REMINDERS: Problem Set 2: Due Monday (Feb 3)

REMINDERS: Problem Set 2: Due Monday (Feb 3) Midterm 1: Next Wednesday, Feb 5 - Lecture material covering chapters 1-5 - Multiple Choice, Short Answers, Definitions - Practice midterm will be on course website - Closed-book, no notes, no calculator. - No scantron or blue book necessary UPCOMING REVIEW SESSION: - Tuesday, Feb 4, 6:30-8:00pm in HSS 1330

Clarifications: 1) I noted on Wednesday, that as a whole, clouds cool the surface. But earlier I said that at night, the presence of a cloud will warm the surface.???? Clouds have 2 effects on surface temp: a) reflect solar radiation => cools surface b) emit infrared radiation => warms surface AT NIGHT, process (a) is gone, so only left with (b)

Clarifications: 2) tropopause Since in tropopause warm air beneath cold air => wouldn't that mean tropopause is always unstable? No, because as we will see, when air rises it cools. The atmosphere only unstable if rising air is warmer than surrounding air.

So, on this question I should have used the wording... Which of these situations is more likely to be unstable? (A) cold air warm air (B) warm air cold air

Stability

Is the Atmosphere Stable or Unstable? Question we ask to see if air will rise. If air rises, clouds may form. Stable: Air parcel pushed up a little, but returns to original level Unstable: Air parcel pushed up a little, and continues to rise.

Also must consider that as air moves up (or down) in the atmosphere, it's temperature will change. ==> changes in pressure cause expansion or compression

Clicker Question Set Clicker Frequency to AD If no condensation takes place, rising air will cool at a rate of approximately 10 C/km. What would happen IF condensation was taking place within the rising air parcel? (A) the air parcel would cool at a faster rate (B) the air parcel would cool at a slower rate (or may even warm) (C) would have no impact on cooling rate

Clicker Question Set Clicker Frequency to AD An air parcel at the surface has a temperature of 30 C and a dew point temperature of 20 C. Assume dry adiabatic lapse rate = 10 C/km. T = 30 C, T DEW = 20 C, Γ DRY = 10 C/km Assuming T DEW does not change, at what height will condensation start forming as the air rises? (A) 0.5 km (B) 1.0 km (C) 1.5 km (D) 2.0 km

Clicker Question Set Clicker Frequency to AD Continuation of last question: Condensation begins at 1 km (this is cloud base) where T=20 C. The air continues to rise to 2 km (this is cloud top). What is the air temperature at 2 km? Γ D = 10 C/km, Γ M = 6 C/km (A) 10 C (B) 14 C (C) 20 C (D) 30 C

- Rising unsaturated air cools at Dry Adiabatic Lapse Rate Γ D =10 C/km - Rising saturated air cools at Moist Adiabatic Lapse Rate Γ M =6 C/km - Sinking air warms at Dry Adiabatic Lapse Rate Γ D =10 C/km Stability Test Case 1 Γ E =4 C/km Γ E =4 C/km Environment Rising Air (dry) 1000 m 26 C 20 C Parcel colder than surroundings cold air more dense than warm air parcel sinks back down Stable (returns to starting point) 0 m 30 C 30 C

- Rising unsaturated air cools at Dry Adiabatic Lapse Rate Γ D =10 C/km - Rising saturated air cools at Moist Adiabatic Lapse Rate Γ M =6 C/km - Sinking air warms at Dry Adiabatic Lapse Rate Γ D =10 C/km Stability Test Case 2 (Γ E =14 C/km) Γ E =14 C/km Environment Rising Air (dry) 1000 m 16 C 20 C Parcel warmer than surroundings warm air less dense than cold air parcel continues to rise Unstable 0 m 30 C 30 C

- Rising unsaturated air cools at Dry Adiabatic Lapse Rate Γ D =10 C/km - Rising saturated air cools at Moist Adiabatic Lapse Rate Γ M =6 C/km - Sinking air warms at Dry Adiabatic Lapse Rate Γ D =10 C/km Stability Test Case 2A (Γ E =14 C/km) Γ E =14 C/km Environment Rising Air (moist, RH=100%) 1000 m 16 C 24 C Parcel warmer than surroundings warm air less dense than cold air parcel continues to rise Unstable 0 m 30 C 30 C If parcel was saturated (RH=100%) parcel temp = 24 C at 1000 m parcel even warmer more unstable more moisture = more unstable

Height Γ M (6 C/km) Γ DRY (10 C/km) Temperature

Height Γ DRY (10 C/km) Γ M (6 C/km) Γ ENV (4 C/km) Temperature

Height Γ DRY (10 C/km) Γ M (6 C/km) Γ ENV (4 C/km) T D < T E T M < T E h T D T M T E Temperature

Height Γ DRY (10 C/km) Γ M (6 C/km) Γ ENV (4 C/km) T D < T E T M < T E h => STABLE T D T M T E Temperature

Height Γ M (6 C/km) Γ DRY (10 C/km) Stable Temperature

Stable Atmosphere: Often occurs during clear night as - surface cools a lot - air above cools a little (air is selective absorber) temperature profile at sunset

Stable Atmosphere: Often occurs during clear night as - surface cools a lot - air above cools a little (air is selective absorber) little cooling of air above temperature profile at sunset much cooling at surface

Stable Atmosphere: Clouds that develop in stable atmosphere tend to be STRATUS clouds

Height Γ M (6 C/km) Γ DRY (10 C/km) Stable Γ ENV (14 C/km) Temperature

Height Γ M (6 C/km) Γ DRY (10 C/km) Stable h Γ ENV (14 C/km) T D > T E T M > T E T E T D T M Temperature

=> UNSTABLE Height Γ M (6 C/km) Γ DRY (10 C/km) Stable h Γ ENV (14 C/km) T D > T E T M > T E T E T D T M Temperature

Height Γ M (6 C/km) Γ DRY (10 C/km) Stable Unstable Temperature

Unstable Atmosphere: Often occurs during strong daytime heating - surface warms fast - air above warms slow (air is selective absorber)

Unstable Atmosphere: - Air forced upwards will continue to rise - As air rises, Temperature decreases and RH increases if RH=100% => condensation and cloud formation => latent heat released => possibility of storm formation

Clicker Question Set Frequency to "AD" Which type of clouds are more likely to form in unstable conditions? (A) stratus clouds (layered) (B) cumulus clouds (vertically developed) (C) fog (cloud in contact with surface)

Unstable Atmosphere: Clouds that develop in unstable atmosphere tend to be CUMULUS clouds

Height Γ ENV (8 C/km) Γ M (6 C/km) Γ DRY (10 C/km) Stable Unstable Temperature

Height Γ ENV (8 C/km) Γ M (6 C/km) Γ DRY (10 C/km) Stable h Unstable T D < T E T M > T E T D T E T M Temperature

=> STABLE or UNSTABLE??? Height Γ ENV (8 C/km) Γ M (6 C/km) Γ DRY (10 C/km) Stable h Unstable T D < T E T M > T E T D T E T M Temperature

Height Conditionally Unstable Γ M (6 C/km) Γ DRY (10 C/km) Stable Unstable Temperature

Conditionally Unstable Atmosphere Whether unstable or not depends on moisture amount more moisture in air => more likely to be unstable

1. WHAT CAUSES ATMOSPHERE TO BECOME MORE/LESS UNSTABLE? 2. WHAT CAUSES AN AIR PARCEL TO INITIALLY RISE?

1. WHAT CAUSES ATMOSPHERE TO BECOME MORE/LESS UNSTABLE?

Temperature 1. WHAT CAUSES ATMOSPHERE TO BECOME MORE/LESS UNSTABLE? Height ONE WAY IS THROUGH MIXING => initial profile of environment air Rising Air Cools Sinking Air Warms expands and cools compresses and warms

Height Conditionally Unstable Γ M (6 C/km) Γ DRY (10 C/km) Stable Unstable Temperature

Temperature 1. WHAT CAUSES ATMOSPHERE TO BECOME MORE/LESS UNSTABLE? Height ONE WAY IS THROUGH MIXING => final profile of environment air initial profile of environment air Rising Air Cools Sinking Air Warms expands and cools compresses and warms

Another way the atmosphere can become more unstable: The large-scale lifting an entire layer of air - here a large-scale layer of air is much larger than a parcel - layer may be 100's of kilometers across - the lifting of a layer typically happens with a low pressure system (more later in course)

Height 1000 m Temperature - Original layer (in blue) is very stable

Height 1500 m dry adiabatic lapse rate (10C/km) 1000 m Temperature - Original layer (in blue) is very stable - As layer rises, it expands - As air rises => cools at dry adiabatic lapse rate (10 C/km) (assume no condensation) - Top of layer rises 500 meters more than bottom of layer => Top of layer cools more than bottom of layer - Result => environment lapse rate within layer more likely unstable This occurs when low pressure over area. Opposite happens with high pressure system. Low Pressure => Rising Air => Increasing INSTABILITY High Pressure => Sinking Air => Increasing STABILITY

Height SPECIAL CASE: CONVECTIVE INSTABILITY 1500 m dry adiabatic lapse rate (10C/km) moist adiabatic lapse rate (6C/km) RH << 100% RH=100% 1000 m - Bottom of layer moist (RH=100%), top of layer dry (RH<<100%) - Bottom of layer cools at moist adiabatic lapse rate (6 C/km) - Top of layer cools at dry adiabatic lapse rate (10 C/km) Temperature => Now even more unstable than before!! CONVECTIVE INSTABILITY