Sea surface skin temperature
Since the skin layer is in radiative equilibrium with the atmosphere and the sun, its temperature underlies a daily cycle.
This makes skin temperature a widely used quantity in weather forecasting and climate science.
Large-scale sea surface skin temperature measurements started with the use of satellites in remote sensing.
The underlying principle of this kind of measurement is to determine the surface temperature via its black body spectrum.
Every wavelength corresponds to different sublayers in the upper 500 μm of the ocean water column.
[3] First satellite measurements of the sea surface were conducted as early as 1964 by Nimbus-I.
The first satellite to carry a sensor operating on multiple infrared bands was launched late in 1978, which enabled atmospheric correction.
[3] This class of sensors is called Advanced very-high-resolution radiometers (AVHRR) and provides information that is also relevant for the tracking of clouds.
[3] The modern satellite array is able to give a global coverage with a resolution of 10 km every ~6 h.[5] Sea surface skin temperature measurements are completed with SSTsubskin measurements in the microwave regime to estimate the sea surface temperature.
[6] These algorithms take additional information like the current wind, cloud cover, precipitation and water vapor content into account and model the heat transfer between the layers.
[6] The determined SST is validated by in-situ measurements from ships, buoys and profilers.
[7] The vertical temperature profile of the surface layer of the ocean is determined by different heat transport processes.
At the very interface, the ocean is in thermal equilibrium with the atmosphere which is dominated by conductive and diffusive heat transfer.
The solar radiation entering the ocean gets heats the surface following the Beer-Lambert law.
Here, approximately five percent of the incoming radiation is absorbed in the upper 1 mm of the ocean.
For the stationary case without external heating, the vertical temperature profile obeys the following energy budget:
observed in the skin layer is positive, which corresponds to a temperature increasing with depth (Note that the z-axis points downward into the ocean).
A common empiric description of the vertical temperature profile within the skin layer of depth
With further increasing depth, the temperature declines, as the proportional heating is smaller and the layer is mixed via turbulent processes.
This results in diurnal warming of the sea surface, high temperatures occur during the day and low temperatures during the night (especially with clear skies and low wind speed conditions).
The increased heat flux due to diurnal warming can reach as high as 50-60 W/m2 and has a temporal mean of 10 W/m2.
[12] The sea surface temperature is also highly dependent on wind and waves.
For example, when rough seas occur during the day, colder water from lower layers are mixed with the ocean skin.
When gravity waves are present at the sea surface, there is a modulation of ocean skin temperature.
[13] On a global scale, skin temperature is an indicator of plankton concentrations.
In areas where a relatively cold SSTskin is measured, abundance of phytoplankton is high.
[14] This effect is caused by the rise of cold, nutrient-rich water from the sea bottom in these regions.
On the other hand, relatively high SSTskin is an indication of higher zooplankton concentrations.
These plankton depend on organic matter to thrive and higher temperatures increase production.
This increased absorption causes the temperature of the sea surface to rise.
