WEATHER

Meteorology -

Study of weather

I. Basic Principles

A. Earth in space

1. earth – spins on own axis & completes one rotation every 24 hrs. (causing day & night)

2. earth – takes 1 year to complete 1 orbit (revolution) around the sun

3. earth’s axis tilted: 1 hemisphere receives more light causing summer; less light – winter

a. equinox – sun directly overhead on equator;

- autumnal equinox – Sept. 21

- spring (vernal) equinox – March 21

b.) solstice –when the sun’s overhead on:

- Tropic of cancer – summer solstice:

June 21st

- Tropic of capricorn – winter solstice:

Dec. 21st

Tilt/Seasons – 0:50

B. Atmosphere

- 310 miles2000 oC or higher

-50 miles/ -120 oC-31 miles/ 0 oC

-ozone layer- 11 miles/ -80 oC

- weather takes place

1. troposphere – lowest region where weather occurs; contains water vapor & clouds; contains 78.08 % (78%) N2 and 20.94% (21%) O2

2. stratosphere – warmer due to ozone (O3) layer; absorbs UV radiation

Our Atmosphere – 2:40

C. 3 causes of weather – pressure, temp., precip.

II. Pressure

- downward force exerted by the weight of the air; greatest at sea level; measured by the weight of the air (barometer)

A. Higher pressure has a higher temp.;

- less pressure - cooler; ex. mt., heat pump

- less pressure – lets air rise faster to make winds

B. Wind – air moves from a high to low pressure (H L)

Pressure moves from H L

C. High pressure systems (H) – move clockwise & generally result in fair weather

D. Low pressure systems (L) – move counterclockwise & generally result in unsettled (bad) weather

E. Isobars – lines on weather maps to connect similar pressures

Air Pressure – 2:11

High/Low Pressure – 1:00

III. Temperature -

Measure of amt. of energy of the molecules; caused by sun; measured by thermometer

A. Sunshine

1. warmth & light

2. photosynthesis – makes food & O2

3. helps in evaporation/transpiration -

drives the water cycle

4. creates optical effects

a. reflection – light bounces off a surface; ex. oceans reflect light

- albedo effect – reflectiveness of a surface; ex. snow & white shirt – high albedo

b. refraction – light moving from 1 medium to another, causes the speed to change & bends the light; ex. mirage

REFLECTION REFRACTION

B. Conduction 1. Heat striking an object transfers

some energy to object; ex. sand gets hot on feet

2. materials vary in amount of heat absorbed (specific heat capacity) before temp. increases; ex. metal heats up faster than wood

C. Density of different temp.

1. heat – less dense, warm air rises 2. cold – more dense, cold air sinks

3. convection current – warm fluid that is less dense & rises; ex. in atmosphere, ocean, under the crust

D. Isotherms – bands used on weather maps to connect similar

temps

Sunlight & Solar Energy – 1:49

E. Temperature Fronts

1. cold front – barometer falls – low; large clouds form; violent storms – thunder & lightning

2. warm front – less violent storms; don’t move as fast but last longer; as warm air rises, it cools & condenses precip.

Fronts – 3:17

IV. Water

A. Importance? Available

B. H2O & the weather – can occur in all 3 states at ordinary temps.

gas boiling condensation liquid

melting freezing Solid (ice)

- takes a great deal of energy to change the temp.

- oceans fluctuate less than land

- cold/warm ocean currents affect the air temp. above it

C. Water Cycle

- 9 places water found: clouds, groundwater, oceans, lakes, rivers, soil, plants, animals, glaciers

D. Clouds and Fog

1. Relative humidity: 100% - air becomes saturated; fog – ground level; clouds – above ground; warm air holds more moisture than cold air

2. water vapor (normally) condenses only onto a surface; ex. Dust, soot, sulfate - the bigger the particle the bigger the droplet; called CCN – cloud condensation nuclei

E. Rain -

water droplets more than .5 mm across collects around CCN; when too heavy they fall as rain

F. Snow & Sleet

1. Snow – water freezes to form crystals

2. Sleet – ice pellets smaller than 5 mm in diameter

G. Hail, thunder, lightning – caused by rising warm air

1. Hail – rising air currents carry water droplets up & they freeze.

This process continues & refreezes in layers. When heavy enough to overcome air currents, they drop

2. Thunder & lightning – rising air currents create convection currents – hot air rises at center while cold air sinks at sides

- thundercloud: has + electrical charge at top & - charge at the bottom. Eventually huge sparks flash between the charges, neutralizing them lightning.

- Lightning releases so much energy – that air which passes through it explodes thunder

- the difference in electrical charge can be more than 305 volts/ft.

What are Thunderstorms? – 0:43

How do Thunderstorms form? – 2:41

Updrafts & Hail – 1:10

H. Dew & water -

Clear skies cause quick cooling, chilling the air next to it. Water vapor condenses on surface dew (dew point reached)

THE END!