Introduction

In this chapter, we shall discuss the mechanisms which maintain the large-scale atmospheric circulation over the Antarctic continent and its immediate surroundings. Observations of the gross features of the circulation were described in Chapter 3; here we shall attempt to explain these observations. The methodology that we have adopted is to examine the budgets of fundamental dynamical and thermodynamic quantities within the Antarctic atmosphere.

First, we examine the heat (or enthalpy) budget. In many ways, this is the fundamental budget, since the Antarctic atmosphere may be regarded as the ‘cold’ end of the global atmospheric heat engine and the requirements of energy balance place strong constraints on the atmospheric circulation. Furthermore, we shall see that the circulation over the Antarctic continent is strongly controlled by the low-level drainage flow that results from persistent cooling over the sloping surfaces of the continental ice sheets. This is discussed in Section 4.3, in which we consider the atmospheric vorticity budget and the resulting circulation. Finally, in Section 4.4, we study the atmospheric water vapour budget. Water plays a rather passive role in the dynamics of the Antarctic atmosphere but is vital to the maintenance of the Antarctic ice sheets.

Studies of the dynamics of the Antarctic atmospheric circulation have been hindered by the lack of suitable data (particularly upper-air observations) from many parts of the continent. Observations from AWSs and satellite sounders have been of value in diagnostic studies, but many recent advances in our understanding of the large-scale dynamics of the Antarctic atmosphere have come from modelling studies using General Circulation Models (GCMs).