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J M Forbes - One of the best experts on this subject based on the ideXlab platform.
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prolonged multiple excitation of large scale traveling Atmospheric Disturbances tads by successive and interacting coronal mass ejections
Journal of Geophysical Research, 2016Co-Authors: Jianpeng Guo, J M Forbes, Fengsi Wei, Xueshang Feng, Yuming Wang, Huixin Liu, Weixing Wan, Zhiliang Yang, Chaoxu LiuAbstract:Successive and interacting coronal mass ejections (CMEs) directed earthward can have significant impacts throughout geospace. While considerable progress has been made in understanding their geomagnetic consequences over the past decade, elucidation of their Atmospheric consequences remains a challenge. During 17-19 January 2005, a compound stream formed due to interaction of six successive halo CMEs impacted Earth's magnetosphere. In this paper, we report one Atmospheric consequence of this impact, namely, the prolonged multiple excitation of large-scale (>approximate to 1000km) traveling Atmospheric Disturbances (TADs). The TADs were effectively excited in auroral regions by sudden injections of energy due to the intermittent southward magnetic fields within the stream. They propagated toward the equator at speeds near 800m/s and produced long-duration (approximate to 2.5days) continuous large-scale density Disturbances of order up 40% in the global thermosphere.
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large scale traveling Atmospheric Disturbances lstads in the thermosphere inferred from champ grace and seta accelerometer data
Journal of Atmospheric and Solar-Terrestrial Physics, 2010Co-Authors: Sean Bruinsma, J M ForbesAbstract:Densities derived from accelerometer measurements on the GRACE, CHAMP, and Air Force/SETA satellites near 490, 390, and 220 km, respectively, are used to elucidate global-scale characteristics of traveling Atmospheric Disturbances (TADs). Several characteristics elucidated in numerical simulations are confirmed in this study, namely: (1) propagation speeds increase from the lower thermosphere to the upper thermosphere; (2) propagation to the equator and even into the opposite hemisphere can occur; (3) greater attenuation of TADs occurs during daytime and at higher levels of solar activity (i.e., more wave activity during nighttime and solar minimum), presumably due to the greater influence of ion drag. In addition, we find that the occurrence of significant TAD activity emanating from the auroral regions does not reflect a clear relation with the level of planetary magnetic activity as measured by Kp. There is also evidence of waves originating in the tropics, presumably due to convective sources; to some extent this may contribute to the Kp and solar flux relationships noted above. Further elucidation of local time, season, and altitude dependences of TAD propagation characteristics may be forthcoming from density measurements from the GOCE and Swarm missions.
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properties of traveling Atmospheric Disturbances tads inferred from champ accelerometer observations
Advances in Space Research, 2009Co-Authors: Sean Bruinsma, J M ForbesAbstract:Abstract Densities derived from accelerometer measurements on the CHAMP satellite near 400 km are used to statistically establish characteristics of large-scale (>1000 km) traveling Atmospheric Disturbances (TADs). Only TADs that at least propagate from the auroral zone to the equator are analyzed here, and a total of 21 identifiable events are found over the years 2001–2007. The average speed of all TADs, regardless of local time, is 646 ± 122 ms −1 . The average speeds on the dayside and nightside are 595 ± 127 ms −1 and 685 ± 106 ms −1 , respectively, i.e., the speed appears to be 10% higher on average on the nightside. On six occasions TADs were only detected on the night side; however, TADs on the dayside often appear more distinctly in the data. Moreover, contrary to some theoretical expectations, dayside TADs do not dissipate more readily than night side TADs, although much less are detected between 8–20 solar local time. No clear dependence of TAD amplitude or phase speed with respect to Kp, or rate of increase of Kp, is found.
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global observation of traveling Atmospheric Disturbances tads in the thermosphere
Geophysical Research Letters, 2007Co-Authors: Sean Bruinsma, J M ForbesAbstract:[1] Densities derived from accelerometer measurements on the CHAMP satellite near 400 km are used to elucidate global-scale characteristics of traveling Atmospheric Disturbances (TADs) in connection with 3 sudden injections of energy at high latitudes on 29 May 2003. Dayside TADs with typical amplitudes ∼20–30% propagate towards the equator from the northern hemisphere (southern hemisphere) auroral region with phase speeds of order 730 ms−1 (460 ms−1). Some evidence is found for TAD penetration from the northern to the southern Hemisphere, and for the first time for trans-polar propagation. Nighttime TAD signatures are less well defined, but have phase speeds similar to the dayside TADs. The above day-night and hemisphere differences possibly reflect dependencies on direction and intensity of the prevailing solar-driven circulation, and on generation efficiency and ion drag dissipation with respect to solar zenith angle.
Sean Bruinsma - One of the best experts on this subject based on the ideXlab platform.
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large scale traveling Atmospheric Disturbances lstads in the thermosphere inferred from champ grace and seta accelerometer data
Journal of Atmospheric and Solar-Terrestrial Physics, 2010Co-Authors: Sean Bruinsma, J M ForbesAbstract:Densities derived from accelerometer measurements on the GRACE, CHAMP, and Air Force/SETA satellites near 490, 390, and 220 km, respectively, are used to elucidate global-scale characteristics of traveling Atmospheric Disturbances (TADs). Several characteristics elucidated in numerical simulations are confirmed in this study, namely: (1) propagation speeds increase from the lower thermosphere to the upper thermosphere; (2) propagation to the equator and even into the opposite hemisphere can occur; (3) greater attenuation of TADs occurs during daytime and at higher levels of solar activity (i.e., more wave activity during nighttime and solar minimum), presumably due to the greater influence of ion drag. In addition, we find that the occurrence of significant TAD activity emanating from the auroral regions does not reflect a clear relation with the level of planetary magnetic activity as measured by Kp. There is also evidence of waves originating in the tropics, presumably due to convective sources; to some extent this may contribute to the Kp and solar flux relationships noted above. Further elucidation of local time, season, and altitude dependences of TAD propagation characteristics may be forthcoming from density measurements from the GOCE and Swarm missions.
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properties of traveling Atmospheric Disturbances tads inferred from champ accelerometer observations
Advances in Space Research, 2009Co-Authors: Sean Bruinsma, J M ForbesAbstract:Abstract Densities derived from accelerometer measurements on the CHAMP satellite near 400 km are used to statistically establish characteristics of large-scale (>1000 km) traveling Atmospheric Disturbances (TADs). Only TADs that at least propagate from the auroral zone to the equator are analyzed here, and a total of 21 identifiable events are found over the years 2001–2007. The average speed of all TADs, regardless of local time, is 646 ± 122 ms −1 . The average speeds on the dayside and nightside are 595 ± 127 ms −1 and 685 ± 106 ms −1 , respectively, i.e., the speed appears to be 10% higher on average on the nightside. On six occasions TADs were only detected on the night side; however, TADs on the dayside often appear more distinctly in the data. Moreover, contrary to some theoretical expectations, dayside TADs do not dissipate more readily than night side TADs, although much less are detected between 8–20 solar local time. No clear dependence of TAD amplitude or phase speed with respect to Kp, or rate of increase of Kp, is found.
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global observation of traveling Atmospheric Disturbances tads in the thermosphere
Geophysical Research Letters, 2007Co-Authors: Sean Bruinsma, J M ForbesAbstract:[1] Densities derived from accelerometer measurements on the CHAMP satellite near 400 km are used to elucidate global-scale characteristics of traveling Atmospheric Disturbances (TADs) in connection with 3 sudden injections of energy at high latitudes on 29 May 2003. Dayside TADs with typical amplitudes ∼20–30% propagate towards the equator from the northern hemisphere (southern hemisphere) auroral region with phase speeds of order 730 ms−1 (460 ms−1). Some evidence is found for TAD penetration from the northern to the southern Hemisphere, and for the first time for trans-polar propagation. Nighttime TAD signatures are less well defined, but have phase speeds similar to the dayside TADs. The above day-night and hemisphere differences possibly reflect dependencies on direction and intensity of the prevailing solar-driven circulation, and on generation efficiency and ion drag dissipation with respect to solar zenith angle.
C C Lee - One of the best experts on this subject based on the ideXlab platform.
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observation and model comparisons of the traveling Atmospheric Disturbances over the western pacific region during the 6 7 april 2000 magnetic storm
Journal of Geophysical Research, 2004Co-Authors: C C Lee, Jannyenq Liu, M Q Chen, H C Yeh, Kenro NozakiAbstract:[1] The ionospheric features of traveling Atmospheric Disturbances (TADs) over the Western Pacific region have been observed by the Wuhan, NCU-DPS, and Cebu ionosondes and the ROCSAT-1 satellite during the 6–7 April 2000 magnetic storm. The nighttime observations are further compared with the simulation results of the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIEGCM). Both observation and model demonstrate that the TADs propagate equatorward with a phase speed of 610–650 m/s. The observations and corresponding TIEGCM simulations show a negative initial correlation between NmF2 and HmF2 caused by equatorward wind surges at various locations from midlatitudes to the equator. These qualitative agreements reveal that the TIEGCM is capable of simulating the TADs. The TIEGCM simulations of two locations located in the downwind hemisphere further show decreases in NmF2 and HmF2 mainly due to the enhanced transequatorial winds. After lowering the F2 layer at the two locations, the HmF2 is raised for several hours and shows slightly enhanced NmF2 daytime values while the meridional wind is at background magnitude. We propose that this effect is caused by accumulation of plasma transported from northern latitudes. However, we also find that the NmF2, HmF2, and the lifetimes of HmF2 uplift phase and equatorial vertical drift in the model results are quantitatively inconsistent with that in the observed data.
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the propagation of traveling Atmospheric Disturbances observed during the april 6 7 2000 ionospheric storm
Geophysical Research Letters, 2002Co-Authors: C C Lee, Jannyenq Liu, B W Reinisch, Yungpo Lee, Libo LiuAbstract:[1] The great magnetic storm of April 6-7, 2000 generated ionospheric Disturbances in the west Pacific region. Two ionosondes at Wuhan (30.6degreesN, 114.4degreesE) and Chung-Li (24.9degreesN, 121 E) observed the ionosphere during this period. The variations of the ionospheric parameters, NmF(2) (plasma density of the F-peak), hmF(2) (height of the F-peak) and h'F (minimum virtual height of the F-layer), show that a traveling Atmospheric disturbance (TAD) affects the ionosphere at middle and low latitudes in this region. The propagation velocities deduced from the time delay of hmF(2) and h F recorded at the two stations are about 655 and 164 m/ s, respectively. Furthermore, a method of deriving the vertical phase and group velocities is applied to the sequences of virtual heights at fixed sounding frequencies. The vertical and associated meridional velocities demonstrate that the upward motions of the ionospheric plasma are caused by a TAD.
Yi Deng - One of the best experts on this subject based on the ideXlab platform.
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nonmodal growth of Atmospheric Disturbances relevant to the east asian pressure surge in boreal winter
Climate Dynamics, 2020Co-Authors: Siyu Zhao, Yi DengAbstract:Significant events of East Asian pressure surge are identified based on sea level pressure for boreal winters of the period 1979–2016. These events typically grow from a high pressure anomaly over Northern Europe and the northwestern Russia and attain their peak over Siberia around ten days after the initiation. The structure of the pressure surge at its peak intensity mimics that of the semi-permanent Siberian High. With a two-level quasi-geostrophic (QG) model, a nonmodal instability analysis of the winter climatological flow reveals that one of the most rapidly amplifying “optimal Disturbances” with an optimization time of 2 days resembles the structure of the East Asian pressure surge. This optimal disturbance originates from small-scale precursor Disturbances over Northern Europe and the Barents Sea. Such initial Disturbances grow in magnitude via Siberia towards East Asia, forming a low-level ridge extending to around 50° N. The optimal disturbance successfully captures the temporal and spatial scales and the overall structure of the circulation anomaly associated with the pressure surge, albeit with varying degrees of accuracy of the location of individual trough/ridge of the surge anomaly. Additional experiments suggest that (1) adding damping effect to the two-level QG model extends the low-level ridge further south to around 40° N and (2) the upper level wave train feature associated with pressure surge can be captured even in a barotropic model by optimal Disturbances with an optimization time of 4 days.
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a causality based view of the interaction between synoptic and planetary scale Atmospheric Disturbances
Journal of the Atmospheric Sciences, 2020Co-Authors: Savini M Samarasinghe, Yi Deng, Imme EbertuphoffAbstract:AbstractThis paper reports preliminary yet encouraging findings on the use of causal discovery methods to understand the interaction between Atmospheric planetary- and synoptic-scale Disturbances i...
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intermediate frequency Atmospheric Disturbances a dynamical bridge connecting western u s extreme precipitation with east asian cold surges
Journal of Geophysical Research, 2014Co-Authors: Tianyu Jiang, Katherine J Evans, Yi Deng, Xiquan DongAbstract:In this study, an Atmospheric river (AR) detection algorithm is developed to investigate the downstream modulation of the eastern North Pacific ARs by another weather extreme, known as the East Asian cold surge (EACS), in both reanalysis data and high-resolution global model simulations. It is shown that following the peak of an EACS, Atmospheric Disturbances of intermediate frequency (IF; 10–30 day period) are excited downstream. This leads to the formation of a persistent cyclonic circulation anomaly over the eastern North Pacific that dramatically enhances the AR occurrence probability and the surface precipitation over the western U.S. between 30°N and 50°N. A diagnosis of the local geopotential height tendency further confirms the essential role of IF Disturbances in establishing the observed persistent anomaly. This downstream modulation effect is then examined in the two simulations of the National Center for Atmospheric Research Community Climate System Model version 4 with different horizontal resolutions (T85 and T341) for the same period (1979–2005). The connection between EACS and AR is much better captured by the T341 version of the model, mainly due to a better representation of the scale interaction and the characteristics of IF Atmospheric Disturbances in the higher-resolution model. The findings here suggest that faithful representations of scale interaction in a global model are critical for modeling and predicting the occurrences of hydrological extremes in the western U.S. and for understanding their potential future changes.
G W Prolss - One of the best experts on this subject based on the ideXlab platform.
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modeling the ionospheric response to traveling Atmospheric Disturbances
Journal of Geophysical Research, 1997Co-Authors: R Bauske, G W ProlssAbstract:Anomalous increases of the ionization density at middle latitudes (positive ionospheric storms) are often a prominent feature of upper Atmospheric storms. One of their possible causes are traveling Atmospheric Disturbances (TADs) which propagate from polar to equatorial latitudes, carrying along equatorward-directed meridional winds. At middle latitudes, these winds cause an increase in the height of the F2 layer which in turn will lead to an enhancement of the ionization density. Using a simple description of a TAD and an ionospheric model, we are able to reproduce the basic properties of such perturbations. We also attempt to simulate an actually observed storm period. Rough agreement is obtained when the wind speed is derived from the height of the F2-layer peak. A more detailed simulation of the initial phase of the storm requires a more refined TAD model with time-dependent height gradients in the wind field.