Liu, Ningyu

Associate Professor
Physics and Space Sciences

Educational Background

Ph.D. in Electrical Engineering, The Pennsylvania State University, 2006

M.S. in Electrical Engineering, Zhejiang University, China, 2001

B.S. in Electrical Engineering, Zhejiang University, China, 1998

Recognition & Awards

NSF CAREER AWARD, 2010

Young Scientist Award, International Union of Radio Science (URSI), 2008

NSF CEDAR Postdoctoral Fellowship, 2006 – 2007

A. J. Ferraro Award for Excellence in Ph.D. Research, Pennsylvania State University, 2005

Outstanding Graduate Student Award, Zhejiang University, 1999
 
Honor of Excellent Graduate of Zhejiang University, Zhejiang University, 1998
 

AWARDS RECEIVED BY ADVISED STUDENTS

  • N. Spiva, Best Undergraduate Poster Prize at NSF CEDAR Workshop, 2014
  • B. Kosar, Best Student Poster Prize at NSF CEDAR Workshop, 2013
  • S. Sadighi, Honorable Mention in Student Paper Competition at American Geophysical Union Fall Meeting, 2012
  • S. Sadighi, Honorable Mention at 2012 NSF CEDAR Student Poster Competition, 2012
  • B. Kosar, Outstanding Student Paper Award at American Geophysical Union Fall Meeting, 2011
  • B. Kosar, Best Student Poster Prize at NSF CEDAR Workshop, 2011
  • S. Sadighi, NSF Graduate Research Fellowship (Honorable Mention), 2011
  • B. Kosar, Outstanding Graduate Student, Florida Tech, 2010
  • G. Naranjo, Student Design Showcase Award, Florida Tech, 2010
  • B. Kosar, Outstanding Graduate Student, Florida Tech, 2009

Current Courses

Undergraduate Courses: Introductory Physics, Modern Physics, Thermodynamics, and Electromagnetic Theory

Graduate Courses: Electromagnetic Theory 1 and 2

Professional Experience

Visiting Scholar, Department of Electrical and Computer Engineering, Duke University, Fall, 2014

Associate Professor, Department of Physics and Space Sciences, Florida Institute of Technology, 2012-present

Assistant Professor, Department of Physics and Space Sciences, Florida Institute of Technology, 2008-2012

NSF CEDAR Postdoc, Department of Electrical Engineering, The Pennsylvania State University, 2006-2007

Adjunct Faculty, Penn State DuBois Campus, The Pennsylvania State University, Fall 2006

Research Assistant, Department of Electrical Engineering, The Pennsylvania State University, 2001-2006

Research Assistant, Department of Electrical Engineering, Zhejiang University, 1998-2001

Current Research

IONOSPHERE PHYSICS AND CHEMSITRY

Dr. Liu is particularly interested in the physics and chemistry of the lower ionosphere spanning from 60 to 100 km altitude, also called the D-region of the ionosphere. This ionospheric region plays an important role in subionospheric propagation of radio signals in the very low frequency (VLF) band that is widely used for long-range communication. It is also the home of various interesting electrodynamic phenomena such as transient luminous events. Dr. Liu studies the electron and ion density profiles of this region and their variability due to the underlying thunderstorm and lightning activities.

TRANSIENT LUMINOUS EVENTS

Transient luminous events are a group of electrical discharge phenomena above thunderstorms, including jets, gigantic jets, sprites, halos and elves. They were discovered in the early 1990s and are not well understood at present. Dr. Liu investigates their dynamics, structures and optical emissions by developing computer simulation models and collecting optical and radio data.

LIGHTNING

Lightning is one of the most fascinating atmospheric phenomena on Earth. However, little is known about how lightning starts in thunderclouds, moves through air, and then strikes objects on ground. Dr. Liu currently focuses on understanding the initiation process of lightning.

ENERGETIC RADIATION FROM THUNDERSTORMS

Thunderstorms have recently been found capable of generating energetic radiation including both x-rays and gamma rays, which has been detected with ground, balloon, airplane and spacecraft based measurements. An emerging research field called high-energy atmospheric physics is dedicated to studying their properties and underlying physics. Dr. Liu studies how the energetic radiation is produced through "electron runaway" phenomena.

APPLICATIONS OF LOW-TEMPERATURE PLASMAS

A critical discharge component of lightning and transient luminous events is streamers, filamentary plasma channels created by a fast propagating ionization wave. At ground pressure, they are typically a fraction of millimeter wide and can propagate far away from the electrode where they originate. They are found in various applications such as microplasma discharge devices and medical treatment. Dr. Liu is interested in applying his expertise in streamer physics to technology development in those areas.

Selected Publications

BOOK CHAPTERS

Liu, N. Y., Upper atmospheric electrical discharges, in The Lightning Flash, ed. V. Cooray, The Institution of Engineering and Technology, p. 725-786, 2014.

REFEREED JOURNAL PUBLICATIONS

Liu, N. Y, N. Spiva, J. R. Dwyer, H. K. Rassoul, D. Free, and S. A. Cummer, Upward electrical discharges observed above Tropical Depression Dorian, Nature Communications, accepted. 

Cramer, E. S., J. R. Dwyer, S. Arabshahi, I. B. Vodopiyanov, N. Y. Liu, and H. K. Rassoul, An analytical approach for calculating energy spectra of relativistic runaway electron avalanches in air, Journal of Geophysical Research, 119, doi: 10.1002/2014JA020265, 2014 [PDF].

Schaal, M. M., J. R. Dwyer, S. Arabshahi, E. Cramer, R. Lucia, N. Y. Liu, H. K. Rassoul, D. Smith, J. Matten, A. Reid, J. Hill, D. Jordan, and M. Uman, The structure of x-ray emissions from triggered lightning leaders measured by a pinhole-type x-ray camera, Journal of Geophysical Research, 119, doi:10.1002/2013JD020266, 2014 [PDF].

Kosar, B. C., N. Y. Liu, and H. K. Rassoul, Formation of sprite streamers at subbreakdown conditions from ionospheric inhomogeneities resembling observed sprite halo structures, Geophysical Research Letters, 40, 6282–6287, doi:10.1002/2013GL058294, 2013 [PDF] .

(Frontier Article in Geophysical Research Letters) Dwyer, J. R., N. Y. Liu, and H. K. Rassoul, Properties of the thundercloud discharges responsible for terrestrial gamma-ray flashes, Geophysical Research Letters, 40(15), 4067-4073, doi:10.1002/grl.50742, 2013 [PDF].

Liu, N. Y., and J. R. Dwyer, Modeling terrestrial gamma-ray flashes produced by relativistic feedback discharges, Journal of Geophysical Research, 118, 2359–2376, doi:10.1002/jgra.50232, 2013 [PDF].

Dwyer, J. R., M. M. Schaal, E. Cramer, S. Arabshahi, N. Y. Liu, H. K. Rassoul, J. D. Hill, D. M. Jordan, and M. A. Uman, Observation of a gamma-ray flash at ground level in association with a cloud-to-ground lightning return stroke, Journal of Geophysical Research, 117, A10303, doi:10.1029/2012JA017810, 2012  [PDF] .

Kosar, B. C., N. Y. Liu, and H. K. Rassoul, Luminosity and propagation characteristics of sprite streamers initiated from small ionospheric disturbances at sub-breakdown conditions, Journal of Geophysical Research, 117, A08328, doi:10.1029/2012JA017632, 2012. [PDF]

Liu, N. Y., B. Kosar, S. Sadighi, J. R. Dwyer, and H. K. Rassoul, Formation of streamer discharges from an isolated ionization column at sub-breakdown conditions, Physical Review Letters, 109, 025002, 2012. [PDF]

Liu, N. Y., J. R. Dwyer, and H. K. Rassoul, Effects of pressure and humidity on positive corona inception from thundercloud hydrometeors, Journal of Atmospheric and Solar-Terrestrial Physics, 10.1016/j.jastp.2012.01.012, 2012. [PDF]

Liu, N. Y., Multiple ion species fluid modeling of sprite halos and the role of electron detachment of O- in their dynamics, Journal of Geophysical Research, 117, A03308, doi:10.1029/2011JA017062, 2012. [PDF]

Liu, N. Y., V. P. Pasko, H. C. Stenbaek-Nielsen, and M. G. McHarg, Sprite streamers imaged at different exposure times, IEEE Transactions on Plasma Science, 39(11), 2710, 2011. [PDF]

Liu, N. Y., Model of sprite streamer luminous trail caused by increasing streamer current, Geophysical Research Letters, L04102, doi:10.1029/2009GL042214, 2010. [PDF]

Liu, N. Y., and V. P. Pasko, NO-gamma emissions from streamer discharges: Direct electron impact excitation versus resonant energy transfer, Journal of Physics D: Applied Physics, 43, 082001, doi:10.1088/0022-3727/43/8/082001, 2010. [PDF]

Liu, N. Y., V. P. Pasko, K. Adams, H. C. Stenbaek-Nielsen, and M. G. McHarg, Comparison of acceleration, expansion and brightness of sprite streamers obtained from modeling and high-speed video observations, Journal of Geophysical Research, 114, A00E03, doi:10.1029/2008JA013720, 2009. [PDF]

Liu, N. Y., V. P. Pasko, H. Frey, S. Mende, H.-T. Su, A. Chen, R. R. Hsu, and L.-C. Lee, Assessment of sprite initiating electric fields and quenching altitude of a1Πg state of N2 using sprite streamer modeling and ISUAL spectrophotometric measurements, Journal of Geophysical Research, 114, A00E02, doi:10.1029/2008JA013735, 2009. [PDF]

Liu, N. Y., S. Celestin, A. Bourdon, V. P. Pasko, P. Segur, and E. Marode, Photoionization and optical emission effects of positive streamers in air at ground pressure, IEEE Transactions on Plasma Science, 36(4), 942, doi:10.1109/TPS.2008.927088, 2008. [PDF]

Liu, N. Y., S. Celestin, A. Bourdon, V. P. Pasko, P. Segur, and E. Marode, Application of photoionization models based on radiative transfer and the Helmholtz equations to studies of streamers in weak electric fields, Applied Physics Letters, 91, 211501, doi:10.1063/1.2816906, 2007. [PDF]

Liu, N. Y., and V. P. Pasko, Modeling studies of NO-gamma emissions of sprites, Geophysical Research Letters, 34, L16103, doi:10.1029/2007GL030352, 2007. [PDF]

Bourdon, A., V. P. Pasko, N. Y. Liu, S. Celestin, P. Segur, and E. Marode, Efficient models for photoionization produced by non-thermal gas discharges in air based on radiative transfer and Helmholtz equations, Plasma Sources Science and Technology, 16, 656-678, doi:10.1088/0963-0252/16/3/026, 2007. [PDF]

Liu, N. Y., and V. P. Pasko, Effects of photoionization on similarity properties of streamers at various pressures in air, Journal of Physics D: Applied Physics, 39, 327-334, doi:10.1088/0022-3727/39/2/013, 2006. [PDF]

Moss, G. D., V. P. Pasko, N. Y. Liu, and G. Veronis, Monte Carlo model for analysis of thermal runaway electrons in streamer tips in transient luminous events and streamer zones of lightning leaders, Journal of Geophysical Research, 111, A02307, doi:10.1029/2005JA011350, 2006. [PDF]

Liu, N. Y., V. P. Pasko, D. H. Burkhardt, H. Frey, S. Mende, H.-T. Su, A. Chen, R. R. Hsu, L.-C. Lee, H. Fukunishi, and Y. Takahashi, Comparison of results from sprite streamer modeling with spectrophotometric measurements by ISUAL instrument on FORMOSAT-2 satellite, Geophysical Research Letters, 33, L01101, doi:10.1029/2005GL024243, 2006. [PDF]

Liu, N. Y., and V. P. Pasko, Molecular nitrogen LBH band system far-UV emissions of sprite streamers, Geophysical Research Letters, 32, L05104, doi:10.1029/2004GL022001, 2005. [PDF]

Liu, N. Y., and V. P. Pasko, Effects of photoionization on propagation and branching of positive and negative streamers in sprites, Journal of Geophysical Research, 109, A04301, doi:10.1029/2003JA010064, 2004. [PDF]

PH.D. THESIS

Liu, N. Y., Dynamics of Positive and Negative Streamers in Sprites, Ph.D. thesis, The Pennsylvania State University, University Park, Pennsylvania, 2006. [PDF]