Thursday, September 15, 2011

New paper shows yet another way the Sun controls climate - via ocean oscillations

A paper recently published in the Journal of Geophysical Research finds a strong positive relationship between solar activity and the North Atlantic Oscillation (NAO) over the past 30 years of the 20th century. The study finds a lagged relationship with changes in solar activity followed by changes in the trend of the NAO a few years later. The NAO in turn has profound effects upon the climate of the Northern Hemisphere, including Arctic sea ice. The IPCC dismisses the role of the Sun on climate by only looking at a single variable - the Total Solar Irradiance (TSI), while ignoring large changes in solar UV and secondary effects such as on cloud formation and ocean oscillations.

Graph (a) is the North Atlantic Oscillation (NAO), smoothed version to right. Graph (b) is the Solar Activity aa index, smoothed version to right. Note the significant increase in solar activity over the 20th century.
Key Points
  • The nonlinear relationship between the geomagnetic aa index and the winter NAO
  • Multidecadal variation of solar activity and trend changes in the winter NAO
  • The aa-NAO relationship is in the declining phase of even-numbered solar cycles
Yun Li
CSIRO Climate Adaptation Flagship, CSIRO Mathematics, Informatics and Statistics, Wembley, Western Australia, Australia
Hua Lu
British Antarctic Survey, Cambridge, UK
Martin J. Jarvis
British Antarctic Survey, Cambridge, UK
Mark A. Clilverd
British Antarctic Survey, Cambridge, UK
Bryson Bates
CSIRO Climate Adaptation Flagship, CSIRO Marine and Atmospheric Research, Wembley, Western Australia, Australia
The relationship between the geomagnetic aa index and the winter North Atlantic Oscillation (NAO) has previously been found to be nonstationary, being weakly negative during the early 20th century and significantly positive since the 1970s. The study reported here applies a statistical method called the generalized additive modeling (GAM) to elucidate the underlying physical reasons. We find that the relationship between aa index and the NAO during the Northern Hemispheric winter is generally nonlinear and can be described by a concave shape with a negative relation for small to medium aa and a positive relation for medium to large aa. The nonstationary character of the aa-NAO relationship may be ascribed to two factors. First, it is modulated by the multidecadal variation of solar activity. This solar modulation is indicated by significant change points of the trends of solar indices around the beginning of solar cycle 14, 20, and 22 (i.e., ∼1902/1903, ∼1962/1963, and ∼1995/1996). Coherent changes of the trend in the winter time NAO followed the solar trend changes a few years later. Second, the aa-NAO relationship is dominated by the aa data from the declining phase of even-numbered solar cycles, implying that the 27 day recurrent solar wind streams may be responsible for the observed aa-NAO relationship. It is possible that an increase of long-duration recurrent solar wind streams from high-latitude coronal holes during solar cycles 20 and 22 may partially account for the significant positive aa-NAO relationship during the last 30 years of the 20th century.

Related: The Medieval Climate Anomaly and NAO






    another paper linking solar activity and NAO

  5. NAO linked to cloud variability