What unit is commonly used to express wind speed in surface observations?

Wind speed in surface observations is often expressed in various units, with one of the most common being knots. Knots are primarily used in aviation and maritime contexts and are defined as nautical miles per hour. This is significant for professionals in those fields, as it aligns with navigation and aircraft operation.

However, kilometers per hour and miles per hour are also valid units for measuring wind speed, especially in general meteorological reports or in specific geographical regions, such as in land-based observations where these units are favored.

Thus, all three options—kilometers per hour, miles per hour, and knots—are indeed utilized in different contexts for expressing wind speed. The option indicating "All of the above" is correct as it recognizes the variability and applicability of different units based on the audience and context of the observations.