Chapter 8: Thunderstorms, Mid-Latitude Cyclones, and Hurricanes

What % of tornados have wind speeds between 65 - 181 kph?

%69

cumulus stage

- a cell of warm humid air rises and cools to form a puffy cumulus cloud - vertical cloud growth during this stage occurs at a rate of 18-72 kph - cumulus clouds form as a result of the condensation of water vapor into liquid water droplets - the conversion of water from gas to liquid releases large amounts of LATENT HEAT - this added energy keeps the air inside the expanding cumulus cloud warmer than the air surronding it - this warmer air also causes circulation inside the cloud to be dominated by updrafts

Cumulonimbus Cloud

- a well developed vertical cloud that often has top shaped like an anvil - very dense with condensed water and deposited ice - when weather happens, called thunderstorm - altitude from a few hundred meters to more than 12,000 above earths surface

Nimbostratus cloud

- dark, gray low altitude cloud that produces continuous precipitation in the form of rain or snow - altitude range from surface to 3,000 meters

air mass

- large body of air of relatively similar temperature and humidity characteristics covering thousands of quare km - classified according to the characteristics of their source region or area of formation - classified by temperature and moisture characteristics

Describe features associated with severe thunderstorm (fig 8.10 and 8.11)

- moves in direction associated with mid-lat cyclone - the upper-level dry air wind is generated from the mid-lat cyclone which cayses the tilting of vertical air currents within the storm so that the updrafts move up and over the downdrafts - green arrows represent the updrafts that are created as warm moist air is forced into the front of the storm - at the back end of the cloud, the updrafts swing around become downdrafts (blue arrows) ** - the LEADING EDGE OF THE DOWNDRAFTS produces a GUST FRONT near the surface - as the gust front passes, the wind of the surface shifts and becomes strong with gusts exceeding 100 kph, temps get cold, surface pressure rises - warm moist air that rises over the gust front may form a ROLL CLOUD

Cumulus Cloud

- puffy clouds with relatively flat bases - form when moist warm air bubbles vertically escape from the Earths surface

describe a verticle cross section of a mid-latitude cyclone

- see how air temp changes as we move from behind cold front to a position ahead of warm front - behind the surface position of the cold front, forawrd moving cold dense air causes the uplift of the warm lighter air before the front -- - because it is a rapid uplift along a steep frontal gradient: condensed water vapor quickly organizes itself into cumulus then cumulonimbus clouds - cumbulonimbus produce heavy precipitation and can develop into severe thunderstorms if conditions are right - above gradually sloping warm front,the lifting moist air produces first nimbostratus followed by altostratus and cirrostratus clouds - precipitation is less intense along the warm front : moderate to light showers SOME DISTANCE AHEAD of the surface position of the warm front

Maritime tropical air mass (mT)

- these air masses are relatively unstable quickly forming cumulonimbus clouds when surface heating is intense

how do thunderstorms form

- when moist, unstable air is lifted vertically into the atmosphere - lifting of this air results in condensation and the release of LATENT HEAT - immediately after lifting begins, the rising parcel of warm moist air beings to cool because of ADIABATIC EXPANSION - at certain elevation the DEW POINT is reached resulting in condensation and the formation of a CUMULUS CLOUD - for the CUMULUS CLOUD to form into a thunderstorm, continued uplift must occur in an UNSTABLE atmosphere - vertical extension of the air cell, the cumulus cloud transforms into a CUMULONIMBUS CLOUD

dissipating stage

- when the mature thunderstorm decreases in intensity it enters dissapating stage -- after about 30 minutes - air currents within the convective storm are now mainly downdrafts as the supply of warm moist air from the lower atmosphere is depleted - the storm is now finished and precipitation has stopped about 1 to 3 hours after its birth

mature stage

- when updrafts reach max altitude in the developing cloud (12-14 km) they change their direction 180 and become downdrafts - this marks mature stage - with the downdrafts, precipitation begins to form through collision and coalescence - the storm is at its most intense stage of development and is not a cumulonimbus cloud - top of cloud takes on usual anvil shape, as strong upper-air winds now distribute ice crystals in the top of the cloud horizontally - as its base, the air mass thunderstorm is several km in diameter

what happens to ground surface as gust front passes?

- wind of surface become strong with gusts exceeding 100 kph - temps become cold - surface pressure rises

ITCZ - intertropical convergence zone

- zone of low atmospheric pressure and ascending air located at or near the equator - rising air currents are due to global wind convergence and convection from thermal heating - location of the thermal equator

the moisture characteristics of air masses can be classified as

1) continental 2) maritime

3 stages of air mass thunderstorm

1) cumulus stage 2) mature stage 3) dissipating stage

a source region can have one out of what four temperature attributes

1) equatorial 2) tropical 3) polar 4) arctic

Combining these categories, was are the possibilities commonly found in NA (5)

1) maritime polar (mP) 2) continental polar (cP) 3) maritime tropical (mT) 4) continental tropical (cT) 5) continental arctic (A)

three general types of storms on planet

1) mid-latitude cyclones 2) hurricanes 3) thunderstorms** *note these storms vary significantly in size and characteristics **thunderstorms component of both mid-latitude cyclones and hurricanes

What are the processes that can initiate vertical lifting and thunderstorm development? (3)

1. unequal warming of the surface of the earth 2. Oropraphic obstruction of airflow 3. The presence of a frontal zone

What types of clouds are associated with thunderstorms?

Cumulus cloud Cumulonimbus cloud

Temporal characteristics of tornados

In US: - april may june july = the months were we get the conditions that are necessary for the formation of severe thunderstorms Times of day: form in afternoon, where the heating of earths surface is at its greatest = intense heating enhances updrafts in severe thunderstorms. it is these updrafts which also lead to formation of a tornado

Where do most thunderstorms occur?

In the tropical land (less frequent over oceans because they do not warm rapidly) around the ITCZ (average 100 storms per year) (convectional heating of moist surface air occurs year round) Outside tropics, occurance is more seasonal occuring in months where solar heating is more intense

What region on earth recieves more tornadoes per square km than any other region of the world

Oklahoma! most severe events in May when warm moist air from the Gulf of Mexico interacts with cold fronts descending from the NW

What altitude cumulus clouds found at?

altitude range between 300-2,000 meters

cyclogenesis stage 1

begins as weak disturbance along the frontal zone (stationary front) where cold air from the poles meets warm air from south

stage 2 and 3

collision of these air masses results in uplift of warm air into upper atmosphere creating a cuclonic spin around a low pressure centre assos with this center of atmospehric circualtion are moving cold and warm fronts

what kind of weather does an air mass thunderstorm have (in mature stage)

contains heavy rain, thunder, lightning, and produces wind gusts directed towards the ground surface

cyclogenesis

life cycle of mid lat cyclone

Thunder

loud sound created when lightning causes the rapid expansion of atmospheric gases along its strike path

coalescence

process where two or more falling rain drops join into a single larger drop because of a midair collision

collision

the formation of rain often involves air turbulance and the collision of small water droplets which then coalesce into larfer droplets

t or f: cold fronts move at greater velocity than warm front

true

T or F: mid-latitude cyclone's winds can be as strong as a weak hurricane?

true!

Updraft

upward movement of air in the atmosphere

when are roll clouds esp prevelent?

when warm moist air rises above gust front, esp prevalent when a TEMPERATURE INVERSION exists near the base of thunderstorm

Describe the patterns of wind flow surface pressure fronts and zones of precipitation associated with a mid-lat cyclone in the Northern Hemisphere

- around the low, winds blow counter clockwise and inwards (clock and inward in souther hemisphere) - West of the low, cold air traveling from the north and northwest creates a cold front extending from the cyclones center to the SW - SE of the low, northward moving warm air from the subtropics produces a warm front - precipitation is located at the center of the low and along the fronts where air is being lifted - mid-latitude cyclones can produce wide variety of precipitation types, but include - rain, freezing rain, hail, ice pellets (sleet), snow pellets, and snow **frozen forms of precipitation (except hail) common with storms occuring in winter

Mid-Latitude Cyclones or Frontal Cyclones

- large traveling cyclonic storms up to 2000 kms in diameter, rarely motionless - can travel about 1200 km in one day - movement is generally EASTWARD - precice movement of this weather sustem is controlled by the orientation of the polar jet stream in the upper troposhere **estimate of future movement of mid-lat cyclone can be determined by the winds directly behind the cold front - centers of low atmospheric pressure - intense mid-latitude cyclones may have surface pressure as low as 970 mb - exist for about 3 to 10 days - are the result of the dynamic interaction of warm TROPICAL and cold POLAR AIR MASSES at the POLAR FRONT - this intersection causes the warm air to be cyclonically lifted vertically into the atmosphere where it combines with colder upper atmosphere air - this process transports excess energy from the lower latitudes to the higher latititudes

air mass thunderstorms

- most common type of thunderstorm - thunderstorms develop an extensive air mass that has the right temperature and humidity characteristics to form many isolated storm cells - normally develop late afternoon when surface heating produces the maximum number of convection currents in the atmosphere - life cycle has 3 distinct stages

mesocyclone

- severe thunderstorms that develop a strong vertical updraft. - measure 3 to 10 km across and extend from the storms base to its top - they are found in the SW quadrant of the storm - in some cases, can overshoot top of storm and form a cloud dome - likely form when strong horizontal upper winds interact with normally occuring updrafts. the shearing effect of this interaction forces the horizontal wind to flow upward, intensifying the updraft

Thunderstorms

- smallest storm - from several km to over 50 km diameter - develop mainly in tropics and in mid-lats - can exist in isolation or as organized clusters often associated with mid-lat cyclones and hurricanes - have a widespread distribution from extending from equator to high lats

Subtropical High Pressure Zone

- surface zone of atmospheric high pressure located at about 30 degrees North and South latitude - these high pressure systems produced by vertically descending air currents from the Hadley Cell

Cumulonimbus clouds can reach what heights above earths surface?

20 km above earths surface

How many thunderstorms occur each day on Earth?

40,000

Fujita Tornado Intensity Scale

F0 or F1: Weak Tornadoes - broken windows, tree branches, shingles blowing off roofs, moving cars pushed from roads - 69% - 65 - 181 kph - path that 1.5 km long and 100 m wide - last only 1 to 3 minutes F2 and F3: strong tornadoes - cause considerable damage - 29% - 182 and 332 kph - can have course up to 100km long and 500 m wide - can last for more than 2 hours F4 and F5 - relatively uncommong - 333-513 kph - very destructive and violent - F4: 2% of time - F5: chance less than 1/1000

T or F: mid-latitude cyclone will cause more damage than hurricanes?

FALSE! cause far less damage but very disruptive in winter months

T or F: Solar heating is the only requirement for thunderstorm formation?

False, one of several requirements Others: - availability of warm moist air

Occluded Front

a transition zone in the atmosphere where an advancing cold air mass sandwiches a warm air mass between another cold air mass, pushing the warm air mass into the upper atmosphere ORRRR are produced when a fast moving cold front catches and overtakes a slower moving warm front two types recognized associated with mid-lat cyclones ***note that in occlusion process the invading mild moist air that was found behind the warm front has been lifted into the upper troposphere

slope of the boundary between warm and cold air masses:

always slopes UPWARDS OVER the cold air this is due to the fact that cold air is much denser than warm air

Frontal cyclones

common weather event in spring and early summer, move from west to east in mid-latitudes. at same time, ground surface in the mid-latitudes is recieving elevated levels of insolation = higher insolation generates more heat and creates ideal conditions for air mass thunderstorm formation. when cold fron or dry line of a frontal cyclone comes in contact with this warm air it pushes it like a bulldozer both horizontally and vertically if this air has a high humidity and extends some distance east, the movement of the mid-lat cyclone enhances verticle uplift in storm and keeps the thunderstorms supplied with moisture and latent heat energy.

stage 7 to 9

day or two after oclusion the occluded front dissapates, wind subsides, stationary front forms on the surface of earth again

Latent Heat

energy required to change a substance to a higher state of matter (s>l>g). This energy is released from the substance with the change of state is reversed.

rain

form of precipitation. it is any liquid deposit that falls from clouds in the atmosphere to the ground surface. diameter usually between 0.5 and 5.0 millimeters.

frontal zone or front

frequently, two air masses, especially in middle latitudes, develop a sharp boundary or interface where the temp difference between them becomes intensified **boundary between the warm and cold air masses ALWAYS slopes upwards over the cold air because cold mroe dense sloping of warm air over the cold leads to FRONTAL UPLIFTING of the warm air

direction of mid-latitude cyclone movement?

generally eastward

What is the severe weather associated with thunderstorms?

hail, strong winds, thunder, lightning, intense rain, and tornadoes

50% of what kind of storm is likely to initiate a tornado?

half of all mesocyclones initiate tornadoes

What's responsible for converting air mass thunderstorms into severe thunderstorms

mid-lat cyclones

Severe Thunderstorms

most thunderstorms air mass thunderstorms, however some can develop into severe if right conditions exist to enhance and extend the mature stage of development defined as convective storms with: - frequent LIGHTNING - local WIND GUSTS of 97 km/ hour, - or HAIL that is 2 cm in diameter or larger - can have TORNADOES. - in most, the movement of the storm in roughly an easterly direction can refresh the storms supply of warm humid air - with continual supply of latent heat energy, the updrafts and downdrafts within the storm become balanced and the storm maintains itself indefinitely - movement of severe storm usually caused by presence of mid-lat cyclone COLD FRONT or a DRY LINE some 100 to 300 km ahead of a cold front. - these storms only dissapate when no more warm moist air is supplied -- this condition occurs several hours after nightfall

stage 6

occur when the cold front overtakes the warm front causing the warm air to be lifted into upper atmosphere resulted boundary is occluded front

cold type occluded front

occurs when the air behind the front is colder than the air ahead of the front

what is a mid-latitude cyclones development related to?

polar jet stream processes

how to predict movement of a mid-latitude cyclone?

precise movement of the weather system controlled by the orientation of the poalr jet stream in upper troposphere an estimate of future movement can be determined by the winds directly behind the cold front

what do three types of storms have in common

produce one or more clouds that extend into the upper troposphere

Tornado Alley

region in US with extremely high number of tornado events per year includes southern plains, south of lake michigan, and west central florida

Technologies that allow us to quickly pinpoint thunderstorms that may generate tornadoes

satellite imaging and weather radar

4 and 5

storm intensifies and the pressure at the storms center drops the warm air south of the lows center and between two fronts is known as the warm sector

Weather associated with a cumulonimbus cloud

strong winds, hail, lightning, tornadoes, thunder, and heavy rain -- this activity then turns it into a thunderstorm

How do strong upper air winds have a influence of mesocyclones?

tendecu tp emajmce thje vertical mesocyclonic circulation occuring inside developing thunderstorms

What weather system is hail typically associated with?

tends to be associated with severe thunderstorms that form along or in front of cold fronts during spring and summer months

what happens when tornado occurs in mesocyclone?

the mesocyclone lengthens vertically, constricts, and spirals down to grounds surface

Frontal lifting

the sloping of warm air over cold air forces the uplift of the warm air **this can cause condensation or deposition to occur and the possibility of precip along the frontal boundary

Convectional Lifting

the verticle lifting of air parcels through convective heating of the atmosphere. this process can initiate ADIABAITIC PROCESSES inside the air parcel

waterspouts

tornadoes that travel across lakes or oceans

front

transition zone between air masses with different air densities and weather characteristics

Cold Front

transition zone in the atmosphere where an advancing cold, dry stable air mass displaces a warm, moist, unstable subtropical air mass solid triangles showing direction of frontal movement move between 15-50 kph in a SE TO E DIRECTION high altitude CIRRUS CLOUDS are found well before the cold front above surface location of cold front, high altitude CIRROSTRATUS and middle altitude ALTOCUMULUS are common precipitation normally found just behind where the front where frontal lifting has caused the development of towering CUMULUS and CUMULONIMBUS CLOUDS

Warm Front

transition zone in the atmosphere where an advancing warm subtropical, moist air mass replaces a retreating cold and dry, polar air mass solid half circles pointing in direction of frontal movement move about 10 kph in a NE DIRECTION gradual frontal lifting ahead of the frontal zone results in the formation of clouds and precipitation high altitude CIRRUS, CIRROSTRATUS, and middle alt ALTOSTATUS CLOUDS are found well before the front about 600 km ahead of front, nimbo stratus clouds occur which produce precipitaion as snow or rain b/w nimbostratus clouds and the surface location of the warm front, low altitude stratus clouds are found few hundred km behind the front scattered stratocumulus are common in the lower troposphere

tornado

vortex of rapidly moving air associated with some severe thunderstorms winds within may exceed 450 km/hr and can also cause damage through sudden air pressure reductions! - air pressure around the tornado center can be as low as 800 mb (avg sea level 1014mb) destructive path about half km wide, no more than 25 km long hotspots: S.A., Aus, Europe, NZ, Northern India, Canada, Argentina, Uruguay and US

warm type occluded front

when air behind the front is warmer than the air ahead of the front common on the West coast of continents and generally form when maritime polar air colides with continental polar or arctic air