1. North-South Variations in West Coast Hydrometeorological Parameters 17
areas have not been extensively validated . According to Henning's computations, the west coast of South America has higher net radiation than
North America in the latitude bands from 5°S to 20°Sand 30°S to 40°S.
These higher values for a particular latitude in South America result from
the fact that the earth is closer to the sun during the South American
summer.
Mean annual albedoes along the coast range from 15% to 25%, with
the highest albedoes in South America occurring in arid regions between
15°S to 35°S and the highest albedoes in North America occurring north
of 58°N, probably resulting from the winter snow cover at these latitudes.
A secondary albedo maximum exists at 31°N in southern California.
A comparison of Figures 1.4 and 1.9 indicates that in spite of the higher
net radiation in South America, air temperatures are lower. With higher
surface temperatures in North America, there will be more long-wave
radiation radiated to space, which will reduce the net radiation absorbed
at the surface. This effect, combined with the lower insolation in the
Northern Hemisphere, accounts for the lower net radiation values. It
should be noted that the values for winter net radiation are very similar at
equivalent latitudes in both hemispheres, with net radiation becoming
negative north of 36°N in December and south of 33°S in June.
The distributions of annual sensible and latent heat fluxes show that the
latent heat flux reaches its peak of 75W1m
2
at 7°N, near the climatological
equator. A latent heat flux of 75W1m
2
corresponds to an evaporative loss
of 108em per year. To the north of this maximum, latent heat fluxes
decrease to 12W/m
2
at 32°N. In the Southern Hemisphere north of 30°S,
latent heat fluxes are at a maximum in January, while farther south, the
maximum occurs in the spring between October and December. In the
more arid regions of South America, the latent heat flux is less than
lOW/m
2
and decreases to 3W/m
2
for the latitudes from 13°S to 31°S,
with the minimum occurring between 13°Sand 18°S. The sensible heat
transfer is correspondingly very large at these latitudes, exceeding
115W/m
2
at latitudes around 20
0S.
As noted earlier, Abreu (1991) indicated that the cause of the aridity at
these latitudes is the intense dynamic subsidence induced by the Andes
mountains, particularly during the winter months. In addition, the
occurrence of high sensible fluxes in an area where air temperatures are
relatively low suggests that the low-level winds may be advecting the
heated air to other regions and replacing it with cooler air from the
ocean. Another possible explanation for these high values may lie in
uncertainties in the values of sensible heat fluxes from Henning (1989).
Net radiation values in South American summers are higher than for
corresponding latitudes in North America. In the higher latitudes, the
average seasonal intensities increase to maximum values of 145W1m
2
at 30°S during the November-to-January period and decrease to 70 to
75W/m
2 in the winter (June to August) . In North America, the highest
areas have not been extensively validated . According to Henning's computations, the west coast of South America has higher net radiation than
North America in the latitude bands from 5°S to 20°Sand 30°S to 40°S.
These higher values for a particular latitude in South America result from
the fact that the earth is closer to the sun during the South American
summer.
Mean annual albedoes along the coast range from 15% to 25%, with
the highest albedoes in South America occurring in arid regions between
15°S to 35°S and the highest albedoes in North America occurring north
of 58°N, probably resulting from the winter snow cover at these latitudes.
A secondary albedo maximum exists at 31°N in southern California.
A comparison of Figures 1.4 and 1.9 indicates that in spite of the higher
net radiation in South America, air temperatures are lower. With higher
surface temperatures in North America, there will be more long-wave
radiation radiated to space, which will reduce the net radiation absorbed
at the surface. This effect, combined with the lower insolation in the
Northern Hemisphere, accounts for the lower net radiation values. It
should be noted that the values for winter net radiation are very similar at
equivalent latitudes in both hemispheres, with net radiation becoming
negative north of 36°N in December and south of 33°S in June.
The distributions of annual sensible and latent heat fluxes show that the
latent heat flux reaches its peak of 75W1m
2
at 7°N, near the climatological
equator. A latent heat flux of 75W1m
2
corresponds to an evaporative loss
of 108em per year. To the north of this maximum, latent heat fluxes
decrease to 12W/m
2
at 32°N. In the Southern Hemisphere north of 30°S,
latent heat fluxes are at a maximum in January, while farther south, the
maximum occurs in the spring between October and December. In the
more arid regions of South America, the latent heat flux is less than
lOW/m
2
and decreases to 3W/m
2
for the latitudes from 13°S to 31°S,
with the minimum occurring between 13°Sand 18°S. The sensible heat
transfer is correspondingly very large at these latitudes, exceeding
115W/m
2
at latitudes around 20
0S.
As noted earlier, Abreu (1991) indicated that the cause of the aridity at
these latitudes is the intense dynamic subsidence induced by the Andes
mountains, particularly during the winter months. In addition, the
occurrence of high sensible fluxes in an area where air temperatures are
relatively low suggests that the low-level winds may be advecting the
heated air to other regions and replacing it with cooler air from the
ocean. Another possible explanation for these high values may lie in
uncertainties in the values of sensible heat fluxes from Henning (1989).
Net radiation values in South American summers are higher than for
corresponding latitudes in North America. In the higher latitudes, the
average seasonal intensities increase to maximum values of 145W1m
2
at 30°S during the November-to-January period and decrease to 70 to
75W/m
2 in the winter (June to August) . In North America, the highest