Concept of Operations
ALOFT will be an exciting exploratory field campaign. TGFs have never been observed directly by the top of clouds. The size and time evolution of gamma-ray glows is still a mystery. We expect the unexpected.
Main content
The ALOFT domain is shown below in Figure 1. The NASA ER-2 aircraft will be based at MacDill Air Force Base (AFB) in Tampa, Florida during July 2023. This location places the aircraft within range of most TGF hotspots over the Gulf of Mexico, Central America, and the Caribbean. A ground-based network of lightning sensors, particularly radio observations, provide overlapping coverage of this region as well. ALOFT will focus its flights on four basic regions: Florida/Bahamas, northern Central America near the Yucatan Peninsula, southern Central America including the islands of San Andres and Providencia off the Nicaraguan coast, and the northeastern Caribbean near Puerto Rico.
The targets for ALOFT are persistent groups of weak-to-moderate thunderstorms. These types of thunderstorms provide a good mix of lightning, TGF, and gamma-ray glow potential without compromising ER-2 safety. ER-2 must fly at least 5000 feet above the tops of thunderstorms, which limits maximum targetable cloud-top height to ~18 km MSL. These thunderstorm clusters allow for long-term loitering by the ER-2 using a mixture of linear, race track, and/or bowtie patterns that will sample a wide variety of thunderstorm structures and evolutionary states.
Figure 1: NASA ER-2 range rings (showing time on station) centered on MacDill AFB. Also shown are TGFs detected by Fermi Gamma-ray Burst Monitor (GBM) and ASIM during June-September (black dots and color contours), plus three possible flight paths.
Daily weather briefings will be provided the ALOFT forecast team. GOES GLM (lightning) and ABI (Vis/IR) with 10-15 minutes updates will also be available. These will assess the potential for thunderstorms in the domain, as well as takeoff/landing weather for the ER-2. ALOFT mission scientists will then – in consultation with the ER-2 team, airborne instruments team, and ground sites team – make decisions about when and where to fly the ER-2 on a given day. A mission scorecard will be maintained and updated throughout the campaign to ensure and document overall success.
When a gamma-glowing thundercloud is encountered, based on realtime UIB-BGO telemetry updates, the ER-2 will be directed to immediately and continually refly the glowing thunderstorm in order to determine the glow’s spatiotemporal extent.
ISS LIS overpasses will be monitored and assessed for their potential to synchronize with targetable thunderstorms in the ALOFT domain. Over Central America and much of the Gulf of Mexico, stereo observations with GLM-16 and GLM-18 are available, enabling vertically resolved measurements of lightning. Similar stereo observations between GLM-16 and Meteosat Third Generation Lightning Imager (MTG-LI) are available near Puerto Rico. Note that MTG-LI data are currently being validated, making underflights with FEGS and LIP potentially attractive to EUMETSAT.
Acknowledgements
We would like to thank the Ministry of the Environment of El Salvador for their assistance with ALOFT weather forecasting.