[FRIAM] pseudo-adiabatic process

[Jon Zingale]

I saw this and liked how it echoes with my post. Science is hard.

On Sat, Oct 5, 2024 at 1:00 PM Nicholas Thompson <thompnickson2 at gmail.com>
wrote:

>
> After bullying GeorgeIV for a couple hours,  I got this superb answer out
> of him.
>
> *Summary:*
>
> In *pseudo-adiabatic calculations*, we disregard:
>
>    - *Condensed water retained in the parcel* (assuming it falls out as
>    precipitation),
>    - *Precipitation drag* (the downward resistance of falling
>    precipitation),
>    - *Heat transfer between the parcel and the environment* (except
>    latent heat release).
>
> These variables are considered *trivial* relative to the dominant forces
> in convective storms, especially the *latent heat release* from
> condensation, which drives strong updrafts and is the primary factor
> determining the parcel’s buoyancy.
>
> Does this clarify the role of simplifications in pseudo-adiabatic
> processes? Would you like to go deeper into any specific part of this?
>
> *You said:*
>
> Ok. Now this all makes sense. But compare your most recent answer to ones
> you made earlier which seemed to suggest that the latent heat released by
> condensation (in addition to the condensed water) is lost to the parcel. No
> heat is lost to the parcel, only mass, and that mass is trivial by
> comparision with the total mass of the parcel since even most air contains
> relatively little mass of water.
>
> *ChatGPT said:*
>
> ChatGPT
>
> You're absolutely right, and I can see how my earlier answers might have
> created some confusion. Let's clear that up, focusing on the distinction
> between *latent heat* and *condensate (water)* in pseudo-adiabatic
> processes.
>
> *Correct Understanding: No Heat is Lost from the Parcel, Only Mass*
>
> In a *pseudo-adiabatic process*, the *latent heat released by
> condensation* is *not lost* from the air parcel. It remains in the parcel
> and directly contributes to:
>
>    - *Warming the parcel*: The *latent heat* released when water vapor
>    condenses into liquid (or ice) *warms* the parcel, slowing the rate at
>    which it cools as it rises. This additional warmth keeps the parcel *more
>    buoyant* compared to its surroundings.
>
> What *is lost*, however, is the *condensate*:
>
>    - *Mass loss*: The condensed water (in liquid or ice form) is assumed
>    to *precipitate out* of the parcel. This *reduces the total mass* of
>    the parcel but has a relatively small impact on the overall mass, since
>    even in moist air, the water vapor content is small compared to the air’s
>    mass. As a result, the *mass loss from precipitation* is considered
>    *trivial* relative to the total parcel mass, but it is a
>    simplification made for the sake of easier calculation.
>
> *Earlier Miscommunication: What Happens to Latent Heat?*
>
> In my earlier explanation, I might have implied that both the *condensate*
> and the *latent heat* are somehow lost from the parcel in the
> pseudo-adiabatic process. That’s not the case. The *latent heat* stays
> with the parcel—it’s only the *water droplets (or ice crystals)* that are
> assumed to fall out.
>
> *Why This Matters:*
>
>    1. *Buoyancy*: The *latent heat* remains inside the parcel, increasing
>    its *temperature* and *buoyancy* as it rises. This helps the parcel
>    remain *warmer* than the surrounding air, driving the upward motion.
>    2. *Mass Loss is Small*: As you correctly pointed out, the *mass of
>    water vapor* in a parcel is generally small relative to the *total
>    mass* of the air parcel (which consists mostly of nitrogen and
>    oxygen). Even in very humid conditions, water vapor usually makes up only a
>    few percent of the total mass of the air. So, the *mass lost to
>    precipitation* is *trivial* when compared to the overall mass of the
>    parcel.
>
> *Summary of Correct Picture:*
>
>    - *Latent heat*: *Remains within the parcel*, keeping it warm and
>    buoyant.
>    - *Condensate*: Assumed to fall out of the parcel, leading to *mass
>    loss*.
>    - *Mass loss is small*: Even though the mass of the parcel decreases
>    due to precipitation, it is considered *trivial* relative to the total
>    mass of the parcel.
>
> In the *pseudo-adiabatic process*, the *main focus is on the latent heat*
> retained by the parcel, as this is what maintains buoyancy. The loss of
> mass due to precipitation is simplified for ease of calculation but is
> relatively minor in the big picture of atmospheric processes.
> --
> Nicholas S. Thompson
> Emeritus Professor of Psychology and Ethology
> Clark University
> nthompson at clarku.edu
> https://wordpress.clarku.edu/nthompson
>
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