Jet stream is a component of upper air circulation. The jet stream is a narrow, fast-flowing, meandering air current in the atmosphere, typically located at high altitudes. It is caused by the interaction between atmospheric pressure systems and the Earth's rotation. The jet stream is characterized by high wind speeds, often exceeding 100 knots (115 mph), and it can extend for thousands of kilometers.

- Definition and Characteristics of Jet Stream:
The jet stream is a high-speed, narrow air current in the upper levels of the atmosphere. It is found near the tropopause, which is the boundary between the troposphere and the stratosphere. The jet stream is characterized by its strong winds, which blow from west to east in the Northern Hemisphere and from east to west in the Southern Hemisphere. It is formed due to the temperature contrast between polar and tropical air masses.

- Importance and Effects of Jet Stream:
The jet stream plays a crucial role in weather patterns and climate. It influences the movement of weather systems, such as cyclones and anticyclones, and affects the distribution of temperature and precipitation. It can also impact aviation, as it can either help or hinder aircraft depending on their direction of travel. The jet stream is also significant for long-range weather forecasting, as changes in its position and strength can indicate changes in weather patterns.

- Types of Jet Streams:
There are different types of jet streams, including the polar jet stream, subtropical jet stream, and tropical easterly jet stream. The polar jet stream is the most well-known and influential, as it forms at the boundary between polar and mid-latitude air masses. It is responsible for most of the weather systems in the mid-latitudes.

- Impact on Weather:
The jet stream plays a crucial role in shaping weather patterns. It can steer storms and weather systems, causing them to intensify or weaken. It can also influence the distribution of temperature and precipitation. For example, if the jet stream is located to the north of a region, it can bring warm and dry conditions, while if it is located to the south, it can bring cold and wet conditions.

In conclusion, the jet stream is an important component of upper air circulation. It is a high-speed air current that influences weather patterns and climate. Its position and strength can impact the movement of weather systems and the distribution of temperature and precipitation.