Detection of Spread-F and foF2 values using Digisonde and VIPIR instruments

Preeti BhanejaTerry Bullett

November 8, 2011

Index

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Introduction Data Analysis – methodology Data Presentation Summary of ionosonde study at midlatitude regions. Future Work

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Introduction

Ionospheric irregularities are temporal and spatial variations of the electron density lasting from a couple minutes to a few hours.

Midlatitude Spread F (MSF) and Equatorial Spread F (ESF) are fundamentally different due to their different magnetic geometry; horizontal magnetic lines at equatorial region and dip angle exceeds 45° at midlatitude regions.

ESF is generally caused by Rayleigh Taylor instability, bubbles and large plumes.

MSF is caused due to gravity waves causing ionospheric layers to move creating density perturbations.

How the MSF and ESF vary with different seasons will be shown in this presentation.

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Introduction

Stations Latitude Longitude Declination DipWallops Island, Virginia 37.95° 74.5° -11° 65.3°Dyess, Texas 32.4° 99.8° 6.9° 66.5°Boulder, Colorado 40° 105.3° 10° 60.7°Vandenberg, California 34.8° 120.5° 13° 58.7°

Jicamarca, Peru 12°S 76.8° 3° 1°

Data analyzed for these stations:

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Data Analysis - Non-spread Ionogram

The O mode trace for an ionogram on a day with no spread F is shown -

Midlatitude Non-Spread F event on 20 November 2004 at 6 UT.

Equatorial Non-Spread F event on 5 June 2010 at 2 UT.

Ionogram traces have a finite thickness due to the finite bandwidth of the ionosonde. This is an instrument effect.

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Data Analysis - Ionogram for a spread event (Midlatitude Region)

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.

This is an ionosphere effect and signifies irregularities in the plasma densities in the ionosphere.

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Data Analysis - Range & Frequency Spread F and foF2 (Midlatitude Region) The spread F observed on ionograms can be classified as range or frequency spread.

Range spread F* refers to

a condition in which there

are multiple echoes at

different ranges for

each frequency.

Frequency spread F* refers

to the case in which

multiple echoes at

different frequencies for each range.

*Definitions different than URSI

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Data Analysis - Range & Frequency Spread F and foF2 (Midlatitude Region)

The software analyzes the ionogram and determines the location of box 1 and box 2. The height and width of box 1 is fixed.

The height and width of box 2 varies with the values of foF2 and hF2.

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.The threshold levels for boxes have been chosen by visually inspecting large number of ionograms.

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Data Analysis - Ionogram for a spread event(Equatorial Region)

Different kinds of spread are observed on ionograms generated from Jicamarca data. Range Spread, Range and Frequency Spread Spread in a form of big blob

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Data Analysis - Spread F Measurement (Equatorial Region)

The location, height and width of box is fixed.Large pixel counts in box correspond to spread event.The threshold levels for boxes have been chosen by visually inspecting large number of ionograms.Spread events have been quantified, and type of spread is not distinguished.foF2 is not measured for spread cases due to lack of clear trace.

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Data Analysis - foF2 Measurement (Equatorial Region)

Similar analysis as used for midlatitude region data, is used for equatorial region data.The height and width of boxes 1 and 2 are changed for equatorial region. Edge detection is done on both the boxes to find the bottom side of box 1 and right side of box 2.foF2 is determined for non spread events.

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Data Presentation - Data Description

Data processed :

Wallops, Dyess, and Vandenberg : 1996-2007.

Boulder : 2004-2007.

Jicamarca : 2010-2011.

We consider only night-time data from 7 PM-5 AM LT.

The digisonde produces ionograms every 15 minutes, 24 hours a day : 44 ionograms/night .

The VIPIR produces ionograms every 1 minute, 24 hours a day : 720 ionograms/night .

Raw data were obtained in binary format and filtered and processed to generate ionograms for statistical

analysis.

This was done for all 4 stations and data for 4 solar cycles have been processed and analyzed for midlatitude

region.

Similar analysis with change in box locations have been done for Jicamarca data.

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Data Presentation – Prototype Plot (midlatitude)

The spread F events, the onset times, duration and type of spread F are determined and these values are stored in a text file. Monthly plot shown for December 2009 using data from Wallops Island.

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Data Presentation – Solar Cycle Variation (MSF)

Number of Spread F Days/Year for an entire solar cycle from 1996-2007.

Most spread F events occur during solar minimum.

No

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Data Presentation – Seasonal Variation (MSF)

Average Number of Spread F Days/Month for an entire solar cycle from 1996-2007.

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Data Presentation – Prototype Plot (equatorial)

The spread F events, the onset time, duration and spread F are determined and these values are stored in a text file. Monthly plot shown for July 2011 using data from Jicamarca.

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Data Presentation – Seasonal Variation (ESF)

Average Number of Spread F Days/Month for 2010-2011.

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Data Presentation – Comparison Plot (midlatitude)

The foF2 values determined for digisonde data and compared again ARTIST scaled values. These values are also checked against manually scaled ionogram values. The plot shows daily foF2 variation for March 16, 2010.

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Data Presentation – Comparison Plot (midlatitude)

The foF2 values determined for both digisonde and VIPIR data are compared again ARTIST and ESIR scaled values. These values are also checked against manually scaled ionogram values. ESIR gives incorrect foF2 values for most of the time and even skips scaling at night-time hours. The plot shows daily foF2 variation for August 10, 2011.

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Data Presentation – Comparison Plot (equatorial)

The foF2 values determined for digisonde data and compared again ARTIST. These values are also checked against manually scaled ionogram values. The ARTIST attempts to scale even the spread ionograms where the foF2 is not visible or clear.The plot shows daily foF2 variation for January 1, 2011.

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Summary of ionosonde study for MSFSolar Cycle Variation

• Spread F occurs more frequently and lasts longer for solar min.

Seasonal Variation• The 4 stations show different seasonal variation patterns. This may be due to the local

angle of declination.

Stations Latitude Longitude Declination Seasonal(more MSF)

Wallops Island, Virginia

37.95° 74.5° -11° Vernal equinox, winter

Dyess, Texas 32.4° 99.8° 6.9° Winter solsticeBoulder, Colorado 40° 105.3° 10° Early summer,

autumn equinoxVandenberg, California

34.8° 120.5° 13° Summer, winter solstice

Future Work

Differentiate ESF into quantity and quality….statistics on ESF occurrence and the type of spread F.

Determine a statistical study of ESF using digisonde and VIPIR data.

Determine the reasons for various kinds of spread in ESF. Find a accurate way to measure foF2 value.

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Acknowledgements

Work in cooperation with NGDC/NOAA.

QUESTIONS ???

Extra