Chasing Lightning: Sferics , Tweeks and Whistlers

1. Phillip A. Webb Kathleen Franzen UMBC/GEST INSPIRE Project Goddard Space Flight Center 518 Sixth Street, SE, Washington, DC 20003 president@theinspireproject.org Greenbelt, MD 20771 phillip.a.webb@nasa.gov Chasing Lightning: Sferics, Tweeks and Whistlers

2. 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

3. 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

4. Very Low Frequency (VLF) • Radio frequencies in the range of 3 kHz to 30 kHz

5. Where do VLF Waves Come From? • Lightning Mostly! • But There are Man Made Sources, too

7. 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”

8. 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

9. 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

10. Sferics - Properties

11. 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

12. Properties of Tweeks

13. 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

14. Properties of Whistlers

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

16. 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

17. INSPIRE VLF Receiver Kits

18. 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

19. 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

20. Course Syllabus I

21. Course Syllabus II

22. 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

23. 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

24. 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!

25. 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

26. 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