In the previous chapter the characteristic scales of phenomena have not been defined; the studies related equally to the air motion both in the matchbox and a cyclone. Now this deficiency will be made up. In Section 2.1 the selection of the scales of objects under consideration makes it possible to simplify the systems of hydrodynamical equations, namely to neglect fast acoustic waves. The simplified system has the third but not the fifth order with respect to time / and therefore
1) may be much more easily solved numerically, see Chapter 4; 2) need in much less initial data for its solving — it is important for the
operative weather forecasting, see Chapter 3.