Richard Mackey “The suns role in regulating the Earth’s climate”
Here are some notes about the lunar nodal cycle. I’ve extracted them from my paper, “The Sun’s role in regulating the Earth’s climate” published recently in the Journal of Energy and Environment paper (VOLUME 20 No. 1 2009).
By way of introduction, here is the Abstract of my paper:
This paper introduces this thesis:
The Sun-Earth system is electromagnetically, magneto-hydrodynamically and gravitationally coupled, dominated by significant non-linear, non-stationary interactions, which vary over time and throughout the three-dimensional structure of the Earth, its atmosphere and oceans. The essential elements of the Sun-Earth system are the solar dynamo, the heliosphere, the lunisolar tides, the Earth’s inner and outer cores, mantle, crust, magnetosphere, oceans and atmosphere. The Sun-Earth system is non-ergodic (i.e. characterised by continuous change, complexity, disorder, improbability, spontaneity, connectivity and the unexpected). Climate dynamics, therefore, are non-ergodic, with highly variable climatological features at any one time.
A theoretical framework for considering the role of the Sun in relation to the Earth’s climate dynamics is outlined and ways in which the Sun affects climate reviewed. The forcing sources (independent variables) that influence climate processes (dependent variables) are analysed. This theoretical framework shows clearly the interaction effects between and amongst the two classes of variables. These seem to have the greatest effect on climate dynamics.
Climate processes are interconnected and oscillating, yielding variable periodicities. Solar processes, especially when interacting, amplify or dampen these periodicities producing distinctive climatic cycles. As solar and climate processes are non-linear, non-stationary and non-ergodic, appropriate analytic methodologies are necessary to reveal satisfactorily solar/climate relationships.
In this context, the Lunar Nodal Cycle is but one of the solar variables (arising from the Sun’s gravitational field) that has to be understood in order to understand fully the many ways by which the Sun regulates the climate of the Earth.
The lunar nodal cycle and climate.
The 18.6 year lunar nodal cycle (LNC) tidal periodicity has a pervasive role in climate change. It is the period of a full rotation of the Moon’s orbital plane around the ecliptic, the geometric plane of the Earth’s orbit around the Sun. It is the clearest tidal signal in the thousands of time series analysed.
The LNC encodes information about the Moon, Earth, Sun geometry that relates to tidal extremes, at least at high latitudes. It defines how the angle of the Moon’s orbit to the Earth’s equatorial plane combines with, or partially cancels out, the tilt in the Earth’s axis. From the perspective of an observer on the Earth, during the LNC the Moon moves along a northern latitude about ten degrees from a position about 18.5 degrees north of the equator to one that is 28.5 degrees, which it reaches after 18.6 years.
The regular sequence of eclipses is a result of the regular, highly predictable rotation of the plane of the Moon’s orbit round the Earth. It has been known since ancient times that eclipses occurred in regular predictable cycles of a little more than 18 years. This period is known as the Saros cycle.
Mazzarella and Palumba (1994) point out that bistable modes of oscillation with respect to time are well known in physical and engineering systems and have been extensively studied. This research from Physics and Engineering demonstrates that a sinusoidal force applied to any dynamic system induces sinusoidal periodicities in the system. Accordingly, the LNC induces bistable sinusoidal periodicities in the atmosphere (pressure, temperature and rainfall) and the ocean (temperature and sea level). The sinusoidal, highly stable 18.6 year LNC has a distinctive and significant effect on the Earth’s climate dynamics.
The elongated tidal bulge necessarily continues to be aligned with the Moon as Figure 2 shows. The bulge moves to the northern (and southern) latitudes as the Moon moves northwards because of the LNC, being the furthest north it can get to at the 18.6 yr point. This last happened on September 16, 2006. Even though the amplitude of the LNC is at most 5 cm, a small tide over a long period has great power. The ocean currents generated by the northward movement of the tidal bulge, in conjunction with the rotation of the Earth through the bulges in the normal manner creating our experience of the tides, brings warmish equatorial water to the Arctic accelerating the warming that had being going on there because of other forms of solar activity as discussed below.
The LNC has maximum effect at higher latitudes, resulting in higher sea levels at these latitudes. It creates tidal currents resulting in diapycnal mixing, bringing the warmer equatorial waters into the Arctic. The LNC is therefore a major determinant of Arctic climate dynamics, influencing long term fluctuations in Arctic ice. As a result, it is a key driver of European climate. Da Silva and Avissar (2005) showed that LNC is unambiguously correlated with the Arctic Oscillation since the 1960s. The authors explain how the LNC tidal forces contribute significantly to the regulation of the Arctic Oscillation, which is a major driver of climate variability in the Northern Hemisphere.
Complex interaction effects between the lunar nodal cycle other solar variables and climate.
The joint effects of the LNC and other solar variables illustrate that solar variables may interact to produce significant climate events, in this case the melting of the ice in the Arctic and higher sea surface temperatures at northern latitudes. In 2006 the LNC jointly with other solar activity during the preceding ten years provide an adequate explanation for the observed recent Arctic warming.
1. Camp and Tung (2007c) established for the first time as statistically significant that the warm ENSO (i.e. El Niño) warms the Arctic. Moderate to very strong El Niño events occurred in the following years since 1972: 1972/3; 1977/78; 1982/83; 1986/88; 1991/92; 1993/94; 1994/95; 1997/98; 2002/03; and 2004/05. The El Niño event which began in early 1997 and continued for about one year was one of the strongest ever recorded, both in terms of sea surface temperatures in the eastern tropical Pacific and atmospheric circulation anomalies reflected in the Southern Oscillation Index. The last El Niño event started in September 2006 and lasted until early 2007, occurring at precisely the same time as the peak of the LNC..
2. Camp and Tung (2007a and 2007b) also revealed the surface pattern of warming caused by the Sun. Amongst other things, polar amplification is shown clearly with the largest warming in the Arctic (treble that of the global mean), followed by that of the Antarctic (double). Surprisingly, the warming over the polar region occurs during late winter and spring.
3. Camp and Tung (2006) found that there is a significant relationship between polar warming and the sunspot cycle.
4. Soon (2005) showed a statistically significant relationship between solar radiance and Arctic-wide surface air temperatures. Solar Cycle 23 peaked during 2000/01, having been preceded by the unusually strong 1997/98 El Niño.
5. Shirochkov et al (2000) report that the extent of Arctic sea ice is largely a function of solar variability. The extent of Arctic sea ice varies directly with all measureable indices of variable solar activity. Specifically, solar wind plays a notable role in the variation of the extent of Arctic sea ice.
6. The ice-albedo (i.e. reflectance) effect will amplify the increased melting of the sea ice resulting from the interaction of El Niño, solar irradiance and the LNC on the Arctic. The increased expanse of ocean warms further as it absorbs more solar irradiance. This will lead to more warming and more sea ice will melt. So the process would continue unless something intervened. Recent observations show Da Silva and Avissar (2005) showed that the LNC accelerates this warming processes. These processes enable a larger volume of liquid water to respond to the tidal forces. In addition, the changes in ocean stratification that follow improve the mixing efficiency.
Since the Moon’s orbit is elliptical, there is a point when the Moon is closest to the Earth (the perigee) and a point where it is furthest (apogee). It is to be noted that the perigee (and therefore the apogee) is not constant. Both vary, largely because of the perturbing effect of the Sun. There is a 40 percent difference between the lunar tidal forces at the perigee and the apogee of the Moon’s orbit. The Moon moves faster at the perigee, and slower at the apogee. This means that tidal currents quicken as the Moon approaches the perigee of its orbit. They are slower at apogee. The Arctic Oscillation (AO) is regulated by the solar cycle in a non-linear manner. Heightened and weakened solar activity activates the large Rossby and Kelvin waves. The effects of these waves on atmospheric circulation are intensified by the creation of Ozone during times of increased solar activity. The AO is stronger with more zonal circulation over mid-latitudes, especially in the European-North Atlantic sector, and more variable during the peak of the solar cycle.
The AO is also regulated by the peak 9.3 year and 18.6 year LNC tidal oscillations. The processes by which the effect occurs are different from those of variable solar activity. The tidal oscillation impacts on atmospheric circulation and on the large Rossby and Kelvin waves. It also impacts on the churning of the oceans. Nevertheless, the two solar processes interact amplifying each other’s contribution. The AO has a key role in Northern Hemisphere climate variability and its behaviour is largely the result of the interaction of the solar cycle and the 9.3 and 18.6 year LNC tidal oscillations. Berger (2007) found that solar modulation of the NAO is amplified by tidal cycles. He found that there is non-linear resonance between solar cycles and tidal cycles, especially the LNC and the perigean tidal cycle the effect of which is to amplify solar modulation of the NAO.
Berger, W. H., 2007. Solar modulation of the North Atlantic Oscillation: Assisted by the tides? Quaternary International, 188, 24-30; doi:10.1016/j.quaint.2007.06.028.
Camp, C. D., and Tung, Ka-Kit, 2006. The Influence of the Solar Cycle and QBO on the Late Winter Stratosphereic Polar Vortex. Journal of Atmospheric Sciences in press.
Camp, C. D., and Tung, Ka-Kit, 2007a. Surface warming by the solar cycle as revealed by the composite mean difference projection, Geophysical Research Letters Vol. 34, L14703, doi:10.1029/2007GL030207..
Camp, C. D., and Tung, Ka-Kit, 2007b. Solar Cycle Warming at the Earth’s Surface and an Observational Determination of Climate Sensitivity, submitted to the Journal of Geophysical Research, and published by the University of Washington on Ka Kit Tung’s departmental website,
Camp, C. D., and Tung, Ka-Kit, 2007c. Stratospheric polar warming by ENSO in winter: a statistical study, Geophysical Research Letters Vol. 34, L14809, doi:10.1029/2006GL03028521..
Da Silva, R. R., and Avissar, R., 2006. The impacts of the Luni-Solar Oscillation on the Artic Oscillation. Geophysical Research Letters 32, L22703, doi:10.1029/2005GL023418,2005.
Goldreich, Peter, 1972. Tides and the Earth-Moon System, Scientific American, 226, 4, pps 42-52.
McCully, J. G., 2006. BEYOND THE MOON A Conversational, Common Sense Guide to Understanding the Tides. World Scientific, Singapore.
Mazzarela, A. and Palumbo, A., 1994. The Lunar Nodal Induced-Signal in Climatic and Ocean Data over the Western Mediterranean Area and on its Bistable Phasing, Theoretical and Applied Climatology 50, 93-102.
Shirochkov, A. V., Makarova, L .N. and Volobuev, D. M., 2000. The arctic sea ice extent as a function of solar variability, presentation to the first conference of S-RAMP (Solar- Terrestrial Energy Program, 1990-1997 Results, Applications and Modeling Phase; A fiveyear (1998-2002) effort to optimize the analysis of data obtained during the Solar-Terrestrial Energy Program, 1990-1997). The conference was held at Sapporo, Japan, October 2-6, 2000. See http://www.kurasc.kyoto-u.ac.jp/s-ramp/abstract/s18.txt
Soon, W. W.-H., 2005. Variable solar irradiance as a plausible agent for multidecadal variations in the Arctic-wide surface air temperature for the past 130 years, Geophysical Research Letters, 32, L16712, doi:10.1029/2005GL023429.
NOTE: THE JPG IMAGES FOR FIGS 1 & 2 WON”T COPY
Figure 1 follows:
Figure 1. The Lunar Nodal Cycle
The diagram is adapted from Goldreich (1972), page 49
The Sun’s gravitational field makes the Moon’s Earthly orbit swivel around in a clockwise manner, over a cycle of 18.6 years, with respect to the plane of the Earth’s orbit, the ecliptic. The Moon moves with respect to the ecliptic up and down a northerly latitude throughout the LNC. This arises because the Earth is titled on it axis and inclined away from the Sun and because the Moon’s orbit is tilted a little relative to the ecliptic, It is as if the Sun strives to pull the plane of the Moon’s orbit into its own plane, the ecliptic. But there is an alternate motion at right angles to the applied force, resulting in a revolution of the pole of the Moon’s orbit around the pole of the ecliptic.
Figure 2. Alignment of the tidal bulge (greatly exaggerated) with the Moon during the LNC
The diagram is adapted from McCully (2006), Illustration 3-3, page 33 As the Moon moves in a northerly direction during the LNC, approaching a maximum of 28.5O, so does the tidal bulge.
Here is the Abstract of a relevant paper only just published. The paper is:
Yasuda, Ichiro (2009) “The 18.6-year period moon-tidal cycle in Pacific Decadal Oscillation reconstructed from tree-rings in western North America”, GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L05605, doi:10.1029/2008GL036880, 2009.
The Abstract reads:
Time-series of Pacific Decadal Oscillation (PDO) reconstructed from tree-rings in Western North America is found to have a statistically significant periodicity of 18.6- year period lunar nodal tidal cycle; negative (positive) PDO tends to occur in the period of strong (weak) diurnal tide. In the 3rd and 5th (10th, 11th and 13rd) year after the maximum diurnal tide, mean-PDO takes significant negative (positive) value, suggesting that the Aleutian Low is weak (strong), western-central North Pacific in 30 50_N is warm (cool) and equator-eastern rim of the Pacific is cool (warm). This contributes to climate predictability with a time-table from the astronomical tidal cycle.