Why is the wind direction and weather in the trade wind area more stable, while there are more stormy weather in the westerlies?

The westerlies in the mid-latitudes are deep. Cold air from high latitude and warm air from low latitude meet at mid-latitude, which makes the westerlies very unstable and fluctuating, usually called long waves, appearing in the form of large troughs and ridges, and there are often frontal and cyclone activities (they are often accompanied by each other, called frontal cyclones), which leads to unstable weather in westerlies, especially in the ocean. Especially in the mid-latitudes of the southern hemisphere, there is a strong westerly wind.

Trade winds are generally distributed at about 5-25 degrees north and south latitude, and are limited to the lower troposphere, with an average thickness of about 4000 meters. Because the trade wind blows to the low latitude and high temperature area, there is no water vapor condensation condition, the nature is dry, the weather is single and stable, and the wind direction is relatively stable.