terrestrial ionosphere - part 2/2

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The Terrestrial Ionosphere

Lecture 2: Factors Affecting Ionospheric

LayersLjiljana R. Cander



The Terrestrial IonosphereThe terrestrial ionosphere is a complex,

highly dynamic, even difficult plasma medium

that exhibits climatology and weather features atall latitudes and longitudes and altitudes.

Ionosphere is an environmental issue.



The Terrestrial Ionosphere

Ionosphere forms an essential part of telecommunication and navigation systems;

either as the medium within which they operate:

– use the ionosphere to function, or

- it is a part of the degradation process – would

function a lot better in its absence.



The Terrestrial Ionosphere and HFFor many years, numerous organisations have been

employing the High Frequency (HF) spectrum to communicate

over long distances. It was recognised in the late 30's thatthese communication systems were subject to marked variations

in performance, directly related to changes in the ionosphere.



The Terrestrial IonosphereThe various radiative, chemical and transport

processes in the ionosphere-thermospheresystem together with the effects of solar,

interplanetary, magnetospheric processes above

and mesospheric processes below generate:

- background ionosphere (ionospheric climatology),

- disturbed ionosphere (ionospheric weather).



Ionospheric Climatology and WeatherIonospheric climatology

is created and affected by

incident EUV radiation,

processes of ion/electron loss

due to neutral constituent

chemical reactions, ionospheric,electrodynamics and ion drag

From thermospheric wind.

NEED FOR IONOSOHERIC

LONG-TERM PREDICTION

Chilton, January 2005

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Ionospheric Climatology and Weather

The ionospheric weather

is created and affected bythe short-term variable

impact of the Sun’s protons,

solar wind particles and/orgeomagnetic field.

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SHORT –TERM FORECASTING

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Ionospheric Climatology and Weather

17 - 19 January 2005

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f o F 2 ( M H z )

Chilton (51.6 N, 358.7 E)

J uliusruh (54.6 N, 13.4 E)

Tortosa (40.5 N, 0.5 E)

El Arenosillo (37.1 N, 353.2 E)

Pruhonice (50 N, 14.6 E)

16 - 23 January 2005 Chilton

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monthly median values



Ionospheric Variations As a consequence, the ionosphere can display

significant variations on timescales ranging

from 11 years of a solar cycleto a few seconds:

- from large scale ionospheric climate, variability,

storms, auroral region, equatorial regions;

- to local and/or regional effects such as sporadic E,

tilts and gradients, small-scale ionospheric

irregularities.



Solar Cycle Changes

The main causes of large scale variations in ionospheric layersare related to the 11-year solar cycle. Figure 1 illustrates the solarcycle as indicated by the Sun Spot Number, SSN. The last solar cyclepeak occurred in 2000-2001. The next peak is expected to occur in

2011-2012.



Solar Cycle Changes

The relationship between solar cycles and E and Fregion frequencies



Solar Cycle ChangesThe relationship between solar cycles and E and F regionfrequencies (74 years of Slough-Chilton ionosonde)



Solar Cycle Changes

Ionospheric electron density profiles



Solar Cycle Changes

February 2002 Hailsham (UK IGS site hers)

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8 February 20029 February 2002

10 February 2002

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15 February 2002

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17 February 200218 February 2002

19 February 2002

20 February 2002

21 February 2002

22 February 2002

23 February 2002

24 February 2002

25 February 2002

26 February 200

27 Ferbruary 2002

28 February 2002

Variation of TEC at hers for every day duringFebruary 2002 (high solar activity, SSN=114.6 )

and February 2005 (low solar activity, SSN=29).HERS (UK GPS site at 0.3 E, 50.9 N) February 2005

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Seasonal Changes Variation of TEC at January (SSN=60.5) and June 2003 SSN= (31.3)



Daily Changes Variation of TEC at low solar activity, SSN=12.1.



Ionospheric Irregularities

Major causes of both large and smallscale irregularities in the distribution

of free electrons in the ionosphere arerelated to plasma drifts causingthe displacement of large massesof free electrons both in altitude and

latitude.

Such a transport of ionizationcharacterizes the ionosphere over

the magnetic equator and the lowlatitudes region. It is responsible forthe development of crests of electroncontent known as Appleton anomalies

causing large horizontal and verticalgradients of electron density.



Ionospheric IrregularitiesThe mechanism generatingTID’s is not definitelyknown, but the suggestionhas been made thatinternal gravity wavestravelling up to the F region

from the lower atmosphereplay an important role.

TEC measurements at GPS

stations on 2, 3, and 4October 2005 in Spain.Notice the significantplasma loss of 20-30%

during the eclipse on 3October 2005.



StormsSimilarly to the terminology used in meteorology,

storms are essentially defined as departures fromthe normal.

Geomagnetic storms (also sometimes calledmagnetic storms) correspond to atypical variationsin the magnetic field of the Earth.

Ionospheric storms correspond to atypicaldistributions of free electrons in the upperatmosphere, in particular in the F-region.



Geomagnetic Storms

Geomagnetic and ionospheric storms are closely related and typicallyoccur together.

Geomagnetic storms may last from a few hours to several daysand evolve in three phases: a usually short “initial phase”,a longer “main phase”, and an even longer “recovery phase” during which they gradually return to normal.

While geomagnetic storms can occur at any point of the solar cycle,the most severe geomagnetic storms tend to occur near the peak andduring the first few years following the peak .



SuperstormsIn the case of severe storms, the Dst index values are below –250 nT while Dst values below –300 nT are observed in extremecases, so called Superstorms. Number of superstorms from

the beginning of 17th solar cycle up to the beginning 23rdsolar cycle is as follows:



Ionospheric Storms

Normal ionospheric conditions exist when the

ionosphere is quiet (i.e., not disturbed), which

is the case approximately 98% of the time.

During the remaining approximately 2% of the

time, storms cause the ionosphere to be disturbed.

The level of ionospheric disturbances can rangefrom minor to severe ionospheric storms.

Storm effects depend strongly on season and timeof storm onset, producing different local ionospheric

responses.



Ionospheric F Region Storms

The F region response to a geomagnetic storm is

the best example of the great degree of ionosphericvariability.

These F region storms resulted from the input of solarwind energy captured by the Earth's magnetosphereand then released and dissipated into the auroralionosphere which set up a complex morphology of temperature, winds, electric fields and composition

changes.They continue for a few hours to several days andlead to significant changes in the ionospheric plasma

parameters.



Ionospheric Storm: foF2 and TEC

Superstorm of October 2003, Dst – 401 nT, Ap 204



Ionospheric Storm: NmF2, hmF2

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Ionospheric Storm: TEC

28, 29, 30 and 31 October 2003

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T E C (

T E C U

Hailsham (0.3 E, 50.9 N)Matera (16.7 E, 40.6 N)

Graz (15.5 E, 47.1 N)Noto (15.0 E, 36.9 N) Tromsoe (18.9 E, 69.7 N)



Ionospheric Storm

At mid-latitudes, thermospheric winds and

electromagnetic fields are believed to play a

dominant role in ionospheric plasma changes seenhere in foF2 and TEC temporal and spatial variations.

Negative storm phases have been attributed tochanges in the atomic to molecular neutraldensity ratio.

Positive phases are generally believed to be causedby uplifting of the F region by equatorward

winds in the early hours of a storm development.



Ionospheric Storm: MUF

28 - 31 October 2003

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12 October




Books about Ionosphere

O.K. Garriott, H.Rishbeth, Introduction to Ionospheric Physics, 1969.

A. Giraud and M. N. Petit, Ionospheric Techniques and Phenomena, 1978.

K.G. Budden, The Propagation of Radio Waves: The Theory of

Radio Waves of Low Power in the Ionosphere and Magnetosphere, 1988.

K. Davies, Ionospheric Radio, 1990.

K. Rawer, Wave Propagation In The Ionosphere,1993.J. K. Hargreaves, The Solar-Terrestrial Environment: An Introduction

to Geospace - the Science of the Terrestrial Upper Atmosphere,

Ionosphere, and Magnetosphere, 1995.R.D. Hunsucker and J. K. Hargreaves, The High-latitude

Ionosphere And Its Effects On Radio Propagation, 2002.

N. Blaunstein and E. Plohotniuc, Ionosphere and Applied Aspects

of Radio Communication and Radar, 2008.

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terrestrial ionosphere - part 2/2