Stimulus area, stimulus dispersion, flash duration, and the scotopic threshold.

1955 ◽  
Vol 49 (6) ◽  
pp. 428-430 ◽  
Author(s):  
Oscar S. Adams ◽  
Davis J. Chambliss ◽  
Arthur J. Riopelle
Keyword(s):  
Flash Duration ◽  
Stimulus Area

scholarly journals The temporal evolution of three-dimensional lightning parameters and their suitability for thunderstorm tracking and nowcasting

2013 ◽  
Vol 13 (1) ◽  
pp. 2217-2242
Author(s):  
V. K. Meyer ◽  
H. Höller ◽  
H. D. Betz
Keyword(s):  
Case Studies ◽  
Temporal Evolution ◽  
Discharge Rate ◽  
Single Cells ◽  
Life Cycles ◽  
Mature Stage ◽  
Cell Area ◽  
Flash Duration ◽  
Discharge Characteristics ◽  
Storm Cells

Abstract. Total lightning (TL) data has been found to provide valuable information about the internal dynamics of a thunderstorm allowing conclusions about its further development as well as indicating potential of thunderstorm-related severe weather at the ground. This paper investigates electrical discharge correlations of strokes and flashes with respect to the temporal evolution of thunderstorms in case studies as well as by statistical means. The recently developed algorithm li-TRAM (tracking and monitoring of lightning-cells, Meyer et al., 2012) has been employed to track and monitor thunderstorms based on three-dimensionally resolved TL lightning data provided as stroke events by the European lightning location network LINET. From statistical investigation of 863 suited thunderstorm life-cycles the cell area turned out to correlate well with (a) the total discharge rate, (b) the in-cloud (IC) discharge rate, and (c) the mean IC discharge height per lightning-cell as identified by li-TRAM. All three parameter correlations consistently show an abrupt change in discharge characteristics around a cell area of 170 km2. Statistical investigations supported by the comparison of three case studies – selected to represent a single storm, a multi-cell and a supercell – strongly suggest that the correlation functions include the temporal evolution as well as the storm type. With the help of volumetric radar data, it can also be suggested that the well defined break observed at 170 km2 marks the region, where the transition occurs from short-lived and rather simple structured single storm cells to better organized, more persistent, and more complex structured thunderstorm forms, e.g. multi-cells and super-cells. All three storm-types experience similar discharge characteristics during their growing and dissipating phases. However, while the poorly organized and short-lived cells preferentially remain small during a short mature phase, mainly the more persistent thunderstorm types develop to sizes above 170 km2 during a pronounced mature stage. At that stage they exhibit on average higher discharge rates at higher altitudes as compared with matured single-cells. With the maximum stroke distance set to 10 km and a flash duration set to 1 s the parameterisation functions found for the stroke rate as function of the cell area has been transformed to a flash rate. The presented study suggests that, with respect to the storm type, stroke and flash correlations can be parameterized. There is also strong evidence, that parameterization functions include the time parameter, so that altogether TL stroke information has good potential to pre-estimate the further evolution (nowcast) of a currently observed storm in an object-oriented thunderstorm nowcasting approach.

Characteristics of membrane currents evoked by photoreleased inositol trisphosphate in Xenopus oocytes

1992 ◽  
Vol 263 (1) ◽  
pp. C154-C165 ◽  
Author(s):  
I. Parker ◽  
I. Ivorra
Keyword(s):  
Xenopus Oocytes ◽  
Threshold Level ◽  
Dose Dependence ◽  
Evoked Responses ◽  
Flash Duration ◽  
Competitive Antagonist ◽  
Study Characteristics ◽  
Time Required ◽  
Threshold Duration ◽  
Interflash Interval

Photorelease of inositol 1,4,5-trisphosphate (InsP3) from a caged precursor was used to study characteristics of Ca(2+)-activated Cl- currents activated in Xenopus oocytes by the InsP3-Ca2+ signaling pathway. Photolysis flashes shorter than a threshold duration evoked no response, but the current amplitude then grew about linearly as the flash duration was further lengthened. Currents directly evoked by photorelease of Ca2+ from a caged precursor grew linearly with increasing flash duration and showed a small threshold before they were activated. However, the major part of the threshold of InsP3-evoked responses appears to arise because a certain concentration of InsP3 (estimated to be approximately 60 nM) is required to evoke Ca2+ liberation. Subthreshold conditioning flashes potentiated responses to subsequent flashes, and the potentiation increased linearly with increasing conditioning flash duration before abruptly declining. The potentiation decayed exponentially with a time constant of approximately 17 s with increasing interflash interval. Currents evoked by photoreleased InsP3 began after a latency that shortened from 10 s or longer to 100 ms as the photolysis intensity was increased. This dose dependence of the latency could be quantitatively explained by the time required for the InsP3 concentration to rise above threshold. Intracellular injection of heparin (a competitive antagonist at the InsP3 receptor) increased the threshold for InsP3 action, as did increased temperature. We conclude that several characteristics of InsP3-evoked responses, including their dose dependence, latency, and facilitation with paired stimuli, arise because a distinct threshold level of InsP3 is required to evoke release of Ca2+ from intracellular stores.

Sign in / Sign up

Export Citation Format

Share Document