NotSparta wrote:Shell Mound wrote:Top reasons why the +AMO has likely ended post 2010:Conclusion: while there is still uncertainty, the weight of evidence suggests that the most recent +AMO ended circa 2010 and no later than 2013, and that this +AMO lasted for a shorter period than previous +AMOs due to the background changes brought about by climate change. Because climate change results in warmer absolute SST globally, we could still end up with higher seasonal ACE in a -AMO cycle today than in past -AMO cycles, yet still be in a -AMO rather than a +AMO. It would be misleading to use a single piece of evidence such as the warm Canary Current and active WAM to argue that we are still in a +AMO, at least in my view.
- There have been only two hyperactive seasons (2017, 2020) over the past decade, compared to seven (1995, 1996, 1998, 1999, 2003, 2004, 2005) over a comparable decade
- Average precipitation over the MDR and Caribbean during two most recent hyperactive seasons was far lower than the mean of the seven previous hyperactive years
- Instability over the MDR and Caribbean during the peak months of ASO has been much lower post 2010 than before
- The subtropics have been consistently warmer than the tropics during most of the past ten seasons
- Long-tracked majors in the MDR and Caribbean have become much less frequent than they used to be
- Seasonal activity is being inflated by short-lived systems in the subtropics that likely went unclassified/undetected prior to advances in detection and changes to the criteria for classification
- More ACE is being generated in the subtropics instead of the tropics, while overall ACE is still decreasing due to the fact that the tropics are generating fewer long-lived, intense storms
- While ACE is still averaging somewhat higher than during the previous -AMO, it is still lower than during the unquestionably +AMO period of 1995–2010; given that warmer global SST due to climate change may result in higher overall ACE in modern-day -AMOs than in pre-global-warming -AMOs, this should not be used to claim that the most recent +AMO did not end
- The changes in the distribution of precipitation and ACE, as well as the decrease in long-lived, intense systems in the tropics, correlates well with the end of the +AMO
- In turn, the end of the +AMO can be attributable to changes in the SST over the far northern North Atlantic that have been brought about by Greenland ice melt and freshwater influx, which in turn is attributable to global warming
Top reasons why the +AMO has (functionally) likely not ended post 2010:
- The last below average season was literally 7 years ago
- In 25 years, the last -AMO had 2 above average seasons (13 below)
- Since 2011 (11 years), there have been 8 above average seasons (3 below)
- 2017
- 2020
Just because the hyperactive seasons don't look "classic" or that we haven't had the same extreme activity that is excessive even for a +AMO doesn't mean it has ended. If we were truly in a -AMO, we would not have seen 2016-21 (and likely 2022). The past 6 years (or even going back to 2010) has had activity far and away above what you'd expect in a -AMO. I understand making this argument in 2014, 2015, 2016, even early 2017. But this argument has become harder and harder to defend with time. Just a fool's errand to argue that we're in a -AMO when we're probably at the precipice of yet another active season (ACE is not significantly affected by short lived storms!). If ACE is this high even in a -AMO due to AGW, we may as well be in a permanent +AMO, because the recent activity is far more consistent with +AMO
Also, let's keep in mind that getting a hyperactive season in the first place is not something you would expect to see every year that passes. In other words, while yes we had back to back hyperactive years like 1995-1996, 1998-1999, 2003-2005, notice how one typically occurs every 2-4 years or so. I don't think we can simply conclude that "oh, we got back to back hyperactive years back then and since 2017 and 2020 are not back to back hyperactive years they are not common anymore." Also, you have to go back 26 years from 1995 to 1969 if you wanted to see another hyperactive year. Like I said, the fact that we are still getting hyperactive seasons imho is way more significant that their timing.