We have analyzed records of these sounds and found that most of their spectrum lies within the infrasound range, i.e. is not audible to humans. What people hear is only a small fraction of the actual power of these sounds. They are low-frequency acoustic emissions in the range between 20 and 100 Hz modulated by ultra-low infrasonic waves from 0.1 to 15 Hz. In geophysics, they are called acoustic-gravity waves; they are formed in the upper atmosphere, at the atmosphere-ionosphere boundary in particular. There can be quite a lot of causes why those waves are generated: earthquakes, volcanic eruptions, hurricanes, storms, tsunamis, etc. However, the scale of the observed humming sound in terms of both the area covered and its power far exceeds those that can be generated by the above-mentioned phenomena.
In that case, what could be causing this humming in the sky?
In our opinion, the source of such powerful and immense manifestation of acoustic-gravity waves must be very large-scale energy processes. These processes include powerful solar flares and huge energy flows generated by them, rushing towards Earth's surface and destabilizing the magnetosphere, ionosphere and upper atmosphere. Thus, the effects of powerful solar flares: the impact of shock waves in the solar wind, streams of corpuscles and bursts of electromagnetic radiation are the main causes of generation of acoustic-gravitation waves following increased solar activity.
Given the surge in solar activity as manifested itself in the higher number and energy of solar flares since mid-2011, we can assume that there is a high probability of impact of the substantial increase in solar activity on the generation of the unusual humming coming from the sky. It should be pointed out that solar activity began to rise sharply since early 2011, with its amplitude significantly higher than all forecasts given by a number of influential scientific institutions in 2010 and 2011. Meanwhile, the observed increase in solar activity is fully consistent with the forecast of the International Committee GEOCHANGE published in the Committee's Report in June 2010. If this growth rate of solar activity continues, its amplitude by the end of 2012 will be higher than the amplitude of 23rd solar cycle, and in 2013-2014 the solar activity will reach its peak the amplitude of which was predicted by us to be 1.5 - 1.7 times higher than the amplitude of the 23rd cycle.
But you said that the cause of the "sky hum" can lie within Earth's core as well, what does it mean?
There is one more possible cause of these sounds and it may lie at the Earth's core. The fact is that the acceleration of the drift of the Earth's north magnetic pole which increased more than fivefold between 1998 and 2003 and is at the same level today points to intensification of energy processes in the Earth's core, since it is processes in the inner and outer core that form the Earth's geomagnetic field. Meanwhile, as we have already reported, on November 15, 2011 all ATROPATENA geophysical stations which record three-dimensional variations of the Earth's gravitational field almost simultaneously registered a powerful gravitational impulse. The stations are deployed in Istanbul, Kiev, Baku, Islamabad and Yogyakarta, with the first and last one being separated by a distance of about 10,000 km. Such a phenomenon is only possible if the source of this emanation is at the Earth's core level. That huge energy release from the Earth's core at the end of the last year was some kind of a start signal indicating the transition of the Earth's internal energy into a new active phase.
In both cases, even though the causes of acoustic-gravity waves are of a quite understandable geophysical nature, they are indicative of the expected significant increase in solar activity and the geodynamic activity of our planet. There is no doubt that processes in the core rule the internal energy of our planet, therefore, we should expect by the end of 2012 a sharp rise in strong earthquakes, volcanic eruptions, tsunamis and extreme weather events with peak levels in 2013 - 2014.
Comment: For further information on "strange sounds from the sky" watch the latest Sott report: Strange Noises in the Sky: Trumpets of the Apocalypse?