Statistical study of ionospheric smallscale irregularities at midlatitudes using GPS measurements

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Statistical study of ionospheric small-scale
irregularities at mid-latitudes using GPS
measurements
IRI/COST 296 Workshop 10 14 July 2007

• Gilles WAUTELET

Royal Meteorological Institute of Belgium
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PLAN

• Introduction
• Number of events Probability of occurrence
• Dependance on the solar cycle
• Local hour analysis seasonal behavior
• Amplitude of RoTEC (TEC time derivative)
• Maximum daily RoTEC several solar phases
• Worst cases study

high solar activity (2002)
low solar activity (2006)
Flare of DOY 301/03
Geomagnetic storm of DOY 303/03
Conclusion
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Introduction

• Computing the ionospheric variability with GPS
  measurements

• Compute the TEC thanks to the Geometric-Free (GF)
  combination

• Compute the RoTEC

TECU/min
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Introduction

• Modelling RoTEC with a low order polynomial

• Compute the residuals RoTEC polynomial

• On 15 minutes periods, compute the

standard deviation s of the residuals ?
ionospheric variability
If s gt 0,08 TECU/min, then an  ionospheric
event  is detected
15 min
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Introduction
TIDs
2 types of small-scale structures
NLS
TIDs (Travelling Ionospheric disturbances)
NLS (Noise-like structures)
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1. Number of events Probability of occurrence

• a) Dependance on the solar cycle

• Month resolution appearance of most disturbed
  months

• Approximation NLS very low
• ? variability TIDs
• Variability observed in all phases of solar cycle
• TIDs occurrence modulated by solar cycle
• Winter months annual peak

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1. Number of events Probability of occurrence

• a) Dependance on the solar cycle

• Day resolution appearance of most disturbed days
  (10)

090/01
310/01
324/03
034/02
GS
303/03
328/01
TID
302/03
276/01
033/02
340/01
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1. Number of events Probability of occurrence

• b) Local hour analysis seasonal behavior

• Solar maximum 2002

15 min time resolution
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1. Number of events Probability of occurrence

• b) Local hour analysis seasonal behavior

winter

• Solar maximum 2002

50
spring
Whole year 2002

autumn
summer
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1. Number of events Probability of occurrence

• b) Local hour analysis seasonal behavior

• Solar minimum 2006

15 min time resolution
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1. Number of events Probability of occurrence

• b) Local hour analysis seasonal behavior

• Solar minimum 2006

winter
spring
Whole year 2006
ltlt
autumn
summer
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2. Amplitude of TEC time derivative
9,839

• a) Maximum daily RoTEC

5,088
2003
Severe geomagnetic storms
2002
Solar maximum
2,211
2006
Solar minimum
1,197 TECU/min
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2. Amplitude of TEC time derivative

• a) Maximum daily RoTEC

• Solar max
• Solar min

• extreme values 10 TECU/min ? geomagn. storms
• high values gt 1 TECU/min ? large TIDs

• extreme values 1,2 TECU/min
• high values gt 0,5 - 0,6 TECU/min

? large TIDs
Maximum daily RoTEC

• quite different from total events number
• BUT indicator of extreme events (like solar
  flares)

Useful to study the worst cases
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2. Amplitude of TEC time derivative

• b) Worst case study DOY 301/03 (28/10/03)

Origin solar flare on disk Local hour at
Brussels 11h ( max ionospheric
effect) Effects in TEC and RoTEC

• biggest in EUV (SOHO/CELIAS-SEM)
• fourth in X-rays ( NOAA X17,2)

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4,7 TECU/min
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2. Amplitude of TEC time derivative

• c) Worst case study DOY 303/03 (30/10/03)

Origin geomagnetic storm caused by a CME
Local hour at Brussels 21 h Effects in TEC
and RoTEC

• DST min -383 nT
• Kp max 9

200
9,8 TECU/min
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Conclusions

• Ionospheric activity during ALL solar phases (but
  modulated)

Strong TIDs even during solar minimum
threat for GNSS applications (RTK)

• Probability of occurrence

• autumn/winter gtgtgt spring/summer
• max around noon

• Maximum daily RoTEC

• during solar maximum
• up to 9 TECU/min (geomagnetic storms)

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THANK YOU FOR YOUR ATTENTION
Questions?