Little Ice Age displaced the tropical rain belt

Posted: April 26, 2017 by oldbrew in climate, research
Tags: ,

The ITCZ is the central band of bright white clouds in this composite image [credit: NASA]


This seems to add weight to the idea that the moving position of the ITCZ can be a useful indicator of natural climate change, in conjunction with other data sources.

The tropical rain belt, also known as the Intertropical Convergence Zone (ITCZ), is in a state of constant migration, as Phys.org reports.

It continuously changes position in response to the seasons and follows the sun’s zenith, with a slight delay. This in turn determines the wet and dry periods in the tropics and subtropics over the course of the year.

The tropical rain belt therefore effectively controls the climate in most of the tropical and subtropical regions, such as the monsoon season in Southeast Asia and Central America.

An international team of researchers led by Franziska Lechleitner from the Geological Institute at ETH Zurich has proven for the first time that the migration of the tropical rain belt is quite sensitive to even small changes in global temperatures.

The team’s findings have been published in the journal Scientific Reports, where they present the most comprehensive reconstruction of rainfall patterns within the Intertropical Convergence Zone for the past 2000 years.

Lower temperatures worldwide

In the past, scientists have only studied the migration of the tropical rain belt over very long timespans, such as glacial and interglacial cycles over tens of thousands of years, with correspondingly sizeable temperature differences of several degrees.

“So far, however, scientists have not investigated the past two millennia on a global scale, when temperature changes have been far less pronounced,” explains the climate geologist.

The ETH researcher and her colleagues have now managed to demonstrate how the tropical weather system shifted a good way south between 1450 and 1850, a period known as the Little Ice Age. “This migration is linked to the lower global temperatures during this time,” explains Lechleitner.

The latest climate reconstructions show that the average temperatures during this period were around 0.4 degrees Celsius lower than before and after the Little Ice Age. The migration of the tropical rain belt also caused substantial changes in the tropical and subtropical climate during this time, affecting the areas of drought and heavy rainfall.

Link to Europe’s weather system

The scientists also found that the climates in the tropical rain belt and the mid-latitudes are interconnected through the North Atlantic Oscillation (NAO). This phenomenon dictates the weather in western and central Europe, and is the result of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high over the North Atlantic.

The NAO is a numeric index: if it is positive, both the Icelandic low and the Azores high are very strong, which generally causes wet weather and strong westerly winds in central Europe, or in extreme cases winter storms and hurricanes, such as the violent Lothar storm in 1999.

However, the NAO index is negative when both the Icelandic low and Azores high are only weak. The west winds die down and shift sideways. This creates damper weather conditions in the Mediterranean region. Central Europe, on the other hand, is more prone to cold air masses sweeping in from the northeast, which can cause icy winters and dry springs.

Continued here.

Scientific report: Tropical rainfall over the last two millennia: evidence for a low-latitude hydrologic seesaw

Comments
  1. oldbrew says:

    The intro to the report starts with this:

    Hemispheric anti-phasing of large-scale precipitation patterns in low- and mid-latitude regions, driven by the seasonal migration of the Intertropical Convergence Zone (ITCZ), has been described over orbital timescales, Dansgaard-Oeschger (DO), and Heinrich events. As part of the upward limb of the Hadley Cells, the ITCZ plays a crucial role in global energy redistribution.

    Related: Heinrich and Dansgaard–Oeschger Events
    http://www.ncdc.noaa.gov/abrupt-climate-change/Heinrich%20and%20Dansgaard%E2%80%93Oeschger%20Events

  2. ren says:

    The loading pattern of the NAO is defined as the first leading mode of Rotated Empirical Orthogonal Function (REOF) analysis of monthly mean 500mb height during 1950-2000 period.

    The loading pattern of the AO is defined as the leading mode of Empirical Orthogonal Function (EOF) analysis of monthly mean 1000mb height during 1979-2000 period.

  3. craigm350 says:

    Reblogged this on WeatherAction News and commented:
    Good find oldbrew

  4. “Our research shows that the global temperature changes do not have to be very extreme in order to shift the position of the tropical rain belt,”

    So small temperature change causes big things:

    Now let’s change a few assumptions:

    “Our research shows that a rather large shift in the position of the tropical rain belt has a relatively small effect on global temperature”

    Large change has a small effect on temperature.

  5. oldbrew says:

    ‘The ITCZ moves farther away from the equator during the Northern summer than the Southern one due to the North-heavy arrangement of the continents.’
    http://en.wikipedia.org/wiki/Intertropical_Convergence_Zone

  6. oldbrew says:

    From the post:
    ‘the tropical weather system shifted a good way south between 1450 and 1850, a period known as the Little Ice Age. “This migration is linked to the lower global temperatures during this time,” explains Lechleitner.’

    And guess what – temperatures have risen since 1850, which just happens to be the convenient starting point for climate alarm theories. What a coincidence – or not 😐

  7. I claim prior knowledge thus:

    “The global albedo changes necessary to produce observed climate variability and the changes in solar energy input to the oceans can be explained by the latitudinal shifts (beyond normal seasonal variation) of all the air circulation systems and in particular the net latitudinal positions of the three main cloud bands namely the two generated by the mid latitude jet streams plus the Inter Tropical Convergence Zone (ITCZ).

    It now appears clear that when the sun is active the jets are more zonal (east to west) with short lines of air mass mixing and less clouds whilst when the sun is less active the jets are more meridional (waving north and south) with longer lines of air mass mixing and more clouds.

    The net effect is to alter the amount of solar energy entering the oceans to fuel the climate system.

    The average position of the ITCZ is situated north of the equator because most ocean is in the southern hemisphere and it is ocean temperatures that dictate its position by governing the rate of energy transfer from oceans to air. Thus if the two mid latitude jets become more meridional and shift equatorward at the same time as the ITCZ moves closer to the equator the combined effect on global albedo and the amount of solar energy able to penetrate the oceans will be substantial and would dwarf any other proposed effects on global albedo from changes in cosmic ray intensity generating changes in cloud totals as per Svensmark.

    The sun causes latitudinal climate zone shifting with changes in the degree of jetstream zonality / meridionality by altering the ozone creation / destruction balance differentially at different height above the tropopause. The net result is a change in the gradient of tropopause height between equator (relatively high) and poles (relatively low).

    The cause appears not to be raw solar power output (TSI) which varies too little but instead, the precise mix of particles and wavelengths from the sun which varies more greatly and affects ozone amounts above the tropopause.

    That allows latitudinal sliding of the jets and climate zones below the tropopause leading to changes in global cloudiness and albedo which alters the amount of energy getting into the oceans.”

    from here:

    http://www.newclimatemodel.com/new-climate-model/

  8. Poly says:

    Ho hum muppets, the importance and factors affecting the ITCZ was identified way back in Suggestions 20 . . . .

    Paul Vaughan says:
    August 30, 2016 at 5:38 am

    Poly acknowledged:

    “The ITCZ is a hugely important rain system for a vast swath of the earth. It has massive economic and agricultural implications. It is scary to see how it can be wildly affected by volcanism.
    […]
    As an aside, there are incredible trading opportunities apparent in this physical connection.”

    Thank you Poly.

    A few things to be aware of and keep in mind:

    It was — in considerable proportion — a modeling study. The authors looked seriously (but incompletely) at observations too. Some of their observation-based conclusions ARE CORRECT. In other areas they struggled.

    Specifically it’s VERY important to note how badly they struggled with ENSO-related spatial patterns. It’s a relief that they acknowledged that clearly and put it aside since they got stuck on it, because many (actually I would guess MOST) would MISinterpret the ENSO spatial patterns because they would not do proper diagnostics to fathom how extremely misleading ENSO-correlated spatial patterns can be. (I’m giving this only a quick mention here — insufficient time now.)

    I looked at a simple North / South split of AOD a number of years ago and at that time it was obvious that that’s not enough. In aggregate there’s something to that when looking at volatility related to north-south land-ocean contrast, but it’s not some simple thing in a mean (…which is all most basically unconsciously ever think about …if they’re thinking at all when they blindly run analyses on auto-pilot).

    With absolute certainty: The mainstream are waking up on this file. They are taking it seriously. They are pulling WAY ahead of sites like wuwt, which are losing ground and moving backwards. Wuwt has dug itself into a hole: They can’t acknowledge this research without setting a double-standard. It would precisely clarify the hypocrisy of their solar bullsh*t. They’ve gotten all stubborn about that. Everyone knows they’re full of sh*t. And it’s a long climb-down from the ridiculous perch they’ve gotten themselves on. They’re f****d no matter what they do now. There isn’t a face-saving option in sight. Not even a genius creative mind will find one. They’re done. They played a rude, severely unethical bluff far, far too aggressively and no one will ever trust them again.

    What’s really telling is that mainstream academia is starting to look orders of magnitude more sensible than them.

    I would far rather side with mainstream academia than with wuwt. They admit their minor errors, but they never admit their big errors — the ones that actually matter.

    With a due sense of urgency they need to be eclipsed.

    The people that were involved in that venture must be excluded from the new venture. (This must be absolutely non-negotiable.) It’s like when a board of directors goes corrupt. You have to do a FULL clean up to restore the confidence of the public, shareholders, and/or stakeholders more generally. No one is ever going to trust any of the core people from that crew again. They need to move on to make way for better people. There are some really, really, really good people out there somewhere ready to do a MUCH better job. We shouldn’t be allowing bad people to block them from the good opportunity they deserve.

    This is a very sincere note. Friends, we need to take real action. Say goodbye and welcome a new beginning.

  9. oldbrew says:

    Another recent paper says ‘the ITCZ may be much less sensitive to inter-hemispheric heating contrasts than previously thought’.

    Coupling of Trade Winds with Ocean Circulation Damps ITCZ Shifts

    Brian Green and John Marshall
    Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, 02139
    Published Online: 8 March 2017

    Abstract
    The position of the inter-tropical convergence zone (ITCZ) is sensitive to the atmosphere’s hemispheric energy balance, lying in the hemisphere most strongly heated by radiative and turbulent surface energy fluxes. This study examines how the ocean circulation, through its cross-equatorial energy transport and associated surface energy fluxes, affects the ITCZ’s response to an imposed inter-hemispheric heating contrast in a coupled atmosphere-ocean general circulation model. Shifts of the ITCZ are strongly damped due to a robust coupling between the atmosphere’s Hadley cells and ocean’s sub-tropical cells by the trade winds and their associated surface stresses. An anomalous oceanic wind-driven cross-equatorial cell transports energy across the equator, strongly offsetting the imposed heating contrast. The circulation of this cell can be described by the combination of trade wind anomalies and the meridional gradient of sea surface temperature, which sets the temperature contrast between its upper and lower branches. The ability of the wind-driven ocean circulation to damp ITCZ shifts represents a previously unappreciated constraint on the atmosphere’s energy budget, and indicates that the position of the ITCZ may be much less sensitive to inter-hemispheric heating contrasts than previously thought. Climatic implications of this damping are discussed.

    http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0818.1

  10. The latitudinal shift in the weather systems, including the ITCZ, is the negative system response to changes in the total power of all forcing elements.
    Only albedo changes will affect the system temperature determined by conduction and convection within the mass of the atmosphere which is constantly overturning within the gravitational field so as to maintain hydrostatic equilibrium.
    Changes caused by GHGs would be too small to measure compared to those caused by sun and oceans over centuries.
    If those GHGs do not cause albedo changes then no change in average surface temperature can occur.

  11. ren says:

    Stephen Wilde says:
    The latitudinal shift in the weather systems, including the ITCZ, is the negative system response to changes in the total power of all forcing elements.
    Only albedo changes will affect the system temperature determined by conduction and convection within the mass of the atmosphere which is constantly overturning within the gravitational field so as to maintain hydrostatic equilibrium.

    The state of the polar vortex may cause anomalies at lower tropospheric temperatures, as seen above.

  12. oldbrew says:

    Albedo changes can’t cause themselves.

  13. suricat says:

    oldbrew says: April 27, 2017 at 10:35 pm

    “Albedo changes can’t cause themselves.”

    Yes they can. However, you need to look in ‘other domains’ to understand how/why this is possible.

    Stephen Wilde says: April 27, 2017 at 5:15 pm

    “The latitudinal shift in the weather systems, including the ITCZ, is the negative system response to changes in the total power of all forcing elements.”

    I disagree. This represents the ‘latent’ quotient IMHO.

    “Only albedo changes will affect the system temperature determined by conduction and convection within the mass of the atmosphere which is constantly overturning within the gravitational field so as to maintain hydrostatic equilibrium.”.

    Yeah! Water vapour is ‘lighter than air’ so would you like to modify your comment?

    “Changes caused by GHGs would be too small to measure compared to those caused by sun and oceans over centuries.”.
    Also; “If those GHGs do not cause albedo changes then no change in average surface temperature can occur.”

    I completely disagree! Changes in ‘albedo’ are totally disconnected from any ‘change in the EM field’.

    Please get back to me Stephen.

    Best regards, Ray.

  14. ren says:

    Suricat
    Jetstream meridional albedo changes due to the increase in cloud cover. This shows the absorption of solar radiation.


  15. ren says:

    It is clear that the Sahara is unable to absorb large amounts of energy.
    The higher energy gas rises, where the temperature immediately falls (the gas expands as the volume rises). Of course, it must be maintained hydrostatic equilibrium.

  16. ren says:

    Energy consumed by the oceans in the equatorial region is used to heat water (with the help of sea currents) but also to evaporate water in areas of strong sunlight.
    Heat capacity of water
    It takes a lot of heat to increase the temperature of liquid water because some of the heat must be used to break hydrogen bonds between the molecules. In other words, water has a high specific heat capacity, which is defined as the amount of heat needed to raise the temperature of one gram of a substance by one degree Celsius. The amount of heat needed to raise the temperature of 1 g water by 1 C is has its own name, the calorie.
    Heat of vaporization of water
    Just as it takes a lot of heat to increase the temperature of liquid water, it also takes an unusual amount of heat to vaporize a given amount of water, because hydrogen bonds must be broken in order for the molecules to fly off as gas. That is, water has a high heat of vaporization, the amount of energy needed to change one gram of a liquid substance to a gas at constant temperature.
    Waters heat of vaporization is around 540 cal/g at 100 C, water’s boiling point. Note that some molecules of water ones that happen to have high kinetic energy will escape from the surface of the water even at lower temperatures.
    https://www.khanacademy.org/science/biology/water-acids-and-bases/water-as-a-solid-liquid-and-gas/v/specific-heat-of-water

  17. ren says:

    “There are only 2 gases in the atmosphere which can trap heat ozone and water vapor those are gases that drive the weather and hence the climate.

    Ozone has a dramatic impact on the weather and hence the climate.

    Carbon dioxide absorbs heat but the excited state decays in nano seconds the heat percolates to the stratosphere.. Its called a greenhouse gas because green is the color of money.”
    https://wattsupwiththat.com/2017/04/24/robust-relationship-between-solar-wind-speed-and-north-atlantic-oscillation-discovered/

  18. ren says:

    Let’s see the cloud cover in the northern hemisphere.

  19. oldbrew says:

    Saying albedo is due to albedo doesn’t work – not for me anyway 🙂

    Too close to circular reasoning.

  20. Tenuc says:

    Very good find Oldbrew, and provides further conformation of how the total solar/galactic photon charge field has a big effect on both short-term temperature and long-term climate change. Thanks.

  21. suricat says:

    ren says: April 28, 2017 at 6:35 am

    Thank you for these images in your comments ren. The “Absorbed” image shows how well ‘energy absorption’ is received by ‘wet’ regions, the “Available” image shows that ‘insolation’ (INcoming SOLar radiATION) is ~equal for all longitudes, and the “Daytime OLR” image shows that ‘dry regions’ ’emit energy’ as its absorbed whereas the ‘wet regions’ ‘retain insolation energy’.

    ren says: April 28, 2017 at 6:44 am

    This graphic may be more difficult to follow, but “The higher energy gas rises, where the temperature immediately falls (the gas expands as the volume rises). Of course, it must be maintained hydrostatic equilibrium.” may be misleading to some.

    ren, some gasses don’t need a temperature difference to ‘rise’! They’re already ‘lighter’ by their atomic ‘make-up, weighting’. Please research this, or ask here.

    ren says: April 28, 2017 at 6:48 am

    I’m sure you mean well here ren, but ‘hygrometry’ doesn’t adhere to a ‘steam tables’ tabulation.

    ren says: April 28, 2017 at 6:53 am

    I concur.

    ren says: April 28, 2017 at 7:12 am

    Yes, Most ‘cloud’ is found above Earth’s ‘ocean’/’sea’ regions. Earth is a ‘water cooled’ planet.

    oldbrew says: April 28, 2017 at 10:40 am

    “Too close to circular reasoning.”

    ‘Water’ is ‘constrained to Earth’ by its physical properties oldbrew. It’s re-cycled!

    Best regards, Ray.

  22. ren says:

    Latitude-height cross section of zonal mean temperature in the Southern Hemisphere.

    You can see how the cold troposphere shrinks over the south pole.

  23. ren says:

    The above graphic also shows that practically in winter the boundary between the troposphere and the stratosphere over the polar circle disappears.

  24. oldbrew says:

    Ray: ‘Water’ is ‘constrained to Earth’ by its physical properties oldbrew. It’s re-cycled!
    – – –
    Sure, but ice albedo can vary +/- otherwise Earth would have become ice-bound millions of years ago. The variability has to come from something other than albedo itself.

  25. suricat says:

    ren says: April 29, 2017 at 8:50 am, and ren says: April 29, 2017 at 8:56 am

    This is due to the ‘altitude’ of/at the South Pole. The most interesting link I can find at this time is here:

    https://www.nationalgeographic.org/encyclopedia/south-pole/

    Its quite logical that an ‘elevated surface’ can ‘escape’ the troposphere during the ‘winter period’ when the ‘troposphere’ is at its ‘lowest altitude’.

    Please realise that the South Pole can achieve a ‘surface altitude’ of ‘~100 meters, plus ~2,700 meters of ice and snow’ (= ~2.8 klicks above sea level). This is no comparison to the ‘~sea level’ altitude observed at the North Pole. They’re ‘poles apart’ (if you’ll pardon the pun 🙂 ).

    Best regards, Ray.

  26. suricat says:

    suricat says: April 30, 2017 at 1:26 am

    “Its quite logical that an ‘elevated surface’ can ‘escape’ the troposphere during the ‘winter period’ when the ‘troposphere’ is at its ‘lowest altitude’.”

    It would be clearer ren, if I’d replaced ‘troposphere’ with ‘tropopause’ in this/that comment. Although the uppermost troposphere altitude alters for a summer/winter period, this should be related to by way of the tropopause altitude which determines the uppermost altitude of the troposphere. Sorry. 😦

    Best regards, Ray.

  27. suricat says:

    oldbrew says: April 29, 2017 at 9:52 am

    “Sure, but ice albedo can vary +/- otherwise Earth would have become ice-bound millions of years ago. The variability has to come from something other than albedo itself.”

    You’re ‘opening a can of “worms” here’ oldbrew. Yes, ice sublimates to ‘WV’ (Water Vapour), but the process doesn’t produce enough ‘clouds’ to ‘maintain the equilibrium’ for a ‘radiative analysis’.

    However, this is of little import. ‘Wet convection’ and its ‘albedo property’ (clouds) rules/regulates the troposphere!

    Best regards, Ray.

  28. ren says:

    Suricat
    Time-height cross section of zonal mean temperature averaged over 60°S – 90°S (top) and time-series representation of vertical components of E-P flux averaged over 30°S – 90°S at the 100-hPa level (bottom).

  29. suricat says:

    ren says: May 1, 2017 at 2:27 pm

    “…”

    ren, your link is to ‘SH’ (Southern Hemisphere) ‘summer’! How can this relate to ‘lowest temps’ and ‘lowest tropopause’ ‘obs’? Please do better!

    Best regards, Ray.

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