Toward Understanding the Day-to-Day
Variability in Structuring of the Nighttime
Equatorial F layer

Roland Tsunoda
Center for Geospace Studies
SRI International
Menlo Park, California, USASRI International• Private, non-profit research institute (staff > 2000)-- contract research; project oriented• Center for Geospace Studies (staff ~ 20)• Current Projects-- Build, deploy and operate incoherent-scatterradars (Resolute Bay, Sondrestrom, Poker Flat,Arecibo)-- Ionospheric, magnetospheric research• Personal interest: Physical processes that lead tothe structuring of ionospheric plasma

Some Background• Quality of radio signals is degraded while propagating
through ionospheric plasma structure• Plasma structure in nighttime equatorial F layer isreferred to as equatorial spread F (ESF)• Propagation effects most severe within plasma-depleted
regions, called equatorial plasma bubbles (EPBs)• Mitigation difficult; avoidance is most viable strategy• Occurrence of ESF/EPBs can vary dramatically fromday-to-day• Reliable methods for short-term forecasting have yet to
be developed – A SPACE-WEATHER CONCERNHow to Best Address the Day-to-Day
Variability Problem• Construct working hypothesis• Test hypothesis with well-designed experiments,
with comparisons to theories or computer
simulation results• Working hypothesis:
Large-scale wave structure (LSWS) controls
when and where ESF/EPBs develop
Main drivers: (1) post-sunset rise (PSSR) of Flayer and (2) eastward neutral windWhat isLSWS?
• LSWS: train ofupwellings inbottomside ofequatorial F layer• Example of asingle upwellingfrom ALTAIR
measurements(right figure)No LSWS (top), LSWS (bottom)

Properties of LSWS
• Very little is known about LSWS-- Zonal wavelength ~ 400 km-- Upwelling amplitude can exceed 100 km• Most of information about upwelling properties
have been obtained with ALTAIR, a fullysteerable incoherent-scatter radar• But, ALTAIR rarely available for basic research• Lack of knowledge about LSWS is a major
reason why we have not yet been able to solve
the day-to-day variability problem

Serious Obstacle to LSWS Measurement• Upwellings are spatial structures, virtuallystationary during their growth phase (PSSR)• Hence, sensors that use temporal variation toinfer spatial structure, by assuming zonal drift
cannot be used
• In lieu of ALTAIR, limited information have been
extracted from ionogram signatures, total
electron content (TEC) derived from beacon
signals transmitted by equatorial-orbiting
satellite (C/NOFS), HF transequatorialpropagation (TEP)Sketch of Working Hypothesis• LSWS grows in amplitude such that each ‘upwelling’ becomes a regional center
within which ESF develops
R.T. Tsunoda, ‘Upwelling, A unit of disturbance in equatorial spread F,’ Prog.
Earth, Planet. Sci., in review, 2015.

Ionogram Signatures of Bottomside Patches• Ionosonde
observations withangle-of-arrival• ESF patches
arrive from west,
recede to east
• East-west
asymmetry isevident

Swooper: Another Bottomside Patch Signature• Doppler shift of continuous-wave radio signals versus UT• Sequence of events: PSSR, arrival of swoopers” from west
• Asymmetry prevents detection of signatures to east of station

HF-TEP Evidence of Bottomside Patches

Multiple striations associated with
off-great-circle (OGC) propagation
paths

Sketch of OGC paths that could
occur in a HF-TEP experimentfrom Australia to JapanEPB Clusters: In Situ Measurements• AE-E ion-density measurements• First pass: LSWS without EPBs
• Second pass: Filling of upwellings with EPBs

Development ofEPB Cluster• Primary EPB fromcrest of upwelling(0907 UT)• Secondary EPBs
along west wall ofupwelling• Eastward transport ofEPBs relative toupwelling• Filling of upwellingwith EPBs

Clear Example of Upwelling Filled with EPBs

Sketch of Working Hypothesis• LSWS grows in amplitude and each upwelling becomes a regional center within
which ESF develops
R.T. Tsunoda, ‘Upwelling, A unit of disturbance in equatorial spread F,’ Prog.
Earth, Planet. Sci., in review, 2015.

Indo-Asian-Pacific Region: Ideal Testbed•••

Uniform geometry
over extended (75°)
longitude sector
Sensor network
includes zonal chainof 6-8 ionosondes
Other sensors
provide descriptionof LSWS (GRBR
network, all-sky
imagers, GPSnetwork, radars, HFTEP experiment)One Useful Experiment• Determine the longitudinal correlation inbehavior of LSWS, PSSR, and ESF/EPB
development• On a given night, compare the above
development process at longitudes spaced 1-2
hrs in LT with “expected” behavior• Do LSWS properties explain observations?
• Can we separate contributions from PSSR andLSWS?

New Opportunity

Formosat-7/COSMIC-2• Constellation Observing System forMeteorology, Ionosphere, and Climate(COSMIC) – total of 12 micro-satellites• First six will be launched in 24° inclination
orbit; will carry radio beacons and VIDI
(velocity, ion density, and irregularities)• Launch: ~ May 2016; SpaceX Falcon-Heavyrocket; from Cape Canaveral, Florida(28.49°N, 80.58°W), or Brownsville, Texas(25.93°N, 97.48°W)

Tandem Beacon Explorer (TBEx)• Two CubeSats will be flown in near-identicalorbits; each will carry a tri-frequency beacon• 150, 400, 1067 MHz• Measurements: Total electron content (TEC),
amplitude scintillations• Objective: Description of LSWS and ESF withhigher temporal resoluton• To be launched with six COSMIC-2 satellites
in low-inclination orbits (~ May 2016)-- COSMIC-2: Ion-drift meter, radio beacons

TBEx• Tandem Beacon
Explorer• Two “3U” CubeSats innear-identical orbits• Orbital inclination ~ 28°• 600 (400) km, apogee(perigee)• Each: Radio beacons at150, 400, 1067 MHz(identical to C/NOFS)

Coordinated Field Campaigns Using
Instrument Clusters• Indo-Asian-Pacific Network• Conduct campaigns during ESF season, moondown conditions (optics), nights of favorable
number of satellite passes• Obtain comprehensive description of LSWS andESF/EPBs• Data analysis, model simulations, etc., for field
campaign periods• Present results at an AOSWA workshop

Possible Collaborations• NICT-- HF-TEP, ionosondes• RISH, Kyoto University-- GRBR (GNU Radio Beacon Receiver) network-- Equatorial Atmosphere Radar (EAR)• STEL, Nagoya University-- 630 nm all-sky imagers-- 30 MHz radar (at EAR)
• UKM-- GRBRs in Malaysia-- GPS receiver network in Malaysia• LAPAN-- GRBRs, ionosondes in Indonesia