GEOL 106 Lecture Notes - Lecture 31: Occluded Front, Natural Hazard, Puffy Amiyumi
26 May 2018
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UNSTABLE AIR
- air movement can also be caused by vertical differences in temperature and pressure in atmosphere
- examine behaviour of small volume or parcel of air
- tendency of air is to remain in pace or change its vertical position → atmospheric stability
o air mass is stable if parcels if parcels of air within it resist vertical movement or return to their
original position after they have moved
o air mass is unstable if parcels within it are rising until they reach air of similar temperature
and density
- atmosphere commonly becomes unstable when lighter warm or moist air is overlain by denser cold
or dry air
o instability causes some parcels of air to sink and others to rise → severe weather like
thunderstorms and tornadoes
- upper atmosphere winds can cause air mases to move over colder or warmer surfaces, increasing or
decreasing atmospheric stability
CASE STUDY 9.1 A CLOSER LOOK CORIOLIS EFFECT PG. 298
FRONTS
- front = boundary between cooler and warmer air mass
o cold front: when cold air is moving into mass of warm air
o warm front: when opposite occurs
o warmer air will always be lifted by colder, denser air mass
- air masses may also have different humidity levels, densities, wind patterns, stability
- as a result with friction with ground, high density cold fronts are slowed at lower levels compared to
higher up in the air mass causing front to become steeper
- cold fronts: as cold front advances, warm air is driven rapidly up steep cold front causing localized
cloud formation, strong updrafts, often heavy precipitation
- warm fronts: tend to be gentler as they override receding cold air mass, updrafts and cloud formations
are more scattered
- fronts may remain stationary for few hours or even days
o boundary between cooler and warmer air that shows little movement = stationary front
o occluded front: 4th type of front, develops when rapidly moving cooler air overtakes another
cooler air mass and warm air is wedged above frontal boundary
- each of the 4 types of fronts can cause inclement weather
o positions of fronts as well as areas of high and low pressure are shown on standard weather
maps of surface atmospheric conditions
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9.5 Hazardous Weather and Geographic Regions at Risk
- thunderstorms, tornadoes, hurricanes, blizzards, icestorms, mountain windstorms, heat waves, dust
storms
THUNDERSTORMS
- 1000s of thunderstorms in progress at any one time
- most occur in equatorial regions like Uganda, East Africa
- in NA: regions with highest annual number of days with thunderstorms are in areas along Front Range
of Rock Mountains in Colorado and New Mexico and in belt that encompasses of all Florida, southern
parts of Georgia, Alabama, Mississippi, Louisiana
- can form at any time, thunderstorms are most common during afternoon and evening hours
especially in spring and summer → 3 basic atmospheric conditions that are required to produce
thunderstorm
1. warm humid air must be available in lower atmosphere to feed clouds and precipitation and
provide energy to storm as it develops
find more resources at oneclass.com
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