First Map of Coherent Low Frequency Continuum Radiation in the Sky
Abstract
Lightning discharges and radio transmitters emit low-frequency ( 3-300 kHz} electromagnetic waves with large electric field strengths and stable phases. This phase stability makes it possible to map the source locations of lightning and transmitters in the sky. Sprite streamers emit electromagnetic waves with much smaller electric field strengths caused by an exponential streamer growth and subsequent branching. These electromagnetic waves generally exhibit a reduced phase stability and blend into an underlying continuum radiation trapped inside the Earth-ionosphere cavity. It is therefore currently not known whether the source locations of low frequency continuum radiation can be determined. Here we show the first map of coherent continuum radiation in the sky above an array of high precision radio receivers. Source locations of coherent continuum radiation are found at elevation angles 30-60 deg above the horizon. The identified source locations are attributed to intermittent distant radio transmitters which emit electromagnetic waves with electric field strengths 2 orders of magnitude below the instrumental noise floor. The results demonstrate that it is possible to simultaneously map the signals from coherent continuum radiation, lightning discharges, and radio transmitters in the sky. This work thereby lays the foundation toward the discovery of many more coherent source locations of low frequency electromagnetic waves in the sky, such as sprite streamers. It is expected that the detected source locations vary with time as a result of the impact of solar variability on the D-region ionosphere. Future studies have therefore the potential to contribute to an advanced remote sensing of sprite streamers and an improved understanding of the D-region ionosphere, influenced by the near-Earth space environment.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMAE21A..07F
- Keywords:
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- 3304 Atmospheric electricity;
- ATMOSPHERIC PROCESSESDE: 3324 Lightning;
- ATMOSPHERIC PROCESSESDE: 3394 Instruments and techniques;
- ATMOSPHERIC PROCESSES