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

SuperDARN Network

Miller, et al SuperDARN 2011 — Mid-Latitude Scatter

SuperDARN Network

Miller, et al SuperDARN 2011 — Mid-Latitude Scatter

SuperDARN Network

Miller, et al SuperDARN 2011 — Mid-Latitude Scatter

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

Wallops Island Climatology

Universal Time [hrs]

Vir

tual

Ran

ge [

km]

0 6 12 18 24

1000

2000

3000

4000

0

20

40

60

2009 Wallops Island SuperDARN beam #7 backscatter power > 10 dB Climatology

Occ

urre

nce

[pct

]

10500 kHz 14500 kHz

Miller, et al SuperDARN 2011 — Mid-Latitude Scatter

Wallops Island Climatology

Universal Time [hrs]

Vir

tual

Ran

ge [

km]

0 6 12 18 24

1000

2000

3000

4000

0

20

40

60

2009 Wallops Island SuperDARN beam #7 backscatter power > 10 dB Climatology

Occ

urre

nce

[pct

]

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

Propagation Mechanisms

Refraction

Miller, et al SuperDARN 2011 — Mid-Latitude Scatter

Propagation Mechanisms

Refraction

kBField-Aligned Irregularities (FAI)

Miller, et al SuperDARN 2011 — Mid-Latitude Scatter

Propagation Mechanisms

Refraction

kBField-Aligned Irregularities (FAI)

SpecularReflection k

Density Structure

Miller, et al SuperDARN 2011 — Mid-Latitude Scatter

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

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

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

Wallops Predictions

−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

]

• Drive with Millstone Hill Digisonde.

• Wallops beam #7 passes directly over Millstone.

Miller, et al SuperDARN 2011 — Mid-Latitude Scatter

Wallops Predictions

1000

2000

3000

4000

1000

2000

3000

4000

0 6 12 18 24

1000

2000

3000

4000

−σ

+σ

1000

2000

3000

4000

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

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

0 100 200 300 400 5000

500

1000

1500

2000

2500

Altitude [km]

Vir

tual

Ran

ge [

km]

foF2 = 4 MHz, fRad = 10.5 MHz

FAI-F

FAI-E

GS-FO-mode

0 100 200 300 400 5000

500

1000

1500

2000

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

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

500

1000

1500

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

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