Effects of Solar Radio Flux on Radio Refractivity

Effects of Solar Radio Flux on Radio Refractivity in Nsukka, Nigeria


This work investigates the effect of Solar Radio Flux on Radio Refractivity in Nsukka Nigeria. The result of the investigation shows that refractivity usually increase during the morning hours when solar outburst is observed low and declines towards evening hours when the solar flux increased gradually. Thus Radio refractivity in Nsukka (January to April 2008) is observed high when there is low outburst of solar radio flux and low when the solar flux is high. These changes in refractivity were observed to be caused by changes/variations in atmospheric parameters of Temperature, Relative humidity and Pressure which thus causes change in refractive index.

Keywords: Atmospheric parameters, Solar radio flux, Refractivity




Radio frequency or radio wave signal are affected, just like other electromagnetic waves, by some phenomena such as reflection, refraction, diffraction, interference, absorption, polarization and scattering (Demetrius and Keneth, 1969). Refraction as encountered in the atmosphere by radio wave is referred to as radio refractivity.

Radio refractivity is, therefore defined as the ratio of the velocity of radio wave in free space to the velocity of the radio wave in a specified medium. It is affected by many factors which include the variation of meteorological factors   such as temperature, humidity and   atmospheric   pressure   (Valma,   Tamosiunaite,   Tamosiunas   and Zillinskas, 2011).

apart from these important meteorological parameters, radio refractivity can also be affected during solar activities.   During the period of high   solar activity,   the upper atmosphere expands (Yusuf, 2011), hence disrupt the process of signal transfer from the less dense medium to a denser medium in a lower atmosphere. This atmospheric phenomenon occurs due to the ionization of the atmosphere caused by Galactic Cosmic rays emanating from the sun. The radio emission from the sun (solar radio flux) at a wavelength of 10.7 centimeters, often called “the 10cm Flux’’, has been found to correlate well with the sunspot number  (Svalgaard, 2009). The radio flux at 10.7 centimeters can be measured relatively easily and has replaced the sunspot number as an index of solar activity. The F10.7 index is the measure of the solar radio flux per unit frequency at a wavelength of 10.7cm near the peak of the observed solar radio emission. It is also defined as the measure of noise level generated by the sun at the wavelength of 10.7cm at the earth’s orbit. It is often expressed in SFU (i.e solar flux unit, where 1SFU =10­-22 Wm-2 Hz-1). Its emission from the sun at wavelength is due primarily to Coronal Plasma trapped in the magnetic fields overlying active regions. The solar F10.7 index is measured daily at local noon in a bandwidth of 100MHz centered on 2800MHz at the pentiction site of the Dominion Radio Astrophysical Observatory (DRAO),Canada. The solar F10.7cm record dated back to 1947, and is the longest direct record of solar activity available other than sun spot related quantities. Sunspot activities has a major effect on long distance radio communications particularly on the short wave band. Although medium wave and low VHF frequencies are also affected, the F10.7 index has been used as an input to ionospheric model as a surrogate for the solar output in wavelengths that produce photoionization in the earth’s ionosphere (in the ultraviolet bands).  This study therefore is focused on the effect of solar radio flux on radio refractivity with a view to ascertain the quality of reception of radio signals and how they affect radio communication at Nsukka, Nigeria.


Changes in meteorological parameters, associated with changes in weather in different seasons of the year have changes in radio refractivity (Famorji, 2013).

Agbo, Okoro and Amechi (2013), also noted that consideration of refraction properties of the lower atmosphere is of certain importance when planning and designing terrestrial communication system because of multipath fading and Interference due to trans-horizon propagation. This effect occurs most often when the same radio wave signals follow different paths thereby having different time of arrival to its targeted point (Farmoji, 2013). Consequently, this large scale variation in the atmosphere refractive index the propagation of the radio wave through the atmosphere becomes progressively curved   towards   the   earth.   Therefore   there   is the   need   to   carry   out   more investigation on radio refractivity effects.


  1. To study the refractive index of radio wave in the atmosphere using data from TRODAN (Tropospheric data acquisition network).
  2. To determine the effects of solar radio flux on radio refractivity at Nsukka.


The effect of atmospheric heating caused by F10.7 solar radio flux on radio refractivity is an important fact that must be considered while planning, designing and constructing a communication system.

The refractive index in the upper atmosphere (ionosphere) increases with the density of free moving electron which makes the radio wave signals to be refracted gradually over a considerable vertical distance, and it becomes useful for its propagation when they are refracted enough to bring them back to earth (Valma et al., 2011).

This allows radio signal to be propagated over a long distance. The possible benefit to radio communication resulting from high solar activity is that of aurora (a natural light displayed in the sky) which can reflect very high frequency signal (VHF) between 30-300 MHZ. Sunspot numbers also affect radio communication because it enhances long distance communication in upper Higher Frequency (HF) and lower Very High Frequency (VHF) range. The presence of electrons in the ionosphere is what affects radio signal across several bands of the spectrum from 3KHZ to 30 GHZ. As electrons in the ionosphere oscillate about its equilibrium position, because of inertia, with a plasma frequency between 1 to 10MHZ which is in Higher Frequency band (HF). HF is consequently the most significant band that can be affected to ionospheric propagation.


The scope of this study centers only at Nsukka in order to investigate the affect of solar radio flux on radio refractivity. The effect of the world wide phenomena of solar radio flux in the area is being investigated. Nsukka is located at the south-eastern part of Nigeria (latitude 60 51¢28.14´´ N and longitude 70 24´28.15´´ E). There are two major seasons usually experienced in the area which include dry and wet season. The dry season is usually characterized by little or no rain between the month of October and March while the wet season is usually characterized by heavy down purr between the intervals of April to September.

Radio transmission link is usually disrupted due to heavy outburst of solar radio flux during dry season and usually less disturbed during the wet season unless by other atmosphere parameters such as temperature variation, atmospheric pressure and relative humidity.

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