By Andy May
The Intertropical Convergence Zone or ITCZ is where the trade winds from the Northern and Southern Hemisphere converge and where the column-integrated meridional (north-south) circulation and the “near-surface meridional mass flux” vanishes according to Adam et al., 2016. For a history of the discovery of the ITCZ see Nicholson, 2018. The ITCZ is not the solar equator, the latitude where the Sun is directly overhead at noon, but it is closely related to it, and they move in a coordinated fashion. The ITCZ is an oceanic phenomenon and doesn’t really exist over land in the same way as described here, except in coastal areas (Nicholson, 2018).
The Sun is almost directly overhead at noon each day in the ITCZ, and it delivers over 940 W m-2 of power to that location at noon, which is enough to raise the water temperature to 86°C or 187°F on a clear day, absent a cooling mechanism. The solar radiation causes intense evaporation which carries away a lot of latent heat. When the heat carried away by convection and conduction is added to the escaping latent heat, the surface water is cooled to a more reasonable 20° to 30°C (Sud et al., 1999). Since water vapor is much less dense than dry air, the moist air rises. The result is deep convection that can sometimes reach the upper troposphere and even the stratosphere (Gettleman et al., 2025). When the rising air hits the more stable stratosphere it spreads horizontally, with a significant poleward component in both hemispheres.
My new paper (May, 2025) shows that the ITCZ location affects the distribution of atmospheric properties and moves the location of the peak altitude of the molar density intersection with it throughout the year. The monthly extremes of the ITCZ are shown in figure 1.
As noted in (Nicholson, 2018), the ITCZ is an oceanic phenomenon, so the extreme positions shown in figure 1 in Asia, Africa, and South America are probably not real. I didn’t use these positions in my study but approximately identified central ITCZ latitudes for each month using several measures.
The location of the ITCZ
A summary of the latitudes and the evidence used is given in Table 1. These recent (~1990 to 2025) locations are approximate and vary from year to year, century to century, and millennia to millennia (Yuan et al., 2023). Yuan, et al. document that the ITCZ moved dramatically northward from ~3500BC to ~2000BC and then dramatically southward from ~500BC to ~500AD when it reached its southernmost position since the last glacial period.
|
Month |
Waliser, 1993, figure 4 |
Zero v_i (N-S wind speed) |
Minimum Total mass flux |
Near zero N-S Mass flux |
ITCZ wind |
ITCZ Latitude used |
|---|---|---|---|---|---|---|
|
January |
-6 |
8 |
-10 |
-10 |
-4.0 |
-5.0 |
|
February |
-5 |
10 |
-10 |
-6 |
-2.0 |
-3.5 |
|
March |
-4 |
2 |
-10 |
-5 |
-4.3 |
-4.2 |
|
April |
0 |
0 |
0 |
-2 |
-0.7 |
-0.3 |
|
May |
4 |
0 |
0 |
0 |
0.0 |
2.0 |
|
June |
5 |
10 |
0 |
-2 |
2.7 |
3.8 |
|
July |
8 |
3 |
20 |
-8 |
5.0 |
6.5 |
|
August |
9 |
10 |
20 |
-1 |
9.7 |
9.3 |
|
September |
8 |
10 |
10 |
11 |
10.3 |
9.2 |
|
October |
5 |
0 |
0 |
0 |
0.0 |
2.5 |
|
November |
1 |
-1 |
0 |
-10 |
-3.7 |
-1.3 |
|
December |
-2 |
3 |
-10 |
-6 |
-4.3 |
-3.2 |
Defining the ITCZ
In both model studies and studies of historical data there is uncertainty about the location of the ITCZ and the distribution of tropical rainfall (Jung et al., 2023). There are many definitions of the ITCZ and none of them are universally accepted, further they often conflict with one another. It has been called the climatic equator or the meteorological equator and represents a narrow, tropical band of low pressure, rising air, and heavy precipitation. One cause of confusion is that the area of lowest tropical pressure and the lowest meridional mass flux is not always the location of the most intense precipitation and the heaviest clouds (Nicholson, 2018). Another source of confusion is that the tropics sometimes seems to contain two ITCZ bands of clouds and storms, this happens often in the month of April, see slide 8 here.
While the definition of the ITCZ is unclear it is one of the central features of the global water cycle and yet modeling it is problematic and very sensitive to model resolution (Yuan et al., 2023) & (Jung et al., 2023). This includes global circulation models as well as weather reanalysis models. This is probably the result of the complexity of the Hadley circulation and the multiple ITCZ definitions used. Is the ITCZ the location where meridional (north-south) mass flux ceases or where the column integrated meridional energy flux vanishes (Adam et al., 2016)? Is it the location where the north-south wind speed vector reaches zero? Is it the location where tropical precipitation is maximal (Jung et al., 2023) and (Marshall et al., 2014)? Or is it the location where the meridional stream function as computed from air pressure is the lowest (Byrne et al., 2018)? All these definitions have been used, and they do not all happen at the same location (Adam et al., 2016) & (Nicholson, 2018).
About one-third of Earth’s precipitation falls within the ITCZ (Clark et al., 2024) and (Kang et al., 2018). All models create an ITCZ-like precipitation feature near the equator due to the intense insolation at that location (Jung et al., 2023). However, the details of the ITCZ vary dramatically as the model’s resolution changes. Increasing the model cell size (decreasing the horizontal resolution), while reducing convection, increases rainfall in the ITCZ, while decreasing the cell size decreases the ITCZ rainfall (Clark et al., 2024). Larger cells produce more low-level clouds, accelerate the Hadley circulation, as well as increasing precipitation. Smaller cells increase energy transport efficiency, weakening the Hadley circulation, and reducing precipitation. This serves as a warning when interpreting model results, many critical weather processes can only be modeled at very small scales, that is at very high resolution.
While the ITCZ is usually thought of as a narrow band of deep convective clouds and intense precipitation that circles the Earth (Adam, et al., 2016), I prefer to think of it as the point where the north-south wind component (meridional transport) reaches zero. Because the radiosonde data is mostly over land this definition is hard to use because the presence of land confuses wind direction and speed measurements. Thus, the ITCZ location is hard to detect with radiosonde measurements. Also, due to land, its location is not a circular path around the earth, but wavy between the extremes shown in Fig. 1 (Britannica & Chmielewski, 2025).
Locating the ITCZ
Exactly why the distinctive tropical band of clouds surrounding the Earth is so complex on average is not completely understood and often hotly debated (Nicholson, 2018). The constantly moving zonal-mean ITCZ central latitude is the origin of the ascending branch of the Hadley circulation (Adam et al., 2016). The cartoon drawings of the so-called northern and southern “Hadley Cells” are oversimplified (Connolly et al., 2021) and (Connolly, 2025), because they do not have a fixed location and their mean air flow is not north and south, but a rather complex constantly moving three-dimensional pattern with a significant meridional (north-south) component.
Besides the mean ITCZ latitudes provided by Waliser, et al. (column 2 in Table 1), the vector-average north-south wind speed (v_i), the minimum total mass flux (in any direction), and the north-south mass flux were all examined by latitude. An example illustration is shown in Fig. 2 for the month of September. The upper left plot in Fig. 2 is the east-west (zonal) wind speed vector (“u”) plotted by latitude. Positive values indicate the u wind component is blowing toward the east, the opposite of the meteorological convention. This measure was initially examined but ultimately rejected as an ITCZ latitude indicator because it disagreed with the other measures.
The top-right plot in Fig. 2 is the north-south wind speed vector (v), with positive values indicating the v wind component is blowing toward the north. The v component crosses zero wind speed at about 10° N, a latitude marked by the vertical line. The lower left plot shows that the north-south total mass flux for July reaches a minimum between the equator and 20° N, the central value at 10° N is lowest so it is the value chosen. The plot on the lower right is the north-south vector average mass flux for September. According to Adam, et al. this is the value that should be zero at or near the ITCZ location. The value reaches very close to zero at about 11° N. Table 1 lists all the values for all months.
How to define and locate the ITCZ is a subject of debate (Nicholson, 2018). But it is usually detected globally by following either the deep convective cloud pattern near the equator or the heavy precipitation that accompanies it (Marshall, et al., 2014) & (Clark et al., 2024). The ITCZ doesn’t really exist in any organized way over land, except in coastal regions, so it may not be detectable in land-based radiosonde data (Nicholson, 2018).
While using tropical cloud patterns and maximum tropical precipitation to locate the ITCZ can be debated, I used these as two of the factors to consider when picking the ITCZ latitudes used in this study (Nicholson, 2018) & (Adam et al., 2016). Further complicating the picture is that the location of the ITCZ does not move smoothly, but mostly in two jumps (Hu et al., 2007). These jumps are from the Southern Hemisphere to the Northern Hemisphere around mid-April and from the Northern Hemisphere to the Southern from around mid-December. This inter-hemispheric movement is accomplished in about 10 days and are the most abrupt jumps in the ITCZ during each year (Hu et al., 2007).
Figure 3 is based only on precipitation and cloud cover, which are only two of the criteria for the ITCZ, but they are important. The precise reason why the ITCZ jumps abruptly across the equator is unknown but probably related several factors: cooler temperatures at the equator due to equatorial upwelling of deeper waters in the Pacific, monsoons, and enhanced convection off the equator (Hu et al., 2007). Convection always favors warmer SSTs, so the ITCZ jumps from one warmer region to the other and skips the cooler temperatures at the equator (Hu et al., 2007).
One known multi-year-scale driver of the ITCZ location is ENSO (Adam et al., 2016), but there may be others. The central latitudes in Table 1 are rough, but act as a guide on the maps. September, August, July, and April have a fairly well-behaved and flat ITCZ in the Pacific, but other months do not. The ITCZ is hard to locate over southeastern Asia due to the South Pacific Convergence Zone northeast of Australia. This zone of converging winds trends southeast to northwest (see Fig. 4) complicates locating the ITCZ over Indonesia.
As described by Adam, et al. (2016), the ITCZ is often considered to be the location of the precipitation maximum in the tropics, the darker colors in Fig. 4. It is also the location of the densest cloud cover in the tropics and the place where the near surface meridional (north/south) mass flux disappears and low-density moist air rises to great heights, sometimes reaching the stratosphere. Further, as Adam, et al. write, it is also the location of the energy flux equator where the column integrated meridional energy flux vanishes. To choose the central ITCZ latitudes shown in Table 1 we examined NOAA’s precipitation maps for 2024 and 2025, our computed North/South wind speed vector (“v”), the total mass flux, and the North/South mass flux vector component.
Plots like figures 2 and 4 for all months can be downloaded and viewed here. The various methods used to pick the central latitude do not always agree, in choosing the central latitude I emphasized the mean north-south mass flux and north-south wind speed vector over the other estimates since these are the most direct measures. The 2024-2025 NOAA precipitation maps were secondary and often the chosen latitude does not look very good on them in the Northern Hemispheric winter, especially in the Pacific, although from March through September they look OK.
September is usually the final month of the Indian monsoon, a period of intense upwelling of moist air in the Indo-Pacific Warm Pool. The monsoon location is easily identified in Fig. 4 as where the ITCZ and the South Pacific Convergence Zone meet north of central Australia. September is also the month with the highest relative humidity in the tropics at the molar density intersection, as shown in Fig. 5, which also shows the molar density intersection relative humidity for all the monsoon months.
The highest molar density intersection is between 20° S and 10° N, and is above 14 km. It is not easy to get water vapor this high, since it normally precipitates out long before reaching this altitude. As you can see in Fig. 5, the highest monthly mean relative humidity seen in the tropics is in September at 51 %. The other monsoon months, June, July, and August are also high in the tropics. To a lesser extent, so are December, February, January, November, and October. While the ITCZ is constantly moving (see the SSEC geostationary satellite Image animations available here), it does lift (through evaporation and updrafts) moisture into the stratosphere (Raymond, 2017). Once the moisture has frozen out of the air, the cooler and drier air descends toward the surface helping to form subtropical deserts and the ocean gyres, see figures 3 & 5 here or (May, 2025).
Discussion
It is clear that the ITCZ moves north and south seasonally, however the precise monthly location is unknown. Since the ITCZ location changes continuously and is the root of the Hadley circulation, it is important to global weather. It can only be approximately located by studying the atmospheric mass flux, wind speed and direction, and the zone of maximum precipitation and cloudiness, thus it is very hard to pin down.
Works Cited
Adam, O., Bischoff, T., & Schneider, T. (2016). Seasonal and Interannual Variations of the Energy Flux Equator and ITCZ. Part I: Zonally Averaged ITCZ Position. Journal of Climate, 29(9). https://doi.org/10.1175/JCLI-D-15-0512.1
Britannica, E., & Chmielewski, K. (2025, November 30). intertropical convergence zone (ITCZ). Retrieved from Encyclopædia Britannica: https://www.britannica.com/science/intertropical-convergence-zone#/media/1/291738/299514
Byrne, M., Pendergrass, A., & Rapp, A. (2018). Response of the Intertropical Convergence Zone to Climate Change: Location, Width, and Strength. Curr Clim Change Rep, 4, 355–370. https://doi.org/10.1007/s40641-018-0110-5
Cheng, H., Sinha, A., & Wang, X. (2012). The Global Paleomonsoon as seen through speleothem records from Asia and the Americas. Climate Dynamics, 39, 1045-1062. https://doi.org/10.1007/s00382-012-1363-7
Clark, J. P., Lin, P., & Hill, S. A. (2024). ITCZ response to disabling parameterized convection in global fixed−SST GFDL-AM4 aquaplanet simulations at 50 and 6 km resolutions. Journal of Advances in Modeling Earth Systems, 16. https://doi.org/10.1029/2023MS003968
Connolly, M. (2025). 20 Million weather balloons: How this data shows that all the climate models are based on wrong assumptions. Retrieved from https://www.youtube.com/watch?v=48Hp9CqSlMQ&t=1026s
Connolly, M., Cionco, R. G., Connolly, R., Soon, W., Herrera, V. M., & Quaranta, N. E. (2021). Analyzing Atmospheric Circulation Patterns Using Mass Fluxes Calculated from Weather Balloon Measurements: North Atlantic Region as a Case Study. Atmosphere, 12. https://doi.org/10.3390/atmos12111439
Gettleman, A., Salby, M., Randel, W., & Sassi, F. (2025). Convection in the Tropical Tropopause Region and Stratosphere-Troposphere Exchange. Retrieved from SPARC: https://www.atmosp.physics.utoronto.ca/SPARC/News17/17_Gettelman.html
Hu, Y., Li, D., & Liu, J. (2007). Abrupt seasonal variation of the ITCZ and the Hadley circulation. Geophysical Research Letters, 34(18). https://doi.org/10.1029/2007GL030950
Jung, H., Knippertz, P., Ruckstuhl, Y., Redl, R., Janjic, T., & Hoose, C. (2023). Understanding the dependence of mean precipitation on convective treatment and horizontal resolution in tropical aquachannel experiments. Weather and Climate Dynamics, 4(4), 1111–1134. https://doi.org/10.5194/wcd-4-1111-2023
Kang, S., Shin, Y., & Xie, S. (2018). Extratropical forcing and tropical rainfall distribution: energetics framework and ocean Ekman advection. npj Clim Atmos Sci, 1. https://doi.org/10.1038/s41612-017-0004-6
Marshall, J., Donohoe, A., & Ferreira, D. (2014). The ocean’s role in setting the mean position of the Inter-Tropical Convergence Zone. Clim. Dyn., 42, 1967–1979. https://doi.org/10.1007/s00382-013-1767-z
May, A. (2025). The Molar Density Tropopause Proxy and its relation to the ITCZ and Hadley Circulation. OSF. https://doi.org/10.17605/OSF.IO/GKF2P
Nicholson, S. (2018). The ITCZ and the seasonal cycle over equatorial Africa. BAMS, 99(2). https://doi.org/10.1175/BAMS-D-16-0287.1
NOAA. (2025, November 30). Climate at a Glance Global Mapping. Retrieved from NCEI.NOAA.gov: https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/global/mapping/pcp/202508/value
Raymond, D. (2017). Convection in the east Pacific Intertropical Convergence Zone. Geophys. Res. Lett., 44. https://doi.org/10.1002/2016GL071554
Sud, Y. C., Walker, G. K., & Lau, K. M. (1999). Mechanisms Regulating Sea-Surface Temperatures and Deep Convection in the Tropics. Geophysical Research Letters, 26(8), 1019-1022. https://doi.org/10.1029/1999GL900197
Waliser, D. E., & Gautier, C. (1993). A Satellite-derived Climatology of the ITCZ. Journal of Climate, 6(11), 2162 – 2174. https://doi.org/10.1175/1520-0442(1993)006<2162:ASDCOT>2.0.CO;2
Weninger, B., Clare, L., Gerritsen, F., Horejs, B., Krauß, R., Linstädter, J., . . . Rohling, E. J. (2014). Neolithisation of the Aegean and Southeast Europe during the 6600–6000 calBC period of Rapid Climate Change. Documenta Praehistorica. https://doi.org/10.4312/dp.41.1
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Yuan, S., Chiang, H., Liu, G., Bijaksana, S., He, S., Jiang, X., . . . Wang, X. (2023). The strength, position, and width changes of the intertropical convergence zone since the Last Glacial Maximum. Proc. Natl. Acad. Sci. U.S.A., 120(47). https://doi.org/10.1073/pnas.2217064120
The ITCZ moves to match outgoing heat from the surface with incoming heat from the sun.
An indiscernible shift would adequately neutralise any effect there may be from human emissions.
Harold The Organic Chemist Says:
At the Mauna Loa Obs. in Hawaii, the concentration of CO2 in dry air is currently 427 ppmv. One cubic meter of this air has a mass of 1,290 g and contains a mere 0.837 g of CO2 at STP. This trace amount of CO2 in air can not cause any global warming or have any effect on weather and climate.
Yes, delayed by about a week at the start, near April 10, after the sun’s sub-solar point crosses over into the northern hemisphere, peaking about 50 days after the NH annual insolation peak.
The insolation curves were derived from 75-years data by subtracting the daily observed F10.7cm solar flux from the daily adjusted flux, then averaged, which tracks with the annual average sun-earth distance cycling between aphelion and perihelion, also time-shifted from the equinoxes and solstices.
I am astounded at the level of academic masturbation. I grew up on a farm in Rhodesia.in the ’60s and 70’s. We knew that if the ITCZ moved South we would get good rains. Who cares if models can predict to the n’th degree. All we wanted to understand was when to plant, and this was decided on gut feel. We have lost the plot in the academic discourse. What are the practical implications and what can we do to mitigate the risk?
Something I have not heard mentioned. Wind and rain are forms of mechanical energy. The source of this energy is thermal energy from the sun. Thus the atmosphere is converting thermal energy into mechanical energy ie: it is a heat engine and the atmosphere is the working fluid. The operation of heat engines was first described by Carnot in the late 18th century. 100% efficiency of conversion of heat to mechanical energy is not possible. Some of the heat must be thrown away. In simple terms the working fluid cycles between a hot high pressure junction where heat energy is injected into the working fluid and a low pressure cold junction where heat energy is lost from the working fluid. Without that cold junction the heat engine cannot function.
For our atmosphere the hot junction is of course the tropics especially around the ITCZ. But where is the cold junction? One opinion is its the poles but this is not possible for 2 reasons. Firstly the poles are not a low pressure region. Secondly there is no direct atmospheric circulation between equator and poles(due to Earth’s rotation). It also cant be the side of the surface away from the sun for the same reasons. The cold unction is infact the tropopause, the top of the convective loop. This is the coldest point in the atmosphere and considerably lower in pressure than the surface. So for the heat engine to function the atmosphere MUST lose energy at the tropopause, but how? Cant be by conduction or convection because the tropopause is the coldest point in the atmosphere. It can only be by radiation and the only place colder is space. So for the heat engine we call weather to function the atmosphere MUST radiate energy to space from the tropopause. But the tropopause is entirely gaseous and a gas that can radiate energy in the thermal IR range is by definition a green house gas. So no green house gases no energy loss from the tropopause (in fact no tropopause) no weather which means no wind, no rain, no clouds and an atmosphere saturated wrt to water vapour! Even more significant, which GHG is dominant for energy loss at this altitude? Remember the tropopause is extremely dry so very little water vapour up there. In fact it is easy to determine. Just look at the spectrum of outgoing long wave radiation. The radiation emanating from a region at 220K (the temperature of the tropopause) is at around 14.7 microns – so CO2. Thus CO2 plays a dominant role in establishing the cold junction for the atmospheric heat engine we call weather. Without it there would be no rain no wind no clouds. The noon temperature in the tropics would every day get to above 100C (without clouds insolation would be 1340 w/sqM not the 930 watts/sqM cited) and even in temperate regions it would be close to 100C. At night it would be far below zero. In short a climate more like the moon than the one we are blessed with on Earth.
You make some good points, but do not call the tropopause “extremely dry.” There is a surprising amount of water vapor left at that altitude, and it also radiates to space. The CO2 percent at 11 km is still 0.04%, at 11 km the average percent water vapor (specific humidity) is the same or a little higher (0.05%), and it emits across a broader spectrum than CO2. Water vapor does not go below 0.01%, on average, until 13 km, see my 2025 paper in the bibliography of this post for more details. Serious emissions from water vapor to space take place between 2.5 km and about 12 km, average height is about 5-6 km.
Harold The Organic Chemist Says:
At 11 km the density of air is 365 g per cubic meter. For a CO2 concentration of 0.04%, the actual mass of CO2 is 0.15 g which is not a lot of CO2.
At 11 km the air temperature is -56.4° C. At this temperature H2O would probably be micro crystals.
Reference for air density and temperature data:
C. Donald Ahrens, “Essentials of Meteorology” page 447.
It can be just dissolved in the air
Andy; it is only the last 1-2 absorbance of the green house gas column that can emit to space. Any emission from lower down will be absorbed by the GHG above it. Essentially all GHG’s in saturation (which all siginificant ones are) will emit as a black body from the top of the ghg column. Thus the emission intensity gives the temperature of the emitting gas via Planks law. Looking at the plots of OLR as measured by satellites with overlayed plank curves shows the only wavelengths emitting at the temperature of the tropopause (220K) are those corresponding to CO2. There is emission from cloud tops, the surface and water vapour but these are from warmer regions ie: lower down in the atmossphere.
mh,
You are forgetting about two important factors, wavelength and absorption power. CO2 is a powerful absorber, but only at ~15 um. Water vapor is weaker, but over a wider frequency range. The emissions of CO2 are very high in the atmosphere (~85km) in its frequency. Outside 15 um, emissions come mostly from water vapor, with some from ozone and at different altitudes. In the in the windows, emissions come from very near the surface or from cloud tops. See here: https://andymaypetrophysicist.com/2021/09/20/the-greenhouse-effect-a-summary-of-wijngaarden-and-happer/
mh, This post tells the rest of the story on emissions. You are correct, but only for the 15 um band. https://andymaypetrophysicist.com/2025/02/01/energy-and-matter/
So does everything warmer than outer space, which is pretty much every particle of matter (solid, liquid, gaseous) on, in, or around, the Earth.
I assume you believe that adding particular gases to air makes thermometers hotter, which is ridiculous. Feel free to correct me if I’m wrong.
Everything emits radiation, true, but only a few gases absorb radiation, which warms the air around them and thermometers. Under the right conditions, these gases can emit that radiation to space, instead of warming their surroundings. However, it is highly frequency dependent! The possible emission height is also highly frequency dependent. Read the two posts cited above and van Wijngaarden and Happer.
Scroll up and read my reply to Stephen Wilde. There is too little CO2 to have any effect on temperature and climate.
Harold; I know it seems there is very little CO2 but the effect depends on how strongly the substance absorbs and emits. CO2 absorbs VERY strongly at 14.7 microns. At 400 ppm the atmospheric column is 3000 times the concentration at which the line center saturates. Because lines do not have a rectangular profile but rather a gaussian like shape, further increase in concentration after the line center saturates causes the absorption profile to broaden which is the reason for the logarithmic relationship betwen energy retained and concentration. You could look up convolution of gaussian profiles for further information. Think of potassium permanganate, a tiny crystal almost too small to see will turn an entire bucket of water dark purple. There is plenty of CO2 in our atmosphere for it to have an effect (does not mean CAGW is correct by the way).
Complete nonsense. 100% CO2 does not make thermometers hotter than 100% N2.
You are either ignorant and gullible, or simply confused. Correct me if you disagree – maybe you have some other reason for talking tosh.
Michael I disagree! and I am not ignorant, gullible nor confused at all. Try standing out in the open mid winter, its pretty cold right? Now go inside to a room say at 20C – still colder than you are. Does it feel warmer? Why? In both cases you radiate (ie lose) exactly the same amount of energy but in the former case the energy radiated on to you comes from outer space at 4K while in the latter case it comes from room surfaces at 20C. In the second case the returned energy is greater (although still less than what you radiate) so net energy loss is less in the second case. Hence you feel warmer inside than outside.
Shown in Fig. 7 is the IR absorption of a sample of Philadelphia inner city air from 400 to 4000 wave numbers (wns). There are additional absorption peaks for H2O down to 200 wns. The gas cell was a 7 cm Al cylinder with KBr windows. The active greenhouse effect range is from 400 to ca. 700 wns. In 1999 the concentration of CO2 at the MLO was 368 ppmv (0.72 g CO2/cu. m. of air) The concentration of CO2 in the city air was not measured.
The absorbance for the CO2 peak at 664 wns is 0.025. If the length of cell was 700 cm (ca. 23 ft) the absorbance would be ca 2.5 and 99+% of the IR light would be absorbed i.e. the absorption of the IR light by CO2 is saturated. Note that the CO2 peak is very narrow and thus is absorbing little IR energy. Most of the IR light is absorbed by H2O.
Based on the above, I stand by what I posted: There is too little CO2 in the air to cause global warming. In winter CO2 hibernates.
PS: Fig 7 was taken from the essay “Climate Change Reexamined” by Joel M. Kauffman. He was a chemist. The essay is 26 pages and can be downloaded for free. Also check Fig 10.
NB: If you click on Fig. 7 it will expand and become clear. Click on “X” in the circle to contract Fig 7 and return to comments.
Harold your plot is correct but somewhat misleading. 4000 wave numbers = 2.5 microns 1500 wavenumbers = about 6.6 microns but Earths surface only emits significant energy from about 8 microns up so all those absorption bands are irrelevant. The gap between the right hand side of the central mass of water bands and the CO2 band at around 660 wavenumbers is the atmospheric window. The relevant absorption bands are those on the right hand end. Yep water vapour has lots from about 18-20 microns and longer but the CO2 band at 660 wavenumbers is relevant.
Great article and figure, thanks. The link to the paper is:
https://www.co2web.info/Kauffman_JSE-21-4-723_2007.pdf
The real problem is less the CO2 concentration (it is saturated) it is the narrow range of frequencies that CO2 absorbs. The yellow in this plot is the difference between 400 ppm and 800 ppm, it does not matter much. At the ~15 um band, the emissions to space are from over 80 km because CO2 is so opaque at that frequency.
No Andy the emissions at 15 microns are NOT from an altitude of 80 km, The emission at 15 microns is effectively coming from a black body (at least a black body that that wavelength) which is another way of saying that the emission is given from Planks law. The emission intensity tells us the emitting gas is at a temperature of 220K and that correspond to the tropopause. The temperature at 80km is far warmer. As to CO2 emissions not mattering much because the band is so narrow, not quite. The absorption/emission bands are not boxcars but something very close to a gaussian (actually a lagrange function). Yes the unbroadened peaks are narrow but each time you double the CO2 concentration it is equivalent to convolving the gaussian with itself. The result is a new gaussian with the same mean but a wider standard deviation. ie: the line broadens and at 400 ppm there have been about 10 doublings since saturation. Each doubling widens the band by about the same amount. The notch at 15 microns shows an emission temperature of 220K corresponding to the tropopause. Yes there is lot of emission at other wavelengths. In the atmospheric window its from the surface. Yes at other wavelengths its from cloud tops or water vapour. Without these effects all emission would be from the surface and would look like a Plank curve and would match conditions on the moon. Atmospheric effects including GHG’s can only reduce this emission intensity (the surface is the warmest region) What is important is the deviation from the Plank curve (your curve in blue) and the notch at 15 microns is probably the biggest artifact. Of course the plot you show is for clear sky conditions (no clouds). With clouds the deviations would be far larger highlighting the importance of clouds. .
“No Andy the emissions at 15 microns are NOT from an altitude of 80 km”
They most certainly are, I’ve provided sufficient documentation of the fact, please read it. The little persistent pip in the middle of the CO2 ditch, proves that at the maximum frequency of CO2 absorption, the altitude is much higher. These frequency bands are very narrow, which is why CO2 has so little effect. The H2O absorption band is much larger, thus it has more of an effect, although its higher concentration in the lower atmosphere also makes a difference. Hopefully this is a better image.
Here is the figure I wanted to post.
Nonsensical word salad, as far as I’m concerned. Adding CO2 to air does not make thermometers hotter, there is no “atmospheric heat engine”, and the Earth has cooled despite four and a half billion years of sunlight.
Yes, without an atmosphere, temperature ranges would be very like those on the Moon.
Like all insulators, the atmosphere works both ways – the result is that about 30% of the radiation from the 5500 K sunlight doesn’t reach the surface, and nighttime temperatures don’t plummet to the levels found on the Moon. Minimum terrestrial temperatures don’t drop below around -95 C or so.
No GHE. As Fourier pointed out, the Earth loses all the heat it receives from the Sun to outer space, plus a little internal heat. Hence the four and a half billion years of continuous sunlight hasn’t prevented the Earth from cooling.
Michael; do you accept that wind is a form of mechanical energy? If you don’t, please explain how a windmill can use wind to generate electrical energy. DO you accept that falling rain is a form of potential mechanical energy? If you don’t please explain how hydro power works. Now there is a fundamental law called the conservation of energy. Energy cannot be created or destroyed, it only changes form. So where does the energy that is now wind and rain come from? Do you accept that it starts as solar energy from the sun? I you don’t, where does it come from. Now remember that a mechanism that converts thermal energy to mechanical energy is called a heat engine, that’s its definition.
So how can you say there is no heat engine. The conversion comes about because of convection in the atmosphere which carries water vapour aloft and the descending air of the Hadley cell at around 30 degrees latitude is moving at the surface speed of the equator which is faster than the ground speed at 30 degrees latitude which manifests as wind. Convection is air moving from the surface (the hot junction) to the tropopause (he cold junction) and then back down again. In order to descend the air has to cool at the tropopause, ie: it has to lose energy. If it cant cool it cant descend and convection stops and then so does water vapour being carried aloft and so does descending air creating wind.
So how does atmospheric insulation work? The energy coming in is radiant energy, how does the atmosphere change it. Does it absorb some incoming radiant energy? Does it block some outgoing radiant energy? And how is the fact that Earth has maintained a reasonable temperature for 4.5 billion years in anyway relevant. No one has suggested the atmosphere stops all outgoing radiation.
“and the descending air of the Hadley cell at around 30 degrees latitude is moving at the surface speed of the equator which is faster than the ground speed at 30 degrees latitude which manifests as wind”
A very nice, clear explanation of this phenomenon.
Why does the wind blow? Now you know! 🙂
You are making an incorrect assumption.
The tropical atmospheric column is the heat engine. Heat is absorbed below the level of free convection mostly at the surface. Heat is loss at the top of the column through long wave emissions to space.
The dehumidified air above the LFC is the compression and convective instability is the valve. Updraft velocity is the SQRT of the convective potential energy that gets up to about 3000J/kg over warm pools. I have attached the current CAPE data for Australia showing 3405J/kg off Broome. That would produce maximum updraft of 58m/s. The ocean temperature at that location is 30.3C. Convective instability prevents the temperature from sustaining more than 30C for long periods.
If you look at warm pools in cyclic instability their average mechanical power is 55W/m^2. The column and surface absorb about 400W/m^2 to do that work. This is the primary engine for global circulations and known as Hadley Cells. The high temperature is 303K and the low temperature down to about 220K.
In an effort to keep my earlier comment to a reasonable length I glossed over a lot of detail. In the absence of CO2 water vapour could function as the GHG responsible for energy loss to space but in that case the “tropopause” would be lower, warmer and at higher pressure where water vapour concentration was high enough to be responsible for the necessary energy loss to space. That would make the energy in the heat engine significantly lower leading to a smaller less energetic Hadley cell. That would of course reflect also on the Ferrel and Polar cells which are essentially driven by the Hadley cell.
Another point, the central claim of CAGW is that rising CO2 progressively reduces Earth’s energy loss to space which creates an energy imbalance. Constant solar input reducing energy loss implies more heat in than out so Earth warms. The OBVIOUS test of this hypothesis is; is Earths energy loss to space (measured s outgoing longwave radiation or OLR) falling as CO rises? We have been measuring OLR since the start of the satellite era and over the entire time period OLR has been steadily rising not falling. In any other field, if the fundamental prediction of a theory was utterly contradicted by experimental observation the theory would be considered disproven!
Very good point. Emissions have risen as the world warms, completely contradicting CAGW, I think Willis wrote a post on that at one time.
The most likely cause of increasing OLR is the reduction in the amount clouds in the air due to the reduction of air pollution.
Harold, I agree reducing cloud cover is an extremely likely reason for the rise in OLR in which case that is probably responsible for most of the warming we are seeing rather than the rise in CO2. Warmists claim falling cloud cover is a feedback effect from warming which to me is illogical. Warming increases evaporation so how does more water vapour lead to less cloud? I suspect its not a feedback but an external forcing. Reduced air pollution is certainly one possible cause but there are others. Svensmarks theory regarding cosmic rays being one such example and there may be others which we have not found as yet.
has the Earth cooled in spite of four and a half billion years of continuous sunlight? Yes, obviously. Hypothesis disproved by fact.
No GHE – that’s a fantasy for the ignorant and gullible – “climate scientists”, for example.
Your assertions are too strong. And you should also refrain from namecalling serious people. It is a bad habit..
Background reading for the ITCZ:
lines 103 through 118 of
The Rime of the Ancient Mariner
[by Samuel Taylor Coleridge (1798)]
Now back to Andy’s text …
Climate models do the ITCZ very poorly. They suffer from a ‘double ITCZ’ bias (producing two [one in each hemisphere] when there is only one that wanders about). Modelers try to remove the double bias via parameter tuning.The double bias was one of two concrete parameter tuning examples in my years ago post here on the inherent problems that parameter tuning drag into GCM climate models.
A number of years ago I was living in Harare, Zimbabwe, when the ITCZ moved over the city and I have never seen so much rain in 24 hours. I remember emptying the 4 inch rain gauge three times and there was even more rain after that. I would have expected massive flooding but the drains had been built – when they had competent engineers – to take a large amount of water so the flooding was restricted to certain low areas..
Everything is so complex I don’t know how people can keep track of it all.
How very true. The more one reads the more confusing climate change becomes. The answer is not simply additional CO2.
The science is definitely Not settled.
Like almost everything in Earth’s climate, it is related to the Sun.
Deep convection requires daily ToA sunlight above 425W/m^2. That is sufficient to get ocean temperature to 30C and start deep convection once the column has reached close to saturation below the LFC. There are thermal lags involved in reaching the near saturated state below the LFC.
Taking 2025 as an example, 10S was above 425 till March 15. The Equator remained above 425 till march 26 and 10N reached 425 on March 31. The thermal response is slightly different in the hemispheres but typically around 16 days for deep convection to set in the NH after reaching 425W/m^2.
For the south going transition, 15N was above 425 until Aug25 when 10N was at 423 and equator at 407. 10S reached 425 on Oct4 while equator was only at 422. 20S exceeded 10S on Oct 17 at 434W/m^2. The thermal lag for deep convection in SH is around 25 days.
The northern transition you have fits well for 2025. The southern transition is a bit later than what would be expected for 2025.
If you select a particular year, I can advise the transition dates.
Braodly based on sunlight, the monsoon days in the NH is trending up and the SH almost static trend. However if you take 1920 as a baseline, 2025 had 1.75 more monsoon days in SH and 2.5 more in the NH. These days are based on the entire tropical zone from Equator to 30 degrees and the proportion of the area reaching 425W/m^2.
For 2026 relative to 2025, there is a reduction of 0.25 days in the SH and no change for the NH.
That sounds very sciency, but what are you trying to say? “Deep convection” requires quite specific conditions, if you’re referring to the convection which results in the formation of thunderstorms, or if slightly less “deep”, cumulus clouds.
In tropics, even over water, blazing equatorial sun doesn’t seem to do much at all on the surface, if you’re becalmed, dripping with perspiration, and praying for a puff of wind. A thunderstorm might provide some blessed relief.
As Andy May said in his post –
I agree, and trying to model something you don’t understand is not likely to prove all that helpful.
Just to complicate the issue, the ITCZ is supposedly a region of low pressure, but caused by prevailing trade winds colliding. One might think that colliding colder winds might cause a pile-up, and higher pressure, but . . .
Not completely understood, for sure. Maybe not even incompletely understood, for all I know.
I am referring to the deep convection over ocean warm pools regulating around 30C surface temperature.
This chart explains what I term as deep convection and how the atmosphere goes into temperature regulating mode once deep convection becomes cyclic:
https://i0.wp.com/wattsupwiththat.com/wp-content/uploads/2022/07/globaloceansurfacetemperatureresponsetosolaremr.webp?w=686&quality=75&ssl=1
Convective instability can occur in the atmosphere once the surface temperature reaches 15C. Above 22C surface temperature, the instability usually brings rain. Cyclic instability sets in just above 30C and operates between 28 and 30C.
As the chart shows, the ocean surface temperature levels off at 30C. It only exceeds that sustainable limit in a few locations globally where a level of free convection does not form such as the Persian Gulf.
So why worry at all about something that has no consistent definition anyway?
Seems like a pointless waste of time, but I suppose that having fun appears a pointless waste of time to the “fun police” (if you know what I mean).
If you enjoy it, keep at it.
Hi Andy, that’s a very interesting approach with some counterintuitive results. Two thoughts on what paleoclimatologists call the bi-polar see-saw (the southern hemisphere historically warms and the northern hemisphere cools when the ITCZ on yearly-average moves south and vice versa):
1) The sudden shift north around April and back south again in Fig. 3 might be due to seasonal changes in the AMOC. During 1997-2006 the Atlantic Multidecadal Oscillation was positive (SH Atlantic on year-average exporting heat to the NH) so the sudden switch to the North in spring may be due to when the North Atlantic Current in the Nordic Seas gets covered by a fresh melt- and runoff water layer, and can no longer lose its heat to the atmosphere, possibly causing a back-log in the North Atlantic Gyre and the NH? NH Atmospheric weather systems might react by exporting the heat south by shifting the ITCZ. Reverse in December. It would be useful to see what Willis Eschenbach’s simple structural model shows, if he can set it up to run on a weekly/monthly basis.
2) “Yuan, et al. document that the ITCZ moved dramatically northward from ~3500BC to ~2000BC and then dramatically southward from ~500BC to ~500AD when it reached its southernmost position since the last glacial period.” There’s an obvious tie-in here with the ~1500 year (warm to cold to warm) Bond cycles as well as the (unnamed?) ~5000 year climate cycles. As Yuan probably points out (I need to read) ~3500 BC is the ~start of the Minoan Warm Period while ~500 AD is the ~start of the Dark Ages Cold period.
Good stuff!
Thanks. Interesting ideas. I’m not sure about the changes during Holocene, they might be related to orbital changes. But the jumps in April and December are most likely just the ITCZ skipping over the cooler water at the equator. Several degrees north and south of the equator the water is warmer than right at the equator, and it is natural to assume that the ITCZ prefers warmer SSTs. See Hu et al., 2007 in the bibliography for a discussion.
It’s just surprising to see it jumps in such a short time, because the weather systems have to shift, too. For example, it’s around the time the Azores high starts migrating towards Bermuda. But the Iceland Low stays put, so I don’t see how an ITCZ shift could be forced by less heat emitted over the Arctic, so you’re probably right. Thanks for the Hu et al. reference.