Final answer:
The Saharan Air Layer (SAL) is a mass of dry, stable air that originates over the Sahara Desert and inhibits tropical cyclone development by introducing dry air into the environment where these storms typically form. The correct answer is option 4.
Step-by-step explanation:
The Saharan Air Layer (SAL) is a phenomenon that affects weather patterns, including the development of tropical cyclones. The SAL is indeed a mass of dry, dusty, and stable air that originates over the Sahara Desert. This dry air mass can be vast enough to cross the Atlantic and affect weather in the Americas. The SAL inhibits tropical cyclone development primarily due to its dry air, which can disrupt the formation of the storms by introducing lower humidity into the environment where cyclones typically form. Additionally, the layer of warmer air acts as a cap and suppresses upward motion, which is critical for the development of thunderstorms that can eventually grow into tropical cyclones.
Sal also has implications on the climate and weather of the regions it affects, contributing to the dry conditions of subtropical deserts, like the Sahara and Namib, where evaporation typically exceeds precipitation. Particularly in Africa, it influences the climatic zones, transitioning from the Sahel with its semi-arid grasslands to the extreme dryness of the Sahara and playing a role in the ecosystem dynamics of areas like the Serengeti savanna.