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Thread: AMOC aka the Gulf Stream System, is it a weakening trend?

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    AMOC aka the Gulf Stream System, is it a weakening trend?

    I have been looking at some evidence such as this
    http://www.realclimate.org/index.php...g-circulation/

    It is a link discussing the reduction in the gulf stream during the last decade. We are reminded this is a highly non linear system and if it declines too much, it will drastically change the climate in the North Atlantic towards the cold end of extreme. It does seem it is weaker now than in recorded history (not necessarily a really long record) but separate records of sea surface temperature may be a good proxy for the current.

    Is it related in any way to the anomaly in Oklahoma where the usual series of tornados in April has not happened?
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
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    I don't know the answer to your question but I don't think AMOC is synonymous with Gulf Stream. The latter is part of the former. Your linked article uses the term Gulf Stream System.

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    Quote Originally Posted by profloater View Post
    Is it related in any way to the anomaly in Oklahoma where the usual series of tornados in April has not happened?
    I don't know, but I think that would be a stretch.

    My understanding is that the tornado activity in the US midwest is powered by two things: warm, moist air coming out of the Gulf of Mexico and the cool air coming from the west over the Rockie Mountains (and the changes in pressure that air encounters). I don't see how the Gulf Stream would directly relate to the Gulf of Mexico.

    I don't know that anyone knows why the tornado season has been quiet so far, but it may also be rapidly change (storm threats in the Midwest today). It may be related to climate change (I think changes in the Gulf Stream almost certainly are), but I don't know that anyone knows.
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    I suppose the ocean currents all link up With their combination of warm surfaces and cold deep salty currents and the article shows the distribution of the heat in the oceans is not obvious so some regions are warming and others cooling. We are seeing Beluga whales near the uk presumably because of local cooling. It's a big picture to comprehend, colder water holds more oxygen. I am really wondering if the slowing Atlantic gulf stream is going to bounce back or continue to decline. The weather has become odd in recent years. That circulation takes warm water to the north pole so one prediction would be a cooling there and recovery of the ice cover with about a twelve year lag due to the ocean heat store. That would be a feed back stabilising the European cooling effect although a cooling trend seems to be happening.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    There is an Oyashio cold current into the north pacific current that ends up travelling down the usa west coast. It is equivalent i guess to the cold greenland current that powers the gulf stream. So if there is that cooling from artic waters, maybe there is a link. It is not one i can find reported but it could be part of the global picture. Fewer tornados might be welcome but colder weather here not so much.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    Quote Originally Posted by geonuc View Post
    I don't know the answer to your question but I don't think AMOC is synonymous with Gulf Stream. The latter is part of the former. Your linked article uses the term Gulf Stream System.
    I agree. I modified the thread title.

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    Quote Originally Posted by grapes View Post
    I agree. I modified the thread title.
    With further reading maybe we should alter the title more because i read that the AMOC is thermodyhamic and density driven while the gulf syream system is wind driven. So they are different and i had not appreciated that through reading journalistic reports. The former is a deep cold current and the latter a surface warm current, (getting cooler at present). It is the change in the density through melt water that may be important while a wind driven flow is harder to understand as a long term diminishing current. The accelerating decline remains alarming for Europe and possibly the East coast USA. The Oshiyo current is not apparently changing in the same way although i believe it is a bigger scale current around Japan and influencing the north pacific warm current. So far i cannot find figures for the up to date Oshiyo temperatures and they would be interesting in this context.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    Quote Originally Posted by profloater View Post
    With further reading maybe we should alter the title more because i read that the AMOC is thermodyhamic and density driven while the gulf syream system is wind driven. So they are different and i had not appreciated that through reading journalistic reports. The former is a deep cold current and the latter a surface warm current, (getting cooler at present). It is the change in the density through melt water that may be important while a wind driven flow is harder to understand as a long term diminishing current. The accelerating decline remains alarming for Europe and possibly the East coast USA. The Oshiyo current is not apparently changing in the same way although i believe it is a bigger scale current around Japan and influencing the north pacific warm current. So far i cannot find figures for the up to date Oshiyo temperatures and they would be interesting in this context.
    The Gulf Stream is wind driven?

    Regardless, there's probably a distinction between Gulf Stream and Gulf Stream System. That article says
    The Atlantic Meridional Overturning Circulation (AMOC, also known as Gulf Stream System)
    I wouldn't completely discount it as a journalist report, the writer seems to be one of the authors of the Nature articles:
    Let’s start with tomorrow’s issue of Nature, which besides the two new studies (one of which I was involved in)

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    Quote Originally Posted by grapes View Post
    The Gulf Stream is wind driven?
    Britannica (https://www.britannica.com/place/Gulf-Stream) says:
    Most of the waters that enter the Gulf Stream system first have been driven westward across the Atlantic by the Northeast Trade Winds.

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    I was surpised by that also, another complexity, the wind also being warmed and wetted in the interaction. A cooler weaker gulf stream, a cooler drier wind system, is that the model? The Uk land mass is warming, many biological markers are evidence. But it is consistent that land masses can be warmed while sea currents cool. The prognostication is not so easy to pin down.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    well now we have had a heat wave which continues and it is widespread. There are NASA maps of the LOTI anomoly available such as this one for May this year
    https://i0.wp.com/climate.nasa.gov/s...50%2C232&ssl=1
    I wonder about the meteorology of heat waves. Typical hot weather causes hot air to rise, bringing in cooler air from outside and cloud formation which ends the land heating. However a heat wave is typically larger so the air from above sinks, getting hotter as it comresses, preventing cloud formation even though there is plenty of water vapour, and increasing the pressure at the ground. This hot high pressure area prevents flows inward, so the heat wave becomes stable for weeks. Despite the water vapour this allows more solar energy to reach the land and that is where the air is mainly heated. At night the heat radiated from the land prevents low level clouds, thinner high level clouds form and the downward pressure is maintained preventing the expected night cooling.

    The map shows that heat waves (May) cover a large area of world land and that is unusual. But there's more:

    New Scientist 4th August P24 covers the slowdown of the AMOC, the cooling of the gulf sream and reports on recent research. A cool patch in the Atlantic is associated with heatwaves and that cool patch is a relatively recent phenomenon. While it is clear the gulf stream varies, (no panic) there is now a recognised long term cooling trend which could lead to collapse of AMOC. (panic) It was weak or absent in the last ice age and nobody knows where a tipping point might lie leading to collapse.

    One aspect is more fresh water ice melt entering at Greenland and the Arctic, this lowers the density of the salty deep return flow from the arctic.

    So could the "day after tomorrow scenario happen? collapse of the AMOC? It might increase air warming with more universal heat waves. Reduced monsoons, elevated sea levels on US East coast, extreme northern winters, stuff like that.

    When consideration of the salt ocean layers was added to models of the oceans, the possibility of AMOC collapse looked more probable.

    One question is whether heatwaves with their lower cloud cover might be a negative feed back on global warming, the night heat radiation to space being higher than average, but then the lower cloud cover lets more sunshine though all day.

    The implications are not too reassuring for climate change in the next years or decades. Heatwaves lead to drought and fires while a colder northern lattitude would hurt all of Europe.

    The official verdict is not to Panic, collapse of the AMOC is a low probability, high impact event. I will watch for more of those LOTI maps with interest and self interest.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    Quote Originally Posted by profloater View Post
    well now we have had a heat wave which continues and it is widespread. There are NASA maps of the LOTI anomoly available such as this one for May this year
    https://i0.wp.com/climate.nasa.gov/s...50%2C232&ssl=1
    I wonder about the meteorology of heat waves. Typical hot weather causes hot air to rise, bringing in cooler air from outside and cloud formation which ends the land heating. However a heat wave is typically larger so the air from above sinks, getting hotter as it comresses, preventing cloud formation even though there is plenty of water vapour, and increasing the pressure at the ground. This hot high pressure area prevents flows inward, so the heat wave becomes stable for weeks. Despite the water vapour this allows more solar energy to reach the land and that is where the air is mainly heated. At night the heat radiated from the land prevents low level clouds, thinner high level clouds form and the downward pressure is maintained preventing the expected night cooling.

    The map shows that heat waves (May) cover a large area of world land and that is unusual. But there's more:

    New Scientist 4th August P24 covers the slowdown of the AMOC, the cooling of the gulf sream and reports on recent research. A cool patch in the Atlantic is associated with heatwaves and that cool patch is a relatively recent phenomenon. While it is clear the gulf stream varies, (no panic) there is now a recognised long term cooling trend which could lead to collapse of AMOC. (panic) It was weak or absent in the last ice age and nobody knows where a tipping point might lie leading to collapse.

    One aspect is more fresh water ice melt entering at Greenland and the Arctic, this lowers the density of the salty deep return flow from the arctic.

    So could the "day after tomorrow scenario happen?
    Isn't that the movie where the killer frost chases them through the streets of New York and they manage to shut the library doors on it just in time, and they survive by burning books in the old open fireplace? or was that one of my daymares?
    collapse of the AMOC? It might increase air warming with more universal heat waves. Reduced monsoons, elevated sea levels on US East coast, extreme northern winters, stuff like that.

    When consideration of the salt ocean layers was added to models of the oceans, the possibility of AMOC collapse looked more probable.

    One question is whether heatwaves with their lower cloud cover might be a negative feed back on global warming, the night heat radiation to space being higher than average, but then the lower cloud cover lets more sunshine though all day.

    The implications are not too reassuring for climate change in the next years or decades. Heatwaves lead to drought and fires while a colder northern lattitude would hurt all of Europe.

    The official verdict is not to Panic, collapse of the AMOC is a low probability, high impact event. I will watch for more of those LOTI maps with interest and self interest.

  13. #13
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    That is the movie but the starting premise was the collapse of the gulf current leading to supercold air, it’s that idea rather than the movie timescale, or the sudden ice age and everyone goes to Mexico. But the heatwaves and the cooling ocean surface are happening right now, will we have a bitter winter after this long hot summer?
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    so I have a question:
    background: climate scientists are reluctant to say the current heat wave is a direct consequence but it is thought to be more likely in the future due to global warming.

    so, is an heat wave over a large part of the land area likely to increase or decrease the greenhouse effect?

    the land and air is hotter, the water vapour content is not necessarily higher, it may be lower (therefore less of a green house mechanism)
    there are less clouds, ditto.

    So assuming we will have more heat waves, is it a positive or negative feedback to the overall picture?
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    No one ventured an answer to my question whether a heat wave is a positive or negative feedback in the heat balance. My guess is that it is a small negative feedback in that a) the land is hotter than normal so radiating more and b) there is less water vapour in the atmosphere above the land, so less greenhouse effect and there are also less clouds but that might be neutral. However the clouds are the key it seems to me, normal cloud cover may reflect the sun and that would make the widespread heat waves a positive feedback with more net insolation. The high pressure over a large area also kept cooling air out at night, i.e.hotter than normal nights. So, it turns out complicated again.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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