by: Mercado, Joey D. BS ChE 4202

The Atmospheric Engine the atmosphere is somewhat like an

engine. It is continually expanding and compressing gases, exchanging heat and generally creating chaos. The driving force of energy comes from the sun.

Highs and LowsAir has a mass it also exerts pressure on

things under it. Like water, which we intuitively understand to exert greater pressures o greater depths, the atmosphere exerts more pressure at the surface than it does at higher elevation.

HIGH & LOW PRESSURE SYSTEM

WIND FLOW DUE TO PRESSURE GRADIENT

Corolis effect

-the angular thrust added to the effect because the Earth rotates.

Anticyclones & Cyclones

Anticyclones was associated with good weather thus the anticylcones associated with bad one.

WIND SPEED apart function of the steepness of the pressure surface. When the isobars are close together, the pressure gradient is said to be steep and the wind relatively high.

ANTICYCLONES WITHOUT COROLIS EFFECT

ANTICYCLONES WITH COROLIS EFFECT

TURBULENCEAddition of random fluctuations of the wind

velocity MECHANICAL TURBULENCE

the fluctuations in part are caused by the fact that atmosphere is being sheared . The sheared is being result by the fact that the wind speed is zero at the ground surface and rises with elevation to near the imposed by the pressure gradient. THERMAL TURBULENCE

Heating of the ground surface causes turbulence in the same fashion that heating bottom of a beaker full of water causes turbulence. At some point below boiling, you can see density currents raising off the bottom.

STABILITYThe tendency of the atmosphere to resist or

enhance vertical motion.UNSTABLE

-mechanical turbulence is enhanced by the thermal structure.

NEUTRAL-neutral atmosphere is one o in which the thermal

structure neither enhance nor resists the mechanical turbulence.

STABLE-when the thermal structure inhibits the

mechanical turbulence.

Cyclones are associated with unstable air. Anticyclones associated with stable air.

NEUTRAL STABILITY

The lapse rate for a neutral atmosphere is defined by the rate of temperature increase or decreased experienced by a parcel of air that expands or contracts adiabatically as it raised through the atmosphere.

Γ (GAMMA) designate “dry adiabatic lapse rate” means

temperature decreases usually -1.0oC. 100 m-1

UNSTABLE ATMOSPHERE

if the temperature of the atmosphere falls greater than Γ the lapse rate is said to be superadiabatic and the atmosphere is unstable.

STABLE ATMOSPHERE

if the temperature of the atmosphere falls at the rate lower than Γ it is called sub adiabatic and the atmosphere is stable.

2 special cases of Sub adiabatic Lapse Rate

Isothermal

when there is no change in temperature

Inversion

when the temperature increases with elevation

TERRAIN EFFECTS

HEAT ISLANDS

LAND AND SEA BREEZES

VALLEYS

HEAT ISLANDS

A heat islands results from a mass material either natural or anthropogenic that absorbs the reradiates heat a greater rate than the surrounding area.

GOOD NEWS For ground level sources of automobiles the bowl

of an stable air that forms will allow a greater air volume for dilution of pollutant.

BAD NEWSUnder stable conditions, plumes from tall stacks

would be carried out over the countryside without increasing ground level pollutants concentrations. Unfortunately instability caused by the heat island mixes these plumes to the ground level.

LAND –SEA BREEZES

The effect of the lake breeze on stability is to imposed a surface based inversion on the temperature profile. As the air moves the water over the warm ground it is heated from below.

Stack plumes originating near the shoreline, the stable lapse rate causes a funning plumes that does not disperse close t the stack.

At some point inland, unstable conditions develop and the plume rapidly descends to the ground causing fumigation at the ground surface.

ValleysPeels off the part of the wind and forces it to follow the

direction of the valley floor.

Understagnating cycloneThe valley will set up its own circulation. Warming of the

valley wall cause the valley air to be warmed. It will became more buoyant and flow up the valley. At night the cooling process will cause the wind to flow down the valley.

Valleys oriented in the north-south directionAre more susceptible to the inversion of the terrain. The

valley walls protect the floor from radiative heating by the sun. Yet the walls are free to radiate heat away to the cold night sky.

Under weak windsThe ground cannot heat the air rapidly enough during to

dissipate the inversion that formed during the night

The end!!!!