Image Source: Meteorologist Gerardo Diaz Jr. Flooding in South-Central Kentucky in February 2019, during a weak El Nino season.
The atmosphere is a dynamic fluid that encompasses the entire planet. As such, it should come to no surprise that any small changes to one section of the fluid can result in exponentially greater changes that can ripple across the entire system. As such, these changes to the system tend to be referred to as atmospheric teleconnections, and can be found all over the world. Scientists have studied these phenomena for decades and while we may not completely understand them, many have been studied to the point where they are routinely used for long-range forecasting. Indeed, they are an integral our understanding of the atmosphere and this article hopes to summarize some of the most commonly-studied teleconnections in the world.
Image Courtesy: NOAA. Normal conditions versus El Nino conditions over the Pacific Basin.
The Madden-Julian Oscillation, or MJO, works in a similar fashion to ENSO but takes its form over the Indian Ocean. However, unlike ENSO, the MJO works at a much more localized scale and a much faster rate than ENSO. In other words, unlike ENSO which occurs over the period of an entire season and requires large-scale alterations to atmospheric wind motions on the order of thousands of miles, the MJO generates a moisture transfer over the entire Indian Ocean, and eventually the entire planet, from west-to-east on the order of every 30 to 60 days.
Its lifespan can be categorized into eight distinct phases. According to the UK MET Office, Phases 1 through 3 revolve around the formation of storms over the far Western Indian Ocean which gradually converge and become one large system. During the middle phases (4-6), the fully-developed MJO makes its way into the eastern Indian Ocean and brings moisture into Oceania and East Asia. And finally, by phases 7 and 8, the cluster of storms gradually weakens and subsides as it enters the Western Pacific. Indeed, while the MJO and ENSO run at different temporal and spatial scales, the MJO’s suppression and introduction of moisture onto opposite ends of the Indian Ocean basin act as a strong analog to ENSO over the Pacific Ocean.
Image Courtesy: MET Office UK. The MJO and its movement across the Indian Ocean and Western Pacific.
While the previously mentioned teleconnections coincide with responses to oceanic conditions as much as atmospheric ones, the North-Atlantic Oscillation, or NAO, is much more atmospheric in its nature in the sense that it is directly related to the formation and suppression or even temporary disappearance of a large-scale atmospheric high pressure system that is commonly referred to as the Azores High. During a positive NAO, this High, which is nestled over the North Atlantic and tends to be centered near or directly over Iceland, is at its strongest intensity. As a result, westerly winds that already normally blow into Europe strengthen significantly, resulting in colder air masses being advected into Europe during the summertime while any hurricanes that make their way across the Atlantic and towards the US Mainland are steered closer to the East and Gulf Coasts of a noticeably warmer-than-average North America. Likewise, a negative NAO results in a much weaker Azores High and causes the exact opposite conditions.
Image Courtesy: NASA. The two phases of the North Atlantic Oscillation
And similarly to the NAO, the Arctic Oscillation, or AO, is yet another teleconnection with stronger atmospheric response conditions than oceanic ones that also comes in two phases. Nevertheless, it revolves entirely around the upper-level wind conditions over the Arctic Ocean and is responsible for the ability of cold, artic air to move into the mid-latitudes. Under a positive phase, the Arctic experiences periods of strong low pressure systems while the middle latitudes tend to experience the movement of high pressure systems across the planet, which in turn allows for a more zonal mid-latitude jet stream. When this phase occurs during the wintertime, the end-result tends to be much warmer winters in the mid-latitudes. This is a sharp contrast to negative AO conditions, in which strong high pressure systems dominate the arctic, resulting in the displacement of cold, arctic air into the mid-latitudes due to a much more zonal mid-latitude jet stream.
Image Courtesy: NOAA. The two phases of the North Atlantic Oscillation
Indeed, these are just some of the few teleconnections that can be found all around the world. And while our understanding about these phenomena has improved greatly in recent decades, there are still a plethora of atmospheric teleconnections that are just now being researched, including the Southern Atlantic Oscillation to name just one. And as we continue to observe and analyze their unique impacts on the atmospheric system as a whole, we can only expect that our long-range forecasts to continue to improve with time.
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© 2019 Meteorologist Gerardo Diaz Jr.