What is meant by adiabatic lapse rate?
the rate at which atmospheric temperature decreases with increasing altitude in conditions of thermal equilibrium
What happens to a parcel of air as it rises?
under lower pressure, so it expands and cools
What happens to a parcel of air as it sinks?
compressed and undergoes adiabatic warming (temperature increase without gain in heat energy)
converted to heat and the air parcel gets warmer
What are the four main causes of air rising?
orographic lifting
frontal wedging
convergence
localized convective lifting
orographic lifting
occurs when air mass is forced from a low elevation to a higher elevation as it moves over rising terrain
as air mass gains altitude, it quickly cools down adiabatically, which can raise the relative humidity to 100% and create clouds, and, under the right conditions, precipitation
frontal wedging
the lifting of air resulting when cool air acts as a barrier over which warmer, lighter air will rise
convergence
a location where airflows or ocean currents meet, characteristically marked by upwelling (of air) or downwelling (of water)
localized convective lifting
unequal surface heating that causes localized pockets of air (thermals) to rise because of their buoyancy
What are the stages of development of a thunderstorm?
early stage
mature stage
dissipating stage
early stage of thunderstorm development
requires continuous supply of rising, warm, moist air to keep updraft and cloud mass growing
mature stage of thunderstorm development
upper-level precipitation begins when ice crystals and water drops become too heavy for updrafts to support
falling rain causes downdrafts, pulling in cooler, dryer air
updrafts and downdrafts blow side by side, creating gusty winds, heavy rain, thunder & lightning, hail
dissipating stage of thunderstorm development
cooling due to evaporation of precipitation and cool air dragged down precipitation itself cut off updrafts necessary to fuel thunderstorm
What are the two types of thunderstorm?
air mass thunderstorm
severe thunderstorm
air mass thunderstorm
also called single cell thunderstorm
warm moist air rises vertically to form thundercloud
most common in tropical locations at low latitudes
severe thunderstorm
also called supercell
tilted updrafts, lots of wind shear
rotation common
rain and hail on leading edge, tornadoes possible on trailing side
common in midlatitudes, warm air forced up over cold front
Describe the airflow movements that cause thunderstorms in (a) Florida and (b) the central and southern states.
a) converging warm, moist air masses are commonly forced upward, triggering the ubiquitous thunderstorms
b) warm moist air form the Gulf of Mexico advances up over the United states, and meet strong, cold air masses moving down from the north, which underride the warm air masses, helping lift the warm air upward
Name the hazards associated with thunderstorms.
heavy rains
flash floods
hail
high-speed winds, which can either be straight-line blasts or rotating tornadoes
lightning-caused deaths and fires
How is lightning generated?
during buildup of tall clouds, charged particles separate, creating an abundance of positive charges up high and an excess of negative charges down low
charge imbalances comes about as the freezing and shattering of super-cooled raindrops in the cloud initiates charge separations that are distributed by updrafts and downdrafts within the thundercloud
charge separations occur during the cloud buildup of the early stage
lightning bolts forth during the mature stage
abundance of negative charges in the basal part of the cloud induces a buildup of positive charges on the ground surface, because the opposite charges attract each other
Discharge begins within cloud, initiates downward stream of electrons ? stepped leader
as stepped leader nears ground, ground electric field increases greatly, sending streamers of positive sparks upward, connecting with stepped leader about 50 m above ground
How does hail form?
buoyant hot air rises from heated ground
upper-level cold air creates large temperature contrasts
strong updrafts keep hailstones aloft while adding layers
Where are large hailstorms most common?
most common in late spring and summer
timing is related to the position of the polar-front jet stream
in April, Texas and Oklahoma receive much hail
by June, most of the hailstorms have migrated northward into Montana, Wyoming, and South Dakota
July - much of the hailstorm activity has moved into Canada
What is the major hazard with hail?
damage to automobiles, aircraft, skylights, glass-roofed structures, livestock, and crops
Where in the world are tornadoes most common?
U.S. and Canada
Where in the U.S. are there the most tornado-related deaths?
Alabama
Missouri
Mississippi
Tennessee
North Carolina
What time of year are there the most tornadoes?
most common in late spring and early summer
What is a mesocyclone?
rotating updraft forms in mid-level of atmosphere
a cyclonic air mass associated with a supercell; its presence is a condition for a tornado warning
Where in a thunderstorm do tornadoes occur? (front, center, rear?)
rear
Why do most tornadoes in the US move in a northeasterly direction?
they are under the influence of the Polar Jet Stream
Which type of thunderstorm are tornadoes most commonly associated with?
severe thunderstorms
What is the name of the scale used to measure tornado intensity?
Fujita scale
How many categories of tornado are there?
6
What are the factors used to measure tornado intensity?
types and severity of damages done by varying tornado speeds
How can tornado hazards be mitigated? (i.e. how can the number of fatalities be reduced?)
get underground or into an interior room on the lowest floor -- stay away from windows
get out of your car or mobile home, move to a sturdier structure
protect your head -- helmet if possible
don't try to outrun a tornado in your car
don't seek shelter under a bridge overpass
tornado warnings -- doppler radar
What should you do during a tornado?
get underground or into an interior room on the lowest floor -- stay away from windows
get out of your car or mobile home, move to a sturdier structure
protect your head -- helmet if possible
don't try to outrun a tornado in your car
don't seek shelter under a bridge overpass
Does Sacramento get tornadoes?
DUH.