Meteorology quiz #2, unit 3

• Clouds regulate Earth's energy balance by reflecting solar radiation and absorbing infrared energy, while also providing visual clues about physical processes.

Atmospheric Stability

• Atmospheric stability refers to a state of equilibrium where:
  • A stable atmosphere returns to its original position after displacement.
  • An unstable atmosphere moves further away from its original position.
• Rising air masses expand and cool, while sinking air masses compress and warm

Adiabatic Process

• This is when air experiences a temperature change without heat exchange with its surroundings.
• Dry adiabatic rate: Constant warming/cooling rate in unsaturated air masses.
• Moist adiabatic rate: Variable warming/cooling rate in saturated air masses (RH=100%).

Lapse Rate

• Lapse rate measures the rate at which air temperature changes with height.

Stable Atmosphere

• A stable atmosphere has a lapse rate less than the moist adiabatic rate.
• Rising air is colder and heavier than its surroundings, resisting upward movement.
• This leads to horizontal, thin clouds with flat tops and bases (stratiform).
• Air inversions, where colder air sinks to the surface, can be deadly in polluted areas.
• Stable atmospheres usually occur near sunrise when surface temperatures are lowest.

Unstable Atmosphere

• An unstable atmosphere has a lapse rate greater than the dry adiabatic rate.
• Rising air is warmer and less dense than surroundings.
• Typically found in shallow layers near the surface on hot, sunny days.

Conditionally Unstable Atmosphere

• This is where the atmosphere is stable if rising air is unsaturated and unstable if it's saturated.
• This happens when the lapse rate is between the moist and dry adiabatic rates.
• Instability increases when air aloft becomes colder (due to winds or cloud radiation) or surface air becomes warmer (due to daytime heating, winds, or warm surfaces).

Causes of Rising Air

• Surface heating and free convection.
• Uplift due to topography (mountains).
• Convergence of surface air.
• Uplift along weather fronts.
• Uneven heating of Earth's surface creates thermals which are pockets of warm air that rise causing condensation and cloud formation.

Orographic Lift

• Air rises and cools as it moves over a mountain.
• Condensation occurs if the air is humid.
• The windward side experiences ample precipitation, while the leeward side often becomes a rain shadow desert.
• Lenticular clouds are lens-shaped clouds that form at the top of mountains, with dry air in between layers of moist air.

Precipitation Definition

• Any form of water (liquid or solid) that falls from a cloud and reaches the ground.
• Cloudy weather with water vapor is not the only factor involved as condensation is also required.

Cloud Droplets

• These are generally too small to fall as rain due to their light weight and tendency to evaporate in drier layers.

Formation of Raindrops

• Roughly 1 million cloud droplets must combine (coalesce) to create one raindrop.
• This process occurs primarily through the collision-coalescence process and the ice crystal process.

Collision-Coalescence Process

• Raindrops form on condensation nuclei or through random collisions of droplets.
• Speed, temperature, rising air currents, cloud thickness, electric charge, and droplet size all have an effect.

Ice Crystal Process (Bergeron Process)

• Occurs more at middle latitudes & polar regions, as clouds extend upwards and are well below freezing.
• Ice crystals form on ice nuclei or freezing nuclei which are more rare than condensation nuclei, resulting in fewer ice crystals than water droplets.
• These ice crystals can collide and stick together and end up as a snowflake.
• Many raindrops begin as snow that melts closer to the surface.

Cloud Seeding

• The ability to inject a cloud with small particles (“seeds”) that can act as condensation nuclei.
• Silver iodide is frequently used.
• Not always reliable and requires supercooled clouds with the correct ice crystal to water droplet ration (1:100,000.)
• Can also occur naturally.

Rain

• A falling drop of liquid water, of which meteorologists classify based on size of the drop.
• Rain is > 0.5mm diameter and Drizzle is