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A short class with Sarah and her students. The other ways are under More.
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Today, let’s talk about temperature profiles as they relate to height. Can anyone tell me what happens to temperature as we go higher in the atmosphere?
I think the temperature decreases as we go up, right?
Exactly! This phenomenon is due to the environmental lapse rate. Can someone explain why the ground level is usually warmer during the day?
Is it because the ground absorbs heat from the sun faster than the air does?
Correct again! The ground heats up quickly, affecting how the air above it behaves. This leads to a positive temperature gradient. Remember the acronym 'GREAT' to recall Ground heats up rapidly, leading to Environmental warming above.
What happens when the sun sets?
Good question! At night, the ground cools faster than the air, causing the temperature gradient to change. This is natural behavior we observe in various weather patterns.
Let’s summarize: during the day, the ground gets hot, creating rising air, while at night, the cooling ground impacts that dynamic. Are there any questions?
Now let’s delve into adiabatic lapse rates. Who can tell me what happens to an air parcel as it rises?
I think it expands and cools down, but I'm not sure about the rates.
Great point! This cooling rate is referred to as the dry adiabatic lapse rate, approximately -9.8°C per kilometer. Imagine a balloon being let go; it expands as it rises, and similarly, an air parcel's temperature drops under less pressure.
So is there any heat exchanged during this process?
That's right—it's assumed there is no heat transfer, hence 'adiabatic.' Think of it as the air parcel maintaining energy balance while moving.
What does this mean for pollutants?
Excellent follow-up! Pollutants can disperse depending on the stability of the atmosphere. Under unstable conditions, they spread out; under stable ones, they can stay trapped. Let’s summarize this session: the dry adiabatic lapse rate governs how rising air parcels cool, crucial for understanding how pollutants behave in the air.
We’ve talked about adiabatic principles; now let’s dive into atmospheric stability. Who remembers the difference between stable and unstable conditions?
In stable conditions, temperature increases with height, right?
Exactly! And unstable means the reverse, where pollutants can disperse easily. Can you remember a situation when we've encountered fog?
Yes! Fog usually happens in the evening when the temperature drops quickly and the air cools faster than the ground, trapping moisture.
Excellent observation! This temperature inversion can lead to an accumulation of pollutants. Remember the mnemonic 'FAT' for Fog Accumulates Trapped pollutants, indicating how fog forms in stable conditions.
What’s the mean mixing height then?
Another great question! The mean mixing height is where adiabatic and environmental lapse rates intersect, crucial for predicting pollutant dispersion. In summary, stable conditions trap pollutants, while unstable conditions promote their spread. Now let's see if you can recall these terms!
The cooling of an air parcel as it rises and expands without heat exchange.
How temperature changes with increasing altitude in the atmosphere.
Refers to whether an air mass will rise or sink, affecting pollutant distribution.
A reversal of the normal temperature trend in the atmosphere that can trap pollutants.
The height at which pollutants mix in the atmosphere, important for dispersion models.
When day turns to night, ground cools with fright; fog forms indeed, trapping air, that's tight.
Imagine a rising balloon on a sunny day. As it climbs, the air gets colder; when it stops, it stays there like trapped air at night. This represents how pollutants may behave in stable conditions.
Remember 'STAB' for Stability Traps Air pollutants Below, a reminder of how stability affects pollution.
GREAT: Ground heats Rapidly, Environmental warming Above, helps recall the daytime temperature gradient.
Term
Environmental Lapse Rate
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Term
Adiabatic Expansion
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Term
Temperature Inversion
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Term
Buoyancy
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Term
Mean Mixing Height
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The rate at which the temperature decreases with an increase in altitude.
The rate at which an air parcel cools as it rises in the atmosphere without heat exchange.
A condition where the temperature increases with altitude instead of decreasing.
The ability of an object to float in a fluid, which in this context relates to the tendency of warm air to rise.
The average height at which pollutants can mix in the atmosphere before stability affects dispersion.
This section discusses the principles of adiabatic expansion and cooling in the context of atmospheric stability and pollutant transport.
The section elaborates on how temperature profiles change with height due to atmospheric conditions, the process of adiabatic expansion, and the significance of stability in the atmosphere. Key concepts such as environmental lapse rates and the behavior of pollutants under different atmospheric conditions are explored.
In this section, we investigate the concept of adiabatic expansion and cooling, which is essential in understanding atmospheric behavior and pollutant transport. The temperature profile of the atmosphere changes with height, primarily observed in a vertical convection driven by thermal forces leading to temperature differences. When discussing the temperature profile, we examine how the ground heats the air above it, especially during the day, creating a positive temperature gradient. As evening falls, this dynamic shifts with the ground cooling faster than the air, leading to phenomena like fog formation.
The concept of environmental lapse rate, which refers to the rate at which temperature decreases with an increase in height, is introduced. The adiabatic lapse rate, on the other hand, describes how a parcel of air cools as it rises in the atmosphere, assuming no heat exchange with its surroundings. When an air parcel rises, it expands and cools, aligning with the dry adiabatic lapse rate, typically at about -9.8°C per kilometer.
The section emphasizes atmospheric stability and how it affects air parcel behavior: unstable, stable, or neutral conditions determine whether pollutants disperse or accumulate. An unstable atmosphere encourages the dilution of pollutants, while a stable environment can trap them, elevating concentrations. The mean mixing height is discussed as a crucial factor in atmospheric dispersion models, informing about pollutant transport under varying conditions.