February 1, 2013
Ocean Circulation Disrupted By A Thinning Antarctic Ozone Layer
redOrbit Staff & Wire Reports - Your Universe Online
The impact of the depleting Antarctic ozone layer on both the shifting direction of the Southern Hemisphere´s jet stream and the way in which the waters of the nearby southern oceans mix together is the topic of research published in this week´s edition of the journal Science.
In one study, a team of researchers led by earth scientist Darryn W. Waugh of Johns Hopkins University wrote that the hole in the region´s ozone layer has caused subtropical intermediate waters to become “younger” and upwelling, circumpolar waters to become “older.”
Those changes, outlined in the study, are “consistent with the fact that surface winds have strengthened as the ozone layer has thinned.”
Waugh and his colleagues measured levels of a chemical substance known as chlorofluorocarbon-12 (CFC-12) in the southern oceans from the early 1990s through the mid-to-late 2000s. The compound--first produced commercially in the 1930s and largely phased out in the 80s and 90s--helped the researchers determine how surface waters have mixed into the depths of those oceans.
“Because they knew that concentrations of CFCs at the ocean surface increased in tandem with those in the atmosphere, they were able to surmise that the higher the concentration of CFC-12 deeper in the ocean, the more recently those waters were at the surface,” the university explained in a statement.
“The inferred age changes — ℠younger´ in the subtropics, ℠older´ nearer the South Pole -- are consistent with the observed intensification of surface westerly winds, which have occurred primarily because of the Antarctic ozone hole, suggesting that stratospheric ozone depletion is the primary cause of the changes in ocean ventilation,” wrote Lisa De Nike for JHU. “As stratospheric ozone recovers over the next 50 years, the changes in ventilation may slow or reverse.”
Similar research conducted by Penn State University (PSU) meteorology professors Sukyoung Lee and Steven Feldstein discovered that the depletion of the Antarctic ozone could actually play a greater role in the shifting of the Southern Hemisphere´s jet stream southward.
Using modeling studies, Lee and Feldstein discovered that, while both factors have contributed to that southward shift, ozone depletion is believed to have contributed more to those changes. They developed a new method to help differentiate between each of the forces, using cluster analysis to study the effects of both ozone and greenhouse gases on multiple different observed wind patterns.
"Previous research suggests that this southward shift in the jet stream has contributed to changes in ocean circulation patterns and precipitation patterns in the Southern Hemisphere, both of which can have important impacts on people's livelihoods," Lee said in a statement.
"Understanding the differences between these two forcings is important in predicting what will happen as the ozone hole recovers,” she added. “The jet stream is expected to shift back toward the north as ozone is replenished, yet the greenhouse-gas effect could negate this.”
Feldstein explained that most researchers focus on a sole wind pattern when studying ozone depletion and greenhouse gases, but that his past research has demonstrated that analyzing more than one pattern can shed more light on the processes that are actually taking place. For this study, he and Lee selected four different wind patterns, each of which corresponded to different shifts with different properties.
The first wind pattern corresponded to an equatorward shift of the midlatitude westerlies toward the equator, and the second traveled in a similar direction but also included a strong tropical component, the researchers explained. The third corresponded to a poleward shift of the westerlies towards the South Pole, with the maximum strength of the jet stream weakening, and the fourth was similar but with a tropical component, like the second.
They then looked at the relationships between the day-to-day weather patterns for each of the four wind patterns using an algorithm. They discovered that the first was associated with greenhouse gases, the third was associated with ozone depletion, and the second and fourth — the two containing tropical components — were not related to either phenomenon.
Ultimately, they concluded that a long-term decline of the first wind pattern´s frequency and a long-term increase in the frequency of the third could explain the changes to the hemisphere´s jet stream.
"Ozone had the bigger impact on the change in the position of the jet stream," Lee explained. "The opposite is likely true for the Northern Hemisphere; we think that ozone has a limited influence on the Northern Hemisphere. Understanding which of these forcings is most important in certain locations may help policy makers as they begin to plan for the future."
"Not only are the results of this paper important for better understanding climate change, but this paper is also important because it uses a new approach to try to better understand climate change; it uses observational data on a short time scale to try to look at cause and effect, which is something that is rarely done in climate research," added Feldstein. "Also, our results are consistent with climate models, so this paper provides support that climate models are performing well at simulating the atmospheric response to ozone and greenhouse gases."