Local Weather: Antarctica Connections
CWG's Ann Posegate has been reporting on weather, climate and environmental research based on her recent National Science Foundation-sponsored visit to Antarctica (see previous posts from her trip). The focus of her reports and focus of the vast majority of Antarctic research is the connection to climate change on time scales of decades to millennia.
The question addressed here is whether conditions over and around the Antarctic affect daily weather in the Northern Hemisphere (NH), and even locally in the eastern U.S. within a given season and from one season to the next. Are there identifiable phenomena directly or indirectly tied to the Antarctic that might influence weather north of the equator?
The answer: Maybe.
Much research remains in order to answer this question more definitively, but the possibilities are certainly plausible given that Antarctica and the Southern Ocean are, in fact, key elements in the global weather and climate system, and there is no wall separating the Southern Hemisphere (SH) and NH.
As shown in the upper-level winds figure from April 2009 (below), for example, one can see the cross-equatorial flow (indicated by the arrows) from the SH interacting with the NH subtropical jet stream (the brighter colors from around 10 to 30 North latitude), especially between 180 and 150 West longitude. Tracing the flow back to the south, it's clear there is a connection to the circumpolar jet around Antarctica.
I cannot yet establish whether this pattern had a recognizable influence over the eastern U.S. several days later on either forecasts or actual conditions, but it's certainly possible considering what we already know about how atmospheric and oceanic conditions in one part of the globe can affect weather in another part. For example, experts believe that El Niño (warmer-than-average surface waters in the equatorial Pacific) has impacted weather this winter and that its effects may persist through the spring.
Not incidentally, examples such as this demonstrate why weather forecast models (e.g., the Global Forecast System) must encompass the globe for predictions more than a few days in advance, and why regional models, such as the North American Mesoscale Model, are restricted in forecast length.
One of the most direct approaches for determining interhemispheric relationships is via teleconnections, recurring and persistent large-scale patterns in pressure and circulation that span vast geographical areas. These patterns, such as persistent high pressure in one part of the world and corresponding low pressure in another, are calculated as indices that are sometimes correlated with certain types of weather across a region or continent. The existence of a teleconnection alone, however, does not necessarily translate to direct cause-and-effect relationships.
A significant teleconnection in the NH is the Arctic Oscillation (AO). The Antarctic Oscillation (AAO) is the SH twin of the AO. The negative phases of both the AO and AAO (relatively high pressure over the polar region and low pressure at midlatitudes) are often associated with cold outbreaks. For example, a negative AO is probably partly to blame for the very cold winter experienced by much of the U.S., while a negative AAO is associated with cold air over central South America and southern regions of Australia during the SH winter.
Moreover, there is a strong likelihood of an interhemispheric teleconnection during the NH winter between the AAO and both the AO and Pacific North American (PNA) pattern. Additionally, there is reasonable evidence that daily positive and negative AAO phases during the SH summer are related to anomalous tropical rainfall patterns associated with the Madden Julian Oscillation and to phases of the El Niño-Southern Oscillation (ENSO).
Independently, the AO, ENSO and PNA -- each related statistically to the AAO -- can alter the circulation pattern over mid-to-high latitudes, including North America, and thereby play a large role in the number and intensity of significant weather events affecting the U.S. As discussed in a previous post, AO, ENSO and PNA can come together in ways that enhance the prospects for major East Coast storms, such as Snomaggedon and Snoverkill. While admittedly it would be difficult to connect the dots, it's plausible that atmospheric conditions over the Antarctic are related to weather even locally in the D.C. area. Perhaps future research will determine whether plausibility translates to reality in some respects.
There are also studies, such as this one, which indicate that variability in the AAO in the SH winter (NH summer) is related to tropical cyclone formation north of the equator, at least over the East China Sea and Japan. Also, as found in this study, during the SH winter a positive (negative) phase of the AAO is associated with anomalous easterlies (westerlies) in middle-to-low latitudes (~30-40°N) and anomalous westerlies (easterlies) in middle-to-high latitudes (~45-65°N) of the upper troposphere (8-12 miles above the surface) about 25-40 days later. This, in turn, could affect the track and intensity of tropical storms as they migrate northward.
Studies have indicated that variations in AAO have links to the East Asian Summer Monsoon (EASM). The EASM dominates weather conditions over much of eastern Asia during summer months, especially in the amounts and distribution of rainfall. Moreover, oscillations in the characteristics of EASM over the course of a summer can remotely influence atmospheric conditions over the NH, including those related to tropical storm development.
Bottom Line: Atmospheric phenomena, even over places as remote as Antarctica, can influence weather conditions on relatively short time scales -- from several days to several weeks -- just about anywhere over the globe, including in eastern North America. However, knowledge and understanding of the processes governing the connections from "there to here" over time is far from complete. Hence, any direct or indirect relationships between the Antarctic and specific weather events, such as the major snowstorms locally, are largely speculative but certainly possible.
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