A negative sensible heat flux indicates that the air is warmer than the earth's surface. Heat must be transported from the air to the earth's surface to reach equilibrium. A zero flux value is indicative of the equilibrium between the air and earth's surface (ARM, 2005).
Latent heat is the rate of heat energy required to change a substance from one phase of matter to another phase (i.e. from liquid water to water vapor). The transfer of latent heat from tropical areas to Polar Regions is the main mechanism the atmosphere uses to attempt to reach thermal equilibrium on a global scale (ARM, 2005).
Due to the high ocean thermal capacity, the heat is transferred by currents and melting ice. However, there are some variations in heat transport due to the difference in the amount of land and the differences between the hemispheres. Most of the earth landmasses lie in the Northern Hemisphere, which is the reason why sensible heat transfer reaches latitudes of 50N and 60N (Bryant, 1997). Changes in temperatures are considerably big in high latitudes; a small latitudinal gradient should reduce poleward heat transport, implying weak thermal forcing in high latitudes. Temperature variations in low/high latitudes can be subject to zonal temperature gradient changes and changes in poleward heat flux (Barry and Carleton, 2001). The air mass can retain its vorticity unless the vortex changes latitude. By changing the latitude, the vortex of the air mass can be affected by the topography as exemplified by mountains in the case of Rossby waves. Rossby waves are formed in the upper atmosphere and are associated with jet stream on the top of the troposphere (Bryant, 1997).
Figure 1: the monthly average temperature anomaly for stations Alborg, Edinburgh, Toulouse and Helsinki from 1951 to 1991.
The annual temperature cycle graph shows the average maximum temperatures in June, July and August. The minimum temperatures are recorded in December, January and February. The highest temperature was recorded in Toulouse in summer 1983 with a value of 24.4 C. The lowest temperature was recorded in Helsinki in winter 1987 with a value of -17.9 C.
The mean (M) and the standard deviation (s) figures have been calculated by using the monthly sets of temperature and precipitation data for the indicated seasons and individual months at each of the stations (Tables