[Origine physique du contraste entre activité électrique au dessus des terres et des océans]
L'origine du contraste prononcé entre activité électrique au dessus des terres et des océans est explorée à l'aide de concepts classiques et de nouvelles méthodes d'analyse. Le comportement des ı̂les, considérées comme similaires à des continents miniatures, est en faveur d'un contrôle de l'activité électrique par un mécanisme thermodynamique plutôt que par la présence d'aérosols. L'activité électrique au-dessus des ı̂les, considérées comme similaires à des continents miniatures, est pilotée par un mécanisme thermodynamique plutôt que par la présence d'aérosols. Les mesures de réflectivité radar dans le cadre de la mission TRMM (Tropical Rainfall Measuring Mission) soulignent le contraste important entre l'intensité des ascendances mesurées au dessus des terres et des océans. Cependant, ce contraste en termes d'ascendance ne peut pas être attribué à une différence d'instabilité convective potentielle (CAPE) déterminée en référence à la flottabilité des masses d'air. Ce problème est résolu en dimensionnant celles-ci selon l'altitude de la base du nuage, comme cela avait été suggéré lors d'études précédentes. Une convection continentale associée à une forte activité électrique est donc favorisée par un rapport de Bowen surfacique plus important et par une plus grande instabilité convective en couche limite. Ceci conduit à une transformation plus efficace de l'instabilité convective potentielle en énergie cinétique des courants ascendants nuageux.
New tests and older ideas are explored to understand the origin of the pronounced contrast in lightning between land and sea. The behavior of islands as miniature continents with variable area supports the traditional thermal hypothesis over the aerosol hypothesis for lightning control. The substantial land–ocean contrast in updraft strength is supported globally by TRMM (Tropical Rainfall Measuring Mission) radar comparisons of mixed phase radar reflectivity. The land–ocean updraft contrast is grossly inconsistent with the land–ocean contrast in CAPE (Convective Available Potential Energy), from the standpoint of parcel theory. This inconsistency is resolved by the scaling of buoyant parcel size with cloud base height, as suggested by earlier investigators. Strongly electrified continental convection is then favored by a larger surface Bowen ratio, and by larger, more strongly buoyant boundary layer parcels which more efficiently transform CAPE to kinetic energy of the updraft in the moist stage of conditional instability.
Mots-clés : aérosols, convection, foudre, thermique, orages, ascendances
Earle Williams 1 ; Sharon Stanfill 2
@article{CRPHYS_2002__3_10_1277_0, author = {Earle Williams and Sharon Stanfill}, title = {The physical origin of the land{\textendash}ocean contrast in lightning activity}, journal = {Comptes Rendus. Physique}, pages = {1277--1292}, publisher = {Elsevier}, volume = {3}, number = {10}, year = {2002}, doi = {10.1016/S1631-0705(02)01407-X}, language = {en}, }
Earle Williams; Sharon Stanfill. The physical origin of the land–ocean contrast in lightning activity. Comptes Rendus. Physique, Volume 3 (2002) no. 10, pp. 1277-1292. doi : 10.1016/S1631-0705(02)01407-X. https://comptes-rendus.academie-sciences.fr/physique/articles/10.1016/S1631-0705(02)01407-X/
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