The Total Exchange Flow analysis framework computes consistent bulk values quantifying the estuarine exchange flow using salinity coordinates since salinity is the main contributor to density in estuaries and the salinity budget is entirely controlled by the exchange flow.
For deeper and larger estuaries temperature may contribute equally or even more to the density. That is why we included potential temperature as a second coordinate to the Total Exchange Flow analysis framework which allows gaining insights in the potential temperature-salinity structure of the exchange flow as well as to compute consistent bulk potential temperature and therefore heat exchange values with the ocean.
We applied this theory to the exchange flow of the Persian Gulf, a shallow, semi-enclosed marginal sea, where dominant evaporation leads to the formation of hyper-saline and dense Gulf water. This drives an inverse estuarine circulation which is analyzed with special interest on the seasonal cycle of the exchange flow. The exchange flow of the Persian Gulf is numerically simulated with the General Estuarine Transport Model (GETM) from 1993 to 2016 and validated against observations. Results show that a clear seasonal cycle exists with stronger exchange flow rates in the first half of the year. Furthermore, the composition of the outflowing water is investigated using passive tracers which mark different surface waters. The results show that in the first half of the year, most outflowing water comes from the southern coast, while in the second half most water originates from the north-western region.
Das Projekt "The stratosphere: Radiation, dynamics, and trace gases" wird/wurde gefördert durch: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung. Es wird/wurde ausgeführt durch: Princeton University, Program in Atmospheric and Oceanic Sciences.Stratospheric trace gas distributions are crucial to Earths radiation budget. While carbon dioxide, for example, is long lived and well mixed, other gases, such as ozone and water vapor, are modified through physical and chemical processes while in the atmosphere. Here, we focus on the stratosphere which is (photo-)chemically active, and which interacts with the underlying troposphere dynamically, radiatively, and through exchange of trace gases. The result is an intrinsically nonlinear environ- ment, where it is difficult to understand cause-and-effect relationships between dif- ferent variables. In both observations and comprehensive numerical models, it is challenging to disentangle effects of single parameters on the general state of the stratosphere. This project proposes to perform a cause-and-effect study with an ide- alized general circulation model. With this model, we can disentangle effects of ra- diation, dynamics, and tracer transport, and find corresponding sensitivities of the stratospheric equilibrium and climatology. For instance, by varying the strength of the meridional overturning circulation in the stratosphere and keeping the radiative equilibrium constant, we can study the effects of the global residual circulation on temperatures, winds, and tracer distributions. Alternatively, perturbations to the ra- diative equilibrium, e.g. simulating the creation and disappearance of the ozone hole, allow to study the leading-order impacts on the dynamical state of the atmosphere and tracer distributions. The interplay between radiation, dynamics, and tracer trans- port comprises still unanswered questions crucial for future predictions of the state of the atmosphere and interpretation of the observational record, as global circulation, radiative equilibrium, and gas tracer distributions will evolve under climate change.