1. North-South Variations in West Coast Hydrometeorological Parameters 11
Temperatures are not symmetric on both sides of the equator. During
their respective summers and winters, temperatures at low and midlatitudes are warmer in the Northern Hemisphere than in the Southern
Hemisphere. The difference is most marked in the latitudes from 55°N to
32°N. However , along the coast of Baja, California, temperatures are
cooler and closer to the values on the coast of Chile than to those
observed along the western coast of mainland Mexico. The mean annual
temperature profile for South America shows more variability than the
corresponding profile for North America . Comparisons with actual data
along this coast as reported by Pefia and Vidal (1993) suggest that the
mean temperatures of individual stations at a given latitude varied by 1°C
to 3°C from the average values. The decreases in temperature at 30°Sand
45°S are associated with high mountains near the coasts, which affect the
mean annual temperatures. Cooler temperatures in South America can
be attributed to higher elevations along the coast and to cooler seasurface temperatures off the coast. Coastal sea-surface temperatures
exceed 25°C between 3°Nand 22°N, and for a given latitude are generally
2°C to 4°C warmer in the North Pacific than in the South Pacific. The
warmer temperatures in the Northern Hemisphere in this latitudinal band
may contribute to the displacement of the mean annual position of the
intertropical convergence zone (ITCZ) north of the equator.
Seasonal temperature changes influence vegetation types. Figure 1.4
shows the variations that occur between December and June along the
coasts of North and South America . According to this graph , the largest
winter-to-summer temperature changes (in excess of 15°C in the mean
monthly temperatures) occur north of 56°N. Changes of 7°C to lOoC are
observed between 23°N and 56°N and between 15°S and 44°S.
Cloud Cover
Cloud cover exerts an important control on the radiation balance and
precipitation patterns along parts of the coast. An analysis of average
annual cloud cover along the coast is shown in Figure 1.5. According to
these large-scale averages, the coast of North America generally has
less cloud than the coast of South America for corresponding latitudes
between 20° and 35°. Just as a large east-west gradient exists in topography in South America , gradients also exist for clouds and precipitation
at latitudes south of 40°S. Comparisons between data from Chilean
climate stations and the averages in Figure 1.5 indicate that the averages
may vary by 10 to 20% coverage from averages at specific stations. While
both hemispheres show a minimum of coastal clouds at latitudes from 20°
to 35°, the reduction is more marked in the Northern Hemisphere. In
spite of the higher occurrence of cloud along the Chilean coast, it is noteworthy that the region is more arid in terms of rainfall and vegetation.
More cloudiness is also found over high-precipitation regions near the
Temperatures are not symmetric on both sides of the equator. During
their respective summers and winters, temperatures at low and midlatitudes are warmer in the Northern Hemisphere than in the Southern
Hemisphere. The difference is most marked in the latitudes from 55°N to
32°N. However , along the coast of Baja, California, temperatures are
cooler and closer to the values on the coast of Chile than to those
observed along the western coast of mainland Mexico. The mean annual
temperature profile for South America shows more variability than the
corresponding profile for North America . Comparisons with actual data
along this coast as reported by Pefia and Vidal (1993) suggest that the
mean temperatures of individual stations at a given latitude varied by 1°C
to 3°C from the average values. The decreases in temperature at 30°Sand
45°S are associated with high mountains near the coasts, which affect the
mean annual temperatures. Cooler temperatures in South America can
be attributed to higher elevations along the coast and to cooler seasurface temperatures off the coast. Coastal sea-surface temperatures
exceed 25°C between 3°Nand 22°N, and for a given latitude are generally
2°C to 4°C warmer in the North Pacific than in the South Pacific. The
warmer temperatures in the Northern Hemisphere in this latitudinal band
may contribute to the displacement of the mean annual position of the
intertropical convergence zone (ITCZ) north of the equator.
Seasonal temperature changes influence vegetation types. Figure 1.4
shows the variations that occur between December and June along the
coasts of North and South America . According to this graph , the largest
winter-to-summer temperature changes (in excess of 15°C in the mean
monthly temperatures) occur north of 56°N. Changes of 7°C to lOoC are
observed between 23°N and 56°N and between 15°S and 44°S.
Cloud Cover
Cloud cover exerts an important control on the radiation balance and
precipitation patterns along parts of the coast. An analysis of average
annual cloud cover along the coast is shown in Figure 1.5. According to
these large-scale averages, the coast of North America generally has
less cloud than the coast of South America for corresponding latitudes
between 20° and 35°. Just as a large east-west gradient exists in topography in South America , gradients also exist for clouds and precipitation
at latitudes south of 40°S. Comparisons between data from Chilean
climate stations and the averages in Figure 1.5 indicate that the averages
may vary by 10 to 20% coverage from averages at specific stations. While
both hemispheres show a minimum of coastal clouds at latitudes from 20°
to 35°, the reduction is more marked in the Northern Hemisphere. In
spite of the higher occurrence of cloud along the Chilean coast, it is noteworthy that the region is more arid in terms of rainfall and vegetation.
More cloudiness is also found over high-precipitation regions near the