REMINDERS: Problem Set 2: Due TODAY Midterm 1: 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

2.  WHAT CAUSES AN AIR PARCEL TO INITIALLY RISE?

A. Surface heating leading to Convection

2.  WHAT CAUSES AN AIR PARCEL TO INITIALLY RISE?

A.  Surface heating leading to Convection

B.  Topography (Mountains) = Orographic Uplift

2.  WHAT CAUSES AN AIR PARCEL TO INITIALLY RISE?

A.  Surface heating leading to Convection

B.  Topography (Mountains) = Orographic Uplift

C.  Ascent due to Convergence

2.  WHAT CAUSES AN AIR PARCEL TO INITIALLY RISE?

A.  Surface heating leading to Convection

B.  Topography (Mountains) = Orographic Uplift

C.  Ascent due to Convergence

D.  Uplift along Weather Fronts

Wind

Windward Side Leeward Side

Clicker Question

Mountain

Which side of the mountain would generally receive more precipitation? (A) Windward

(B) Leeward

(C) Both sides would receive equal amounts

Set Frequency to "AD"

Wind

Windward Side Leeward Side

Clicker Question

Mountain

Which side of the mountain would generally receive more precipitation? (A) Windward

(B) Leeward

(C) Both sides would receive equal amounts

Set Frequency to "AD"

Wind

Windward Side Leeward Side

Mountain

On Windward side: - rising air - temperature decreases - relative humidity increases - may get to saturation => clouds and maybe precipitation

On Leeward side - sinking air - temperature increases - relative humidity decreases - Clouds evaporate => little or no precipitation

Wind

Windward Side Leeward Side

Mountain

On Windward side: - rising air - temperature decreases - relative humidity increases - may get to saturation => clouds and maybe precipitation

On Leeward side - sinking air - temperature increases - relative humidity decreases - Clouds evaporate => little or no precipitation

Mountain range often produce RAIN SHADOW on Leeward Side

Region of reduced precipitation

Prevailing Wind

Prevailing Wind

Falling raindrops have flat shape

Collision - Coalescence Process (Warm process)

Clicker Question

The collision-coalescence process is most efficient when: (A) all the cloud droplets are small (B) all the cloud droplets are large (C) there is a mix of small and large cloud droplets

Set Frequency to "AD"

Clicker Question

The collision-coalescence process is most efficient when: (A) all the cloud droplets are small (B) all the cloud droplets are large (C) there is a mix of small and large cloud droplets

Set Frequency to "AD"

Clicker Question

In general, which cloud would you expect to produce larger rain drops through the collision-coalescence process? (A) cumulus cloud (B) stratus cloud (C) cirrus cloud

Set Frequency to "AD"

Clicker Question

In general, which cloud would you expect to produce larger rain drops through the collision-coalescence process? (A) cumulus cloud (B) stratus cloud (C) cirrus cloud

Set Frequency to "AD"

Cloud Droplet Growth Processes: 1) Collision-Coalescence

- warmer clouds, liquid water only - different size drops fall at different speeds

2) Ice-Crystal Process

- colder clouds with both liquid water and ice

T=0°C (Freezing level)

T=-40°C

Liquid Only

Supercooled Liquid and Ice

Ice Only

Surface

Tall Cumulonimbus Cloud

This region is where Ice-Crystal Process occurs

Question: How can liquid water exist below freezing point? - need freezing nuclei for liquid water to freeze into ice crystal if temperature is between 0 and -40°C. - similar idea as cloud condensation nuclei, except the structure of freezing nuclei must be similar to the structure of ice crystal ==> As a result, much fewer freezing nuclei in atmosphere compared to number of cloud condensation nuclei

In Equilibrium: Condensation = Evaporation

Liquid Drop and Water Vapor

Ice Crystal and Water Vapor

More Water Vapor Around Liquid Drop

Less Water Vapor Around Ice Crystal

water vapor liquid water ice crystal

Now, put Liquid Drop and Ice Crystal Together

water vapor liquid water ice crystal

Now, put Liquid Drop and Ice Crystal Together

Now more water vapor around Ice Crystal => Vapor condenses on Ice

water vapor liquid water ice crystal

Now, put Liquid Drop and Ice Crystal Together

Now more water vapor around Ice Crystal => Vapor condenses on Ice

water vapor liquid water ice crystal

Now, put Liquid Drop and Ice Crystal Together

Now more water vapor around Ice Crystal => Vapor condenses on Ice As water vapor decreases => Liquid water evaporates from drops

water vapor liquid water ice crystal

Now, put Liquid Drop and Ice Crystal Together

water vapor liquid water ice crystal

Now more water vapor around Ice Crystal => Vapor condenses on Ice As water vapor decreases => Liquid water evaporates from drops

=> Ice Crystal Grows => Liquid Drop Shrinks

Ice Crystal Process (also referred to as Bergeron Process)

Sleet - rain refreezes before hitting surface - deeper cold layer near surface

Sleet

Freezing Rain - rain refreezes on contact with surface - shallow cold layer near surface

Sleet - rain refreezes before hitting surface - deeper cold layer near surface

Freezing Rain

Freezing Rain

Freezing Salt Water Spray?

Rime: Fog droplets freeze on contact