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Transcript of terrestrial ionosphere - part 2/2
7/30/2019 terrestrial ionosphere - part 2/2
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The Terrestrial Ionosphere
Lecture 2: Factors Affecting Ionospheric
LayersLjiljana R. Cander
7/30/2019 terrestrial ionosphere - part 2/2
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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.
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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.
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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.
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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).
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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.
NEED FOR IONOSOHERIC
SHORT –TERM FORECASTING
Chilton, January 2005
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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
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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.
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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.
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Solar Cycle Changes
The relationship between solar cycles and E and Fregion frequencies
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Solar Cycle ChangesThe relationship between solar cycles and E and F regionfrequencies (74 years of Slough-Chilton ionosonde)
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Solar Cycle Changes
Ionospheric electron density profiles
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Solar Cycle Changes
February 2002 Hailsham (UK IGS site hers)
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2 February 2002
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8 February 20029 February 2002
10 February 2002
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17 February 200218 February 2002
19 February 2002
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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)
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Daily Changes Variation of TEC at low solar activity, SSN=12.1.
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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.
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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.
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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.
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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 .
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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:
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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.
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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.
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Ionospheric Storm: foF2 and TEC
Superstorm of October 2003, Dst – 401 nT, Ap 204
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Ionospheric Storm: NmF2, hmF2
b)
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Chilton
Juliusruh IRI
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Superstorm of October 2003, Dst – 401 nT, Ap 204
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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)
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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.
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Ionospheric Storm: MUF
28 - 31 October 2003
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12 October
Superstorm of October 2003, Dst – 401 nT, Ap 204
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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.