Researchers in the US have compiled the largest-ever dataset of high-frequency radio signals from lightning to investigate how a bolt’s altitude within a cloud influences how its energy radiates.
The research, carried out by scientists at New Mexico’s Los Alamos National Laboratory, showed that the strength difference between two very high-frequency radio pulses in lightning is closely related to the altitude of the lightning in the cloud.
The team reportedly harnessed machine learning and satellite technology to shed light on a decades-old question about the energy radiation of lightning, which is considered one of nature’s most powerful forces.
According to the laboratory, the findings offer valuable insight into the processes behind lightning initiation in a particularly powerful kind of in-cloud lightning.
Behind the study
For the research, the team collected the largest dataset of trans-ionospheric pulse pairs (TIPPs), which are considered the most powerful natural radio signals on the planet that are generated by lightning.
A radio frequency sensor they developed observed more than 76,000 TIPPs, matching them to lightning detected from the ground aboard a satellite in geostationary orbit. This is the circular path 22,236 miles above the equator, where a satellite moves with Earth’s rotation and stays over the same spot.
“An estimated 95 percent of the lightning events detected by radio frequency sensors are TIPPs, while the rest are cloud-to-ground lightning discharges,” the lab explained.
Erin Lay, PhD, a research scientist at Los Alamos National Laboratory and lead author of the study, explained that scientists have long known the first pulse of a TIPP is caused by the lightning signal traveling through the ionosphere and reaching the satellite directly.
The second pulse occurs when the signal reflects off the Earth’s surface before reaching the satellite. “Sometimes this second pulse is stronger than the first, but we didn’t know why.”
The study explained that the difference is a result of the lightning’s altitude within the cloud and its elevation angle relative to the satellite.
Mapping lightning with precision
The researchers further emphasized that the experiments provided additional evidence that TIPPs are the space-based signature of compact intracloud discharges. These discharges are a particularly fast and short-lived form of lightning inside the cloud.
“Our measurements could lead to even more accurate measurements of how high the convective regions of clouds are, which can help them verify their data,” Lay elaborated in a press release.
She emphasized that a sudden jump in the altitude of TIPPs could indicate rapid changes in the storm’s convection, helping researchers better interpret cloud dynamics.
The team now hopes the new, extensive database of 76,000 TIPPs will add greater specificity to Global Lightning Mapper (GLM) data. This could, in turn, help refine satellite-based observations and enhance our understanding of storm behavior.
Lay stated that the GLM instruments aboard the National Oceanic and Atmospheric Administration’s (NOAA) GOES-R satellites and the co-located Advanced Baseline Imager provide researchers with an estimate of cloud height.
The paper, ” Statistical Analysis of Trans-Ionospheric Pulse Pairs and Inferences on Their Characteristics, ” has been published in the Journal of Geophysical Research.