Cloud seeders disperse silver iodide (with acetone) specifically into thunderstorms to prevent hail. Smoke is often used in air shows, or to study wake turbulence. Water can be used for the same purpose. As part of military operations clouds can be manipulated to create rain. Such interventions are internationally regulated in the ENMOD provision of the United Nations. During the Vietnam war, ''agent orange'' was used to defoliate forests. In case of an emergency, planes are allowed to dump fuel. Contrary to contrails, smoke trails form directly at the outlet, while contrails form in a clear distance behind the engines.
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Cloud seeders disperse silver iodide (with acetone) specifically into thunderstorms to prevent hail. Smoke is often used in air shows, or to study wake turbulence. Water can be used for the same purpose. As part of military operations clouds can be manipulated to create rain. Such interventions are internationally regulated in the ENMOD provision of the United Nations. During the Vietnam war, ''Agent Orange'' was used to defoliate forests. In case of an emergency, planes are allowed to dump fuel. Contrary to contrails, smoke trails form directly at the outlet, while contrails form in a clear distance behind the engines.