scholarly journals Modeling of the Stepping Process of Negative Lightning Stepped Leaders

2017 ◽  
Author(s):  
Vernon Cooray ◽  
Liliana Arevalo
Keyword(s):  
Physical Model ◽  
Reasonable Agreement ◽  
Propagation Speed ◽  
Step Length ◽  
Experimental Investigations ◽  
Small Length ◽  
Return Stroke ◽  
Subsequent Formation ◽  
Peak Current ◽  
Model Based

A physical model based on the mechanism observed in experimental investigations is introduced to describe the formation of negative leader steps. Starting with a small length of a space leader located at the periphery of the negative streamer system of the stepped leader the model simulates the growth and the subsequent formation of the leader step. Based on the model, the average step length, the average step forming time and the average stepped leader propagation speed is estimated as a function of prospective return stroke peak current. The results show that the average step length and the average leader speed increases with increasing prospective return stroke current. The results also show that the speed of the stepped leader increases as it approaches the ground. For a 30 kA prospective return stroke current the average leader speed obtained is about 5 x 105 m/s and the average step length was about 10 m. The results obtained are in reasonable agreement with the experimental observations. 

New Model of a Basin-Type Solar Still

2002 ◽  
Vol 124 (3) ◽  
pp. 311-314 ◽  
Author(s):  
Irene De Paul
Keyword(s):  
Flow Visualization ◽  
Physical Model ◽  
Thermal Inertia ◽  
Thermal Conditions ◽  
Salt Deposit ◽  
Solar Still ◽  
New Model ◽  
Model Based ◽  
Productivity Measurements ◽  
Real Scale

Thermal and productivity measurements and flow visualization experiences were performed on a real scale module of a basin type solar still, whose geometry and thermal conditions could be changed in a controlled way. The convective stage was studied with the aim of acquiring information about the nature of the medium inside it and the influence of different parameters over the productivity. Literature shows a great number of experimental and numerical works dealing with different aspects of the performance of solar stills: thermal losses, vapor losses, salt deposit on the tray, geometry, thermal inertia, etc. Few works are reported that take into account convective phenomena and the fluiddynamic characteristics of the medium inside the still. Most of these works are based on Dunkle’s and Copper’s models of the still that does not take into account the characteristics of the environment. A new physical model based on these experiments is presented.

Comment on “Grazing incidence X-ray fluorescence of periodic structures – a comparison between X-ray standing waves and geometrical optics calculations” by F. Reinhardt, S. H. Nowak, B. Beckhoff, J-C. Dousse and M. Schoengen, JAAS, 2014, 29, 1778

2015 ◽  
Vol 30 (12) ◽  
pp. 2548-2550
Author(s):  
W. Jark ◽  
D. Eichert
Keyword(s):  
Physical Model ◽  
Periodic Structures ◽  
Standing Waves ◽  
Grazing Incidence ◽  
Data Interpretation ◽  
Geometrical Optics ◽  
X Ray ◽  
Model Based ◽  
Published Paper

The data interpretation in the recently published paper with the above title is criticized and it is shown that an alternative more physical model based on diffraction in periodic structures can explain the data better and more consistently.

scholarly journals Foreshock cavitons and spontaneous hot flow anomalies: A statistical study with a global hybrid-Vlasov simulation

2021 ◽  
Author(s):  
Vertti Tarvus ◽  
Lucile Turc ◽  
Markus Battarbee ◽  
Jonas Suni ◽  
Xóchitl Blanco-Cano ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Rest Frame ◽  
Statistical Study ◽  
Plasma Temperature ◽  
Propagation Speed ◽  
Bow Shock ◽  
Ulf Waves ◽  
Subsequent Formation ◽  
Comparable Amount

Abstract. The foreshock located upstream of Earth's bow shock hosts a wide variety of phenomena related to the reflection of solar wind particles from the bow shock and the subsequent formation of ultra-low frequency (ULF) waves. In this work, we investigate foreshock cavitons, which are transient structures resulting from the non-linear evolution of ULF waves, and spontaneous hot flow anomalies (SHFAs), which evolve from cavitons as they accumulate suprathermal ions while being carried to the bow shock by the solar wind. Using the global hybrid-Vlasov simulation model Vlasiator, we have conducted a statistical study in which we track the motion of individual cavitons and SHFAs in order to examine their properties and evolution. In our simulation run where the interplanetary magnetic field (IMF) is directed at a sunward-southward angle of 45 degrees, continuous formation of cavitons is found up to ~ 11 Earth radii (RE) from the bow shock (along the IMF direction), and caviton-to-SHFA evolution takes place within ~ 2 RE from the shock. A third of the cavitons in our run evolve into SHFAs, and we find a comparable amount of SHFAs forming independently near the bow shock. We compare the properties of cavitons and SHFAs to prior spacecraft observations and simulations, finding good agreement. We also investigate the variation of the properties as a function of position in the foreshock, showing that the transients close to the bow shock are associated with larger depletions in the plasma density and magnetic field magnitude, along with larger increases in the plasma temperature and the level of bulk flow deflection. Our measurements of the propagation velocities of cavitons and SHFAs agree with earlier studies, showing that the transients propagate sunward in the solar wind rest frame. We show that SHFAs have a greater solar wind rest frame propagation speed than cavitons, which is related to an increase in the magnetosonic speed near the bow shock.

scholarly journals A Study of Coherent Radiation Generated in an Ablative Capillary Discharge

10.14311/1787 ◽  
2013 ◽  
Vol 53 (2) ◽  
Author(s):  
Jakub Hübner ◽  
Pavel Vrba
Keyword(s):  
Physical Model ◽  
Spontaneous Emission ◽  
Amplified Spontaneous Emission ◽  
Coherent Radiation ◽  
Capillary Discharge ◽  
Mhd Equations ◽  
One Dimensional ◽  
X Ray ◽  
Model Based ◽  
Set Up

Feasible soft-X-ray amplification in the CVI and NVII Balmer transition is investigated in a capillary discharge. The best conditions and parameters for the experimental set-up are found for an ablative capillary. The most optimistic results have shown that the gain would be greater than one, which is the condition for successful ASE (Amplified spontaneous emission) in capillary discharges. The capillary discharge evolution is modeled using the NPINCH program, employing a one-dimensional physical model based on MHD equations. The information about the capillary discharge evolution is processed in the FLY, FLYPAPER, FLYSPEC programs, enabling the population to be modeled on specific levels during capillary discharge.

scholarly journals Foreshock cavitons and spontaneous hot flow anomalies: a statistical study with a global hybrid-Vlasov simulation

2021 ◽  
Vol 39 (5) ◽  
pp. 911-928
Author(s):  
Vertti Tarvus ◽  
Lucile Turc ◽  
Markus Battarbee ◽  
Jonas Suni ◽  
Xóchitl Blanco-Cano ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Rest Frame ◽  
Statistical Study ◽  
Plasma Temperature ◽  
Propagation Speed ◽  
Bow Shock ◽  
Ulf Waves ◽  
Subsequent Formation ◽  
Comparable Amount

Abstract. The foreshock located upstream of Earth's bow shock hosts a wide variety of phenomena related to the reflection of solar wind particles from the bow shock and the subsequent formation of ultra-low-frequency (ULF) waves. In this work, we investigate foreshock cavitons, which are transient structures resulting from the non-linear evolution of ULF waves, and spontaneous hot flow anomalies (SHFAs), which are thought to evolve from cavitons as they accumulate suprathermal ions while being carried to the bow shock by the solar wind. Using the global hybrid-Vlasov simulation model Vlasiator, we have conducted a statistical study in which we track the motion of individual cavitons and SHFAs in order to examine their properties and evolution. In our simulation run where the interplanetary magnetic field (IMF) is directed at a sunward–southward angle of 45∘, continuous formation of cavitons is found up to ∼11 Earth radii (RE) from the bow shock (along the IMF direction), and caviton-to-SHFA evolution takes place within ∼2 RE from the shock. A third of the cavitons in our run evolve into SHFAs, and we find a comparable amount of SHFAs forming independently near the bow shock. We compare the properties of cavitons and SHFAs to prior spacecraft observations and simulations, finding good agreement. We also investigate the variation of the properties as a function of position in the foreshock, showing that transients close to the bow shock are associated with larger depletions in the plasma density and magnetic field magnitude, along with larger increases in the plasma temperature and the level of bulk flow deflection. Our measurements of the propagation velocities of cavitons and SHFAs agree with earlier studies, showing that the transients propagate sunward in the solar wind rest frame. We show that SHFAs have a greater solar wind rest frame propagation speed than cavitons, which is related to an increase in the magnetosonic speed near the bow shock.

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