(—THIS SIDEBAR DOES NOT PRINT—)

DES IG N G U IDE

This PowerPoint 2007 template produces a 100cmx100cm presentation

poster. You can use it to create your research poster and save valuable

time placing titles, subtitles, text, and graphics.

We provide a series of online tutorials that will guide you through the

poster design process and answer your poster production questions. To

view our template tutorials, go online to PosterPresentations.com

and click on HELP DESK.

When you are ready to print your poster, go online to

PosterPresentations.com

Need assistance? Call us at 1.510.649.3001

QU ICK START

Zoom in and out As you work on your poster zoom in and out to the level that is

more comfortable to you. Go to VIEW > ZOOM.

Title, Authors, and Affiliations Start designing your poster by adding the title, the names of the authors, and the

affiliated institutions. You can type or paste text into the provided boxes. The

template will automatically adjust the size of your text to fit the title box. You

can manually override this feature and change the size of your text.

TIP: The font size of your title should be bigger than your name(s) and institution

name(s).

Adding Logos / Seals Most often, logos are added on each side of the title. You can insert a logo by

dragging and dropping it from your desktop, copy and paste or by going to INSERT

> PICTURES. Logos taken from web sites are likely to be low quality when printed.

Zoom it at 100% to see what the logo will look like on the final poster and make

any necessary adjustments.

TIP: See if your school’s logo is available on our free poster templates page.

Photographs / Graphics You can add images by dragging and dropping from your desktop, copy and paste,

or by going to INSERT > PICTURES. Resize images proportionally by holding down

the SHIFT key and dragging one of the corner handles. For a professional-looking

poster, do not distort your images by enlarging them disproportionally.

Image Quality Check Zoom in and look at your images at 100% magnification. If they look good they will

print well.

ORIGINAL DISTORTED Corner handles

Go

od

pri

nti

ng

qu

alit

y

Bad

pri

nti

ng

qu

alit

y

QU ICK START ( con t . )

How to change the template color theme You can easily change the color theme of your poster by going to the DESIGN

menu, click on COLORS, and choose the color theme of your choice. You can also

create your own color theme.

You can also manually change the color of your background by going to VIEW >

SLIDE MASTER. After you finish working on the master be sure to go to VIEW >

NORMAL to continue working on your poster.

How to add Text The template comes with a number of pre-formatted

placeholders for headers and text blocks. You can add

more blocks by copying and pasting the existing ones or

by adding a text box from the HOME menu.

Text size Adjust the size of your text based on how much content you have to present.

The default template text offers a good starting point. Follow the conference

requirements.

How to add Tables To add a table from scratch go to the INSERT menu and

click on TABLE. A drop-down box will help you select rows and

columns.

You can also copy and a paste a table from Word or another PowerPoint document.

A pasted table may need to be re-formatted by RIGHT-CLICK > FORMAT SHAPE,

TEXT BOX, Margins.

Graphs / Charts You can simply copy and paste charts and graphs from Excel or Word. Some

reformatting may be required depending on how the original document has been

created.

How to change the column configuration RIGHT-CLICK on the poster background and select LAYOUT to see the column

options available for this template. The poster columns can also be customized on

the Master. VIEW > MASTER.

How to remove the info bars If you are working in PowerPoint for Windows and have finished your poster, save

as PDF and the bars will not be included. You can also delete them by going to

VIEW > MASTER. On the Mac adjust the Page-Setup to match the Page-Setup in

PowerPoint before you create a PDF. You can also delete them from the Slide

Master.

Save your work Save your template as a PowerPoint document. For printing, save as PowerPoint or

“Print-quality” PDF.

Print your poster When you are ready to have your poster printed go online to

PosterPresentations.com and click on the “Order Your Poster” button. Choose the

poster type the best suits your needs and submit your order. If you submit a

PowerPoint document you will be receiving a PDF proof for your approval prior to

printing. If your order is placed and paid for before noon, Pacific, Monday through

Friday, your order will ship out that same day. Next day, Second day, Third day,

and Free Ground services are offered. Go to PosterPresentations.com for more

information.

Student discounts are available on our Facebook page.

Go to PosterPresentations.com and click on the FB icon.

© 2015 PosterPresentations.com 2117 Fourth Street , Unit C Berkeley CA 94710

posterpresenter@gmail.com RESEARCH POSTER PRESENTATION DESIGN © 2015

www.PosterPresentations.com

Overdense meteors (electron line density 1016 ≤ q ≤ 1019 electrons m-1 and diameters dm ≥ 4 mm up to small fireballs) are in the size regime of the meteoroids capable of generating shockwaves (Fig. 1) during the lower transitional flow regimes and prior to their terminal stage in the MLT (Mesosphere-Lower Thermosphere) region of the atmosphere, at altitudes between 75 km and 100 km [1].

However, small scale physico-chemical processes that accompany the early evolution of the high T meteor train remain poorly understood.

Primarily it is of interest to understand the mechanism behind subsequent rapid and intense electron removal from the postadiabatically expanding meteor train within the first 0.1 s after its formation (Fig. 2). A comprehensive background on the topic can be found in [2].

We examine subsequent hyperthermal chemistry occurring on the early diffusing boundary of the high temperature postadiabatically formed meteor train and the shock modified ambient atmosphere in the MLT region.

This study has been motivated by the recent observational evidence [3] that suggest slower thermalization times of the postadiabatically formed meteor trains which is conducive for hyperthermal chemistry.

1. INTRODUCTION

A theoretical approach was applied to approximate the temperature of the ambient atmosphere near the meteor train, which is heated by the passage of the overdense meteor cylindrical shock wave. This was accomplished by considering the meteor velocity and energy deposition, and evaluating the pressure ratios between the ablation amplified shock front and the ambient atmosphere (see Fig. 3 and [2] for further details about this treatment). We have modeled hypersonic meteor flow in the MLT region using a simplified model without ablation, incorporated into the computational fluid dynamics (CFD) software package ANSYS Fluent (Figs. 4, 5). The computation was performed using O2 and N2 as the only major species, at an altitude of 80 km. A spherically shaped meteoroid is assumed to have velocity of 35 km/s (M80km = 124.6). Two meteoroid sizes were modeled, dm = 2.5 cm and dm = 10 cm. Further details about the model are given in [2].

2. THEORETICAL & MODELING APPROACH

3. RESULTS

4. DISCUSSION AND CONCLUSION

The cylindrical shock waves produced by overdense meteors are strong enough to heat the ambient atmosphere to temperatures of ~6,000 K in the near field and subsequently dissociate oxygen and minor species such as O3, but insufficient to dissociate N2. This substantially alters the considerations of the chemical processes taking place at the meteor train boundary. We demonstrate that ambient O2

which survives the cylindrical shockwave, along with small quantities of O2 that originates from the shock dissociation of O3, participate primarily in high temperature oxidation of meteoric metal ions, forming metal ion oxide. For the case of overdense meteor trains, the subsequently formed meteoric metal oxide ions are predominantly responsible for the initial intense and short lasting electron removal from the boundary of the expanding meteor train, through a process of fast temperature independent dissociative recombination. This altitude dependent process is typically completed within 0.1 - 0.3 s, which in good agreement with the results suggesting substantially slower cooling of meteor wakes [3]. The rate of this process is also strongly dependent on the second Damköhler number. The potential implications of results presented here, toward the behavior of strong underdense radio meteors, should be further investigated. The full scope of implications of this work is presented in [2].

5. REFERENCES

[1] Bronshten V.A. (1983) Physics of meteoric phenomena. Dordrecht, D. Reidel. [2] Silber E.A. et al. (2017), MNRAS, 469(2), 1869-1882 (and references therein). [3] Jenniskens P. et al. (2004) AsBio, 4(81). [4] Baggaley W. and Fisher G. (1980) PSS, 28, 575 [5] Hocking W.K. et al (2016) AnGeo, 34, 1119, [6] Jones W. and Jones J. (1990) JSTP, 52, 185.

ACKNOWLEDGEMENTS

EAS gratefully acknowledges the Natural Sciences and

Engineering Research Council of Canada (NSERC) Postdoctoral

Fellowship programme for partly funding this project. WKH

acknowledges a Discovery Grant from the NSERC. MG

acknowledges support from the ERC, the Russian Foundation for

Basic Research and the Russian Science Foundation. RES

thanks NSERC Collaborative Research and Training Experience

(CREATE) Program for Integrating Atmospheric Chemistry and

Physics from Earth to Space (IACPES), and a Northern Scientific

Training Program grant.

E. A. Silber1, W. K. Hocking2, M. L. Niculescu3, M. Gritsevich4,5, R. E. Silber6

ON THE MECHANISM OF EARLY RAPID REMOVAL OF ELECRONS FROM POSTADIABATICALLY EXPANDING OVERDENSE METEOR TRAINS

Figure 2: Schematic depiction of an overdense meteor's early evolution, in which three distinct stages can be recognized. In the first

stage, the ablating meteoroid with the shock front in front sweeps the cylindrical volume of ambient atmosphere (depicted by the small

gray circle), ionizing and dissociating atmospheric gasses. This stage also coincides with the cylindrical shock wave expanding radially

outward, perpendicular to the meteor axis of propagation, with enough energy deposited within R0 to dissociate O2 and O3 in the

ambient atmosphere, but not enough for N2 dissociation (see [2] for the extended discussion). In stage two, the adiabatically formed

meteor train (which can be approximated as quasineutral plasma with the Gaussian radial electron distribution), begins to expand

under ambipolar diffusion and thermalizes. This stage coincides with formation of metal ion oxides which takes place and is

appreciable between approximately (3,000 – 1,500 K) at the boundary region of the diffusing trail. In this reaction, an ablated meteoric

metal ion will react in a thermally driven reaction with the shock-dissociated product of ozone (O2 in ground and excited states). In the

stage three, in the almost thermalized train, the newly formed metal ion oxide will consume electrons rapidly by temperature

independent dissociative recombination (see [2] for discussion).

Figure 1: Schematics of the meteor shock wave(s), flow fields and near wake.

The meteoroid is considered as a blunt body (with the spherical shape)

propagating at hypersonic velocity. (1) Bow (cylindrical) shock wave front; (2)

The “ballistic” shock front; (3) Sonic region; (4) Boundary layer; (5) Stagnation

point; (6) Turbulent region (in some older literature, this is referred as the dead

water region); (7) Meteoroid; (8) The neck and recompression region; (9) The

‘free’ shear layer; (10) The recompression vapour (or a true cylindrical) shock

wave front; (11) The region of turbulent vapour flow and adiabatic expansion.

Note that small circles with positive and negative signs indicate regions affected

by the presence of ions and electrons respectively. The diagram is only for the

illustrative purpose and is not to scale.

Figure 5: The temperature distribution around the (a) 2.5 cm and (b) 10 cm

meteoroid. Note that (a) and (b) have different axes scaling.

Figure 4: The mass fraction of O2 as a function of radial distance

from the propagation axis of the (a) 2.5 cm and (b) 10 cm meteoroid.

The top boundary (“white space” in the plot) represents a numerical

boundary condition without any physical significance (it is set up to

be far enough away from the body (meteoroid), such that the

influence of the body (meteoroid) no longer has any effect. Note that

(a) and (b) have different axes scaling. The colour scheme is

represented in log scale.

Figure 3: (a) Plotted are the initial radius (r0) of a typical bright overdense meteor (from [4]) and the radius of the meteor (rm) trail after t

= 0.3 s. These are compared to R0 as a function of constant energy deposition (see eq (1) in [2]) of 100 J/m and 1000 J/m for altitudes

from 80 km to 100 km. For rm at 0.3 s, we applied the geometrically averaged hot plasma and ambient atmosphere ambipolar diffusion

coefficients as per [5]. (b) The initial radius r0, plotted along rm at t = 0.3 s [6]. Here, shown is the comparison between rm as calculated

in panel (a), and rm as calculated using the Massey’s formula for the theoretical diffusion coefficient.

3. RESULTS – CONT’D

1Department of Earth, Environmental and Planetary Science, Brown University, Providence, RI, USA (e-mail: elizabeth_silber@brown.edu), 2Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada 3INCAS - National Institute for Aerospace Research "Elie Carafoli", Flow Physics Department, Numerical Simulation Unit, Bucharest, Romania, 4Department of Physics, University of Helsinki, Helsinki, Finland (email: maria.gritsevich@helsinki.fi),

5Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russia, 6Department of Earth Sciences, The University of Western Ontario, London, Ontario, Canada (e-mail: reynold.silber@uwo.ca)