Yajin walƙiya ko walƙiya shine fitarwar lantarki tsakanin yanayi da ƙasa. Yawancin ya samo asali ne a cikin gajimare na cumulonimbus kuma yana ƙarewa a ƙasa, wanda ake kira walƙiya -zuwa ƙasa (CG). Wani nau'in yajin da ba a saba sabawa ba, walƙiya daga ƙasa zuwa gajimare (GC), walƙiya ce mai haɓakawa zuwa sama wanda aka fara daga wani abu mai tsayi kuma yana shiga cikin gajimare. Kusan kashi 69 cikin 100 na duk abubuwan da ke faruwa na walƙiya a duk duniya suna faruwa ne tsakanin yanayi da abubuwan da ke daure ƙasa. Yawancin su ne intracloud (IC) walƙiya da gajimare-zuwa-girgije (CC), inda fitarwa kawai ke faruwa a cikin sararin samaniya. Walƙiya tana afkawa matsakaicin jirgin sama na kasuwanci aƙalla sau ɗaya a shekara, amma injiniyanci da ƙira na zamani yana nufin wannan ba matsala bace. Motsin jirage ta cikin gajimare na iya haifar da tashin walƙiya. Walƙiya guda ɗaya ita ce "flash", wanda ke da sarƙaƙƙiya, tsari mai yawa, wasu sassa waɗanda ba a fahimta sosai ba.