Worldwide lightning location (WWLL) using only 30 lightning sensors has been successfully achieved by using only VLF propagation in the Earth-ionosphere waveguide (EIWG). Ground propagation or mixed "sky" and ground propagation is avoided by requiring evidence of Earth-ionosphere waveguide dispersion. A further requirement is that the lightning strike must be inside the perimeter defined by the lightning sensor sites detecting the stroke. Under these conditions, the time and the location of the stroke can be determined, along with the rms errors. Lightning strokes with errors exceeding 30 Ps or To assist with identifying impulses from the same lightning stroke, the lightning sensor threshold is automatically adjusted to allow an average detection rate of three per second. This largely limits detection to the strongest 4% of all lightning strokes, of which about 40% meet the accuracy requirements for time and location.

Educational attainment affects cognitive function in older inpatients. The strong association between cognitive impairment and nutritional variables suggests that every effort to improve nutritional status is needed in approaching cognitive impairment in older patients.

The global convective diagnostic (GCD) is a bispectral (infrared and water vapor), day-night scheme for operationally mapping deep convection by means of geostationary satellite images. This article describes a test of GCD performance over tropical and subtropical waters near North America. The test consists of six cases, each involving a convective cloud complex. A seventh case treats convection over land. For each case, a map of deep convection was constructed from image pairs from Geostationary Operational Environmental Satellite-12 (GOES-12). Case by case and for all maritime cases together, the GCD map was compared with a convective parameter derived from the radar on the Tropical Rainfall Measuring Mission (TRMM), a polar-orbiting satellite. In general, each GCD map showed a bloblike feature. In each case, the radar convective pixels typically fell within the GCD blob. However, (except for the land case) the GCD predicted far too many convective pixels. In the maritime cases overprediction was reduced (without correspondingly impairing other measures of performance) by lowering the nominal GCD threshold. With this adjustment in place, for the six maritime cases taken individually, the GCD tended to yield more consistent results than did a monospectral (infrared) convective scheme. With the cases combined, at the lower threshold the GCD performed somewhat better than one of the more stable versions of the infrared scheme. Comparison with lightning events (also observed by TRMM) suggests the possibility of future improvement to the GCD through the incorporation of geostationary satellite observations of lightning.

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The use of numerical models has greatly increased our understanding of the electrical and microphysical process within electrified clouds. We use the University of Washington, 1.5dimensional thunderstorm model to examine the effects of including a runaway electron based lightning initiation mechanism. We find that this mechanism can significantly alter the electrification history of modeled storms and produce vertical electric field profiles that are very similar to those of observed storms. To cite this article: R. Solomon et al., C. R. Physique 3 (2002) 1325-1333.  2002 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS numerical model / thunderstorm electrification / lightning initiation / runaway electrons Un mécanisme de déclenchement de l'éclair : application à la modélisation du nuage d'orage Résumé L'utilisation des modèles numériques à considérablement augmenté notre compréhension des processus électriques et microphysiques dans les nuages électrisés. Nous utilisons un modèle 1.5D du nuage d'orage, développé par l'Université de Washington, dans lequel on introduit un mécanisme de déclenchement de l'éclair par es électrons « runaway ». Il apparaît que ce mécanisme peut modifier de manière significative le développement de l'électrisation dans le nuage ainsi modélisé, et conduire à des profils verticaux de champ électrique calculé très similaires à ceux observés expérimentalement. Pour citer cet article : R.