Convergence, Shrinking and Implosion versus Divergence, Expansion and Explosion during Condensation

Why am I growing?

Why am I growing?


Some confusion apparently continues to surround the question of whether condensation lowers local pressure (and hence leads to convergence towards the condensation area) or whether it leads to a rise in local pressure and hence divergence of air from the condensation area. Three quotes below from colleagues whose diverse attitudes towards condensation-induced dynamics span the entire spectrum of possible attitudes, provide an illustration.

“Cloud formation looks like an explosion and not like an implosion. So the expansion due to the temperature rise is clearly stronger than the pressure drop due to condensation.”

“If condensation drives winds by a decreasing the number density of water vapor in the air, then as clouds form they should shrink in size due to the negative pressure. OTOH, if the release of the heat of condensation is the primary driver, they should expand. Guess what?

“Yesterday I was gazing upon a deep blue sky when a puffy white cloud came into view. It was small, but I could notice its slow growth at the diffuse edges, which I could see due to the stark contrast to the blue background. I kept watching for a time, as it grew and grew, remembering one of the classic explanations from the conventional meteorology, that is, clouds grow as a response to “latent heat” release and ensuing expansion.”

Let us try to clarify this issue.

First of all, anyone accepting that condensation occurs in the ascending air must accept — to respect the mass conservation law — that the air comes to the area of ascent in the lower part of the atmospheric column and leaves the area of ascent somewhere higher in the atmosphere. Independent of what drives convection and cloud formation, these processes are accompanied by both convergence and divergence.

The wide-spread view is that latent heat release drives the divergence aloft: the warm air expands and leaves the atmospheric column where the ascent occurs. This lowers hydrostatic pressure at the surface and causes convergence below the cloud. In contrast, according to condensation-induced dynamics, condensation lowers pressure at the surface as the water vapor leaves the gaseous phase. This causes convergence in the lower part of the atmosphere, of which the divergence aloft is an indispensable consequence. It is caused dynamically and would take place irrespective of whether latent heat remains within the column (if the ascent is adiabatic) or not (if it is diabatic).

While the first view is indeed wide-spread, it can be better characterized as a kind of vox populi rather than a professional consensus. Indeed, in the meteorological literature it is debated. The following questions are considered: (A) Is the potential energy associated with latent heat release sufficient to drive the circulation leading to deep convection or, alternatively, (B) Is convection driven dynamically by surface pressure gradients that are associated with surface temperature gradients (see, e.g., Back and Bretherton (2009) for a discussion). Condensation-driven dynamics partially supports view B and quantifies these surface pressure gradients — although showing that they are not related to surface temperature and can exist on a horizontally isothermal surface as well.

Thus, when we are looking at a growing puffy cloud we should keep at least two things in mind. First, when the cloud grows in the horizontal dimension
it means that its convergence zone expands — i.e. the low pressure zone at the surface grows, allowing for a more extensive convergence. In other words, when the cloud becomes thicker while growing, it is not because the cloudy air continuously expands — it is the condensation area, i.e the area of convergence (“shrinking”, “implosion”), that is growing. This is illustrated very well in the following animated picture taken from the University of Albany web site.

Stages of deep convection

Stages of deep convection

As we can see, early in its life the cloud expands in all directions, meanwhile the air continues to converge towards the (growing) condensation area. This process is at the core of condensation-induced dynamics: as condensation occurs and local pressure drops, this initiates convergence and ascent. They, in their turn, feedback positively on condensation intensity, such that the air pressure lowers further, convergence becomes more extensive and so on — as long as there is enough water vapor around to feed the process.

Another point to consider — and this holds true for quasi-stationary clouds as well — is that condensation intensity declines with height following the decrease in the partial pressure of atmospheric water vapor (see, for example, Fig. 2 here and Fig. 4f here). Therefore, according to condensation-induced dynamics, the intensity of convergence (“shrinking”, “implosion”) should be maximal immediately below the cloud base and then decline with growing height. This agrees well with observations.

On the other hand, the conventional latent-heat-based line of thought presumes that if the air ascends moist adiabatically it becomes warmer than the surroundings only above the level of free convection (LFC). Thus, despite latent heat is being released most rapidly near the cloud base (where condensation intensity is at its maximum), this does not immediately make the ascending air warmer than its surroundings and does not help the air expand (diverge, explode) until it reaches the LFC. So even the conventional wisdom prohibits such an expansion.

Furthermore, as one can see in the animation, even above the LFC convergence dominates in most part of the atmospheric column despite, as indicated by the isotherms, the cloudy air is apparently warmer than the surroundings. This shows that the low pressure caused by condensation spreads upwards up to a few kilometers in the atmosphere, see Makarieva et al. (2013), Fig. 1c. This prevents the rising air from divergence, which is therefore confined to the upper atmospheric layers where condensation is minimal. As soon as condensation discontinues during the later stages of cloud development, the divergence aloft markedly intensifies eventhough the air is no longer warmer than the surroundings. All these processes are consistent with the dominating dynamical role of condensation-induced pressure drop over latent heat release. (Note also that the air flow can transport condensate particles well outside the area where condensation actually occurs.)

Convective clouds

Cloud formation in June approx. 70oN. Left photo: local time 21:53, a second high cloud starts to develop to the left of the one already formed. Right photo: the same system 45 minutes later. One can see an outflow formed by the second cloud.

We conclude that without a somewhat deeper quantitative understanding of the dynamic processes accompanying condensation it is not possible to meaningfully interpret even the very common every-day observations like those of cloud formation.

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16 responses to “Convergence, Shrinking and Implosion versus Divergence, Expansion and Explosion during Condensation

  1. Hi, I think the key thing about the biotic pump is that the water vapour/clouds mean that the low pressure area lasts into the night and that means the air is rising (slowly) day and night. Compare that to the desert. No biotic pump but similar amount of energy raining down from the sun. Clear sky at night, heat is lost by radiation and temperature goes from 30 plus C down to about 3 or 4. Very cold and high pressure. So by day, strong land breeze from the sea inland. and by night strong sea breeze from land to sea. So on balance, nothing happens. But with the biotic pump there is this gentle slowly building low pressure suck day and night. Very different situation and all because of the water vapour and cloud that prevents the rapid radiation of heat away at night. So the heat escapes slowly by convection and lifts moist air up with it. until about 10 km up when the water condenses As it condenses, it releases heat to the air molecules around it, but it is very different at 10 km high than at surface level in the desert.

  2. I have been doing the “cloud in a bottle” experiment. Does it settle the argument? 2 to 5 ml of water in a 2 liter bottle, a bit of smoke and lid on tight. Squeeze and release the bottle a couple of times and you get a “cloud”. So you have your cloud. Squeeze the bottle and you get both a temperature rise AND a pressure rise. AND? THE cloud disappears! Doesn’t that PROVE that the cloud is a low pressure situation? Lower the pressure and you get the cloud, increase the pressure and it disappears. So, I think the cloud is actually an implosion. The cloud is an expanding low pressure area. As it expands, the conversion of vapor to droplets takes place at the edge of the expansion zone.

    • Brian, thank you very much for your comments. We will write more as we have more time to think on your explanation.

      Regarding the breezes in Sahara, consider that breezes with a typical wind speed of a few meters per second in half a day could only penetrate about 200 km inland. If the air was rising over land it could generate rainfall (so the net impact would not be zero), but only in a narrow strip of land near the coast (as we emphasized in our early papers in 2007 and 2009).

      Regarding the latent heat, it is not the driver of the biotic pump, which is instead driven by pressure drop which arises when the amount of gas in the atmosphere is reduced by condensation.

      Concerning the high/low pressure during condensation, the bottle experiment is really nice! However, there is much confusion in this question. Consider the receiver area (where air rises and it rains) and donor area (where the air descends, no rain). If we compare air pressure between the two areas, we will see that in the receiver area pressure is lower at the surface, but it can be higher in the upper atmosphere (see for example pressure profiles in Figure 2 in our recent paper). The question is whether the air circulation is driven by the pressure surplus aloft (standard view) or, rather, by the pressure shortage at the surface (biotic pump view).

      Note also that there is also much confusion about what it means “circulation is driven by something”. For example, in the geostrophic balance there are winds, but the rate of generation of wind energy is zero. Our main theoretical argument (supported by observations) is that condensation determines the rate at which wind energy is generated.

  3. This article has a link to a paper that describes one way how your biotic pump gets seeded for condensation nuclei. The process they discribe is a 2 part process. Needs fungi to release tiny particles of potassium salts into the air. And then trees release turpines and they aggregate on the salt (like smog formation) to produce the condensation neuclei. So to have these condensation neuclei, you need, Tall mature trees that have fungi on them, so that the potassium release can be relatively high up in the air. http://scitechdaily.com/how-aerosol-particles-form-in-the-amazon/

  4. A.M., thoroughly enjoyed your article, I am the same wayne that discussed a number of things at a site called wuwt a couple of years ago as you presented your paper there. Been following your work on and off ever since, and to me, you have this right in the physics. Have you ever thought of considering the Bernoulli effect from the increased (quite high!) velocity accelerating up those developing towers? I have generally always thought that was one of the force always keeping them so tall, narrow and horizontally contained.

  5. solvingtornadoes

    Low pressure is delivered through the jet stream. It does not emerge locally. Moist air is heavier, not lighter, than dry air.

    You need to get basic facts correct before you start to create new explanations, IMO.

    http://www.solvingtornadoes.com

    • Moist air is lighter than dry air. H20 weighs? 18 per molecule! O2 weighs about 32 and N2 weighs about 28 for an average around 29. This has been measured so please don’t embarrass yourself with baseless opinions.

      • solvingtornadoes

        Moist air is heavier, not lighter, than dry air. The mistake you (and everybody else) is making is to assume that the H2O in moist air (at ambient temperatures) is gas. It isn’t. It’s still a liquid. You have no evidence that disputes this. Sorry to burst your bubble. There is a lot of BS in meteorology. You are just scratching the surface.

      • solvingtornadoes

        Why Water is Weird
        http://wp.me/p4JijN-49C

  6. solvingtornadoes

    Brian White:
    “Squeeze the bottle and you get both a temperature rise AND a pressure rise. AND? THE cloud disappears! Doesn’t that PROVE that the cloud is a low pressure situation? Lower the pressure and you get the cloud, increase the pressure and it disappears.”

    This is a very interesting and very relevant observation. It demonstrates/proves that air molecules (N2 and O2) dictate the size of H2O droplets in the air. Reduction in air pressure releases their effect allowing the droplets to join together into larger droplets. Reestablishment of air pressure allows the droplets to re-divide.

    Meteorologists are just dumb. They believe in cold steam in our atmosphere. In reality moist air is always in droplets. Therefore it always makes moist air heavier, not lighter, than dry air. Being brain-dead stupid meteorologists don’t get this.

    Moisture is suspended in air due to electro-static forces. Buoyancy has no effect at all. Buoyancy is a nonsense notion that should have been excluded from meteorology a long time ago. But now it is part of their belief system. In my experience, believers never stop believing.

    Meteorologists are just dumb and ignorant.

    http://www.solvingtornadoes.com

  7. solvingtornadoes

    Many have assumed that the reason moist air is associated with atmospheric instability (energy) is because moist air convects through dry air. This is false. The reason moist air is associated with instability is because vortices bring energy with them as they grown down from the jet stream and moisture is the resource that they grow into to make the plasma that allows vortices to grow.

  8. solvingtornadoes

    Author:
    The wide-spread view is that latent heat release drives the divergence aloft: the warm air expands and leaves the atmospheric column where the ascent occurs.

    Jim McGinn of Solving Tornadoes:
    You describe the wide-spread view about as well as any nonsense can be described. But, if you think about it, the notion is plainly nonsensical right from the outset. If condensation produced heat that would result in hotter air and hotter air has an increased capacity to absorb moisture, in which case condensation would be halted.

    Author:
    While the first view is indeed wide-spread, it can be better characterized as a kind of vox populi rather than a professional consensus.

    Jim McGinn of Solving Tornadoes:
    Almost everything about meteorology’s approach to storm theory is, “vox populi.” The same can be said for the notion that moist air is lighter than dry air and/or that storms are caused by convection.

    Author:
    Indeed, in the meteorological literature it is debated.

    Jim McGinn of Solving Tornadoes:
    It’s a BS debate because none of it is based on anything empirical. Moreover, the whole debate pivots off the existence of something that is physically impossible, cold steam. Without this imaginary notion there is no basis for convection or latent heat. The reason meteorologists insist that moist air is lighter than dry air is because without it there models are worthless.

    Author:
    . . . the conventional latent-heat-based line of thought presumes that if the air ascends moist adiabatically it becomes warmer than the surroundings only above the level of free convection (LFC). Thus, despite latent heat is being released most rapidly near the cloud base (where condensation intensity is at its maximum), this does not immediately make the ascending air warmer than its surroundings and does not help the air expand (diverge, explode) until it reaches the LFC. So even the conventional wisdom prohibits such an expansion.

    Jim McGinn of Solving Tornadoes:
    Right. It’s rather obvious nonsense.

    Author:
    Furthermore, as one can see in the animation, even above the LFC convergence dominates in most part of the atmospheric column despite, as indicated by the isotherms, the cloudy air is apparently warmer than the surroundings. This shows that the low pressure caused by condensation spreads upwards up to a few kilometers in the atmosphere, see Makarieva et al. (2013), Fig. 1c.

    Jim McGinn of Solving Tornadoes:
    You can’t see low pressure nor can you see what is causing it. So the animation doesn’t show low pressure spreading upwards, or anthing like that.

    Author:
    We conclude that without a somewhat deeper quantitative understanding of the dynamic processes accompanying condensation it is not possible to meaningfully interpret even the very common every-day observations like those of cloud formation.

    Jim McGinn of Solving Tornadoes:
    Well, I agree. It is missing elements to the explanation that are essential. Electro-static force is one of the elements missing from the explanation. Another problem is the inability to recognize that condensation involves liquid to liquid, not gas to liquid. But an even greater shortcoming to the explanation involve the origins of low pressure in the atmosphere. It does not emerge locally:

    Jim McGinn of Solving Tornadoes:
    Many have assumed that the reason moist air is associated with atmospheric instability (low pressure energy) is because moist air convects through dry air. This is false. The reason moist air is associated with instability is because vortices bring low pressure energy with them as they grown down from the jet stream and moisture is the resource that they grow into to make the plasma that allows vortices to grow. Many have assumed that the reason moist air is associated with atmospheric instability (low pressure energy) is because moist air convects through dry air. This is false. The reason moist air is associated with instability is because vortices bring energy with them as they grown down from the jet stream and moisture is the resource that they grow into to make the plasma that allows vortices to grow.

    The Fourth Phase of Water:
    http://wp.me/p4JijN-5A

  9. solvingtornadoes

    2s3c:
    Our main theoretical argument (supported by observations) is that condensation determines the rate at which wind energy is generated.

    Jim McGinn of Solving Tornadoes:
    I think for your theoretical model to be accepted it would have to explain all winds, including the 300 mile an hour winds of the jet streams. And I don’t think you will be able to achieve that. So I would suggest that you abandon this theory and instead look for a theory that can explain the jet streams, then extrapolate details (local winds) from there.

    Where Do Winds Come From:
    http://wp.me/p4JijN-45v

  10. Dr. Makarieva,
    Posted this on Tallblokes thread on your Hurricane paper.
    Has anyone at this talkshop actually considered then actual significance of Dr. Anastassia Makarieva’s previous work on the effects of atmospheric WV condensation? Just to give a picture:
    Near the surface 100 gm of atmosphere would occupy approximately 80 litres of volume, say (20cm)^3. 20cm x 20cm x 20cm. Perhaps this volume has 1 gm of WV in it. Easy to do at 20 Celsius. Let’s take that temperature down to 0 Celsius. and the WV turns to airborne condensate, but does not precipitate (same 100gm). Look at what must happen to that 80 litres (20×20 x20) cm cube. The WV contracts by 1600. The atmosphere contracts by a factor of 16 to a volume of 5 litres or (8x8x8) cm cube.
    This of course cannot happen in an atmosphere of self buoyant and constant pressure (at that altitude). But where did that extra 75 litres of atmosphere originate? What if that condensing cloud were a cubic km (1km^3). Where did that other 0.9375km^3 atmosphere come from? This is unbelievable! Why has meteorology never figured out where winds (come from)/(go to)? 😦
    All the best! -will-

  11. Hi, all. I try to visualize stuff because most of us cannot do the math. The biggest problem for the meteorologists that oppose the theory is that condensation releases a lot of energy. (They insist on calling it heat). Where does the energy go? But if we look at the cloud as a 2 phase fluid flow air pump we can get an answer. Cloud droplets are falling down. This means that if the cloud stays at the same level air must be rising (seeping up) through the cloud. Imagine an airship. It is HUGE (probably an alien invasion force). It is shaped like a big doughnut with a big hole in the middle. In the middle hole there is a propeller. Now imagine a fleet of those airships and they are parked over the amazon rainforest. They are designed to float at 10,000 ft. and the fleet is just sitting there. Orders come in from the alien high command. The fleet must now fly at 5000 ft. So what happens? They all turn on their propellers at once and the doughnut fleet descends to 5000 ft. Then they slow down the propellers to stay there. Now what is happening? The fleet propellers are sucking in air from below and sending it up through the doughnuts! Isn’t this the same thing as what happens in cumulus clouds? Especially in thunder clouds there is a central chimney of fast moving air. So lets think of the clouds as fleets of doughnut shaped alien spaceships. They are definitely causing a low pressure zone! As they pump air up into the sky trying to keep within the zone where water vapor can exist in the atmosphere.
    Brian

  12. Will Janoschka | September 9, 2015 at 10:35 am | Reply

    Dr. Makarieva,
    And all others, Please disregard the 9 Sept post!
    I have no idea where my head went! I was sharing latent hear release with the continuum for a 23 Celsius overall increase in temperature, and got carried away. The 1% by weight WV only shrinks the volume by 1.3% not a factor of 16. Sorry! Way different than WV being the ‘only’ gas as in steam engines. Atmospheres are hard enough to describe, let alone understand.
    All the best! -will-

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