Snow falling upwards?

[font=Trebuchet MS]I’ve done the tutorial on falling [/font][font=Trebuchet MS][color=yellowgreen]snow[/color][/font][font=Trebuchet MS] but what I really want it to do is fall upwards… like bubbles on water.[/font]
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[font=Trebuchet MS]Does anyone know what part of the code I need to change… and to what? Help wpuld be greatly appreciated :D[/font]
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[font=Trebuchet MS][color=sienna]/mette[/color][/font]