A Global Analysis of the Atmospheric Available Energy and its Trends

Open Access
Author:
Hay, Stephanie Ella
Graduate Program:
Meteorology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 02, 2014
Committee Members:
  • Peter R Bannon, Thesis Advisor
Keywords:
  • available energy
  • walker circulation
  • atmospheric circulation
  • storm track
Abstract:
The available energy is the sum of the internal and potential energies relative to an isothermal and hydrostatic equilibrium atmosphere. It includes both baroclinic and convective contributions. The method used to determine the equilibrium atmosphere is general and includes contributions due to terrain, dry air, water vapor, and hydrometeors. The available energy of the atmosphere is calculated using monthly mean ECMWF ERA-Interim data from 1979 to 2012. The analysis is done for water vapor and dry air only, but the effects of hydrometeors are estimated. The effect of using a single climatological equilibrium temperature or allowing it to vary is demonstrated. The trends in the global available energy as well as in the global available energies of dry air and water vapor are examined in terms of annual and seasonal means. The geographical and vertical distribution of the available energy and the trends are also examined in terms of column integrals, zonal means, and tropical means. The available energy is also linearized to determine the available elastic and available potential contributions. Finally, the available energy is compared to traditional measures of available potential energy (e.g., the available potential energy of Lorenz, the convective available potential energy) and potential and kinetic energies. Globally, the dry air component accounts for approximately 80% of the available energy, with the rest being made up of that of water vapor. The analysis indicates that the global available energy of the atmosphere has been increasing over the period analyzed. Geographically, the largest values of available energy are near the surface in the tropics coincident with the highest sea surface temperatures and the equatorial rainforests, at the tropopause and in the upper stratosphere. Trends vary geographically and seasonally, though a common feature indicates that the Walker circulation is increasing in strength. Using a single equilibrium temperature found for that month, the available energy is calculated each six hours during the March 1993 “storm of the century” to evaluate the evolution of available energy in a mid-latitude cyclone. The cyclone modifies the mean available energy field up to 200 hPa, and depletes it near the center of the storm. The variability in the distribution of the vapor available energy is demonstrated in this case.