Browsing by Author "Swartz, Wesley E."
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Item Restricted Foreword to the special issue on papers presented at the Jicamarca 40th Anniversary Workshop: 40 years of equatorial aeronomy sparked by the Jicamarca Radio Observatory(Elsevier, 2004-11) Swartz, Wesley E.; Chau Chong Shing, Jorge LuisIn May 2002 the Jicamarca Radio Observatory hosted a workshop to celebrate its 40th anniversary. Fifty-one scientists from 11 different countries participated and presented not only a number of reviews of past highlights of the science generated at Jicamarca, but also up-to-date reports on various aspects of equatorial and low latitude aeronomy. Almost all the past directors of Jicamarca attended, as well as several of the ‘‘old timers’’ from the early 1960s, including Kenneth Bowles, the Observatory builder and first director. This special issue of the Journal of Atmospheric and Solar-Terrestrial Physics includes a selection of fourteen papers from the workshop covering a number of the topics including both emerging theories and new observations.Item Open Access Measuring ionospheric densities, temperatures and drift velocities simultaneously at Jicamarca(American Geophysical Union, 1997-11-15) Aponte, Nestor; Woodman Pollitt, Ronald Francisco; Swartz, Wesley E.; Farley, Donald T.Incoherent scatter autocorrelation function measurements are difficult to make in the F región at Jicamarca because of very strong clutter contamination by coherent echoes from unstable plasma waves in the -B-region electrojet that are aligned with the magnetic field. We have developed a more effective way to deal with this clutter that improves the quality of the temperature (and composition when light ions are present) data. Other coherent echoes (much weaker than electrojet echoes but stronger than incoherent scatter) are also received through the antenna sidelobes from fieldaligned irregularities in the 140-170 km altitude range during daytime. These latter echoes have a very narrow bandwidth, and so it is easy to measure their Doppler shift and obtain the vertical plasma drift velocity, which is proportional to the zonal electric field.Item Restricted Mid-latitude ionospheric fluctuation spectra due to secondary E x B instabilities(Elsevier, 2004-09-03) Kelley, Michael C.; Swartz, Wesley E.; Makela, Jonathan J.The most spectacular night of mid-latitude spread F ever recorded at Arecibo is analyzed and compared with barium cloud observations made in the 1970s and with equatorial spread F. Strong evidence is found for a secondary instability driven either by a poleward electric field and a westward density gradient (both presumably due to a primary Perkins instability), or by a zero-order eastward wind flowing across the westward gradient. Spectra computed from the incoherent scatter density profiles of this event are very similar to the spectra of both barium striations and equatorial spread F. Estimates of the strength of the radar wave scattering expected from the fluctuation spectra are in good agreement with the VHF observations from that night. Finally, a poleward-surging, mid-latitude plasma bubble is seen to bifurcate in a manner similar to equatorial spread-F simulations.Item Restricted Plasma instabilities observed in the E region over Arecibo and a proposed nonlocal theory(Elsevier, 2004-12) Rosado-Román, José M.; Swartz, Wesley E.; Farley, Donald T.We describe simultaneous radar observations made with the Cornell University Portable Radar Interferometer (CUPRI) at 50 MHz and the Arecibo incoherent scatter radar (ISR) at 430 MHz during the El Coquí campaign of 1992 in Puerto Rico. The goal was to study the plasma instabilities that cause coherent radar backscatter from the E region at mid-latitudes. The common volume data reveal that the coherent CUPRI echoes come from sporadic-E layers that exhibit no obvious gravity wave modulation but possess high densities and sharp gradients. The echoes with positive (negative) Doppler shifts, i.e. eastward (westward) plasma wave phase velocities, come from the top (bottom) of the layer, in agreement with simple local equatorial gradient-drift instability theory, even though this theory is not valid at mid-latitudes, where nonlocal shorting effects along magnetic field lines play a crucial role. We have developed a nonlocal theory that takes these effects into account. Our theory, which is discussed in detail in a companion paper, does not invoke any unusual layer geometry, in contrast to the ideas proposed in several papers in recent years. The unstable eigenmodes are a sum of plane waves with k-vectors having a small component parallel to the geomagnetic field, such that the modes are confined primarily to either the top or bottom of the layer, depending on the driving electric field. The direction of these k-vectors deviates from normal to the magnetic field by at most a few tenths of a degree. The k-vectors are also approximately aligned with the E×B drift. While both the density and potential fluctuations peak in amplitude on the unstable side of the layer, the density peak is closer to the maximum of the layer than is the potential peak. We do not in this paper deal with the “quasi-periodic” or QP nature of the radar echoes that is sometimes, but certainly not always, seen.Item Open Access Same night observations of spread‐F by the Jicamarca Radio Observatory in Peru and CUPRI in Alcântara, Brazil(American Geophysical Union, 1998-01) Swartz, Wesley E.; Woodman Pollitt, Ronald Francisco50‐MHz echoes from equatorial spread‐F were observed on several nights by both the Jicamarca Radio Observatory (JRO) in Peru and the Cornell University Portable Radar Interferometer (CUPRI) in Alcântara, Brazil. Although little detailed correlation is expected between sites separated by such large distances, the night of October 17, 1994 shows some remarkable similarities between Peru and Brazil. On this night spread‐F commenced at both Jicamarca and Alcântara as thin bottomside layers situated near 320 km altitude at nearly the same local times. Later, major plumes erupted that reached to over 1000 km altitude at both sites. Since plumes normally drift west to east, these are obviously not the same structures but the similarities indicate that conditions for spawning them must have been coincidentally very similar on this night. The next two nights which produced plumes over Brazil, but only bottomside layers over Peru, emphasize that local conditions on the same night can be very different at the two locations. The importance of having a sufficiently wide beam for exploring spread‐F over a large altitude range at the Alcântara site is also explored.Item Restricted Spread in aspect angles of equatorial E region irregularities(American Geophysical Union, 2008-11-12) Lu, Fei; Farley, Donald T.; Swartz, Wesley E.We revisit and extend the 50 MHz radar aspect angle study made in Peru by Kudeki and Farley in 1985, taking advantage of upgraded facilities at Jicamarca. We discuss here (1) type 1 and 2 echoes from the electrojet region, (2) early evening echoes from somewhat above the electrojet, and (3) daytime “150 km” echoes from the ∼145 to 170 km altitude region. Our electrojet data (1) confirm the earlier results for weak type 2 conditions, namely, that the rms aspect angle θrms decreases from about 0.3° at 99 km to slightly less than 0.2° at 108 km, and (2) provide much more information about the aspect angles of type 1 echoes and the apparent nonlinear interaction between type 1 waves and slower waves. Type 1 waves, with phase velocities near the ion‐acoustic velocity, have θrms decreasing from about 0.15° near 104 km to about 0.10° near 110 km. There is strong evidence that horizontally traveling type 1 waves in the upper midday electrojet, where upward electron density gradients are absent, can sometimes nonlinearly couple to slow, vertically traveling waves with aspect angles sometimes larger than 0.5°. In the early evening we often observe echoes in the 125–135 km region with θrms ≤ 0.05°. During daytime the relatively weak “150 km” echoes have even smaller θrms. At the end of the paper we discuss ideas concerning the nonlinear coupling of the plasma waves.Item Restricted Spread-F-like irregularities observed by the Jicamarca radar during the day-time(Elsevier, 1985-08) Woodman Pollitt, Ronald Francisco; Pingree, Joseph E.; Swartz, Wesley E.Until now the presence of F-region irregularities responsible for spread-F (sp-F) traces in ionograms has been considered as a purely night-time phenomenon extending sporadically lo the early morning hours. We here in respond that, on two occasions (26 March 1974 and 1 February 1984) similar irregularities were observed between 1400 and 1600 hours local time with the Jicamarca radar. These irregularities caused enhancements in the power of the radar echo of as much as two orders of magnitude, were found over a region of a few hundred kilometers on the topside of the F-region extending from around 600 to 1000 km altitude and persisted for 1-2 h. The irregularities were aspect sensitive (aligned with the magnetic field) and produced echoes with a fading rate of the order of one lo a few seconds. The background zonal electric field, inferred from the vertical drift velocity, was fairly constant in altitude, with values smaller than 0.1 mV. m-1. During the duration of the events, zonal components of both signs occurred, with the component passing through zero several times. We have no information on the vertical component of E. These irregularities could not be observed with ground-based ionosondes, since they are on the topside of the F-region. They may be related to fossil bubbles that are responsible for HF ducting observed by satellites.