Wind is the movement of air across the Earth’s surface, resulting from differences in atmospheric pressure. This horizontal flow is a fundamental element of weather, influencing daily temperatures and global climate patterns. Understanding the direction of this air movement is a primary step in meteorology and weather forecasting. Knowing the convention used to describe wind direction allows for accurate prediction of where weather systems are headed.
Defining Wind Direction: The Source Rule
The direction of a south wind is determined by a universal convention used by meteorologists worldwide, known as the source rule. Winds are always named for the cardinal direction from which they originate. Therefore, a south wind is an air current blowing from the south and traveling toward the north.
This naming convention can feel counter-intuitive, as many assume the name refers to the wind’s destination. Meteorologists maintain this distinction because the air’s point of origin determines its specific physical characteristics, such as temperature and moisture content. For instance, a wind arriving from the north often carries cooler, drier air, while one from the south transports warmer, more moist air toward a region.
Applying this rule, a west wind moves from the west and progresses eastward. Similarly, a northerly wind flows out of the north and heads directly to the south. This consistent focus on the point of origin provides a standardized, unambiguous reference for weather reporting and aviation across the globe.
Interpreting Wind Indicators
The source rule is reflected in how common weather instruments function. A wind vane, often seen on rooftops, works by orienting its arrow directly into the wind. This indicates the direction the air is coming from; therefore, a wind vane showing a south wind would have its arrow pointing South.
In contrast, a windsock, frequently used at airports, provides a visual representation of the air’s flow path. The wide opening faces the direction of origin, but the fabric cone trails and points away from the wind’s source. For a south wind, the windsock streams out toward the north, clearly illustrating the air’s direction of travel. Both instruments, despite their opposing visual indications, accurately confirm the wind’s origin is the south, helping observers determine both the source and the path of the moving air mass.