Properties of atmosphere

1.temperature

2.Moisture

3.Pressure

4.Wind

Temperature

  • air temperature is a measure of the average internal kinetic energy of air molecules

  • increase in internal kinetic energy in front of the form of molecular motions are manifested as increases in temperature of the body.

units of temperature

Fahrenheit (F) is used for surface temperature but (C) is used for upper atmospheric temperature

Celcius (C)

c=(f-32)/1.8

Kelvin (K) = a si unit

K=C+273

1 Kelvin = 1 C greater than 1 F

Vertical thermal Structure

  • Troposhere ( overturning sphere )

  • contains 80% of the mass

  • surface heated by solar radiation

  • strong vertical motion

  • where most weather event occur

Stratosphere ( layer sphere )

  • Weak vertical motions

  • dominated by radiative processes

  • heated by ozone absorption of solar ultraviolet rays

  • warmest (coldest temperature at summer (winter) pole

mesosphere

  • heated by solar radiation at the base

  • heat dispersed upward by vertical motion

Thermosphere

  • very little mass

Polarward heat flux is needed to transport radiation energy from tropics to higher latitudes

New understanding of cyclone after WW2

  • Carl Gustav Rossby mathematically expressed relationships between mid-latitude cyclones and the upper air during WW2.

  • Mid latitude cyclones are large scale waves ( now called Rossby waves ) that grow from the baroclinic instabiloity associated with the north-south temperature differences in middle latitudes.

Rotating annulus experiment - cooling outside heating inside

Properties of the three cells

hadelycell - Ferrel cell - polar cell

Thermally direct circulation - Hadley cell and Polar cell

El Nino can affect western us climate by changing the locations and strengths of the polar and subtropical jet streams.

Cyclones prefferentially from in five locations in north america.

  1. East of the rocky mountains

  2. East of canadian rockies.

  3. gulf coast of the us

  4. east coast of the us

  5. bering sea and gulf of alaska

Pressure

  • the weight of a column of the atmosphere above a unit area of surface.

one atmospheric pressure

  • the average air pressure ate sea level is equivalent to the pressure produced by a column of water about 10 meters or about 76cm of mercury column; or about 14.71b/in²

  • this standard atmosphere pressure is often expressed as 1013mb (milibars), which means a pressure of about 1 kilogram per square meter.

Units of atmospheric pressure

  • Pascal (Pa) a SI unit for air pressure

  • 1 pa = force of 1 newton acting on a surface of 1 square meter

  • 1 hectopascal (hPa) = 1 milibar (mb) ( hecto = one hundred = 100

Bar: a more popular unit for air pressure.

1 bar = a force of 100,000 newtons acting on a surface of one square meter

  • = 100,000 pa

  • 1000 hPa

  • 1000 mb

one atmospheric pressure = standard value of atmospheric at sea level

= 1010.25 mb = 1013.25 hPa

Aneroid barometer - a barograph continually records air pressure through time.

Pressure correction for elevation

  • pressure decreases with height

  • recording actual pressures may be misleading as a result

  • all recording stations are reduced to sea level pressure equivalents to facilitate horizontal comparisons.

  • Near the surface, the pressure decreases of about 100mb by moving 1km higher in elevation.

Isobar

  • is useful to examine horizontal pressure differences across space.

  • Pressure maps depict isobars, lines of equal pressure

  • through analysis of isobaric charts, pressure gradients are apparent

  • steep ( weak ) pressure gradients are indicated by closely ( widely ) spaced isobars.

Pressure gradient force

  • PG = (pressure differences)/ distance

  • pressure gradient force goes from high pressure to low pressure.

  • closely spaced isobars on a weather map indicate steep pressure gradient.

Measuring winds

  • Wind direction always indicates the direction from which the wind blows

  • An Anemometer indicates both wind speed and direction

  • official measurements of wind at surface are made at an elevation of 10 meters, which is reffered to as the anemometer height.

  • meteorologists typically measure wind speed in knots.

  • 1 knot = 1.15mph =0.51 m/sec

vapor pressure

  • The air’s content of moisture can be measured by the pressure exerted by the water vapor in the air.

  • the total pressure inside an air parcel is equal to the sum of pressures of the individual gases.

  • in the left figure, the total pressure of the air parcel is equal to the sum of vapor pressure plus the pressures exerted by the nitrogen and oxygen.

  • high vapor pressure indicates large numbers of water vapor molecules.

  • unit of vapor pressure is usually in mb

Saturation vapor pressure describes how much water vapor is needed to make the air saturated at any given temperature.

saturation vapor pressure depends primarily on the air temperature in the Clausuis-clayperon Equation

saturation pressure increases exponentially with air temperature.

Relative humidity

-on a day when moisture content of the air does not change.

Cloud type based on properties

Four basic cloud categories

  1. Cirrus - thin, wispy cloud of ice

  2. stratus - layered cloud

  3. cumulus - clouds having vertical development

  4. nimbus - rain producing cloud

these basic cloud types can be combined to generate 10 different cloud types, such as cirrostratus clouds that have the characteristics of cirrus clouds and stratus cloud.

cloud types based on height.

  • if based on cloud base height, the ten principal cloud types can then grouped into four cloud types:

    1. high clouds

      • cloud base 6 to 15km above sea level

      • have low cloud temperature and low water content and consists of mostly ice crystals.

      a. cirrus - feathery streaks

      b. cirrostratus - Translucent to transparent sheet, like a veil across the sky.

      c. cirruscumulus. - small ripples and delicate puffs

    2. middle clouds

      • cloud base 2 to 6 km above sea level

      • usually composite of liquid droplets

      • they block more sunlight to the surface than the high clouds

      A. altostratus - Uniform white to gray sheet covering the sky

      B. altocumulus - White to dark gray puffs and elongate ripples

    3. low clouds

      • cloud base below 2km above sea level

      • low, thick , layered clouds with large horizontal extends, which can exceed that of several states.

      A. stratus -uniform dull gray cover, over the sky.

      B. stratocumulus - patches of soft gray

      C. nimbostratus - uniform gray cover

    4. clouds with extensive vertical development

      • They are clouds with substantial vertical development and occur when the air is absolute or conditionally unstable.

      A. cumulus -Puffy cauliflower type

      B. Cumulonimbus - Anvil shaped