It is considered that the kosa as a weather phenomenon occurs when the states of the earth and atmosphere, for example, the state of soil, from which dust is generated, and that of the airflow that carries dust together with sandstorms, meets certain conditions.
気象現象としての黄砂は、砂塵（砂ぼこり）の元になる土壌の状態、砂嵐とともに砂塵を運ぶ気流など、地や大気の条件が整うと発生すると考えられている。