In the summer (MEC) it possesss maximum performance, that is, occurs distole, that it is the biggest dilatao. Therefore, as Mendona (2007) is the time where hot air finds more easiness of development in south direction, influencing the atmosphere of all the provincial portion of the South America, dislocating itself for chains of the northwest, west and southwest from its center of action, known as waves of heat of the northwest in the center-south of Brazil. However, in the winter it withdraws occurring to sstole, that is, minor dilatao, limiting itself it High Amazon and the Black River. Atlantic Equatorial Massa (MEA) Is hot and humid air masses formed in the centers of high Subtropical pressures of the North Atlantic (in the Aores) and of the South Atlantic (Helena Saint) that they are dirigem for the region of low Equatorial pressures. In accordance with Coutinho (1991), is in the ciclonal zone that it acquires for thermal effect positive gradient, characterizing great instability. Both are attracted for the continent in function of the difference of pressure between the surfaces continental and oceanic.
According to Mendona (2007), these air masses mainly act in the portions north and northeast extremity of the South America, being that in the summer it presents greater thermal amplitude. At the same time, the Equatorial one of the South Atlantic has its bigger expression due to the positioning of the anticyclone Helena Saint, that favors its performance on the Brazilian northeast coast. The area of expansion of these masses and the rhythm of precipitations depend on the oscillations of the convergence band of the trade winds, therefore alone they do not provoke rains, therefore, the presence of it in Brazil, is function of the oscillations of Convergncia Intertropical (CIT). The Zone of Convergncia Intertropical (ZCIT) in accordance with Mendona (2007), is formed in the area of low latitudes with the meeting of the trade winds southeastern with the northeast one, creating an ancestry of the air masses, that limit atmospheric circulation between the hemisphere North and the South hemisphere.
