Weather and Climate Exam 3

Hydrologic Cycle

regular cycle of water through the earth-atmosphere system

Liquification

occurs frequently at normal earth temperatures and occurs when air is saturated in respect to water vapor

Evaporation

occurs if energy is available to water surface and water vapor increases in air

Deposition

water vapor changes directly to ice

Sublimation

ice changes directly to water vapor

Humidity

indicates amount of water vapor in the air

Indices of water vapor content

1. humidity

2. vapor pressure

3. absolute humidity

4. relative humidity

5. specific humidity

6. mixing ratio

7. dew point

Vapor Pressure

amount of pressure exerted on the atmosphere by water vapor - dependent on temperature and density

Saturation vapor pressure

maximum water vapor pressure that can occur - temperature dependent

Absolute Humidity

indicates the density of water vapor expressed in g/m³ and changes as air volume changes

Specific Humidity

represents a given mass of water vapor per mass of air in g/kg, does not vary with air volume fluxes and does not change with temperature

Saturation specific humidity

saturated air has the highest specific humidity for a given temperature and pressure

Mixing Ratio

expresses amount of water vapor relative to only a mass of dry air

Relative Humidity

indicates amount of water vapor in the air relative to the possible maximum given as a percentage and describes the amount of air present relative to a saturation point 

More water vapor occurs in

warm air rather than cold air

Dew point temperature

temperature at which saturation occurs in air reached by increasing water vapor content or chilling air

Dew Point

1. good indicator of moisture content in air

2. can be = or less than air temperatures

3. high dew points mean more moisture in atmosphere

Frost point

when air reaches saturation at temperatures below freezing

Methods of achieving saturation

1. addition of water vapor to air at a constant temperature

2. mixing cold air with warm moist air

3. cooling air to the dew point

Supersaturation 

air contains more water vapor than it can hold at saturation resulting in a RH of over 100% - can reach 300%

Heterogeneous Nucleiation

condensation onto hygroscopic aerosols causing dissolution

Hygroscopic Nuclei

abound in atmosphere from natural sources (salt, dust, ash, bacteria)

Atmospheric water does not freeze at

0 degrees C (32 degrees C) - leads to supercooled water

ice nuclei become active at temperatures below

-4 degrees C

Temperatures between -10 and -30 degrees C

formation of ice crystals, supercooled drops, or both

Below -30 degrees C

clouds are composed solely of ice crystals

At or below -40 degrees C or F

spontaneous nucleation and direct deposition of ice with no nuclei present

Diabatic processes

air temperature changes from direct energy exchanges (addition or removal of heat)

Adiabatic processes

air temperature changes with no net energy exchange

2nd Law of Thermodynamics

energy is always transferred from areas of high temperature toward those of lower temperatures

Dry adiabatic lapse rate

1 degree C / 100 m

Saturated adiabatic lapse rate

-0.5 degrees C / 100m

Dew

diabatic - liquid condensation on surface objects

Frost

diabatic - forms when surface temperatures are below freezing

Frozen Dew

diabatic - forms when normal dew processes occur followed by drop in temperature to below freezing - causes black ice

Fog

diabatic - surface cloud forms when air cools to the dew point and has moisture added 

Radiation Fog

diabatic - near surface air chills diabatically to saturation through terrestrial radiation loss on clear cool nights

Advection Fog

diabatic - warm moist air moves across cool surfaces - common on US west coast

Upslope Fog

fog developed through adiabatic processes - air is advected over land masses which increase in elevation

orographic lift

air is displaced over topographic barriers like mountains

Frontal lifting

boundaries between unlike temperatures of air migrate and warmer air is pushed aloft

Convergence 

atmospheric mass is non-uniformly distributed over earth - advects from areas of abundant mass to less mass

Entrainment

ambient air intrusions into parcels which limits vertical cloud development

High clouds

bases above 6000 m - cirrus, composed of ice, mares tail, cirrostratus, cirrocumulus

Middle Clouds

bases between 2000 and 6000m, composed of liquid drops, altostratus, altocumulus 

Low Clouds

bases below 2000m, composed of liquid water, nimbostratus, stratocumulus

Clouds with vertical development

cumulus humulis, cumulus congestus, cumulonimbus

Unusual Clouds

lenticular, banner, mammatus, nacreous, mother of pearl, nocticulent 

Collision Coalescence 

generates precipitation beginning with large collector drops 

Collision

collector drops collide with smaller drops

Coalescence

when collisions occur drops either bounce apart or coalesce into one larger drop

Bergeron Process

coexistence of ice and supercooled water is critical to the creation of cool cloud precipitation

Collisions between falling crystals and and drops cause growth through

riming and aggregation

Riming

liquid water freezing onto ice crystals producing rapid growth

Aggregation

the joining of multiple ice crystals

Snow results from 

the Bergeron process - riming + aggregation 

Rain

exclusively associated with warm clouds and cool clouds when surface temps are above freezing

Rainshowers

episodic precipitation events associated with connective activity from cumulus clouds

Raindrop shape 

begins as spherical, changes to mushroom shape, flattens, and splits into max size of 5mm

Graupel

ice crystals that undergo extensive riming

Hail

concentric layers of ice built around graupel

Sleet

ice crystals that melt into rain through mid level inversion 

Freezing Rain

similar to sleet, drops do not completely solidify before striking surface

Cloud Seeding

dry ice used to lower cloud drops to freezing point to stimulate ice crystal production leading to Bergeron process, silver iodide initiates Bergeron process

Zonal Winds

blow parallel to lines of latitude

Meridional Winds

move along lines of latitude

In the Winter

AH is low and RH is high (opposite in summer)

Parcel Theory

density does not change, temperature drops, RH cooling, hits 100% saturation, adiabatic cooling

Environmental lapse rate

-0.65 degrees C / 100 m

Dry adiabatic lapse rate

-1.0 degrees C / 100 m

Adiabatic warming

1.0 degrees C / 100 - warming by compression

Adiabatic Cooling

cooling by expansion

Wet adiabatic lapse rate

-.5 degrees C / 100m

Types of lift

1. thermodynamic 

2. orographic

3. convergence

4. frontal

Two clouds that precipitate

nimbostratus and cumulonimbus

90 degrees

high pressure, polar high, polar easterlies

60 degrees

low pressure, sub polar low, westerlies

30 degrees

High pressure, sub tropical high, north east and south east tradewinds

0 degrees

low pressure, equatorial low

Single-Cell model

George Hadley, ocean-only planet idea, single convection cell per hemisphere

Three-Cell model

each hemisphere divided into 3 pressure cells, Hadley, ferrel and polar,

Hadley Cell

in tropics air is heated through high solar angles and constant day length

Intertropical Convergence Zone

(doldrums) expanding and ascending surface air found near vertical solar ray characterized by clouds and precipitation

Ferrel Cell

indirect cell formed form air motions initiated by adjacent cells

Ridges

high heights extending poleward

Troughs

equatorward dipping lower heights