What causes variations in altimeter settings between weather reporting points?

The correct answer identifies that unequal heating of the Earth's surface leads to variations in altimeter settings between weather reporting points. This phenomenon occurs because different areas of the Earth's surface absorb and radiate heat at different rates, affecting air pressure. When the sun heats the ground, it causes changes in temperature and pressure in the atmosphere above, resulting in variations in atmospheric pressure from one location to another.

As air heats up, it becomes less dense and rises, which can lower the pressure at a reporting point. Conversely, cooler areas have denser air, which increases the pressure. These pressure differences directly affect altimeter readings and can cause discrepancies between weather stations, as each will report the local pressure, which takes into account the current atmospheric conditions influenced by temperature. Therefore, pilots must adjust their altimeters to reflect these variations for accurate altitude measurements.

The other options relate to different atmospheric or environmental factors that do not directly cause variations in altimeter settings due to pressure changes. For instance, terrain elevation can affect the absolute altitude but not the variations in pressure itself. Coriolis force influences wind patterns rather than pressure measurements, and seasonal changes are broader and less immediate in their effect on local atmospheric pressure variations compared to the daily and hourly fluctuations caused by unequal heating.