Chasing Lightning: Sferics, Tweeks and Whistlers

Phillip A. Webb Kathleen FranzenUMBC/GEST INSPIRE Project Goddard Space Flight Center 518 Sixth Street, SE, Washington, DC 20003 president@theinspireproject.orgGreenbelt, MD 20771phillip.a.webb@nasa.gov

Talk Overview

Interactive NASA Space Physics Ionosphere Radio Experiments (INSPIRE)

Radio interview Overview of Very Low

Frequency (VLF) INSPIRE program INSPIRE VLF

electronic kits UMBC INSPIRE based

first year course Summary

Radio Interview

On 11 August 2008 the following pre-recorded interview was broadcast on Baltimore’s NPR station WYPR as part of their Maryland Morning show

Guest “experts” were Kathleen Franzen, Leonard Garcia, and Phillip Webb

Very Low Frequency (VLF)

Radio frequencies in the range of 3 kHz to 30 kHz

Where do VLF Waves Come From? Lightning Mostly!

But There are Man Made Sources, too

Lightning Properties

40 kA electrical current main current channel from cloud

to ground approximately one cm wide

Current channel is made up of plasma, so acts as a wire!

Current moving acts like an antenna and so the lightning “transmits”

Earth-Ionosphere Waveguide

Certain radio waves can propagate in the space between the ground and the boundary of the ionosphere

Cavity behaves as a large waveguide

VLF frequency signals can propagate efficiently in this waveguide

Sferics

Short for "atmospherics“ Range from a few hertz to millions of Hz Audio range is up to about 15 kHz Characterized by vertical lines on the

frequency-time graph indicating the simultaneous arrival of all of the audio frequencies

Caused by lightning strokes within a couple of thousand kilometers of the receiver

Sferics - Properties

Tweeks

Tweeks result when sferics are ducted in the earth-ionosphere waveguide distances much greater than a couple of thousand km

The distance can be as great as halfway around the Earth (20,000 km)

The spectrogram of a tweek shows a vertical line at the higher frequencies with a curved section (called the "hook") appearing at a frequency of about 2 kHz – result of dispersion of VLF wave in waveguide

Properties of Tweeks

Whistlers

Under the right conditions the VLF signal travels out away from the Earth and returns by traveling along a magnetic field line

During this long path, dispersion is much greater than with tweeks

The sound of a whistler is a musical descending tone that lasts for a second or more

On the spectrogram, whistlers appear as long sweeping arcs showing the sequential arrival of the EM waves different frequencies

Properties of Whistlers

INSPIRE Project WWW site http://theinspireproject.org/

INSPIRE – Nearly 20 Years of Success

INSPRE will have its 20’th birthday this year

Kits currently cost $120 plus shipping

Distributed over 2800 INSPIRE VLF kits worldwide

Originally used in high schools in the USA and around the world as a teaching project

Participants around the world are using kits for special projects, not just for VLF instruction

INSPIRE VLF Receiver Kits

New INSPIRE Course

Won a NASA New Investigator Proposal (NIP) a few years ago

Teaching an INSPIRE based course at the university level was part of the proposal – not done before

Undergraduate course was taught in the Fall 2008 semester at University of Maryland Baltimore County (UMBC)

UMBC First Year Seminar (FYS) series

Course Goals

To develop a college/university level course for the INSPIRE program

Make the students aware of science

Show the students that there is more to lightning than meets the eye – you know, VLF….

To get the students hands “dirty” doing some electronics => shows that electronics is not just a black box

Teach the students about the presentation of scientific material

Course Syllabus I

Grading Policy Final 10% Project 20% (presentation) / 20% (project) Laboratory 10% Collection of data and report 10% Classroom tests 5% Classroom participation 25% Lectures and Laboratories Class held every Tuesday and Thursday, 4.30pm to 6.00pm Lecture Room: PHYS401 Electronic Laboratory: PHYS209

Course Syllabus IIPreliminary Schedule Class Date Activity 1 Thursday 28th August Overview of course, assignment of workings groups, and

choice of research topics 2 Tuesday 2nd September Physics 101 – terminology and definitions 3 Thursday 4th September LAB – Introduction and lamp kit assembly 4 Tuesday 9th September Introduction to INSPIRE kit and electronics 5 Thursday 11th September LAB – Begin assembly of INSPIRE VLF kit 6 Tuesday 16th September GUEST SPEAKER 7 Thursday 18th September LAB – Assembly INSPIRE VLF kit 8 Tuesday 23rd September Electromagnetic theory and VLF, Student feedback session 9 Thursday 25th September LAB – Assembly INSPIRE VLF kit 10 Tuesday 30th September Atmospheric physics and VLF 11 Thursday 2nd October GUEST SPEAKER 12 Tuesday 7th October Atmospheric physics and VLF 13 Thursday 9th October LAB - Assembly and final testing of INSPIRE VLF kit 14 Tuesday 14th October Introduction to Research and Presentation 15 Thursday 16th October LAB - Field trip to grounds of UMBC 16 Tuesday 21st October Space physics and VLF, Student feedback session 17 Thursday 23rd October GUEST SPEAKER 18 Tuesday 28th October Introduction to data analysis 19 Thursday 30th October LAB – Field trip to Patapsco Valley State Park 20 Tuesday 4th November Final preparation of reports 21 Thursday 6th November LAB – Analysis of data collected by VLF receiver 22 Tuesday 11th November Space physics and VLF 23 Thursday 13th November LAB –Write report on collected data 24 Tuesday 18th November Final preparation of presentations, Student feedback session 25 Thursday 20th November GUEST SPEAKER 26 Tuesday 25th November Student Presentations I HOLIDAY Thursday 27th November Thanksgiving 27 Tuesday 2nd December Student Presentations II 28 Thursday 4th December Student Presentations III, Student feedback session 29 Tuesday 9th December Final Exam

Guest Speakers

Kathleen Franzen - history of INSPIRE

Dr. Leonard Garcia - detection of radio signals from Jupiter, which were discovered in Maryland

Dr. Bob Benson - atmospheric physics and participating in the first wintering-over party at the South Pole in 1957

Dr. James Green - VLF waves in space plasmas at Earth and other planets

Field Trip to National Radio Astronomy Observatory (NRAO)

Green Bank, West Virginia

Overnight trip Federally enforced EM

quiet zone Used student assembled

INSPIRE kits in the evening to collect data

Tour of telescopes and visitors center following morning

Summary

INSPIRE running for 20 years A university level course was

taught in the Fall 2008 based on the INSPIRE kit

Covers different disciplines electromagnetic theory atmospheric science space science electronics

Allows the students hands-on experience, data collection, analysis, and theory – they enjoy this variety!

Student Testimonials I

I did not originally plan on taking the Freshman Seminar Class called “Chasing Lightening.” After spending four years at a Math, Science, and Engineering magnet school, I was mostly put off with the idea of taking more science. However, the day of my freshman orientation my adviser mentioned the class. I read the description and decided to take it to balance out my schedule. The idea of being in a smaller class environment and learning about lightning, an area that we never spent too much time in science class throughout my education seemed appealing. I would have to say that I do not regret taking this course. I learned a lot more about electricity, the atmosphere, and physics in general than I ever have. The fact that we had a hands-on project that had real-world use made the class very fun. I looked forward to going to our lab and building our VLF kits. We worked on them throughout the semester and it balanced out having lecture earlier in the week. In the end, whether they did work and it was a success or you were one of the unlucky who’s kits did not, everyone was proud of the work they had done. We gained knowledge of building an electronic object--something many people cannot do. I am very glad that I took this class my freshman year, it made me like science a lot more.

- Katherine Parris

Student Testimonials II

  The INSPIRE program is a really cool way to learn about lightning. I never knew anything like sferics, tweeks, and whistlers existed before this class. I'm a hands on person, so getting to make my own kit and then listen to the radio waves it made was much cooler than just listening to the waves of some other machine. I am also a welder and haven't been able to weld since I arrived at college, so learning that we were going to get to solder was a pleasant surprise. Overall, I had a great experience in this program.- Heather D'Ambrosio