Résumé
The tachocline</u> region inside the Sun, where the rigidly rotating radiative core meets the differentially rotating convection zone, is thought to be crucial for generating the Sun's magnetic field. Low-mass fully convective stars do not possess a tachocline</u> and were originally expected to generate only weak small-scale magnetic fields. Observations, however, have painted a different picture of magnetism in rapidly-rotating fully convective stars: (1) Zeeman</u> broadening measurements revealed average surface field of several kiloGauss</u> (kG</u>), which is similar to the typical field strength found in sunspots. (2) Zeeman</u>-Doppler-Imaging (ZDI</u>) technique discovered large-scale magnetic fields with a morphology often similar to the Earth's dipole-dominated field. (3) Comparison of Zeeman</u> broadening and ZDI</u> results showed that more than 80% of the magnetic flux resides at small scales. So far, theoretical and computer simulation efforts have not been able to reproduce these features simultaneously. Here we present a self-consistent global model of magnetic field generation in low-mass fully convective stars. A distributed dynamo working in the model spontaneously produces a dipole-dominated surface magnetic field of the observed strength. The interaction of this field with the turbulent convection in outer layers shreds it, producing small-scale fields that carry most of the magnetic flux. The ZDI</u> technique applied to synthetic spectropolarimetric</u> data based on our model recovers most of the large-scale field. Our model simultaneously reproduces the morphology and magnitude of the large-scale field as well as the magnitude of the small-scale field observed on low-mass fully convective stars.