8:00 AM | *The fast approaching solar minimum and its potential impact on the upcoming winter season*

The current solar image shows a blank sun and it has been spotless 58% of the time this year as we head into the solar minimum phase; courtesy NASA/NOAA, spaceweather.com

Overview

In the long term, the sun is the main driver of all weather and climate and multi-decadal trends in solar activity can have major impacts on oceanic and atmospheric temperatures. In addition, empirical observations have shown that the sun can have important ramifications on weather and climate on shorter time scales including those associated with the average solar cycle of around 11-years. For example, there is evidence that low solar activity during solar minimum years tend to be well-correlated with more frequent “high-latitude blocking” events compared to normal and this type of atmospheric phenomenon can play an important role in the winter season.

Discussion

Weather conditions and snowpack during the fall and winter seasons in cold air source regions such as Greenland and northeastern Canada can, in turn, have quite an impact on the conditions experienced in the eastern US. These particular regions of North America are where many cold air masses originate and the fact that Greenland, for example, has been particularly cold since late July is quite a bullish sign for the formation of deep, cold air masses. [By the way, the temperature at Summit Station, Greenland at 4 PM on Sunday was minus 38 degrees (F)].

It is not only important to monitor the potential for the formation of cold air masses in these particular regions, it is also important to determine if there will be a mechanism to bring the cold air masses southward from the northern latitudes into the mid-latitudes including the Mid-Atlantic region. “High-latitude blocking” is a phrase given to just such an atmospheric phenomenon that indeed can bring cold air masses into the eastern US from these cold air source regions and with the “block” in the atmosphere during these events, cold air can stick around for awhile which is often an important pre-requisite for accumulating snow in some places such as the big cities of the I-95 corridor. “High-latitude blocking” during the winter season is characterized by persistent high pressure in northern latitude areas such as Greenland, northeastern Canada, and Iceland. There is evidence that low solar activity during solar minimum years tend to be well-correlated with more frequent “high-latitude blocking” events compared to normal.

This plot shows the daily observations of the number of sunspots during the last four solar cycles back to 1 January 1977 according to Solar Influences Data Analysis Center (SIDC). The thin blue line indicates the daily sunspot number, while the dark blue line indicates the running annual average. The current low sunspot activity is indicated by the arrow at the lower right of the plot. Last day shown: 30 Sep 2018. Data source: climate4you.com.

In terms of solar activity, we are now at the very end of the weakest solar cycle (#24) in more than a century and are rapidly approaching the next solar minimum – usually the least active time in a given solar cycle. In truth, there is a chance that we have already entered into the solar minimum phase which is not always known until “after-the-fact”. The last solar minimum that took place from 2007-to-2009 turned out to be the quietest period in at least a century and signs point to another deep solar minimum over the next couple of years. The last time an inactive sun coincided with a moderate El Nino event – somewhat similar to expectations for this winter - was during the winter of 2009-2010 and the Mid-Atlantic region experienced quite a cold and snowy winter with, for example, Washington, DC experiencing their snowiest winter ever. Looking back to the preceding solar minimum which occurred in 1995-1996, there also was a “gangbuster” winter season in the I-95 corridor which included one of the biggest snowstorms ever on January 6-9, 1996.

Low solar activity during solar minimum years is well correlated with abnormally high heights at 500 mb (indicated by red, orange, yellow in boxed region) in the winter season over high-latitude regions such as Greenland and Iceland (i.e.,“high-latitude blocking” pattern). Data courtesy NOAA/NCAR

The 500 mb height composite anomaly plot in previous low solar activity years during solar minimum phases features a clear and strong signal of higher heights than normal over Greenland and Iceland which is often associated with “high-latitude blocking” events. Based on these observations from previous low solar activity years, odds certainly would favor frequent “high-latitude blocking” events this upcoming winter given the very strong likelihood for low solar activity. This is one of many factors discussed in the “2018-2019 Winter Outlook” that suggest a colder and snowier than normal winter season in much of the eastern half of the nation.

In solar maximum years, while there still are higher heights than normal at 500 mb over Greenland, the overall “high-latitude blocking signal” is considerably weaker in the same January-March time period. Data courtesy NOAA/NCAR

Other impacts of the solar minimum

One of the most important ways the solar cycle affects our planet is by cooling off the thermosphere during solar minimum. The thermosphere is the part of the earth's atmosphere that begins at about 50 miles (80 kilometers) above the earth's surface, extends to outer space, and is characterized by steadily increasing temperature with height. New data from NASA’s SABER instrument confirms the notion that our atmosphere is losing heat energy near the edge of space as we approach solar minimum. In fact, if current trends continue, it could soon set a Space Age record for cold according to NASA . The SABER instrument monitors infrared radiation from carbon dioxide (CO2) and nitric oxide (NO), two substances that play a vital role in the energy output of our thermosphere, the very top level of our atmosphere.

There is good news and bad news in all of this. The good news is that when the thermosphere cools, it actually shrinks, thereby reducing drag on satellites in low Earth orbit which can increase the life of a satellite. The bad news is that this cooling aloft tends to delay the natural decay of space junk resulting in a more cluttered environment around Earth.

In addition to the impact on the thermosphere, low solar activity during solar minimum phases are usually associated with an increase in the number of galactic cosmic rays that reach the upper atmosphere as the sun’s magnetic field is weaker meaning it provides less of a shield from these highly energetic particles. The shielding action of the sun is strongest during Solar Maximum and weakest during Solar Minimum with the weakening magnetic field and solar wind. The intensity of cosmic rays varies globally by about 15% over a solar cycle because of changes in the strength of the solar wind. For more information on the recent increase in cosmic rays during this low solar activity period click here.

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com