Atmospheric Moisture Flashcards
What is the hydrologic cycle?
The transfer of water from earth to the atmosphere and back again
What are the two types of moisture in the atmosphere?
- Absolute Humidity
2. Relative Humidity
What is absolute humidity?
Mass of water vapor in a given volume of air; e.g. 20 gr H2O / 1 m3 air
What is relative humidity?
RATIO (%)
Actual water content of air/ potential amt. water air could hold
What controls the water capacity of an air parcel?
Temperature
What has a greater capacity to hold water vapor, warmer or cooler air?
Warmer air has a greater capacity to hold water vapor
What is dew?
When condensation occurs directly on a surface
What is dew point?
DEW POINTis the temp at which saturation occurs (RH=100%) and condensation begins, DEW FORMS
What happens if the dew point is less then the freezing point?
water vapor sublimates (gas to solid) as ice crystals = FROST
When does Frost and Dew form and why?
FROSTFrost and Dew form at night (or early morning) due to radiationalcooling:earth radiates heat away and cools
What is Dew Point a clear indicator of?
The water content of the air
If there is a high dew point what does that mean?
Moist air
If there is a low dew point temperature what does that mean?
Dry air
What are clouds?
CLOUDS= Condensation forms that develop above the ground
What are two important points to remember about clouds?
- Condensation does NOT= Precipitation (PPT)
2. Clouds consist of solid or liquidwater… NOT water vapor which is a gas
How are clouds classified?
By height and shape
What are the three main types of cloud I need to know?
- Cirrus
- Stratus
- Cumulus
What happens when you add nimbus or nimbo to these clouds?
It means that the clouds produce rain.
Examples –nimbostratus, cumulonimbus
What are Cirrus clouds?
Cirrus–highest, wispy, consist of ice crystals
What do Cirrus clouds signal?
Approaching weather (a front)
What are Stratus clouds?
Stratus –horizontal (layer) clouds that form a continuous sheet near the surface(altostratus would be mid-level)
What are Cumulus clouds?
Cumulus–“fair weather cumulus”puffy clouds, show vertical development( indicating convection)–Known by flat bases, distinct outlines
What do towering cumulus clouds indicate>
Towering cumulus clouds indicate intense convection! Much larger, more vertical development than fair weather cumulus
What is fog?
FOG = “cloud on the ground”. Thick layer of moist air cooled to its dew point
What are the 5 types of fog?
- Advection Fog
- Radiation Fog
- Valley Fog
- Orographic(upslope) Fog
- Steam Fog
What is advection fog?
Involves horizontal movementof air warm air moves over cold surface, is chilled to dew point
Where is advection fog found?
West coast, often involves coastal setting
What is radiation fog?
Radiational cooling of ground surface, chills moist air and condensation occurs, usually pre-dawn hours under H-press. It is stationary rather than moving and always touching ground
Where is radiation fog found?
In most of the world!
Where is valley fog common?
common in Appalachians, any mountains except deserts. It is also common in early mornings with radiational cooling
What is Orgographic fog?
upslope movement of moist air, Cools to dew point. (cloud spilling over mountains)
Where is orgographic fog common?
common in all mountains, e.g., Appalachians and TROPICAL mountains.
When is steam fog common?
Common in fall. also common where there are rivers and lakes and source of cool/ cold air
Where are the foggiest places in the U.S.?
West coast, east coast, south , by great lakes (any where by water pretty much)
What is valley fog?
Heavy cold air drains into valleys, reaches dew point and condensation occurs.
What is convection?
Convection: Thermal heating of land, local heating
What kind of precipitation happens when ITCZ or STH are dominant?
wet summer when ITCZ dominates
dry winter when STH dominates
What is steam fog?
cold air moves over warmer water surface (rivers/lakes)
What has to happen to get from condensation to precipitation?
- Small drops coalesce on condensation nuclei (e.g. dust, smoke)
- Drops get larger and larger, gravity brings them down
To get precipitation to occur what must first happen?
We must chill air to the dew point. We do this by lifting the air to cool it.
What are the three majoring complicating factors that disrupt the expect zonal pattern of precipitation?
- Mountains
- Continental Effects
- Cold Ocean Currents
Where is convection common?
Common in tropics, subtropics year-round and mid-latitudes in summer
When do thermal convection cells occur?
Often occurs in afternoon or evening when land is heated to the maxWhat
What is convergence?
Area of low pressure pushes air upwards
What are the four ways to lift air?
- Convection
- Convergence
- Orographic lifting
- Frontal
What is orographic lifting?
Orographic lifting –air forced upslope, cools
-mountains create wet and dry locations
Where is orographic lifting common?
Anywhere on mountains
What is orographic lifting responsible for?
It is responsible for the rainiest places in the world, like Hawaii
When is steam fog common?
Common in fall. also common where there are rivers and lakes and source of cool/ cold air
What is frontal lifting?
It is when cold air is heavier so warm air rises and then cools
Where is frontal lifting common?
It is common in mid-latitudes and along the polar front
Where are the rainiest places in the U.S. and why?
North West coast (washington), East coast, especially in the south. This is due to these places having multiple lifting mechanism, onshore winds, access to moisture, and mountains
Why are mountains a major complicating factor that disrupts the expect zonal pattern of precipitation?
Mountains life and cool air.
Orographic–high PPT in otherwise drier locations
Rainshadow–deserts in potentially moist places
Why are cold oceans a major complicating factor that disrupts the expect zonal pattern of precipitation?
Cold currents stabilize ATM and reduce precip
What else is a big factor in precipitation?
Seasonality. As sun’s direct rays move N&S, wind & pressure belts follow.
What are seasonal changes in lifting mechanism?
Rainfall in eastern U.S. in SUMMER, mostly CONVECTIVE (T-storms). In Winter, eastern U.S. gets mostly FRONTAL precipitation.
