Visualizing sporadic E using aeronautical navigation signals at VHF frequencies

Keisuke Hosokawa,Ichiro Tomizawa,Mamoru Ishii,Michi Nishioka,Jun Sakai,Takuya Tsugawa,Susumu Saito,Kotaku Kimura

doi:10.1051/swsc/2020075

Abstract

To understand the dynamical properties of sporadic E layer (Es), we have developed a method to visualize the two-dimensional spatial structure of Es by monitoring the occurrence of anomalous propagation of VHF waves used for aeronautical navigation systems in combination with the electron density disturbance index ROTI, that is the Rate of total electron content (TEC) Index obtained from ground-based GPS receivers. We introduce a case of strong Es layer which occurred for ~4 h during daytime of July 4, 2019. In this interval, we succeeded in imaging the structure of Es elongating more in the east–west direction and moving northward gradually. This result indicates that the combination of network observations of aeronautical navigation signals and ROTI is capable of imaging the 2D structure of Es in a wide area including the sea surface, which enables us to discuss the dynamical characteristics and generation mechanism of Es.

Highlights

The sporadic E layer (Es) has been known as one of the outstanding phenomena in the E region ionosphere
We introduce a 2D mapping method of Es that combines the observation of Es anomalous propagation (EsAP) of VHF NAV signals with the rate of total electron content (TEC) index (ROTI) from ground-based GPS receivers
The receiver in Oarai detected the signature of EsAP in 49 channels when the ionosonde at Kokubunji observed an increase of frequencies of Es trace (foEs)

Summary

Introduction

The sporadic E layer (Es) has been known as one of the outstanding phenomena in the E region ionosphere. During intervals of Es, the electron density at an altitude of 100 km is extremely enhanced, often exceeding the maximum electron density in the F region (Whitehead, 1989; Mathews, 1998; Haldoupis, 2011). At mid-latitudes, Es generally appears in summer months with two occurrence peaks in the daytime and nighttime, respectively (i.e., semi-diurnal variation in its local time distribution). An increase of the critical frequency due to Es has a potential to cause reflection of radio waves of oblique incidence at frequencies up to 150 MHz (Davis et al, 1959). The effects of Es on analogue television and FM radio in such a frequency range have been well-known for a long time. They statistically showed that Es anomalous propagation (EsAP) of NAV

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