[1] Since 1998 the Los Alamos Sferic Array (LASA) has recorded electric field change signals from lightning in support of radio frequency (RF) and optical observations by the Fast On-orbit Recording of Transient Events (FORTE) satellite. By “sferic” (a colloquial abbreviation for “atmospheric”), we refer to a remote measurement of the transient electric field produced by a lightning flash. LASA consisted of five stations in New Mexico in 1998 and was expanded to 11 stations in New Mexico, Texas, Florida, and Nebraska in 1999. During the 2 years of operation described in this paper, the remote stations acquired triggered 8- or 16-ms duration, 12-bit waveforms and GPS-based sferic time tags 24 hours per day year-round. Source locations were determined daily using differential time of arrival techniques, and the waveforms from all geolocated events were transferred to Los Alamos National Laboratory (LANL), where they have been archived for further analysis, including event classification and characterization. We evaluated LASA location accuracy by comparing temporally coincident (occurring within 100 μs) LASA and National Lightning Detection Network (NLDN) event locations. Approximately one half of the locations agreed to within 2 km, with better agreement for events that occurred within the confines of LASA subarrays in New Mexico and Florida. Of the ∼900,000 events located by the sferic array in 1998 and 1999, nearly 13,000 produced distinctive narrow bipolar field change pulses resembling those previously identified as intracloud discharges.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JD000502

The Los Alamos Sferic Array: A research tool for lightning investigations

[1] Investigating mare basalt compositions, at both the sample and remote-sensing level for the Apollo and Luna mare sites, reveals the need for a more complex regression procedure than previously proposed in order to extract accurate TiO2 concentrations from Clementine spectral reflectance (CSR) data. The TiO2 algorithm of Lucey and coworkers is modified by using two different sets of regression parameters to relate measured regolith compositions from sampling locations to the CSR properties of these sites. One regression trend fits the majority of Apollo data, and the second regression is a fit to the Apollo 11, Luna 16, and Luna 24 data, which were considered to be anomalous in previous TiO2 calibrations. These three sites have unusually low albedo compared to other mare landing sites, and some 32% of nearside mare regions appear to share this characteristic. Possible reasons for these differences related to proximity of the other sites to mare-highland boundaries are discussed. Using the dual-regression method, we find (1) that TiO2 concentrations calculated for the basaltic landing sites faithfully reproduce a bimodal distribution as seen in the sample data, (2) that when coupled with the effects of other thermal neutron absorbers, Ti concentrations are more consistent with observed epithermal-to-thermal neutron-flux ratios than are previous Clementine-based derivations of TiO2 for basaltic regions, and (3) that basalts of intermediate-TiO2 concentrations occur most frequently in the Oceanus Procellarum region and that these intermediate concentrations appear to be inherent to the flows underlying the regolith and presumably to the basalt source regions.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JE001515

A revised algorithm for calculating TiO2 from Clementine UVVIS data: A synthesis of rock, soil, and remotely sensed TiO2 concentrations

The Fast Auroral SnapshoT (FAST) explorer frequently observes the auroral density cavity, which is the source region for Auroral Kilometric Radiation (AKR). An important factor in the generation of AKR is the relative abundance of hot and cold electrons within the cavity, since hot electrons introduce relativistic modifications to the wave dispersion. VLF wave-form data acquired by FAST within the auroral density cavity show clear signatures of whistler-mode waves propagating on the resonance cone. This allows us to obtain the electron plasma frequency, and the cavity often has densities <1 cm−3. Moreover, the hot electrons can be the dominant electron species, enabling AKR to be generated below the cold electron gyro-frequency.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98GL00664

FAST observations of VLF waves in the auroral zone: Evidence of very low plasma densities

[1] Observations from several satellites in geosynchronous orbit, combined with solar wind observations from the ACE spacecraft, demonstrate that cold, dense plasma sheet material can be delivered into the inner magnetosphere under two scenarios: (1) a sudden southward IMF preceded by an extended interval of northward field and (2) a very strong magnetospheric compression caused by a large increase in the solar wind dynamic pressure, also under conditions of northward IMF. Examination of 30 “superdense” plasma sheet events observed during 15 months in 2001 and 2002 shows that these two mechanisms are probably responsible for the occurrence of most superdense events, if “northward IMF” is generalized to “northward or very weak IMF Bz.” Previous work has shown that a superdense plasma sheet contributes to a strong ring current and geomagnetic disturbance if it is accompanied by strong magnetospheric convection (which requires southward IMF). Hence this study suggests that the formation of a strong geomagnetic storm should be favored by an extended interval of strong southward IMF that is preceded by an earlier interval of northward field or very weak Bz, during which the plasma sheet fills with cool, dense plasma.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JA009544

Delivery of cold, dense plasma sheet material into the near-Earth region

[1] A suite of instruments including incoherent scatter radar, ionosonde, and a satellite-bourne GPS receiver observed the ionosphere immediately following the passage of a tropical storm. Tropical Storm Odette formed on 4 December 2003 and proceeded northeasterly over the next 4 days, passing within 600 km of the Arecibo Observatory (AO). On the night of 7–8 December AO measured F region plasma densities and velocities nearly coincident with the storm. Large velocity variations, 10–80 m/s, are evident in the plasma drift components. The variations appear wave-like with an average period of 90 min at 367 km. Zonal drifts were observed with magnitudes significantly greater than commonly observed for similar geomagnetic conditions. The Ramey ionosonde observed intense midlatitude spread F on the night following the closest passage of the storm. GPS occultations within the storm path showed an increase in gravity wave activity and F region scintillation. Combining the local increase in gravity wave activity with the large drift variations and dominant meridional electric field observed immediately following the storm's traversal of the flux tube coincident with the AO observing volume provide insight into coupling between mesoscale weather systems and the ionosphere.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006JA011668

Arecibo observations of ionospheric perturbations associated with the passage of Tropical Storm Odette

Space and atmospheric sciences

: This is the final report of a feasibility study of an experiment to measure the first-order precession, predicted by Einstein's General Theory of Relativity, of an earth-orbiting, free gyroscope. The results of this study show that a relatively inexpensive experiment, using an unshielded gyro and a passive data-readout and telemetry system, is now feasible for measuring this precession to an accuracy of about 1%. (Author)

D. H. Cooper

Papers

Space and atmospheric sciences

A proposed test of the einstein theory of gravitation by means of an unshielded orbiting gyro using passive telemetry