THE NEAR-SURFACE LAYER OF THE OCEAN
The primary infrared sensor on the U.S. meteorological satellites has
been the Advanced Very High Resolution Radiometer (AVHRR). AVHRR
has five measuring channels. Channel 3 (O = 3.55-3.93 µm), Channel 4 (O =
10.30-11.30 µm), and Channel 5 (O = 11.50-12.50 µm) are in the window of
atmospheric transparency and are used for SST measurements.
The Terra and Aqua satellites carry the Moderate Resolution Imaging
Spectroradiometer (MODIS), which is a 36-band spectroradiometer
measuring, among other parameters, visible and infrared radiation. The
accuracy of the SST measurement with MODIS is several times higher than
with AVHRR, approaching 0.1
o K in favorable conditions.
The infrared satellite sensor receives signals from the upper several
micrometers of the ocean. The SST depends on many factors. Among the
most important factors causing SST to deviate from the bulk temperature of
the upper ocean mixed layer are the effects of short and longwave radiation,
latent and sensible heat fluxes, freshwater input, convection, and wind and
wave mixing.
The wind-wave mixing and convection produce the surface mixed layer.
The surface mixed layer participates in large-scale air-sea interaction, has
substantial heat capacity, and is an important element of the weather and
climate system. How the SST is connected to the temperature structure of the
surface mixed layer is of interest for many practical applications, including
the development of remote sensing techniques for monitoring the climate
and global carbon cycles. In fact, the SST differs from the temperature of the
bulk of mixed layer due to the aqueous thermal molecular sublayer, the cool
skin of the ocean (Section 2.1.2), diurnal warming (Section 4.1.1), and
freshwater addition by precipitation (Sections 2.5 and 4.1).
The temperature difference across the cool skin of the ocean is typically
of the order of 0.2-0.3
o C but can increase to 0.4-0.6
o C under low wind speed
conditions. Intense insolation at midday and/or air temperature exceeding
water temperature can reverse the temperature gradient within the thermal
molecular sublayer; the sea surface can become slightly warmer than the
underlying water (Section 2.4). With the accuracy of the satellite techniques
approaching 0.1
o C, the aqueous thermal molecular sublayer has already been
included in some advanced remote sensing algorithms (e.g.,
et al.,
1990).
Under light winds the near-surface layer of the ocean is often re-stratified
due to diurnal warming and/or precipitation effects. A thin near-surface
mixed layer is formed. Its heat capacity is comparable to the heat capacity of
the atmospheric boundary layer. Under these conditions, the near-surface
layer of the ocean can rapidly respond to changes in the atmospheric state; as
a result, both oceanic and atmospheric processes determine the SST.
442
Schl ssel
ü
The primary infrared sensor on the U.S. meteorological satellites has
been the Advanced Very High Resolution Radiometer (AVHRR). AVHRR
has five measuring channels. Channel 3 (O = 3.55-3.93 µm), Channel 4 (O =
10.30-11.30 µm), and Channel 5 (O = 11.50-12.50 µm) are in the window of
atmospheric transparency and are used for SST measurements.
The Terra and Aqua satellites carry the Moderate Resolution Imaging
Spectroradiometer (MODIS), which is a 36-band spectroradiometer
measuring, among other parameters, visible and infrared radiation. The
accuracy of the SST measurement with MODIS is several times higher than
with AVHRR, approaching 0.1
o K in favorable conditions.
The infrared satellite sensor receives signals from the upper several
micrometers of the ocean. The SST depends on many factors. Among the
most important factors causing SST to deviate from the bulk temperature of
the upper ocean mixed layer are the effects of short and longwave radiation,
latent and sensible heat fluxes, freshwater input, convection, and wind and
wave mixing.
The wind-wave mixing and convection produce the surface mixed layer.
The surface mixed layer participates in large-scale air-sea interaction, has
substantial heat capacity, and is an important element of the weather and
climate system. How the SST is connected to the temperature structure of the
surface mixed layer is of interest for many practical applications, including
the development of remote sensing techniques for monitoring the climate
and global carbon cycles. In fact, the SST differs from the temperature of the
bulk of mixed layer due to the aqueous thermal molecular sublayer, the cool
skin of the ocean (Section 2.1.2), diurnal warming (Section 4.1.1), and
freshwater addition by precipitation (Sections 2.5 and 4.1).
The temperature difference across the cool skin of the ocean is typically
of the order of 0.2-0.3
o C but can increase to 0.4-0.6
o C under low wind speed
conditions. Intense insolation at midday and/or air temperature exceeding
water temperature can reverse the temperature gradient within the thermal
molecular sublayer; the sea surface can become slightly warmer than the
underlying water (Section 2.4). With the accuracy of the satellite techniques
approaching 0.1
o C, the aqueous thermal molecular sublayer has already been
included in some advanced remote sensing algorithms (e.g.,
et al.,
1990).
Under light winds the near-surface layer of the ocean is often re-stratified
due to diurnal warming and/or precipitation effects. A thin near-surface
mixed layer is formed. Its heat capacity is comparable to the heat capacity of
the atmospheric boundary layer. Under these conditions, the near-surface
layer of the ocean can rapidly respond to changes in the atmospheric state; as
a result, both oceanic and atmospheric processes determine the SST.
442
Schl ssel
ü