Solar – Geo Interaction : – A Discussion


There has been a great deal of – often turbulent – discussion on this subject in recent times. Without getting too complicated, it might be useful to make a brief attempt to openly assess and discuss the level of data we have on the subject at present.

One of the advantages of the extended period of solar quiet seen during the recent solar minimum, is that it gave us the opportunity to observe and study the behaviour of the terrestrial upper atmosphere under what might be termed “baseline” conditions, without the influence of large scale solar impacts.

One of the effects that became most starkly evident was the upper atmospheric response under the influence of “Russell-Macpherron” effect, together with the steady decline in general values, as is shown in the following extract from the “Thermosphere Climate Index” (TCI) chart.


TCI_Cropped Jpeg

In this chart – dated around July 2020 – the Spring and Autumn Equinox peaks and the Summer and Winter Solstice dips are clearly evident, an aspect that is not so readily apparent during “busier” periods – although it can, to a degree, be seen in the data. Of interest is also the clear dominance of the Autumnal peak throughout this period of solar minimum. The possibility exists that this dominance may be reversed during periods when the solar magnetic field is in its opposite phase, unfortunately the prolonged, stable solar minimum conditions which have enabled the present assessment have not existed during other recent solar minima. 

It is also worth noting that, whilst one might reasonably expect that peak to be coincident with the equinox, data shows that it most commonly occurs towards the end of October, often around 30th of that month. This is noted to be one complete Carrington Rotation after equinox; the implications of this may be that a mutual magnetic interaction occurs at and around equinox, the results of which appear as an increased level of solar magnetic turbulence which becomes evident as that disturbed area of the solar surface turns again towards earth. However at the present level of understanding, this is largely speculative.

The levels that were predicted in July 2020 for the latter half of the year are marked ‘X’ and ‘Z’ on the above chart. At that time, the prediction was that the October peak would be around 4.9 – 5.0 x10*10 W. on 30th October.



ises-solar-cycle-sunspot (4)

In the event, it actually peaked at that point in time at around 5.5, hesitated, then increased to around 6.0 and plateaued there for December and most of January before declining. This was coincident with, and followed immediately upon, the sudden upsurge in solar cycle activity over the last few months of 2020 ; as is shown in the Sunspot Progression chart of that time.


We may then examine the behaviour of the TCI during the sharp upswing in activity associated with the commencement of Solar Cycle 25 as is shown in the Sunspot Progression Chart for that period.

ises-solar-cycle-sunspot (6)


In directly comparing the relevant graphs in this manner, it becomes starkly apparent that the relationship between solar impact and Thermosphere Climate Index is very close.


The “Stratospheric Radiation” chart displaying cosmic rays in the atmosphere are rapidly subsiding following the commencement of Solar Cycle 25. In the past year alone, radiation levels in the air high above California have plummeted more than 15%, the flat period associated with Solar Minimum is also well illustrated. The CLOUD experiment (at CERN) studies how ions produced by high-energy particles  -cosmic rays – affect aerosol particles, clouds and the climate.


  ap-index 2017-8                  tci 2017 -2018

Ap INDEX                                                 TC INDEX

A well documented consequence of conditions during the period of solar minimum, was the cooling of the thermosphere and its resulting physical contraction. It is widely said that this cooling is the result of “Thermal Opacity” arising from the increased level of atmospheric CO2, this preventing surface level heat from radiating upwards. Whilst this is inevitably a factor that is present – as with any natural phenomenon factors contributing to it are many and varied – statistical data on that aspect is extremely limited. However if we view other statistical information such as the charts for planetary Ap index side by side with the TC index (As Above) it quickly becomes evident where the principle influencing factor originates.

Overall, the Thermosphere Climate Index closely follows the general trend of sunspot activity, modulated by “Kp”/”Ap” impacts. This may be confirmed by cross referencing the Solar Cycle Sunspot Number Progression Chart with the Thermosphere Climate Index Chart for any given period.


Thermosphere Climate Mod

Assessing what effect this has on the atmosphere at lower levels is where it gets complicated. We are, after all, dealing with a fluid medium, on a rotating sphere, with centrifugal and gravitational factors involved plus variations in the nature of the surface all playing a part.

That thermosphere expansion and contraction does penetrate downwards, shifting the pressure and thermal gradients in what has been described as an almost “tide-like” manner, is both logical and evident in the data. If you have some knowledge and experience with meteorological charts you may find the following relevant and informative.

Historical Charts

The charts go back to 1870. The older charts are re-analyses using original data fed in to modern computer systems, but they do represent a valid image of the situation at that time. It is again relevant to bear in mind that older (up to around 1980) readings were taken by hand; those involving temperature using whole-degree Fahrenheit measurements, whereas now they are mostly mechanical/digital/centigrade readings, giving rise to potential conversion error during the change-over period.

This is an open discussion and comment and debate is encouraged – but it must be polite and well reasoned with relevant reference and data as appropriate.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s