Statistics of 150-km echoes over Jicamarca based on low-power VHF observations

Abstract

Abstract. In this work we summarize the statistics of the socalled 150-km echoes obtained with a low-power VHF radar operation at the Jicamarca Radio Observatory (11.97 • S, 76.87 • W, and 1.3 • dip angle at 150-km altitude) in Peru. Our results are based on almost four years of observations between August 2001 and July 2005 (approximately 150 days per year). The majority of the observations have been conducted between 08:00 and 17:00 LT. We present the statistics of occurrence of the echoes for each of the four seasons as a function of time of day and altitude. The occurrence frequency of the echoes is ∼75% around noon and start decreasing after 15:00 LT and disappear after 17:00 LT in all seasons. As shown in previous campaign observations, the 150-echoes appear at a higher altitude (>150 km) in narrow layers in the morning, reaching lower altitudes (∼135 km) around noon, and disappear at higher altitudes (>150 km) after 17:00 LT. We show that although 150-km echoes are observed all year long, they exhibit a clear seasonal variability on altitudinal coverage and the percentage of occurrence around noon and early in the morning. We also show that there is a strong day-to-day variability, and no correlation with magnetic activity. Although our results do not solve the 150-km riddle, they should be taken into account when a reasonable theory is proposed.

On the characteristics of 150-km echoes observed in the Brazilian longitude sector by the 30 MHz São Luís radar

“…Their results indicate a high occurrence (>70 %) of echoes for all seasons but with slightly higher occurrence (>85 %) during June Solstice months. Chau and Kudeki (2006) results challenge the hypothesis of Tsunoda and Ecklund (2004) about the control of E s layers over the occurrence of 150-km echoes since off-equatorial E s layers occur more frequently during the December solstice in the Peruvian sector. Statistics of the occurrence of off-equatorial 150-km echoes in the Indian sector were also presented by Patra and Rao (2007).…”

“…Because of the similarity with the seasonal variation of sporadic E layers (E s ) in that longitude sector, they suggested that the ionospheric irregularities causing 150-km echoes could be created by an off-equator E s instability (Cosgrove and Tsunoda, 2002). Using observations made by the JULIA (Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere) mode of the Jicamarca radar, Chau and Kudeki (2006) South American) sector. They found that 150-km echoes are observed virtually every day over Jicamarca.…”

“…The occurrence of 150-km echoes have already been detected, for instance, in the Peruvian sector (e.g. Kudeki and Fawcett, 1993;Chau and Kudeki, 2006), in Pohmpei, Micronesia (e.g. Kudeki et al, 1998;Tsunoda and Ecklund, 2004), in Indonesia (Patra et al, 2008;Yokoyama et al, 2009), and in the Indian sector (Choudhary et al, 2004;Patra and Rao, 2007).…”

Longitudinal and seasonal structure of the ionospheric equatorial electric field

“…JULIA (Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere) uses a coherent scatter radar to accurately measure the drift velocities of plasma irregularities near 150 km altitude [Chau and Kudeki, 2006]. We convert these drift velocities to electric field values using the IGRF and compare the eastward electric field component with simultaneous IVM measurements during C/NOFS overflights of Jicamarca.…”

“…This electric field is a fundamental parameter in any model describing equatorial ionospheric electrodynamics. However, direct measurements of the EEF have been restricted to a very few ground-based radars [Chau and Kudeki, 2006] and a small number of satellite missions [Fejer et al, 2008; de la Beaujardière and the C/NOFS Science Definition Team, 2004].…”