Now showing items 1-11 of 11

    • A broadband low-reflection metamaterial absorber 

      Gu, S; Barrett, JP; Hand, TH; Popa, BI; Cummer, SA (Journal of Applied Physics, 2010-09-15)
      Artificially engineered metamaterials have enabled the creation of electromagnetic materials with properties not found in nature. Recent work has demonstrated the feasibility of developing high performance, narrowband ...
    • A lightning discharge producing a beam of relativistic electrons into space 

      Cohen, MB; Inan, US; Said, RK; Briggs, MS; Fishman, GJ; Connaughton, V; Cummer, SA (Geophysical Research Letters, 2010-09-01)
      Strong electric fields associated with lightning generate brief (∼1 ms) but intense Terrestrial Gamma-ray Flashes (TGFs), detected by spacecrafts. A few events are thought to be the signature of a relativistic electron beam ...
    • A survey of ELF and VLF research on lightning-ionosphere interactions and causative discharges 

      Inan, US; Cummer, SA; Marshall, RA (Journal of Geophysical Research: Space Physics, 2010-01-01)
      Extremely low frequency (ELF) and very low frequency (VLF) observations have formed the cornerstone of measurement and interpretation of effects of lightning discharges on the overlying upper atmospheric regions, as well ...
    • Contrasting the efficiency of radiation belt losses caused by ducted and nonducted whistler-mode waves from ground-based transmitters 

      Rodger, CJ; Carson, BR; Cummer, SA; Gamble, RJ; Clilverd, MA; Green, JC; Sauvaud, JA; ... (9 authors) (Journal of Geophysical Research: Space Physics, 2010-01-01)
      It has long been recognized that whistler-mode waves can be trapped in plasmaspheric whistler ducts which guide the waves. For nonguided cases these waves are said to be "nonducted", which is dominant for L < 1.6. Wave-particle ...
    • Design of layered transformation-optics devices of arbitrary shape 

      Popa, BI; Cummer, SA (Physical Review A - Atomic, Molecular, and Optical Physics, 2010-09-30)
      Transformation-optics devices of arbitrary shapes usually result in material parameters inside the device that feature level sets of different shapes. Consequently, these devices cannot easily be implemented using a layered ...
    • Gigantic jets with negative and positive polarity streamers 

      Chou, JK; Kuo, CL; Tsai, LY; Chen, AB; Su, HT; Hsu, RR; Cummer, SA; ... (12 authors) (JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, 2010-07-15)
    • Lightning mapping observation of a terrestrial gamma-ray flash 

      Lu, G; Blakeslee, RJ; Li, J; Smith, DM; Shao, XM; McCaul, EW; Buechler, DE; ... (10 authors) (Geophysical Research Letters, 2010-06-01)
      We report the observation with the North Alabama Lightning Mapping Array (LMA) related to a terrestrial gamma-ray flash (TGF) detected by RHESSI on 26 July 2008. The LMA data explicitly show the TGF was produced during the ...
    • Midlatitude daytime D region ionosphere variations measured from radio atmospherics 

      Han, F; Cummer, SA (Journal of Geophysical Research: Space Physics, 2010-01-01)
      We measured the midlatitude daytime ionospheric D region electron density profile height variations in July and August 2005 near Duke University by using radio atmospherics (or sferics for short), which are the high-power, ...
    • Midlatitude nighttime D region ionosphere variability on hourly to monthly time scales 

      Han, F; Cummer, SA (Journal of Geophysical Research: Space Physics, 2010-01-01)
      Significant temporal variability of the nighttime D region is well known, but its inaccessibility means that the time scales, magnitudes, and sources for that variability are not well understood. We probed the ionospheric ...
    • Multi-instrumental observations of a positive gigantic jet produced by a winter thunderstorm in Europe 

      Van Der Velde, OA; Bór, J; Li, J; Cummer, SA; Arnone, E; Zanotti, F; Füllekrug, M; ... (10 authors) (Journal of Geophysical Research Atmospheres, 2010-01-01)
      At 2336:56 UTC on 12 December 2009, a bright gigantic jet (GJ) was recorded by an observer in Italy. Forty-nine additional sprites, elves, halos and two cases of upward lightning were observed that night. The location of ...
    • Transient luminous events above two mesoscale convective systems: Storm structure and evolution 

      Lang, TJ; Lyons, WA; Rutledge, SA; Meyer, JD; MacGorman, DR; Cummer, SA (Journal of Geophysical Research: Space Physics, 2010-01-01)
      Two warm-season mesoscale convective systems (MCSs) were analyzed with respect to their production of transient luminous events (TLEs), mainly sprites. The 20 June 2007 symmetric MCS produced 282 observed TLEs over a 4 h ...