Els fluxos d'energia en el sistema acoblat oceà-atmosfera i el seu impacte en el clima de la terra
- Autores: Josep-Miquel Roca Sans
- Directores de la Tesis: José Luis Pelegrí Llopart (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2020
- Idioma: español
- Programa de doctorado: Programa de Doctorado en Ciencias del Mar por la Universidad de Barcelona y la Universidad Politécnica de Catalunya
- Materias:
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- Resumen
This thesis aims to develop simple models that allow evaluating the relevance of the principal parameters that condition the energy flows in the ocean-atmosphere system, and how changes in these parameters impact the climate of the planet.
The first model studies the meridional overturning circulation (MOC) within one hemisphere, using a simple two-box system (lowand high-latitude compartments) that is widely applied in oceanography and meteorology. Each box has a different behavior, with the high latitudes acting as a negative or inverse estuary and the equatorial and tropical latitudes as a positive estuary. The conditioning energy flow is the loss of latent heat at high latitudes and the same heat gain at low latitudes. This ocean-atmosphere heat exchange leads to changes in internal energy, as well as in salinity and mass through evaporation-precipitation. These scenarios help identify under what conditions the meridional overturning circulation will remain as we know it today —in the south-north direction in the upper layers of the ocean and in the north-south direction in its deep layers— and what would be necessary for the flow direction to be reversed.
The second model consists of three interconnected zonal bands, established in terms of the sign of the difference between shortwave radiation reaching the Earth and long-wave radiation emitted to space. From a geographical perspective, these bands represent the equatorial-tropical, temperate and subpolar-polar climatic regions. The unknown variables are the temperature of each zone and their latitudinal limits. The energy balance of each zone arises from the short- and long-wave radiations and the exchange between the adjacent compartments, being largely determined by both the albedo and the greenhouse factors. The system of equations is closed with the requirement that the latitudinal energy flow is maximized. This key hypothesis follows the principles of the constructive law, being widely applied to study living beings as well as physical or mechanical systems. We apply the model to three climatic moments of our Planet: the last glacial maximum, the modern times and the foreseeable future at the end of this century. The results allow us to visualize the trends in the evolution of our climate, from the glacial past to modern times (preindustrial times to nowadays), and the perspective for year 2100. The results show that the future will lead to a widening of the low and high-latitude zones, with a major warming (as much as 20°C) of the high-latitude areas.
The third model, based on the same radiative concepts of the previous work, considers the heat balance at each latitudinal ring for both atmospheric and oceanic compartments. The model is developed as a single high-order differential equation for the climatic temperature that can be resolved provided we set proper boundary conditions at the equator. The model requires setting the greenhouse and albedo values; the greenhouse is chosen as uniform and the albedo is allowed to change with latitude. The model is tuned to reproduce the present state. After this tuning, the model is employed to explore (a) the diffusive and advective oceanic and atmospheric contributions to the total latitudinal heat flux, and (b) how the temperature and these contributions will change from the last glacial maximum to the end of the 21st century. The results show a progressive warming of the entire planet, with the major variations, of about 15°C, occurring at intermediate and high latitudes. The model also reveals that both advection and particularly diffusion represent a heat sink at low latitudes while diffusion is the only source for heat gain at intermediate and high latitudes.
These contributions have opposite trends from the glacial to the near future, being an important mechanism for mitigating the projected future changes.
