History of study into solar variations 400 year history of sunspot numbers The longest recorded aspect of solar variations are changes in sunspots The first record of sunspots dates to around 800 BC in China and the oldest surviving drawing of a sunspot dates to 1128 In 1610 astronomers began using the telescope to make observations of sunspots and their motions Initial study was focused on their nature and behavior Although the physical aspects of sunspots were not identified until the 1900s observations continued Study was hampered during the 1600s and 1700s due to the low number of sunspots during what is now recognized as an extended period of low solar activity known as the Maunder Minimum By the 1800s there was a long enough record of sunspot numbers to infer periodic cycles in sunspot activity In 1845 Princeton University professors Joseph Henry and Stephen Alexander observed the Sun with a thermopile and determined that sunspots emitted less radiation than surround ing areas of the Sun The emission of higher than average amounts of radiation later were observed from the solar faculae Around 1900 researchers began to explore connections between solar variations and weather on Earth Of particular note is the work of Charles Greeley Abbot Abbot was assigned by the Smithsonian Astrophysical Observatory SAO to detect changes in the radiation of the Sun His team had to begin by inventing instruments to measure solar radiation Later when Abbot was head of the SAO it established a solar station at Calama Chile to complement its data from Mount Wilson Observatory He detected 27 harmonic periods within the 273 month Hale cycles including 7 13 and 39 month patterns He looked for connections to weather by means such as matching opposing solar trends during a month to opposing temperature and precipitation trends in cities With the advent of dendrochronology scientists such as Waldo S Glock attempted to connect variation in tree growth to periodic solar variations in the extant record and infer long term secular variability in the solar constant from similar variations in millennial scale chronologies Statistical studies that correlate weather and climate with solar activity have been popular for centuries dating back at least to 1801 when William Herschel noted an apparent connection between wheat prices and sunspot records They now often involve high density global datasets compiled from surface networks and weather satellite observations and or the forcing of climate models with synthetic or observed solar variability to investigate the detailed processes by which the effects of solar variations propagate through the Earth s climate system Solar activity and irradiance measurement Direct irradiance measurements have only been available during the last three cycles and are based on a composite of many different observing satellites However the high correlation between irradiance measurements and other proxies of sol ar activity make it reasonable to estimate past solar activity Most important among these proxies is the record of sunspot observations that has been recorded since 1610 Since sunspots and associated faculae are directly responsible for small changes in the brightness of the sun they are closely correlated to changes in solar output Direct measurements of radio emissions from the Sun at 10 7 cm also provide a proxy of solar activity that can be measured from the ground since the Earth s atmosphere is transparent at this wavelength Lastly solar flares are a type of solar activity that can impact human life on Earth by affecting electrical systems especially satellites Flares usually occur in the presence of sunspots and hence the two are correlated but flares themselves make only tiny perturbations of the solar luminosity Recently it has been claimed that the total solar irradiance is varying in ways that aren t duplicated by changes in sunspot observations or radio emissions However this conclusion is disputed Some believe that shifts in irradiance may be the result of calibration problems in the measuring satellites These speculations also admit the possibility that a small long term trend might exist in solar irradiance though the data chosen for this plot do not have a significant trend Also the differences in flare activity over the three cycles would not be related to possible measurement artifacts in irradiance Sunspots Graph showing proxies of solar activity including changes in sunspot number and cosmogenic isotope production Sunspots are relatively dark areas on the radiating surface photosphere of the Sun where intense magnetic activity inhibits convection and cools the photosphere Faculae are slightly brighter areas that form around sunspot groups as the flow of energy to the photosphere is re established and both the normal flow and the sunspot blocked energy elevate the radiating surface temperature Scientists have speculated on po ssible relationships between sunspots and solar luminosity since the historical sunspot area record began in the 17th century Correlations are now known to exist with decreases in luminosity caused by sunspots generally 100 years have been detected in sea surface temperatures In contrast to older reconstructions most recent reconstructions of total solar irradiance point to an only small increase of only about 0 05 to 0 1 between Maunder Minimum and the present One reconstruction from the ACRIM data show a 0 04 per decade trend of increased solar output between solar minima over the short span of the data set ACRIM graphics These display a high degree of correlation with solar magnetic activity as measured by Greenwich Sunspot Number Changes in ultraviolet irradiance Ultraviolet irradiance EUV varies by approximately 1 5 percent from solar maxima to minima for 200 to 300 nm UV Energy changes in the UV wavelengths involved in production and loss of ozone have atmospheric effe cts The 30 hPa atmospheric pressure level has changed height in phase with solar activity during the last 4 solar cycles UV irradiance increase causes higher ozone production leading to stratospheric heating and to poleward displacements in the stratospheric and tropospheric wind systems A proxy study estimates that UV has increased by 3 since the Maunder Minimum citation needed Changes in the solar wind and the Sun s magnetic flux A more active solar wind and stronger magnetic field reduces the cosmic rays striking the Earth s atmosphere Variations in the solar wind affect the size and intensity of the heliosphere the volume larger than the Solar System filled with solar wind particles Cosmogenic production of 14C 10Be and 36Cl show changes tied to solar activity Cosmic ray ionization in the upper atmosphere does change but significant effects are not obvious As the solar coronal source magnetic flux doubled during the past century the cosmic ray flux has decreased by about 15 The Sun s total magnetic flux rose by a factor of 1 41 from 19641996 and by a factor of 2 3 since 1901 Effects on clouds Cosmic rays have been hypothesized to affect formation of clouds through possible effects on production of cloud condensation nuclei Observational evidence for such a relationship is inconclusive 19831994 data from the International Satellite Cloud Climatology Project ISCCP showed that global low cloud formation was highly correlated with cosmic ray flux subsequent to this the correlation breaks down The Earth s albedo decreased by about 2 5 over 5 years during the most recent solar cycle as measured by lunar Earthshine Similar reduction was measured by satellites during the previous cycle citation needed Mediterranean core study of plankton detected a solar related 11 year cycle and an increase 3 7 times larger between 1760 and 1950 A considerable reduction in cloud cover is proposed citation needed A laboratory experiment conducted by Henrik Svensmar k at the Danish National Space Center was able to produce particles as a result of cosmic ray like irradiation though these particles do not resemble actual cloud condensation nuclei found in nature A 2009 peer reviewed article investigating the effects of a Forbush decrease found that low clouds contain less liquid water following Forbush decreases and for the most influential events the liquid water in the oceanic atmosphere can diminish by as much as 7 Other effects due to solar variation Interaction of solar particles the solar magnetic field and the Earth s magnetic field cause variations in the particle and electromagnetic fields at the surface of the planet Extreme solar events can affect electrical devices Weakening of the Sun s magnetic field is believed to increase the number of interstellar cosmic rays which reach Earth s atmosphere altering the types of particles reaching the surface It has been speculated that a change in cosmic rays could cause an increase in c ertain types of clouds affecting Earth s albedo Geomagnetic effects Solar particles interact with Earth s magnetosphere The Earth s polar aurorae are visual displays created by interactions between the solar wind the solar magnetosphere the Earth s magnetic field and the Earth s atmosphere Variations in any of these affect aurora displays Sudden changes can cause the intense disturbances in the Earth s magnetic fields which are called geomagnetic storms Solar proton events Energetic protons can reach Earth within 30 minutes of a major flare s peak During such a solar proton event Earth is showered in energetic solar particles primarily protons released from the flare site Some of these particles spiral down Earth s magnetic field lines penetrating the upper layers of our atmosphere where they produce additional ionization and may produce a significant increase in the radiation environment Galactic cosmic rays Solar wind and magnetic field create heliosphere around solar syst em An increase in solar activity more sunspots is accompanied by an increase in the solar wind which is an outflow of ionized particles mostly protons and electrons from the sun The Earth s geomagnetic field the solar wind and the solar magnetic field deflect galactic cosmic rays GCR A decrease in solar activity increases the GCR penetration of the troposphere and stratosphere GCR particles are the primary source of ionization in the troposphere above 1 km below 1 km radon is a dominant source of ionization in many areas Levels of GCRs have been indirectly recorded by their influence on the production of carbon 14 and beryllium 10 The Hallstatt solar cycle length of approximately 2300 years is reflected by climatic Dansgaard Oeschger events The 8090 year solar Gleissberg cycles appear to vary in length depending upon the lengths of the concurrent 11 year solar cycles and there also appear to be similar climate patterns occurring on this time scale Cloud effects Changes in io nization affect the abundance of aerosols that serve as the nuclei of condensation for cloud formation As a result ionization levels potentially affect levels of condensation low clouds relative humidity and albedo due to clouds Clouds formed from greater amounts of condensation nuclei are brighter longer lived and likely to produce less precipitation Changes of 34 in cloudiness and concurrent changes in cloud top temperatures have been correlated to the 11 and 22 year solar sunspot cycles with increased GCR levels during antiparallel cycles Global average cloud cover change has been found to be 1 52 Several studies of GCR and cloud cover variations have found positive correlation at latitudes greater than 50 and negative correlation at lower latitudes However not all scientists accept this correlation as statistically significant and some that do attribute it to other solar variability e g UV or total irradiance variations rather than directly to GCR changes Difficulties in interpreting such correlations include the fact that many aspects of solar variability change at similar times and some climate systems have delayed responses Carbon 14 production Sunspot record blue with 14C inverted There is approximately a 60 year delay between sunspot levels and radiocarbon changes The production of carbon 14 radiocarbon 14C also is related to solar activity Carbon 14 is produced in the upper atmosphere when cosmic ray bombardment of atmospheric nitrogen 14N induces the Nitrogen to undergo decay thus transforming into an unusual isotope of Carbon with an atomic weight of 14 rather than the more common 12 Paradoxically increased solar activity results in a reduction of cosmic rays reaching the earth s atmosphere and reduces 14C production This is because cosmic rays are partially excluded from the Solar System by the outward sweep of magnetic fields in the solar wind Thus the cosmic ray intensity and carbon 14 production vary inversely to the general lev el of solar activity Therefore the atmospheric 14C concentration is lower during sunspot maxima and higher during sunspot minima By measuring the captured 14C in wood and counting tree rings production of radiocarbon relative to recent wood can be measured and dated A reconstruction of the past 10 000 years shows that the 14C production was much higher during the mid Holocene 7 000 years ago and decreased until 1 000 years ago In addition to variations in solar activity the long term trends in carbon 14 production are influenced by changes in the Earth s geomagnetic field and by changes in carbon cycling within the biosphere particularly those associated with changes in the extent of vegetation since the last ice age Global warming See also Global warming CO2 temperature and sunspot activity since 1850 The scientific consensus is that solar variations do not play a major role in determining present day observed climate change The Intergovernmental Panel on Climate Change Thi rd Assessment Report states that the measured magnitude of recent solar variation is much smaller than the effect due to greenhouse gases In 2002 Lean et al
0
