Browsing by Author "Veliz, Oscar"
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Item Restricted 3D Imaging of the OH mesospheric emissive layer(Elsevier, 2010-01-15) Kouahla, M. N.; Moreels, G.; Faivre, M.; Clairemidi, J.; Meriwether, J. W.; Lehmacher, G. A.; Vidal Safor, Erick; Veliz, OscarA new and original stereo imaging method is introduced to measure the altitude of the OH nightglow layer and provide a 3D perspective map of the altitude of the layer centroid. Near-IR photographs of the OH layer are taken at two sites separated by a 645 km distance. Each photograph is processed in order to provide a satellite view of the layer. When superposed, the two views present a common diamond-shaped area. Pairs of matched points that correspond to a physical emissive point in the common area are identified in calculating a normalized cross-correlation coefficient (NCC). This method is suitable for obtaining 3D representations in the case of low-contrast objects. An observational campaign was conducted in July 2006 in Peru. The images were taken simultaneously at Cerro Cosmos (12 09 08.2 S, 75 33 49.3 W, altitude 4630 m) close to Huancayo and Cerro Verde Tellolo (16 33 17.6 S, 71 39 59.4 W, altitude 2272 m) close to Arequipa. 3D maps of the layer surface were retrieved and compared with pseudo-relief intensity maps of the same region. The mean altitude of the emission barycenter is located at 86.3 km on July 26. Comparable relief wavy features appear in the 3D and intensity maps. It is shown that the vertical amplitude of the wave system varies as exp (z/2H) within the altitude range z = 83.5–88.0 km, H being the scale height. The oscillatory kinetic energy at the altitude of the OH layer is comprised between 3 × 10−4 and 5.4 × 10−4 J/m3, which is 2–3 times smaller than the values derived from partial radio wave at 52N latitude.Item Open Access Abnormal evening vertical plasma drift and effects on ESF and EIA over Brazil-South Atlantic sector during the 30 October 2003 superstorm(American Geophysical Union, 2008-11) Abdu, M. A.; De Paula, E. R.; Batista, I. S.; Reinisch, B. W.; Matsuoka, M. T.; Camargo, P. O.; Veliz, Oscar; Denardini, C. M.; Sobral, J. H. A.; Kherani, E. A.; De Siqueira, P. M.Equatorial F region vertical plasma drifts, spread F and anomaly responses, in the south American longitude sector during the superstorm of 30 October 2003, are analyzed using data from an array of instruments consisting of Digisondes, a VHF radar, GPS TEC and scintillation receivers in Brazil, and a Digisonde and a magnetometer in Jicamarca, Peru. Prompt penetrating eastward electric field of abnormally large intensity drove the F layer plasma up at a velocity 1200 ms−1 during post dusk hours in the eastern sector over Brazil. The equatorial anomaly was intensified and expanded poleward while the development of spread F/plasma bubble irregularities and GPS signal scintillations were weaker than their quiet time intensity. Significantly weaker F region response over Jicamarca presented a striking difference in the intensity of prompt penetration electric field between Peru and eastern longitudes of Brazil. The enhanced post dusk sector vertical drift over Brazil is attributed to electro-dynamics effects arising energetic particle precipitation in the South Atlantic Magnetic Anomaly (SAMA). These extraordinary results and their longitudinal differences are presented and discussed in this paper.Item Open Access Actualización de instrumento óptico FPI en estación óptica del ROJ(Instituto Geofísico del Perú, 2010-09) Navarro, L.; Veliz, OscarEn el presente reporte se detalla los cambios realizados al instrumento óptico Interferometro Fabry-Perot de la estación óptica del Radio Observatorio de Jicamarca (11°57'31.38"S, 76°51'36.84"W) mediante los cuales se ha incrementado su sensibilidad al doble de órdenes interferométricos de la línea OI de la luminiscencia nocturna.Item Open Access Assimilation of sparse continuous near-earth weather measurements by NECTAR model morphing(American Geophysical Union, 2020-11) Galkin, I. A.; Reinisch, B. W.; Vesnin, A. M.; Bilitza, D.; Fridman, S.; Habarulema, J. B.; Veliz, OscarNon-linear Error Compensation Technique with Associative Restoration (NECTAR) is a novel approach to the assimilation of fragmentary sensor data to produce a global nowcast of the near-Earth space weather. NECTAR restores missing information by iteratively transforming (“morphing”) an underlying global climatology model into agreement with currently available sensor data. The morphing procedure benefits from analysis of the inherent multiscale diurnal periodicity of the geosystems by processing 24-hr time histories of the differences between measured and climate-expected values at each sensor site. The 24-hr deviation time series are used to compute and then globally interpolate the diurnal deviation harmonics. NECTAR therefore views the geosystem in terms of its periodic planetary-scale basis to associate observed fragments of the activity with the grand-scale weather processes of the matching variability scales. Such approach strengthens the restorative capability of the assimilation, specifically when only a limited number of observatories is available for the weather nowcast. Scenarios where the NECTAR concept works best are common in planetary-scale near-Earth weather applications, especially where sensor instrumentation is complex, expensive, and therefore scarce. To conduct the assimilation process, NECTAR employs a Hopfield feedback recurrent neural network commonly used in the associative memory architectures. Associative memories mimic human capability to restore full information from its initial fragments. When applied to the sparse spatial data, such a neural network becomes a nonlinear multiscale interpolator of missing information. Early tests of the NECTAR morphing reveal its enhanced capability to predict system dynamics over no-data regions (spatial interpolation).Item Open Access Daytime vertical E × B drift velocities inferred from ground‐based magnetometer observations at low latitudes(American Geophysical Union, 2004-11) Anderson, David; Anghel, Adela; Chau Chong Shing, Jorge Luis; Veliz, OscarThe daytime equatorial electrojet is a narrow band of enhanced eastward current flowing in the 100–120 km altitude region within ±2° latitude of the dip equator. A unique way of determining the daytime strength of the electrojet is to observe the difference in the magnitudes of the horizontal (H) component between a magnetometer placed directly on the magnetic equator and one displaced 6°–9° away. The difference between these measured H values provides a direct measure of the daytime electrojet current and, in turn, the magnitude of the vertical E × B drift velocity in the F region ionosphere. This paper discusses a recent study where 27 months of magnetometer H component observations and daytime, vertical E × B drift velocities were obtained in the Peruvian longitude sector between August 2001 and December 2003. In order to establish the relationships between ΔH and E × B drift velocities for the 270 days of observations, three approaches were chosen: (1) a linear regression analysis, (2) a multiple regression approach, and (3) a neural network approach. The neural network method gives slightly lower RMS error values compared with the other two methods. The relationships for all three techniques are validated using an independent set of E × B drift observations from the Jicamarca incoherent scatter radar (ISR) located at Jicamarca, Peru. The techniques presented here will be incorporated into a recently developed, real‐time Global Assimilation of Ionospheric Measurements (GAIM) model.Item Open Access Development of JROMAG-M103 magnetometer for geomagnetism studies in Peru(Instituto Geofísico del Perú, 2021-06) Rojas, Ricardo; Veliz, OscarSince 2007 a three-axis fluxgate magnetometer has been in development and under continuous improvement at Jicamarca Radio Observatory of the Geophysical Institute of Peru. It is based on the Fluxgate Mag-03 magnetic detector by Bartington Instruments. The JROMAG-M103 was developed to meet specific requirements of sensitivity, resolution, robustness, among others. This magnetometer, called JROMAG-M103, is being used in several geomagnetic monitoring networks, from different research institutions in South America. This poster presents the design aspects and technical specifications of the magnetometer and introduces further improvements that will be included in future versions.Item Open Access Electric field and magnetometer observations of the equatorial electrojet: An IEEY program(Instituto Geofísico del Perú, Radio Observatorio de Jicamarca, 1994) Woodman Pollitt, Ronald Francisco; Veliz, OscarAs part of the IEEY program, a chain of magnetometers was deployed along the Peruvian sector crossing the equatorial electrojet. Simultaneous vertical drift measurements were made using Jicamarca's normal I.S. F-region vertical drift mode as well as oblique coherent E-W electrojet drift measurements. The electrojet component of the magnetogram records can be extracted by subtracting the signature from the non-equatorial stations. As expected there is high correlation between this component and the drifts measured by both radar experiments. One of the days was magnetically disturbed. The distribution and density of the chain of magnetometers should allow us to determine the latitude extend of the fluctuating currents responding to the fluctuating electric field.Item Open Access F-region electric field and electrojet observations during the november 3, 1994, total eclipse(Instituto Geofísico del Perú, Radio Observatorio de Jicamarca, 1994-11-03) Woodman Pollitt, Ronald Francisco; Veliz, Oscar; Sarango A., M.; Aquino Q., F.; Villanueva R., F.On November 3, 1994, a total solar eclipse occurred at about 7:10 a.m. local time, with a maximum occultation path tangent to the southern coast of Peru. Occultation was not total at Jicamarca; it was 95%. The maximum occultation path touched tangencially the magnetic equator 700 km west of Jicamarca. Multiple instrument observations were made including incoherent scatter of the F-region, coherent backscatter of the Electrojet, Digisonde observations and a longitudinal chain of magnetograms. During a previous total eclipse which occurred on November 12, 1966, an interesting enhancement of the electric field occurred. This motivated us to run the Jicamarca radar in a vertical drift (E-W E-field) mode. Total backscattered power was also recorded, which also allowed simultaneous measurements of the electron density profiles. In addition to the I.S. measurements, a coherent radar was used with an antenna beam pointing 60 degrees west, sampling electrojet echoes up to 500 km west of Jicamarca. Apart of the radar data, the Jicamarca Digisonde was run, and a chain of magnetometers including points right under the maximum occultation were deployed. Preliminary results of these observations will be presented. Electron depletions are observed as expected, but no obvious electric field effects were noticed. The latter, if present, were obscured by the slight magnetic disturbance effects of magnetospheric origin occurring during the eclipse.Item Restricted Forecasting the occurrence of ionospheric scintillation activity in the equatorial ionosphere on a day-to-day basis(Elsevier, 2004-11) Anderson, David N.; Reinisch, Bodo; Valladare, Cesar; Chau Chong Shing, Jorge Luis; Veliz, OscarIn the low-latitude ionospheric F region, ambient conditions after sunset are often conducive to the generation of small-scale plasma density structures by the Rayleigh–Taylor instability mechanism. Radio wave signals passing through these electron density irregularities experience amplitude fluctuations that lead to radio wave “scintillation”. The scintillation index, S4, is a measure of the severity of these amplitude fluctuations. It is well known that the occurrence frequency of scintillation activity depends on solar cycle, season, longitude and local time, with a large day-to-day variability. In this paper, we present the results of a continuing study that utilizes a ground-based digital sounder at the magnetic equator to provide a “forecast” of the subsequent occurrence of scintillation activity and a network of UHF and L-band receivers that measure the S4 index, on a night-to-night basis. To establish the “forecasting” relationship, observations were carried out in 1998 and 1999 in the Peruvian/Chilean longitude sector. The relationship between the magnitude of the vertical E x B drift velocity enhancement just after sunset as determined by the Jicamarca Digisonde and the magnitude of the S4 index subsequently observed an hour or two later by the scintillation receivers at Ancon, Peru and Antofagasta, Chile was established. In most cases at both UHF and L-band frequencies, this relationship is not linear, but there appears to be a “threshold” in E x B drift of 20 m/s. On nights when E x B drift was less than 20 m/s, the UHF S4 index generally was less than 0.5, while on nights when E x B drift exceeded 20 m/s, the S4 index was greater than 0.5. The day-to-day variability of this relationship will be presented and discussed. Since October 1, 2001, the Jicamarca Digisonde has been used to “forecast” the occurrence of UHF S4 > 0.5 or S4 < 0.5 on a night-to-night basis. The validity of the “forecast” is subsequently confirmed by UHF S4 observations at Ancon, Peru and Antofagasta, Chile. The resulting statistics for these nightly S4 forecasts from November 1, 2001 to April 30, 2002 will be presented and discussed.Item Restricted Formation of an F3 layer in the equatorial ionosphere: A result from strong IMF changes(Elsevier, 2007-07) Paznukhov, V. V.; Reinisch, B. W.; Song, P.; Huang, X.; Bullet, T. W.; Veliz, OscarWe analyzed ionospheric observations made with digisondes in Jicamarca, Ramey, Wallops Island, Ascension Island, and Kwajalein Island during the major magnetic storm of November 9–10, 2004, which was associated with rapid interplanetary magnetic field (IMF) Bz changes. The strongest ionospheric responses to the southward IMF Bz turning were observed at the dip equator at Jicamarca where during the magnetic disturbance a dramatic F2 peak density depletion occurred at around 15:00 local time, accompanied by a fast upward motion of the plasma. In this process, an additional ionospheric layer, the F3 layer, formed with peak densities NmF3 exceeding NmF2. This observation may be considered evidence of an equatorial plasma fountain enhancement caused by the magnetic field disturbance. Responses were observed in a large range of latitudes and local times. The best indicator of the responses appears to be the peak height of the F layer, since competing processes determine the peak densities. The observed responses at low latitude locations in the morning and dusk sectors pose challenges to the simple penetrating electric field model because the upward motion is inconsistent with the E×B drift associated with a dawn–dusk electric field. Clear responses in the Jicamarca local time sector occurred at latitudes as high as 28, at Ramey, Puerto Rico. This latitude range appears to be beyond the range of the flux tube corresponding to the 900 km F3 layer peak height at Jicamarca, indicating a more extended uplifting of flux tubes.Item Open Access Geospace activities at the Geophysical Institute of Peru(Instituto Geofísico del Perú, 2010) Chau Chong Shing, Jorge Luis; Milla, Marco; Woodman Pollitt, Ronald Francisco; Veliz, Oscar; Ishitsuka, José K.; Rosales Corilloclla, DomingoOutline: • Space Weather and Equatorial Aeronomy • Clustered Instruments ▫ Incoherent and Coherent Scatter Radars ▫ LISN ▫ Magnetometers ▫ Optical Instruments ▫ Solar and Astronomical Instruments • Equatorial and Low latitude Ionospheric Effects due to Planetary Wave Atmospheric forcing.Item Open Access LISN activities at Jicamarca 2009-2010(Instituto Geofísico del Perú, 2010) Chau Chong Shing, Jorge Luis; De la Jara, César; Espinoza, Jhan Carlo; Veliz, Oscar; Amaya, F.Diapositivas presentadas en el 2010 CEDAR Workshop, University of Colorado, Boulder, CO, 20-25 June 2010.Item Open Access Localized field-aligned currents and 4-min TEC and ground magnetic oscillations during the 2015 eruption of Chile’s Calbuco volcano(SpringerOpen, 2016-08-31) Aoyama, Tadashi; Iyemori, Toshihiko; Nakanishi, Kunihito; Nishioka, Michi; Rosales Corilloclla, Domingo; Veliz, Oscar; Vidal Safor, ErickThe Calbuco volcano in southern Chile erupted on April 22, 2015. About 2 h after the first eruption, a Swarm satellite passed above the volcano and observed enhancement of small-amplitude (~0.5 nT) magnetic fluctuations with wave-packet structure which extends 15° in latitude. Similar wave packet is seen at the geomagnetic conjugate point of the volcano. Just after the eruption, geomagnetic fluctuations with the spectral peaks around the vertical acoustic resonance periods, 215 and 260 s, were also observed at Huancayo Geomagnetic Observatory located on the magnetic equator. Besides these observations, around 4-min, i.e., 175, 205 and 260 s, oscillations of total electron content (TEC) were observed at global positioning system stations near the volcano. The horizontal propagation velocity and the spatial scale of the TEC oscillation are estimated to be 720 m/s and 1600 km, respectively. These observations strongly suggest that the atmospheric waves induced by explosive volcanic eruption generate TEC variation and electric currents. The Swarm observation may be explained as a manifestation of their magnetic effects observed in the topside ionosphere.Item Open Access New results on equatorial thermospheric winds and the midnight temperature maximum(European Geosciences Union (EGU), 2008-03-26) Meriwether, J.; Faivre, M.; Fesen, C.; Sherwood, P.; Veliz, OscarOptical observations of thermospheric winds and temperatures determined with high resolution measurements of Doppler shifts and Doppler widths of the OI 630-nm equatorial nightglow emission have been made with improved accuracy at Arequipa, Peru (16.4° S, 71.4° W) with an imaging Fabry-Perot interferometer. An observing procedure previously used at Arecibo Observatory was applied to achieve increased spatial and temporal sampling of the thermospheric wind and temperature with the selection of eight azimuthal directions, equally spaced from 0 to 360°, at a zenith angle of 60°. By assuming the equivalence of longitude and local time, the data obtained using this technique is analyzed to determine the mean neutral wind speeds and mean horizontal gradients of the wind field in the zonal and meridional directions. The new temperature measurements obtained with the improved instrumental accuracy clearly show the midnight temperature maximum (MTM) peak with amplitudes of 25 to 200 K in all directions observed for most nights. The horizontal wind field maps calculated from the mean winds and gradients show the MTM peak is always preceded by an equatorward wind surge lasting 1–2 h. The results also show for winter events a meridional wind abatement seen after the MTM peak. On one occasion, near the September equinox, a reversal was observed during the poleward transit of the MTM over Arequipa. Analysis inferring vertical winds from the observed convergence yielded inconsistent results, calling into question the validity of this calculation for the MTM structure at equatorial latitudes during solar minimum. Comparison of the observations with the predictions of the NCAR general circulation model indicates that the model fails to reproduce the observed amplitude by a factor of 5 or more. This is attributed in part to the lack of adequate spatial resolution in the model as the MTM phenomenon takes place within a scale of 300–500 km and ~45 min in local time. The model shortcoming is also attributed in part to the need for the model to include a hydrodynamical mechanism to describe the merging of the zonal wind with the meridional tidal winds that converge onto the geographical equator. Finally, a conclusion of this work is that the MTM compressional heating takes place along the perimeter of the pressure bulge rather than within the bulge, an issue previously not appreciated.Item Open Access Pasado, presente y futuro de estudios de aeronomía usando FPI en Perú(Instituto Geofísico del Perú, 2010) Navarro, L.; Veliz, Oscar; Chau Chong Shing, Jorge Luis; Meriwether, J. W.Diapositivas presentadas en el XIII Encuentro Científico Internacional, (ECI 2010i), realizado del 2 al 6 de agosto de 2010 en la ciudad de Lima.Item Restricted Prompt effects of solar wind variations on the inner magnetosphere and midlatitude ionosphere(Elsevier, 2005) Huang, Chao-Shong; Foster, J. C.; Yumoto, K.; Chau Chong Shing, Jorge Luis; Veliz, OscarIt is well known that the solar wind can significantly affect high-latitude ionospheric dynamics. However, the effects of the solar wind on the middle- and low-latitude ionosphere are much less studied. In this paper, we report observations that large perturbations in the middle- and low-latitude ionosphere are well correlated with solar wind variations. In one event, a significant (20–30%) decrease of the midlatitude ionospheric electron density over a large latitudinal range was related to a sudden drop in the solar wind pressure and a northward turning of the interplanetary magnetic field, and the density decrease became larger at lower latitudes. In another event, periodic perturbations in the dayside equatorial ionospheric E × B drift and electrojet were closely associated with variations in the interplanetary electric field. Since the solar wind is always changing with time, it can be a very important and common source of ionospheric perturbations at middle- and low-latitudes. The relationship between solar wind variations and significant ionospheric perturbations has important applications in space weather.Item Restricted Quantifying solar flux and geomagnetic main field influence on the equatorial ionospheric current system at the geomagnetic observatory Huancayo(Elsevier, 2017-10) Matzka, Jürgen; Siddiqui, Tarique A.; Lilienkamp, Henning; Stolle, Claudia; Veliz, OscarIn order to analyse the sensitivity of the equatorial ionospheric current system, i.e. the solar quiet current system and the equatorial electrojet, to solar cycle variations and to the secular variation of the geomagnetic main field, we have analysed 51 years (1935–1985) of geomagnetic observatory data from Huancayo, Peru. This period is ideal to analyse the influence of the main field strength on the amplitude of the quiet daily variation, since the main field decreases significantly from 1935 to 1985, while the distance of the magnetic equator to the observatory remains stable. To this end, we digitised some 19 years of hourly mean values of the horizontal component (H), which have not been available digitally at the World Data Centres. Then, the sensitivity of the amplitude ΔH of the quiet daily variation to both solar cycle variations (in terms of sunspot numbers and solar flux F10.7) and changes of the geomagnetic main field strength (due to secular variation) was determined. We confirm an increase of ΔH for the decreasing main field in this period, as expected from physics based models (Cnossen, 2016), but with a somewhat smaller rate of 4.4% (5.8% considering one standard error) compared with 6.9% predicted by the physics based model.Item Open Access Red de interferómetros Fabry-Perot en Perú para estudios de aeronomía(Instituto Geofísico del Perú, 2010) Navarro, L.; Meriwether, J.; Veliz, Oscar; Chau Chong Shing, Jorge LuisPresentación interna del Radio Observatorio de Jicamarca-IGP.Item Open Access Reprocessing of data from Fabry-Perot interferometers (FPI) belonging to the IGP network of optical instruments(Instituto Geofísico del Perú, 2021-06) Barbaran Meza, J.; Rojas, R.; Navarro, L.; Veliz, Oscar; De la Jara, César; Milla, MarcoIGP network of optical instruments consist of two types of imaging instrumentation: Fabry-Perot Interferometers (FPI) and All-Sky imagers (ASI). The FPI can obtain two dimensional interferograms that are used to study the dynamics of the upper atmosphere. Since the deployment of the first FPI in 1985 and up to the implementation of the FPI network in 2009, which was fully operational in 2011, a processing technique based on Fourier decomposition of the interferogram spectra has been used. An improvement of this technique has been released with a better representation and fitting scheme of the Airy function parameters needed for better estimation of the airglow neutral winds and temperatures. Given that the new processing technique has potentially the ability to generate better products, reprocessing of the IGPs optical data base is being evaluated. First, the two methods need to be compared. In this work we present an analysis of the two methods comparison, showing differences, advantages, and possible improvements to implement.Item Open Access Simultaneous measurements of thermospheric winds and ion drifts at Jicamarca and Arequipa, Peru(Instituto Geofísico del Perú, 2010) Navarro, L.; Veliz, Oscar; Chau Chong Shing, Jorge Luis; Meriwether, J. W.Ponencia presentada en el 2010 CEDAR Workshop, University of Colorado, Boulder, CO, 20-25 June 2010.