Post on 01-Apr-2018
transcript
Ionospheric Scintillation in
Africa: A SCINDA Perspective
AMISR Meeting
Boston College
01 March 2012
Keith Groves1 Ron Caton2
Charles Carrano1 Chris Bridgwood1
Joshua Orfield2
1Boston College 2Air Force Research Lab
• Motivation: Scintillation Effects
• SCIntillation Network Decision Aid (SCINDA)
• International Space Weather Initiative (ISWI)
• Some Results
• Current and Future Efforts
OUTLINE
PRN 7
2
What is Scintillation?
• Regional UHF SATCOM outages for extended periods (hours)
• Increased GNSS position/navigation/timing errors
• Degraded High Frequency (HF) radio communication 3
SCINTILLATION =
Rapid amplitude
and phase
fluctuations of
radio signals in
space due to
turbulence
AFRL Best Climatology Model had a
Gap in the Atlantic
• Gap in scintillation activity
predicted by climatological
model near equinoxes in the
Atlantic sector
• The gap existed because of an
artifact in the model and an
absence of information (data) to
improve it
• Raised the question: What about
the validity of results over Africa?
• Model remains unvalidated, but
data collection from solar min to
solar max will enable
improvement
Scintillation Activity in Africa
• Scintillation activity across Africa
assumed high based on satellite
observations, but ground-based
measurements are needed
• C/NOFS sees similar maximum in
activity over Africa
• Worked with IHY (2005-09) & ISWI
(2009-present) to identify host nation
partners & collaborators
• Goal is to establish robust
monitoring network with scientific
collaboration across Africa, Asia and
South America
Strength of scintillations over Africa
unknown
Adapted from S.Y. Su, 2005
Present and anticipated thru 2013
SCINDA Ground Stations
30N
0
30S
210E 240E 270E 300E 330E 0 30E 60E 90E 120E 150E
Existing Sites Future UN ISWI Sites Other collaboration
LISN Domain Recent
SCINDA Focus
SCINDA Science
• Exploit data for more scientific studies on both local and global scintillation phenomena
– Identify and explain differences (and similarities) between activity and irregularities in Africa relative to other longitude sectors
– Storm-time behavior; SEDS/SAPS in African sector; African landmass spans low- to north and south mid-latitudes
– Terrestrial coupling; 4-cell pattern in TEC/scintillation, local gradients, anomaly characteristics
– Ultimate goal is to forecast equatorial Spread F
Longitudinal Variations: Continental Scale
Synoptic scale features can be resolved with current network, but better resolution is needed
ASI
KIN
ZNZ ZNZ ZNZ ZNZ
ASI ASI ASI
KIN KIN KIN
EA
ST
W
ES
T
CE
NT
RA
L
14 Oct 15 Oct 16 Oct 27 Oct
DMSP Bubbles 1989 - 2002 D
ay o
f Y
ear
Longitude
365
273
182
91
1
Africa India Pacific America Atlantic
0 30 60 90 120 150 180 210 240 270 300 330 360
45-50
40-45
35-40
30-35
25-30
20-25
15-20
10-15
5-10
0-5
EPB Occurrence
Rate
Magnetic field aligned
with terminator
From Burke & Huang, 2004
Equatorial Bubbles in Africa
• Bubble envelop frequently shows
very large longitudinal extent relative
to other longitude sectors
• Occurrence frequency peaks over
Africa as well
• Equatorial coherent backscatter
radar can address this issue
Satellite observations exhibit
unique characteristics
Determining Bubble Altitude
• For scintillation activity to reach Ascension Island, bubbles must rise to more than 1000 km altitude, spreading to over 3000 km N-S extent
• During solar minimum, almost no bubbles reach these altitudes; N-S extent typically ~ 2000 km
12
SOLAR MIN NOW
Relative Occurrence of Bubbles Exceeding 1000 km Altitude
• Sites at different latitudes see different levels of activity depending on bubble altitude
• Bubbles need to extend above 1000 km to reach ASI; only ~400 km to reach Cape Verde
• Data will improve model for predicting bubble extent and understanding electrodynamics 13
Longitudinal Climatology 2011
14
• Africa shows elements of the climatology from both the Pacific and the American sectors
• Unusual distribution of late activity (~midnight) development needs explanation; not observed elsewhere
Frequency Dependence of Scintillation Climatology
• Differences in seasonal and diurnal occurrence statistics of VHF & GPS scintillation in western South America
• GPS L1 signals not sensitive for detecting irregularities in low density plasmas (< 106 e/cc, ~< 50 TEC)
L-band peaks here
VHF peaks here
Requires local
ground-based
observations
to detect
16
• Climatology across central-west Africa different from anywhere else
• Not all features explained by magnetic terminator alignment
• Terrestrial coupling may play a role
Continent-scale Climatology
2011-2013 Plans (unofficial)
• Install an additional 4-5 sites in Africa, 2-3 other locations in S.E. Asia/Pacific
– Higher sensor density needed for detailed studies, e.g. LISN
• Improve infrastructure/capability at functional sites in Africa
– Solar panels, robust power systems, mobile data transfer
– Add VHF scintillation/drift sensors and possibly optical imagers
• Develop improved multi-frequency LEO beacon receiver systems focused on next-generation beacon design (still TBD); up to six equatorial satellites in constellation (2015)
– New sensors useful throughout SCINDA & LISN networks
• Install a coherent backscatter VHF radar near magnetic equator (talk tomorrow at 09:30 a.m.!)
Summary
• Preliminary review of results from Africa confirm satellite climatology, but temporal dependence for June/July period are surprising
• Infrastructure remains an issue but improvements are tractable
– Critical for both long-term and case studies
• VHF coherent backscatter radar combined with satellite observations (C/NOFS) near peak of solar cycle should provide more insight on the nature of bubbles over Africa
• Incoherent scatter radar will provide unique knowledge of the regional structure of the African ionosphere as well as the physics of the associated electrodynamics