Atmosphere, wind circulation and deserts

Composition of the atmosphere

Oxygen, nitrogen, carbon dioxide water vapor

Vertical structure of the atmosphere

Pressure:

millibars Standard pressure 1013.25 millibars

Moisture and Precipitation

Humidity and condensation:

Mass of water in air/volume of air

Saturation - depends on pressure and temperature

Relative humidity: amount of water in air/amount at saturation x 100

Effect of cooling - condensation. Clouds, mist

Types of clouds

Precipitation

Orographic ppt

Convectional ppt

fronts

Motion in the atmosphere: wind

Fundamentally causedby inequalities in air pressure; most of these generated by differential heating

high pressure - cold air, low pressure - warmer air

Sea breeze, land breeze

Wind velocity

km/hr 1 Calm

1-19 breeze

20-49 strong breeze

50-89 gale

89-117 storm

>117 hurricane (typhoon)

Spiraling air motions - Coriolis effect

Global atmospheric circulation pattern

Jet stream

sub tropical polar front

Air masses and fronts

Air masses can originate from polar regions(cold) or tropics (warm)

Can be maritime (wet) or continental (dry)

Cold air mass movement in North America

Front where one air mass meets another Cold front, warm front

Cold fronts characterized by thunderstorms

Thunderstorms and tornadoes

Cumulonimbus clouds

Precipiation in thunder storms

"funnel" clouds

tornadoes - funnel shaped vortex of air

descending air at core, rising air sheath around this (dust envelope)

Cyclones and Hurricanes

Polar front cyclones

Tropical cyclones:

Hurricanes (N. Atlantic, NE Pacific) =typhoons (NW Pacific) = cyclones(SW Pacific and Indian oceans)

Anatomy of a hurricane

Formation and development of hurricane

tropical disturbance -> tropical depression(20-34 knots) -> tropical storm(35-64 knots -> hurricane (>64knots/74mph)

motion of hurricanes

NE quadrant worst because speed added to wind speed

Wind as an agent of sediment transport

Only dust and sand

finer grains (mud sized) in suspension

sand by saltation and rolling

Atmosphere has staggering capacity to hold dust. Can also be transported over great distances. Eg Saharan dust found in Caribbean/S. Florida

Erosion by Wind

deflation (winnowing) desert pavement

[Damage to desert environments by All Terrain Vehicles, motor cycles eyc]

sand-blasting frosted surface of grains

ventifacts

pedestal rocks and arches

Deposition by wind

Sand dunes

drifting of sand dunes

Barchan, transverse, blowout dunes

ergs - sea of dunes

Loess

deposits of yellowish silty material formed of wind blown dust

Many of large deposits underlying praires, steppes, pampas formed at the end of the ice age in the Pleistocene

(hamburger connection - wheat and ranching)

Desert Environment

This is where work of wind is so obvious. Less than 25 mm/year

Streams are still the most powerful erosive agent. Flash floods.

Playa lakes - tempoary lakes; evaporate leaving sodium carbonate, borax (sod borate) etc