SSN, SFI, Solar Data for HF Radio Propagation
The data-set is presented in two formats below. They are the graph format and a tabular metrics format. The graph which displays the history of measured SSN and SFI derived SSN – SSNf(10.7) that prevailed over the last 60 days is updated once a day, while the Solar terrestrial data metrics table is updated on an hourly basis.
This page also explains each and every Solar Data Parameter that we have covered here, so that amateur radio operators irrespective of their technical understanding could get a reasonable insight into how HF radio propagation on Earth is influenced by the Sun’s activity. This way, one can watch for changes in various critical parameters and make informed decision related to HF radio band opening prospects.
Why is SSN regarded as important parameter for HF radio Propagation assessment?
The above illustration displays two graphs. The blue colored curve represents the SSN that is measured by counting of observed Sun-Spots at several solar observatories around the world. The red colored curve is derived from the measured Solar Flux Index (SFI). SFI is measured in the microwave band at a wavelength of 10.7 cm (2800 MHz) using a receiver with a capture window of 100 MHz. This is the global standard. The equivalent SSN, designated as SSNf(10.7) is computed from the SFI value using a standardized set of equations. This SFI derived SSN provides us a more realistic correlation to the actual effective SSN that prevails at any point in time... The SFI derived SSN (red curve) is usually a better choice and yields far more accurate results.
What are the other Solar data attributes that influence HF Radio Propagation?
This is a Solar Activity Data Metrics Table which is updated every hour at the turn of UTC hour. The table presents several vital parameters which determine the ionospheric condition and HF Radio propagation behavior around the world. Although some parameter change less frequently, there are others that change on an hourly basis.
SSN - The daily SSN values are derived from visual count of sunspots and spot clusters on the surface of the sun between 16-26 degrees latitude of the Sun. They are counted using optical telescopes at various observatories around the world according to "Wolf" method. The observations are collated and averaged to arrive at the global Sunspot Number. A 24 hour smoothed value is presented as SSN. These Daily SSN values are never ever directly used for forecasting or computing propagation conditions. The ionospheric behavior is far more complex than having a direct correlation to daily SSN. Our ionosphere is very lethargic to change and has large inherent momentum.
SSNe - This is the true effective Sunspot number and is as close to realism as it could be. SSNe (Effective) is based on actual hourly measurements of F2 layer Critical frequency (f0F2) taken at 29 distinctively separate geographic locations around the world. The raw f0F2 data drawn from 29 observatories is collated and go through complex computations to arrive at SSNe value. We do automated hourly computations and updates at our end and maintain a database of SSNe values.
SSNe5 - This parameter is a 5 days exponential moving average of the hourly SSNe values. SSNe5 is also computed every hour based on previous 120 SSNe hourly values by deriving an exponential moving average.
SSNf(10.7) - This is the SSN value computed from the Solar Flux Index (SFI). Hourly SFI feed from the value measured by orbiting satellites. SFI data is processed using established algorithms to determine an equivalent SSN value. Since it is derived from SFI this parameter is termed as SSNf.
SSNf90 - This parameter is a 90 days exponential moving average of the hourly SSNf values. SSNf90 is also computed every hour based on previous 2160 SSNf hourly values by deriving an exponential moving average.
SFI - This is the Solar Flux Index (SFI). It is measured using sensitive satellite borne microwave receivers operating at 2800MHz (10.7cm λ) with a capture bandwidth of 100MHz. The received signal is integrated over the capture (noise) window and the strength of this signal is used to determine SFI.
SFI90 - This parameter is a 90 days exponential moving average of the hourly SFI values. SFI90 is also computed every hour based on previous 2160 SFI hourly values by deriving an exponential moving average.
SWS-T - This is the T-Index from the Australian Ionospheric Prediction Service (IPS). This parameter SWS-T is also another method of measurement similar to SSN but it has no direct correlation to SSN. Like SSNe it also uses a measurement paradigm based on foF2 ionosonde measurements but the methods are different. Although SWS-T is relatively new, it tends to correlate with SSNe values to a considerable extent and appears to be very promising.
X-Ray - This is the measurement of X-Ray at the wavelength of 1-8 Angstrom region (0.1-0.8 nm). Hence it is known as "1-8A X-Ray". The values are typically displayed for instance as B2.4, where "B" represents e-7 (to the power -7). Therefore B2.4 means 2.4e-7. Similarly "A" is e-8 and "C" is e-6 and so on. The measurements are taken by NOAA's GOES satellites with an integration interval of 1 minute. Solar X-ray emissions are measured by sensitive instruments on board GOES satellites. The X-ray radiations from the sun take approximately 500 seconds (8.33 minutes) to cover the distance from sun to Earth. Any solar event like Flares or CME results in sudden increase in X-ray energy emission from the Sun. This in turn reflects itself as enhanced X-ray field strength reaching earth. Though solar X-ray is very important maintaining good ionospheric health and maintain healthy slab densities, excessive X-ray often penetrates deep through the earth's upper atmosphere and the upper ionospheric region to cause excessive ionization at the D-layer region. This could lead to HF communication difficulties or blackouts.
ap Index - This an estimated Geomagnetic Index estimated by integration over 3 hours. ap index is related to the amplitude” of magnetic activity based on K index data from 11 Northern and 2 Southern Hemisphere magnetic observatories between the geomagnetic latitudes of 46 and 63 degrees. ap Index is derived from Kp index and features a scale from 0-400
Ap Index - It is a planetary average of A-Index. This an estimated Geomagnetic Index estimated by integration over 24 hours and presented as simple moving average of 8 values every 3 hours. Ap scale is from 0-400
Kp Index - This an estimated Geomagnetic Index estimated by integration over 3 hours and a planetary average of K Index. This is a different unit of measurement in comparison to Ap. The Kp scale is between 0-9 with a resolution of 0.33 and has a quasi-logarithmic scale. The Kp Index is represented either a centric value like 3o meaning 3.0 or 3- meaning 2.66 or 3+ meaning 3.33 and so on. Kp Index is derived from measurements obtained from 13 geomagnetic observatories between 44 degrees and 60 degrees northern or southern geomagnetic latitude