Engineering topics

T Lang

Publications and source records attributed to T Lang.

4 records

NASA NTRS2024

Flickering Gamma Flashes, the Missing Link Between Gamma Glows and TGFs

Two different hard radiation phenomena are known to originate from thunderclouds: Terrestrial Gamma-ray Flashes (TGFs) and gamma-ray glows. Both involve avalanche of electrons accelerated to relativistic energies but are different phenomena. Glows are known to last for one-to-hundreds of seconds, have moderate intensities and originate from quasi-stationary thundercloud fields. TGFs exhibit high intensities and have characteristic durations of tens-to-hundreds of microseconds. TGFs often show close association with emission of strong radio signals and optical pulses indicating involvement of lightning leaders in their generation. Here we report unique observations of a different phenomenon, which we call Flickering Gamma-ray Flashes (FGFs). FGFs resemble usual multi-pulse TGFs, but with larger number of pulses and each pulse has a longer duration than ordinary TGFs. FGF durations span from 20 to 250 milliseconds, which reaches the lower boundary of the gamma-ray glow duration. FGFs are radio and optically silent, which makes them distinct from normal TGFs. An FGF starts as an ordinary gamma-ray glow, then suddenly increases exponentially in intensity, and turns into an unstable, “flickering” mode with a sequence of pulses. FGFs could be the missing link between the gamma-ray glows and conventional TGFs, whose absence has been puzzling atmospheric electricity community for two decades.

N Østgaard↗

NASA NTRS2024

Highly Dynamic Gamma-Ray Emissions Are Common in Tropical Thunderclouds

Thunderstorms emit fluxes of gamma rays known as gamma-ray glows, sporadically observed by aircraft, balloons and from ground. Glows are observed as increased gamma-ray emissions by tens of percent up to two orders of magnitude above the background, sometimes abruptly terminated by lightning discharges. Glows are produced by the acceleration of energetic electrons in high electric field regions within thunderclouds, and contribute to charge dissipation. Glows are considered as quasi-stationary phenomena, with durations up to a few tens of seconds and spatial scales up to 10-20 kilometers. No measurement of the full extension in space and time of a gamma ray glow region and their occurring frequency has been reported so far. Here we show that tropical thunderclouds over ocean and coastal regions commonly emit gamma rays for hours over areas up to a few thousands of square kilometers. Emission is associated with deep convective cores; it is not uniform and continuous but shows characteristic timescales of 1-10 seconds and even sub-second for individual glows. The dynamics of gamma-glowing thunderclouds starkly contradicts the quasi-stationary picture of glows, but rather resembles that of a huge gamma-glowing «boiling pot» both in pattern and behavior.

M Marisaldi↗

NASA NTRSDate not supplied

Quality Assurance of ISS LIS lightning Data

Optical lighting detection from space has been ongoing since 1995 from the Optical Transient detector (1995-2000), then later by the Lightning Imaging Sensors (LIS) on the Tropical Rainfall Measuring Mission (TRMM) satellite (1997-2015) and the International Space Station (ISS) (ISS 2017-present). A rapid readout (2 ms) 128x128 pixel CCD (Charge-coupled Device) array detects optical transients from lightning (events) and transmits the observations to ground. Ground processing determines whether individual events are likely due to lightning or noise. Likely lightning events are then grouped into groups, flashes, and areas and their location on the earth are determined. The lightning data are saved in orbit files; each file containing the time, location, and intensity of the lightning events, groups, flashes, and areas detected during one orbit. Even after this processing anomalies may exist in some of the orbits. A manual quality assurance (QA) procedure is performed monthly to assess the data and omit orbits with obvious anomalies from the dataset. These files are not included in the final dataset that has undergone QA. The manual QA was developed during the OTD mission to identify artifacts that made it through ground processing algorithms. The manual QA process was continued for the TRMM and ISS LIS missions. Many anomalies have been identified and software updates now address many of them. However, some anomalies still occur in the processed datasets. The manual QA process examines the data for obvious issues in the lightning files that passed through the processing algorithms. These files are considered anomalous and are not included in the final QA dataset. Some issues that may cause an orbit to be considered anomalous include: obvious noise (excess events that make it through the processing), suspect geolocation, and excessive missing data packets. As an example, one way noise manifests is as “streaks” in lightning climatology plots. These streaks are especially apparent in low lightning rate regions (eg., over oceans). Since there is no method at present to extract these anomalies during processing, orbit files with significant anomalies are identified and removed from the final QA ISS LIS dataset. The final QA dataset can be obtained files from the Global Hydrometeorological Resource Center (GHRC). This presentation will provide examples of the various anomalies and examine how often the various anomalies occur and how much data is lost due to the omission of the anomalous orbits. Comparisons with OTD and TRMM LIS will also be examined.

ISS↗

NASA NTRSDate not supplied

Simulations to Inform NASA's Future Lightning Missions

3-D monitoring of lightning with optical and VHF sensors in LEOCLIDE. CubeSpark is a constellation of small satellites acting as a 3D lightning mapping network in space. VHF radio measurements map lightning structure inside clouds. Bispectral, high-resolution optical measurements enhance detection of lightning in severe and anomalous thunderstorms and flashes that extend upward from cloud-top.

lightning↗