Space Weather:
The Sun,
Magnetosphere,
Ionosphere
Source of Space Weather /
Ionospheric Disturbances: The Sun
The Sun:
Facts (approximate values):
• 149 million kilometers away
• Diameter: 1.4 million km
• Mass: 2.0x1030 kg
• 4.5 billion years old
• 11 Year sunspot cycle
• Surface temp. 5,900 K.
• Rotation Period: 27 days at
equator
The Sun for a a couple months in 2001
Close-up of a Sun Spot
Local Internal Dynamics
Coronal “loops” on the Sun
Animation showing our present understanding
Coronal Mass
Ejections
Super prominence
EUV images of Sun with corona as observed from SOHO
Coronal Mass Ejection
Causing the Aurora
Magnetosphere
Other effects include satellite damage, power outages, GPS errors,
radio interruptions, etc.
The Magnetosphere
The Aurora
As seen in Alaska
As seen from space
Solar Flares
•
•
•
EUV
X-RAY
“White Light”
Flare
X-ray
Extreme Ultraviolet (EUV)
Nighttime
F2-Region
F2-Region
200 km

Thermosphere
Daytime
F1-Region
100 km

300 km

Neutral Atmosphere
E-Region
D-Region
Stratosphere
Troposphere
Height
Mesosphere
Mt. Everest
Formation of the Ionosphere
SUN
EUV Light
Positively
Charged Ion
Free Electrons, these
reflect radio waves

Photo-ionization
Neutral Atoms
A (Atom)

 A+ (Ion) + e- (electron)
Photo-ionization occurs when Extreme Ultraviolet (EUV) from the
Sun strikes neutral atoms to produce positively charged Ions
Types of Atoms: primarily Oxygen & Nitrogen
Types of Molecules: O2, N2, NO
Two Types of Recombination:
Dissociation recombination, 2 steps:
Ion X+

Neutral Atom X
Electron splits AX+
apart
A
AX+
o

Charge Exchange
X+ + A2  AX+ + A
Molecule A2
Dissociation Recombination
AX+ + e-  A + X
Radiative recombination, 1 step:
A
e-

Ion X+
Single
Atom A
Radiative Recombination
X+ + e-  A + Radiated Energy
Reflectivity of the Ionosphere







When ions are “let go” they oscillate in simple harmonic motion
at an Angular Frequency 
2 = N e2 / 0 m
N = Electron Density
e = Charge on electron
m = Mass of an electron
0 = Permittivity of free space
Angular Plasma Frequency
fN = 2 / 
fN2 = 80.5 N
fc  9 x 10-6 √Nm
(maximum usable frequency):
fN = Plasma frequency in Hertz
Substituting Atomic Constants
fc = Critical Frequency,
Nm = Electron density
Electron Density vs. Height
Source:
“The Ionosphere: Communications, Surveillance,
and Direction Finding”
Leo F. McNamara1991
ISBN: 0-89464-040-2
F2
•
•
•
- Region
300 Km
106 Ne/cm3 (noon)
105 Ne/cm3 (Midnight)
F1
•
•
•
- Region
200 Km
2.5x105 Ne/cm3 (noon)
Absent at night
E - Region
• 110 Km
• 1.5x105 Ne/cm3 (noon)
• 1.0x104 Ne/cm3 (Night)
D - Region
• 90 Km, Lower following solar flare
• 1.5x104 Ne/cm3 (noon)
• Absent at Night
Maximum
Useable
Frequency
The Maximum
Useable Frequency
(MUF) is the largest
frequency that can
be reflected by the
ionosphere at
vertical incidence
Source:
“The Ionosphere: Communications, Surveillance,
and Direction Finding”
Leo F. McNamara1991
ISBN: 0-89464-040-2
Variability of the Ionosphere
•
•
•
•
•
Source:
Diurnal (Thru the day)
Seasonal (Thru the year)
Location (Geographic & Geomagnetic)
Solar Activity (Solar Cycles & Disturbances)
Height (at different layers)
“The Ionosphere: Communications, Surveillance,
and Direction Finding”
Leo F. McNamara1991
ISBN: 0-89464-040-2