why the northeast and southeast trade winds are steady in strength and direction year round but the Northern Hemisphere westerlies alternate from northwest to southwest with summer and winter along the west coast of the United States.
The steady strength and direction of the Northeast and Southeast trade winds and the alternating nature of the Northern Hemisphere westerlies can be attributed to a combination of factors, including the Earth's rotation, the distribution of land and sea, and the seasonal variations in temperature.
1. Coriolis Effect: Due to the Earth's rotation, the Coriolis effect comes into play. The Coriolis effect causes moving air or fluids to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This effect influences the direction of the winds.
2. Trade Winds: The Northeast and Southeast trade winds are the prevailing winds that blow towards the equator from the subtropical high-pressure belts at around 30 degrees latitude. In the Northern Hemisphere, the Northeast trade winds blow from the northeast, while in the Southern Hemisphere, the Southeast trade winds blow from the southeast.
3. Hadley Cells: These trade winds are a result of the Hadley Cell circulation, where warm air rises at the equator, flows towards the poles, and eventually descends around 30 degrees latitude, creating high-pressure belts. The air then flows back towards the equator at the surface, forming the trade winds.
4. Land-Sea Distribution: The distribution of land and sea creates seasonal variations in temperature, which influence the strength and direction of winds. The oceans have a higher heat capacity than land, leading to slower temperature changes. As a result, the trade winds over the oceans remain relatively consistent in both strength and direction throughout the year.
5. Northern Hemisphere Westerlies: The westerlies are winds that blow from west to east between the subtropical high-pressure belts and the mid-latitude low-pressure belts. In the Northern Hemisphere, the westerlies flow from the Southwest to the Northwest. However, along the west coast of the United States, their direction changes with the seasons.
6. Seasonal Temperature Variation: The alternating nature of the Northern Hemisphere westerlies along the west coast of the United States is influenced by the temperature difference between the land and the adjacent ocean. In summer, the land heats up faster than the ocean, creating a low-pressure system over the land. This causes the westerlies to change direction, flowing from the Northwest towards the Southwest. In winter, the situation reverses, with cooler land leading to high-pressure systems, causing the westerlies to flow from the Southwest towards the Northwest.
In conclusion, the steady strength and direction of the Northeast and Southeast trade winds are a result of the Earth's rotation, the Hadley Cell circulation, and the consistent temperature patterns over the oceans. On the other hand, the alternating nature of the Northern Hemisphere westerlies along the west coast of the United States is influenced by the seasonal temperature variations between the land and the ocean.