Chapter 5 Meteorology

Mount everest

world’s tallest mountain of 8850 m/29035 ft, same latitude as Tampa, FL, decline temps w/ alt, summit always cold, shrouded clouds w/ monsoon winds, survival difficult, air thins, wind-chill factor, most ascents in May

What does air exert?

force on the surface of allobjects it contacts

Force equation

mass x acceleration

Air molecules

random motion with exerting a force as it collides w/ other molecules

Total air pressure

cumulative force of these collisions/unit area

Dalton’s law

total pressure exerted by mixture of gases equals sum of pressures produced by each constituent gas

Air pressure

depends on mass of molecules and kinetic molecular energy, weight of overlying air acting on area, all directions and doesn’t collapse, 1.0 kg/cm²

Weight

force of gravity exerted on a mass

Weight equation

mass x acceleration of gravity

Barometer

instrument used to measure air pressure and monitor changes

Mercury barometer

air pressure supports column of mercury in a tube, at sea level supports mercury to a height of 760mm, height of column changes w/ air pressure

What is the mercury barometer adjusted for?

expansion and contraction of mercury w/ temp, gravity variations w/ latitude and altitude

Aneroid barometer

more portable/less precise, chamber w/ partial vacuum, new version depends on effect of air pressure on electrical properties of crystalline substance, fair, changeable, and stormy scale

Chamber of partial vacuum in aneroid barometer

changes in air pressure collapse/expand the chamber, moves pointer on scale calibrated equivalent to mm/in of mercury

Air pressure tendency

change in air pressure over a specific time interval, important for local forecasting

Barographs

barometer linked to a pen that records on a clock-driven drum chart, provides a continuous trace of air pressure variations w/ time, easier to determine pressure tendency

Units of length

mm/in

Units of pressure

pascal (Pa), US uses millibar (mb)

What happens w/ the overlying air compressing the atmosphere?

greatest pressure at lowest elevation w/ gas molecules closely spaced at Earth’s surface (density) and spacing between molecules increases w/ increasing alt, number density, 18 km the air density is only 10% of sea level

Number density

number of gas molecules/unit volume, decreases w/ alt

Compressible air

drop in pressure w/ alt is greater in the lower troposphere, more gradual aloft

Standard atmosphere

vertical profiles of average air pressure and temp based on, state of atm averaged for all lat and szns

What happens with density and pressure with altitude?

drops with it, half atm mass below 5500 m, 99% of mass below 32 km, Denver average air pressure is 83% of Boston

What is more important to meteorologists?

horizontal variations more important than vertical, local pressures at elevations adjusted to equivalent sea-level values, mapped by connecting points of equal equivalent sea-level pressure to produce isobars

What are horizontal changes in air pressure accompanied by?

changes in weather, middle lat. w/ procession of different air masses brings changes in pressure and weather w/ temp more pronounced effect on air pressure than humidity, weather becomes stormy when air pressure falls and clears/remains fair when pressure rises

What happens with rising air temperature?

increase in average kinetic molecular activity

What happens in a closed container?

heated air exerts more pressure on the sides due to density in a closed container not changing b/c no air has been added/removed

Atmosphere not being a closed container

heating the atm causes the molecules to space themselves farther apart due to increased kinetic energy, molecules placed farther apart have a lower mass/unit volumbe, heated air is less dense and lighter

Hot air balloons

ascend w/n the atm b/c the heated air w/n the balloon is less dense than the cooler air surrounding the balloon

What happens to air pressure in cold air?

drops more rapidly w/ alt, cold air is dense and less kinetic energy, molecules closer together, 500 mb surfaces represent where half of the atm is above and half below the mass at a lower alt. in colder air than warmer

What happens when the humidity is increased?

less dense air, muggy

Cold and dry air masses

densest, generally produce higher surface pressures

warm and dry air masses

exert higher pressure than warm and humid air masses

What do pressure differences create?

horizontal pressure gradients causing cold and warm air advection

What do air mass modifications produce?

changes in surface pressures

Converging winds

blow towards a column of air

Diverging winds

blow away from a column of air

What are converging/diverging winds caused by?

horizontal winds blowing toward/away from a location, wind speed changes in downstream direction

What happens if more air diverges at surface than converges aloft?

air density and surface air pressure decrease

What happens if more air converges aloft than diverges at the surface?

density and surface pressure increase

Isobars

lines passing through locations w/ same air pressure, drawn on a map, US convention at every 4-mb interval (996 mb, 1000 mb, 1004 mb)

High/anticyclone

area where pressure is higher than surrounding air, usually fair weather systems, sinking columns of air, surface winds blow clockwise and diverge outward

Low/cyclone

area where pressure is lower than the surrounding air, stormy weather systems, rising columns of air necessary for precipitation formation, surface winds blow counterclockwise and converge inward

Variables of state

variations in temp, pressure, and density, magnitudes change from another across Earth’s surface w/ alt. above Earth’s surface and w/ time

Ideal gas law

combination of Charles and Boyle’s law, pressure exerted by air is directly proportional to the product of its density and pressure, all 3 variables change simultaneously

Pressure equation

gas constant x density x temp

When are pressure and temp directly proportional?

fixed density

When is pressure directly proportional to density?

fixed temp

When is temp inversely proportional to density?

fixed pressure

Expansional cooling

when an air parcel expands, temps of the gas drops

Example of expansional cooling

air released through open valve of a bike tire feels cool

Compressional warming

when the pressure on an air parcel increases, parcel is compressed and temp rises

Example of compressional warming

heating of the cylinder wall of a tire pump as air is pumped into a tire

What happens to ascending and descending currents?

ascending currents of air updraft cool whereas descending currents of air downdraft warm

Law of energy conservation

1st law of thermodynamics, heat energy gained by an air parcel either increases the parcel’s interna; energy/used to do work on parcel

What is the change in internal energy directly proportional to?

change in temp of the parcel, transfer heat to the parcel raising its temp, transfer heat from the parcel lowers its temp

What does work done on the parcel mean?

compression/expansion of the parcel

What happens if air is compressed?

energy is used to do work on the air

What happens if air expands?

air does work ont he surroundings

Adiabatic process

no heat exchanged between air parcel and surroundings, dry adiabatic lapse rate, moist adiabatic lapse rate

Dry adiabatic lapse rate

9.8 C/1000 m, temp of an ascending/descending unsaturated parcel changes in response to expansion/compression only

Dry

any parcel that’s not saturated w/ water vapor

Moist adiabatic lapse rate

6 C/1000 m, saturated rising parcel, latent heat released to the environment during condensation/deposition partially counters expansional cooling, actual rate varies w/ temp

Conclusion

air pressure drops rapidly w/ alt in lower troposphere and more gradually aloft no clearly defined top to atm, surface air pressure depends on air density governed by air temp and to a lesser extent the concentration of water vapor and diverging/converging winds affect air density and surface air pressure