Why does a strong gust of wind blow from above when a convenience store's automatic door opens?

Whenever you enter a convenience store or supermarket and the automatic door opens, you often feel a strong gust of wind blowing down from above. Many people think it's just the air conditioning vent, but it's actually a device called an 'air curtain' (or air screen). This machine's main purpose isn't to cool the air, but to use a high-pressure airflow sprayed from top to bottom to create an invisible protective wall at the entrance. This air wall has two important functions: 1. Prevents cold air loss: It blocks the hot outside air, preventing the indoor cold air from escaping instantly when the door opens. 2. Blocks insects and dust: Flying insects and dust are blown away by this high-pressure airflow and cannot enter the store. Without this air curtain, the store's air conditioning compressor would have to run at full speed constantly, and the inside would easily be filled with insects.