Tag Archives: condensation

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.

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Why so many?

This post is about our work “The key physical parameters governing frictional dissipation in a precipitating atmosphere” (Makarieva, Gorshkov, Nefiodov, Sheil, Nobre, Bunyard, Li). This paper was submitted to the Journal of the Atmospheric Sciences on August 18, 2012. The topic of this paper relates directly to what is currently discussed in the mainstream meteorology. We outlined this in the accompanying cover letter:

The general topic has generated recent interest and will interest your readers. In this paper we clarify and solve a number of challenges in estimating the power density of frictional dissipation associated with precipitation. In doing this we have identified and addressed a number of errors and discrepancies in some other recent publications on this topic. This notably includes one in this journal Pauluis, et al. 2000: J. Atmos. Sci., 57, 989-994. (Please note that we have written to two authors to potentially initiate a discussion, Dr. Pauluis and
Dr. Dias, initially concerning discrepancies in their recent paper in Science, but we have not heard a reply to date and we do not feel we should wait).

We had not heard from the Editors until December 19, 2012, when in response to our second query about the paper’s status the Journal responded to the corresponding author (the emphasis is ours):

Dear Dr. Sheil,
We had a hard time finding a 2nd reviewer for this paper.  Over 20 invites went out but finally we found one.  The 2nd review is not due until the first week of January.  Assuming all goes as it should, you should receive an initial decision shortly into the new year.

Best regards,
Ed Asst, JAS

I would not discuss this in public had it not been for the fact that our recent meteorological paper had been under peer-review for over two and a half years. There too the Journal had enormous difficulties in finding the reviewers. (Actually the authors had to do that themselves.) What are the implications of this situation?

UPDATE 18-January-2013

CORRECTIONS AND CLARIFICATIONS, Science, vol. 339, p. 271:

Reports: “Satellite estimates of precipitation-induced dissipation in the atmosphere,” by O. Pauluis and J. Dias (24 February 2012, p. 953). The authors inadvertently used a “rectangular” method for the integration rather a “trapezoidal” method. This led to an overestimation of the integral and the dissipation rate by about 20%. In the published paper, the dissipation rate is said to be about 1.8 W/m2. The new calculations yield 1.5 W/m2. The corrected Figs. 1 and 3 are shown here (right). The authors thank A. Makarieva, V. Gorshkov, A. Nefiodov, D. Sheil, A. Nobre, P. Bunyard, and B.-L. Li for bringing this problem to their attention.

Does biotic pump work on a small scale?

“Biotic pump theory explains the role of forests in atmospheric circulation on a planetary scale. However, if it is a major mechanism behind the water cycle it should also be applicable on a smaller scale (a watershed for example) influencing creation of a microclimate and a pattern of water distribution. Do you have any data to suggest smaller scale biotic pump action? After all Nature works on principle of fractals and it should be applicable to any scale. This seems to be evident from empirical work of Peter Andrews on restoration projects in Australia. His Natural Sequence Farming principles of landscape management described in his books “On the Brink” and “Back from the Brink” I think confirms it.”
Answered 11 December 2012.
Question author: Sergei Karabut.
Asked 20 November 2012.

The biotic pump mechanism transports atmospheric moisture from the ocean to the forest-covered continent. This large-scale process is based on cumulative performance of many similar small-scale functional units in the forest. We termed these units “local ecological communities”. A local ecological community in the forest ecosystem is a tree with all the spatially associated local biota (including soil) — including bacteria, fungi, small invertebrates etc. Please see Section 4.3 of Gorshkov et al. (2004) for a discussion.

In simple words, the biotic pump emerges as a sum of reactions of individual trees and the associated organisms. Information about how to perform the needed reactions, like, for example, production of condensation nuclei by tree-dwelling fungi, is written in the genome of forest species. This information appeared in the course of biological evolution. They must therefore impart some noticeable advantage to individual ecological communities on a local scale. (Please see Section 4 “Biological principles of the biotic pump of atmospheric moisture” in Makarieva and Gorshkov (2007) for a more extensive discussion of this topic.)

To evaluate the biotic pump performance of a single tree or a small forested area it is necessary to measure how the local influx of atmospheric moisture has changed upon the tree re-growth. Whether it is measurable depends on the sensitivity of natural selection. If it is higher than the accuracy of our measurements, it will not be possible to detect a small-scale biotic pump. The signal from a small area will be lost in the high fluctuations of the local moisture transport and rainfall processes.

The biotic pump enabled life to colonize land. The first plants capable of running the pump originated at the coastline. This narrow band of plants was obviously unable to draw moisture far inland. However, these plants might have been able to slightly increase local rainfall making the prevailing winds to slightly change their path. For example, the plants could enhance intensity of local condensation and modify local pressure gradients by emitting biogenic condensation nuclei. Gradually spreading inland the plants were bringing moisture with them — by enhancing the atmospheric water vapor flow. Thus, a group of trees planted in the desert may not have any biotic pump potential at all, as it has no link to the oceanic source of moisture.

On the other hand, the biotic pump is based on a large number of evolutionary properties of various species. Among them is the ability of the ecological community to efficiently store moisture in soil, to regulate the vertical temperature gradient under the canopy, to modify aerodynamic roughness of the area etc. These properties profoundly influence the local microclimate and are readily observable on a small scale.

Morning fog

Brief history of the winds paper

The letter below was emailed by A. Makarieva on 31 March 2012 to about 30 recipients.

Dear Science & Environment Thinkers

We are an interdisciplinary team doing environmental science. Recently in a number of papers* we proposed, and substantiated by evidence and theoretical analysis, that condensation of water vapor in the terrestrial atmosphere is a major and previously overlooked driver of winds. This proposition has environmental implications, of which perhaps the most important is the recognition that natural forests, by means of maintaining high rates of water vapor phase transitions over land, drive coast-to-interior atmospheric moisture transport. The potential environmental, economic and social consequences of the on-going large-scale deforestation in the boreal and the equatorial zones are substantially more negative than is widely recognized.

We welcome constructive scientific skepticism. It is right and proper that our work should be examined and questioned. We undertake efforts to make our work available for critique and discussion and we respond to comments and challenges. That is how science should work: a healthy debate is essential. Knowing your interest in this process, the nature of scientific progress, and the implications of our work, we decided to share our recent experiences with you.

On April 2nd 2010, we submitted our work “Where do winds come from? A new theory of how water vapor condensation influences atmospheric pressure and dynamics” to an open access journal Atmospheric Chemistry and Physics (Discussions). In that paper we provided an overview of the physical principles of condensation-induced atmospheric dynamics and its relevance to the meteorological theory. Though almost two years has now passed no decision has yet been taken by the Editors.

Upon submission, it took four months to assign a handling editor for our manuscript. During the next six months it proved impossible to find two referees for our work. While it is well-known that approximately half of all scientists are shy to post their reviews openly, in our case the proportion was noticeably different: among at least ten referees nominated only one accepted (it also should be noted that the reviews for ACPD, while open for the public, can be published anonymously). The first referee advised that the paper could be published upon a revision.

We then undertook efforts to assist the journal in finding the second referee. We asked colleagues and posted an appeal on a highly visible Internet resource. A leading NOAA hydrologist circulated our work among many of his colleagues. One indicated willingness to be a referee and indicated that he had objections to our work. We suggested that the Editor should invite the referee — recognizing that we would be able to reply and hopefully address the concerns raised (the journal allows authors to respond in detail and to revise the text). After this second more critical review was posted, we replied to the criticisms online (as required) and submitted a revised version of the paper. That process was completed in April 2011. Since then the manuscript has remained with the Editors. This is an extraordinary length of time for a journal that usually takes less than one month to reach a conclusion on a revised manuscript.

We have no doubts that the Journal is doing their best. Editors are unpaid, have other work to attend to, and likely find our paper difficult to deal with. We recognize these difficulties and appreciate their efforts. But what can justify such an extended delay? If our paper has fundamental errors, violating some basic laws of physics, the Editors and reviewers should have been able to recognize them, and the paper could be rejected. The paper has not been rejected implying that such basic errors have not been found. If no errors have been found, what is impeding the editorial decision on a paper that brings new ideas to a highly challenging problem?**

The discussion at the ACPD web site provides a useful overview of many of the misunderstandings we have confronted.

These include:

  • The very limited previous evaluations, either theoretical or empirical, of condensation related atmospheric pressure gradients;
  • The physical pitfalls inherent in the analytical approximations, short-cuts and assumptions commonly used by meteorologists who consider condensation;
  • The key physical differences between the two facets of condensation a) latent heat release and b) changing numbers of gas molecules;
  • Understanding why condensation influences air pressure irrespective of whether the droplets remain suspended in the air column;
  • And understanding why the available numerical models currently relied on (particularly those of hurricanes), despite many opinions to the contrary, do not shed light on condensation physics as they do not embody a coherent physical system (theoretical or otherwise) but mimic reality by tuning key parameters.

Our own view of these issues are summarized in these two comments.

Thank you very much for your attention. We are happy to provide further details if you are interested.

Yours sincerely,

Anastassia Makarieva
Victor Gorshkov
Douglas Sheil
Antonio Nobre
Larry Li

*A complete list of publications on the topic of condensation-induced atmospheric dynamics can be found here: http://www.bioticregulation.ru/pump/pump7.php
In the last two and a half years several papers on condensation-induced atmospheric dynamics and related issues were accepted to publication in the Proceedings of the Royal Society Series A, Physics Letters A, Theoretical and Applied Climatology and the Journal of Experimental and Theoretical Physics.

**Indeed, theory of moist atmospheric processes is a commonly recognized “hole” in climate science.

Condensation Rate: Devil in a Detail

When gas disappears somewhere in the atmosphere, local pressure is lowered and a compensating air inflow from the surrounding areas is initiated. In our paper “Where do winds come from?” (M10) we derive the magnitude of a stationary horizontal pressure gradient \partial p/\partial x that is associated with water vapor condensation — the process by which the vapor gas molecules are packed into a thousand of times smaller liquid volume and thus effectively disappear from the atmosphere.

There has been much critical discussion in the blogosphere and further on the ACPD web site of our Equation 34 for condensation rate S that is key to the presented derivation. At various times and places, including Section 4.2 of our paper, it was pointed out that if one formulates S in terms of water vapor mixing ratio \gamma_d \equiv N_v/N_d = p_v/p_d one obtains \partial p/\partial x = 0. If one instead uses the relative partial pressure of water vapor, \gamma \equiv N_v/N = p_v/p, a horizontal pressure gradient is obtained that appears to be so significant as to substantiate the claim for a dominant role in the whole planetary dynamics. (Here N_v, N_d, N = N_v + N_d, p_v, p_d, p = p_v + p_d are molar density and pressure of water vapor, dry air and air as a whole, respectively.)

A typical value of water vapor partial pressure p_v in the lower atmosphere is around 1-3 per cent. This means that the mixing ratio and relative partial pressure \gamma_d and \gamma differ very insignificantly. Reckoning up the preceding criticisms, our second referee Dr. Isaac Held referred to this difference as to “a detail”. It is the purpose of this note to show that the \gamma/\gamma_d dichotomy is precisely the devilish detail that, as it increasingly appears, is responsible for the fact that the condensation-induced dynamics has not received the attention it deserves.

Consider the stationary continuity (mass conservation) equations written for dry air and water vapor (Eqs. 32 and 33 in M10): \nabla N_d \mathbf{v} = 0,      \nabla N_v \mathbf{v} = S.      These equations only tell us that the dry air mass is conserved, while the vapor mass may be conserved or it may be not: there can be a local source or sink of vapor S. Irrespective of the existence/nature/magnitude of the vapor sink/source S, the above equations can be combined with use of elementary algebra such that their left-hand parts take various forms. In his review Dr. Held chose N_d \mathbf{v} \nabla (N_v/N_d) = S, which is equivalent to

\mathbf{v} (\nabla N_v - \gamma_d \nabla N_d) = S.    [1]

In the two-dimensional circulation considered in M10 the velocity vector is the sum of the horizontal and vertical components, \mathbf{v} = \mathbf{u} + \mathbf{w}. We also consider a horizontally uniform surface temperature, which dictates a constant saturated pressure of water vapor, such that \mathbf{u} \nabla N_v = 0.     [2] (If water vapor is not saturated, this assumption corresponds to a horizontally uniform surface temperature and constant relative humidity.) Combining [1] and [2] we obtain

\displaystyle \mathbf{u} \nabla N_d = \left(S - S_d\right)\frac{1}{\gamma_d},     where S_d \equiv \mathbf{w} \left(\nabla N_v - \gamma_d \nabla N_d \right).    [3]

Equation [3] has two important implications for any given horizontal velocity u \ne 0. First, it shows that when S = S_d, the horizontal density gradient \partial N/\partial x = \partial N/\partial x = 0. Second, it shows that if S and S_d differ by a small relative magnitude of the order of \gamma_d \ll 1, this magnitude is multiplied by a large relative magnitude 1/\gamma_d \gg 1 to determine the horizontal density gradient \partial N/\partial x.

We should emphasize that the two above conclusions are unrelated to any ideas about what the condensation rate could look like. The value of S in [3] is unknown. Equation [3] shows that any minor difference of the order of \gamma_d in the theoretical formulation of S — whatever the latter might be — is not a detail but is the zeroth order term in determining the horizontal density and pressure gradients associated with vapor condensation.