- IONOSPHERIC DIGITAL DATABASE ON CD
- IONOSPHERIC DATA IN THE INTERACTIVE SPIDR SYSTEM
- IONOSPHERIC DATA IN OTHER FORMS
1.1. The Ionosphere
The ionosphere is that part of the upper atmosphere where
free electrons occur in sufficient density to have an
appreciable influence on the propagation of radio frequency
electromagnetic waves. This ionization depends primarily on
the Sun and its activity. Ionospheric structures and peak
densities in the ionosphere vary greatly with time (sunspot
cycle, seasonally, and diurnally), with geographical
location (polar regions, auroral zones, mid latitudes, and
equatorial regions), and with certain solar-related
The major part of the ionization is produced by solar X-ray
and ultraviolet radiation and by corpuscular radiation from
the Sun. The most noticeable effect is seen as the Earth
rotates with respect to the Sun; ionization increases in the
sunlit hemisphere and decreases on the shadowed side.
Although the Sun is the largest contributor toward the
ionization, cosmic rays also make a small contribution. Any
atmospheric disturbance affects the distribution of the
The ionosphere is a dynamic system controlled by many
parameters including acoustic motions of the atmosphere,
electromagnetic emissions, and variations in the geomagnetic
field. Because of its extreme sensitivity to atmospheric
changes, the ionosphere can be used as a sensitive monitor
of atmospheric events.
1.2. Definitions of the Ionospheric Regions
The ionosphere is divided into four broad regions called D,
E, F, and topside. These regions may be further divided
into several regularly occurring layers, such as F1 or F2.
D Region: The region between about 75 and 95km above the
Earth in which the (relatively weak) ionization is mainly
responsible for absorption of high-frequency radio waves.
E Region: The region between about 95 and 150km above the
Earth that marks the height of the regular daytime E layer.
Other subdivisions isolating separate layers of irregular
occurrence within this region are also labeled with an
E prefix, such as the thick layer, E2, and a highly variable
thin layer, Sporadic E. Ions in this region are mainly O2+.
F Region: The region above about 150km in which the
important reflecting layer, F2, is found. Other layers
within this region are also described using the prefix F,
such as a temperate-latitude regular stratification, F1, and
a low-latitude, semi-regular stratification, F1.5. Ions in
the lower part of the F layer are mainly NO+ and are
predominantly O+ in the upper part. The F layer is the
region of primary interest for radio communications.
Topside: This part of the ionosphere starts at the height
of the maximum density of the F2 layer of the ionosphere and
extends upward with decreasing density to a transition
height where O+ ions become less numerous than H+ and He+
ions. The transition height varies but seldom drops below
500km at night or 800km in the daytime, although it may lie
above 1000km. Above the transition height, the weak
ionization has little influence on transionospheric radio
1.3. History of Vertical Incidence Soundings
Sounding of the ionosphere began in 1925. By 1947, an
instrument known as the ionosonde was routinely used to
measure automatically the characteristics of the ionosphere.
During the International Geophysical Year (IGY) of
1957-1958, an international cooperative effort created a
worldwide network of ionosondes to record vertical incidence
measurements for the 1957-1959 period of maximum solar
The IGY ionosonde was a relatively simple, robust,
inexpensive piece of equipment by today's standards.
Several countries built IGY ionosondes with few differences
among them and thus provided similar worldwide photographic
records called ionograms.
Since the IGY, a loosely coordinated worldwide network of
vertical incidence ionosondes, varying between 100 and 200
sites, has operated continuously.
Ionograms are recorded tracings of reflected high frequency
radio pulses generated by an ionosonde. Unique
relationships exist between the sounding frequency and the
ionization densities which can reflect it. As the sounder
sweeps from lower to higher frequencies, the signal rises
above the noise of commercial radio sources and records the
return signal reflected from the different layers of the
These echoes form characteristic patterns or "traces" that
comprise the ionogram. Radio pulses travel more slowly
within the ionosphere than in free space, therefore, the
apparent or "virtual" height is recorded instead of a true
height. For frequencies approaching the level of maximum
plasma frequency in a layer, the virtual height tends to
infinity, because the pulse must travel a finite distance at
effectively zero speed. The frequencies at which this
occurs are called critical frequencies.
Characteristic values of virtual heights (designated h'E,
h'F, and h'F2, etc.) and critical frequencies (designated
foE, foF1, and foF2, etc.) of each layer are scaled,
manually or by computer, from these ionograms. Typically,
an ionosonde station obtains one ionogram recording every 15
minutes. When the scaling is done manually, only the hourly
recordings are routinely reduced to numerical data
(parameters). Modern ionosondes with computer-driven
automatic scaling procedures routinely scale all the
2. IONOSPHERIC DIGITAL DATABASE ON CD
The Ionospheric Digital Database compact discs contain
approximately 40,000 station years (1.35 gigabytes) of
scaled digital vertical incidence parameters from about
130 sites around the world. These data have been
contributed through a major cooperative effort among the
World Data Centers and many ionosonde network organizations.
All the data placed on this CD database come from 1957
through 1990 and have been digitized, reformatted, and
converted to Universal Time.
3. IONOSPHERIC DATA IN THE INTERACTIVE SPIDR SYSTEM
Online Data in interactive forms in new interactive system "Space Physics Ineractive Data Resource" - "SPIDR" 4. IONOSPHERIC DATA IN OTHER FORMS
Hourly mean values of ionospheric parameters for global observatory nets (328 stations) from 1957 in SPIDR
Microfilms of ionogramm for worlds network of ionosphere stations.
Click here to see the list of stations we have data for.
Data may be ordered by e-mail .