An El Niño event can tell us a lot about the current state of the atmosphere. You will see how El Niño grows, how it operates, and how it is expected to affect the upcoming 2023/2024 winter season on many levels. El Niño is the warm phase of ENSO, which stands for "El Niño Southern Oscillation". This region of the equatorial Pacific Ocean transitions between warm and cold phases. There is usually a phase change about every 1-3 years. We are currently entering a warm phase called El Niño. The cold phase of ENSO is called La Niña, which has been active for the past three winters. The (cold/warm) phase usually develops between late summer and early fall. Then it lasts until spring, but some events can last up to two or three years. Each phase of ENSO affects pressure and weather in the tropics differently. It has a different accompanying circulation and thus creates a different atmospheric response. This affects the overall global circulation over time and changes seasonal weather patterns around the world. El Niño can be seen in the latest ocean anomaly analysis for November 2023. It stands out as a warm band of above-normal ocean temperatures across the tropical Pacific Ocean. This anomaly affects the atmosphere, but also indicates changes in the pressure pattern on a global scale. (Andrej Flis)