Define wind
The horizontal movement of the air
What initiates the movement of air
The pressure difference in the horizontal causes air to move
Define pressure gradient force
The force that starts the movement of air directly from a region of high pressure to a region of lower pressure.
The effect of the earth’s rotation on wind’s direction is called: and what direction does it deflect it
The coriolis effect. to the right
What is Buys-Ballot law?
if you stand with your back to the wind in the northern hemisphere the lower pressure will lie to your left.
when a low or high pressure system passes to the north of your station the winds will:
veer
wind speeds are ________ to the pressure gradient
directly proportional
Define friction force
The force which results from the wind interacting with the earth’s surface
Friction ______ wind speed and ______ wind direction. What does it do to the coriolis effect?
diminishes and modifies. It counteracts the coriolis effect.
Is the greatest friction over land or sea?
land
During ascent from sfc to 1000m wind will?
increase and veer
During descent from 1000m to sfc wind will
decrease and back
During daytime heating, wind will?
During nightime cooling, wind will?
- Veer and increase
2 back and decrease
Define Gust
A relatively rapid increase in wind speed that lasts only briefly
Define Squall
Wind speed increases suddenly and maintains a peak speed for several minutes before diminishing
Sea breeze
A diurnal coastal breeze that blows onshore from the sea to the land
Land breeze
a diurnal coastal breeze that blows offshore from the land to the sea
Katabatic Winds
Winds that flow down ice free slopes at night or flows down ice covered slopes day and night.
anabatic winds
Winds that blow up slopes during the day due to differential daytime heating
Gusts are caused by what 2 ways?
- Mechanical turbulence
2. Unequal heating of the earth’s surface
what are the 2 principal causes of squalls?
- Well developed Thunderstorms
2. fast moving cold fronts
How are katabatic winds generated?
Sides of the valley are cooled by radiation at night and the air will flow down the slope.
How are anabatic winds generated
the sides of a valley are heated during the daytime and the air rises. Cooler air from the bottom of the valley rushes up the sides to replace the rising air.
What are the 3 topographical effects on air circulation
- Barrier effect
- Funnel effect
- Valley effect
Define air mass
A large section of the troposphere that has relatively uniform temperature and moisture in the horizontal
How are air masses formed?
An air mass is formed when a large section of air acquires the temperature and moisture characteristics of a vast area of the earth’s surface.
What 2 terms are used to describe the moisture content of air masses?
- Continental
2. Maritime
What 3 terms are used to describe the temperature of air masses in NA
- Arctic
- Polar
- Tropical
Name the 4 air masses that occur over NA in winter
- Continental Arctic
- Maritime Arctic
- Maritime polar
- Maritime tropical
what are the typical trajectories of the 4 airmasses
1 cA - southward
2 mA - South eastward and eastward
3. mP - Eastward and north eastward
4. mT - northerly
describe the stability of each airmass
- Ca to mT Stable to unstable.
with respect to stability, if the air is cooled from below, will it become more or less stable?
More stable
What are the 6 factors that may change the temperature of airmasses?
- Changes in latitude
- change of season
- ocean currents
4 movement from over water or over land - Diurnal variations
- topography
How would an air mass become destabilized?
- heating from below
2 cooling aloft (advection)
how would an airmass become stabilized?
- By cooling from below (radiation cooling)
2. by heating aloft (advection)
state the relationship between moisture content and air mass temperature
Warmer air masses can hold more water vapour than colder ones.
what are 3 types of moisture increases and 1 type of moisture decrease in air masses?
- Movement over water
- Melting/evaporation of snow
- movement over regions of dense vegetation
1b. Condensation/precipitation
define front
the transition zone between 2 air masses
name the 3 frontal systems located over Canada in the winter
- Continental Arctic
- Maritime Arctic
- Maritime Polar
Define Frontal surface
The transition zone separating warm and cold air aloft
Define Surface front
The transition zone separating warm and cold air touching the earth’s surface
Define Cold front
A transition zone between warm air and advancing cold air. A cold front is always followed by cold air
Define warm front
A transition zone between warm air and retreating cold air.
Stationary front
A transition zone between two air masses that are not moving.
The severity of the weather caused by a front depends on which factors (5)
- The slope of the frontal surface
- The speed of the front
- Temperature of the lifted air mass
- Moisture content of the lifted air mass
- Stability of the lifted air mass
With respect to temperature, dew point temperature and pressure, what happens when a cold front or warm front passes
Cold front: Decrease in temperature (maybe a slight increase before the drop), decrease in dew point temperature and pressure rises.
Warm front: Increase in temperature, increase in dew point, a general fall in pressure as a warm front approaches.
what are the average slopes of warm, cold and stationary fronts
Cold: 1:50
Warm 1:200
Stationary 1:100
At a warm front, describe the 3 factors that determine cloud type and precipitation
- The moisture content of the overrunning air
- The stability of the overrunning air
- The degree of overrunning
At a cold front, describe the 3 factors that determine cloud type and precipitation
- The moisture content of the lifted warm air
- The stability of the lifted warm air
- The degree of lift a. the slope of the frontal surface b. the speed of the front
If warm air is moist and stable, expect the following clouds as the warm front approaches your station
1.CI,CS,AS,NS and continuous precipitiation.
If the warm air is moist and unstable, expect the following clouds as the warm front approaches your station
- CI,CS,AS,NS and embedded CBs.continuous precipitation.
As the cold front approaches, in moist and stable air what type of clouds will form when the front approaches rapidly and slowly
slowly: wide spread layer clouds and intermittent or continuous precipitation
Rapidly: Narrower band of clouds and continuous or intermittent precipitation
Define frontal wave
A wave shaped distortion on a front usually associated with a trough
what is frontogenesis and frontolysis?
Frontogenesis is the formation of a front
Frontolysis is the dissipation of a front.
What is the area between a warm front and a cold front in a frontal wave called?
Warm sector
What are the 3 main factors that determine cloud characteristics?
- Stability of the air
- moisture available in the air
- temperature of the air