Bibliography
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Found 18 entries in the Bibliography.
Showing entries from 1 through 18
| 2015 |
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Auroral precipitation models and space weather Newell, Patrick; Liou, Kan; Zhang, Yongliang; Sotirelis, Thomas; Mitchell, EJ; Mitchell, Elizabeth; Published by: Auroral dynamics and space weather Published on: |
| 2014 |
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Local Geomagnetic Indices and the Prediction of Auroral Power The aurora has been related to magnetometer observations for centuries, and to geomagnetic indices for decades. As the number of stations and data processing power increases, just how auroral power (AP) relates to geomagnetic observations becomes a more tractable question. This paper compares Polar UVI AP observations during 1997 with a variety of indices. Local time (LT) versions of the SuperMAG auroral electrojet (SME) are introduced and examined, along with the corresponding upper and lower envelopes (SMU and SML). Also, the East\textendashwest component, BE, is investigated. We also consider whether using any of the local indices is actually better at predicting local AP than a single global index. Each index is separated into 24 LT indices with a sliding 3-h MLT window. The ability to predict AP varies greatly with LT, peaking at 1900 MLT, where about 75\% of the variance (r2) is predicted at 1-min cadence. The aurora is fairly predictable from 1700 MLT \textendash 0400 MLT, roughly the region in which substorms occur. AP is poorly predicted from auroral electrojet indices from 0500 MLT \textendash 1500 MLT, with the minimum at 1000\textendash1300 MLT. In the region of high predictability, the local index which works best is BE (East\textendashwest), in contrast to long-standing expectations. However using global SME is better than any local index. AP is best predicted by combining global SME with a local index: BE from 1500\textendash0300 MLT, and either SMU or SML from 0300\textendash1500 MLT. In the region of the diffuse aurora, it is better to use a 30 min average than the cotemporaneous 1-min SME value, while from 1500\textendash0200 MLT the cotemporaneous 1-min SME works best, suggesting a more direct physical relationship with the auroral circuit. These results suggest a significant role for discrete auroral currents closing locally with Pedersen currents. Published by: Journal of Geophysical Research: Space Physics Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014JA020524 AURORA; auroral electrojet; indices; Pedersen current; Prediction |
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OVATION Prime-2013: Extension of auroral precipitation model to higher disturbance levels OVATION Prime (OP) is an auroral precipitation model parameterized by solar wind driving. Distinguishing features of the model include an optimized solar wind-magnetosphere coupling function (dΦMP/dt) which predicts auroral power significantly better than\ Kp\ or other traditional parameters, the separation of aurora into categories (diffuse aurora, monoenergetic, broadband, and ion), the inclusion of seasonal variations, and separate parameter fits for each magnetic latitude (MLAT) \texttimes magnetic local time (MLT) bin, thus permitting each type of aurora and each location to have differing responses to season and solar wind input\textemdashas indeed they do. We here introduce OVATION Prime-2013, an upgrade to the 2010 version currently widely available. The most notable advantage of OP-2013 is that it uses UV images from the GUVI instrument on the satellite TIMED for high disturbance levels (dΦMP/dt \> 1.2 MWb/s which roughly corresponds toKp = 5+ or 6-). The range of validity is approximately 0 \< dΦMP/dt <= 3.0 MWb/s (Kp\ about 8+). Other upgrades include a reduced susceptibility to salt-and-pepper noise, and smoother interpolation across the postmidnight data gap. The model is tested against an independent data set of hemispheric auroral power from Polar UVI. Over the common range of validity of OP-2010 and OP-2013, the two models predict auroral power essentially identically, primarily because hemispheric power calculations were done in a way to minimize the impact of OP-2010s noise. To quantitatively demonstrate the improvement at high disturbance levels would require multiple very large substorms, which are rare, and insufficiently present in the limited data set of Polar UVI hemispheric power values. Nonetheless, although OP-2010 breaks down in a variety of ways above\ Kp = 5+ or 6-, OP-2013 continues to show the auroral oval advancing equatorward, at least to 55\textdegree MLAT or a bit less, and OP-2013 does not develop spurious large noise patches. We will also discuss the advantages and disadvantages of other precipitation models more generally, as no one model fits best all possible uses. Newell, P.; Liou, K.; Zhang, Y.; Sotirelis, T.; Paxton, L.; Mitchell, E.; Published by: Space Weather Published on: 06/2014 YEAR: 2014 DOI: 10.1002/swe.v12.610.1002/2014SW001056 |
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Developing a Multi-Element Geospace Investigation to Understand the Impact of Hemispheric Assymetry Paxton, Larry; Newell, Patrick; Stromme, Anja; Ridley, Aaron; Kozyra, Janet; Mitchell, Elizabeth; Published by: Published on: |
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Understanding Hemispheric Asymmetry and Space Weather I Posters Paxton, Larry; Newell, Patrick; Stromme, Anja; Ridley, Aaron; Published by: Published on: |
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Newell, Patrick; Liou, Kan; Zhang, Yongliang; Sotirelis, Thomas; Paxton, Larry; Mitchell, Elizabeth; Published by: Published on: |
| 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 |
| 2012 |
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Evaluation of OVATION Prime as a forecast model for visible aurorae This study evaluates the ability of the OVATION Prime auroral precipitation model to provide operational forecasts of the visible aurora. An operational implementation would primarily provide the general public with some guidance for viewing the aurora. We evaluate the likelihood that if aurorae are predicted to be visible at a location, they will be seen there within the hour. Nighttime model forecasts were validated with Polar Ultraviolet Imager data for Kp >= 3 and for the years 1997 and 1998. The overall forecasts for a visible aurora to occur or to not occur were correct 77\% of the time. The most important prediction for public auroral viewing is that the visible aurora will occur, and these forecasts were correct 86\% of the time. Machol, Janet; Green, Janet; Redmon, Robert; Viereck, Rodney; Newell, Patrick; Published by: Space Weather: The International Journal of Research and Applications Published on: 09/2012 YEAR: 2012 DOI: 10.1029/2011SW000746 |
| 2011 |
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Lu, G.; Li, W.; Raeder, J.; Deng, Y.; Rich, F.; Ober, D.; Zhang, Y.; Paxton, L.; Ruohoniemi, J.; Hairston, M.; Newell, P.; Published by: Journal of Geophysical Research Published on: Jan-01-2011 YEAR: 2011 DOI: 10.1029/2011JA017043 |
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TIMED/GUVI observation of solar illumination effect on auroral energy deposition Liou, K.; Zhang, Y.-L.; Newell, P.; Paxton, L.; Carbary, J.; Published by: Journal of Geophysical Research Published on: Jan-01-2011 YEAR: 2011 DOI: 10.1029/2010JA016402 |
| 2010 |
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Predictive ability of four auroral precipitation models as evaluated using Polar UVI global images Newell, P.; Sotirelis, T.; Liou, K.; Lee, A.; Wing, S.; Green, J.; Redmon, R.; Published by: Space Weather Published on: Jan-01-2010 YEAR: 2010 DOI: 10.1029/2010SW000604 |
| 2009 |
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Ionospheric control of auroral occurrence Liou, Kan; Zhang, Yongliang; Newell, Patrick; Paxton, Larry; Published by: Published on: |
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Does the polar cap disappear under an extended strong northward IMF? Zhang, Yongliang; Paxton, Larry; Newell, Patrick; Meng, Ching-I; Published by: Journal of atmospheric and solar-terrestrial physics Published on: |
| 2005 |
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The coincident TIMED/Global Ultraviolet Imager (TIMED/GUVI) optical and DMSP particle observations have revealed new features of the optical signature of the polar cusp under a southward interplanetary magnetic field (IMF). We have found that cusp auroras usually take the shape of a thin arc with a width around 100\textendash200 km. This provides the first far-ultraviolet evidence of the narrow cusp under a southward IMF [Newell and Meng, 1987]. The cusp auroras could extend down to 0800 magnetic local time (MLT) in the morningside and 1400 MLT in the duskside. Its length is about a few thousand kilometers. A large solar wind density, speed, and IMF are necessary conditions for GUVI to observe the cusp aurora. We found that the cusp location at 1200 MLT changes linearly (-10 nT\ Bz\ \< 0 nT) and nonlinearly (Bz\ \< -10 nT) with the IMF\ Bz. The nonlinear effect can be explained by an\ L-3\ dependence of the Earth\textquoterights equatorial magnetic field. Zhang, Y; Meng, C-I; Paxton, LJ; Morrison, D; Wolven, B; Kil, H; Newell, P; Wing, S; Christensen, AB; Published by: Journal of Geophysical Research: Space Physics (1978\textendash2012) Published on: YEAR: 2005 DOI: 10.1029/2004JA010707 |
| 2003 |
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Optical Signature of Polar Cusp During Southward IMF Bz Observed by TIMED/GUVI and DMSP The GUVI instrument on board the TIMED satellite provides unique multi-wavelength observations of polar region emissions. In this study we focus on the identification of the polar cusp region during southward IMF conditions. Using simultaneous DMSP particle observations, the optical signatures and dynamics of the polar cusp region are investigated. We will address which of the five GUVI wavelengths can best be used for optical identification of the cusp precipitation by comparing images of various wavelengths. These new GUVI observations suggest that cusp aurora in the FUV extends over a relatively wide MLT range during a large southward IMF Bz. Characteristics and morphology of the cusp auroras in the FUV will also be discussed. Zhang, Y.; Meng, C.~I.; Paxton, L.~J.; Morrison, D.; Wolven, B.; Kil, H.; Newell, P.; Wing, S.; Christensen, A.~B.; Published by: AGU Fall Meeting Abstracts Published on: 2455 Particle precipitation; 2704 Auroral phenomena (2407); 2724 Magnetopause; and boundary layers; cusp |
| 2002 |
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Meng, CI; Zhang, Y; Paxton, LJ; Newell, PT; Sotirelis, TS; Christensen, AB; Published by: Published on: |
| 2000 |
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Lui, ATY; Chapman, SC; Liou, K; Newell, PT; Meng, CI; Brittnacher, M; Parks, GK; Williams, DJ; McEntire, RW; Christon, SP; , others; Published by: JOHNS HOPKINS APL TECHNICAL DIGEST Published on: |
| 1999 |
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Advancing our understanding of the atmosphere and ionosphere using remote sensing techniques Greenwald, Raymond; Lloyd, Steven; Newell, Patrick; Paxton, Larry; Yee, Jeng-Hwa; Published by: Johns Hopkins APL technical digest Published on: |
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