weather
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
I. Basic Principles
A. Earth in space
1. earth – spins on own axis & completes one rotation every 24 hrs. (causing day & night)
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
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
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
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
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
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
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.
IV. Water
A. Importance? Available
B. H2O & the weather – can occur in all 3 states at ordinary temps.
- 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
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
H. Dew & water -
Clear skies cause quick cooling, chilling the air next to it. Water vapor condenses on surface dew (dew point reached)