Adiabatic Process
Sunday, June 28, 2026 11:13 PM
A lapse rate is the rate of temp decrease w/ altitude (not latitude). Within the troposphere temps
normally decrease w/ height aka the normal or average lapse rate. The Average Lapse Rate (ALR)
means temps drop at an average of 3.6 degrees F every 1000 ft in altitude; The idea is that as air rises, it
expands & molecules have more space w/ less pressure higher in the atmosphere, causing the cooling
of air. Warming occurs as air descends b/c it compresses, air molecules collide & rub together, more
constricted near the earth's surface
I.E. If you pump up a bike tire, the air being squeezed into the tube warms b/c it’s compressed into
the tube. If you feel the valve, it warms up, as air is released, air coming out feels cool b/c the air
expands & cools. BUT, all of the atmosphere doesn't just sit still. Imagine a bubble of air, about the
size of a room that can rise through the atmosphere w/o exchanging energy w/ the surrounding
air. This is why it's called "adiabatic."
- "Diabatic" means occurring w/ an exchange of heat
- "Adiabatic" means occurring w/o a loss or gain of heat
○ The process happens so quickly the bubble of air doesn't mix w/ the surrounding air! This is the
process by which ALL clouds are formed. There are 2 different rates of cooling for a rising parcel
of air
1. The Dry Adiabatic Lapse Rate:
i. When a bubble of air forms in the surrounding air, it rises & cools at a rate called the “Dry
Adiabatic Lapse Rate” (DALR)
• This lapse rate of a rising parcel of air, as air rises, its pressure decreases (higher in
elevation) expands & cools at a rate of about 5.5 degrees F every 1000 ft.
• This rate of cooling is called “dry adiabatic lapse rate” (dry b/c the air is not saturated
& has not reached its dew point.) If the air mass rises high enough, it cools to the dew
point (the temp of saturation), then condensation begins & clouds form. The altitude
where this occurs is the “Lifting Condensation Level” & in the sky would be marked by
the base of the clouds. The temp of the LCL is the dew point temperature for that
atmosphere & temp depends on the saturation of the air
2. The Saturated Adiabatic Lapse Rate:
- 3.3 F/1000'. Once condensation begins, energy stored in water vapor in the air (aka latent
heat) is released, it slows the rate of cooling of this rising parcel of air. The air now cools at
the Saturated Adiabatic Lapse Rate (SALR). This is a rate of cooling that varies, but averages
at about 3.3F every 1000 ft. The more humidity in the air, the more latent heat is released &
the slower the rate of cooling. It’s a weaker rate of cooling than dry adiabatic lapse rate,
which is 5.5F/1000ft.
3. Dry Adiabatic Lapse Rate: 5.5 F/1000'. Adiabatic warming occurs when air descends, it increases
in temperature & its ability to hold moisture, so the air becomes unsaturated & warms at the Dry
Adiabatic Lapse Rate (5.5F/1000ft).
Clouds
- Many clouds have definite shapes that look solid, they are parcels of water droplets & ice crystals
floating in the air (too light to fall to the surface). Though their make-up is clear, clouds appear
white b/c liquid water droplets & ice scatter sunlight evenly, giving a white color. If they appear
gray/black, it is b/c they are so thick they block out sunlight
○ All clouds form from rising air, what varies cloud to cloud is what causes air to rise. B/c air
cools as it rises, it becomes less able to hold water vapor, it reaches its dew point & condenses
to form tiny droplets of water
- Each droplet must form on a nucleus of solid matter; they act as seeds that water condenses to
form droplets. The cloud condensation nuclei (CCN) are tiny particles of smoke, dust, pollen, sand
grains & salt crystals. They are extremely small, about .001mm & smaller! The bigger the
condensation nucleus, the bigger the droplet. Over land there are usually 5-6 million CCN per liter
of air, over the oceans there are 1 million/L of air.
- Water vapor droplets condensate on the CCN, stick together & grow in size. In order to fall, millions
of droplets are needed. They must reach a size of 1/10-1/4 inch to be heavy enough to fall to the
surface. So, most clouds don’t produce rain b/c the water vapor droplets arent large enough. We
usually think of rainwater as pure, but each cloud droplet has a tiny impurity at its center, the
condensation nucleus.
Temperature Inversions
- A temp inversion is the exception to normal lapse rate. Instead of decreasing in temp as you go
higher in elevation, it increase as you go higher in elevation. In temp inversion, a gain in altitude
will result in a gain in temp! There are surface inversions & upper air inversions
- There are 3 Surface Inversions
1. A radiational inversion happens when land emits longwave radiation as it cools on a long, winter
night. Longwave radiation rises & warms the air, while the air near the surface cools
2. An advectional inversion happens when cool ocean air blows in toward the coast in a sea
breeze. The warm land cools & the warm air over the land rises
3. Cold-air drainage inversion happens when cold, heavy air slides down a valley slope at night &
lighter, warm air at the bottom of the valley (from the day) is pushed upward. The result is cold
air at the surface and warm air (like a ceiling) above it
Upper Air Inversion
1) An upper air inversion is associated w/ high pressure above earth's surface. Air sinks & warms, this
brings warm air from above, down toward a cooler surface. This may trap pollutants below the warm
air
○ Remember along the equator, there is low pressure. Air is warm so it rises above the equator
& moves poleward (30 degrees latitude), until it gets cold & heavy it sinks into regions of
subtropical high pressure; this is the Hadley Cell.
○ This mass of descending air in the Pacific between Hawaii & Cali is known as the Hawaiian High. It
shifts N during the summer when direct rays from the sun is at its northernmost position (23.5
N). It shifts southward, over Hawaii during the winter, when the sun's direct ray migrates south
- This high pressure cell sits off the coast during the summer & dominates California's weather
hovering over the area for months when the sun is highest & strongest. The Hawaiian High sends
air spinning downward, creating warm, clear weather. It’s so dominant it infrequently allows any
low pressure systems to migrate where it sits; during the summer, SoCal is protected from storms.
This is why we have such dry summers each year
Sunday, June 28, 2026 11:13 PM
A lapse rate is the rate of temp decrease w/ altitude (not latitude). Within the troposphere temps
normally decrease w/ height aka the normal or average lapse rate. The Average Lapse Rate (ALR)
means temps drop at an average of 3.6 degrees F every 1000 ft in altitude; The idea is that as air rises, it
expands & molecules have more space w/ less pressure higher in the atmosphere, causing the cooling
of air. Warming occurs as air descends b/c it compresses, air molecules collide & rub together, more
constricted near the earth's surface
I.E. If you pump up a bike tire, the air being squeezed into the tube warms b/c it’s compressed into
the tube. If you feel the valve, it warms up, as air is released, air coming out feels cool b/c the air
expands & cools. BUT, all of the atmosphere doesn't just sit still. Imagine a bubble of air, about the
size of a room that can rise through the atmosphere w/o exchanging energy w/ the surrounding
air. This is why it's called "adiabatic."
- "Diabatic" means occurring w/ an exchange of heat
- "Adiabatic" means occurring w/o a loss or gain of heat
○ The process happens so quickly the bubble of air doesn't mix w/ the surrounding air! This is the
process by which ALL clouds are formed. There are 2 different rates of cooling for a rising parcel
of air
1. The Dry Adiabatic Lapse Rate:
i. When a bubble of air forms in the surrounding air, it rises & cools at a rate called the “Dry
Adiabatic Lapse Rate” (DALR)
• This lapse rate of a rising parcel of air, as air rises, its pressure decreases (higher in
elevation) expands & cools at a rate of about 5.5 degrees F every 1000 ft.
• This rate of cooling is called “dry adiabatic lapse rate” (dry b/c the air is not saturated
& has not reached its dew point.) If the air mass rises high enough, it cools to the dew
point (the temp of saturation), then condensation begins & clouds form. The altitude
where this occurs is the “Lifting Condensation Level” & in the sky would be marked by
the base of the clouds. The temp of the LCL is the dew point temperature for that
atmosphere & temp depends on the saturation of the air
2. The Saturated Adiabatic Lapse Rate:
- 3.3 F/1000'. Once condensation begins, energy stored in water vapor in the air (aka latent
heat) is released, it slows the rate of cooling of this rising parcel of air. The air now cools at
the Saturated Adiabatic Lapse Rate (SALR). This is a rate of cooling that varies, but averages
at about 3.3F every 1000 ft. The more humidity in the air, the more latent heat is released &
the slower the rate of cooling. It’s a weaker rate of cooling than dry adiabatic lapse rate,
which is 5.5F/1000ft.
3. Dry Adiabatic Lapse Rate: 5.5 F/1000'. Adiabatic warming occurs when air descends, it increases
in temperature & its ability to hold moisture, so the air becomes unsaturated & warms at the Dry
Adiabatic Lapse Rate (5.5F/1000ft).
Clouds
- Many clouds have definite shapes that look solid, they are parcels of water droplets & ice crystals
floating in the air (too light to fall to the surface). Though their make-up is clear, clouds appear
white b/c liquid water droplets & ice scatter sunlight evenly, giving a white color. If they appear
gray/black, it is b/c they are so thick they block out sunlight
○ All clouds form from rising air, what varies cloud to cloud is what causes air to rise. B/c air
cools as it rises, it becomes less able to hold water vapor, it reaches its dew point & condenses
to form tiny droplets of water
- Each droplet must form on a nucleus of solid matter; they act as seeds that water condenses to
form droplets. The cloud condensation nuclei (CCN) are tiny particles of smoke, dust, pollen, sand
grains & salt crystals. They are extremely small, about .001mm & smaller! The bigger the
condensation nucleus, the bigger the droplet. Over land there are usually 5-6 million CCN per liter
of air, over the oceans there are 1 million/L of air.
- Water vapor droplets condensate on the CCN, stick together & grow in size. In order to fall, millions
of droplets are needed. They must reach a size of 1/10-1/4 inch to be heavy enough to fall to the
surface. So, most clouds don’t produce rain b/c the water vapor droplets arent large enough. We
usually think of rainwater as pure, but each cloud droplet has a tiny impurity at its center, the
condensation nucleus.
Temperature Inversions
- A temp inversion is the exception to normal lapse rate. Instead of decreasing in temp as you go
higher in elevation, it increase as you go higher in elevation. In temp inversion, a gain in altitude
will result in a gain in temp! There are surface inversions & upper air inversions
- There are 3 Surface Inversions
1. A radiational inversion happens when land emits longwave radiation as it cools on a long, winter
night. Longwave radiation rises & warms the air, while the air near the surface cools
2. An advectional inversion happens when cool ocean air blows in toward the coast in a sea
breeze. The warm land cools & the warm air over the land rises
3. Cold-air drainage inversion happens when cold, heavy air slides down a valley slope at night &
lighter, warm air at the bottom of the valley (from the day) is pushed upward. The result is cold
air at the surface and warm air (like a ceiling) above it
Upper Air Inversion
1) An upper air inversion is associated w/ high pressure above earth's surface. Air sinks & warms, this
brings warm air from above, down toward a cooler surface. This may trap pollutants below the warm
air
○ Remember along the equator, there is low pressure. Air is warm so it rises above the equator
& moves poleward (30 degrees latitude), until it gets cold & heavy it sinks into regions of
subtropical high pressure; this is the Hadley Cell.
○ This mass of descending air in the Pacific between Hawaii & Cali is known as the Hawaiian High. It
shifts N during the summer when direct rays from the sun is at its northernmost position (23.5
N). It shifts southward, over Hawaii during the winter, when the sun's direct ray migrates south
- This high pressure cell sits off the coast during the summer & dominates California's weather
hovering over the area for months when the sun is highest & strongest. The Hawaiian High sends
air spinning downward, creating warm, clear weather. It’s so dominant it infrequently allows any
low pressure systems to migrate where it sits; during the summer, SoCal is protected from storms.
This is why we have such dry summers each year
