Seasonal Structure of a Simple Monsoon System

Abstract

With a structure based on observational studies which indicate that the monsoon occurs on extremely large spatial scales and shows distinct seasonal character, a model is developed with the aim of discerning the basic driving mechanisms of the mean seasonal monsoon. It is argued that for the macroscale monsoon an appropriate facsimile is a zonally, symmetric, moist and primitive equation atmosphere coupled to an interactive and mobile ocean. Via experimentation with the model a hypothesis is tested which states that the character of the mean seasonal monsoon is determined by an interplay between the basic drive of the monsoon system (i.e., the differential heating between an interactive ocean and continental regimes) and the hydrologic cycle. A seasonal structure of a simple monsoon system was developed and its character discussed. With full hydrology and an ocean-continent differential beating, the model displays many features of the observed mean monsoon. Comparisons between moist and dry and oceanic and ocean-continental systems indicate the importance of the various mechanisms of the monsoon circulations. For example, scale contraction is noted with the introduction of moist processes and simple arguments are introduced to explain the scale change. It is shown that the mean summer structure of the model monsoon is made up of low-frequency variations or transients which occupy a large fraction of the variance. The manner in which the model will be used to investigate the monsoon transients is discussed.