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Douglas G. Torr - One of the best experts on this subject based on the ideXlab platform.
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the dependence of modeled oi 1356 and n2 lyman birge hopfield auroral emissions on the Neutral Atmosphere
Journal of Geophysical Research, 1990Co-Authors: Marsha R. Torr, P. G. Richards, Douglas G. TorrAbstract:Images of the entire auroral oval at carefully selected wavelengths contain information on the global energy influx due to energetic particles and some information on the characteristic energy of the precipitating particles. In this paper we investigate the sensitivity of selected auroral emissions to changes in the Neutral Atmosphere. In particular, we examine the behavior of OI 1356 A and two Lyman Birge Hopfield (LBH) bands and their ratios to each other with changing atmospheric composition. The two LBH bands are selected so that one lies in the region of strong O2 absorption (1464 A) and one lies at a wavelength where O2 absorption is effectively negligible (1838 A). We find that for anticipated average uncertainties in the Neutral Atmosphere (factor of 2 at auroral altitudes), the resultant change in the modeled intensities is comparable to or less than the uncertainty in the Neutral Atmosphere. The smallest variations, for example, are for I 1838 (approximately 10 to 20%) while the largest variation is seen in the OI 1356 A emission which is linear with [O] to within 20%. We have also investigated the dependence of these intensities, and their ratios, to much larger changes in the composition (i.e., [O]/[N2]) such as might be encountered in large magnetic storms, or over seasonal or solar cycle extremes. We find that the variation in the I 1356/I 1838 ratio over the equivalent of a solar cycle is less than 50%. The summer-to-winter changes are approximately a factor of 2. The I 1356/I 1838 ratio is a very sensitive indicator of the charactenstic energy, showing a change of 13 over the energy range 200 eV to 10 keV. The corresponding change in the LBH long-to-short wavelength ratio is much less (about a factor of 3). However, the latter is insensitive to changes in the Neutral Atmosphere (<20% changes in LBH emission ratio for large changes in N2). The three emissions therefore potentially provide a most valuable diagnostic of particle characteristic energy and energy flux.
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The dependence of modeled OI 1356 and N2 Lyman Birge Hopfield auroral emissions on the Neutral Atmosphere
Journal of Geophysical Research, 1990Co-Authors: Marsha R. Torr, P. G. Richards, Douglas G. TorrAbstract:Images of the entire auroral oval at carefully selected wavelengths contain information on the global energy influx due to energetic particles and some information on the characteristic energy of the precipitating particles. In this paper we investigate the sensitivity of selected auroral emissions to changes in the Neutral Atmosphere. In particular, we examine the behavior of OI 1356 A and two Lyman Birge Hopfield (LBH) bands and their ratios to each other with changing atmospheric composition. The two LBH bands are selected so that one lies in the region of strong O2 absorption (1464 A) and one lies at a wavelength where O2 absorption is effectively negligible (1838 A). We find that for anticipated average uncertainties in the Neutral Atmosphere (factor of 2 at auroral altitudes), the resultant change in the modeled intensities is comparable to or less than the uncertainty in the Neutral Atmosphere. The smallest variations, for example, are for I 1838 (approximately 10 to 20%) while the largest variation is seen in the OI 1356 A emission which is linear with [O] to within 20%. We have also investigated the dependence of these intensities, and their ratios, to much larger changes in the composition (i.e., [O]/[N2]) such as might be encountered in large magnetic storms, or over seasonal or solar cycle extremes. We find that the variation in the I 1356/I 1838 ratio over the equivalent of a solar cycle is less than 50%. The summer-to-winter changes are approximately a factor of 2. The I 1356/I 1838 ratio is a very sensitive indicator of the charactenstic energy, showing a change of 13 over the energy range 200 eV to 10 keV. The corresponding change in the LBH long-to-short wavelength ratio is much less (about a factor of 3). However, the latter is insensitive to changes in the Neutral Atmosphere (
D. P. Hinson - One of the best experts on this subject based on the ideXlab platform.
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Characteristics of Mini-Magnetospheres Formed by Paleo-Magnetic Fields of Mars
2020Co-Authors: Norman F. Ness, A. M. Krymskii, D. H. Crider, T. K. Breus, Mario H. Acuña, D. P. Hinson, K. K. BarashyanAbstract:The intensely and non-uniformly magnetized crustal sources generate an effective large-scale magnetic field. In the Southern hemisphere the strongest crustal fields lead to the formation of large-scale mini-magnetospheres. In the Northern hemisphere, the crustal fields are rather weak and there are only isolated mini-magnetospheres. Re-connection with the interplanetary magnetic field (IMF) occurs in many localized regions. This may occur not only in cusp-like structures above nearly vertical field anomalies but also in halos extending several hundreds of kilometers from these sources. Re-connection will permit solar wind (SW) and more energetic particles to precipitate into and heat the Neutral Atmosphere. Electron density profiles of the ionosphere of Mars derived from radio occultation data obtained by the Radio Science Mars Global Surveyor (MGS) experiment are concentrated in the near polar regions. The effective scale-height of the Neutral Atmosphere density in the vicinity of the ionization peak has been derived for each of the profiles studied. The effective scale-heights have been compared with the crustal magnetic fields measured by the MGS Magnetometer/Electron Reflectometer (MAG/ER) experiment. A significant difference between the large-scale mini-magnetospheres and regions outside of them has been found. The Neutral Atmosphere is cooler inside the large-scale mini-magnetospheres. It appears that outside of the cusps the strong crustal magnetic fields prevent additional heating of the Neutral Atmosphere by direct interaction of the SW. The scale-height of the Neutral Atmosphere density derived from the experiment with the MGS Accelerometer has been compared with MAG/ER data. The scale-height was found to be usually larger than mean value near the boundaries of potential mini-magnetospheres and around cusps . It may indicate that the paleo-magnetic/IMF field re-connection is characteristic of the mini-magnetospheres at Mars.
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radio occultation measurements of pluto s Neutral Atmosphere with new horizons
Icarus, 2017Co-Authors: D. P. Hinson, Ivan Linscott, Leslie A. Young, G. L. Tyler, S. A. Stern, Ross A. Beyer, M. K. Bird, Kimberly Ennico, G. R. Gladstone, Catherine B. OlkinAbstract:Abstract On 14 July 2015 New Horizons performed a radio occultation (RO) that sounded Pluto’s Atmosphere down to the surface. The sensitivity of the measurements was enhanced by a unique configuration of ground equipment and spacecraft instrumentation. Signals were transmitted simultaneously by four antennas of the NASA Deep Space Network, each radiating 20 kW at a wavelength of 4.2 cm. The polarization was right circular for one pair of signals and left circular for the other pair. New Horizons received the four signals and separated them by polarization for processing by two independent receivers, each referenced to a different ultra-stable oscillator. The two data streams were digitized, filtered, and stored on the spacecraft for later transmission to Earth. The results reported here are the first to utilize the complete set of observations. We calibrated each signal to remove effects not associated with Pluto’s Atmosphere, including the limb diffraction pattern. We then applied a specialized method of analysis to retrieve profiles of number density, pressure, and temperature from the combined phase measurements. Occultation entry sounded the Atmosphere at sunset at 193.5°E, 17.0°S — on the southeast margin of an ice-filled basin known informally as Sputnik Planitia (SP); occultation exit occurred at sunrise at 15.7°E, 15.1°N — near the center of the Charon-facing hemisphere. Above 1215 km radius (∼25 km altitude) there is no discernible difference between the measurements at entry and exit, and the RO profiles are consistent with results derived from ground-based stellar occultation measurements. At lower altitudes the RO measurements reveal horizontal variations in atmospheric structure that had not been observed previously, and they are the first to reach the ground. The entry profile has a strong temperature inversion that ends 3.5 km above the surface, and the temperature in the cold boundary layer beneath the inversion is nearly constant, 38.9 ± 2.1 K, and close to the saturation temperature of N 2 . The exit profile has a much weaker inversion that extends all the way to the ground, where the air temperature is 51.6 ± 3.8 K. Three factors appear to be responsible for the presence of a cold boundary layer in the entry profile (Forget et al., 2017): a substantial diurnal cycle of sublimation and condensation of N 2 ice in SP, the local time of the RO observation, and confinement within SP by the surrounding topography and katabatic winds. We have also determined the surface pressure and the local radius at both entry and exit. The best pressure reference is the mean value: 11.5 ± 0.7 microbar at 1189.9 ± 0.2 km.
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Solar wind interaction with the ionosphere/Atmosphere and crustal magnetic fields at Mars: Mars Global Surveyor Magnetometer/Electron Reflectometer, radio science, and accelerometer data
Journal of Geophysical Research, 2004Co-Authors: A. M. Krymskii, Norman F. Ness, D. H. Crider, T. K. Breus, Mario H. Acuña, D. P. HinsonAbstract:[1] The solar wind (SW) mainly interacts with the Martian ionosphere/Atmosphere. However, the intense crustal magnetization creates localized minimagnetospheres above the surface. The interplanetary magnetic field (IMF) can reconnect with these crustal fields and this allows SW and more energetic particles to precipitate into and heat the Neutral Atmosphere in localized regions, especially in the southern hemisphere. A study of 907 electron density profiles obtained by the MGS Radio Science (RS) experiment at latitudes from +63° to +77° and 219 profiles at latitudes −69° to −64.5° has been conducted. The role of the magnetic field as a driving force of the cross-terminator convection is discussed. Longitudinal variations of Neutral Atmosphere scale height Hpeak derived from the MGS RS data have been analyzed. Ionospheric parameters are found to be more variable in the southern than in the northern hemisphere. This correlates well with the variability of the magnetic field direction from local zenith. The scale height of Neutral Atmosphere density HACC derived from the MGS accelerometer data is also found to be more variable in the southern than in the northern hemisphere.
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mars global surveyor radio science electron density profiles Neutral Atmosphere implications
Geophysical Research Letters, 2001Co-Authors: S W Bougher, D. P. Hinson, S Engel, J M ForbesAbstract:The Mars Global Surveyor (MGS) Radio Sci- ence (RS) experiment permits retrieval of electron density prof iles versus height (∼90-200 km) from occultation mea- surements. An initial set of electron profiles is examined spanning high northern latitudes, early morning solar local times and high solar zenith angles (78 to 81 ◦ ) near aphelion. Sampling for these 32-profiles is well distributed over longi- tude. The height of the photochemically driven ionospheric peak is observed to respond to the background Neutral den- sity structure, with a mean height during this season at this location of ∼134.4 km. Strong wave-3 oscillations about this mean are clearly observed as a function of longitude, and correspond to Neutral density variations measured by the MGS Accelerometer (ACC) experiment. The wave-3 tidal pattern implicated by both the RS and ACC datasets is consistent with a semi-diurnal wave frequency. Clearly, the height of the martian dayside ionospheric peak is a sensitive indicator of the state of the underlying Mars Atmosphere. This ionospheric peak height can be used as a proxy of the longitude specific non-migrating tidal variations present in the Mars lower thermosphere.
Marsha R. Torr - One of the best experts on this subject based on the ideXlab platform.
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the dependence of modeled oi 1356 and n2 lyman birge hopfield auroral emissions on the Neutral Atmosphere
Journal of Geophysical Research, 1990Co-Authors: Marsha R. Torr, P. G. Richards, Douglas G. TorrAbstract:Images of the entire auroral oval at carefully selected wavelengths contain information on the global energy influx due to energetic particles and some information on the characteristic energy of the precipitating particles. In this paper we investigate the sensitivity of selected auroral emissions to changes in the Neutral Atmosphere. In particular, we examine the behavior of OI 1356 A and two Lyman Birge Hopfield (LBH) bands and their ratios to each other with changing atmospheric composition. The two LBH bands are selected so that one lies in the region of strong O2 absorption (1464 A) and one lies at a wavelength where O2 absorption is effectively negligible (1838 A). We find that for anticipated average uncertainties in the Neutral Atmosphere (factor of 2 at auroral altitudes), the resultant change in the modeled intensities is comparable to or less than the uncertainty in the Neutral Atmosphere. The smallest variations, for example, are for I 1838 (approximately 10 to 20%) while the largest variation is seen in the OI 1356 A emission which is linear with [O] to within 20%. We have also investigated the dependence of these intensities, and their ratios, to much larger changes in the composition (i.e., [O]/[N2]) such as might be encountered in large magnetic storms, or over seasonal or solar cycle extremes. We find that the variation in the I 1356/I 1838 ratio over the equivalent of a solar cycle is less than 50%. The summer-to-winter changes are approximately a factor of 2. The I 1356/I 1838 ratio is a very sensitive indicator of the charactenstic energy, showing a change of 13 over the energy range 200 eV to 10 keV. The corresponding change in the LBH long-to-short wavelength ratio is much less (about a factor of 3). However, the latter is insensitive to changes in the Neutral Atmosphere (<20% changes in LBH emission ratio for large changes in N2). The three emissions therefore potentially provide a most valuable diagnostic of particle characteristic energy and energy flux.
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The dependence of modeled OI 1356 and N2 Lyman Birge Hopfield auroral emissions on the Neutral Atmosphere
Journal of Geophysical Research, 1990Co-Authors: Marsha R. Torr, P. G. Richards, Douglas G. TorrAbstract:Images of the entire auroral oval at carefully selected wavelengths contain information on the global energy influx due to energetic particles and some information on the characteristic energy of the precipitating particles. In this paper we investigate the sensitivity of selected auroral emissions to changes in the Neutral Atmosphere. In particular, we examine the behavior of OI 1356 A and two Lyman Birge Hopfield (LBH) bands and their ratios to each other with changing atmospheric composition. The two LBH bands are selected so that one lies in the region of strong O2 absorption (1464 A) and one lies at a wavelength where O2 absorption is effectively negligible (1838 A). We find that for anticipated average uncertainties in the Neutral Atmosphere (factor of 2 at auroral altitudes), the resultant change in the modeled intensities is comparable to or less than the uncertainty in the Neutral Atmosphere. The smallest variations, for example, are for I 1838 (approximately 10 to 20%) while the largest variation is seen in the OI 1356 A emission which is linear with [O] to within 20%. We have also investigated the dependence of these intensities, and their ratios, to much larger changes in the composition (i.e., [O]/[N2]) such as might be encountered in large magnetic storms, or over seasonal or solar cycle extremes. We find that the variation in the I 1356/I 1838 ratio over the equivalent of a solar cycle is less than 50%. The summer-to-winter changes are approximately a factor of 2. The I 1356/I 1838 ratio is a very sensitive indicator of the charactenstic energy, showing a change of 13 over the energy range 200 eV to 10 keV. The corresponding change in the LBH long-to-short wavelength ratio is much less (about a factor of 3). However, the latter is insensitive to changes in the Neutral Atmosphere (
Richard B Langley - One of the best experts on this subject based on the ideXlab platform.
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a web based package for ray tracing the Neutral Atmosphere radiometric path delay
Computers & Geosciences, 2009Co-Authors: Reza Ghoddousifard, Peter Dare, Richard B LangleyAbstract:An online ray-tracing package has been developed to provide zenith and slant Neutral Atmosphere delays using RAdiosonde OBservation (RAOB) and numerical weather prediction (NWP) models to users worldwide to assist precise global navigation satellite systems positioning scenarios. The package includes a web interface, necessary scripts to access RAOB and NWP data, and ray-tracing software capable of using both types of data. In addition, global maps of zenith hydrostatic delay, zenith non-hydrostatic or wet delay, north-south, east-west and total gradient and comparison maps of the University of New Brunswick climate-based models, and values calculated from NWP models every 3h are also provided. In this paper, the theoretical aspects of ray tracing will be reviewed. The structure of the software and web page, validation of results using different data sources, and further development for gradient calculations are explained.
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a north america wide area Neutral Atmosphere model for gnss applications
Annual of Navigation, 2009Co-Authors: Rodrigo Leandro, Marcelo C Santos, Richard B LangleyAbstract:: In this paper we are introducing a new Neutral Atmosphere model, which was designed to provide better predictions for different regions inside a delimited wide area. The goal of this new development is to have a more reliable model for wide area augmentation system users, with some homogeneity in terms of accuracy performance over the area of interest. The approach for creating the new wide area Neutral Atmosphere model for North America (UNBw.na) is comprehensively described and discussed. All result analyses took into consideration the most recent version of the UNB models, until now, UNB3m. Results for prediction of meteorological parameters show that the new grid-based model can perform better than a latitude (only) based model (such as UNB3m). The analyses showed that UNBw.na is consistently better than UNB3m in several aspects, and the adopted procedure for a meteorological parameter grid calibration has resulted in a reliable model.
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unb3m_pack a Neutral Atmosphere delay package for radiometric space techniques
Gps Solutions, 2008Co-Authors: Rodrigo Leandro, Richard B Langley, Marcelo C SantosAbstract:Several hybrid Neutral Atmosphere delay models have been developed at the University of New Brunswick. In this paper we are presenting UNB3m_pack, a package with subroutines in FORTRAN and corresponding functions in MatLab which provides Neutral atmospheric information estimated using the UNB3m model. The main goal of UNB3m is to provide reliable predicted Neutral Atmosphere delays for users of global navigation satellite systems (GNSS) and other transatmospheric radiometric techniques. Slant Neutral Atmosphere delays are the main output of the package, however, it can be used to estimate zenith delays, Niell mapping functions values, delay rates, mapping function rates, station pressure, temperature, relative humidity and the mean temperature of water vapor in the atmospheric column. The subroutines work using day of year, latitude, height and elevation angle as input values. The files of the package have a commented section at the beginning, explaining how the subroutines work and what the input and output parameters are. The subroutines are self-contained, i.e., they do not need any auxiliary files. The user has simply to add to his/her software one or more of the available files and call them in the appropriate way.
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wide area Neutral Atmosphere models for gnss applications
Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), 2006Co-Authors: Rodrigo Leandro, Marcelo C Santos, Richard B LangleyAbstract:In this work we discuss developments related to Neutral Atmosphere delay prediction models at UNB. We are introducing a new model, which was designed to provide better predictions for different regions inside a delimited wide area. The goal of this new development is to have a more reliable model for wide area augmentation system users, with some homogeneity in terms of performance over the area of interest. The approach to create the new wide area Neutral Atmosphere model for North America (UNBw.na) is comprehensively described and discussed. All result analyses took into consideration the most recent version of UNB models, until now, UNB3m. Results for meteorological parameters prediction showed that the new grid-based model could perform better than a latitude (only) based model (such as UNB3m). The general results do not show a spectacular improvement for the new model, however it is consistently better than its predecessor, and, the improvement for certain regions is more significant than others. Regions where the performance of the old model was not satisfactory had results significantly improved with the new model. A validation of UNBw.na predicted zenith delays was realized using radiosonde-derived delays as reference. This analysis showed that different regions of the continent manifested improvement for the estimations with the new model. Investigation of the performance of both models (UNBw.na and UNB3m) with radiosonde ray-raced delays at a few sample stations showed that UNBw.na generally has a better fit to the yearly behavior of the zenith delays. It was also possible to notice that results from UNBw.na are more consistent between stations at different locations than when using UNB3m. UNBw.na was shown to be consistently better than UNB3m in several aspects, and the adopted procedure for the grid calibration works in an adequate way, resulting in a reliable model. INTRODUCTION Mitigating the Neutral Atmosphere refraction is a crucial step in GNSS positioning. Also often called tropospheric delays, the Neutral Atmosphere delays are one of the main sources of measurement errors in GNSS. One usual way to account for these effects is using prediction models. There are also other alternatives for Neutral Atmosphere delay mitigation, such as the parameterization of the zenith delay in the positioning model, when dual frequency carrier-phase measurements are available. However, even in this case, the parameter is commonly a
Yannick Beniguel - One of the best experts on this subject based on the ideXlab platform.
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empirical model of the ionosphere based on cosmic formosat 3 for Neutral Atmosphere radio occultation processing
Atmospheric Measurement Techniques Discussions, 2017Co-Authors: Miquel Garciafernandez, M Hernandezpajares, A Rius, Riccardo Notarpietro, Axel Von Engeln, Yannick BeniguelAbstract:Abstract. The Radio Occultation instrument at the upcoming EUMETSAT Polar System – Second Generation (EPS-SG) mission will be devoted primarily to monitor the Neutral Atmosphere through this payload, consisting of a GNSS receiver and occultation antennae pointing slightly below the Earth's limb. The resulting data will be processed by EUMETSAT (primarily for L1B data) and by the ROMSAF's Radio Occultation Processing Package (ROPP) software to obtain the vertical profiles of temperature, pressure and other relevant level 2 parameters of the Neutral Atmosphere. Newer versions of this software might include a feature by which empirical models of the ionosphere (i.e. vertical profiles of electron density) can be included in the processing in order to increase the accuracy of the inverted bending angle profiles. In order to test this new feature, this work includes the efforts that have been made in order to provide an empirical model of the ionosphere purely based on vertical profiles of electron density inverted from data of previous radio occultation (RO) missions (i.e. COSMIC/FORMOSAT-3). The methodology used in this work is based on using the separability hypothesis, to overcome the spherical symmetry assumption of the Abel inversion as well as a new mechanization of the inversion process, based on a joint processing of all the occultation data via a linear mean square filter, rather than adopting the classical peel onion approach. Additionally, with the development of this empirical model, efforts have been made to construct a proxy index for scintillation monitoring based on the inverted profiles (Occultation Scintillation Proxy Index or OSPI), which shows reasonable correlation with the amplitude scintillation index S 4 .
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Empirical model of the ionosphere based on COSMIC/FORMOSAT-3 for Neutral Atmosphere radio occultation processing
Atmospheric Measurement Techniques Discussions, 2017Co-Authors: Miquel Garcia-fernandez, A Rius, Riccardo Notarpietro, Axel Von Engeln, Manuel Hernández-pajares, Yannick BeniguelAbstract:Abstract. The Radio Occultation instrument at the upcoming EUMETSAT Polar System – Second Generation (EPS-SG) mission will be devoted primarily to monitor the Neutral Atmosphere through this payload, consisting of a GNSS receiver and occultation antennae pointing slightly below the Earth's limb. The resulting data will be processed by EUMETSAT (primarily for L1B data) and by the ROMSAF's Radio Occultation Processing Package (ROPP) software to obtain the vertical profiles of temperature, pressure and other relevant level 2 parameters of the Neutral Atmosphere. Newer versions of this software might include a feature by which empirical models of the ionosphere (i.e. vertical profiles of electron density) can be included in the processing in order to increase the accuracy of the inverted bending angle profiles. In order to test this new feature, this work includes the efforts that have been made in order to provide an empirical model of the ionosphere purely based on vertical profiles of electron density inverted from data of previous radio occultation (RO) missions (i.e. COSMIC/FORMOSAT-3). The methodology used in this work is based on using the separability hypothesis, to overcome the spherical symmetry assumption of the Abel inversion as well as a new mechanization of the inversion process, based on a joint processing of all the occultation data via a linear mean square filter, rather than adopting the classical peel onion approach. Additionally, with the development of this empirical model, efforts have been made to construct a proxy index for scintillation monitoring based on the inverted profiles (Occultation Scintillation Proxy Index or OSPI), which shows reasonable correlation with the amplitude scintillation index S 4 .