Abstract
The Low Frequency Array (LOFAR) is designed to observe the early universe at radio wavelengths. When radio waves from a distance astronomical source traverse the ionosphere, structures in this plasma affect this signal. Refraction depends upon the local refractive index, which varies with plasma density, leading to strong lensing effects. Interference of the scattered radio waves can result in a diffraction pattern, with ionospheric structures acting as a diffraction screen. The high temporal resolution available (~tens of ms), the large range of frequencies observed (10-80 MHz & 120-240 MHz) and the large number of receiving stations (currently 52 across Europe) mean that LOFAR can observe the effects of the midlatitude ionosphere in a level of detail never seen before.
On the 14th July 2018 LOFAR stations across the Netherlands observed Cygnus A between 17:00 UT and 18:00 UT. At approximately 17:30 UT a deep fade in the intensity of the received signal was observed, lasting some 15 minutes. Immediately before and after this deep fade rapid variations of signal strength were observed, lasting less than five minutes. Frequency dependent behaviour was observed, with an earlier onset and later ending of this effect at lower frequencies. Both the deep fade and the surrounding intensity variations are attributed to the effect of a structure in the ionosphere. The time at which these effects were observed and the nature of the structuring varied between station, with the structure moved in a north-westerly direction and evolving as it travelled. The geomagnetic conditions at the time of the observation were quiet, as were the solar conditions. It is suggested that this structure is driven by variations within the neutral atmosphere and possible sources are discussed.
On the 14th July 2018 LOFAR stations across the Netherlands observed Cygnus A between 17:00 UT and 18:00 UT. At approximately 17:30 UT a deep fade in the intensity of the received signal was observed, lasting some 15 minutes. Immediately before and after this deep fade rapid variations of signal strength were observed, lasting less than five minutes. Frequency dependent behaviour was observed, with an earlier onset and later ending of this effect at lower frequencies. Both the deep fade and the surrounding intensity variations are attributed to the effect of a structure in the ionosphere. The time at which these effects were observed and the nature of the structuring varied between station, with the structure moved in a north-westerly direction and evolving as it travelled. The geomagnetic conditions at the time of the observation were quiet, as were the solar conditions. It is suggested that this structure is driven by variations within the neutral atmosphere and possible sources are discussed.
Original language | English |
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Publication status | Published - Oct 2022 |
Event | 17th European Space Weather Week - Technology Innovation Centre, Glasgow, United Kingdom Duration: 25 Oct 2021 → 29 Oct 2021 http://esww17.iopconfs.org/home |
Conference
Conference | 17th European Space Weather Week |
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Abbreviated title | ESWW17 |
Country/Territory | United Kingdom |
City | Glasgow |
Period | 25/10/21 → 29/10/21 |
Internet address |