How to Read the Solar Flux Index
Solar Indices: Solar Flux A K Kp Alphabetize
As the radiation from the Sun is the major influence on the ionosphere, solar indices including the solar flux, A index, Ap index, K index and the Kp index are all important in predicting the state of the ionosphere and HF ionospheric radio propagation.
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Equally electromagnetic waves, and in this instance, radio signals travel, they interact with objects and the media in which they travel. Equally they do this the radio signals can be reflected, refracted or diffracted. These interactions cause the radio signals to change direction, and to accomplish areas which would not exist possible if the radio signals travelled in a directly line.
Ionospheric radio propagation is notoriously changeable. Withal for many applications radio propagation prediction is necessary. For example for dissemination every bit well as for users of two way radio communications links that utilise the HF bands as well as mobile radio communications, maritime radio communications, and many other signal to point radio users, a cognition of the propagation patterns that will exist in existence at a particular time are almost essential. In this mode radio communications users who require propagation via the ionosphere can choose the best times and frequencies in which to establish their radio communications.
Epitome Coutesy NASA
Radio propagation prediction
There are many indicators that enable the HF radio propagation conditions to exist predicted. Notwithstanding it is indicators of the level of solar radiation and geomagnetic activity that requite the best clues to the possible land of radio communications propagation conditions via the ionosphere. The chief solar indices are the solar flux and the geomagnetic indices known as the A and K indices. Using these it is possible to manually deduce what conditions may be like. Still there several packages of radio propagation prediction software that are available. These have the diverse indices into account along with the position on the globe, time of 24-hour interval, season, and the position in the sunspot bicycle.
Solar flux
One of the major indicators of solar activity used for radio propagation prediction is known every bit the solar flux and it has a major touch on radio communications propagation conditions. Information technology provides an indication of the level of radiation that is being received from the Dominicus. This solar alphabetize is measured by detecting the level of radio noise emitted at a frequency of 2800 MHz (10.7 cms). The alphabetize is quoted in terms of Solar Flux Units (SFU). An SFU has the units 10-22 Watts per metre2 per Hz.
The level of solar radiations varies around the globe. Even when correction factors have been applied it is non easy to be able to provide a consist series of figures. To overcome this, the standard is taken as the reading from the Penticton Radio Observatory in British Columbia, Canada. Thus these figures are of great interest for ionospheric radio propagation prediction.
The level of ionising radiation that is received from the Sun is approximately proportional to the Solar Flux. At that place is a statistical relationship rather than a direct one because the level of radio noise received at 2800 MHz is well-nigh a million times less in intensity than that of the radiation that creates the ionisation in the ionosphere. Nonetheless the Solar Flux provides a good first lodge approximation, especially for the F region that is responsible for most long distance ionospheric radio communications propagation. The best correlation is with levels of the Smoothed Sunspot Number (SSN).
It is possible to relate the daily sunspot number to the Solar Flux. A number of equations are available just the i given below is straightforward and sufficiently accurate for most purposes:
Where R is the daily sunspot or Wolf number.
A slightly more authentic, although more than complicated equation indicates the human relationship between the two values is not totally linear.
The values of Solar Flux vary over a wide range. At their lowest (typically during the periods of the sunspot minima) they may be equally low every bit 50 just rise to maximum values of around 300 (around the times of the sunspot maxima).
As the values of Solar Flux provide an indication of the level of ionisation in the ionosphere. In plough this gives an indication of what the Maximum Usable Frequency (MUF) for radio communications may be. Low values of Solar Flux signal that MUF figures may exist depression. Loftier values of Solar Flux indicate that the MUF may exist higher. It should be remembered that there must be several consecutive days of sustained high solar radiation with the absence of solar disturbances for high MUFs for HF band radio communications.
Geomagnetic indices
Autonomously from the Solar Flux, some other important influence on the ionosphere and hence radio propagation prediction is the level of geomagnetic activity. While the geomagnetic activity is a measure of the state of the Earth's magnetic field, this in plow is influenced by the Lord's day. To indicate the state of Geomagnetic activity, there are 2 indices that are used that are related to each other:
- K index
- a Alphabetize
Although different, both these indices requite indications of the severity of magnetic fluctuations, and hence the level of disturbance to the ionosphere.
M Index
The Thousand index is a three hourly measurement of the variation of the World's magnetic field compared to what are "quiet 24-hour interval" weather. The measurement is made using a magnetometer. This indicates the variation of the magnetic flux in nanoTeslas. This reading is then converted to the K index. The relationship is quasi-logarithmic, i.eastward. an almost directly proportional on a logarithmic scale..
The 1000 index is measured at many different places around the globe. The magnetic field varies around the globe and accordingly a unlike value for the One thousand alphabetize is created at each measurement station. Owing to the fact that the magnetic field varies in different means around the globe dependent upon the mode in which the magnetosphere is afflicted, information technology is not possible to have a elementary relationship betwixt 1 station and a global K alphabetize. Instead the individual K indices are averaged effectually the world to give what is termed the Kp or planetary K index.
Kp Index
The planetary or Kp index has values that range betwixt 0 and 9. The values of the kp index give a skilful indication of geomagnetic activeness: values between 0 and 1 bespeak tranquillity magnetic atmospheric condition and would requite rise to virtually no degradation in HF ring radio communications conditions. Values for the kp index betwixt 2 and 4 provide an indication of unsettled magnetic weather condition that point the possibility of some degradation on the HF bands for radio communications. A value of 5 signifies a pocket-size storm and half dozen a larger one. Values through to 9 indicate steadily worsening conditions with nine representing a major storm that is likely to result in a blackout in HF ionospheric propagation for several hours.
A Index
The A alphabetize is a linear measure of the World'southward field. Equally a effect of this, its values extend over a much wider range. It is derived from the Yard index by scaling it to give a linear value which is termed the "a" index. This is then averaged over the menstruum of a 24-hour interval to requite the A alphabetize. Like the K alphabetize, values are averaged around the earth to requite the planetary Ap alphabetize.
Values for the A index range up to 100 during a storm and may rise equally far as 400 in a severe geomagnetic storm.
A index & Kp index relationship
Although the A alphabetize and 1000 index are dissimilar values it is possible to relate these indices together. A summary of this human relationship is given int he table below.
| Relationship between Kp alphabetize and a Index | ||
|---|---|---|
| Ap Index | Kp Index | Description |
| 0 | 0 | Serenity |
| four | ane | Repose |
| seven | 2 | Unsettled |
| 15 | 3 | Unsettled |
| 27 | 4 | Active |
| 48 | 5 | Minor storm |
| 80 | six | Major storm |
| 132 | 7 | Severe storm |
| 208 | 8 | Very major storm |
| 400 | ix | Very major storm |
Geomagnetic and ionospheric storms are very closely related. Nevertheless they are separate effects. Geomagnetic storms chronicle to disturbances of the Globe's magnetic field, and ionospheric storms chronicle to disturbances of the ionosphere. Still it is found that geomagnetic storms oft lead to ionospheric ones, but not on every occasion.
Interpreting the figures
The easiest way to use these figures for radio propagation prediction is to enter them into radio propagation prediction software. This will provide the most accurate prediction of what might be happening. These programmes volition accept into business relationship factors such every bit signal paths because some will cross the poles and they will be far more affected by storms that will those across the equator.
Even so it is nonetheless possible to proceeds a good insight into what the figures mean in terms of radio propagation for all forms of radio communications using ionospheric propagation purely past assessing them mentally. Obviously high levels of solar flux are needed for skillful radio communications propagation. More often than not the college the flux the ameliorate the conditions volition be. However the levels need to exist maintained for some days. In this way the overall level of ionisation in the F2 layer will build up. Typically values of 150 and more will ensure proficient HF propagation weather, although levels of 200 and more than will ensure they are at their peak. In this manner the maximum useable frequencies will rise, thereby providing practiced weather for HF band radio communications.
The level of geomagnetic activity has an adverse bear upon, depressing the maximum useable frequencies. The higher the level of activity and hence the higher the Ap and Kp indices the greater the low of the MUFs. The actual amount of depression will depend not merely on the severity of the storm, just too its duration.
Having an understanding of the solar indices is of great help when using HF radio communications, be information technology two way radio communications, mobile radio communications, radio broadcasting or whatsoever form of betoken to betoken radio communications using ionospheric or HF propagation. It helps with radio propagation prediction and enables a quick assessment to be made of the possibility of communications existence disrupted. Also having a full general agreement enables whatever errors in entering information into the programmes to be quickly noted and corrected. In this way information technology enables the best to be made of the radio communications equipment and the most reliable communications to be obtained.
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