Heaving, Stretching, Spicing and Isopycnal Analysis
Climate variability in the ocean can be generated by two basic mechanisms: the internal nonlinear dynamics or the external forcing anomalies. The later can be further separated into three basic terms: anomalies in momentum, heat and freshwater fluxes thro
- PDF / 18,036,913 Bytes
- 100 Pages / 504.567 x 720 pts Page_size
- 48 Downloads / 166 Views
Heaving, Stretching, Spicing and Isopycnal Analysis
3.1
Heaving, Stretching and Spicing Modes
3.1.1 Adiabatic and Isentropic Processes Climate variability in the ocean can be generated by two basic mechanisms: the internal nonlinear dynamics or the external forcing anomalies. The later can be further separated into three basic terms: anomalies in momentum, heat and freshwater fluxes through the air-sea interface. Tidal dissipation anomalies can also induce climate variability; however, such variability is characterized by much longer time scales, and thus will not be discussed here. Climate processes under the condition of no heat exchange are called isothermal, and they are often called adiabatic. Similarly, processes generating climate variability under the condition of no salt flux anomaly may be called isohaline. The other major cause of climate variability is the wind stress anomaly. Wind-driven circulation is mostly confined to the upper 1–1.5 km of the ocean, so that climate variability induced by wind stress anomalies can penetrate into the depth of 1.5 km in the ocean. There are also evidences indicating that the effects of wind stress perturbations can penetrate into the deep ocean, as discussed in Chap. 2. Motions in the ocean generated under the conditions of no heat/salt flux anomalies are sometime called isentropic. However, this may not
be an accurate term to describe such processes. In fact, the entropy of seawater is a complicated function of salinity, temperature and pressure. Although for a long time there was no standard subroutine available for calculating entropy of seawater, the situation is now quite different. In fact, one can use the standard subroutines in the TEOS_10 to calculate seawater thermodynamic variable, including entropy and others. Seawater entropy is a function of temperature, salinity and pressure; at the sea level, entropy changes are primarily owing to the variability of temperature. However, salinity can also affect entropy. In fact, entropy under isothermal condition can change slightly due to the increase of salinity. Therefore, using the term “adiabatic” to describe motions induced by wind stress perturbations alone is inaccurate. Furthermore, even the commonly used word of isentropic is not accurate. In fact, through a process of weak mixing of temperature and salinity, both temperature and salinity of a water parcel can be changed, but the entropy remains unchanged. Accordingly, a process induced by wind stress change, but under isothermal and isohaline conditions, cannot be simply called an “isentropic” process. In this book, we will occasionally use a new term “isoTS” process to indicate that the process is reversible and it is under both isothermal and isohaline conditions, so that it is also isentropic. In order to understand climate variability, it is desirable to separate the causes of such variability, i.e., whether it is induced by an anomaly
© Higher Education Press and Springer Nature Singapore Pte Ltd. 2020 R. X. Huang, Heaving, Stretching and Spicing M
Data Loading...
