Some pilot studies were initiated in 1990. These will be extended to an enhanced monitoring network in the period 1991-1994. An intensive observational period is currently planned for fall of 1993. Both the Eastern North Pacific and the Eastern North Atlantic locales exhibit a high frequency of low-level marine stratus, a key cloud type governing the global energy budget that persists for long periods of time over relatively large areas of the Earth. Although they can have a significant impact on radiative transfer and the Earth's heat budget, these clouds are poorly understood and inadequately treated in climate models.
Transitions commonly occur between marine stratus and broken cloud conditions.
Understanding the mechanisms and developing models for this transition are crucial to the simulation of climate change. The region of the Eastern North Atlantic Ocean extending from the Azores to Africa also offers a variety of marine cloud types, including the transition from marine stratus to stratocumulus to fair-weather cumulus. An ARM site in either of these locales would meet the requirements of an eastern ocean margin locale. For an ocean locale, the Eastern North Pacific Ocean affords substantial logistical advantages and synergistic possibilities. The locale is easily accessible and ice free.