Solar activity

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Recent visual sun

The Sun seen on January 30, 2012. Photo by courtesy of SOHO/MDI/spaceweather.com. Click here and here to read the latest about the just passed long solar minimum. Click here, here, here and here to read about predictions on the current and the next sunspot cycle, cycle 24 and 25, respectively.  

 

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Recent sunspot activity

Daily observations of the number of sunspots since 1 January 1977 according to Solar Influences Data Analysis Center (SIDC). The thin line indicates the daily sunspot number, while the dark grey line indicates the running annual average. The recent low sunspot activity is clearly reflected in the recent low values for the total solar irradiance. Last day shown: 31 December 2011. Last diagram update: 2 January 2012.

 

In 1848 the Swiss astronomer Johann Rudolph Wolf introduced a daily measurement of sunspot number. His method, which is still used today, counts the total number of spots visible on the face of the sun and the number of groups into which they cluster, because neither quantity alone satisfactorily measures sunspot activity (NOAA's National Geophysical Data Center; NGDC) .

An observer computes a daily sunspot number by multiplying the number of groups he sees by ten and then adding this product to his total count of individual spots. Results, however, vary greatly, since the measurement strongly depends on observer interpretation and experience and on the stability of the Earth's atmosphere above the observing site. Moreover, the use of Earth as a platform from which to record these numbers contributes to their variability, too, because the sun rotates and the evolving spot groups are distributed unevenly across solar longitudes. To compensate for these limitations, each daily international number is computed as a weighted average of measurements made from a network of cooperating observatories. Today, much more sophisticated measurements of solar activity are made routinely, but none has the link with the past that sunspot numbers have (NOAA's National Geophysical Data Center; NGDC) . 

 

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Recent solar irradiance

Total solar irradiance since 25 February 2003, according to the Laboratory of Atmospheric and Space Physics (LASP). These data are obtained using the SORCE Total Irradiance Monitor (TIM). The thin line indicates daily TSI values, while the thick line represents the running simple 183 day (c. 6 months) average. The measured values for the total solar irradiation (TSI) are somewhat lower than reported by most other TSI-measuring instruments, which typically report TSI values around 1366 W/m2. Click here to read about the background for this difference, or see the text paragraphs below this diagram. However, the low sunspot activity 2006-2010 is clearly reflected in the TIM data provided by LASP. Last day shown: 24 January 2012. Last diagram update: 31 January 2012.

  • Click here to download the entire series of TSI data from the Laboratory of Atmospheric and Space Physics (LASP).

  • Click here to make use of an online data plot facility kindly made available by LASP.

  • Click here to read about data smoothing.

 

The SORCE Total Irradiance Monitor (TIM) measures the Total Solar Irradiance (TSI), a measure of the absolute intensity of solar radiation, integrated over the entire solar irradiance spectrum.

The TIM's measured value of TSI at 1 AU is lower than that reported by other TSI-measuring instruments; an upcoming solar minimum value of 1361 W/m2 is estimated from the above TIM data. This is due to unresolved differences between the various TSI instruments in operation. The TIM measures TSI values 4.7 W/m2 lower than the VIRGO and 5.1 W/m2 lower than ACRIM III.

This difference exceeds the ~0.1% stated uncertainties on both the ACRIM and VIRGO instruments. Differences between the various data sets are solely instrumental and will only be resolved by careful and detailed analyses of each instrument's uncertainty budget. LASP report only the TSI measurements from the TIM, and make no attempt to adjust these to other TSI data records.

The TIM TSI data available are based on fundamental ground calibrations done at CU/LASP, NIST, and NASA. On-orbit calibrations measure the effects of background thermal emission, instrument sensitivity changes, and electronic gain. The TIM TSI data products have been corrected for instrument sensitivity and degradation, background thermal emission, instrument position and velocity, and electronic gain. The TIM relies on several component-level calibrations, as no calibration source or detector is available with the level of accuracy desired for this instrument -- a level of accuracy nearly 10 times better than that previously attempted for space-based radiometry.

 

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Sunspot activity since 1700

Annual sunspot activity since 1700 according to the Solar Influences Data Analysis Center (SIDC). The blue line shows annual values, red line shows the running 11 yr average. Last year shown: 2010. Last diagram update: 5 February 2011.

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Solar irradiance and sunspot number

 

Solar irradiance and sunspot number since January 1979 according to NOAA's National Geophysical Data Center; NGDC. The thin lines indicate the daily irradiance (red) and sunspot number (blue), while the thick lines indicate the running annual average for these two parametres. The total variation in solar irradiance is about 1.3 W/m2 during one sunspot cycle, as an order of magnitude.

 

The number of sunspots correlates with the intensity of solar radiation over the period (since 1979) when satellite measurements of absolute radiative flux were available. Since sunspots are darker than the surrounding photosphere it might be expected that more sunspots would lead to less solar radiation and a decreased solar constant. However, the surrounding margins of sunspots are hotter than the average, and so are brighter; overall, more sunspots increase the sun's solar constant or brightness. 

The variation caused by the sunspot cycle to solar output is relatively small, on the order of 0.1% of the solar constant (a peak-to-trough range of 1.3 W/m2 compared to 1366 W/m2 for the average solar constant). This number refers to the projected area of planet Earth, as seen from the Sun. However, the total surface area of the planet is four times the projected area, and the variation of 1.3 W/m2 therefore corresponds to about 0.325 W/m2 for the entire planet surface. This value might be compared with the IPCC 2007 estimate of 1.6 W/m2 for the total effect of all recognized climatic drivers 1750-2006, including release of greenhouse gasses from the burning of fossil fuels.

During the Maunder Minimum in the 17th Century (c.1650-1720) there were hardly any sunspots at all, and in all likelihood, the intensity of solar radiation was low. This event coincides with a documented period of maximum cooling within the Little Ice Age.

Irradiance is the radiometry term for the power of electromagnetic radiation at a surface, per unit area. Irradiance due to solar radiation is also called insolation. Total solar irradiance describes the radiant energy emitted by the sun over all wavelengths that falls each second on 1 square meter outside the earth's atmosphere, a quantity proportional to the "solar constant" observed earlier in this century. It measures the solar energy flux in Watts/square meter.

 

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Solar irradiance reconstructed since 1610

Solar irradiance since 1610 as reconstructed by Lean et al (1995) and Lean (2000). The thin line indicates the annual reconstructed solar irradiance, while the thick line shows the running 11 average. The values shown include a background component. See Lean (2000) for discussion of the amplitude of the background component. Last year included in the Lean (2000) analysis: 2000. The small green columns in the bottom panel indicate different kind of historical evidence for past climate change effects. Click on the green columns for more information on each of these events. Last diagram update: 24 April 2009.

  • Click here to download the data series of reconstructed solar irradiance 1610-2000.

  • Click here to read about data smoothing.

 

 

Solar irradiance since 1610 as reconstructed by Lean et al (1995) and Lean (2000), until 2000. The thin line indicates the annual reconstructed solar irradiance, while the thick line shows the running 11 average. The values shown include a background component. See Lean (2000) for discussion of the amplitude of the background component. Last year included in the Lean (2000) analysis: 2000. From 2001 two possible values for the irradiance are shown. The blue line is based SIDC annual sunspot number and the result of a a simple linear regression analysis between the SIDC data and the Lean values 1700-2000. The red line shows a simple extrapolation using irradiation values read from this and this source. The extrapolations beyond 2000 should therefore be considered approximate only. Last diagram update: 13 April 2011.

 

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Global temperature and sunspot number

 

Variation of global surface air temperature (HadCRUT3) and observed sunspot number (NOAA's National Geophysical Data Center; NGDC) since 1960. The global monthly average surface air temperature is a cooperative effort between the Hadley Centre for Climate Prediction and Research and the University of East Anglia's Climatic Research Unit (CRU), UK. The thin lines represent the monthly values, while the thick lines is the simple running 37 month average, nearly corresponding to a running 3 yr average. The variation in global temperature is about 0.2oC during one sunspot period, superimposed on the general increasing temperature trend during the period shown. The somewhat asymmetrical temperature 'bumps' around 1973 and 1998 are reflecting oceanographic El Niño effects. Last month incorporated: September 2010 (HadCRUT3) and September 2010 (NOAA). Last diagram update: 18 October 2010.

  • Click here to download the entire series of estimated HadCRUT3 global monthly surface air temperatures since January 1850.

  • Click here to download the entire series of monthly NOAA NGDC sunspot number since January 1749.

  • Click here to read about data smoothing.

 

Variation of global sea surface temperature (HadSST2) and observed sunspot number (NOAA's National Geophysical Data Center; NGDC) since 1960. The global monthly average sea surface temperature is estimated by University of East Anglia's Climatic Research Unit (CRU), UK. The HadSST2 data series are described by Ranier et al. (2006). Base period: 1961-1990. The thin lines in the diagram represent the monthly values, while the thick lines is the simple running 37 month average, nearly corresponding to a running 3 yr average. The variation in global sea surface temperature is 0.15 - 0.2oC during one sunspot period, superimposed on the general increasing temperature trend during the period shown. The somewhat asymmetrical temperature 'bumps' around 1973 and 1998 are reflecting oceanographic El Niño effects. Last month incorporated: September 2010 (HadSST2) and September 2010 (NOAA). Last diagram update: 18 October 2009.

  • Click here to download the entire HadSST2 temperature series since 1850.

  • Click here to download the entire series of monthly NOAA NGDC sunspot number since January 1749.

  • Click here to read about data smoothing.

 

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Cosmic ray intensity and sunspot activity

 

Variation of cosmic ray intensity and monthly sunspot activity since 1958 according to the Germany Cosmic Ray Monitor in Kiel  (GCRM) and NOAA's National Geophysical Data Center (NGDC), respectively. High sunspot activity correlates with low cosmic ray intensity, and vice versa. Last month incorporated: August 2009 (GCRM) and October 2009 (NGDC). Last diagram update: 6 November 2009.

  • Click here to download the entire series of monthly GCRM cosmic ray counts since January 1958.

  • Click here to download the entire series of monthly NOAA NGDC sunspot number since January 1749.

 

Galactic cosmic rays (GCR) are energetic particles originating from space that impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are protons, about 9% are helium nuclei (alpha particles) and about 1% are electrons (beta minus particles). The term "ray" is a misnomer, as cosmic particles arrive individually, not in the form of a ray or beam of particles.

The flux of galactic cosmic rays varies inversely with the solar cycle. Svensmark and Friis-Christensen (1997) suggested that galactic cosmic rays enhance low cloud formation, explaining variations on the order of 3 percent global total cloud cover over a solar cycle. A 3 percent cloud cover change corresponds to a radiative net change of about 0.5 W/m2, which may be compared with the IPCC 2007 estimate of 1.6 W/m2 for the total effect of all recognized climatic drivers 1750-2006, including release of greenhouse gasses from the burning of fossil fuels. Click here to read more about clouds in general, and click here to read more about the climatic influence of clouds.

 

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