## 1 Introduction
### Bottom-Up Lithosphere-Atmosphere-Ionosphere Coupling Interaction Mechanisms
Other bottom-up lithosphere-atmosphere-ionosphere effects based on electromagnetic interactions could be possible, as we represented in the sketch of Figure 2B. For example, the uplift of the magma could open several micro-cracks in the rocks that can create separation of the electrical charges and the following generation of Ultra-Low-Frequency (ULF) electromagnetic waves, as proposed by [PERSON] and [PERSON] for earthquakes [41; 42]. In the case of the volcano, small earthquakes are generated, but they are due to volcanic activity and not tectonic activity. In principle, the same ULF electromagnetic wave theory from microfractures on the rocks can still be considered. The ULF electromagnetic wave can be theoretically recorded both at the Earth's surface with geomagnetic ground observatories (as reported by [PERSON] et al. [43; 44] for Japanese earthquakes) or in the ionosphere by satellites (as reported by [PERSON] et al. [45; 46] before several earthquakes). [PERSON] [47] proposed that variation of electric resistivity in the lithosphere could produce a ring current in the ionosphere for an induction system. His model for earthquakes is constructed in a subduction context, the one where the volcanos are generally localized, in particular on the forearc of the subduction slab. Therefore, this model can also be considered for a possible explanation of pre-volcano phenomena in lithosphere-atmosphere-ionosphere. Due to the \"pure\" electromagnetic interaction mechanism of this second scenario, we do not expect a direct effect in the atmosphere, even if, in principle, the currents can facilitate the accumulation of aerosol (that are easily polarized particles) in clouds. Other possible bottom-up propagation ways could be based on acoustic gravity waves as proposed, for example, by [PERSON] [48], but we do not consider them in this paper. Finally, we would remark that the main two proposed scenarios in Figure 2 are not exclusive, and they could exist at the same time or in different stages of preparation of the eruption, for example, in function of the depth of the magma uplifting movements. Finally, in this paper, multiparametric analysis of lithosphere, atmosphere, and ionosphere before the La Palma volcano eruption of 19 September 2021 is provided in order  
Figure 2: Possible ways of bottom-up lithosphere–atmosphere–ionosphere effects in the contest of La Palma volcano. The drawing is just a sketch of the possible phenomena, and the dimensions are not in scale. Grey lines represent the conceptual interactions chain. Two main scenarios are illustrated: (**A**) the first hypothesis based on the temperature increase and corresponding demagnetization due to the uplift of magma; (**B**) the second hypothesis based on the microfractures or rock resistivity changes produced by the uplift of magma. to extract anomalies in these three geo-layers, providing a brief description of data and methods in Section 2 and the results in Section 3. To the authors' knowledge, this is the first time a comprehensive analysis has been provided for this volcano, and very few examples exist in the literature about other volcano eruptions as the papers often investigated only one or few parameters and not in a multi-layer approach. Our results are discussed in the view of lithosphere-atmosphere-ionosphere bottom-up interactions in Section 4; even if this study does not pretend to demonstrate the geo-layers interactions but only support them by observations and empirical considerations, future studies are vital to address better this point. We provided our conclusions in Section 5 and some Appendixes and Supplementary Materials, with additional details of the investigations and validations of the used datasets.