a high-altitude radar plume beginning at about 0045 UT (1945 LT). In nature and in simulation, 
such layers are telltale of vertical currents which drive fast-growing irregularities in the bottomside 
and are prone to initiate topside ESF. 

The plasma irregularities produced radar clutter and contaminated the incoherent scatter data, 
causing gaps in the record at certain altitudes and times. It was nonetheless possible to measure 
an uncontaminated electron density profile at 2330 UT (1830 LT) as well as the time history of the 
average vertical plasma drifts. The vertical drifts were very large on this night, reaching almost 50 
m/s at 2330 UT, and remained upward through about 0100 UT (2000 LT) or about an hour longer 
than on the following evening when no ESF occurred. The unseasonably strong and sustained 
upward drifts were undoubtedly responsible for the high level of ESF activity. 

Our numerical simulation draws initial and background parameters from a combination of em¬ 
pirical models tuned to reflect day-to-day variability in the campaign data. We use the PIM model 
to initialize the electron number density throughout the simulation space. A model is necessary 
here because our simulation requires initialization over a broad span of locations and local times 
and not just the places and local times when measurements are available. We feed PIM a proxy 
value of the FI0.7 solar flux index so that it predicts a number density profile which is congruent 
with the radar data at the start of the simulation. The initial ion composition is taken from the 
IRI-2007 model [Bilitza and Reinisch , 2008]. Neutral parameters necessary for calculating ion- and 


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Wed Apr 23 18:42:52 2014 



19:00 19:30 20:00 20:30 2l!oO 21:3 

Local time (hr) 


Figure 1: Jicamarca observations of ESF April 23/24, 2014. Top row, from left to right: electron 
density, electron density profiles at 2330 UT, zonal plasma drifts, and vertical plasma drifts. Bottom 
row left: Measured zonal plasma drift profiles at 2330 UT (solid line with error bars) together with 
the computed drift profile (plotted points) at the start of the numerical simulation. Bottom row 
right: coherent backscatter. Note that UT = LT + 5 hr. 


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after 25 min. 


after 75 min. 


500 



-400 -200 0 200 400 



-400 -200 0 200 400 -10 0 10 

Ground dx (km) E z (mV/m) 



-400 -200 0 200 400 



-400 -200 0 200 400 -10 0 10 

Ground dx (km) E z (mV/m) 


Figure 2: Numerical simulation of events on Apr. 23/24, 2014 initialized at 2330 UT. The panels 
on the left and right show simulated results after 25 and 75 min., respectively. The top panels 
show plasma number density, with red, green, and blue tones representing molecular, atomic, and 
protonic ion abundances, respectively. The Bottom panels indicate vector current density in the 
equatorial plane in nA/m 2 according to the circular legend shown. White lines are equipotentials, 
approximate streamlines of the flow. The vertical electric field through the midpoint of the simula¬ 
tion is plotted in profiles to the right of the current density plots. Note that diamagnetic currents 
have no effect on dynamics and are not included in the current densities shown. 

electron-neutral collision frequencies are taken from the NRLMSISE-00 model [Picone et al ., 2002]. 
The neutral parameters from NRLMSISE-00 are updated dynamically throughout the simulation. 

The background zonal electric field used in the simulation is specified according to the ISR 
vertical drifts measurements. Finally, the neutral winds in the simulation are provided by the new 
Horizontal Wind Model ’14 (HWM14) model [Drob et al., 2015]. The latest version of the HWM 
model was found to reproduce ground-based Fabry Perot interferometer data from the American 
sector much more accurately than older versions of the model. The model winds are rescaled in our 
simulations in order to account for day-to-day variability. Specifically, the zonal neutral winds are 
scaled by a single, constant factor meant to optimize congmity between the predicted and measured 
zonal plasma drift profiles at the initial time of simulations. (The meridional winds are imported 
but not scaled.) We refer to the multiplicative scaling constant below as s. 

Fig. 2 shows simulation results for the high-activity event of the April, 2014, campaign. After 25 
min., the F layer in the Apr. 23/24 simulation ascended noticeably farther than in the simulation 
for the following day, when no ESF plumes were predicted. The upward tilt in the layer from west 


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2014/94/23 20 03 » 



2014*4/23 Mil 10 



Figure 3: Aperture synthesis radar imagery for Apr. 23, 2014. 

to east, from earlier to later local times, is an indicator of continuing, rapid ascent. After just 25 
min., distinct plasma density irregularities formed in the strata between about 350-400 km altitude. 
This matches the height range where bottom-type layers emerged initially in the campaign data. 
This altitude range is also coincident with the region of vertical current which is signified by violet 
hues in the transverse current density panel. 

By the 75-min. time step (0045 UT, 1945 LT), the F layer ascended further, and irregularities 
grew, developed, and ascended to altitude strata where the current was mainly eastward and strong. 
The irregularities penetrated into the topside and through the upper boundary of the simulation 
space in some cases. The simulation reproduced the topside plumes clearly evident in the campaign 
data which ascended to 700 km by 0045 UT (1945 LT) when they first drifted over the radar. 

Radar images for two distinct radar plumes observed on April 23, 2014, are shown in Fig. 3. 
The images depict signal-to-noise ratio versus range and azimuth in the equatorial plane given 
an incoherent integration period of about 10 s. The signal-to-noise ratio is represented by the 
brightness of the pixels in the image in dB in the range indicated. The hue and saturation of the 
pixels reflect Doppler spectral information, but we make no attempt to interpret that information 
in this instance since most of the echoes are strongly frequency aliased. The resolution of the pixels 
is finer than 1 km x 1 km. Animated sequences of images (not shown) reveal that the irregularities 
in question are undergoing creation and destruction while moving in an inhomogeneous flow field, 
i.e., not simply frozen into a uniform background flow. 

In previous experiments, we have found that backscatter at this spatial scale arrives from the 
most deeply depleted regions and channels within the irregularities and so delineate the gross 
irregularity structure [Hysell et al., 2009]. There is therefore some basis for comparison between 
these images and the numerical simulations. However, coherent scatter signifies the presence of 
plasma density irregularities at the Bragg scale only and so the correspondence is imperfect at 
best. 

The radar plumes in Fig. 3 are typical of ESF, manifesting backward “C” shapes, narrow 


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Fri Dec 19 23:59:30 20140, 



Figure 4: Data from a single HF beacon link (Ancon-Jicamarca) at a single frequency. The figure 
shows received power versus time and group range. The brightness of each pixel indicates SNR, and 
the hue indicates Doppler shift. White plotter symbols indicate the group range of the first-hop 
echo. These are the primary data used by our ionospheric recovery method at present. Ampli¬ 
tude, Doppler shift, and arrival bearing are other observables that can eventually be utilized for 
ionospheric recovery. 

vertical channels, and a high degree of structuring indicating secondary interchange instability 
driven mainly by zonal winds. The plumes exhibit modest tilts from the vertical and occasionally 
bifurcate. The width of the imaged region is approximately 100 km at 600-krn altitude which is 
sufficient to contain one or sometimes two different plumes. Comparison with Fig. 2 reveals these 
characteristics to be shared by the radar plumes that develop in simulation. 

We turn now to our HF-beacon work which is necessary to expand the regional coverage around 
the Jicamarca radar and to help account for the events we sometimes observe which defy simulation 
predictions in being overly active. Figure 4 shows representative data for the Ancon-Jicamarca HF 
link for an evening during one of our campaigns when ESF occurred. The figure shows echo power 
versus group range and local time. The brightness of each pixel denotes the signal-to-noise ratio, 
and the hue denotes the Doppler shift, with red (blue) tones indicating red (blue) shifts. White 
plotter symbols are the result of an algorithm which attempts to find the virtual height of the first 
hop. These are presently the primary data used for ionospheric reconstruction. 

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The figure shows that the bottomside of the ionosphere rose quickly between 1800-2000 LT. 
Some small but distinct wavelike perturbations were present prior to about 1845 LT, but the trace 
was fairly smooth thereafter. This particular dataset does not indicate obvious ESF precursors or 
“sufficient conditions.” 

Group-delay estimates for all four links have been combined with ISR-derived density profiles 
from Jicamarca and modeled according to the methodology described briefly above. The results 
for observations of Aug. 25, 2015, are shown in Figure 5. Six panels depict results for four local 
times prior to the passage of the radar plume. Quasi-isodensity contours for n e = 5 x 10 4 cm 3 
and n e = 5 x 10 5 cm 3 are indicated in each panel by the green and cyan surfaces, respectively. 
The isodensity surfaces are found to be nearly horizontal planes in the interval shown. In order 
to emphasize differences from pure horizontal stratification, the surfaces actually show the average 
height plus the deviation from the average multiplied by a factor of five. 

The ionospheric reconstruction captures the gradual postsunset ascent of the F layer over time 
as well as the east-west ionospheric tilt that follows the passage of the solar terminator. Animated 
sequences of figures like those in Figure 5 also suggest subtle ionospheric structuring at the spatial 
and temporal scales being analyzed. The number of links is too few to specify whether features are 
propagating or advecting through the region, however. 

Significantly, perturbations in the group delays of the four links are accounted for by the model 
not through wholesale layer ascent and descent but instead mainly through layer tilts. A tilted 
ionosphere forces the rays to propagate away from great-circle paths. Very subtle tilts can induce 
significant changes in group delay this way. It is therefore incorrect to interpret group delay as 
a proxy measurement for layer height at the reflection point. The modeled layer height barely 
changes on time scales during which the measured group delays vary significantly. 


Future challenges 

One of the main challenges at this point is finding a way to render the ionospheric specification 
in such a way that details are more apparent. Volumetric rendering of scientific data is still an 
unsolved problem. Another problem involves data fusion and the combination of the beacon project 
with the aforementioned ISR campaigns and numerical simulations. 

Quite a few improvements to the data inversion method can be made. One is the generalization 
of the altitude model to include both an F-region and and F-region Chapman layer. Such a model 
would be better at representing the plasma density in the valley region where the density can be 
uniform over broad altitude spans. Another is parallelization, which will be necessary as the number 
of links is increased. As each link can be traced individually, parallelization should be efficient. 

In the future, it should also be possible to utilize more of the observables in the data inversion. 
The ray tracing code predicts the phase delay, power, and bearing of the received O- and X-mode 
signals already. Measured Doppler shifts prescribe the time rate of change of the phase delay from 
one timestep to the next. Discrepancies between the observables and the model prescriptions can 
readily be added to the objective function used in the outer loop if the inverse method. 

Still other observables are available from the HF signals, although their utility to the project 
is less certain and requires investigation. It should be possible to observe the Faraday rotation of 
the signals received at Jicamarca. This is another indication of the line-integrated electron number 


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density. Like the phase delay, the Faraday angle is a modulo-two-pi quantity that is best used to 
constrain the time evolution of the ionosphere. Both the Faraday angle and the phase delay are 
continuous quantities, unlike the group delay which is quantized at the level of the range resolution 
of the beacon system. The precision is therefore potentially greater. 


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0:10 


12:00 



Figure 5: Ionospheric reconstructions based on beacon and ISR data. The six panels correspond 
to six different local times, as indicated. The ragged line in each panel is the Pacific coastline. 
The plotted surfaces are two isodensity contours. The black profile is the model density profile 
evaluated over Jicamarca. The four rays represent the four HF beacon links. The underlying 
ionospheric model is consistent with all available data at the given time. 


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Bibliography 


Bilitza, D., and B. W. Reinisch, International Reference Ionosphere 2007: Improvements and new 
parameters, Adv. Space Res., 4%, 599-609, 2008. 

Drob, D. P., et al., An update to the Horizontal Wind Model (HWM): The quiet time thermosphere, 
Earth and Space Science, 2, doi:10.1002/2014EA000,089, 2015. 

Eccles, J. V., N. Maynard, and G. Wilson, Study of the evening drift vortex in the low-latitude 
ionosphere using San Marco electric field measurements, J. Geophys. Res., 104 , 28,133, 1999. 

Haerendel, G., J. V. Eccles, and S. Cakir, Theory for modeling the equatorial evening ionosphere 
and the origin of the shear in the horizontal plasma flow, J. Geophys. Res., 97, 1209, 1992. 

Hysell, D. L., and E. Kudeki, Collisional shear instability in the eqautorial F region ionosphere, J. 
Geophys. Res., 109, (All,301), 2004. 

Hysell, D. L., R. B. Hedden, J. L. Chau, F. R. Galindo, P. A. Roddy, and R. F. Pfaff, Comparing F 
region ionospheric irregularity observations from C/NOFS and Jicamarca, Geophys. Res. Lett., 
36, L00C01, doi:10.1029/2009GL038,983, 2009. 

Kelley, M. C., J. J. Makela, O. de la Beaujardiere, and J. Retterer, Convective ionospheric storms: 
A review, Rev. Geophys., 49, doi:10.1029/2010RG000,340, 2011. 

Kudeki, E., and S. Bhattacharyya, Post-sunset vortex in equatorial F-region plasma drifts and 
implications for bottomside spread- F, J. Geophys. Res., 104, 28,163, 1999. 

Kudeki, E., B. G. Fejer, D. T. Farley, and H. M. Ierkic, Interferometer studies of equatorial F 
region irregularities and drifts, Geophys. Res. Lett., 8, 377, 1981. 

Picone, J. M., A. E. Hedin, D. P. Drob, and A. C. Aikin, NRLMSISE-00 empirical model of 
the atmosphere: Statistical comparisons and scientific issues, J. Geophys. Res., 107, A12, doi: 
10.1029/2002JA009,430, 2002. 

Tsunoda, R. T., R. C. Livingston, and C. L. Rino, Evidence of a velocity shear in bulk plasma 
motion associated with the post-sunset rise of the equatorial Flayer, Geophys. Res. Lett., 8, 807, 
1981. 

Woodman, R. F., Spread F- An old equatorial aeronomy problem finally resolved?, Ann. Geophys., 
27, 1915-1934, 2009. 


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Response ID:6516 Data 


1 . 

1. Report Type 
Final Report 
Primary Contact E-mail 

Contact email if there is a problem with the report. 

dlh37@cornell.edu 

Primary Contact Phone Number 

Contact phone number if there is a problem with the report 

607-255-0630 

Organization / Institution name 

Cornell University 

Grant/Contract Title 

The full title of the funded effort. 

Three-Dimensional Simulations of Ionospheric Plasma Irregularities and Forecast Studies of Equatorial 
Spread F 

Grant/Contract Number 

AFOSR assigned control number. It must begin with "FA9550" or "F49620" or "FA2386". 

FA9550-12-1-0462 

Principal Investigator Name 

The full name of the principal investigator on the grant or contract. 

David Hysell 

Program Manager 

The AFOSR Program Manager currently assigned to the award 

Julie Moses 

Reporting Period Start Date 

09/15/2015 

Reporting Period End Date 

09/14/2016 

Abstract 

Progress simulating equatorial spread F (ESF) in pursuit of a space-weather forecast capability is 
summarized. ESF is the main manifestation of space weather at low magnetic latitudes in the ionosphere 
and is responsible for disrupting communication, navigation, imaging, and surveillance systems important 
to the Air Force and other federal agencies. 

A 3D numerical simulation of the plasma instabilities responsible for ESF written at Cornell has been 

developed and upgraded under this award. Plasma number density, electric field, and neutral wind data 

necessary for driving the simulation have been collected in campaigns at the Jicamarca Radio Observatory 

conducted approximately semi-annually. The simulation code is initialized and forced using campaign 

data. Simulation results, specifically the plasma depletions and plumes characteristic of ESF, are compared 

with coherent scatter radar imagery of ESF irregularities made at Jicamarca. Such imagery is directly 

comparable to the 3D simulation products, offering a prediction-assessment strategy that is uniquely 

conducive to closure. In multiple campaign studies, the simulation was able to recover the ionospheric 

dynamics that unfolded in nature including the occurrence or non-occurrence of ESF. The positive results 

indicate that the important processes underlying ESF have been taken into consideration in the modelling. 
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Most importantly, the simulation has produced no "false alarms," meaning that no necessary conditions for 
ESF are being overlooked. 

Sometimes, the numerical simulations fail to predict ESF depletions. We suspect that the cause of the 
depletions lies outside the immediate field of view of Jicamarca and outside the scope of our simulations 
We have therefore built, programmed, and fielded a new kind of multistatic, software-defined HF 
radar/sounder/beacon system for observing the ionosphere regionally. The system uses HF signals to 
probe the ionosphere along multiple ground-to-ground ray paths. Complete knowledge of the state of the F 
region ionosphere would permit us to predict the main characteristics of the received HF signals (range 
and group delay, arrival bearing, amplitude, and polarization). Our objective has been to go the other way 
and to infer the regional ionospheric state from the totality of the beacon data. The ionospheric specification 
thus rendered should reveal the presence of nascent irregularities in the ionosphere that could 
precondition or "seed" it for ESF events. Such irregularities would constitute "sufficient conditions" for ESF 
not accounted for in our simulation studies. 

Our beacon network now includes four stations -- one transmitting station at Ancon, two receiving stations 
at Jicamarca, and one receiving station at Huancayo, Peru. The stations utilize two frequencies, doubling 
the number of ray paths otherwise available and increasing the span of altitudes being probed. Data from a 
campaign conducted in August of 2015 have been processed using a new, end-to-end inversion method. 

The method is able to reproduce the ionosphere which would give rise to the HF propagation paths 
observed while being minimally structured. While the method is computationally expensive, it is scalable 
and stable. The first results from the beacon network and the data inversion are presented. 

Distribution Statement 

This is block 12 on the SF298 form. 

Distribution A - Approved for Public Release 

Explanation for Distribution Statement 

If this is not approved for public release, please provide a short explanation. E.g., contains proprietary information. 
SF298 Form 

Please attach your SF298 form. A blank SF298 can be found here. Please do not password protect or secure the PDF 
The maximum file size for an SF298 is 50MB. 

AFD-070820-035.pdf 

Upload the Report Document. File must be a PDF. Please do not password protect or secure the PDF. The 
maximum file size for the Report Document is 50MB. 

afosr_f.pdf 

Upload a Report Document, if any. The maximum file size for the Report Document is 50MB. 

Archival Publications (published) during reporting period: 

Hysell, D. L., R. Jafari, M. A. Milla, and J. W. Meriwether 
(2014), Data-driven numerical simulations of equatorial spread F in 
the Peruvian sector, J. Geophys. Res. Space Physics, 119, 3815a3827, 
doi :10.1002/2014JA019889. 

Hysell, D. L., M. A. Milla, L. Condori, and J. W. Meriwether (2014), Data-driven numerical simulations of 
equatorial spread F in the Peruvian sector: 2. Autumnal equinox, J. Geophys. Res. Space Physics, 119, 

6981 a6993, doi:10.1002/2014JA020345. 

Hysell, D. L., M. A. Milla, L. Condori, and J. Vierinen (2015), Data-driven numerical simulations of 
equatorial spread F in the Peruvian sector 3: Solstice, J. Geophys. Res. Space Physics, 120, 

10,809\u201310,822, doi:10.1002/2015JA021877. 

Hysell, D. L., M. A. Milla, and J. Vierinen (2016), A multistatic HF beacon network for ionospheric 
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specification in the Peruvian sector, Radio Sci., 51,392\u2013401, doi:10.1002/2016RS005951. 

2. New discoveries, inventions, or patent disclosures: 

Do you have any discoveries, inventions, or patent disclosures to report for this period? 

No 

Please describe and include any notable dates 

Do you plan to pursue a claim for personal or organizational intellectual property? 

Changes in research objectives (if any): 

Change in AFOSR Program Manager, if any: 

Kent Miller retired as the manager of this program and was replaced by Julie Moses during the award. 

Extensions granted or milestones slipped, if any: 

This project was granted a no-cost extension which has been completed. 

AFOSR LRIR Number 
LRIR Title 
Reporting Period 
Laboratory Task Manager 
Program Officer 
Research Objectives 


Technical Summary 

Funding Summary by Cost Category (by FY, $K) 



Starting FY 

FY+1 

FY+2 

Salary 




Equipment/Facilities 




Supplies 




Total 





Report Document 

Report Document - Text Analysis 

Report Document - Text Analysis 

Appendix Documents 

2. Thank You 

E-mail user 

Jul 13, 2016 11:52:40 Success: Email Sent to: dlh37@cornell.edu 


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