Jet streams
fast flowing upper-level air current; near tropopause
Polar Jet stream
found between large boundaries if war and cold air in midlatitudes
-the bigger in radiation and temperature differences and bigger density and pressure differences
jet streams meander
ridges (pushing jet stream to the north) and troughs (digging jet streams towards the south)
Midlatitude cyclone
- Surface low pressure system
- central pressure near 990-1000 mb
- Jet streams usually responsible for formation
- exists between 35-70 latitude
- roughly 1600 km in size
- converging counterclockwise circulation (northern hemisphere)
- rising motion
- circulation creates fronts
LIFE CYCLE OF MIDLATITUDE CYCLONES
a) stationary front : separating cold air mass and warm air mass; beginning of the formation of the surface low due to divergence aloft
b) wave stage: winds begin to circulate around the center of low pressure
- open wave stage: during this stage the system has well defined fronts; cold front forms and warm front; heavy precipitation on cold front, light precipitation on warm front, center has precipitation; warm sector between warm and cold front
- occlusion stage: eventually, the surging cold front will catch up with the warm front
- warm air begins lifting from the surface as the cold “dense” air forces it upwards
- occluded front created
- cyclone starts to weaken or “dissipate”
- dissipating stage: once the storm has elevated all warm air
MIDLATITUDE ANTICYCLONES
- surface high pressure system
- upper level convergence due to jet streams
- diverging clockwise circulation
- sinking motion
- no fronts
- moves slower than cyclones
WHAT IS A TROPICAL CYCLONE
- a surface low pressure system
- thrive off warm waters
- typically, between 5N and 25N
- don’t form towards the equator because there is no Coriolis; there is a ton of warm convection but there is no spin
- persist 3-12 days and cover large areas
tropical cyclone season
august, September, October
tropical cyclone formation
- warm water and latent heat fuel
- evaporation of warm water at the surface creates a moist environment
- as warm moist air rises, condensation occurs in the upper atmosphere which release latent heat
- leads to warm buoyant air that will continue to rise
types of tropical cyclones
-Easterly waves/tropical depressions
a) develop in the tropics
b) Strong convergence occurs near ITCZ
c)Coriolis
d)cumulus clouds and precipitation occur as cloud clusters; associated with cyclonic rotation
- as easterly wave strengthens and low pressure decreases and becomes more organized it is named a tropical depression (sustained winds between 23-38 mph)
-Tropical storms
a) sustained winds are between 39-73 mph
-Hurricanes
a) tightly organized low pressure system; winds greater than 74 mph; warm core systems; can produce tornados
Hurricanes
-wind speeds are high because of very low pressure
-Saffir Simpson scale
Eyewall
towering ring of cumulonimbus clouds that surround the eye; rapid rising motion from outside the eye fuels the storms (strongest winds and heaviest storms)
eye
located in the center of a hurricane; generally calm/clear conditions (light winds and rain); sinking motion because pressure rises before gets to center
rainbands
convective bands of heavy precipitation that spirals inward toward the center of the storm
Storm surge
an abnormal rise of water generated by a storm over and above the predicted tides
Storm tide
The water level rises due to the combination of storm surge and astronomical tide
Reason for storm surge/tide
water is pushing against the coastline by winds
-pressure; low pressure=less weight causing the water to bubble up
WHAT CAUSES HURRICANES TO FALL APART?
- make them go into cold ocean
- landfall because there is no warm water
- sheer; chaotic winds in atmosphere rips hurricane to shreds
similarities
- surface low pressure systems
- rising motion/precipitation
- synoptic systems: large scale
- both spin counterclockwise with cumulonimbus clouds
differences
- forming mechanisms
- tropical cyclones do not have fronts
- tropical cyclone typically have lower central pressures
- tropical cyclones have higher wind speeds
- Sandy converged with midlatitude cyclone (Post tropical cyclone)
(top)Divergence
uplift, low convergence;To the east of the upper level trough axis winds speed up and spread far apart (divergence)
-creates surface low pressure; air rises
(top)Convergence
Subsidence. High divergence; -As upper level winds approach an upper level through axis from the west , the winds slow down and come together
-creates surface high pressure; air subsides
relationships to cyclones
Anticyclone follows a cyclone
• Anticyclones typically reside behind cyclone’s cold front
