WEAX 201 Lesson 6 - Wind, Causes, & Effects

wind velocity is a?

vector

what is wind velocity?

• () & ()

• speed (kt) and direction (degrees azimuth FROM which the wind is blowing)

what is wind direction reported in?

• reported in degrees (), except it is reported () through ATC

• reported in degrees TRUE, except it is reported MAGNETIC through ATC

for example, a westerly wind would be coming from the?

west

what component is only measured in the METAR?

• horizontal

what are the cardinal directions?

• north

• south

• east

• west

• north: 360

• south: 180

• east: 090

• west: 270

wind vector can be added to…?

• to add vectors, arrange them from…

• example: true () & () = true () & ()

• navigating with the wind can save…

• wind vector can be added to other vectors

• example: true heading and airspeed = true course and ground speed

• navigating with the wind can save time

how is wind speed measured?

• measured by anemometer

how is wind direction measured?

• wind vane

what are the 3 various types?

• 3-cup

• fan

• ultrasonic anemometers

what helps estimate winds?

• wind sock

what is a surface wind report?

• an official () or () of the () and () of the wind blowing near the Earth's surface

• typically measured at a standard height of () meters or about () ft AGL

• an official measurement or broadcast of the speed and direction of the wind blowing near the Earth's surface

• typically measured at a standard height of 10 meters or about 33 ft AGL

for example: what does 23022G35KT mean?

• indicates that the 2-min average of wind speed is 22kt and direction is 230 degrees TRUE

for example: what does 23022G35KT mean?

• in past 10 min, the wind varied rapidly by more than 10 kt and strongest (or gust) was 35 kt, that is the MAXIMUM

what does gusty wind indicate?

• weather conditions marked by sudden, short bursts of strong wind that alternate with periods of calmer air

• MAXIMUM wind

how do you read wind symbols on a map?

• wind speed is rounded to nearest () kt

• each line (barb) resembles () kts but a half line (half barb) is () kts

• when there is a flag, it resembles () kts

• when there is a circle, wind is ()

• flaps and barbs point to () pressure

• the symbol points toward the direction () which the wind is blowing (EXAMPLE: if the line points north, the wind is coming from the () and blowing () )

• wind speed is rounded to nearest 5 kt

• each line (barb) resembles 10 kts but a half line (half barb) is 5 kts

• when there is a flag, it resembles 50 kts

• when there is a circle, wind is calm

• flaps and barbs point to LOW pressure

• the symbol points toward the direction FROM which the wind is blowing (EXAMPLE: if the line points north, the wind is coming from the north and blowing south)

according to (…), the velocity of () will not change unless acted upon by a ()

• newton’s laws of motion

• the velocity of air will not change unless acted upon by a force

what are the three forces that can act on a parcel of air?

• pressure…

• frictional…

• coriolis…

• pressure gradient force

• frictional force

• coriolis force

what are pressure gradients?

• gradient = ()/()

• pressure gradients force air from () pressure toward () pressure, () to the isobars

• gradient = change/distance

• pressure gradients force air from HIGHER pressure toward LOWER pressure, perpendicular to the isobars

what kind of pressure causes horizontal wind?

horizontal pressure gradients

what is hydrostatic balance?

• () pressure gradient force () in most situations balanced by () force ()

• upward pressure gradient force upward in most situations balanced by gravitational force downward

does wind always blow directly to from high to low pressure?

• no due to the coriolis effect and friction

what are isobars?

• lines of…

• lines of constant pressure

PGF and wind will be the strongest where…

• the isobars are the closest together

what is thermal circulation?

• a local wind pattern created directly by () in air () and ()

• a local wind pattern created directly by differences in air temperature and pressure

what causes pressure gradients?

• temperature differences

a thermal circulation develops as follows: warm column has () pressure aloft

• warm column has higher pressure aloft because warm air is less dense and occupies a larger vertical volume than cool air

• At any given high altitude (aloft), there is more remaining air weight above you in a warm column than in a cold column, resulting in higher pressure

a thermal circulation develops as follows: PGF causes air to flow from high to low aloft

• winds fly parallel to isobars rather than straight across them

below, what happens?

• an opposite () forms, so at the surface, a () return flow develops from the () pressure (() area) to the () pressure (() area)

• example: () breeze (late morning to evening)

• an opposite PGF forms, so at the surface, a cool return flow develops from the high pressure (cool area) to the low pressure (warm area)

• example: sea breeze (late morning to evening)

what is a land breeze?

• at ()

• land () much () than water and the air over the warmer water becomes () and (), then (), () air from the land flows out to the water to replace it

• at night

• land cools much faster than water and the air over the warmer water becomes lighter and rises, then cooler, denser air from the land flows out to the water to replace it

what is a sea breeze?

• during the ()

• the sun () the () faster but then () the water, the air over the land gets (), becomes () and (), so ()/() air flows in to take the place of the () warm air

• during the day

• the sun heats the land faster but then heats the water, the air over the land gets warm, becomes lighter, and rises, so cooler/heavier air flows in to take the place of the rising warm air

warm air rises →

cool air sinks →

air moves from () to ()

• warm air rises → low pressure

• cool air sinks → high pressure

• air moves from high to low

what is global thermal circulation?

• thermal circulation that affects the ()

• The () are warmer than the (), and so you get () pressure over the tropics, () pressure over the mid-latitudes.

  That's why we have () in the mid— in the subtropics, like in Arizona.

• This () air comes northward and sinks, creates () pressure, and then that high pressure drives the air () the tropics.

• So you get this circulation like this, and that explains why there's so much () in the tropics, because there's so much () motion, (), () air rising, that we get a lot of rain there.

• thermal circulation that affects the globe

• The tropics are warmer than the mid-latitudes, and so you get high pressure over the tropics, lower pressure over the mid-latitudes.

  That's why we have deserts in the mid— in the subtropics, like in Arizona.

• This tropical air comes northward and sinks, creates high pressure, and then that high pressure drives the air towards the tropics.

• So you get this circulation like this, and that explains why there's so much rain in the tropics, because there's so much rising motion, moist warm air rising, that we get a lot of rain there.