Weather & Climate

Air Pressure
The force exerted per unit area, or the force exerted on a surface by the air.
Characteristics of Air Pressure
1) It can vary both spatially and temporally
2) The avg. surface pressure is 1013 mb.
3) It is shown on a map as lines of equal pressure or H (high) & L (low)
Pressure Gradient Force (PGF)
A force that arises from spatial variation in pressure, or the difference in air pressure from one point on the Earth’s surface to another.
Winds flow from areas of _____ pressure to areas of _____ pressure.
_____ _______ & the PGF determine wind direction & strength or speed
Air Pressure
Differential Heating
the motive force behind land breezes and sea breezes (or, in the case of larger lakes, lake breezes), also known as on- or off-shore winds. Land is a rapid absorber/radiator of heat, whereas water absorbs heat more slowly but also releases it over a greater period of time
Coriolis Effect
A deflective force arising from Earth’s rotation that is used to account for motions measured relative to the surface, or the apparent deflection in path or movement of an object moving over the Earth’s surface due to Earth’s rotation.
Characteristics of Coriolis Effect
1) It’s strongest at the poles & zero at the equator
2) An object’s speed will alter the amount of deflection, increase speed = increase deflection
3) It alters direction, but NOT the speed of an object
4) It affects not only wind, but ocean currents, flight paths of planes and missiles, etc.
Types of Wind
Geostrophic & Surface
Geostrophic Winds
Upper level winds, > 1-2 km’s above the surface.
Characteristics of Geostrophic Winds
1) They’re affected by PGF & CF
2) They blow parallel to isobars with little or no friction
Main Patterns of Geostrophic Winds
1) Zonal Flow = a more ‘flattened’ air flow with primarily an east-west flow
2) Meridional Flow = a more north-south or curved flow with distinct ridges (High Pressure) and troughs (Low Pressure)
Jet Stream
A meandering “river” of air usually 9 to 12 km above sea level, with high wind speeds. They are highly turbulent and their speeds and location will vary considerably.
Rossby Waves
Waves in the mid-latitude westerlies having wavelengths on the order of thousands of km’s. They often circle the planet, forming a pattern of ridges and troughs.
Surface Winds
Winds below 1-2 km that are in contact with the Earth’s surface.
Characteristic of Surface Winds
1) They’re affected by PGF, CF, and Friction
Low Pressure Cells
* have cyclonic or counterclockwise flow in the NH
* have anticyclonic or clockwise flow in the SH
High Pressure Cells
* have anticyclonic or clockwise flow in the NH
* have cyclonic or counterclockwise flow in the SH
Wind Measurements
Direction & speed
N, S, E, W, NE, SE, NW, SW
* Winds are always named for the direction they are coming from
* Usually recorded by an anemometer in mph or kph
Measuring Scales for Wind
Macroscale, Mesoscale, Microscale, & Planetary Scale
Planetary Scale Winds
1) Trade Winds – in the tropics; NH has the NE tradewind, SH has the SE tradewind
2) Westerlies – Subtropics; NH & SH
3) Easterlies – Subpolar; NH & SH; High pressure
Types of Local Winds
1) Land/Sea Breezes
2) Valley/Mountain Breezes
3) Chinook
4) Katabatic
Land/Sea Breezes
Occurs in coastal areas; dependent on position of local High & Low pressure cells
* High pressure over the land = Land breeze
* High pressure over the sea = Sea breeze
Valley/Mountain Breezes
Warm wind going up the mountain during the day and cool wind coming down at night
Chinook Wind
Warm, dry wind coming off (down) the mountains. Also known as the Santa Ana winds in California.
Katabatic Wind
A flow of dense, cold air downslope under the influence of gravity. Primarily found over large ice sheets, such as those found in Greenland and Antarctica.
Idealized Pattern of Pressure
* Changes temporally & spatially
* It’s altered from the idealized pattern by land masses & seasonality, differential heating
Low Belts
Areas of uplift with convergence at the surface; usually unstable
Examples: ITCZ & Subtropical Lows (SPL)
High Belts
Areas of subsidence and divergence at the surface; usually stable
Examples: STH, Polar High (PH)
Hydrologic Cycle
the continuous movement of water from the Earth’s surface to the atmosphere and back to the surface, then to the atmosphere..
Hydrologic Cycle’s Basic Processes
Evaporation & Transpiration (Evapotranspiration), Condensation, Precipitation, Runoff
Difference Between Transpiration and Evapotranspiration
* Transpiration – the water absorbed by vegetation & then released to the atmosphere
*Evapotranspiration – the combined amount of water lose by evaporation & transpiration
States of Water (Matter)
Solid, liquid, gas
The amount of water vapor in the air that can be measured in different ways
Specific Humidity
* g of H2Ov (water vapor) / kg of air
Absolute Humidity
g of H2Ov / m3 of air
Relative Humidity
* Actual H2Ov content / H2Ov capacity x 100
* When RH = 100%, the air is saturated
* This is controlled by water vapor content & the air’s capacity, which is controlled by Temp.
Partial Pressure
Each component of the atmosphere makes up a part of the total air pressure
Water Vapor Pressure
the portion of the air pressure which is made up by water vapor
* When the air is holding all the water vapor it can
* Warmer air can hold more water vapor
* Saturation vapor pressure increases with increasing T
Dew Point
The T to which air must be cooled to become saturated
Dew Point Temperature
* The T at which saturation will occur, given sufficient cooling
* It is an indication of the moisture level in the air
* It is controlled by vapor pressure, not by air T
How to change the RH
1) By adding or subtracting water vapor
2) lowering or raising the T

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