11/1/2023 0 Comments Maria arecibo telescope![]() ![]() VLF beacons reflect from the D-region (60-90 km), so a temporal-spatial oscillation in the D-region manifests as oscillations in the amplitude (and phase) of that beacon signal. The amplitude of a VLF (24 kHz) beacon in Maine, known as NAA, oscillated with ~3-minute period, which was also observed on a beacon originating from North Dakota (not shown). As Maria progressed northward away from PR, a VLF receiver operating at AO confirmed fluctuations in the D-region ionospheric conditions via the observed GW. Another intriguing detection is the appearance of smaller periodicities (of ~5.6 hours) in both parameters when the EWS was very close or over AO. Besides, it seems that these periodicities only acted on the hmF2 when the EWS was southeast, and over AO, after that, they vanished. The power spectrum map shows the domain of a few periodicities before, during, and after Maria landfall in AO with a domain of ~11 and ~23 hours for the entire period of foF2 registers, but not for hmF2. A wavelet spectrum analysis of the residual between 20 (2017 minus 2018) revealed an interesting behavior of foF2 and hmF2. An ionosonde also operated during EWS Maria's approach and landfall in AO as a major Hurricane. This unusual propagation direction seems to be strongly related to the EWS Maria. An ASI at AO registered wavefronts propagating northwestward (away from the EWS source) in three wavelengths: OI5577, OI6300, and OI7774. ![]() On the night of Sept 17-18, 2017, Maria was located ~ 900 km southeast from AO and transiting from a Tropical Storm to a Hurricane. On the night of Sep 15-16, when Maria was in its initial phase (Tropical Depression) ~ 1500km southeast from AO, a decrease in the airglow brightness of ~ 15 Rayleigh was registered by a Fabry-Perot Interferometer and two photometers in both red and green airglow emissions. A marked variability on the MLT and IT systems related to EWS category IV Hurricane Maria passage over the Caribbean was observed at Arecibo Observatory (AO) in Sep 2017.
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