scholarly journals The dayside high-latitude trough under quiet geomagnetic conditions: Radio tomography and the CTIP model

2005 ◽  
Vol 23 (4) ◽  
pp. 1199-1206 ◽  
Author(s):  
S. E. Pryse ◽  
K. L. Dewis ◽  
R. L. Balthazor ◽  
H. R. Middleton ◽  
M. H. Denton
Keyword(s):  
High Latitude ◽  
Large Scale ◽  
Physical Models ◽  
Physical Processes ◽  
Winter Solstice ◽  
Ion Density ◽  
Plasma Production ◽  
Radio Tomography ◽  
High Latitude Ionosphere

Abstract. The dayside high-latitude trough is a persistent feature of the post-noon wintertime auroral ionosphere. Radio tomography observations have been used to map its location and latitudinal structure under quiet geomagnetic conditions (Kp≤2) near winter solstice. The trough is also a clear feature in the ion density distribution of the Coupled Thermosphere-Ionosphere-Plasmasphere model (CTIP) under similar geophysical conditions. Comparisons of the measured and modelled distributions show that the plasma production equatorward of the trough is mainly controlled by solar radiation, but there are also other processes maintaining the equatorward trough-wall that are open to debate. The poleward trough-wall is produced by particle precipitation, but the densities are significantly overestimated by the model. At the trough minimum the observed densities are consistent with low nighttime densities convecting sunward to displace the higher daytime densities, but this is not borne out by the CTIP model. The study shows the potential of combining radio tomography and modelling to interpret the balance of the physical processes responsible for large-scale structuring of the high-latitude ionosphere, and highlights the role of tomographic imaging in validating and developing physical models.

scholarly journals The atomic hydrogen/molecular cloud association: an unavoidable relationship

1991 ◽  
Vol 147 ◽  
pp. 37-40
Author(s):  
G. Joncas
Keyword(s):  
Atomic Hydrogen ◽  
Molecular Clouds ◽  
Large Scale ◽  
Young Stars ◽  
Physical Processes ◽  
Star Forming ◽  
Dark Clouds ◽  
Star Forming Regions ◽  
The Impact

The presence of HI in the interstellar medium is ubiquitous. HI is the principal actor in the majority of the physical processes at work in our Galaxy. Restricting ourselves to the topics of this symposium, atomic hydrogen is involved with the formation of molecular clouds and is one of the byproducts of their destruction by young stars. HI has different roles during a molecular cloud's life. I will discuss here a case of coexisting HI and H2 at large scale and the origin of HI in star forming regions. For completeness' sake, it should be mentionned that there are at least three other aspects of HI involvement: HI envelopes around molecular clouds, the impact of SNRs (see work on IC 443), and the role of HI in quiescent dark clouds (see van der Werf's work).

scholarly journals The atomic hydrogen/molecular cloud association: an unavoidable relationship

1991 ◽  
Vol 147 ◽  
pp. 37-40
Author(s):  
G. Joncas
Keyword(s):  
Atomic Hydrogen ◽  
Molecular Clouds ◽  
Large Scale ◽  
Young Stars ◽  
Physical Processes ◽  
Star Forming ◽  
Dark Clouds ◽  
Star Forming Regions ◽  
The Impact

The presence of HI in the interstellar medium is ubiquitous. HI is the principal actor in the majority of the physical processes at work in our Galaxy. Restricting ourselves to the topics of this symposium, atomic hydrogen is involved with the formation of molecular clouds and is one of the byproducts of their destruction by young stars. HI has different roles during a molecular cloud's life. I will discuss here a case of coexisting HI and H2 at large scale and the origin of HI in star forming regions. For completeness' sake, it should be mentionned that there are at least three other aspects of HI involvement: HI envelopes around molecular clouds, the impact of SNRs (see work on IC 443), and the role of HI in quiescent dark clouds (see van der Werf's work).

scholarly journals Modeling the electron temperature distribution in F2 region of high-latitude ionosphere for winter solstice conditions

2016 ◽  
Vol 2 (4) ◽  
pp. 54-62
Author(s):  
Иннокентий Голиков ◽  
Innokentiy Golikov ◽  
Артем Гололобов ◽  
Artem Gololobov ◽  
Василий Попов ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Electron Temperature ◽  
High Latitude ◽  
Temporal Distribution ◽  
Universal Time ◽  
Western Hemisphere ◽  
Three Dimensional Model ◽  
Winter Solstice ◽  
Eastern Hemisphere ◽  
High Latitude Ionosphere

Using the three-dimensional model of the high-latitude ionosphere in Euler variables, which takes into account the mismatch between geographical and geomagnetic poles, we study the behavior of the electron temperature Te in the F2 region as a function of universal time. We present results of the numerical modeling of spatial-temporal distribution of electron temperature in the F2 region for winter solstice, minimum solar activity, and moderate geomagnetic activity. The electron temperature distribution in the F2 region of the high-latitude ionosphere in winter is shown to be characterized by a Te increase in dawn and dusk sectors. Further, the mismatch between the poles leads to regular longitudinal features in Te distribution during Earth’s daily rotation. Thus, at 05 UT, when the Eastern Hemisphere is illuminated, the elevated Te zone is formed only in the dawn sector, and at 17 UT, when the Western Hemisphere is illuminated, such zones are observed in both the sectors. We discuss reasons for the formation of the regions with elevated electron temperature depending on the universal time. The results of numerical experiments are compared with similar results obtained with other models.

scholarly journals Modeling the electron temperature distribution in F2 region of high-latitude ionosphere for winter solstice conditions

2017 ◽  
Vol 2 (4) ◽  
pp. 70-80 ◽  
Author(s):  
Иннокентий Голиков ◽  
Innokentiy Golikov ◽  
Артем Гололобов ◽  
Artem Gololobov ◽  
Василий Попов ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Electron Temperature ◽  
High Latitude ◽  
Temporal Distribution ◽  
Universal Time ◽  
Western Hemisphere ◽  
Three Dimensional Model ◽  
Winter Solstice ◽  
Eastern Hemisphere ◽  
High Latitude Ionosphere

Using the three-dimensional model of the high-latitude ionosphere in Euler variables, which takes into account the mismatch between geographic and geomagnetic poles, we study the behavior of the electron temperature Te in the F2 region as a function of universal time. We present results of the numerical modeling of spatial-temporal distribution of electron temperature in the F2 region for winter solstice, minimum solar activity, and moderate geomagnetic activity. The electron temperature distribution in the F2 region of the high-latitude ionosphere in winter is shown to be characterized by a Te increase in dawn and dusk sectors. Further, the mismatch between the poles leads to regular longitudinal features in Te distribution during Earth’s daily rotation. Thus, at 05 UT, when the Eastern Hemisphere is illuminated, the elevated Te zone is formed only in the dawn sector, and at 17 UT, when the Western Hemisphere is illuminated such zones are observed in both the sectors. We discuss reasons for the formation of the regions with elevated electron temperature depending on the universal time. Results of numerical experiments are compared with similar results obtained with other models.

scholarly journals A phenomenological model for fountain-top entrainment

2016 ◽  
Vol 796 ◽  
pp. 195-210 ◽  
Author(s):  
Antoine L. R. Debugne ◽  
Gary R. Hunt
Keyword(s):  
Phenomenological Model ◽  
Large Scale ◽  
Predictive Ability ◽  
Dynamical Behaviour ◽  
Volume Flux ◽  
Ambient Fluid ◽  
Physical Processes ◽  
Energetic Balance ◽  
Periodic Fluctuations

In theoretical treatments of turbulent fountains, the entrainment of ambient fluid into the top of the fountain, hereinafter fountain-top entrainment $Q_{top}$ ($\text{m}^{3}~\text{s}^{-1}$), has been neglected until now. This neglect, which modifies the energetic balance in a fountain, compromises the predictive ability of existing models. Our aim is to quantify $Q_{top}$ by shedding light on the physical processes that are responsible for fountain-top entrainment. First, estimates for $Q_{top}$ are obtained by applying, in turn, an entrainment closure in the vein of Morton et al. (Proc. R. Soc. Lond., vol. 234, 1956, pp. 1–23) and then of Shrinivas & Hunt (J. Fluid Mech., vol. 757, 2014, pp. 573–598) to the time-averaged fountain top. Unravelling the assumptions that underlie these approaches, we argue that neither capture the dynamical behaviour of the flow observed at the fountain top; the top being characterised by quasi-periodic fluctuations, during which large-scale eddies reverse and engulf parcels of ambient fluid into the fountain. Therefore, shifting our mindset to a periodical framework, we develop a new phenomenological model in which we emphasise the role of the fluctuations in entraining external fluid. Our model suggests that $Q_{top}$ is similar in magnitude to the volume flux supplied to the fountain top by the upflow ($Q_{u}$), i.e. $Q_{top}\sim Q_{u}$, in agreement with experimental evidence. We conclude by providing guidance on how to implement fountain-top entrainment in existing models of turbulent fountains.

scholarly journals Exploration of spontaneous vortex formation and intermittent behavior in ECR plasmas: The HYPER-I experiments

2014 ◽  
Vol 81 (2) ◽  
Author(s):  
S. Yoshimura ◽  
K. Terasaka ◽  
E. Tanaka ◽  
M. Aramaki ◽  
A. Okamoto ◽  
...  
Keyword(s):  
Large Scale ◽  
Electron Cyclotron Resonance ◽  
Vortex Formation ◽  
Field Measurements ◽  
Physical Processes ◽  
Langmuir Probes ◽  
Plasma Production ◽  
Intermittent Behavior ◽  
Plasma Experiment ◽  
Large Scale Flow

HYPER-I (High Density Plasma Experiment-I) is a linear device that combines a wide operation range of plasma production with flexible diagnostics. The plasmas are produced by the electron cyclotron resonance (ECR) heating with parallel injection of right-handed circularly polarized microwaves of 2.45 GHz from the high-field side. The maximum attainable electron density is more than two orders of magnitude higher than the cutoff density of ordinary waves. Spontaneous formation of a variety of large-scale flow structures, or vortices, has been observed in the HYPER-I plasmas. Flow-velocity field measurements using directional Langmuir probes (DLPs) and laser-induced fluorescence (LIF) method have clarified the physical processes behind such vortex formations. Recently, a new intermittent behavior of local electron temperature has also been observed. Statistical analysis of the floating potential changes has revealed that the phenomenon is characterized by a stationary Poisson process.

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