Chapter 10 Adiabatic processes, lapse rates and rising air

00:10:56
https://www.youtube.com/watch?v=ObnWb7yspxA

Summary

TLDRThe video discusses the mechanisms of temperature change in air parcels through diabetic and adiabatic processes. Diabetic processes involve direct energy exchanges, while adiabatic processes involve temperature changes due to compression or expansion without energy exchange. The dry adiabatic lapse rate is 10°C per 1,000 meters, while the moist adiabatic lapse rate is about 5°C per 1,000 meters. The video also explains how air rises due to gravitational and buoyancy forces, and the impact of altitude on air pressure and temperature. Various lifting mechanisms, such as orographic and frontal lifting, are also covered, along with the concept of temperature inversions and environmental lapse rates.

Takeaways

  • 🌡️ Diabetic processes involve direct energy exchanges.
  • 📉 Adiabatic processes change temperature without energy exchange.
  • ⬆️ Rising air parcels expand and cool due to lower pressure.
  • 📏 Dry adiabatic lapse rate: 10°C per 1,000m.
  • 💧 Moist adiabatic lapse rate: ~5°C per 1,000m.
  • 🏔️ Orographic lifting occurs when air rises over mountains.
  • 🌬️ Temperature inversions lead to colder near-surface air.
  • 📊 Environmental lapse rate varies with time and place.
  • ⚖️ Buoyancy force causes less dense air to rise.
  • 🌡️ Air density is affected by temperature.

Timeline

  • 00:00:00 - 00:05:00

    The temperature of an air parcel can change through two processes: diabetic and adiabatic. Diabetic processes involve direct energy exchanges, such as heating or cooling as air moves over surfaces. In contrast, adiabatic processes involve no net energy exchange; instead, temperature changes occur due to compression or expansion of the air. For instance, compressing air increases its temperature, while expanding it cools the air down. As air rises, it encounters lower pressure, leading to expansion and cooling, while sinking air compresses and warms. The dry adiabatic lapse rate indicates that rising air cools at a rate of 10°C per 1,000 meters until it reaches the lifting condensation level, where condensation occurs, forming clouds and releasing energy, which alters the cooling rate to the moist adiabatic lapse rate of about 5°C per 1,000 meters.

  • 00:05:00 - 00:10:56

    The environmental lapse rate (ELR) describes how temperature decreases with altitude, influenced by surface temperatures and solar radiation. During the day, surface heating leads to a higher ELR, while nighttime cooling results in a lower ELR. Temperature inversions occur when near-surface air is colder than upper air. Various mechanisms can lift air parcels, including orographic lifting, frontal lifting, convergence, and convection. Orographic lifting occurs when air rises over mountains, leading to cooling and cloud formation on the windward side, while the leeward side experiences warming and dryness. Frontal lifting happens when warm air rises over cold air masses, and free convection occurs due to localized heating. The balance between gravitational and buoyancy forces determines whether an air parcel rises or sinks, with temperature affecting air density: warmer air is less dense and rises, while cooler air is denser and sinks.

Mind Map

Video Q&A

  • What are diabetic processes?

    Diabetic processes involve direct energy exchanges, such as heating or cooling of air as it moves across hot or cold surfaces.

  • What are adiabatic processes?

    Adiabatic processes do not involve net energy exchange; temperature changes occur due to compression or expansion of air.

  • What is the dry adiabatic lapse rate?

    The dry adiabatic lapse rate is the rate at which the temperature of a rising air parcel decreases, approximately 10°C per 1,000 meters.

  • What happens when an air parcel rises?

    When an air parcel rises, it expands and cools due to lower air pressure at higher altitudes.

  • What is the moist adiabatic lapse rate?

    The moist adiabatic lapse rate is the rate of temperature decrease for a rising air parcel that is saturated with water vapor, approximately 5°C per 1,000 meters.

  • What causes orographic lifting?

    Orographic lifting occurs when mountains act as barriers to air flow, causing air to ascend and cool.

  • What is a temperature inversion?

    A temperature inversion occurs when near-surface air is colder than the air above it, leading to a small environmental lapse rate.

  • What is the environmental lapse rate (ELR)?

    The environmental lapse rate is the rate at which temperature decreases with altitude in the atmosphere, varying with time and place.

  • What is the role of buoyancy force in air movement?

    Buoyancy force causes air parcels to rise if they are less dense than the surrounding air.

  • How does temperature affect air density?

    Lower temperatures result in higher density, while higher temperatures result in lower density of air parcels.

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  • 00:00:02
    there are basically two ways in which
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    the temperature of an air parcel can be
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    changed so-called diabetic processes
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    involve Direct Energy exchanges an
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    example is the heating or cooling of the
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    air as it moves across a hot or cold
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    surface so-called adiabetic processes do
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    not involve net energy exchange heating
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    or cooling is achieved by compression or
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    expansion of the
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    air here is how a diabetic processes
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    work imagine you have air molecules
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    flying around in a chamber high
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    temperature means that the molecules
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    have high kinetic energy they're flying
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    very fast if I compress the air then the
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    air molecules will start flying faster
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    which means that the air is getting
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    warmer when I expand the air again the
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    air mole mules are flying at a slower
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    speed or in other words the air cools
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    down that is an adiabatic
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    process that backs the question how air
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    in nature is compressed or
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    expanded remember that air pressure
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    decreases with
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    altitude so if an air passel rises for
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    whatever reason it will get into a
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    region of lower air
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    pressure as a result it will
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    expand and
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    cool if we force an air parel to rise it
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    will expand and
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    cool if we force an air parcel to sink
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    it will contract and
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    warm as long as there is no condensation
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    involved the temperature of a rising air
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    passle decreases at a fixed
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    rate this rate is called the dry
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    adiabetic lapse rate it is 10° C per
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    1,000
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    M that means if your surface air
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    temperature happens to be 32° C and you
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    force the air to rise up to 1,000 M the
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    temperature will be 22° C you force it
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    up to 2,000 M it will cool down another
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    10° so its temperature is 12° and so on
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    the opposite happens when you force it
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    to come down it will increase its
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    temperature again at 10° per 1,000
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    M if an air parcel is lifted high enough
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    it will eventually get so cold that it
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    cannot hold the water vapor any longer
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    this is the height at which saturation
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    occurs it is also called the lifting
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    condensation level because further
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    lifting will cause condensation
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    condensation means that water vapor gets
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    from the gases into the liquid States we
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    see the formation of clouds in this
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    example the dupoint temperature which as
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    you know depends on the water vapor
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    content of the air is 2° C at 3,000 M
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    the air reaches its dueo 2° C so any
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    further lifting will cause further
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    condensation and formation of the cloud
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    the pro process of condensation releases
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    energy therefore the rate at which the
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    air temperature decreases from the
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    lifting condensation level upward will
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    be
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    less the air parcel still expands it
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    still cools down but not So Much Anymore
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    due to the fact that energy is released
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    through
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    condensation beyond the lifting
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    condensation level air Parcels cool at
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    the moist adiabetic lapse rate which is
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    approximately 5° C per 1,000 M it is
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    also called saturated or wet adiabetic
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    laps
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    rate the real value can be between 4 and
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    9° C per thousand M depending on the
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    amount of water vapor that condenses
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    during the lifting remember that the dry
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    and wet adiabatic laps rates are values
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    for the temperature decrease of a lifted
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    air parcel these are not values for
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    temperature decrease with altitude that
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    can be measured by taking temperature
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    readings at different
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    altitudes in Chapter 2 we have already
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    talked about the fact that the
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    temperature within the troposphere
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    decreases with
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    altitude this decrease of temperature
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    with altitude is expressed by the
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    so-called environmental laps rate ELR
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    which is also named ambient laps rate
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    similar to the other laps rates it's
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    expressed in temperature difference per
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    1,000 M altitude
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    difference the environmental laps rate
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    varies with time and place it depends
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    strongly on Surface
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    temperatures solar radiation causes
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    surface heating during the day this
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    generally leads to high temperatures
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    near the surface and consequently a high
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    environmental laps rate in the lower
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    atmosphere terrestrial radiation causes
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    surface cooling during the night which
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    typically results in a small
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    environmental abps rate when the near
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    surface air is even colder than the
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    upper air we call this a temperature
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    inversion the horizontal transport of
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    air called advection is another factor
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    that influences the environmental lapse
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    rate advection of cold or warm air at
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    different levels for for example due to
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    varying wind direction with altitude
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    causes changes in the environmental laps
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    rate I mentioned earlier that adiabetic
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    cooling occurs when air expands because
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    it is
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    lifted four principal mechanisms can
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    initiate the lifting of an air parcel
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    orographic lifting frontal lifting
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    convergence and convection orographic
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    uplift occurs when mountains act as
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    barriers to the flow of air air ascends
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    the mountain slope causes adiabetic
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    cooling this often generates clouds many
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    of the world's rainiest places are
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    located on Windward Mountain
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    slopes when air reaches the leward side
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    of the mountain much of the moisture has
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    been lost air descends warms ad
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    diabatically and condensation and
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    precipitation are not
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    likely the results are rain shadow
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    deserts such as the Great Basin Desert
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    in the Western United States and the
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    Patagonia desert in
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    Argentina the rising air on the windward
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    side of the mountain range cools first
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    dry a diabatically and later wet
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    adiabatically the sinking air on the
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    leward side of of the mountain range
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    warms only dry air
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    diabatically the results are warm Downs
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    slope winds on the leeward side such as
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    the chinuk winds in the Rocky Mountains
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    or the fern winds in the
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    Alps a front is a line where cold and
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    warm air masses
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    Collide this causes the lifting of warm
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    air which is called frontal lifting a
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    low press Center also called called a
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    cyclone always causes air to
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    converge horizontal convergence always
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    causes air to rise free convection
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    occurs when air is lifted as the result
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    of heating near the
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    surface this is localized over fairly
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    limited areas and can result in
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    localized Thunders
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    showers
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    e e
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    so what makes air rise in nature there
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    are two forces working on an air parcel
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    gravitational force tries to pull it
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    down to the Earth's surface buoyancy
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    Force tries to pull it upward buoyancy
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    force is simply the result of the fact
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    that we have higher air pressure near
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    the ground low air pressure in the upper
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    atmosphere and as a result air should be
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    moving
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    upward given that these two forces
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    gravitational force and bancy force are
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    at an equilibrium there is as of now no
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    reason for an air parcel to rise or
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    sink however that changes when the
  • 00:10:16
    density of the air parel changes if you
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    have an air parel that has a higher
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    density than its surrounding air then it
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    will sink towards the Earth's surface if
  • 00:10:28
    the density of of the air parcel is
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    lower than the surrounding air then it
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    will rise but what determines the
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    density of
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    air the answer is simple it's the
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    temperature lower temperature higher
  • 00:10:43
    density higher temperature lower density
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    so an air parcel that is warmer than its
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    surrounding will rise an air parcel that
  • 00:10:53
    is colder than its surrounding will sink
Tags
  • adiabatic processes
  • diabetic processes
  • air parcel
  • temperature change
  • lapse rate
  • buoyancy force
  • gravitational force
  • orographic lifting
  • frontal lifting
  • environmental lapse rate