<P> The flow of the atmosphere generally moves in a west to east direction . This, however, can often become interrupted, creating a more north to south or south to north flow . These scenarios are often described in meteorology as zonal or meridional . These terms, however, tend to be used in reference to localised areas of atmosphere (at a synoptic scale). A fuller explanation of the flow of atmosphere around the Earth as a whole can be found in the three - cell model . </P> <P> A zonal flow regime is the meteorological term meaning that the general flow pattern is west to east along the Earth's latitude lines, with weak shortwaves embedded in the flow . The use of the word "zone" refers to the flow being along the Earth's latitudinal "zones". This pattern can buckle and thus become a meridional flow . </P> <P> When the zonal flow buckles, the atmosphere can flow in a more longitudinal (or meridional) direction, and thus the term "meridional flow" arises . Meridional flow patterns feature strong, amplified troughs of low pressure and ridges of high pressure, with more north - south flow in the general pattern than west - to - east flow . </P> <P> The three cells model of the atmosphere attempts to describe the actual flow of the Earth's atmosphere as a whole . It divides the Earth into the tropical (Hadley cell), mid latitude (Ferrel cell), and polar (polar cell) regions, to describe energy flow and global atmospheric circulation (mass flow). Its fundamental principle is that of balance--the energy that the Earth absorbs from the sun each year is equal to that which it loses to space by radiation . This overall Earth energy balance, however, does not apply in each latitude due to the varying strength of the sun in each "cell" as a result of the tilt of the Earth's axis in relation to its orbit . The result is a circulation of the atmosphere that transports warm air poleward from the tropics and cold air equatorward from the poles . The effect of the three cells is the tendency to even out the heat and moisture in the Earth's atmosphere around the planet . </P>

In the troposphere which of the following decreases as altitude increases