Air Masses, Global Winds, & Types of Rain

A large part of Brazil has two air masses for  consideration. One is the unmodified maritime tropical air which is the regular air mass from the Atlantic. The other originates in the Atlantic; but by the time it spreads over the huge Amazon River basin, it undergoes two key changes - the addition of heat and moisture. Resulting with strong summer heating, a warm dry continental tropical air mass. The air masses of Southern Brazil vary. Polar maritime air masses originate in the region of the belt of low pressures or “brave west winds” of the Antarctic circle. The are found south of Brazil as anticyclones, which come in contact with the tropical air masses and form cold fronts which develop storms. In winter, these masses are convectively unstable. They have low values of temperature and relative humidity since they are moving over the regions. In summer, humidity is at a maximum an results with abundant rainfall at cold front passages, the other characteristics remain unchanged. Modified polar maritime appears within lower latitudes, the polar air decreases in velocity, and a modification takes place. This decreases cloudiness and the gradual fusion wight he tropical Atlantic air. In the winter this causes greater stability at low levels, more pronounced stratification, surface temperature inversions and a decrease in relative humidity. In the summer there is little difference between polar maritime and modified polar maritime although the latter air masses do have a lower relative humidity value. The tropical atlantic air masses originate in the centre of action of the south Atlantic and are transported by NE, N and NW winds. In winter they show great instability at the surface, due to local heating and small lapse rates. Over the vast continental forest the air masses include tropical continental. Northern Brazil appears to have Westerlies wind with flow ranging around 35 degrees and southern Brazil has trade winds which flow around 15 degrees. 

Over the year, the most common forms of precipitation are light rain, thunderstorms and moderate rain in Brazil. Light rain is the most severe precipitation observed during 34% of the days. It is most limey around October 21, when it is observed during 20% of the days. Thunderstorms are the most severe precipitation observed during 31% of the days. They are most likely around February 4, when it is observed 27% of the days. Moderate rain is the most severe precipitation observed 31% of the days as well. It is most likely around January 20, when it is observed 17% of all days. During the warm season which lasts from December 9 to March 29, there is a 56% average chance for precipitation throughout the day. When it does occur it is most commonly in the form of thunderstorms. During the cold season, which lasts from June 4 to September 24 there is a 39% average chance for precipitation to occur throughout the day. When it does, it is most often in the form of light rain. Brazil’s most intense rain falls around the mouth of the Amazon near the city of Belém, and in the upper regions of the Amazonia also.