Entity

Time filter

Source Type


Hysell D.L.,Cornell University | Milla M.A.,Jicamarca Radio Observatory | Rodrigues F.S.,University of Texas at Dallas | Varney R.H.,SRI International | Huba J.D.,U.S. Navy
Journal of Geophysical Research A: Space Physics | Year: 2015

We present observations of the topside ionosphere made at the Jicamarca Radio Observatory in March and September 2013, made using a full-profile analysis approach. Recent updates to the methodology employed at Jicamarca are also described. Measurements of plasma number density, electron and ion temperatures, and hydrogen and helium ion fractions up to 1500 km altitude are presented for 3 days in March and September. The main features of the observations include a sawtooth-like diurnal variation in ht, the transition height where the O+ ion fraction falls to 50%, the appearance of weak He+ layers just below ht, and a dramatic increase in plasma temperature at dawn followed by a sharp temperature depression around local noon. These features are consistent from day to day and between March and September. Coupled Ion Neutral Dynamics Investigation data from the Communication Navigation Outage Forecast System satellite are used to help validate the March Jicamarca data. The SAMI2-PE model was able to recover many of the features of the topside observations, including the morphology of the plasma density profiles and the light-ion composition. The model, forced using convection speeds and meridional thermospheric winds based on climatological averages, did not reproduce the extreme temperature changes in the topside between sunrise and noon. Some possible causes of the discrepancies are discussed. Key Points New ISR mode at Jicamarca measures topside parameters ISR data compared with C/NOFS CINDI measurements, SAMI2-PE model Extreme, rapid temperature variations in topside poorly understood ©2015. American Geophysical Union. All Rights Reserved.


Rodrigues F.S.,University of Texas at Dallas | Nicolls M.J.,SRI International | Milla M.A.,Jicamarca Radio Observatory | Smith J.M.,University of Texas at Dallas | And 4 more authors.
Geophysical Research Letters | Year: 2015

A new, 14-panel Advanced Modular Incoherent Scatter Radar (AMISR-14) system was recently deployed at the Jicamarca Radio Observatory. We present results of the first coherent backscatter radar observations of equatorial spread F(ESF) irregularities made with the system. Colocation with the 50MHz Jicamarca Unattended Long-term studies of the Ionosphere and Atmosphere (JULIA) radar allowed unique simultaneous observations of meter and submeter irregularities. Observations from both systems produced similar Range-Time-Intensity maps during bottom-type and bottomside ESF events. We were also able to use the electronic beam steering capability of AMISR-14 to "image" scattering structures in the magnetic equatorial plane and track their appearance, evolution, and decay with a much larger field of view than previously possible at Jicamarca. The results suggest zonal variations in the instability conditions leading to irregularities and demonstrate the dynamic behavior of F region scattering structures as they evolve and drift across the radar beams. Key Points First AMISR-14 observations Detection of submeter ESF irregularities Temporal and spatial variability of ESF. © 2015. American Geophysical Union. All Rights Reserved.


Rodrigues F.S.,University of Texas at Dallas | Smith J.M.,University of Texas at Dallas | Milla M.,Jicamarca Radio Observatory | Stoneback R.A.,University of Texas at Dallas
Journal of Geophysical Research A: Space Physics | Year: 2015

One of the most interesting observations made by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite mission was the detection of average equatorial ionospheric vertical drifts that largely differed from model predictions. C/NOFS measurements showed, in particular, downward drifts in the afternoon sector, and upward drifts around local midnight hours during the 2008 and 2009 extreme solar minimum. The unexpected behavior of the drifts has important implications for ionospheric modeling and suggests the necessity for a better understanding of the low-latitude electrodynamics. We used ground-based radar measurements to quantify the seasonal and solar flux variability of daytime equatorial drifts at lower altitudes (150 km) than those probed by C/NOFS (above 400 km). We found that average vertical drifts at 150 km altitude are in good agreement with model predictions of F region drifts and did not show the signatures of an enhanced semidiurnal pattern, as seen by C/NOFS. Comparison of the 150 km echo drifts with model predictions also shows that the increase (decrease) with height of the vertical drifts in the morning (afternoon) hours is a regular feature of the equatorial ionosphere. It occurred in all seasons and solar flux conditions between 2001 and 2011. ©2015. American Geophysical Union. All Rights Reserved.


Hysell D.L.,Cornell University | Milla M.A.,Jicamarca Radio Observatory
2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014 | Year: 2014

A full-profile incoherent scatter analysis, in which all ionospheric state variables at all altitudes are estimated simultaneously, has been implemented at Jicamarca for topside research. Such an analysis is particularly expedient at Jicamarca where the correlation time of the 50-MHz echoes is long. Long pulses are interleaved with short double pulses which provide complementary measurements at altitudes below and near the F peak. Absolute number density calibration is performed by exploiting Faraday rotation. We compute range-lag ambiguity functions for lag profile forward modeling in a general way. Autocorrelation function calculations take into account the small magnetic aspect angles of Jicamarca observations. Regularization is used to confine the solution space of the analysis and confer stability. A grid search provides the initial state for the iterative method we use. The overall algorithm can be made to run in real time on a single i7 processor core. Representative data are used to demonstrate the efficacy of the algorithm. © 2014 IEEE.


Hysell D.L.,Cornell University | Milla M.A.,Jicamarca Radio Observatory
2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014 | Year: 2014

Ionospheric state parameters including plasma number density and vector drift profiles were measured at the Jicamarca Radio Observatory during campaigns throughout 2013. Neutral winds were measured by the redline Fabry Perot interferometer at Jicamarca. Coherent radar backscatter from plasma irregularities associated with equatorial spread F (ESF) was also recorded. Radar imagery of the morphology of the large-scale ESF irregularities is also available from simultaneous measurements. A 3D numerical simulation of ionospheric irregularities, initialized and forced using parametrizations derived from a combination of measurements and empirical models, has been used to reproduce the ESF activity that occurred on a number of different, representative campaign nights. The simulations were able to recover many of the most salient features of the irregularities that formed in each case. The campaign data, numerical simulations, and protocols used to associate them are presented. © 2014 IEEE.

Discover hidden collaborations