Browsing by Author "Swartz, W. E."
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Item Open Access Electron energy balance in the F region above Jicamarca(American Geophysical Union, 1999-05-01) Aponte, N.; Swartz, W. E.; Farley, D. T.Incoherent scatter measurements from Jicamarca, Peru, show that current models and cross sections account quite well for the heating and cooling of F region electrons, in marked contrast to earlier similar studies at low and middle latitudes. The latter showed discrepancies of the order of a factor of 2 between the calculated energy input and loss rates. The equatorial F region ionosphere provides the simplest configuration for such studies because the horizontal magnetic field eliminates vertical photoelectron transport and thermal conduction. We based our estimates of electron heating on photoelectron energy spectra computed from recently developed solar flux models and new absorption and ionization cross sections and included the additional energy source clue to quenching of the 2D metastable state of nitrogen. This extra source is sometimes significant. Electron and ion temperatures and densities measured with the Jicamarca incoherent scatter radar were used to complete the calculations of the heating and cooling rates. We present here data from 2 days, one with low solar activity and one with moderate activity, over the altitude range 220–325 km. The heating/cooling rates ranged from about 500 to 6000 eV cm−3 s−1. Over this entire range the calculated heating and cooling rates differed by 10% or less when the data quality was good.Item Open Access Magnetic aspect sensitivity of 3‐m F‐region field‐aligned plasma density irregularities over Jicamarca(American Geophysical Union, 2011-10) Hysell, D. L.; Hedden, R. B.; Swartz, W. E.; Farley, D. T.; Chau Chong Shing, Jorge Luis; Milla, MarcoThe magnetic aspect angle sensitivity of 3‐m plasma density irregularities in the F‐region ionosphere over Jicamarca has been measured during the passage of a radar plume in an equatorial spread‐F event. The measurement technique utilizes radar interferometry with a number of antenna baselines with different lengths and orientations. Several corrections are applied to the data to reduce experimental biases. The RMS aspect angle half widths (the square root of the angular variance, the standard deviation) were found to be 0.01 ± 0.005° in a bottomside layer and near the top of the plume and 0.02 ± 0.005° in the central channel of the plume near F‐peak altitudes. In the frequency domain, the magnetic aspect width was narrowest at small Doppler shifts and broader in the wings of the spectra when wings existed. These findings appear to be reasonably consistent with theoretical predictions, although questions remain.Item Restricted SAMI2‐PE: A model of the ionosphere including multistream interhemispheric photoelectron transport(American Geophysical Union, 2012-06-29) Varney, R. H.; Swartz, W. E.; Hysell, D. L.; Huba, J. D.In order to improve model comparisons with recently improved incoherent scatter radar measurements at the Jicamarca Radio Observatory we have added photoelectron transport and energy redistribution to the two dimensional SAMI2 ionospheric model. The photoelectron model uses multiple pitch angle bins, includes effects associated with curved magnetic field lines, and uses an energy degradation procedure which conserves energy on coarse, non‐uniformly spaced energy grids. The photoelectron model generates secondary electron production rates and thermal electron heating rates which are then passed to the fluid equations in SAMI2. We then compare electron and ion temperatures and electron densities of this modified SAMI2 model with measurements of these parameters over a range of altitudes from 90 km to 1650 km (L = 1.26) over a 24 hour period. The new electron heating model is a significant improvement over the semi‐empirical model used in SAMI2. The electron temperatures above the F‐peak from the modified model qualitatively reproduce the shape of the measurements as functions of time and altitude and quantitatively agree with the measurements to within ∼30% or better during the entire day, including during the rapid temperature increase at dawn.Item Restricted Seeding and layering of equatorial spread F by gravity waves(American Geophysical Union, 1990-10) Hysel, D. L.; Kelley, M. C.; Swartz, W. E.; Woodman Pollitt, Ronald FranciscoStudies dating back more than 15 years have presented evidence that atmospheric gravity waves play a role in initiating nighttime equatorial F region instabilities. This paper analyzes a spectacular spread F event that for the first time demonstrates a layering which, we argue, is controlled by a gravity wave effect. The 50-km vertical wavelength of a gravity wave which we have found is related theoretically to a plasma layering irregularity that originated at low altitudes and then was convected, intact, to higher altitudes. Gravity waves also seem to have determined bottomside intermediate scale undulations, although this fact is not as clear in the data. The neutral wind dynamo effect yields wave number conditions on the gravity wave's ability to modulate the Rayleigh-Taylor instability process. Finally, after evaluating the gravity wave dispersion relation and spatial resonance conditions, we estimate the properties of the seeding wave.