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Seasonal Variation
Figure 6 shows a 310-day composite of the outgoing longwave
radiation for 10 Januarys (Bess et al, 1989). A notable feature of this plot is that, while the South American and African minima in outgoing
longwave radiation are confined to the continental borders, the
longitudinally extended minimum in outgoing longwave radiation over
Indonesia is much larger and spans a large area of ocean. This particular
region of enhanced amount of deep cloudiness will be discussed later when
we discuss the Southern Oscillation and El Nino effects.
Figure 7 (Bess et al, 1989) for a composite of 10 Julys shows a general northward seasonal shift, reflecting summer in the Northern Hemisphere and winter in the Southern Hemisphere, and marked reduction of the South American and African cloudiness patterns. The Indonesian pattern has shifted northward and westward to encompass the Indian Monsoon phenomenon. The South American pattern also has evolved into what is known as the Mexican Monsoon. The regions of highest outgoing radiation are again the subtropical high-pressure zones which now have drifted somewhat northward with the movement of the season into North Africa, and the Mediterranean and Middle East Regions.
