Proceedings with Extended Abstracts (single PDF file) - Radio ...

RECENT OBSERVATIONS OF E REGION FIELD-ALIGNEDIRREGULARITIES AT LOW LATITUDESJ. L. Chau 1,2 , D. L. Hysell 3 , and M. A. Milla 11 Radio Observatorio de Jicamarca, Instituto Geofísico del Perú, Lima2Laboratorio de Física, Universidad de Piura, Piura, Perú3Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York, USA1. IntroductionIn this work we present a summary of recent observations made of E region fieldaligned irregularities at low latitudes, particularly those from the Jicamarca RadioObservatory (~1 o N dip latitude) and those from the Piura VHF radar (~7 o N dip latitude) bothlocated in Peru. Although the observations at Jicamarca, under the magnetic equator, insidethe equatorial electrojet (EEJ) region, started more than 40 years ago, there have been veryfew of them (few hundred hours a year) until the JULIA (Jicamarca unattended long-terminvestigations of the atmosphere) system started few years ago. Nowadays we are observingmore than 4000 hours per year.In the case of the Piura radar, which was originally conceived as a wind profiler, wehave also started the E-region observations on campaign basis [Woodman et al., 1999; Chauand Woodman, 1999] by pointing perpendicular to the magnetic field, i.e., 14 o N off vertical.Since January 2000, a special observing mode has been added to the normal operations of thePiura radar to get quasi continuous measurements of the E-region every 11 minutes [Chau etal., 2002]It is important to mention that observations of E-region irregularities started duringthe International Geophysical Year (IGY) in 1957. At that time measurements wereconducted using bistatic configurations shown in Figure 1. Measurements were conducted atthe magnetic equator (over Huancayo), 5 o North (over Trujillo), and 5 o S (over Arequipa).The main conclusions relevant to this work are (a) E-region echoes were stronger during theday at the magnetic Equator and at 5 o S; (b) E-region scatter signals at 5 o N were weaker thanthose at the magnetic equator and 5 o S, independent of season, and absent, most of the time,during the day [Cohen and Bowles, 1963]. The locations of the Jicamarca and Piura radarsare indicated in the Figure 1 for reference.First we will describe the different E region observing modes currently available atJicamarca including preliminary statistics based on JULIA observations. Then we describethe observations with the Piura radar along with recent statistics. Finally we summarize themain characteristics of the EEJ and Piura E region irregularities, and different parameters thatcan be derived from those observations at Jicamarca and Piura2. Jicamarca E region modesThe main operating mode at Jicamarca is the Incoherent Scatter Radar (ISR) modethat allows the measurements of densities, temperatures, compositions and drifts of theionosphere [e.g., Farley, 1991; Kudeki et al., 1999]. Due to the presence of strongirregularities at E region heights, i.e., EEJ [e.g., Farley, 1985], the ISR measurements are notpossible at those heights. Given this limitation, in recent years, a number of observing modeshas been implemented at Jicamarca to try to derive the state parameters of the ionosphere(e.g., density profiles, electric fields) from observing the E region irregularities. These modescan be classified as (a) interferometer, (b) oblique, (c) bistatic, and (d) imaging modes.76