URSIGA, New Delhi, 23-29 Oct 2005 Coordinated Observations of Ionospheric Scintillations, Density...

URSIGA, New Delhi, 23-29 Oct 2005

Coordinated Observations of Ionospheric Scintillations, Density Profiles and Total Electron

Content on a Common Magnetic Flux Tube

K. M. Groves1, S. Basu1, T. R. Pedersen1 T. L. Beach1, J. M. Quinn1, B. Taliaferro1

E. R. de Paula, I. S. Batista, M. A. Abdu, R.C. Livingston, P. Ning, C. Carrano

1Space Vehicles Directorate

Space Weather Center of Excellence

Air Force Research Laboratory

2005 URSI General Assembly, New Delhi, IndiaGF1B: Atmosphere-Ionosphere Sounding by Using Global Navigation Satellite Systems


Spread F Meridional Dependence

• Motivation: Regional specification from 1-D measurements

• COPEX Campaign Overview

• Ionospheric variations at conjugate locations

• Summary

Outline


Data Assimilation Methods

• Constraining model output

• Developing statistical interpolation techniques

• Adjusting model drivers– Kalman filter– Adjoint methods

Real-time Scintillation Nowcastingfrom Space

The satellite provides only a one-dimensional sampling of the parameters.

Need to specify the ionosphere in 3-D

Communication/Navigation Outage Forecast System (C/NOFS)


Motivation: Observation Extrapolation

The Challenge: Map 1-D scintillation estimates into 2-D representations

Satellite measurement ground track

Current assumption: Symmetry about the magnetic equator—Inconsistent with asymmetric density structure near solstice

Current assumption: Symmetry about the magnetic equator—Inconsistent with asymmetric density structure near solstice

Simulated scintillation structures


COPEX CampaignOct-Nov 2002

• Magnetic equator & conjugate location observations

• Conducted by INPE with AFRL & University collaboration

• Objective is to understand initiation, growth and dynamics of young plume structures

• Critical to understanding large-scale structure of depletion development

• Multi-diagnostics at three locations will measure required ionospheric parameters


Principal Instrumentation

• Instruments operated from Oct to 07 Dec 2002• Sites on common flux tube; Campo Grande and Boa

Vista magnetically conjugate• Combination of these data with available ROCSAT

passes and other ancillary data sets provide basis to investigate meridional variations in detail

Campo Grande Cachimbo/ *Alta Floresta Boa Vista

Digisonde

VHF scint & drift

GPS TEC & scint

All-sky imager

Digisonde

VHF scint & drift

GPS TEC & scint

All-sky imager

Digisonde

VHF scint & drift*

GPS TEC & scint*

All-sky imager

VHF coherent

backscatter radar*

GEO 20.5S 54.7W 9.5S 54.8W/ 9.9S 56.1W 2.8N 60.7W

MAG 10.8S 14.0E 0.7S 15.2E 12.6N 13.5E


Mla

t

VTEC

TEC Structure Oct-Nov 2002

• TEC data reveals asymmetric anomaly structure driven by inter-hemispheric neutral wind

• Mean TEC levels decreasing ~30%+ from October to December

Local Time

VTEC

Mla

t

Local Time

VTEC

13-19 October

3-9 November1-7 December


Mla

t

S4

S4 Structure Oct-Nov 2002GPS L1 (1575 MHz) Scintillation

• Scintillation activity and intensity peak in December despite ~20% decrease in overall peak density

• Scintillation intensity symmetric as a function of magnetic latitude

Local Time

S4

Mla

t

Local Time

S4

13-19 October

3-9 November 1-7 December


• Examine daily plots between 0000-0200 UT (~2030-2230 LT)

• No observations below 30° elevation angle used in analysis

• Consider results statistically

when scintillation occurred and data was present at both “high latitude” stations

CGR AFL BVB

Analysis Approach


TEC Characterization

• Overall TEC decreases 20-50% from October to December• Largest decreases observed in southern anomaly• North/South TEC ratio increases from 1.2 in October to about 1.4

in December (40% higher!)

Avg TEC 00-02 UT North/South Ratio


Peak Density Characterization

• On average, F0F2 remains relatively constant over observing period• Largest decreases observed in southern anomaly• North/South F0F2 ratio increases from unity in October to about 1.1

in December (approximately 20% higher peak density)• Variations increase significantly during latter half of campaign

– May be related to reading ionograms with increased spread F

Avg F0F2 00-02 UT North/South F0F2 Ratio


Slab Thickness

• Effective slab thickness (TEC/NmF2) exhibits similar decrease over time

• Thicknesses generally 10-20% greater in northern hemisphere, becoming quite variable during 2nd half of campaign (Nov-Dec)

Avg Slab Thickness 00-02 UT North/South Slab Thickness Ratio


What About Scintillation?

• ~10% decrease in S4 ( N) over campaign period not entirely consistent with decrease in NmF2 (~20%)

• North/south ratio is

essentially unity (no asymmetry)


Statistical View

• Distribution of scintillation activity and intensity are statistically identical in both hemispheres despite differences in TEC and, to lesser extent, F0F2

• Activity increases in frequency during latter half of campaign

• Intensity distribution is essentially unchanged (2-3% decrease in monthly statistics)

795 Samples

Percentile S4

25: 0.333

50: 0.371

75: 0.426

90: 0.479

877 Samples

Percentile S4

25: 0.329

50: 0.363

75: 0.417

90: 0.482

895 Samples

Percentile S4

25: 0.328

50: 0.366

75: 0.416

90: 0.467

1083 Samples

Percentile S4

25: 0.324

50: 0.357

75: 0.408

90: 0.457

a) b)

c) d)


• Scintillation intensity appears relatively independent of background TEC variations near the anomaly crests

• TEC decreases markedly approaching summer solstice, particularly in the southern magnetic hemisphere; change in NmF2 less than half observed TEC decrease

• On average TEC, NmF2 and slab thickness greater in the northern magnetic hemisphere during this time period (Oct-Dec 2002)

• S4 appears to be essentially symmetric at the same magnetic latitude in both hemispheres, despite variations in TEC, slab thickness, and NmF2

• Vertical distribution of irregularities non-homogenous; propagation effects dominated by layer near F-region peak

Conclusions

URSIGA, New Delhi, 23-29 Oct 2005 Coordinated Observations of Ionospheric Scintillations, Density...

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