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GOES XRS. GOES SXI. GOES EUV. POES SBUV. 10 5. X-RAY. EUV. UV. VIS. IR. 1000. Solar Irradiance. 10. Solar Variability (max – min)/min. 0.1. 0.1. 1.0. 10. 100. 1000. 10000. Wavelength (nm). Derived Total Solar Irradiance. Beer et al., 2000. Wilson, 1997.

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Solar Irradiance


Solar Variability

(max – min)/min








Wavelength (nm)

Derived Total Solar Irradiance

Beer et al., 2000

Wilson, 1997

Frolich and Lean, 1998

Solar Irradiance Variability

SOHO EIT EUV Images of the Sun at 19.5 nm Showing the Change from Solar Min Toward Solar Max

Spectral Variability

Rodney Viereck

NOAA Space Environment Center

  • NOAA Satellite Observations Across the Solar Spectrum
  • The solar spectrum (black curve) is highly variable (green curve).
  • The UV and EUV portions of the spectrum have the most variability.
  • NOAA will monitor the sun at wavelengths critical to the atmosphere and climate change.
  • Until the complete data set is available, we have established a CRADA to develop a model of the solar spectrum and to distribute it on a daily basis from the forecast center.

New Directions in Solar Variability and Climate Change

  • Sun-Climate Correlations
  • The Total Solar Irradiance has changed by only 0.3-0.6% since the early 1800s.
  • The climate has warmed by 0.5 to 1.0 degrees C in the same period.
  • Many argue that such a small change in solar output could not have caused the change in temperature that has been observed.
  • The correlation between the solar and climate records can be seen in this figure comparing polynomial fits to the sunspot record and the global mean sea-surface temperature. The Similarity is remarkable.
  • There are many other climate parameters that show similar correlations with the solar record.
  • It is difficult to imagine that two unrelated phenomena can have such similar features.
  • SEC has begun to pursue new directions in solar variability and climate change. We hope to work together with other OAR labs to establish a NOAA Sun-Climate program.


Sunspot Number

NOAA SPACE Environment Center has long been involved with monitoring the variability of the sun. Sunspots are usually considered the primary long-term measure of the solar output but there are other measurements and proxies that are used as indicators of the solar variability. It has been proposed that as much as 20-40% of the climate warming of the last 150 years may, in fact, be driven by the sun. This poster presents both present topics and future directions for the NOAA Space Environment Center in monitoring and predicting solar variability and its effects on Earth


Past, Present, and Future Solar Variability

Sea Surface Temperature

(0.01 K Departure from Mean)

  • The NOAA Mg II Index:
  • A 22 Year Measure of Solar UV Irradiance
  • NOAA Mg II core to wing Index goes back 22 years and covers two complete solar cycles.
  • It is an incredibly robust index allowing the use of multiple satellite data sets and it is capable of overcoming instrument degradation.
  • From this index many proxies of solar activity are created such as UV, EUV, and total Irradiance indices. As part of the afore-mentioned CRADA, we are developing an EUV product based on this index
  • Estimates of Past Solar Variability
  • Estimates of the total solar irradiance over the last 150 years are critical in understanding the role of the sun in climate change
  • SEC is proposing to play an active role in addressing the historic variability of the sun. We hope to obtain the Be10 record to use as a proxy for past solar activity.

Estimates of Past Solar Irradiance

Reid, ISSI Proceedings, Bern, 2000

Hoyt and Schatten, 1993 (-5 W/m2)

Lean et al., 1995

Mende, 2000



  • Solar Forcing of Climate:
  • A Mathematical Approach
  • Comparing the global temperature record, the solar record, and the anthropogenic forcing function leads to the conclusion that a significant part of the global warming may be due to increased solar irradiance

Measured Global Temperature Anomalies

Modeled Global Temperature Anomalies

(Solar + Anthropogenic)

Mende 2000


  • The Progression of the Present Solar Cycle
  • The measures of solar activity (sunspots, F10.7, geomagnetic activity) have all been lower than SEC predictions of the solar cycle made in 1996. However, If the present cycle is scaled to cycle 15, there is still room for hope (see Figure).
  • We will examine the various predictions, identify techniques that have provided the best estimates in the past, and continue to make predictions of solar variability

Present Cycle (23) and Cycle 15

Mg II Index as a proxy for the Solar EUV

  • Solar EUV varies by factors of 2 to 10.
  • Solar variability in the EUV drives the ionosphere and thermosphere, producing order-of-magnitude changes in neutral and electron densities.
  • Based on the stability of the NOAA Mg II Index, and the excellent correlation between the Mg II and the SOHO SEM EUV data, we are developing a proxy to the solar EUV flux.
  • By using the Mg II Index as a proxy for the solar EUV flux, the Air Force has reduced its satellite tracking error by 13%.
  • Along with our CRADA partner, we will develop better proxies to the solar EUV flux using the Mg II Index
  • Within the next few years NOAA will launch an Solar EUV instrument on the GOES spacecraft

Global Warming Since 1850

65% Anthropogenic (0.4oC)

35% Solar (0.2oC)

Mende et al., ISSI Proceedings, Bern, 2000

Mende 2000

Total Solar Irradiance:

Better Measurements are Needed

  • 20 years of data from 6 different spacecraft show solar cycle dependence but there are discrepancies in the absolute scales and trends (left plot)
  • Removing trends and combining the data has proved difficult (middle plots).
  • With the launch of NPOESS, NOAA will be responsible for maintaining the total solar irradiance record for the climate community

Joselyn, Private Communication, 2000

88 Year Period in the Solar and Climate Record

  • Future Solar Variability
  • Using time series of the past solar record and the assumption that the sun has internal-oscillation behavior that is periodic, then it should be possible to estimate future solar irradiance and variability.
  • We will continue to monitor the success of various predictions and draw upon new techniques from the research community in an effort to improve our ability to estimate solar irradiance trends and the magnitude of the next solar cycle.
  • These techniques may applicable to solar-induced variability of climate change (see Figure).

Solar Record from


Most Often Cited Analysis


Most often cited Total Irradiances

208 Year Period in the Solar Record

Solar irradiance variability ranges from 0.1% to factors or 10 or more depending on wavelength. There is strong evidence that the past solar output has changed and this change has been responsible for changes in the climate. If the sun is cyclic in nature, it may be possible to forecast future solar irradiance changes. NOAA has been measuring solar irradiance in the x-ray and UV parts of the spectrum, NOAA will make measurements of the EUV and Visible parts of the Spectrum. NOAA SEC, along with NGDC, will become the repository and distributor of the NOAA Solar Irradiance Data

Mende 2000

Mende, Private Communication, 2000

Fröhlich and Lean, GRL, 25, Dec. 1998