Chapter 4

 

-          Water enters the atmosphere through evaporation, which is greatest when it is warmer, winds are high, and atmospheric pressure is low.

-          Saturation occurs when the rate of molecules condensing is equal to the number of molecules leaving the liquid (rate of return is equal to rate of escape).

-          Measuring water vapor is important because water vapor is the source of all clouds and precipitation and it is the most important greenhouse gas.

-          Mixing ratio is one to express the amount of water vapor in the atmosphere.It is the ratio of the weight of water vapor to the weight of the other molecules in a given volume of air.

-          Vapor pressure is the pressure exerted by water vapor molecules.Increases with increasing temperature.

-          Similarly, when air is saturated, the pressure exerted by water vapor molecules is called Saturation Vapor Pressure.

-          Saturation Vapor Pressure increases rapidly as temperature increases because the speed of the molecules is increased and the number of molecules with enough kinetic energy to evaporate also increases.

-          Relative humidity indicates how closely the air is to being saturated and is the ratio of vapor pressure to the saturation vapor pressure multiplied by 100%.

-          Saturated air has a relative humidity of 100%.

-          Water evaporates more slowly in air with a high relative humidity, and more quickly in air with a low relative humidity.

-          Adding water vapor or cooling the air, or both, increases relative humidity, while removing water vapor, warming the air, or both decrease relative humidity.

-          Dew occurs when relative humidity is beyond 100% (point when air cannot contain any more moisture) and the excess moisture must condense out of the air until the humidity returns to 100%.

-          The Dew Point is the temperature to which air must be cooled to become saturated without changing the pressure.The closer the dew point is to the air temperature, the closer the air is to saturation.Dew point temperature cannot be greater than the air temperature.

-          Frost forms similarly to dew, but only when temperatures are below freezing and deposition (vapor to solid) occurs rather than condensation (vapor to liquid).

 

Clouds

 

-          Clouds are composed of particles of liquid water called Cloud Droplets, and particles of ice called Ice Crystals.

-          Typically, clouds are formed when air is cooled and the temperature equals the dew point (100% humidity) resulting in condensation, which produces clouds.

-          Over oceans, the ability of dissolved salt to hold onto water molecules is called the Solute Effect.This allows cloud formation at relative humidities of less than 100%.

-          The Curvature Effect refers to even if air is saturated on a flat surface, it may be unsaturated on a curved surface (which clouds normally are).

-          Supersaturation is a condition when airís relative humidity is beyond 100%.

-          Nucleation is the initial formation of a cloud droplet around any type of particle.

-          There are two types of nucleation: Heterogeneous and Homogeneous.

-          Homogeneous nucleation is when a droplet is formed only by water molecules as they form a cluster, or particle.

-          Heterogeneous nucleation, the most common, occurs when small, non-water particles (usually aerosols called Condensation Nuclei) serve as sites for cloud droplet formation.

-          Examples of condensation nuclei are dust, salt, and pollen.

-          Ice Nuclei, the particles around which the ice crystals form, are important in the beginning stages of ice crystal formation.Ice particles can form in 4 ways: deposition nucleation, freezing nucleation, immersion nucleation, and contact nucleation.

-          Supercooled Water is liquid water at a temperature below 0 degrees Celsius.

-          Fog is a cloud at the ground.There are four kinds of fog: radiation fog, advection fog, evaporation fog, and upslope fog.

 

Lifting Mechanisms that Form Clouds

 

-          Most clouds form when air cools to the dew point as a parcel of air rises vertically.

-          There are four lifting mechanisms that form clouds: Orographic Lifting, Convection, Convergence, and Updraft.

-          Orographic lifting is when air cannot go through a mountain, and so it flows over it.

-          Frontal Lifting is when less dense warm air is forced to rise over cooler, denser air as a weather fronts move.Most common in winter.

-          Convection is when solar energy passes through the atmosphere and heats the surface, where the air becomes less dense than the air around it, making it rise.

-          Convergence lifting is when air near the surface flows together and is pushed upward when it is squeezed together.

-          The rising air in all lifting mechanisms causes an Updraft, which keeps cloud particles suspended regardless of gravity.

 

Cloud Classification

 

-          Clouds are given names corresponding to their appearance, layered or convective, and their altitude, as well as if they are precipitating.

-          Layered Clouds are much wider than tall.Stratus describes the layered cloud category and generally formed in stable air.

-          Convective Clouds are as tall, or taller, than they are wide.Cumulo describes the cloud category and generally formed in unstable air.

-          Cirro describes a high cloud that is composed of wispy crystals.

-          Alto is used to indicate a cloud in the middle of the troposphere.

-          Nimbus donetes a cloud that is causing precipitation.

-          Low Clouds consist of Stratus, Stratocumulus, and Cumulus clouds.

-          Middle Clouds consist of Altostratus and Altocumulus clouds.

-          High Clouds consist of Cirrocumulus, Cirrostratus, and Cirrus clouds.

-          Precipitating Clouds consist of Nimbostratus and Cumulonimbus clouds.

 

- ††† Clouds have both warming and cooling effects.They cool by reflecting solar energy back to space and warm by blocking the emission of longwave radiation to space and inhibit the ability of the plant to emit its absorbed solar energy to space.

-          The altitude of a given cloud is important in determining how much it warms the planet as well.

-          Stratus clouds warm the planet, but not as much as Cirrus clouds warm.

-          Clouds composed of small particles have a higher albedo and reflect more solar radiation into space, causing more cooling than clouds with large particles.

-          The composition of a cloud includes the phase of the water in it, the number and side of particles, and the shape of any ice particles.

-          There are more cloud condensation nuclei over land than over oceans, so continental clouds tend to have a greater number of water droplets than maritime clouds.

-          Ice crystals have four basic shapes based on temperature preferences: Hexagonal plate, Needle, Column, and Dendrite.

 

Precipitation

 

-          Precipitation is any liquid or solid water particles that falls from the atmosphere and reaches the ground.

-          Rain, snow, sleep, freezing rain, and hail are all forms of precipitation.

-          About 1 million cloud droplets have to combine to form a single raindrop.

-          Precipitation is not formed through growth by condensation because it would take a very long time to form a full-sized raindrop this way, and it forms much quicker.

-          Collision-Coalescence is a process combining very small particles by having them bump into each other and merge together, or coalesce.