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Found 7 entries in the Bibliography.
Showing entries from 1 through 7
| 2014 |
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Multiple instrumental observations including GPS total electron content (TEC), foF2 and hmF2 from ionosondes, vertical ion drift measurements from Communication/Navigation Outage Forecasting System, magnetometer data, and far ultraviolet airglow measured by Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (TIMED/GUVI) are used to investigate the profound ionospheric disturbances at midlatitude and low latitude during the 14\textendash17 July 2012 geomagnetic storm event, which was featured by prolonged southward interplanetary geomagnetic field component for about 30 h below -10 nT. In the East Asian/Australian sector, latitudinal profile of TEC variations in the main phase were characterized by three bands of increments and separated by weak depressions in the equatorial ionospheric anomaly (EIA) crest regions, which were caused by the combined effects of disturbance dynamo electric fields (DDEF) and equatorward neutral winds. In the recovery phase, strong inhibition of EIA occurred and the summer crest of EIA disappeared on 16 July due to the combined effects of intrusion of neutral composition disturbance zone as shown by the TIMED/GUVI O/N2 measurements and long-lasting daytime westward DDEF inferred from the equatorial electrojet observations. The transit time of DDEF over the dip equator from westward to eastward is around 2200 LT. In the American longitude, the salient ionospheric disturbances in the summer hemisphere were characterized by daytime periodical intrusion of negative phase for three consecutive days in the recovery phase, preceded by storm-enhanced density plume in the initial phase. In addition, multiple short-lived prompt penetration electric fields appeared during stable southward interplanetary magnetic field (IMF) Bz in the recovery phase and were responsible for enhanced the EIA and equatorial ionospheric uplift around sunset. Liu, Jing; Liu, Libo; Nakamura, Takuji; Zhao, Biqiang; Ning, Baiqi; Yoshikawa, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.910.1002/2014JA020273 GUVI; Ionospheric storm; prompt penetration electric fields; TIMED |
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Gravity wave activity and dissipation in the height range from the low stratosphere to the low thermosphere (25\textendash115 km) covering latitudes between 50\textdegreeS and 50\textdegreeN are statistically studied by using 9-year (January 22, 2002\textendashDecember 31, 2010) SABER/TIMED temperature data. We propose a method to extract realistic gravity wave fluctuations from the temperature profiles and treat square temperature fluctuations as GW activity. Overall, the gravity wave activity generally increases with height. Near the equator (0\textdegree\textendash10\textdegree), the gravity wave activity shows a quasi-biennial variation in the stratosphere (below 40 km) while from 20\textdegree to 30\textdegree, it exhibits an annual variation below 40 km; in low latitudes (0\textdegree\textendash30\textdegree) between the upper stratosphere and the low thermosphere (40\textendash115 km), the gravity wave activity shows a semi-annual variation. In middle latitudes (40\textdegree\textendash50\textdegree), the gravity wave activity has a clear annual variation below 85 km. In addition, we observe a four-monthly variation with peaks occurring usually in April, August, December in the northern hemisphere and in February, June, October in the southern hemisphere, respectively, above 85 km in middle latitudes, which has been seldom reported in gravity wave activity. In order to study the dissipation of gravity wave propagation, we calculate the gravity wave dissipation ratio, which is defined as the ratio of the gravity wave growth scale height to the atmosphere density scale height. The height variation of the dissipation ratio indicates that strong gravity wave dissipation mainly concentrates in the three height regions: the stratosphere (30\textendash60 km), the mesopause (around 85 km) and the low thermosphere (above 100 km). Besides, gravity wave energy enhancement can be also observed in the background atmosphere. Shuai, Jing; Zhang, ShaoDong; Huang, ChunMing; YI, Fan; Huang, KaiMing; Gan, Quan; Gong, Yun; Published by: Science China Technological Sciences Published on: 05/2014 YEAR: 2014 DOI: 10.1007/s11431-014-5527-z climatology; dissipation; gravity wave; middle and high atmosphere; SABER; TIMED |
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Polar cap arcs correlated with solar wind entry at the high latitude magnetosphere Polar cap arcs are sun-aligned aurora structures occurring during northward turnings of the Interplanetary Magnetic Field (IMF) Bz component. At the same time, a new region of solar wind entry at the high latitude magnetosphere, tailward of the cusp region, was found recently at the periods of northward IMF Bz. We propose a study to see the relationship of these entry events with the transpolar arc formation. Data of Global Ultraviolet Imager (GUVI) onboard TIMED mission is examined to see the transpolar aurora arcs during the given time periods of the solar wind entry. Initial results show that in approximately 20\% of cases transpolar arcs occur related to the solar wind entry processes. Mailyan, B.; Shi, Q.; Gou, X.; Published by: Published on: YEAR: 2014 DOI: 10.1109/URSIGASS.2014.6929926 aurora interplanetary; GUVI; magnetic fields; magnetosphere; solar wind; TIMED |
| 2013 |
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Statistical comparison of isolated and non-isolated auroral substorms The present study compares isolated and non-isolated substorms in terms of their global morphology and energy deposition. The analysis is based on a list of geomagnetic substorm onsets identified with magnetometer data from SuperMAG and published previously by Newell and Gjerlove (2011a). Isolated substorms are defined as those with separation of two consecutive onsets no less than 3 h. The auroral data are obtained from the global ultraviolet imager (GUVI) on board the TIMED satellite and are rebinned into typical magnetic latitude-magnetic local time maps. The auroral maps are then averaged in 1 min intervals to show the dynamic change of the aurora. The three phases of the substorm are clearly demonstrated in both isolated and non-isolated substorms. However, there are noticeable differences between the two types of substorms: (1) While the nighttime auroral power for both types of substorms slightly increases in the growth phase, isolated (non-isolated) substorms are associated with smaller (greater) nighttime auroral power. (2) In the expansion phase, isolated substorms are associated with greater and more explosive energy release than non-isolated substorms. (3) The time for the recovery phase is ~2 times longer for isolated than for non-isolated substorms. (4) The winter-to-summer auroral power ratio is approximately constant throughout the three substorm phases and the ratio is larger for isolated (~30\%) than that for non-isolated (~10\%) substorms. It is also found that the polar cap area increases during the growth phase until ~10 min prior to the magnetic substorm onset and decreases rapidly thereafter. The decrease is found to result from the closure of the nightside polar cap associated with substorm expansion. It is found that the observed differences between the two types of substorms simply reflect the differences in the solar wind and EUV drivers. Thus, we conclude that there is no intrinsic difference between isolated and non-isolated substorms in terms of auroral energy release and subsequent auroral power decay. Liou, Kan; Newell, Patrick; Zhang, Yong-Liang; Paxton, Larry; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2013 YEAR: 2013 DOI: 10.1002/jgra.50218 |
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Auroral nighttime infrared emission observed by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere\textendashIonosphere\textendashMesosphere Energetics and Dynamics (TIMED) satellite is used to develop an empirical model of geomagnetic storm enhancements to E-region electron densities. The empirical model is called STORM-E and will be incorporated into the 2012 release of the International Reference Ionosphere (IRI). The proxy for characterizing the E-region response to geomagnetic forcing is NO+(v) Volume Emission Rates (VER) derived from the TIMED/SABER 4.3\ μm channel limb radiance measurements. The storm-time response of the NO+(v) 4.3\ μm VER is most sensitive to auroral particle precipitation. A statistical database of storm-time to climatological quiet-time ratios of SABER-observed NO+(v) 4.3\ μm VER are fit to widely available geomagnetic indices using the theoretical framework of linear impulse-response theory. The STORM-E model provides a dynamic storm-time correction factor to adjust a known nighttime quiescent E-region electron density peak concentration for geomagnetic enhancements due to auroral particle precipitation. Part I of this series gives a detailed description of the algorithms and methodologies used to derive NO+(v) VER from SABER 4.3\ μm limb emission measurements. In this paper, Part II of the series, the development of the E-region electron density storm-time correction factor is described. The STORM-E storm-time correction factor is fit to a single geomagnetic index. There are four versions of the STORM-E model, which are currently independent of magnetic local time. Each version is fit to one of the following indices: HP, AE, Ap, or Dst. High-latitude Incoherent Scatter Radar (ISR) E-region electron density measurements are compared to STORM-E predictions for various geomagnetic storm periods during solar cycle 23. These comparisons show that STORM-E significantly improves the prediction of E-region electron density enhancements due to auroral particle precipitation, in comparison to the nominal IRI model or to the quiet-time baseline electron density concentrations measured by ISR. The STORM-E/ISR comparisons indicate that the STORM-E fits to the Ap-, AE-, and HP-indices are comparable in both absolute accuracy and relative dynamical response. Contrarily, the Dst-index does not appear to be a suitable input driver to parameterize the E-region electron density response to geomagnetic activity. Mertens, Christopher; Xu, Xiaojing; Bilitza, Dieter; Mlynczak, Martin; Russell, James; Published by: Advances in Space Research Published on: 02/2013 YEAR: 2013 DOI: 10.1016/j.asr.2012.09.014 AURORA; Auroral particle precipitation; E-region; Infrared remote sensing; Ionosphere; Magnetic storm; TIMED |
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The quiet nighttime low-latitude ionosphere as observed by TIMED/GUVI In this paper, we examine the nighttime ionosphere climatology structure in the low latitude region and discrepancies between Global Ultraviolet Imager (GUVI) observations and the IRI model predictions using (1) the magnetic zonal mean of electron number density as a function of altitude and magnetic latitude, (2) vertical electron density profiles at various levels of F10.7 index, (3) nighttime descent and magnitude decrease of the ionosphere, (4) point-to-point comparisons of F-peak height (hmF2) and density (NmF2), and (5) the magnetic longitudinal variations of hmF2 and NmF2. The data collected from the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) mission since its launch in December 2001 have provided great opportunities for many scientific investigations of the ionosphere. In this analysis, we investigate the climatology of the nighttime low-latitude ionosphere under low geomagnetic activity (kp\ ⩽\ 4) using the electron density profiles inferred from the airglow measurements obtained by the GUVI aboard the TIMED spacecraft and compared with the results obtained from IRI (International Reference Ionosphere) model-2001. The observed climatology is an essential tool for further understanding the electrodynamics in the low-latitude region and improving the model\textquoterights prediction capability. The time range of the GUVI data used in this study is from 2002 (day 053) to 2006 (day 304), and the IRI model predictions were produced at every GUVI location. The ionosphere observed is generally of greater density than what IRI predicts throughout the night for all four seasons for low and moderate solar activity while the model over-predicts the electron density near the F-region peak at high solar activity before midnight. Observations show that the height of the F-region peak has a steep descent from dusk to midnight and near midnight the height of layer is insensitive to solar conditions, significantly different than what is predicted by IRI. Longitudinal features shown in GUVI data are present in the low-latitude ionosphere after sunset and continue through to midnight after which the low-latitude ionosphere is largely zonally symmetric. Talaat, E.R.; Yee, J.-H.; Hsieh, S.-Y.; Paxton, L.J.; DeMajistre, R.; Christensen, A.B.; Bilitza, D.; Published by: Advances in Space Research Published on: 02/2013 YEAR: 2013 DOI: 10.1016/j.asr.2012.11.012 |
| 2005 |
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The NASA TIMED/GUVI experiment obtained unprecedented far ultraviolet images of thermospheric composition and temperature during the intense geomagnetic storm on 20\textendash21 November 2003. Geographic maps of the atomic oxygen to molecular nitrogen column density ratio show severe depletions that extend to the equator near the peak of the storm. This ratio is a key indicator of how the thermospheric composition is disrupted at high latitudes and how the perturbed air moves globally as a result of dynamical forcing. For example, migrating regions of low oxygen-to-nitrogen air are invariably found to correlate with high thermospheric temperatures. As well, GUVI obtained altitudinal-latitudinal (limb) images of temperature and composition, which show how the disturbances vary at different heights. The ASPEN thermospheric global circulation model was used to test our understanding of these remarkable images. The resulting simulations of thermospheric response show good agreement with GUVI data prior to the peak of the storm on 20 November. During the peak and recovery phases, serious discrepancies between data and model are seen. Although this initial attempt to model the storm is encouraging, much more detailed analysis is required, especially of the high-latitude inputs. The GUVI images demonstrate that far ultraviolet imaging is becoming a crucial component of space weather research and development. Meier, R.; Crowley, G.; Strickland, D.; Christensen, A.; Paxton, L.; Morrison, D.; Hackert, C.; Published by: Journal of Geophysical Research Published on: 09/2005 YEAR: 2005 DOI: 10.1029/2004JA010990 dayglow; geomagnetic storm; GUVI; remote sensing; thermospheric composition; TIMED |
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