[FRIAM] pseudo-adiabatic process

[Nicholas Thompson]

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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