On the dynamics of Hawaiian cloud bands: island forcing

We show that the band cloud is a complex three-dimensional phenomenon which is inseparable from the airflow around the island. The band cloud is found to arise primarily from the dynamic interaction of the trade winds with the island. The upwind surface flow forms a separation line with an associated stagnation point. A low-level convergence zone forms along this line, resulting in an updraft line. If the updrafts are strong enough, a band cloud forms. A simple criterion for the occurrence of a strong band cloud is offered in terms of the height of the island, trade-wind speed, environmental stability, and the lifted condensation and/or free convection level. -from Authors