Chapter19(2)

Chapter 19 – Moisture, Chapter 19 – Moisture, Clouds, and Weather Clouds, and Weather

Earth Science and the Environment Earth Science and the Environment (4(4thth ed) ed)

Thompson & TurkThompson & Turk

19.1 Moisture in air19.1 Moisture in air

►Precipitation can only occur when Precipitation can only occur when there is moisture in the airthere is moisture in the air

►Humidity – the amount of water Humidity – the amount of water vapor in the airvapor in the air Absolute humidity – mass of water Absolute humidity – mass of water vapor in a given volume of airvapor in a given volume of air

Relative humidity – amount of water Relative humidity – amount of water vapor relative to the amount the air vapor relative to the amount the air can hold at a given temperature can hold at a given temperature

19.1 Moisture in air19.1 Moisture in air►Saturation – when the relative Saturation – when the relative humidity reaches 100%humidity reaches 100%

►Dew point – if saturated air cools Dew point – if saturated air cools below the point where saturation below the point where saturation occurs, moisture will condenseoccurs, moisture will condense

►Supersaturation – in particulate Supersaturation – in particulate free air (high up), the relative free air (high up), the relative humidity can go above 100%humidity can go above 100%

► Supercooling – water that remains Supercooling – water that remains liquid past its freezing point liquid past its freezing point

19CO, p.470

Fig. 19.1, p.471

19.2 Cooling and 19.2 Cooling and condensationcondensation

►Radiation cooling – re-emission of Radiation cooling – re-emission of heat from the ground, plants, heat from the ground, plants, water, etc.water, etc.

►Contact cooling – dew and frostContact cooling – dew and frost Dew – condensation cause by moist air Dew – condensation cause by moist air contacting a cooler surface (below contacting a cooler surface (below its dew point) its dew point)

Frost – when that dew point is below Frost – when that dew point is below freezing, the condensate is solid icefreezing, the condensate is solid ice


►Cooling of rising air - adiabatic Cooling of rising air - adiabatic temperature change temperature change rising air expands rising air expands expansion requires “work” from the expansion requires “work” from the moleculesmolecules

Work is a loss of energy – thereby cooling Work is a loss of energy – thereby cooling the airthe air

Dry adiabatic lapse rate – dry air cools Dry adiabatic lapse rate – dry air cools 1010ooC/kmC/km

Wet adiabatic lapse rate varies, but Wet adiabatic lapse rate varies, but ranges from 5ranges from 5ooC to 9C to 9ooC/kmC/km


►Sinking air compresses and heats Sinking air compresses and heats upup Warm air can hold more moisture, so Warm air can hold more moisture, so latent heat is not releasedlatent heat is not released

The amount of rise being the proper The amount of rise being the proper adiabatic lapse rateadiabatic lapse rate

Fig. 19.2, p.472

Fig. 19.3, p.473

Fig. 19.4, p.474

19.3 Rising air and 19.3 Rising air and precipitationprecipitation

►Air may rise by various meansAir may rise by various means Orographic lifting – air flows over Orographic lifting – air flows over mountains, and goes upmountains, and goes up

Frontal wedging – moving cold air Frontal wedging – moving cold air meets and slides under warmer air, meets and slides under warmer air, moving it upwardsmoving it upwards

19.3 Rising air and 19.3 Rising air and precipitationprecipitation

Convection/convergence – if a portion Convection/convergence – if a portion of air becomes warmer it will expand of air becomes warmer it will expand and rise (e.g.: like over a very warm and rise (e.g.: like over a very warm parch of ground)parch of ground)

Convection and clouds – air neither Convection and clouds – air neither rising nor falling cools at the rising nor falling cools at the “normal lapse rate” of 6“normal lapse rate” of 6ooC/kmC/km

Unstable air – warm moist rises Unstable air – warm moist rises quickly, forms clouds and rainsquickly, forms clouds and rains

Stable air – warm dry air rises, but Stable air – warm dry air rises, but leads to neither clouds nor rain leads to neither clouds nor rain

Fig. 19.5, p.474

Fig. 19.5a, p.474

Fig. 19.5b, p.474

Fig. 19.5c, p.474

Fig. 19.6, p.475

p.476a

p.476b

p.477a

p.477b

19.4 Types of clouds19.4 Types of clouds

►Different meteorological conditions Different meteorological conditions create different cloudscreate different clouds Cirrus – high altitude clouds composed Cirrus – high altitude clouds composed of ice crystalsof ice crystals

Stratus - low horizontal sheets, often Stratus - low horizontal sheets, often associated with steady rainassociated with steady rain

Cumulus – billowing columns of fluffy Cumulus – billowing columns of fluffy whitewhite

Combination names – cumulonimbus, Combination names – cumulonimbus, stratocumulus, nimbostratus (see fig. stratocumulus, nimbostratus (see fig. 19.10)19.10)

19.4 Types of clouds19.4 Types of clouds►Types of precipitationTypes of precipitation

Rain – forms from coalescence of tiny Rain – forms from coalescence of tiny droplet or ice crystalsdroplet or ice crystals►Most rain starts as ice that melts on the Most rain starts as ice that melts on the way downway down

Snow– if the air temperature is too low, Snow– if the air temperature is too low, the ice crystals remain frozenthe ice crystals remain frozen

Sleet – liquid rain that passes through Sleet – liquid rain that passes through cold aircold air

Glaze – very cold rain that strikes Glaze – very cold rain that strikes freezing surfaces to form ice in placefreezing surfaces to form ice in place

Hail – ice crystals that get several Hail – ice crystals that get several coatscoats

Fig. 19.7, p.477

Fig. 19.8, p.478

Fig. 19.9, p.478

Fig. 19.10, p.478

Fig. 19.11, p.479

Fig. 19.12, p.480

19.5 Fog19.5 Fog

►Water droplets forming close to the Water droplets forming close to the groundground Advection fog – warm, moist sea air Advection fog – warm, moist sea air blows over cool landblows over cool land

Radiation fog – air & ground cool at Radiation fog – air & ground cool at night, as dew point is reached, fog night, as dew point is reached, fog forms and settles in low pointforms and settles in low point

Evaporation fog – air cooling of Evaporation fog – air cooling of lake/river vaporlake/river vapor

Upslope fog – air cools as it rises Upslope fog – air cools as it rises along a land surfacealong a land surface

Fig. 19.13, p.481

19.6 Pressure and wind19.6 Pressure and wind

►Warm air is less dense than cold Warm air is less dense than cold airair Warm air exerts a lower pressure than Warm air exerts a lower pressure than cold aircold air

Wind – movement of air from high to Wind – movement of air from high to low pressure areaslow pressure areas

Pressure gradient – the difference Pressure gradient – the difference between a high and low pressure areabetween a high and low pressure area

Isobars – lines on a weather map that Isobars – lines on a weather map that connect point of equal pressure connect point of equal pressure


►Coriolis effect – deflects both Coriolis effect – deflects both ocean currents and windsocean currents and winds Rightward in the northern hemisphereRightward in the northern hemisphere Leftward in the southern hemisphereLeftward in the southern hemisphere

►Friction – winds due to rising Friction – winds due to rising and falling air at height do not and falling air at height do not experience surface frictionexperience surface friction Jet stream – the high velocity wind Jet stream – the high velocity wind currents generated at high altitudescurrents generated at high altitudes


►Cyclone – a low pressure system and Cyclone – a low pressure system and its accompanying surface windsits accompanying surface winds

►Anticyclone – a high pressure system Anticyclone – a high pressure system and its accompanying surface windsand its accompanying surface winds

►Pressure change & weatherPressure change & weather Rising air (low pressure) clouds and Rising air (low pressure) clouds and rainrain

Falling air (high pressure) fair and dryFalling air (high pressure) fair and dry

Fig. 19.14, p.482

Fig. 19.14a, p.482

Fig. 19.14b, p.482

Fig. 19.15, p.483

Fig. 19.16, p.483

Fig. 19.17, p.484

Fig. 19.18, p.485

19.7 Fronts and frontal 19.7 Fronts and frontal weatherweather

►Front – the boundary between a Front – the boundary between a warm air mass and a cool onewarm air mass and a cool one Air masses can retain their Air masses can retain their integrity for days before mixingintegrity for days before mixing

Fronts may be warm, cold, occluded Fronts may be warm, cold, occluded or stationaryor stationary


►Warm front – warm air collides with Warm front – warm air collides with a stationary or slow-moving cold a stationary or slow-moving cold air massair mass Warm air rises over the cooler air and Warm air rises over the cooler air and cools adiabaticallycools adiabatically

►Cold front – fast-moving cold air Cold front – fast-moving cold air overtakes warm air and shoves overtakes warm air and shoves underneath it, creating a steep underneath it, creating a steep contactcontact Warm air rises rapidly making more Warm air rises rapidly making more unstable airunstable air


►Occluded front – a faster-moving Occluded front – a faster-moving cold air mass traps warm air cold air mass traps warm air against another cold air mass against another cold air mass the two colds meet and lift the the two colds meet and lift the warm air up causing rainwarm air up causing rain

►Stationary front –the boundary Stationary front –the boundary of two stationary air massesof two stationary air masses Often drizzly and foggyOften drizzly and foggy


►Mid-latitude cyclones – occur Mid-latitude cyclones – occur between polar and tropical air between polar and tropical air massesmasses High temperature differenceHigh temperature difference Disturbance in boundary causes a Disturbance in boundary causes a “kink”“kink”

Air twists around the kink falling Air twists around the kink falling down large pressure gradientsdown large pressure gradients

Storm tracks – the generally W to E Storm tracks – the generally W to E path of mid-latitude cyclonespath of mid-latitude cyclones

Fig. 19.19, p.486

Table 19.1, p.486

Fig. 19.20, p.486

Fig. 19.21, p.487

Fig. 19.22, p.487

Fig. 19.23, p.488

Fig. 19.23a, p.488

Fig. 19.23b, p.488

Fig. 19.24, p.489

Fig. 19.24a, p.489

Fig. 19.24b, p.489

Fig. 19.24c, p.489

Fig. 19.24d, p.489

Fig. 19.25, p.489

19.8 How Earths’ surface 19.8 How Earths’ surface features affect weather features affect weather

►Mountain ranges and rain-shadow desertsMountain ranges and rain-shadow deserts Orographic winds rain out adiabaticallyOrographic winds rain out adiabatically Falling down the leeward side they heat, Falling down the leeward side they heat, but are dry, causing arid landsbut are dry, causing arid lands

►Sea and land breezes – due to uneven Sea and land breezes – due to uneven heating/cooling of land and waterheating/cooling of land and water

►Monsoons – heavy rains due to uneven Monsoons – heavy rains due to uneven heating of ocean and continents heating of ocean and continents

Fig. 19.26, p.490

Fig. 19.27, p.491

19.9 Thunderstorms19.9 Thunderstorms

►Caused by rising warm, moist airCaused by rising warm, moist air Wind convergence – i.e.: FL where land Wind convergence – i.e.: FL where land heating draws moist air from both heating draws moist air from both ocean sidesocean sides

Convection – rising moist air over Convection – rising moist air over continental interiorscontinental interiors

Orographic lifting – warm, moist air Orographic lifting – warm, moist air lifting over hills or mountainslifting over hills or mountains

Frontal thunderstorms – along frontal Frontal thunderstorms – along frontal boundaries, usually cold fronts boundaries, usually cold fronts

19.9 Thunderstorms19.9 Thunderstorms

►Lightning – discharge of static Lightning – discharge of static electricity built up in clouds, but electricity built up in clouds, but how and why?how and why? Static between winds and ice crystals in Static between winds and ice crystals in cumulonimbus cloudscumulonimbus clouds►Positive high up, negative down lowPositive high up, negative down low

Cosmic rays hit cloud tops producing ionsCosmic rays hit cloud tops producing ions►Other ions occur by wind friction along the Other ions occur by wind friction along the groundground

In either case, when charge differential In either case, when charge differential is large enough – it dischargesis large enough – it discharges

Fig. 19.28, p.492

Fig. 19.29, p.492

Fig. 19.30, p.493

Fig. 19.30a, p.493

Fig. 19.30b, p.493

19.10 Tornadoes & tropical 19.10 Tornadoes & tropical cyclonescyclones

►Tornadoes – short-lived funnel Tornadoes – short-lived funnel cloud that protrudes from the cloud that protrudes from the bottom of a cumulonimbus cloudbottom of a cumulonimbus cloud Very low pressureVery low pressure 2m to 3km in diameter with rotational 2m to 3km in diameter with rotational wind speeds up to 800km/hrwind speeds up to 800km/hr

Move across landscape at speed of 0-Move across landscape at speed of 0-70km/hr70km/hr

Most destructive storms on any given Most destructive storms on any given areaarea

19.10 Tornadoes & tropical 19.10 Tornadoes & tropical cyclonescyclones

►Tropical cyclones – less intense, Tropical cyclones – less intense, but larger and longer-lived than but larger and longer-lived than tornadoestornadoes Hurricane in N America, typhoon in Hurricane in N America, typhoon in west Pacific, cyclone in Indian Oceanwest Pacific, cyclone in Indian Ocean

Storm surge – sea-surface rises under Storm surge – sea-surface rises under low pressure and is driven ashore by low pressure and is driven ashore by high windshigh winds

Driven by latent heat of condensation Driven by latent heat of condensation and rising airand rising air

Fig. 19.31a, p.493

Fig. 19.31b, p.493

Table 19.2, p.493

Fig. 19.32, p.495

Fig. 19.33, p.495

Table 19.3, p.496

19.11 Hurricane Katrina19.11 Hurricane Katrina

►Formed 8/23/2005 – passed over FL Formed 8/23/2005 – passed over FL as a Category 1as a Category 1

►Grew to a category 5 in Gulf of Grew to a category 5 in Gulf of MexicoMexico

►Made landfall as a 3-4Made landfall as a 3-4►8.5m storm surge inundated New 8.5m storm surge inundated New Orleans and the MI coastOrleans and the MI coast

►Death toll between 1,300 and 4,000Death toll between 1,300 and 4,000


►Gulf coast and hurricanesGulf coast and hurricanes Long history of tropical stormsLong history of tropical storms 10 deadliest storms – before 195510 deadliest storms – before 1955 10 costliest – after 1955, more 10 costliest – after 1955, more than half after 1989than half after 1989►More people live on coasts now – More people live on coasts now – property damageproperty damage

►Earlier warning – people get out of the Earlier warning – people get out of the way more efficientlyway more efficiently

So why was Katrina so devastating?So why was Katrina so devastating?


►Barrier islands, costal wetlands, Barrier islands, costal wetlands, delta lands, all absorb a storm’s delta lands, all absorb a storm’s energyenergy Over the past century, 1/3 of the coastal Over the past century, 1/3 of the coastal wetlands has disappearedwetlands has disappeared

Human activity has reduced sediment flow Human activity has reduced sediment flow to the delta (chap 11)to the delta (chap 11)

The delta is massive enough to depress The delta is massive enough to depress the crust – less sediment leads to net the crust – less sediment leads to net subsidencesubsidence

Canals have killed plants with salt waterCanals have killed plants with salt water


►Levee failure – portions of the Levee failure – portions of the levee system were built atop peat levee system were built atop peat soilssoils Peat is weak and transmits water readilyPeat is weak and transmits water readily Lead to catastrophic failureLead to catastrophic failure

►Add in that much of the city is below sea Add in that much of the city is below sea levellevel

2005 had a record number of tropical 2005 had a record number of tropical storms and hurricanesstorms and hurricanes►A portent of things to come?A portent of things to come?

Fig. 19.34a, p.496

Fig. 19.34b, p.496

Table 19.4a, p.497

Fig. 19.35, p.498

Fig. 19.36, p.498

Fig. 19.37, p.499

Fig. 19.38a, p.500

Fig. 19.38b, p.500

19.12 El Niño19.12 El Niño

►An anomalous current that brings An anomalous current that brings warmer water to the west cost of warmer water to the west cost of South AmericaSouth America Occurs every 3-7 years for a yearOccurs every 3-7 years for a year Weakens trade winds which reduces Weakens trade winds which reduces cold upwellingcold upwelling►This creates warmer surface waterThis creates warmer surface water►Depresses fisheriesDepresses fisheries►Changes weather patterns in may placesChanges weather patterns in may places

Fig. 19.39, p.501

Fig. 19.40, p.502

Chapter19(2)

Technology

Transcript of Chapter19(2)