8 - Weather Systems

Abstract

Rainfall that sustains life on Earth is not the bounty of cloud microphysical processes alone. Without vigorous and sustained motions, the atmospheric branch of the hydrological cycle would stagnate. Much of the ascent that drives the hydrologic cycle in the Earth's atmosphere occurs in association with weather systems with well-defined structures and life cycles. A small fraction of these systems achieve the status of storms capable of disrupting human activities and, in some instances, inflicting damage. This chapter introduces the structure and underlying dynamics of weather systems and their associated weather phenomena. The chapter deals with large-scale extratropical weather systems (baroclinic waves and the associated extratropical cyclones) and their embedded mesoscale fronts. It discusses some of the effects of terrain on large-scale weather systems and some of the associated weather phenomena. It describes the modes of mesoscale organization of deep cumulus convection and a special form of organization in which a mesoscale convective system acquires strong rotation. These tropical cyclones tend to be tighter, more axially symmetric, and more intense than their extratropical counterparts.