Details at theSI Weather, where I have selected a segment which may be of interest blog readers.
Consequences of a weak solar cycle
First, the weak solar cycle has resulted in rather benign “space weather” in recent times with generally weaker-than-normal geomagnetic storms. By all Earth-based measures of geomagnetic and geoeffective solar activity, this cycle has been extremely quiet. However, there is some evidence that most large events such as strong solar flares and significant geomagnetic storms tend to occur in the declining phase of the solar cycle. In other words, there is still a chance for significant solar activity in the months and years ahead.
Second, it is pretty well understood that solar activity has a direct impact on temperatures at very high altitudes in a part of the Earth’s atmosphere called the thermosphere. This is the biggest layer of the Earth’s atmosphere which lies directly above the mesosphere and below the exosphere. Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation and are highly dependent on solar activity.
Finally, if history is a guide, it is safe to say that weak solar activity for a prolonged period of time can have a negative impact on global temperatures in the troposphere which is the bottom-most layer of Earth’s atmosphere – and where we all live. There have been two notable historical periods with decades-long episodes of low solar activity. The first period is known as the “Maunder Minimum”, named after the solar astronomer Edward Maunder, and it lasted from around 1645 to 1715. The second one is referred to as the “Dalton Minimum”, named for the English meteorologist John Dalton, and it lasted from about 1790 to 1830. Both of these historical periods coincided with below-normal global temperatures in an era now referred to by many as the “Little Ice Age”. In addition, research studies in just the past couple of decades have found a complicated relationship between solar activity, cosmic rays, and clouds on Earth. This research suggests that in times of low solar activity where solar winds are typically weak; more cosmic rays reach the Earth’s atmosphere which, in turn, has been found to lead to an increase in certain types of clouds that can act to cool the Earth.
According to solar experts, the “general consensus is that we’ve passed the peak” of the current ~11-year solar cycle. If solar geomagnetic activity has also peaked for the current solar cycle, the Ap index of geomagnetic activity declined about 66% so far at solar maxima over the past three solar cycles. The Ap index is one of many indicators of solar activity including total solar irradiance, sunspots, radio flux, and several others, and has particular relevance to the Svensmark cosmic ray theory of climate.
Solar geomagnetic activity shields galactic cosmic rays from Earth, which according to Svensmark’s theory, nucleate cloud formation. It will be interesting over the next several years to see if this decline in solar geomagnetic activity is found to increase cloud formation and potentially surface cooling.
Hat Tip to HockeySchtick
In the past, a decline in solar activity has resulted in a cooler planet. Stay Tuned!