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In this lengthy letter, we wanted to discuss the concept of climate based on definitions established for over a century and direct observations that we have been collecting for more than a century as well. To do this, we present and discuss the remarkably stable maps over time of the various physical parameters that make up the climate corpus: solar temperature, atmospheric pressure, winds, precipitation, temperature anomalies. This impressionistic tableau that we are gradually sketching as our reflection unfolds leads us to the following proposition: What if, as Laplace first proposed in 1799 and later Milankovi\{'}c in 1920, ground temperature were merely a consequence of climate and not a separate parameter of climate in its own right?, Comment: 24 pages, 11 Figures

In his mathematical theory, Milankovic finds a link between the heat received by the Earth surface per unit time as a function of the solar ephemerids and derives a model of climate changes at periods longer than a few thousand years and more. In this paper, we investigate the potential connections of global temperature and Earth rotation at much shorter periods, in the complementary range of one to a few hundred years. For temperature, we select the HadCrut05. For Earth rotation, defined by pole coordinates and length of day, we use the IERS data sets. Using iterative Singular Spectrum Analysis (iSSA), we extract the trend and quasi-periodic components of these time series. The first quasi-periodic components (period ~80-90 years) are expressions of the Gleissberg cycle and are identical (at the level of uncertainty of the data). Taken together, the trend and Gleissberg components allow one to reconstruct 87% of the variance of the data for lod and 48% for temperature. The next four iSSA components, with periods ~40, 22, 15 and 9 years. The Lagrange and Laplace theories imply that the derivative of pole motion should be identical to lod variations: this strong check is passed by the trend + Gleissberg reconstructions. The annual oscillations of pole motion and lod are linked to annual variations in Sun-Earth distance, in agreement with an astronomical, but not a climatic origin. The results obtained in this paper for the observed temperature/rotation couple add to the growing list of evidence of solar and planetary forcings of gravitational nature on a number of geophysical processes (including sea-level, sea-level pressure, sea-ice extent, oceanic climate indices)., Comment: 16 pages, 13 figures

In the report he submitted to the Acad\'emie des Sciences, Poisson imagined a set of concentric spheres at the origin of the Earth's magnetic field. It may come as a surprise to many that Poisson as well as Gauss both considered the magnetic field to be constant. We propose in this study to test this surprising assertion for the first time evoked by Poisson (1826). First, we will present a development of Maxwell's equations in the framework of a static electric field and a static magnetic field in order to draw the necessary consequences for the Poisson hypothesis. In a second step, we will see if the observations can be in agreement with Poisson (1826). To do so, we have chosen to compare 1) the polar motion drift and the secular variation of the Earth's magnetic field, 2) the seasonal pseudo-cycles of day length together with those of the sea level recorded by different tide gauges around the globe and those of the Earth's magnetic field recorded in different magnetic observatories. We then propose a mechanism, in the spirit of Poisson, to explain the presence of the 11-year in the magnetic field. We test this mechanism with observations and finally we study closely the evolution of the g10 coefficient of the IGFR over time.

Earth rotation is determined by polar motion (PM) and length of day (lod). The excitation sources of PM are torques linked to fluid circulations ("geophysical excitations"), and those of lod to luni-solar tides ("astronomical excitations"). We explore the links between the rotations and revolutions of planets, following Lagrange's (1853) presentation of mechanics. The energy of a planet in motion in a central field is the sum of kinetic, centrifugal (planet dependent) and centripetal (identical for all planets) energies. For each planet, one can calculate a "constant of gravitation" Gp . For the giant planets, Gp decreases as a function of aphelia. There is no such organized behavior for the terrestrial planets. The perturbing potential of other planets generates a small angular contribution to the displacement : this happens to be identical to Einstein's famous formula for precession. Delays in the planet's perihelia follow a (-5/2) power law of a. This is readily understood in the Lagrange formalism (the centrifugal term takes over for small distances). The telluric planets have lost energy, probably transferred to the planets rotations. The ratio of areal velocities to rotation obeys a -5/2 power law of a. The ratio of areal velocity to integrated period R also fits a -5/2 power dependence, implying linearity of the energy exchange between revolution and rotation. For Einstein deformation of space-time by the Sun is the origin of the field perturbation. For Lagrange the perturbation could only be due to the interactions of torques. The perihelion delays, the areal velocities and the planetary rotations display power laws of aphelia, whose behavior contrasts with that of the kinetic moment. The areal velocity being linearly linked to the kinetic moment of planets, this must be the level at which the transfer is achieved.

The Earth's revolution is modified by changes in inclination of its rotation axis. Despite the fact that the gravity field is central, the Earth's trajectory is not closed and the equinoxes drift. Milankovic (1920) argued that the shortest precession period of solstices is 20,7kyr: the Summer solstice in one hemisphere takes place alternately every 11kyr at perihelion and at aphelion. We have submitted the time series for the Earth's pole of rotation, global mean surface temperature and ephemeris to iterative Singular Spectrum Analysis. iSSA extracts from each a trend, a 1yr and a 60yr component. Both the apparent drift of solstices of Earth around the Sun and the global mean temperature exhibit a strong 60yr oscillation. The "fixed dates" of solstices actually drift. Comparing the time evolution of the Winter and Summer solstices positions of the rotation pole and the first iSSA component (trend) of the temperature allows one to recognize some common features. A basic equation from Milankovic links the derivative of heat received at a given location on Earth to solar insolation, known functions of the location coordinates, solar declination and hour angle, with an inverse square dependence on the Sun-Earth distance. We have translated the drift of solstices as a function of distance to the Sun into the geometrical insolation theory of Milankovic. Shifting the inverse square of the 60yr iSSA drift of solstices by 15 years with respect to the first derivative of the 60yr iSSA trend of temperature, that is exactly a quadrature in time, puts the two curves in quasi-exact superimposition. The probability of a chance coincidence appears very low. Correlation does not imply causality when there is no accompanying model. Here Milankovic's equation can be considered as a model that is widely accepted. This paper identifies a case of agreement between observations and a mathematical formulation.

This paper proposes a joint analysis of variations of global sea-level pressure and of Earth's rotation (RP), expressed as the coordinates of the rotation pole and length of day. Sea-Level-Pressure (SLP) extracted components are a weak trend, eleven quasi-periodic or periodic components ($\sim$130, 90, 50, 22, 15, 4, 1.8 yr), an annual cycle and its first three harmonics. These periods are characteristic of the space-time evolution of the Earth's rotation axis and are present in many characteristic features of solar and terrestrial physics. We focus mainly on the annual and to a lesser extent semi-annual components. Maps of the first three components of SLP (that together comprise more than 85% of the data variance) reveal interesting symmetries. The trend is very stable and forms a triskel structure that can be modeled as Taylor-Couette flow of mode 3. The annual component is characterized by a large negative anomaly extending over Eurasia in the NH Summer (and the opposite in the NH Winter) and three large positive anomalies over Australia and the southern tips of South America and South Africa in the SH Spring (and the opposite in the SH Autumn) forming a triskel. The semi-annual component is characterized by three positive anomalies (an irregular triskel) in the NH Spring and Autumn (and the opposite in the NH Summer and Winter), and in the SH Spring and Autumn by a strong stable pattern consisting of three large negative anomalies forming a clear triskel within the 40$^{\circ}$-60$^{\circ}$ annulus formed by the southern oceans. A large positive anomaly centered over Antarctica, with its maximum displaced toward Australia, and a smaller one centered over Southern Africa complement the pattern.

The time series of northern hemisphere (NHSI) and southern hemisphere (SHSI) sea-ice extent are submitted to singular spectral analysis (SSA). The components are analyzed with Laplace's formulation of the Liouville-Euler system. As already shown in a previous work, the trends observed in the time series are quasi linear, decreasing for NHSI and increasing for SHSI. The amplitude of annual variations in the Antarctic is double that in the Arctic, they are in phase opposition, modulated. The semi-annual components are in quadrature. The first 3 components of both NHSI and SHSI at 1, 1/2 and 1/3 yr account for more than 95% of the signal variance. We complement previous analyses of variations in pole position (PM = m1, m2) and length of day (lod). Whereas SSA of lod is dominated by the same first 3 components as sea-ice, SSA of PM contains only the 1 yr and the Chandler components. The 1 yr component of NHSI is in phase with that of lod and in phase opposition with m1. The reverse holds for the 1 yr component of SHSI. We note that the semi-annual component appears in lod not in m1. The annual and semi-annual components of NHSI and SHSI are much larger than the trends observed since 1978, that leads us to test whether a first order geophysical or astronomical forcing should not be preferred to the mechanisms generally suggested as a forcing factor of the trends. The lack of modulation of the largest forced component suggests an alternate mechanism. In Laplace's paradigm, the torques exerted by the Moon, Sun and planets play the leading role as the source of forcing of many geophysical phenomena. These forces lead to changes in the inclination of the Earth's rotation axis, setting Earth masses in motion and resulting in thermal dissipation. It is variations in inclination of the rotation axis that lead to the large annual components of melting and re-freezing of sea-ice.

Variations in sea-level, based on tide gauge data (GSLTG) and on combining tide gauges and satellite data (GSLl) are subjected to singular spectrum analysis (SSA), to determine their trends and periodic or quasi-periodic components. GLSTG increases by 90 mm from 1860 to 2020, a contribution of 0.56 mm/yr to the mean rise rate. Annual to multi-decadal periods of ~90/80, 60, 30, 20, 10/11, and 4/5 years are found in both GSLTG and GSLl. These periods are commensurable periods of the Jovian planets, combinations of the periods of Neptune (165 yr), Uranus (84 yr), Saturn (29 yr) and Jupiter (12 yr). These same periods are encountered in sea-level changes, motion of the rotation pole RP and evolution of global pressure GP, suggesting physical links. The first SSA components comprise most of the signal variance: 95% for GSLTG, 89% for GSLI, 98% for GP, 75% for RP. Laplace derived the Liouville-Euler equations that govern the rotation and translation of the rotation axis of any celestial body. He emphasized that one must consider the orbital kinetic moments of all planets in addition to gravitational attractions and concluded that the Earth's rotation axis should undergo motions that carry the combinations of periods of the Sun, Moon and planets. Almost all the periods found in the SSA components of sea-level (GSLl and GSLTG), global pressure (GP) and polar motion (RP), of their modulations and their derivatives can be associated with the Jovian planets. It would be of interest to search for data series with longer time spans, that could allow one to test whether the trends themselves could be segments of components with still longer periodicities (e.g. 175 yr Jose cycle).

The evolution of mean sea-level atmospheric pressure since 1850 is analyzed using singular spectrum analysis. Maps of the main components (the trends) reveal striking symmetries of order 3 and 4. The northern hemisphere (NH) displays a set of three positive features, forming an almost perfect equilateral triangle. The southern hemisphere (SH) displays a set of three positive features arranged as an isosceles triangle, with a possible fourth (weaker) feature. This geometry can be modeled as Taylor-Couette flow of mode 3 (NH) or 4 (SH). The remarkable regularity and order three symmetry of the NH triskel occurs despite the lack of cylindrical symmetry of the northern continents. The stronger intensity and larger size of features in the SH is linked to the presence of the annular AAO. In addition to the dominant trends, quasi-periodic components of 130, 90, 50, 22, 15, 4, 1.8, 1, 0.5, 0.33, and 0.25 years, i.e. the Jose, Gleissberg, Hale and Schwabe cycles, the annual cycle and its first three harmonics are identified.

Differences in interpretation may arise from differences in formulation of the equations of celestial mechanics. This paper focuses on the Liouville system of differential equations. In a "modern" presentation of the equations, variations in polar motion (PM) and variations in length of day (lod) are decoupled. Their source terms result from redistribution of masses and torques. Elasticity of the Earth, large earthquakes, or external forcing by the fluid envelopes have been successively invoked in the "modern" approach. In the "classical" presentation, PM is governed by the inclination of Earth's rotation pole and the derivative of its declination (close to the derivative of lod). These are coupled by the Liouville system and all "source" terms are astronomical. The "classical" approach also implies that there should be a link between the rotations and the torques exerted by the planets of the solar system. A sufficiently strong source of energy can be found. There is remarkable agreement between the sum of forces exerted by the four Jovian planets and components of Earth's polar motion. Since 1970, lod tends to decrease, but a recent acceleration of rotation velocity, that contradicts previous models, finds a simple explanation with the "classical" formalism. Analysis of lod finds nine components, all with physical sense: first comes a "trend", then pseudo-oscillations with periods 80 yr , 18.6 yr, 11 yr , 1 year and 0.5 yr, 27.54 days, 13.66 days, 13.63 days and 9.13 days. The longer periods, 1 yr, 11 yr, 18.6 yr and 80 yr are common to lod and PM. The Liouville system of equations in the "classical" analysis implies a strong link between the two: the straightening of the inclination of the axis of rotation should accompany a decrease in lod.Also, if this link is valid, all the components with extraterrestrial periods should be present in the series of sunspots and indeed they are.

Atmospheric electric field (AEF) measurements were carried out in three different sites forming a triangular array in Southern Portugal. The campaign was performed during the summer characterized by Saharan dust outbreaks; the 16th-17th July 2014 desert dust event is considered here. Evidence of long-range dust electrification is attributed to the air-Earth electrical current creating a positive space-charge inside of the dust layer. An increase of ~23 V/m is observed in AEF on the day of the dust event corresponding to space-charges of ~20-2 pCm-3 (charge layer thicknesses ~10-100 m). A reduction of AEF is observed after the dust event., Comment: 27 pages, 8 figures, a regular publication

Cosmogenic isotopes provide the only quantitative proxy for analyzing the long-term solar variability over a centennial timescale. While essential progress has been achieved in both measurements and modeling of the cosmogenic proxy, uncertainties still remain in the determination of the geomagnetic dipole moment evolution. Here we improve the reconstruction of solar activity over the past nine millennia using a multi-proxy approach. We used records of the 14C and 10Be cosmogenic isotopes, current numerical models of the isotope production and transport in Earth's atmosphere, and available geomagnetic field reconstructions, including a new reconstruction relying on an updated archeo-/paleointensity database. The obtained series were analyzed using the singular spectrum analysis (SSA) method to study the millennial-scale trends. A new reconstruction of the geomagnetic dipole field moment, GMAG.9k, is built for the last nine millennia. New reconstructions of solar activity covering the last nine millennia, quantified in sunspot numbers, are presented and analyzed. A conservative list of grand minima and maxima is provided. The primary components of the reconstructed solar activity, as determined using the SSA method, are different for the series based on 14C and 10Be. These primary components can only be ascribed to long-term changes in the terrestrial system and not to the Sun. They have been removed from the reconstructed series. In contrast, the secondary SSA components of the reconstructed solar activity are found to be dominated by a common ~2400-yr quasi-periodicity, the so-called Hallstatt cycle, in both the 14C and 10Be based series. This Hallstatt cycle thus appears to be related to solar activity. Finally, we show that the grand minima and maxima occurred intermittently over the studied period, with clustering near highs and lows of the Hallstatt cycle, respectively., Comment: In press in Astronomy & Astrophysics, doi: 10.1051/0004-6361/201527295