Which visual aids can be used to estimate wind direction?

Wind cones, leaves, and smoke are effective visual aids for estimating wind direction because they react to the movement of air in the environment. Wind cones, often seen at airports, are designed to show wind direction clearly by indicating which way the tip of the cone is pointing when the wind blows. Leaves and smoke provide a more natural indication; leaves flutter or move with the wind, showcasing its direction, while smoke is carried by the air, providing an observable path that visually indicates which way the wind is blowing.

The other options include instruments and objects that are not primarily designed for indicating wind direction. Flags can show wind direction but require specific conditions to be effective, and thermometers primarily measure temperature, not wind. Similarly, while clouds can indicate wind patterns at different altitudes, they do not provide a direct measure of surface-level wind direction. Windsocks are specifically designed for wind direction, but rain gauges and barometers measure precipitation and atmospheric pressure, respectively, which have no relation to wind direction. Lastly, a compass indicates geographic direction rather than wind direction, and although radar can observe weather patterns, it does not serve to measure wind direction itself, and altimeters measure altitude rather than wind.