Ionospheric ULF oscillations driven from above Arecibo

Abstract

Understanding the coupling between the surface of the sun, the solar corona, the solar wind, the Earth's magnetosphere and ionosphere is a major focus of today's space research. Over 20 years ago, detailed observations of the ionospheric electron density at Arecibo revealed short period fluctuations (3 minutes), but their cause was never determined. Also, in the past 20 years a number of papers have reported observations of discrete (1–5 mHz) waves at persistent “magic frequencies” in magnetometer data and radar observations of ionospheric drift. Such observations have been generally interpreted as standing waves excited by magnetospheric cavity compressional modes. This assertion has been recently challenged by suggestions that these magic frequencies are not standing waves, but are due to inherent oscillations in the solar wind. Here we show that a subset of discrete 1.7 mHz oscillations in the solar wind plasma density are likely transmitted via a passive magnetospheric oscillation, and are observed as small amplitude (0.1%), discrete 1.7 mHz oscillations in the ionospheric plasma line using the extremely sensitive ionospheric measurements over Arecibo, Puerto Rico. We present over three hours of data using the electron plasma line component of the Arecibo radar incoherent scatter radar spectrum, solar wind number density from the WIND satellite, and magnetic field from the GOES satellite. This paper demonstrates a link between the solar wind and low latitude ionosphere.