How many types of turbulence are there on an aircraft?

The assertion that there are four types of turbulence is correct based on standard classifications in aviation. The main categories typically referenced include:

1. Clear Air Turbulence (CAT): This occurs at higher altitudes and is often not associated with visible weather phenomena such as thunderstorms. It is challenging to detect and can catch pilots by surprise.

2. Mechanical Turbulence: This type arises when airflow is disrupted by terrain, buildings, or other structures, leading to erratic patterns in the air. It is commonly encountered at lower altitudes, especially during takeoff and landing.

3. Wake Turbulence: Generated by the passage of an aircraft through the air, this turbulence is created when large aircraft disturb the airflow, leaving behind a wake that can affect following aircraft.

4. Thermal Turbulence: Also known as convective turbulence, this occurs during daytime heating of the earth's surface when rising hot air bubbles disrupt the smooth flow of air, leading to varying degrees of turbulence.

These four categories comprehensively cover the different situations in which turbulence can occur during flight.