Spatial and temporal long-term trends in HF propagation paths expected from Earth?s magnetic field variations

MARIANO FAGRE; ZENÓN SAAVEDRA; ANA G. ELIAS; YIGIT, ERDAL; BRUNO S. ZOSSI; KILCIK, ALI

Hefei

Workshop; 10th Workshop on Long-Term Changes and Trends in the Atmosphere; 2018

University of Science and Technology of China

The ionosphere is an anisotropic and dispersive medium for the propagation of HF radio waves due to the presence of an intrinsic magnetic field and free charges. Ray tracing is a powerful and useful tool that allows determining the exact path of radio waves but requires a precise knowledge of ionospheric conditions along the propagation path. The detailed physics of electromagnetic wave propagation through plasmas is even more complex when there is an external magnetic field, as is the case of the ionosphere embedded in Earth?s magnetic field. Even though for many purposes this field can be neglected, the effects on waves which propagate and reflect in the ionosphere, like ground range and reflection height, are detectable and depend not only on the field intensity, but also on the angle between the ray and field vector. Taking into account that Earth?s magnetic field varies greatly, with the most drastic change being a polarity reversal, in the present work the spatial and temporal variation of the ground range and reflection height are analyzed in terms of the geomagnetic field using a numerical ray tracing algorithm, considering two possible scenarios: a 50% decrease of the dipolar component while keeping constant the multipolar field contribution, and a purely multipolar field. In addition to the changes observed in the ground range and reflection height, interesting effects such as the ?spitze? and phase paths modifications are analyzed. In general, studying long-term trends is a challenging scientific endeavor. It is predicted that Earth?s magnetic field variations will become more noticeable in the future due to the drastic changes expected during the next reversal. It is thus necessary to systematically study various aspects of the geomagnetic field variations and the associated impact in the ionosphere.