Midlatitude Spread F Dissertation Proposal

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Midlatitude Spread F(Dissertation Proposal)

• Preeti Bhaneja 8 November
  2007

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Acknowledgements

• Dr. Greg Earle
• Dr. R. Heelis
• Dr. P. Anderson
• Dr. X.Lou
• Dr. M.Hairston
• Overall project help - Dr.Rebecca Bishop
• Wallops Island Data Terry Bullet
• Rob Redmon
• Justin Mabie
• UTD Michael Perdue
• Keith Swaim
• Patrick Roddy
• Jeff Klenzing
• Brandon Drummond
• Friends and peers at UTD
• Marjorie Renfrow

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Index

• Introduction
• Theory
• Data Analysis - method
• Data Presentation
• Summary of ionosonde study
• Future ionosonde work
• Experimental study
• Conclusions
• Timeline

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• INTRODUCTION

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• The ionosphere is the partially ionized region of
  the atmosphere above about 60 km.
• It is divided into different layers or regions
  D, E, F1 and F2. These regions correspond to
  different altitude, composition and electron
  density levels.
• In the nighttime, there is no solar radiation to
  produce ionization, so recombination makes the D,
  E and F1 layers disappear.
• Typical daytime and
• nighttime profiles
• at midlatitudes are
• shown in the figure.
• The F2 layer does not
• disappear at sunset,
• instead its density
• slowly decreases
• throughout the night.

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• Ionospheric irregularities are temporal and
  spatial variations of the electron density
  lasting from a couple minutes to a few hours.
• In the lower latitudes of the F region of the
  ionosphere, these irregularities are called
  Equatorial Spread F.
• Occurrence of similar irregularities in the
  midlatitude F region is also called spread F.
• Density perturbations form the basis of spread F.
• Gravity waves are also widely recognized as a
  major cause for these density perturbations in
  the F region.

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• THEORY

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Various Theories

• Various theories have been proposed to explain
• MSF (midlatitude spread F) -
• 1. Perkins Instability 1973
• 2. Gravity wave induced instability by
  Miller-1997
• 3. E and F region coupling by Cosgrove and
• Tsunoda -2003
• None of these theories is completely compatible
  with
• observations. For example, they cannot explain
  the
• observed growth rate or the differences between
• range and frequency spread F.

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• DATA ANALYSIS - METHOD

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MEASUREMENTS

• Data are obtained from the ionosonde at Wallops
  Island, Virginia (37.95 N, 284.53 E, 67.5 dip
  angle).
• Ionosondes send swept frequency signals into the
  ionosphere.
• The frequency at which reflection occurs is
  related to the plasma density at the reflection
  altitude.

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• Electromagnetic propagation in the ionosphere is
  described by the Appleton-Hartree equation-
• angular plasma frequency,
  electron gyro frequency
• longitudinal (parallel) traverse
  (perpendicular) component,
  component
• electron collision frequency,
  angular wave frequency

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• Easy to remember formulas can be obtained by
  ignoring collisions and the magnetic field

• Based on these simple expressions, the frequency
  at which the reflection occurs is related to the
  plasma density by

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2. IONOGRAM

• The reflected pulses are recorded as traces and
  the plot made with these traces is known as the
  ionogram.
• The O mode traces for an ionogram on a day with
  no spread F is shown -

Midlatitude Non-Spread F event on 20 November
2004 at 6 UT.
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• 2 Movies will be shown non spread F and spread
  F.
• The two traces are O and X mode.
• Top pink trace O mode
• Bottom green trace X mode
• The first movie is a non-spread F event on 24
  September 2004.

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Movie for Non-Spread Ionogram
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Ionogram for a spread F event

• Ionograms obtained for spread F show thickness or
  spread in the F region which is more than that
  obtained for a normal ionosphere.

Midlatitude Spread F event on 1 November 2003 at
6 UT.
Next slide shows a movie for a spread event on 21
November 2004.
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Movie for Spread Ionogram
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• In my analysis, only the O-mode traces are used.
• The reasons are
• - The spreading occurs on both the modes
• equally.
• - The O-mode is unaffected by the earths
  magnetic field for transverse propagation, and
  can be more easily related to the plasma density.

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Range and Frequency Spread F

• The spread F observed
• on the ionograms can
• be classified
• as range or frequency
• spread.
• Range spread F refers
• to a condition in which
• there are multiple echoes
• at different heights for
• each frequency.
• Frequency spread F
• refers to the case in
• which multiple echoes at
• different frequencies for
• each height.

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Range and Frequency Spread F

• The software analyzes the ionogram and determines
  the location of box 1 and box 2.
• The height and width of both boxes are fixed.
• Edge detection is done on both the boxes to find
  the bottom side of box 1 and right side of box 2.
  
• Large pixel counts
• in box 1 correspond
• to range spreading.
• Large pixel counts
• in box 2 correspond to
• frequency spreading.

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• DATA PRESENTATION

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• DATA DESCRIPTION
• Data are obtained from Wallops Island (37.95 N,
  284.53 E, 67.5 dip angle).
• A complete solar cycle has been studied
  (1996-2006).
• Data were obtained in binary format and filtered
  and processed for generating plots, called
  ionograms, as seen in previous slides.
• The ionograms are taken every 15 minutes, 24
  hours a day.
• We consider only nighttime data from 0-10 UT.

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• 1. The spread F events, the onset times, duration
  and type of spread F are determined and these
  values are stored in a text file and used to
  generate plots for statistical analysis.

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2. Plot below shows the percentage of spread F
days/month and the percentage of available
data/month for 2005.
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3. Average Number of Spread F Days/Month for an
entire solar cycle from 1996-2006.

• Most spread F events occur in the fall and winter
  seasons.

4. Average Hours of Spread F/Night for each month
in an entire solar cycle from 1996-2006.

• Longest spread F events occur in the fall season.

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5. This is the same plot as shown previously,
plotted with the angle of the dusk terminator
relative to the magnetic field at Wallops for all
the months in a year. The angle is closest to
zero in the months of February and October.
Electric fields will map between hemispheres most
efficiently when the angle is zero.
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Flux Tube Alignment Criterion (Equinox)
Flux tube for negative declination
Flux tube for zero declination
Rotation Axis
Flux tubes aligned with the terminator create low
conductivity all along B, which leads to a
condition in which E does not get shorted out.
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6. Number of Spread F Days/Year for an entire
solar cycle from 1996-2006.

• Most spread F events occur during solar minimum.

7. Average Number of Spread F Hours/night for an
entire solar cycle from 1996-2006.

• Longest spread F events occur during solar
  minimum.

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8. Explicit comparison of range and frequency
spread F characteristics during solar minimum and
solar maximum years.
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Summary of Ionosonde Study

• Seasonal Variation
• Spread F is most prevalent in the fall and
  winter seasons.
• Solar cycle variation
• Spread F occurs most frequently during
  solar minimum.

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Future Ionosonde Work

• 1. Correlation studies between various
  geomagnetic
• indices and spread F AE,DST,F10.7.
• 2. Percentage of occurrence of spread due to
  aurora and
• weather.
• 3. Are the results from Wallops Island robust?
  Will similar
• data from other sites confirm our results?
  Data from
• another midlatitude site (Vandenberg AFB,
  California)
• may provide more insight into midlatitude
  spread F.

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We are beginning to study the correlation of the
AE index with the spread F statistics. The plot
below shows range spread F duration vs. AE
values. The dotted lines separate the events into
quiet, intermediate and active categories for
both solar max (2000) and solar min (2005).
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EXPERIMENTAL STUDY

• Rocket Launch happened in the early morning of
  October 30 2007, 1212 AM.
• In-situ electric field, wind
• and plasma density will
• be analyzed and studied
• for a particular spread
• event.

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CONCLUSIONS

• Our statistical study has established the
  seasonal and solar cycle variations of
  midlatitude spread F at Wallops Island. This work
  will be submitted for publication soon.
• My thesis work will assimilate the ground based
  and in-situ measurements to produce the most
  complete MSF study ever performed.
• Timeline for completion
• Statistical results submitted for publication
  (Spring 2008).
• Rocket data analyzed (Summer 2008).
• Write thesis (Throughout 2008-2009).
• Defend thesis (Spring 2009).
• Get job, get a life!

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Questions !!!