ABSTRACT
Motions in planetary atmospheres obey the laws of hydrodynamics that are valid for any ¥uid subjected to the general restrictions that apply to a planet: (1) spherical geometry (or spheroid) and (2) planetary rotation (atmospheric motions are considered relative to a non-inertial reference frame). Planetary atmospheres have an open boundary with the outer space (the exosphere, Chapters 1 and 6) and a rigid surface as a lower boundary in some cases (terrestrial planets, dwarf planets, and satellites), or a deep, not well-determined, lower boundary in the case of giant ¥uid planets. Atmospheres have external and internal energy sources to drive the motions (Chapter 1). They are by de˜nition gaseous, and therefore are compressible ¥uids (obeying the perfect gas law as a ˜rst, in general good approach except in some particular cases). A large part of their mass is electrically neutral (called neutral atmosphere), and the motions can be described without the inclusion of electromagnetic forces. Therefore, motions in ionospheres are not considered here.
