Longitudinal variation of equatorial ionosphere long-term trends expected from the magnetic equator secular displacement

ELIAS, ANA G.; DURAN, TRINIDAD; MEDINA, FRANCO D.; DE HARO BARBAS, BLAS F.

Simposio; 5th ISEE Symposium: Toward the Future of Space?Earth Environmental Research; 2022

The Earth’s ionosphere at equatorial latitudes depends strongly on solar radiation, thegeomagnetic field, and atmospheric conditions, all of which present variabilities indifferent time scales. In particular, long-term trends have been of interest since thepioneering study in 1989 by Roble and Dickinson, suggesting that the long-termincrease of greenhouse gases concentration would produce a global cooling in theupper atmosphere. Even though anthropogenic forcing seems the main trend driveruntil now, there are also other trend forcings of natural origin, and among them is thesecular variation of the Earth’s magnetic field, which affects not only the electrondensity, but ionospheric conductivity and currents, and radio wave propagation, amongothers. The present field can be approximated by a geocentric magnetic dipole with itsaxis tilted ~11° with respect to Earth’s rotational axis. This dipole, which accounts for~80% of the magnetic field power at the Earth’s surface, has been rapidly decreasingduring the last decades. In fact, the intrinsic Earth’s magnetic field has been decayingat a rate of ~5% per century since at least 1840. This has led to thinking of anundergoing reversal or excursion even though there is also the possibility of a recoverywithout the occurrence of an extreme event. In any case, the intensity of the globalfield will continue to decrease in the near future with its consequent changes in theionosphere dynamics and the weakening of our planet’s magnetic shield, among othereffects. For space weather events, for example, the main impacts are expected fromthe rapid decay of the dipole field and the expansion of the South Atlantic Anomaly. Inthe equatorial ionosphere case, the shift in the magnetic equator may be of greaterimportance, and this is linked not to the dipole field decay, but to the dipolar axisorientation and its center position variation, together with the growth of multipolarcomponents. These may induce more noticeable and significant changes through theireffect over the magnetic equator. In this work, the consequent spatial pattern of trendsnoticed in several ionospheric features at equatorial latitudes, consisting of alternatingbands of positive and negative values, with strong longitudinal gradients are analyzedbased on a theoretical analysis. The geomagnetic field secular variation, through theeffects induced by its equator displacement, may be currently the dominant trendsource in the Atlantic region ionosphere.P71