Atmosphere Disturbance Pt 2 Flashcards
hurricane
circular low-pressure center w. steep pressure gradient outward
winds spiral inward
Hurricane formation “ingredients”
1) Needs pre-existing instability (from this latent heat released + fuels hurricane)
2) Need rotation = Coriolis effect SO needs to form at least 3 degrees off equator + cannot cross over equator
3) warm ocean temperatures ~80 degrees F w. depth of 50 meters
4) NO WIND SHEAR
types of tropical disturbances
1) tropical depression, winds 38 mph, closed wind circulation pattern
2) tropical storm, winds 39-73 mph
3) hurricane, winds 74+
hurricane characteristic
converging cyclonic wind pulls in war, moist air
rising air cools adiabatically –> large clouds –> condensation –> tons of rain
condensation releases latent heat, adding to instability of storm + strengthening it
hurricane vs midlatitude cyclone
hurricane has NO fronts, only warm moist air
eye of hurricane
calm center, wind speeds highest at eye wall + most updrafts around eye
weather pattern symmetrical around eye
spiral bands
dense cumulus + cumulonimbus clouds curving in from edge of storm to eyewall
wind shear
changes in wind direction
for hurricane to form, air has to be relatively same temp, to allow air to rise vertically + clouds form via adiabatic cooling
If there’s wind shear –> lose the latent heat so storm won’t increase in size
where do hurricanes form
1) east of Philippines
2) west of southern Mexico + Central America
3) Gulf of Mexico + Caribbean area
where do most hurricanes that hit North America form
west coast of Africa, travels along fetch (vast ocean without landmass) + increases in size before hitting North America
why don’t hurricanes go within 3 degrees of equator + or form in south atlantic
1) Coriolis effect - minimal to nonexistant at equator so hurricanes cannot form there
2) south atlantic - water too cold + too much wind shear
general track of hurricane
1) trade winds affect it –> move east to west
2) may go on east-west path for some time + then curve poleward
3) go up east coast of continents (warm currents there)
Life span of hurricane
average 1 week, max is 4 weeks
WHY? = once it hits land, it’s cut off from its source of warm, moist water
lack of water + colder temps kill it
hurricanes often enmesh into midlatitude cyclones
Saffir Simpson scale
intensity of hurricanes (1 = lowest, 5 = horrific)
measures wind speeds –> relates to pressure gradient
storm surge
wind from hurricane increases water height of waves by ~7.5 m more than normal tide
low pressure eye causes water to bulge an additional 1 m, adding more water
most dangerous part of hurricane
hurricane deaths caused by:
water (storm surges, flooding)
seasonality of hurricanes
restricted mainly to later summer/fall
peak = september in northern hemisphere since ocean temps warmest here + ITCZ shifted farthest poleward
Atlantic Multi-Decadal Signal
idea that higher sea-surface temperature, lower vertical wind shear, expanded westward flow of atmosphere off North Africa –> increased frequency of hurricanes
increase in # hurricanes NOT tied to humans
Intensity of hurricanes
hurricanes have been getting more intense + will continue to do so
human contribution to increased intensity low
thunderstorm
localized short lived convective storm accompanied w. thunder + lightning
*often accompany hurricanes, fronts (cold ones especially) + orographic lifting
tornado
intense vortex of deep low pressure cell surrounded by violently whirling cylinder of wind
goes from southwest to northeast in US
What tornadoes caused by
severe thunderstorms
extreme pressure diff from center to outside of funnel –> fuels extremely fast (300 mph) winds
Funnel clouds
tornado before it hits the ground, you can see rotating vortex
tornado size
generally 150 feet wide, moving at 35 mph, last for few minutes
some can be a mile wind, go at 60 mph, last for an hour
Tornado formation
develop in warm, moist, unstable air similar to midlatitude cyclone
all tornadoes can be made by thunderstorms –> need strong vertical wind shear
vertical wind shear turns supercell thunderstorm into mesocyclone –> wall cloud –> 25% of mesocyclones become tornadoes
4 ingredients for tornado formation
1) contrasting air masses - sharper contrast = more instability = stronger storm
2) flat terrain (allows uninhibited interaction btwn air masses = more instability)
3) vertical wind shear = shifts horizontal instability to vertical
4) severe thunderstorm
when do tornadoes form
spring/early summer bc of sharp air-mass contrasts
generally occur midafternoon (max heating)
why does america have 75% tornadoes
flat terrain of central + southeast US
canadian cP hitting Gulf mT masses creates conditions needed for tornado (tornadoes need conditions like midlatitude cyclones so they NEED a front)
enhanced fujita scale
measures tornado strength (EF 1 - light to EF 5 incredibly devastating)
storm watch vs storm warning
storm watch - advisory where conditions COULD produce severe weather
storm warning = storm HAS BEEN OBSERVED
El Nino
warm water on ocean surface + causes rain/drought + pacific fisheries disrupted
Describe onset of El Nino Southern Oscillation
1) for many months, trade winds pile up warm water in Western Pacific, creating bulge of warm water = Kelvin wave
2) Kelvin wave slowly moves East + deflected to South America coast
3) causes sea level off south america to rise, weakening high pressure in subtropics, warming water + reducing upwelling of cold water
4) Drought strikes Australia, Indonesia, South Asian monsoon fails + California/Arizona get more powerful winter storms + flooding since jet winds rerouted to southwestern US
La Nina
opposite happens, so water off South American coast COOLS, making Australia/Indonesia WETTER and southwestern US DRIER
Causes/effects El Nino Southern Oscillation
causes not fully understood
even effects, which are generalized, do not always happen
