William Rison - Profile on Academia.edu (original) (raw)

Papers by William Rison

Journal of Geophysical Research: Atmospheres, 2013

Correlated Lightning Mapping Array and vertical-scan radar images are presented for three rocket-... more Correlated Lightning Mapping Array and vertical-scan radar images are presented for three rocket-and-wire triggered lightning flashes that occurred sequentially within 17 min in the presence of a decaying multicellular convective storm system over north-central Florida. The initial stage (IS) of each flash propagated generally vertically to the altitude of the 0°C melting level, about 5 km, and then subsequently propagated for many kilometers horizontally along the melting level contour. Radar images suggest that the propagation paths of the IS channels below and above the melting level were heavily influenced by precipitation gradients. Flash UF 11-24 exhibited a 12.6 km unbranched IS channel, the longest unbranched channel observed in the study by a factor of three. During flash UF 11-25 (119 ms following the cessation of the measured IS current at ground and prior to the first return stroke), a natural cloud-to-ground discharge, perhaps induced by the IS, initiated between 2.5 and 4 km altitude and struck ground 5 to 7 km from the launching facility. The IS of flash UF 11-26 propagated upward through a descending precipitation packet and apparently induced a naturally appearing bi-level intracloud discharge via an upwardnegative leader that initiated within the IS breakdown region 3.5 km from the launching facility. The upward-negative leader propagated from 5.6 to 9.3 km altitude in a time of 11 ms. The electrical current measured at ground during the IS of flash UF 11-26 exhibited a 57 ms polarity reversal, transferring 19 C of positive charge to ground.

Using VHF Lightning Observations to Monitor Explosive Volcanic Activity

Lightning is an integral part of explosive volcanic eruptions and volcanic lightning measurements... more Lightning is an integral part of explosive volcanic eruptions and volcanic lightning measurements are a useful tool for volcano monitoring. VHF measurements of volcanic lightning can be made remotely, at distances of up to 100 km. A strategically placed network of 6 or more VHF ground stations could locate lightning in eruption columns from several regional volcanoes, and a minimum of two stations could be used to monitor a single volcano. Such a network would be particularly useful for detection or confirmation of explosive activity in situations where volcanoes are remotely located, and thus lack visual observations, or are not well instrumented with seismic networks. Furthermore, clouds are fully transparent to VHF signals, making lightning detection possible even when weather obscures visual observations. Recent VHF observations of volcanic lightning at Augustine Volcano (Alaska, USA, 2006), Redoubt Volcano (Alaska, USA, 2009) and Eyjafjallajökull (Iceland, 2010) have shown that...

Lightning during several of the eruptions were observed using a technique that we use to observe ... more Lightning during several of the eruptions were observed using a technique that we use to observe thunderstorms. Very high frequency radio emissions (60 MHz) emitted by electrical discharges are located by their times of arrival at several receiving stations. In a typical thunderstorm lightning flash we locate several thousand events giving a 3-D map of the lightning. In mid January we set up two stations about 100 km east of the volcano, near Homer, AK. We received and located the source of thousands of radio emissions from the vicinity of Mt Augustine during the January 28 eruption. With two stations we were able to determine the azimuthal direction to the sources, their power, the time history and relationship to other pulses. On one lightning flash we used an interferometric effect to infer altitude. We observed two distinct forms of electrical activity. The first was many short bursts (less than a milliseconds) that occurred coincident with the explosive eruption. These seemed t...

Journal of Geophysical Research: Atmospheres, 2014

Six Lightning Mapping Array (LMA) stations were deployed in April 2010 around Eyjafjallajökull vo... more Six Lightning Mapping Array (LMA) stations were deployed in April 2010 around Eyjafjallajökull volcano in southern Iceland. Single-station LMA observations were made during the first explosive period (14-18 April), and three-dimensional LMA observations were made during the second explosive period (5-22 May). The single-station observations revealed that continuous RF electrical activity caused by high rates of small vent discharges occurred during the first explosive period, but not the second, indicating that the strength of vent charging varied between the first and second explosive periods. During the second explosive period, very little lightning was detected between 5 and 10 May, while moderate rates of lightning were detected between 11 and 21 May, signaling that another change occurred on 11 May that affected plume electrification. The data do not make clear if it was changing eruptive activity or changing meteorological activity that resulted in the sudden onset of lightning. The plume charge structure during the second explosive period was inferred from the three-dimensional lightning data, showing that the dominant charge structure varied between a positive monopole and a negative-over-positive dipole. The predominance of a low-altitude region of positive charge and the observation that electrical activity was concentrated near the vent indicate that net positive vent charging was dominating the electrification.

SAE Technical Paper Series, 2001

A lightning mapping system has been developed that locates the sources of VHF radiation from ligh... more A lightning mapping system has been developed that locates the sources of VHF radiation from lightning discharges in three spatial dimensions and time. The system consists of several VHF receivers distributed over an area of about 100 km diameter. The system locates VHF radiation sources over the array with an accuracy of about 100 m. The system locates sources out to 250 km from the center of the array with reduced accuracy. The observations are found to reflect the basic charge structure of electrified storms.

Monthly Weather Review, 2005

Balloon soundings were made through two supercell storms during the Severe Thunderstorm Electrifi... more Balloon soundings were made through two supercell storms during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) in summer 2000. Instruments measured the vector electric field, temperature, pressure, relative humidity, and balloon location. For the first time, soundings penetrated both the strong updraft and the rainy downdraft region of the same supercell storm. In both storms, the strong updraft had fewer vertically separated charge regions than found near the rainy downdraft, and the updraft’s lowest charge was elevated higher, its bottom being near the 40-dBZ boundary of the weak-echo vault. The simpler, elevated charge structure is consistent with the noninductive graupel–ice mechanism dominating charge generation in updrafts. In the weak-echo vault, the amount of frozen precipitation and the time for particle interactions are too small for significant charging. Inductive charging mechanisms and lightning may contribute to the additional charge regions fo...

Journal of Volcanology and Geothermal Research, 1988

Helium isotope ratios in gases of thirty hot springs and geothermal wells and of five natural gas... more Helium isotope ratios in gases of thirty hot springs and geothermal wells and of five natural gas wells in the western United States show no relationship to regional conductive heat flow, but do show a correlation with magma-based thermal activity and reservoir fluid temperature (or total convective heat discharge). Gases from high-T ( > 200 °C) reservoirs have 3He/4He > 2 × the atmospheric value, with high He concentrations due to the input of magmatic helium. Low-T reservoirs generally have 3He/4He less than the atmospheric ratio, with very low H2 contents, which appear to be qualitative criteria for the absence of a magmatic heat source. To first order, He/( C02 + H2S ) ratios are inversely correlated with 3He/4He and are consistent with a two-component mixture of radiogenic (crustal) and magmatic ( mantle ) helium. The '~He-enriched high-T component has a restricted range of He/(CO2 + H2S ) between about 5 and 50 ppmv. On the premise that C02 and H2S concentrations are T-dependent due to mineral-fluid equilibria, the correlation of reservoir temperature and 3He/4He ratio, together with the restricted range of He/(C02 + H2S) ratios observed in high-T magmatic systems, suggests that the amount of magmatic He and the amount of C02 (and H._,S ) in these geothermal reservoirs are related to fluid temperature via the amount of magmatic heat and volatiles input to a particular geothermal reservoir.

PHETS (Permanent High Explosive Test Site) Lightning Hardening Program: Misty Picture Event

... UNCLASSI FIED SECURITY CLASSIFICATION OF THIS 3AT T ABITO REPORT DOCUMENTATION PAGE Ia. REPOR... more ... UNCLASSI FIED SECURITY CLASSIFICATION OF THIS 3AT T ABITO REPORT DOCUMENTATION PAGE Ia. REPORT SECURITY CLASSIFICATION lb. ... PERSONAL AUTHOR(S) Chapman, GP,; Gardner, RL; Lu, GS; Rison, W.; and Gurbaxani, SH 13a. TYPE OF ...

Lightning and electrical activity during the 2009 eruptions of Redoubt Volcano

The warning of the impending eruption of Redoubt by the Alaska Volcano Observatory enabled us to ... more The warning of the impending eruption of Redoubt by the Alaska Volcano Observatory enabled us to set up a 4-station VHF Lightning Mapping Array (LMA) along the Kenai coast in time to capture the complete sequence of eruptions. The network was situated along a 60 km long north-south line, 70-80 km east of Redoubt on the opposite side of Cook