Atmospheric Expansion Under the Influence of
Incoming Solar Energy Impacts.
The following courtesy of Space Weather Prediction Center
National Oceanic and Atmospheric Administration
(See Illustration Above)
The drag force on satellites increases during times when the Sun is active. When the Sun adds extra energy to the atmosphere the low density layers of air at LEO altitudes rise and are replaced by higher density layers that were previously at lower altitudes. As a result, the spacecraft now flies through the higher density layer and experiences a stronger drag force. When the Sun is quiet, satellites in LEO have to boost their orbits about four times per year to make up for atmospheric drag. When solar activity is at its greatest over the 11-year solar cycle, satellites may have to be manoeuvred every 2-3 weeks to maintain their orbit.
In addition to these long-term changes in upper atmospheric temperature and density caused by the solar cycle, interactions between the solar wind and the Earth’s magnetic field during geomagnetic storms can produce large short-term increases in upper atmosphere temperature and density, increasing drag on satellites and changing their orbits. The North American Aerospace Defense Command (NORAD) has to re-identify hundreds of objects and record their new orbits after a large solar storm event .
During the March 1989 storm event, for example, the NASA’s Solar Maximum Mission (SMM) spacecraft was reported to have “dropped as if it hit a brick wall” due to the increased atmospheric drag.
This particular storm was responsible for the collapse of Quebec’s electricity transmission system, blacking out large parts of eastern Canada. The storm impact of March 12/13 1989 resulted from a CME event occurring March 9th. A few days before, on March 6th, a very large, geo-effective, X15 flare also occurred.
Bearing this effect in mind, we now have the opportunity to examine what happens as a result of the phenomenon penetrating deeper in to the atmospheric structure; how far does this ‘swelling’ penetrate and what impact does it have at lower levels.
It is, coincidentally, one of the few large scale events occurring during times when we have had sufficient technology to monitor both the event and the various areas within the Earth environment that may be affected.
This incident potentially gives us the opportunity to examine whether any identifiable reaction occurred within the atmospheric structure that may have resulted from either the flare or the CME impact. We can clearly see the effect on the low obit satellite population arising from increased drag as the atmosphere ‘swelled’ under the influence of the energy input but can we tell if there was any reaction deeper in to the atmosphere?
We have historical charts of the atmospheric and meteorological structure that we can examine which, although detailed, need to be treated with some degree of caution. Whilst we have numerous satellites that provide information and can be closely monitored and of course we have a wide range of ground based weather stations, our ability to monitor mid-level activity with any degree of accuracy is severely limited.Any such chart is based to a great extent upon human interpolation of available data and computer modelling which may, or may not, be accurate.
If we make an attempt to predict what is likely to happen as a result of a solar impact we can then seek to assess and understand the behaviour we actually observe. Firstly, an impact consisting of a purely radiant energy might be expected to penetrate deeply into the atmosphere, exert its influence and then dissipate, whilst an impact comprising high energy particles, and associated fields travelling at sub light velocities would be expected to interact with the atmosphere and with the Earth’s magnetic fields on a broader basis, energy being injected, fields distorted then re-establishing and oscillating over a more prolonged period as the atmosphere expanded and was then pulled back by gravity to more normal levels. It might be expected that an ‘inflated’ atmosphere when pulled back would tend to expand sideways – a bit like a squashed balloon! This latter would tend to show up as a movement or compression of the mid level profiles.
Under the influence of a radiant energy injection it would be expected that, as far as the European charts were concerned, we would see a northward distortion of the ‘steering level’, a compression of the associated gradients and a resultant intensification of any associated surface level activity but that this may be expected to be relatively short term.
Under the influence of a CME, similar behaviour may be observed but de-stabilisation of the whole profile structure over a longer time period may also be expected. It would seem reasonable to expect that distortions in the ‘Steering Level’ profile would be both later and longer lasting as the atmosphere first expanded outwards, then settled back, with possible oscillatory effects, and the volumetric expansion was maintained until all of the huge amount of energy involved had been dissipated.
04 March 1989
This shows the situation prior to the 1989 storm, with the ‘Steering Level’ in a seasonally normal position across North Atlantic and Europe, an average gradient profile and a moderately severe South Greenland low pressure area.
08 March 1989
Immediately after the ‘Flash’, the steering level has distorted northwards across Europe, the gradient has steepened and the low pressure intensified sharply.
13 March 1989
A few days later and the steering level has returned to its original position, the gradient has slackened and the low pressure filled.
23 March 1989
Within 10 days of the CME impact, The steering level has again distorted northwards, the gradient increased and the surface low pressure population increased and intensified. This disturbed behaviour continued for some time afterwards.
Although we must avoid over-interpreting this data, it is a useful indicator that there is an observable link between Solar activity, geo-effective impacts and both deep atmosphere structure and surface responses.
Planetary Ap Index.
The ‘Satellite Tracking Chart’ above, shows clearly the immediate swelling of the atmosphere in reaction to the Ap storminess index. We can see also by cross referencing other available data that there is a close relationship between the Ap index and what is actually happening on the ground.
We may observe that the sharp dips in the Ap Index graph over the years 2009/10/11/12/13 are coincident with a series of very severe winters observed in UK and Europe over those years, whilst the upswing 2015 was coincident with reports of ‘Warmest Ever December’ and serious flooding in northern parts of the UK, together with ‘Historic Low’ temperatures and ‘Once in a Century’ snowfall in northern and eastern USA, January 2016. The infamous ‘European Heat Wave’ of 2003 was coincident with a massive spike in Ap activity.
UK Snow December 2010
UK snow January 2013
The chart above shows the surging in the geomagnetic field that resulted from a quite moderate CME on the dates shown.
In order to more fully understand the relationship between what we experience on the ground and what we can see in the graphs, we are able to examine the atmospheric charts for the relevant points in time to see how the two inter-relate and how the surface weather may be influenced.
In this chart, December 20th 2010 we see that, coincident with the extended period of low solar activity (see sun spot chart) and the deep dip in the Ap graph, the ‘Steering Level’ has advanced to North Mediterranean latitudes, the gradient is quite slack and cold temperatures well advanced southwards.
Comparing that with this second chart, December 2oth 2015, coincident with an uptick during the declining phase of Solar Cycle 24, and the upsurge in the Ap graph, we can see that the ‘Steering Level’ is much further north on the European side of the Atlantic, the gradient much steeper and Atlantic low pressure activity much more intense while in continental USA southward progress was much faster.
The charts remained ‘stalled’ in this position for several weeks resulting in repetitive streams of warm wet air inundating the UK over that period.