Search for: All records

Abstract We analyze the drivers, distribution, and properties of the relativistic electron precipitation (REP) detected near midnight by the Polar Orbiting Environmental Satellites (POES) and Meteorological Operational (MetOp) satellites, critical for understanding radiation belt losses and nightside atmospheric energy input. REP is either driven by wave‐particle interactions (isolated precipitation within the outer radiation belt), or current sheet scattering (CSS; precipitation with energy dispersion), or a combination of the two. We evaluate the L‐MLT distribution for the identified REP events in which only one process evidently drove the precipitation (∼10% of the REP near midnight). We show that the two mechanisms coexist and drive precipitation in a broadL‐shell range (4–7). However, wave‐driven REP was also observed atL < 4, whereas CSS‐driven REP was also detected atL > 7. Moreover, we estimate the magnetotail stretching during each REP event using the magnetic field observations from the Geostationary Operational Environmental Satellite (GOES). Both wave‐particle interactions and CSS drive REP in association with a stretched magnetotail, although CSS‐driven REP potentially shows more pronounced stretching. Wave‐driven REP events are localized inLshell and often occur on spatial scales of <0.3 L. Using either proton precipitation (observed by POES/MetOp during wave‐driven REP) as a proxy for electromagnetic ion cyclotron (EMIC) wave activity or wave observations (from GOES and the Van Allen Probes) at the conjugate event location, we find that ∼73% wave‐driven REP events are associated with EMIC waves. 

Abstract We provide evidence that Terrestrial Gamma‐Ray Flashes (TGFs), in well isolated thunderstorms, tend to occur during periods of low and declining flash rates, and when the flash amplitudes are larger than average. This conclusion comes from examining the results of 371 manually tracked TGF‐producing thunderstorms. Fermi‐GBM identified TGFs are used for this analysis and lightning data come from both World Wide Lightning Location Network and Earth Networks Total Lightning Network. The data from these storms suggest that TGFs are likely to occur in almost every phase of storms that last longer than an hour, but tend to occur later on in shorter storms. We also note that, in short storms, TGFs are more likely to accompany a flash when the flash rates of the storm are lower than average, and they are less likely per flash during the peak flash rate periods of the storms. We find that the tendency for TGFs to occur while the flash rate is falling and when the amplitudes of flashes (the sum of the absolute values of peak currents of all constituent sferics in the flash) are larger than average, does not depend strongly on the duration of the storms. This implies that not just any lightning flash can or even will produce a TGF, but that the electrical conditions of the storm play a crucial role in TGF production. 

Abstract We evaluate the location, extent, and energy range of electron precipitation driven by ElectroMagnetic Ion Cyclotron (EMIC) waves using coordinated multisatellite observations from near‐equatorial and Low‐Earth‐Orbit (LEO) missions. Electron precipitation was analyzed using the Focused Investigations of Relativistic Electron Burst Intensity, Range and Dynamics (FIREBIRD‐II) CubeSats, in conjunction either with typical EMIC‐driven precipitation signatures observed by Polar Orbiting Environmental Satellites (POES) or with in situ EMIC wave observations from Van Allen Probes. The multievent analysis shows that electron precipitation occurred in a broad region near dusk (16–23 MLT), mostly confined to 3.5–7.5 L‐shells. Each precipitation event occurred on localized radial scales, on average ∼0.3 L. Most importantly, FIREBIRD‐II recorded electron precipitation from ∼200 to 300 keV to the expected ∼MeV energies for most cases, suggesting that EMIC waves can efficiently scatter a wide energy range of electrons. 

International Ocean Discovery Program (IODP) Expedition 358 was carried out from October 2018 through March 2019 on the D/V Chikyu in an attempt to reach a plate boundary fault zone at seismogenic depths for the first time in scientific ocean drilling. The goal was to extend Hole C0002P from ~2900 to ~5200 meters below seafloor (mbsf) and cross the seismically interpreted main décollement fault zone with logging while drilling, downhole stress measurements, cuttings sampling, mud gas sampling, and partial coring by drilling a sidetrack to create a new hole (C0002Q). Although drilling reached 3262.5 mbsf, the deepest to date in all of scientific ocean drilling, the effort to drill to and sample the target—the megathrust fault zone—was not successful. Operational challenges in establishing sidetrack holes and advancing them at reasonable rates of penetration limited the new cased hole interval to less than 60 m total at a depth shallower than the previously established casing depth of 2922 mbsf. Combined, the cuttings, logs, and ~60 cm of recovered core from sidetrack Holes C0002Q–C0002T revealed hemipelagic sediments and fine silty turbidites consistent in lithology and physical properties with those recovered in the same depth interval at the same site during Integrated Ocean Drilling Program Expedition 348. Cuttings revealed evidence of only weakly deformed rock, with relatively common calcite veins but few other structural indicators. Because no downhole leak-off tests were made and very little borehole imaging was performed, no further insight into the tectonic context was acquired. After riser drilling at Site C0002 was terminated, drilling at alternate contingency Sites C0024 and C0025 was carried out. Site C0024 targeted the frontal thrust region to sample and log hanging wall rocks and the shallow portion of the décollement zone, and Site C0025 accessed sediments in the Kumano fore-arc basin. At Site C0024, a dedicated logging hole was drilled and a very complete suite of logs were acquired from 0 to 869 mbsf. Preliminary interpretation of log response and images suggests the frontal thrust zone was encountered from about 813 mbsf to the base of the hole, with a zone of notably low resistivity and steep bedding from 850 mbsf to the bottom of the hole. Core samples revealed lithologic units interpreted to be hemipelagic and turbiditic basin fill, trench fill, and Shikoku Basin sediments and encountered deformation potentially associated with a back thrust imaged in seismic reflection data. However, coring had to be terminated at about 620 mbsf, well short of the frontal thrust zone. Site C0025 recovered fore-arc basin sediments underlain by those interpreted to have been deposited in a trench-slope basin setting; no clear transition into older, inner accretionary wedge material was identified during the preliminary analysis. Coring from 400 to 571 mbsf yielded datable material and possible evidence for diapiric intrusion of sediments. 

This chapter documents the methods used for shipboard measurements and analyses during International Ocean Discovery Program (IODP) Expedition 358. We conducted riser drilling from 2887.3 to 3262.5 meters below seafloor (mbsf) at Site C0002 (see Table T1 in the Expedition 358 summary chapter [Tobin et al., 2020a]) as a continuation of riser drilling in Hole C0002F begun during Integrated Ocean Drilling Program Expedition 326 (Expedition 326 Scientists, 2011) and deepened during Integrated Ocean Drilling Program Expeditions 338 and 348 (Strasser et al., 2014b; Tobin et al., 2015b). Please note that the top of Hole C0002Q begins from the top of the window cut into the Hole C0002P casing. Previous Integrated Ocean Drilling Program work at Site C0002 included logging and coring during Integrated Ocean Drilling Program Expeditions 314 (logging while drilling [LWD]), 315 (riserless coring), 332 (LWD and long-term monitoring observatory installation), 338 (riser drilling and riserless coring), and 348 (riser drilling) (Expedition 314 Scientists, 2009; Expedition 315 Scientists, 2009b; Expedition 332 Scientists, 2011; Strasser et al., 2014b; Tobin et al., 2015b). Riserless contingency drilling was also conducted at Site C0024 (LWD and coring) near the deformation front of the Nankai accretionary prism off the Kii Peninsula and at Site C0025 (coring only) in the Kumano fore-arc basin. Riser operations began with connection of the riser to the Hole C0002F wellhead, sidetrack drilling out the cement shoes from 2798 to 2966 mbsf to establish a new hole, and then running a cement bond log to check the integrity of the Hole C0002P casing-formation bonding. A new sidetrack was established parallel to previous Hole C0002P drilling and designated as Hole C0002Q to distinguish it from the overlapping interval in Hole C0002P. Several new kick offs were established (Holes C0002R–C0002T) in attempts to overcome problems drilling to the target depth and then, in the end, to collect core samples. During riser operations, we collected drilling mud, mud gas, cuttings, downhole logs, core samples, and drilling parameters (including mud flow rate, weight on bit [WOB], torque on bit, and downhole pressure, among others). Gas from drilling mud was analyzed in near–real time in a special mud-gas monitoring laboratory (MGML) and was sampled for further postcruise research. Continuous LWD data were transmitted on board and displayed in real time for QC and for initial assessment of borehole environment and formation properties. Recorded-mode LWD data provided higher spatial sampling of downhole parameters and conditions. Cuttings were sampled for standard shipboard analyses and shore-based research. Small-diameter rotary core barrel (SD-RCB; 8½ inch) coring in Hole C0002T provided only minimal core. Riserless coring at Sites C0024 and C0025 with a 10⅝ inch rotary core barrel (RCB) and hydraulic piston coring system (HPCS)/extended punch coring system (EPCS)/extended shoe coring system (ESCS) bottom-hole assembly (BHA) provided most of the core used for standard shipboard and shore-based research.