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Browsing Artículos Científicos by Subject "150‐km echoes"
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Item Restricted Discovery of two distinct types of equatorial 150-km radar echoes(American Geophysical Union, 2013-08-24) Chau Chong Shing, Jorge Luis; Kudeki, E.We show here that VHF signals scattered from the 150 km region above Jicamaca exhibit two distinct types of features. In one type (type A), the Doppler spectral width increases with the echo strength and the corresponding signal-to-noise ratio (SNR). A second type (type B) of higher SNR echoes exhibits SNR-independent Doppler spectral widths that are much narrower than those observed in the first type. The type A echo population is by far the dominant population. Comparisons with earlier data sets collected at Jicamarca and elsewhere suggest that the type A and type B are likely to be associated with a naturally enhanced incoherent scattering (NEIS) process and the unstable growth of field-aligned irregularities (FAIs), respectively. We conjecture that small radar systems operated near the geomagnetic equator that have reported 150 km echo observations detected FAI echoes and that the NEIS echoes can only be seen by high sensitivity systems.Item Restricted VIPIR and 50 MHz radar studies of gravity wave signatures in 150‐km echoes observed at Jicamarca(American Geophysical Union, 2020-08) Reyes, Pablo M.; Kudeki, Erhan; Lehmacher, Gerald A.; Chau, Jorge L.; Milla, MarcoRange‐time‐intensity (RTI) plots of 50 MHz radar backscatter detected at Jicamarca from the 150‐km region of the equatorial ionosphere exhibit necklace‐shaped multilayered structures first reported by Kudeki and Fawcett (1993, https://doi.org/10.1029/93GL01256). The backscatter layers also exhibit quasi‐periodic intensity fluctuations with periods of about 5–15 min and are separated from adjacent layers by thin and undulating regions of no detectible power returns. A study of the fluctuating backscatter layers and undulating gap regions will be presented using VIPIR ionosonde data taken at the Jicamarca Radio Observatory simultaneously with high‐resolution 50‐MHz radar backscatter data. VIPIR virtual reflection height variations in time are noted to match the RTI gap‐region undulations very closely at selected VIPIR frequencies (or, equivalently, electron densities at reflection heights). This matching enables assigning “true heights” to VIPIR virtual height contour maps, and a joint study of the contour maps with the 50‐MHz radar RTI maps strongly suggests that correlated fluctuations and undulations observed in VIPIR and 50‐MHz radar data are indicative of gravity wave‐induced variations in the 150‐km region ionosphere. Accordingly, a complete explanation of the 150‐km echo phenomenon will need to include gravity wave coupling and forcing effects in the enhancement and suppression processes that can account for the observed fluctuations and gap‐region features of necklace‐shaped 150‐km echo maps.