Life Sciences Essay: Exponential Leap-Forward Gradient Scheme for Determining the Isothermal Layer Depth from Profile Data

Exponential Leap-Forward Gradient Scheme for Determining the Isothermal Layer Depth from Profile Data
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Exponential Leap-Forward Gradient Scheme for Determining the Isothermal Layer Depth from Profile Data
Oceanography involves the study of the different aspects of the ocean, such as life in the ocean as well as the different layers of waters and diffusivity. The study applies geology, chemistry, biology, and meteorology, among other branches of science in studying the ocean. Understanding the various aspects of the ocean has become increasingly important today due to pollution, climate change, as well as other factors that threaten the ocean and the marine life in it. Profile analysis and profile evaluation are some of the effective ways of enhancing understanding of the exponential leap-forward gradient scheme and its application in determining the isothermal layer using profile data.
Part 1: Profile Analysis
Explain the gist of the Chu-Fan method (hint: diagrams and equations are helpful);
According to Chu and Fan (2017), upper oceans usually have a vertically quasi-uniform layer of temperature (T, which is the isothermal layer), and density (ρ, which is the mixed layer). Below of the two layers, there is another layer which has a strong vertical gradient, like the thermocline (in terms of temperature) and pycnocline (in regard to density). There also exists an intense vertical turbulent mixing near the water surface, and this causes the formation of the vertically quasi-uniform layer. The mixed layer is of key interest in studies on climate as well as the relationship between the Deep Ocean and atmosphere (Chu 1993). It has a direct influence on the air-sea exchange of gases, momentum, and heat. The depth, Hmix of the mixed layer (also known as the isothermal layer), is an important parameter due to the effect that it has on the evolution of the Sea Surface Temperature (SST).
As such, the Chu-Fan method is centered on the need to develop a simplified objective method for use in the determination of the depth of the mixed layer and its capacity to handle noisy data. As such, Chu and Fan (2017) conducted their study with the objective of presenting such a method which is based on the existence of the quasi-homogenous, near-surface layer. The method that they proposed is rather easy to implement and it is effective when implemented against glider-based observations made on the mixed layer in the ocean.
In the study, the researchers established a new method which is simple when applied in identifying the depth of the mixed layer using profile data. The first approach in the step was using a linear polynomial in fitting the profile data, starting from the point nearest to the surface to a depth. They then computed the error ratio of absolute bias of the data points that were beneath that depth against the root mean square error of the data points lying between the surface to the depth and the fitted data.


In the next step, the depth of the mixed layer corresponding to the maximum ratio obtained from the root mean square error is computed. This method has become a common approach to determining the depth of the mixed layer (the isothermal layer).


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