Archives par mot-clé : Solar Cycles

Earth’s upper atmosphere cooling off dramatically and cosmic rays continue to increase as deep solar minimum approaches

by Paul Dorian, November 5, 2018 in PerspectaWeather


The sun is blank again today and has been without sunspots about 60% of the time this year as the current historically weak solar cycle heads towards the next solar minimum. Solar cycle 24 is currently on pace to be the weakest sunspot cycle with the fewest sunspots since cycle 14 peaked in February 1906. Solar cycle 24 continues a recent trend of weakening solar cycles which began with solar cycle 21 that peaked around 1980. The last time the sun was this blank in a given year on a percentage basis was 2009 during the last solar minimum when 71% of the time was spotless. That last solar minimum actually reached a nadir in 2008 when an astounding 73% of the year featured a spotless sun – the most spotless days in a given year since 1913. All indications are that the fast-approaching next solar minimum may be even quieter than the last one which was the deepest in nearly a century.

One of the natural consequences of a solar minimum is for the upper part of the Earth’s atmosphere to cool down. Another natural impact of decreasing solar activity is the weakening of the ambient solar wind and its magnetic field which, in turn, allows more cosmic rays to penetrate the solar system. The intensification of cosmic rays can have important consequences on such things as the safety of airline passengers and astronauts in space, Earth’s cloud cover and climate, and possibly even on lightning.

Daily observations of the number of sunspots since 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 recent low sunspot activity is clearly reflected in the recent low values for the total solar irradiance. Compare also with the geomagnetic Ap-index. Data source: WDC-SILSO, Royal Observatory of Belgium, Brussels. Last day shown: 31 October 2018. Last diagram update: 1 November 2018.