Toward Scatter Classi cation at Middle...
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Toward Scatter Classification at Middle Latitudes E. S. Miller and E. R. Talaat Geospace and Earth Science Group Johns Hopkins University Applied Physics Laboratory 31 May 2011 Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
Transcript of Toward Scatter Classi cation at Middle...
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Toward Scatter Classification at Middle
Latitudes
E. S. Miller and E. R. Talaat
Geospace and Earth Science GroupJohns Hopkins University Applied Physics Laboratory
31 May 2011
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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SuperDARN Network
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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SuperDARN Network
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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SuperDARN Network
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Mid-Latitude SuperDARN
• Installed to observe expansion of convection patternequatorward of traditional SuperDARN boundaries.• This happens with some regularity, but quiet conditions
prevail.
• What is observed during quiet time?
• Signal to one is noise to another.• scatter ∈ {ionospheric, ground} does not describe
mid-latitude variability accurately.• scatter ∈ {ionospheric, ground} algorithm does not
describe mid-latitude physics accurately.
• Consider first climatological behavior.
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Wallops Island Climatology
Universal Time [hrs]
Vir
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km]
0 6 12 18 24
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2009 Wallops Island SuperDARN beam #7 backscatter power > 10 dB Climatology
Occ
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nce
[pct
]
10500 kHz 14500 kHz
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Wallops Island Climatology
Universal Time [hrs]
Vir
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km]
0 6 12 18 24
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0
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2009 Wallops Island SuperDARN beam #7 backscatter power > 10 dB Climatology
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Sub-Auroral TroughMeteor Echoes
Ground Scatter
Irregularities in the sub-auroral trough produce significant backscatter on many nights. (See Talaat, et al, poster.)
Ablating meteors deposit trails of metallic ions in the E region. Sporadic-E layers also contribute to this prevalence.
Echoes returned off of the land or sea.
10500 kHz 14500 kHz
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Propagation Mechanisms
Refraction
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Propagation Mechanisms
Refraction
kBField-Aligned Irregularities (FAI)
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Propagation Mechanisms
Refraction
kBField-Aligned Irregularities (FAI)
SpecularReflection k
Density Structure
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Meteor Scatter
• Essentially all SuperDARN meteor scatter is specular.• FAI typically observed by powerful IS-class radars.
• Meteor trails have short lifetimes (∼ 100 ms).
• Individual trails usually only appear in one range gate inspace and time.
• Ensemble of many trails yields “cloud” of scatter at closeranges.
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Sporadic-E
• Thin, dense, turbulentlayer of metallic ions atE -region altitudes.
• Specular echoes, FAI,ground scatter, allpossibilities.
• Separating specular echoesfrom FAI?
Sporadic-E over Arecibo. After Swartz, et al, 2002.
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Raytracing
• Need not be complicated to be informative.• Parabolic or Chapman profiles driven by standard URSI
coefficients. Or interpolate other datasets, use IRI(called directly from MATLAB).
• Geomagnetic field (IGRF is easy in MATLAB).• Basic Appleton-Hartree magneto-ionic effects.• Loosely based on Jones-Stephenson code, but only for
2.5D.
• Find ground scatter location.
• Find k ⊥ B → possible FAI location.
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Wallops Predictions
−80−75
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Wallops Island SuperDARN beam #7 10500 kHz O-mode
Bk
East Geographic Longitude [deg] North Geographic Latitude [deg]
Alti
tude
[km
]
• Drive with Millstone Hill Digisonde.
• Wallops beam #7 passes directly over Millstone.
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Wallops Predictions
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0 6 12 18 24
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−σ
+σ
1000
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Universal Time [hr]
Vir
tual
Ran
ge [
km]
2005-2010
2005-2010 mean
2005-2010
2009
FAI
GS
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Scatter Geolocation Tool
−80−75
−70−65
−60−55
−50−45 35
4045
5055
6065
0
100
200
300
400
500Wallops Island Millstone Hill
Wallops Island SuperDARN beam #7 10500 kHz O-mode
Bk
East Geographic Longitude [deg] North Geographic Latitude [deg]
Alti
tude
[km
]
• Convert pretty (butuseless) 3D plot to VirtualRange vs altitude.
SuperDARN Wallops Island beam #7
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Altitude [km]
Vir
tual
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ge [
km]
foF2 = 4 MHz, fRad = 10.5 MHz
FAI-F
FAI-E
GS-FO-mode
0 100 200 300 400 5000
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1000
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2500
Altitude [km]
Vir
tual
Ran
ge [
km]
foF2 = 5 MHz, fRad = 10.5 MHz
O-mode
FAI-FFAI-E
GS-F
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Scatter Geolocation Tool
• Triple-hop sporadic-E (G-Es) ground scatter 0000–0045UT.
• Field-aligned irregularity (FAI) scatter from locationswhere k ⊥ B.
• Differentiate between FAI-F and G-Es using Dopplervelocity.
0 100 200 300 400 5000
200
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Altitude [km]
Vir
tual
Ran
ge [
km]
F ground scatter
Es ground scatter
F FAI scatter
E FAI scatter0 1 2 3 4200
500
1000
1500
Universal Time [hrs]
15 May 2010 - Wallops Island SuperDARN beam #7 - 10.5 MHz
G-Es
FAI-Es
FAI-F
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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Discussion
• Mid-latitudes exhibit new and subtle sources ofSuperDARN scatter.• Non-auroral FAI.• Sporadic-E .
• Raytracing and phenomenology provide some guidance.• Not operational, but good for case studies.• Interferometer elevation can also help (not active at
Wallops presently).• Raytracing in inhomogeneous ionosphere for irregularity
studies.
Miller, et al SuperDARN 2011 — Mid-Latitude Scatter
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