1 / 23

Snow

Snow. Precipitation composed of white or translucent ice crystals, chiefly in complex branched hexagonal form and often agglormerated into snowflakes. Dendrites -- Fernlike, branched Columns -- Taller than thin Plates -- Flat Other types. Snow.

Télécharger la présentation

Snow

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Snow • Precipitation composed of white or translucent ice crystals, chiefly in complex branched hexagonal form and often agglormerated into snowflakes. • Dendrites -- Fernlike, branched • Columns -- Taller than thin • Plates -- Flat • Other types

  2. Snow • Snow shapes, or habits, are temperature dependent. Temperature (C)Crystal Habit 0 to -4 Thin Plates -4 to -10 Columns -10 to -12 Plates -12 to -16 Dendrites -16 to -22 Plates Much of the snow we see are aggregates of these crystal habits.

  3. Snow • The warmer the air, but still below freezing, often the heavier the snowfall. • Warmer temperatures have a higher saturation vapor pressure so there are more vapor molecules that can allow crystals to grow. • Greater chance of large aggregates of crystals forming in warmer temperatures.

  4. Snow • Snow Shower: A form of precipitation from a convective cloud that is short in duration, starts and stops suddenly, and often has a rapid change in intensity. • Flurries: A very light and usually brief show shower. • Snow Squall: A sudden wind associated with snowfall that occurs suddenly and is usually intense and short lived.

  5. Freezing Rain • Precipitation that falls to the ground as a liquid then freezes upon impact with the ground or exposed objects. Forms a glaze of ice on the objects and ground.

  6. Freezing Rain Cold: T < 0C Warm: T > 0C Rain freezes upon contact with below freezing surface. Shallow freezing layer

  7. Sleet -- Ice Pellets Cold: T < 0C Warm: T > 0C Rain freezes before reaching the surface. Deep freezing layer

  8. Measuring Precipitation • Rain Gauge • Standard • Weighing Gauge • Tipping Bucket • Radar • Optical Rain Gauge

  9. State Variables • State variables are quantities that tell us the state of a gas -- the atmosphere. Several of these deserve special attention: • Temperature • Density • Pressure

  10. State Variables -- Temperature • Temperature: The temperature of a substance is a measure of the average kinetic energy of the molecules in that substance. Thus atmospheric temperature is proportional to the speed of the air molecules.

  11. Temperature T ~ mV2, or as T , V Records: Low: -1270 F in Vostok ,Antarctica, High: + 1360 F in El Azizia, Libya.

  12. Temperature T1 > T2 m1v12 > m2v22 (Kinetic Energy) If m1 = m2 then: v1 > v2

  13. Temperature Scales • Three (3) temperature scales and their units: • Fahrenheit (F) -- German • Celsius (C) -- Swedish • Absolute (K) -- “Scientific”

  14. Density • The density of a substance is defined as the amount of mass of a substance in a given volume. • It can also be defined by a number density that tells us the number of “things” in a given volume. • Number of students in M204 • Number of water drops in a cubic centimeter of cloud

  15. Density Unit mass V1 = V2 m1 < m2 m1/v1 < m2 /v2 1 < 2

  16. Pressure • The air pressure is the force per unit area that the atmosphere exerts on any surface it touches. • The molecules of the air are in constant rapid motion. • When a molecule collides with a surface, such as your skin, the molecule exerts a force on that surface.

  17. Pressure • Pressure is the cumulative effect of these air molecules colliding with a surface. Air Pressure Depends On: The mass of the molecules Gravity The kinetic molecular activity (temperature)

  18. Pressure • Pressure is the force per unit area: • In meteorology we us the units millibars • “Typical” sea-level pressure is approximately 1013 mb. F P = A

  19. Ideal Gas Law • We have now investigated three state variables: • Temperature • Pressure • Density • These variables change from place to place and in time but they do not do so independently. • This interrelationship is known as the Ideal Gas Law.

  20. Ideal Gas Law: P = R  T • If the density is constant • If T increases then p increases • If T decreases then p decreases • If the temperature is constant • If p increases then  increases • If p decreases then  decreases • If the pressure is constant • If T increases then  decreases • If T decreases then  increases

  21. Ideal Gas Law: Reprise • We can substitute the definition for density to put the ideal gas law into terms that we can easily measure: temperature, pressure, volume. m  = P = R  T V PV = m R T

  22. Ideal Gas Law: Reprise • We see that for a given mass of gas: • For a constant p, T increases, V increases • For a constant V, T increases, p increases • For a constant T, p increases, V decreases PV = constant T

  23. Pressure Balanced by air pressure. Gravity But, the air doesn’t fall down!!! Pressure: Force due to gravity that the mass of the atmosphere exerts on a unit area of surface.

More Related