Atmospheric Humidity and Lifting Mechanisms

Humidity

• Humidity is a measure of the amount of water vapor in the air
• Relative Humidity (RH) is the percentage of water vapor in the air compared to the maximum amount of water vapor the air can hold at a given temperature
• Specific Humidity (SH) is the mass of water vapor per unit mass of air

Spatial Patterns of Humidity

• Latitude: humidity decreases as latitude increases
• Land vs. Water: humidity is higher over water than over land

Air Temperature and Humidity

• As air temperature increases, RH decreases
• As air temperature decreases, RH increases

Dew Point

• Dew point is the temperature at which the air becomes saturated with water vapor and dew or frost begins to form
• Dew point is a measure of the absolute humidity of the air

Daily Pattern of RH and TPW

• TPW (Total Precipitable Water) is the total amount of water vapor in the atmosphere
• Daily pattern of RH: RH is highest in the morning and lowest in the afternoon

Fog

• Fog is a type of cloud that forms at ground level
• Types of fog: radiation fog, advection fog, steam fog, and upslope fog

Lifting Mechanisms

• There are four lifting mechanisms: orographic, frontal, convergence, and updraft
• Each lifting mechanism leads to the formation of clouds and precipitation

Clouds

• Clouds are collections of water droplets or ice crystals suspended in the air
• Types of clouds: cumulus, stratus, cirrus, and nimbus
• Clouds are associated with different types of precipitation: cumulus clouds are associated with light precipitation, stratus clouds are associated with light to moderate precipitation, and nimbus clouds are associated with heavy precipitation

Precipitation Forming Mechanisms

• Precipitation forms when water vapor in the air condenses and falls to the ground
• Precipitation forming mechanisms: collision-coalescence, accretion, and ice-crystal process

Hail Formation

• Hail forms when updrafts in thunderstorms carry water droplets up into the freezing level of the atmosphere, where they freeze into small balls of ice

Latent Heat and Phase Changes

• Latent heat is the energy released or absorbed when water changes phase from liquid to solid (freezing) or from liquid to gas (evaporation)
• Latent heat is released during condensation and freezing, and absorbed during evaporation and melting

Air Masses

• Air masses are large bodies of air that have similar temperature and humidity characteristics
• Air masses are classified into four types: maritime tropical, maritime polar, continental tropical, and continental polar
• Air masses influence the weather in different regions of the US

Fronts

• A front is the boundary between two air masses of different temperatures and humidity
• Types of fronts: cold front, warm front, stationary front, and occluded front
• Weather associated with each type of front: cold front (clouds, precipitation, and wind), warm front (clouds, precipitation, and wind), stationary front (clouds, precipitation, and little wind), and occluded front (clouds, precipitation, and wind)

Mid-Latitude Cyclones

• Mid-latitude cyclones are low-pressure systems that form in the mid-latitudes and are associated with clouds, precipitation, and wind
• Basic structure of a mid-latitude cyclone: center of low pressure, cold front, warm front, and occluded front
• Relationship between mid-latitude cyclones and the polar jet stream: mid-latitude cyclones form when the polar jet stream is strong and moves southward

Thunderstorms

• Thunderstorms are intense storms that form when there is a strong updraft of warm air
• Three stages of thunderstorms: cumulus stage, mature stage, and dissipating stage
• Characteristics of thunderstorms: updrafts, downdrafts, lightning, thunder, and heavy precipitation
• Relationship between air masses and thunderstorm occurrence: thunderstorms are more likely to occur when there is a strong temperature gradient between two air masses

This quiz covers the concepts of humidity, spatial patterns, and lifting mechanisms in the atmosphere. Topics include relative humidity, specific humidity, dew point, and types of fog. It also covers the application of dry and wet rates to a parcel of air and the concept of the LCL.