What is the primary reason winds aloft flow parallel to isobars?

Winds aloft flow parallel to isobars primarily due to the Coriolis force, which is a result of the Earth's rotation. As air moves from areas of higher pressure to areas of lower pressure, the Coriolis force acts on the moving air, causing it to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection causes the wind to turn and flow in a direction that is parallel to the isobars, rather than directly from high to low pressure.

At higher altitudes, where the influence of surface friction is minimal, the balance between the pressure gradient force (which drives the wind from high to low pressure) and the Coriolis force determines the wind's direction. The result is a steady flow that runs parallel to the isobars, allowing meteorologists to understand and predict wind patterns more effectively.

While surface friction does affect winds at lower levels, it is not the primary factor at higher altitudes. Additionally, temperature differences and air density can influence atmospheric behavior, but they do not directly cause the parallel flow of winds to isobars like the Coriolis force does.