THE NEAR-SURFACE LAYER OF THE OCEAN
time scales from minutes to decades (Figure 1-4). The largest variations of
up to a few tenths of a percent occurs on time scales from days to several
months and are related to the photospheric features of solar activity.
solar constant is
associated with the well-known 11-year solar activity cycle and with less studied
longer-term changes (Foukal, 2003).
Figure 1-4. Composite total solar irradiance at the top of the Earth’s atmosphere (solar
constant) monitored since 1978 with satellites. (After Fröhlich, 2000.)
The total (spectrally integrated) downwelling solar energy at the ocean
surface, I 6 , which is also called the surface solar irradiance or insolation,
substantially depends on the latitude, season, time of day, and optical
properties of the earth’s atmosphere. While satellites accurately measure the
solar constant, the surface solar irradiance is much more difficult to assess.
Passing through the earth’s atmosphere, the sunlight is absorbed and
scattered. Absorption in the atmosphere occurs mainly in the ultraviolet and
infrared bands and is weak in the visible band. The ultraviolet part of the
solar radiation spectrum is absorbed essentially by ozone. The ozone
absorption limits the solar irradiance at sea level to wavelengths greater than
0.29 Pm. The infrared part of the solar spectrum is absorbed by CO 2 and
even more strongly by water vapor.
22
Decreases in the irradiance occur during the appearance of sunspots; increases
due to bright faculae. The long-term modulation of the
time scales from minutes to decades (Figure 1-4). The largest variations of
up to a few tenths of a percent occurs on time scales from days to several
months and are related to the photospheric features of solar activity.
solar constant is
associated with the well-known 11-year solar activity cycle and with less studied
longer-term changes (Foukal, 2003).
Figure 1-4. Composite total solar irradiance at the top of the Earth’s atmosphere (solar
constant) monitored since 1978 with satellites. (After Fröhlich, 2000.)
The total (spectrally integrated) downwelling solar energy at the ocean
surface, I 6 , which is also called the surface solar irradiance or insolation,
substantially depends on the latitude, season, time of day, and optical
properties of the earth’s atmosphere. While satellites accurately measure the
solar constant, the surface solar irradiance is much more difficult to assess.
Passing through the earth’s atmosphere, the sunlight is absorbed and
scattered. Absorption in the atmosphere occurs mainly in the ultraviolet and
infrared bands and is weak in the visible band. The ultraviolet part of the
solar radiation spectrum is absorbed essentially by ozone. The ozone
absorption limits the solar irradiance at sea level to wavelengths greater than
0.29 Pm. The infrared part of the solar spectrum is absorbed by CO 2 and
even more strongly by water vapor.
22
Decreases in the irradiance occur during the appearance of sunspots; increases
due to bright faculae. The long-term modulation of the