Abstract
In this research, one aspect of the climate that is not commonly referred to, namely, the long-term changes in the components of the atmospheric energy, is investigated. In this respect, the changes in four energy forms are considered, namely, Kinetic Energy (KE), Thermal Energy (TE), Internal Energy (IE), Potential Energy (PE) and Latent Energy (LE); the Energy Conversion (EC) between Kinetic Energy and Potential plus Internal Energy (PIE) is also considered. The area considered in this long-term energetics analysis covers the entire Mediterranean basin, the Middle East and a large part of North Africa. This broad geographical area has been identified by many researchers as a hot spot of climate change. Analyses of climatic data have indeed shown that this region has been experiencing marked changes regarding several climatic variables. The present energetics analysis makes use of the ERA-Interim database for the period from 1979 to 2018. In this 40-year period, the long-term changes in the above energetics components are studied. The monthly means of daily means for all the above energy forms and Energy Conversion comprise the basis for the present research. The results are presented in the form of monthly means, annual means and spatial distributions of the energetics components. They show the dominant role of the subtropical jet-stream in the KE regime. During the study period, the tendency is for KE to decrease with time, with this decrease found to be more coherent in the last decade. The tendency for TE is to increase with time, with this increase being more pronounced in the most recent years, with the maximum in the annual mean in KE noted in 2015. The sum of Potential and Internal energies (PIE) and the sum of Potential, Internal and Latent energies (PILE) follow closely the patterns established for TE. In particular, the strong seasonal influence on the monthly means is evident with minima of PIE and PILE noted in winters, whereas, maxima are registered during summers. In addition, both PIE and PILE exhibit a tendency to increase with time in the 40-year period, with this increase being more firmly noted in the more recent years. Although local conversion from KE into PIE is notable, the area averaging of EC shows that the overall conversion is in the direction of increasing the PIE content of the area at the expense of the KE content. EC behaves rather erratically during the study period, with values ranging from 0.5 to 3.7 × 102 W m−2. Averaged over the study area, the Energy Conversion term operates in the direction of converting KE into PIE; it also lacks a seasonal behavior.
Highlights
Several studies have pointed to the Mediterranean, Middle East and North Africa (MedMENA)region as a hot spot of climate change [1,2,3]
Performing a Ljung–Box autocorrelation test with a time lag of twelve months, it has produced extremely low values of the relevant test statistic [16], in support of the view that the pattern in Figure 2 left is not random but a seasonality of Kinetic Energy (KE) content could be inferred
The four forms of energy and the Energy Conversion term that were studied exhibit some interesting temporal changes and trends that can be traced during this period
Summary
Several studies have pointed to the Mediterranean, Middle East and North Africa (MedMENA)region as a hot spot of climate change [1,2,3]. The present research examines one aspect of the climate that is not frequently referred to. This study examines the long-term changes in components of the atmospheric energetics. The forms of energy that are considered in the present study are: Kinetic Energy (KE—is the energy of the atmosphere due to its motion; only horizontal motion is considered in the calculation of this component); Thermal Energy (TE—is equal to enthalpy, which is the sum of the Internal Energy and the energy associated with the pressure of the air on its surroundings); Internal Energy (IE—the energy contained within the atmosphere related to the microscopic energy of the air molecules); Potential Energy (PE—the amount of work that would have to be done, against the force of gravity, to lift the air to that location from mean sea level); Latent Energy (LE—the energy associated with the presence of atmospheric water vapour being equal to the energy required to convert liquid water into water vapour). When we add to this latter combined form the Latent Energy, we obtain a form of combined energies, which embraces
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