Airborne Lightning Observatory for FEGS and TGFs (ALOFT)

Scientific Objectives

Only 30 years ago it was discovered that a thunderstorm is the birthplace of the most energetic natural particle acceleration on Earth and Terrestrial Gamma-ray Flashes (TGFs) are the most explosive manifestation of such a process capable of delivering 1018 high-energy photons from thunderclouds to space in a few tens of microseconds. Lightning and TGFs are closely related but the details of this relationship are yet to be understood.

Illustration of a Terrestrial Gamma Flash
NASA/Goddard Space Flight Center/J. Dwyer/Florida Inst. of Technology

Main content

Gamma-ray glows are another hard radiation phenomenon in thunderstorms. They have much lower flux than the TGFs, but since they probably extend thousands of square kilometers and last for tens of minutes or even hours, they can have a much larger effect on the atmosphere locally. Flying over the source thunderstorm and making high-resolution measurements of the gamma-rays, optical signals, and electric-field changes is key to solving the questions:

  • How and under what conditions are TGFs produced?
  • How extended in space and time are gamma-ray glows?

In addition ALOFT will:

  1. Perform International Space Station Lightning Imaging Sensor (ISS LIS) and Geostationary Lightning Mapper (GLM) validation using improved suborbital instrumentation.
  2. Evaluate new design concepts for next-generation spaceborne lightning mappers.
  3. Make combined microwave and lightning measurements of tropical convection from a suborbital platform.

The ALOFT campaign will make measurements of TGFs and gamma-ray glows with unprecedented temporal and spatial resolution. Coordinated optical, gamma-ray, and electric field change measurements will provide the foundation needed to uncover the detailed physics that enables the production of high energy radiation from thunderstorms. Since gamma-ray glows require strong electric fields throughout a thunderstorm, it has been suggested that gamma-ray glows might be a prerequisite for producing TGFs. However, the two phenomena have never been observed simultaneously from space.

ALOFT also will enhance spaceborne lightning mapper performance validation and characterization in the tropics and oceanic regions where very little detailed ground validation is available. The year 2023 is likely the last full year for the ISS LIS mission, so target-of-opportunity underflights of LIS are needed to confirm mission performance near its end-of-life, complementing the early mission ER-2 observations made in 2017. In addition, GLM algorithms have been retuned multiple times since the GOES-R 2017 campaign. ALOFT will help confirm the new parameter settings using very similar optical observations.

Illustration of thunder cloud and TGF
M. Marisaldi