Small Scale Observations with the EISCAT Svalbard Radar

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Small Scale Observations with the EISCAT Svalbard
Radar
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What do we mean by Small Scales

• The term small scales refer to both spatial and
  temporal structures
• Spatial Significantly smaller than the radar
  beam
• horizontal width of 10-100 meters
• Temporal Shorter than traditional
  pre-integration time - on the order of a few
  IPP-length
• temporal variations of 0.1 seconds

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Motivation for Small Scale studies (1)
...or even worse it does!
Guisdap does not fit
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Motivation for Small Scale Studies (2)
Temporal......
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Motivation for Small Scale Studies (2)
Temporal......
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Motivation for Small Scale Studies (3)
Spatial...
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Motivation for Small Scale Studies (3)
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Interferometric Observations
Grydeland et al. 2003 (GRL) Grydeland et al 2004
(Ann. Geophys.)
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Enhancement level
Previous reports of NEIAL power has been on the
order of 1 to 2 orders of magnitude above IS
level.
B
Recent observations by Grydeland et al., 2003,
estimating the horizontal size of the scattering
structure to be on the order of a hundred meters.
The increased scattering hence originates from as
little as 0.3 of the scattering volume, giving a
actual enhancement of 4 to 5 order of magnitudes.
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Correlation between small scale field-aligned
currents and NEIAL
Strømme at al. 2004c (to be submitted to Ann.
Geophys.)
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Data from the Ørsted satellite
3 lt Bz lt 10 nT
0 lt BT lt 5 nT
1 lt DSW lt 5 cm-3
-10 lt Bz lt -3 nT
5 lt BT lt 15 nT
5 lt DSW lt 15 cm-3
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Data from the EISCAT UHF radar
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Small parallel structures
5 lt BT lt 15 nT
NEIAL occurrence, EISCAT UHF
from Rietveld et al., 1996
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• These very high temporal and spatial resolution
  data were an important step for determining the
  cause for the unusual echoes - or the Naturally
  Enhanced Ion Acoustic Lines (NEIALs) - as
  observed over the last decades with high latitude
  IS radars.
• gt The simultaneous enhancement in the up- and
  down-shifted ion lines cannot be explained as a
  temporal and/or a spatial averaging.

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Langmuir Turbulence
Initial Decay

• L0 w L1 w S1
• kL0kL1kS1

Secondary Decay

• Lj w L(j1) w S(j1)
• kLjkL(j1)kS(j1)

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1
- Dispersion relation for ion acoustic
waves - Dispersion relation for Langmuir
waves
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1
- Dispersion relation for ion acoustic
waves - Dispersion relation for Langmuir
waves
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1
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- Dispersion relation for ion acoustic
waves - Dispersion relation for Langmuir
waves
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Simultaneous Enhancements in Both Ion Lines
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Co-existing enhanced plasma lines
Strømme et. al 2004a, submitted to GRL
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Conditions for simultaneous ion and plasma line
enhancement
Dv1/3 v0
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Observed with Millstone Hill, EISCAT UHF, VHF and
ESR, but never with Sondrestrom IS radar
Invariant Latitude
EISCAT VHF
ESR
Millstone Hill
Sondrestrom
ESR
EISCAT UHF and VHF
EISCAT UHF
Sondrestrom
Millstone Hill
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• Observed with Millstone Hill, EISCAT UHF, VHF and
  ESR, but never with Sondrestrom IS radar

Invariant Latitude
EISCAT VHF
ESR
Millstone Hill
Sondrestrom
ESR
EISCAT UHF and VHF
EISCAT UHF
Sondrestrom
Appears to be strongly wave vector dependent!
Millstone Hill
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ESR
Sondrestrom
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• The Future......

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Grydeland et al 2004b (accepted in Ann. Geo.)
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Scanning Antenna/Sub-Reflector
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Scanning Antenna/Sub-Reflector
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Scanning Antenna/Sub-Reflector
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Scanning Antenna/Sub-Reflector




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Spinning Antenna/Sub-Reflector

• Can be used for
• Naturally Occurring Narrow Coherent Structures
  (NEIAL)
• Heating Enhanced Echoes
• PMSE
• Meteor Studies
• Space Debris Detection
• Clutter Subtraction Down to Lower Altitudes
• ...
• ...
• ...

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Summary/Conclusion

• Order of magnitude improvement in spatial (and
  temporal) resolution has recently been obtained
  for the study of coherent structures associated
  with the NEIAL
• This has restricted the possible explanations for
  generation mechanism strongly
• First step towards imaging is done through
• adding small antennas in the vicinity of the ESR
  antennas (Grydeland, UiTø)
• Spinning antenna (multi feed)

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