Sprites, halos, jets, and elves are members of a family of transient luminous events (TLEs) that illuminate the stratosphere and mesosphere above thunderstorms (click here for an overview of sprites). In addition to their intrinsic physical interest, there are numerous broader implications for TLE events. In particular, they may charge or discharge the global electrical circuit, produce NOx, transfer energy from the troposphere to the upper atmosphere, and drive electron density changes in the lower ionosphere. Thus, TLEs may adversely affect radio communication systems, GPS, and aircraft. The figure to the right shows sprites imaged over Argentina on 23 Feb. 2006 (see Publications 7 and 9 for more info).

My previous research focused on using in situ measurements and a numerical model of electromagnetic fields above thunderstorms to investigate how TLEs initiate and grow. The in situ data were obtained during the Brazil Sprite Balloon Campaign, which included electric and magnetic field instruments, x-ray sensors, and conductivity measurements. I was involved in all aspects of the project and developed a new electric field sensor [Publication 3]. During the campaign, we measured thousands of electric and magnetic field excursions correlated with lightning.  I also developed a numerical model to compare with these electric fields. Figure 1 shows vertical and radial components of the largest electric field change ever measured in the stratosphere, along with the output of my numerical model. Using the best-fit parameters to this comparison between model and data, I predicted and compared the electric fields at sprite initiation altitudes to the fields needed to cause electrical breakdown that leads to sprites [Publications 4-5].

Other in situ measurements I have analyzed include electric and magnetic fields driven by distant lightning. My analysis [Publication 6] showed that cloud-to-ground lightning drive low frequency fields in the stratosphere, but that only a small percentage of lightning drive currents (such as sprites) in the middle atmosphere. In addition to working with in situ data, I have also analyzed data and helped with hardware for the World Wide Lightning Location Network (WWLLN, wwlln.net), the only real time lightning network that covers the entire globe. I have compared in situ electric fields to WWLLN events [Publication 2].

I am currently examining numerous historical in situ data sets, both balloon- and rocket-borne, to further our understanding of electrical discharges above thunderstorms. I will soon be submitting an article to JGR that presents some rare examples of lightning-driven electric field changes obtained at 75-130 km altitude during a sounding rocket flight from Wallops Island, VA in 1995. These data provide direct insight into how TLEs are produced and how they affect the ionosphere. Additionally, I have been involved with ground-based imaging and RF measurements of TLEs and their parent lightning. I have managed an international project in the south of Brazil.  We imaged more than 600 TLEs during two storm systems, including the third most productive TLE storm ever reported. These observations have been followed closely by the atmospheric electricity and space physics community, including an EOS cover article [Publication 7] and invited talks at the AGU Fall Meeting and two URSI meetings [see invited presentations].