When will the multi-decade active era that began in 1995 end?

[InfernoFlameCat]

Why? If other factors indicate IYO that we've entered a cool phase, how much longer do you wait for storms to catch up before one must re-evaluate this time period as an anomalously short cool phase or that it hasn't begun yet?

I was discussing this with Klotzbach the other day. Taking a closer look at the AMO data on his website, it appears that in 3 of the past 4 seasons (not 2018), the AMO was cool all year EXCEPT the peak of hurricane season. Here's a zoomed in plot that I made. The AMO was quite cool outside of peak season in 2017, 2019, and 2020.

http://wxman57.com/images/AMO.JPG

My personal hypothesis is that interglacial warm periods, including the recent spate of global warming, may actually be correlated with -AMO rather than +AMO historically. If I recall correctly, a number of studies have suggested that the Atlantic basin was hyperactive during the Little Ice Age but less active during the Medieval Warm Period. This makes sense, actually. A warmer globe correlates with a weaker AMOC due to freshwater ice melt in the Arctic. This contributes to decreased salinity and allows North Atlantic Deep Water to percolate southward into the MDR. The same forces that contribute to a weaker AMOC also may result in weaker tornado seasons over parts of North America due to expanding Hadley cells pushing the jet stream farther north. (Incidentally, a warmer climate also tends to amplify the ITCZ vis-à-vis the African monsoon and a wetter Sahel, so storms tend to exit West Africa much farther north and hence fail to develop as they would had they stayed in the MDR.) So I think that AGW may have led to this recent +AMO having ended much earlier than previous +AMOs in the nineteenth and early twentieth centuries, which lasted longer because the global climate or base state was cooler then. I never understood why many studies pointed to storms becoming stronger due to AGW. My view has always been that AGW may actually lead to less extreme Atlantic TC and North-American tornado seasons, owing to changes in the oceanic-atmospheric circulation and feedback (loop).

Yes but... there may be less storms but they will almost certainly be more powerful when they do develop. Keep that in mind when saying there will be less active seasons. Like we will see less 2020s but more 2017s.

[Shell Mound]

Clearly, the AMO, related to the Atlantic thermohaline circulation, is only one factor that governs activity. Temperature and salinity measurements over the past 7-8 years do indicate that a cool cycle has begun. However, the tropics have yet to respond. Also, I think we put too much weight on the number of named storms when determining activity. With better detection and a changing naming methodology, we should only consider hurricanes and major hurricanes. Weak tropical storms or subtropical storms that last less than 48 hours should be excluded. Many of the storms that are currently named would not have been named in the past.

Looking at the AMO over the past 120 seasons, it appears that it was in a cool phase from around 1900-1925, warm from 1926 to 1969, cool from 1970 to 1994, and warm from 1995-2012. There were some quite bad hurricane impacts during cool cycles. In general, though, the number of hurricanes and major hurricanes decreased during cool cycles.

Why? If other factors indicate IYO that we've entered a cool phase, how much longer do you wait for storms to catch up before one must re-evaluate this time period as an anomalously short cool phase or that it hasn't begun yet?

I was discussing this with Klotzbach the other day. Taking a closer look at the AMO data on his website, it appears that in 3 of the past 4 seasons (not 2018), the AMO was cool all year EXCEPT the peak of hurricane season. Here's a zoomed in plot that I made. The AMO was quite cool outside of peak season in 2017, 2019, and 2020.

http://wxman57.com/images/AMO.JPG

Wxman57, do you think that climate change may have had something to do with this latest +AMO ending earlier than previous ones?

[xironman]

The AMO itself is probably the result of volcanic forcing, you can't get any better science on that than this.

https://science.sciencemag.org/content/ ... l%20pacing.

[aspen]

The AMO itself is probably the result of volcanic forcing, you can't get any better science on that than this.

https://science.sciencemag.org/content/ ... l%20pacing.

I’m a little surprised volcanism on Earth is even powerful enough to cause significant long-term impacts on the atmosphere, beyond several year time frames of disruptions from particularly large eruptions like Krakatoa and Pinatubo. I’m more used to seeing evidence of significant volcanic influences on other planets, like Venus’ runaway greenhouse effect or the outgassed H2 atmosphere of GJ 1132b.

[xironman]

I’m a little surprised volcanism on Earth is even powerful enough to cause significant long-term impacts on the atmosphere, beyond several year time frames of disruptions from particularly large eruptions like Krakatoa and Pinatubo. I’m more used to seeing evidence of significant volcanic influences on other planets, like Venus’ runaway greenhouse effect or the outgassed H2 atmosphere of GJ 1132b.

Sulfate aerosols can strongly effect climate

Past research argues for an internal multidecadal (40- to 60-year) oscillation distinct from climate noise. Recent studies have claimed that this so-termed Atlantic Multidecadal Oscillation is instead a manifestation of competing time-varying effects of anthropogenic greenhouse gases and sulfate aerosols. That conclusion is bolstered by the absence of robust multidecadal climate oscillations in control simulations of current-generation models. Paleoclimate data, however, do demonstrate multidecadal oscillatory behavior during the preindustrial era. By comparing control and forced “Last Millennium” simulations, we show that these apparent multidecadal oscillations are an artifact of pulses of volcanic activity during the preindustrial era that project markedly onto the multidecadal (50- to 70-year) frequency band. We conclude that there is no compelling evidence for internal multidecadal oscillations in the climate system.

[wxman57]

The AMO itself is probably the result of volcanic forcing, you can't get any better science on that than this.

https://science.sciencemag.org/content/ ... l%20pacing.

Correlation does not equal causation. I believe that the AMO is driven by the Atlantic thermohaline circulation, as touted by Dr. Bill Gray for decades. Warm very saline near-surface ocean current travels northward toward Greenland during a warm cycle. This dense, saline water sinks, causing the current to increase further. Over time, this leads to increased rainfall and warmer temperatures farther north. The additional rainfall and melting ice and diluting the salinity up north. As salinity decreases, the current slows. Ice re-forms, leading to a cool AMO cycle. The building of ice and decreased rainfall leads to an increase in salinity, jumpstarting the thermohaline current again, leading to another warm cycle. Very simple.

[aspen]

So it looks like we’re divided into two camps:

1.) AMO is a statistical artifact caused by a competition between volcanic aerosols and anthropogenic greenhouse gas emissions.

2.) AMO is a genuine oceanic/atmospheric cycle, likely driven by salinity levels.

Regardless of which is the case, there’s a clear long-term cyclic variation in seasonal ACE going back to 1850.

[TROPICALCYCLONEALERT]

So it looks like we’re divided into two camps:

1.) AMO is a statistical artifact caused by a competition between volcanic aerosols and anthropogenic greenhouse gas emissions.

2.) AMO is a genuine oceanic/atmospheric cycle, likely driven by salinity levels.

Regardless of which is the case, there’s a clear long-term cyclic variation in seasonal ACE going back to 1850.

Why not a combination of both? Natural influences definitely have an impact on the perceived oscillation (things like the NAO and WAM most evidently), but it's not unreasonable to assume that AGW/volcanic emissions can do the same as well.

[wxman57]

Wxman57, do you think that climate change may have had something to do with this latest +AMO ending earlier than previous ones?

I would say that we have too little data to even determine what is early or what is late. The climate has been changing for millions of years. We've been slowly coming out of the last ice age over the past 500 years.

[Hurricane Mike]

Everyone keeps lumping 2018 and 2019 into this recent "active" trend, but in my mind, I think of 2018 and 2019 as busy but not "super busy" seasons. If Florence had turned out to sea and Michael not developed into the rare October Cat 5 U.S. monster, 2018 would be uneventful.

I also don't remember much of anything from 2019 except Hurricane Dorian.

So while these were "active" seasons, in my mind they don't fit the 2004/2017/2020 type of pattern of hyperactive crazy hurricanes that I think of. Perhaps 2018 and 2019 were more "average with a couple bad storms" type of season, similar to 2002.

[toad strangler]

x

[DorkyMcDorkface]

Everyone keeps lumping 2018 and 2019 into this recent "active" trend, but in my mind, I think of 2018 and 2019 as busy but not "super busy" seasons. If Florence had turned out to sea and Michael not developed into the rare October Cat 5 U.S. monster, 2018 would be uneventful.

I also don't remember much of anything from 2019 except Hurricane Dorian.

So while these were "active" seasons, in my mind they don't fit the 2004/2017/2020 type of pattern of hyperactive crazy hurricanes that I think of. Perhaps 2018 and 2019 were more "average with a couple bad storms" type of season, similar to 2002.

,
2018 and 2019 definitely weren't crazy active, but when you consider the overall conditions for both seasons were less-than-optimal (2018 especially with a developing Nino, cold tropics and hyperactive EPAC) they overperformed greatly, and I think that says something. If either season took place in the low-activity/-AMO phase (1970-1994) they would have likely been completely dead. At the same time though I'd argue the strength of the West African Monsoon/African Standing Wave really helped to bolster both of those seasons by providing a strong wave train and warming up the MDR to acceptable levels by ASO, as well as handicapping El Niño development in both years (both the 2018-19 and 2019-20 El Niño events were weak and did not really blossom until the winter).

[Blown Away]

Wxman57, do you think that climate change may have had something to do with this latest +AMO ending earlier than previous ones?

I would say that we have too little data to even determine what is early or what is late. The climate has been changing for millions of years. We've been slowly coming out of the last ice age over the past 500 years.

If we are still in the "Warm Phase AMO" since mid 90's and the difference between Warm & Cold Phase AMO is @1 degree F and the planet is warming maybe we stay in this phase?

[Category5Kaiju]

Everyone keeps lumping 2018 and 2019 into this recent "active" trend, but in my mind, I think of 2018 and 2019 as busy but not "super busy" seasons. If Florence had turned out to sea and Michael not developed into the rare October Cat 5 U.S. monster, 2018 would be uneventful.

I also don't remember much of anything from 2019 except Hurricane Dorian.

So while these were "active" seasons, in my mind they don't fit the 2004/2017/2020 type of pattern of hyperactive crazy hurricanes that I think of. Perhaps 2018 and 2019 were more "average with a couple bad storms" type of season, similar to 2002.

You could even argue 2016 to be like 2018 and 2019; if not due to Matthew and maybe Otto, it would have been a very uneventful and forgotten season. In fact, Matthew alone generated like 40+ ACE, and without that storm the total ACE of the season would have been somewhere in the low 100s or so. 2016 was plagued by dry air during the heart of the season, which is why August and September were pretty quiet.

[Shell Mound]

Note that most single-day TC-related rainfall records occurred during periods of cooler global temperatures.

[ElectricStorm]

https://uploads.disquscdn.com/images/0a5d10278ae9c3495ed9449cd5b9259b1d92adfdf82533d0dcdd70ef58d23b01.jpg
https://uploads.disquscdn.com/images/f0272cbb59d530626664df898beba284dbe6d3d21128fed78dee90fb92332e66.jpg

Note that most single-day TC-related rainfall records occurred during periods of cooler global temperatures.

You can't compare those sets of years though because that's an active era compared to an inactive one...

[Shell Mound]

https://uploads.disquscdn.com/images/0a5d10278ae9c3495ed9449cd5b9259b1d92adfdf82533d0dcdd70ef58d23b01.jpg
https://uploads.disquscdn.com/images/f0272cbb59d530626664df898beba284dbe6d3d21128fed78dee90fb92332e66.jpg

Note that most single-day TC-related rainfall records occurred during periods of cooler global temperatures.

You can't compare those sets of years though because that's an active era compared to an inactive one...

The point is that cooler global temperatures have tended to coincide with more intense Atlantic hurricane seasons and longer-lived +AMO cycles.

[ElectricStorm]

https://uploads.disquscdn.com/images/0a5d10278ae9c3495ed9449cd5b9259b1d92adfdf82533d0dcdd70ef58d23b01.jpg
https://uploads.disquscdn.com/images/f0272cbb59d530626664df898beba284dbe6d3d21128fed78dee90fb92332e66.jpg

Note that most single-day TC-related rainfall records occurred during periods of cooler global temperatures.

You can't compare those sets of years though because that's an active era compared to an inactive one...

The point is that cooler global temperatures have tended to coincide with more intense Atlantic hurricane seasons and longer-lived +AMO cycles.

But we've been warming and we've been in a +AMO since 1995... Maybe I'm missing something but to me that doesn't add up

[tolakram]

Is 'globe cooling' accurate? How about steady?

[HurricaneEnzo]

https://uploads.disquscdn.com/images/0a5d10278ae9c3495ed9449cd5b9259b1d92adfdf82533d0dcdd70ef58d23b01.jpg
https://uploads.disquscdn.com/images/f0272cbb59d530626664df898beba284dbe6d3d21128fed78dee90fb92332e66.jpg

Note that most single-day TC-related rainfall records occurred during periods of cooler global temperatures.

You can't compare those sets of years though because that's an active era compared to an inactive one...

The point is that cooler global temperatures have tended to coincide with more intense Atlantic hurricane seasons and longer-lived +AMO cycles.

To me it just means a lot of Hurricanes were overestimated in the 'cool era' pictured. Recon was in its infancy, no satellite, no SFMR led to a lot of overestimated storms. They were estimating wind speed by looking at what the ocean looked like below them from the plane. It was the best they could do at the time but HIGHLY unreliable.

That is just my personal opinion though.