The FORTE (Fast On-orbit Recording of Transient Events) satellite records bursts of electromagnetic waves arising from near the Earth’s surface in the radio frequency (rf) range of 30 to 300 MHz with a dual polarization antenna. We investigate the possible rf signature of ultrahigh energy cosmic-ray particles in the form of coherent Cherenkov radiation from cascades in ice. We calculate the sensitivity of the FORTE satellite to ultrahigh energy neutrino (UHE $\nu )$ fluxes at different energies beyond the Greisen-Zatsepin-Kuzmin cutoff. Some constraints on supersymmetry model parameters are also estimated due to the limits that FORTE sets on the UHE neutralino flux. The FORTE database consists of over 4 million recorded events to date, including in principle some events associated with UHE $\nu .$ We search for candidate FORTE events in the period from September 1997 to December 1999. The candidate production mechanism is via coherent VHF radiation from a UHE $\nu$ shower in the Greenland ice sheet. We demonstrate a high efficiency for selection against lightning and anthropogenic backgrounds. A single candidate out of several thousand raw triggers survives all cuts, and we set limits on the corresponding particle fluxes assuming this event represents our background level.

The Atmosphere‐Space Interactions Monitor (ASIM) was launched to the International Space Station on 2 April 2018. The ASIM payload consists of two main instruments, the Modular X‐ray and Gamma‐ray Sensor (MXGS) for imaging and spectral analysis of Terrestrial Gamma‐ray Flashes (TGFs) and the Modular Multi‐spectral Imaging Array for detection, imaging, and spectral analysis of Transient Luminous Events and lightning. ASIM is the first space mission designed for simultaneous observations of Transient Luminous Events, TGFs, and optical lightning. During the first 10 months of operation (2 June 2018 to 1 April 2019) the MXGS has observed 217 TGFs. In this paper we report several unprecedented measurements and new scientific results obtained by ASIM during this period: (1) simultaneous TGF observations by Fermi Gamma‐ray Burst Monitor and ASIM MXGS revealing the very good detection capability of ASIM MXGS and showing substructures in the TGF, (2) TGFs and Elves produced during the same lightning flash and even simultaneously have been observed, (3) first imaging of TGFs giving a unique source location, (4) strong statistical support for TGFs being produced during the upward propagation of a leader just before a large current pulse heats up the channel and emits a strong optical pulse, and (5) the t₅₀ duration of TGFs observed from space is shorter than previously reported.