Lecture 14 Flashcards
Types of air masses
- continental polar
- maritime polar
- continental tropical
- maritime tropical
Types of fronts
Warm fronts
Cold fronts
Air masses
Weather conditions are controlled by air masses up to 2000 km wide
Continental artic
- cA
- very cold dry air masses formed over northernmost continent
Continental polar
- cP
- cold dry air masses formed over continent (central Canada)
Maritime polar
- mP
- cool moist air masses formed over ocean
Continental tropical
- cT
- hot dry air masses formed over continent
Maritime tropical
- mT
- warm moist air masses formed over ocean
Fronts
-boundaries between air masses
Warm front
- warm air is advancing on cold
- warm air mass flows up and over cold
- shown with rounded teeth on weather map
Cold front
- Cold air is advancing on warm
- cold air mass flows under warm
- shown with pointed teeth on weather map
Wind speed and direction
- wind speed is specified according to the direction it comes from
- typical wind speeds average 10-30 km/hr
- fastest average speed 70 km/hr
- hurricane and storm winds up to 335 km/hr
- highest ever recorded 372 km/ hr
Review flag thing for weather map
Wind chill
- skin cools faster in moving air
- there is a boundary layer of very slow moving air that acts as an insulator and thins as speed increases
- windchill equivalent temperature (windchill factor) measures rate of heat loss from exposed skin
Wind speed is controlled by
- Pressure gradients
Isobars far apart=low pressure gradient and low speed winds
Isobars close together=steep pressure gradient and high speed winds - Coriolis effect
- Friction with the earth’s surface
Geostrophic winds
- winds driven by a balance between pressure gradient and coriolis effect
- parallel to isobars
Low level pressure gradient winds
- direction modified by friction
- slows wind and reduces coriolis effect
- smooth surface (e.g. sea) deflection 10-20 degrees
- rough surface (e.g. forest) deflection up to 50 degrees
Always toward low pressure direction
Monsoon winds
- seasonal migration of pressure belts reverse wind directions
- affect India, Australia, Africa
Winter:
- ITCZ lies S of India
- dry NE trade winds from land
Summer:
- ITCZ migrates North
- SW winds from ocean brings heavy rain
Sea breezes
- local pressure gradient winds
- day: land heats faster than sea
- air rises over land: low pressure
- sea breeze blows towards land
Land breezes
- local pressure gradient wind
- night: land cools faster than sea
- air rises over sea: low pressure
- land breeze blows towards sea
Mountain and valley winds
Day: sun heats south facing slopes (in N hemisphere)
- warm air rises
- air flows up from valley
-opposite at night
Katabatic winds
- cold dense air accumulates over high plateau, glacier, or ice cap
- cold air spills into valley
Chinooks
- regional air flow forces air across mountains
- descending air warms adiabatically
Thunderstorms
- form in warm moist air masses, during daytime heating
- especially along cold fronts where mT air contacts cP air
- density lifting is assisted by condensation, which releases latent heat
- high winds drawn in to storm
- strong upward air flow carries ice particles upward repeatedly, freezing of supercooled water can produce large hail
- top of storm reaches typically an ice cloud “anvil”
Thunderstorms: Lightening
- strong air currents cause ionization of air molecules
- electric discharges heat air explosively (cloud to cloud, cloud to ground)
- resulting sound is thunder
