WIND AND PRESSURE (Chapter 5 Book) Wind is the movement of air, generally is horizontal Air tends to move from high to low pressure HL When pressure in two locations is unequal: We have a pressure gradient And a Pressure Gradient Force will produce a wind

A CONVECTIVE WIND SYSTEM (Page 130): HLL HLLHLL H H L

SEA AND LAND BREEZES An example of a convective wind system

THE CORIOLIS EFFECT AND WINDS We know that: air moves from high to low pressure HL F F is the pressure gradient force GLOBAL SCALE: Direction of wind is somewhat different due to Coriolis effect WHAT IS THE CORIOLIS EFFECT? It’s a result of the Earth’s rotation It undergoes an apparent deflection of objects in movement: TO THE RIGHT: Northern Hemisphere TO LEFT: Southern Hemisphere

HOW IS THE CORIOLIS EFFECT IN WINDS? Once air has been set in motion by the pressure gradient force, there is an apparent deflection from its path, as seen by an observer on the Earth. HOW WOULD BE THE RESULTING PATH IN THE SOUTHERN HEMISPHERE?

SURFACE WINDS ON AN IDEAL EARTH IDEAL EARTH: No complicated pattern of land and water No seasonal changes

GLOBAL SURFACE WINDS Because air rises at Equator, a surface LOW is generated At 30° latitude a surface HIGH is generated (air descends as part of Hadley Cell) At 60° cold climate: surface LOW

SUBTROPICAL HIGH PRESSURE BELTS Southern Hemisphere: a similar pattern with “ideal Earth”. There are 4 centers (3 over the oceans and one over Australia) Northern Hemisphere: 2 centers of High pressure (Hawaiian High and Azores High). They move northward during summer They have influence on North America during summer ACTUAL SURFACE WINDS AND PRESSURE PATTERNS (Figure 5.14 Book, very important for climate processes)

THE ITCZ AND MONSOON CIRCULATION ACTUAL SURFACE WINDS AND PRESSURE PATTERNS Sun is directly overhead: equator, tropics of Cancer and Capricorn, depending on season Hadley cell circulation is driven by this heating. The ITCZ changes with seasons (South America, Africa, Asia) Movement of ITCZ Change in pressure pattern Monsoon (in Asia) Monsoon:

Summer Monsoon: WET Warm, humid air comes from Indian Ocean and southwest Pacific Winter Monsoon: DRY Dry, continental air from north

HIGHER LATITUDES : ACTUAL SURFACE WINDS AND PRESSURE PATTERNS Southern and Northern hemisphere are different: NH: two large continental masses SH: large ocean, and a cold glacier land (Antartic) Northern Hemisphere: Continents: surface HIGH pressure in winter (strong Siberian High) surface LOW pressure in summer Southern Hemisphere: Permanent ice sheet of Antartica permanent anticyclone (South Polar High)

OCEAN SURFACE CURRENTS (Figure 5.22, relate with Figure 5.14) Exchanging heat between low and high latitudes (important regulators of air temperature)

WHAT IS UPWELLING? It’s the rising of deeper colder water Nutrient-rich water rises from deeper levels to replace the surface water that has drifted away Large fishing population in these areas

WHAT IS EL NIÑO? It’s a disruption of the ocean- atmosphere system in the Tropical Pacific, having important consequences for weather around the world NORMAL CONDITIONS Trade winds blows toward west across the Tropical Pacific warm water is piled up in the west Pacific

EL NIÑO CONDITIONS WHAT IS EL NIÑO? Trade winds relax in central and western Pacific Depression of thermocline in eastern Pacific Reduce upwelling to cool Rise in Sea Surface Temperature in central and East Pacific (coast of South America) global impacts This phenomena takes place at intervals of ~3-8 years ( and were the last extreme events)

WINDS ALOFT How does air move at higher elevations? The gradient force INCREASES with altitude stronger winds How does pressure changes with elevation?

HL Sea level H2 950mb H3 H4 900mb 850mb 800mb Reasons why winds are stronger at upper levels (in mid-high latitudes) 1.Difference of temperature (poles and 30° lat for example) 2. Pressure decreases with elevation : SLOWER in WARMER air FASTER in COLD air 950mb 900mb 850mb 800mb High Height Low Height Height (of pressure): HIGH in WARMER air LOW in COLDER air warmer colder HL H1 L H Figure 5.17, Page 139 POLE (90°) 30° latitude

ROSSBY WAVES 1. Waves arise in the Polar Front Undulations of upper air westerlies 2. Warm air pushes pole ward and a tongue of cold air pushes southward (undulation development) 3. Waves are strongly developed. Cold air are “troughs” of low pressure 4. Waves are pinched off, forming cyclones of cold air Formation:

ROSSBY WAVES They are important for poleward heat transport Reason for variable weather in midlatitudes

JET STREAMS Regions at high elevation with strong wind streams, wind speed more than: 58 knots They take place where atmospheric pressure gradients are strong The greater the contrast in temperature, the stronger the jet streams blow Jet streams tend to be weaker in summer than in winter Jet streams are less intense in the Southern Hemisphere due to smaller land masses

Upper level weather map (200mb) for June 27 th 2005

AIR MASSES (Chapter 6) A large body of air with uniform temperature and moisture characteristics. They acquire their characteristics in source regions Air masses move from one region to another (due to pressure gradient, upper level winds, jet stream) When moving, the properties are influenced by the new environment

TYPICAL AIR MASSES Air massSymbolSource regionProperties Maritime equatorialmEwarm oceans in equatorial region warm, very moist Maritime TropicalmTwarm oceans in tropical region Warm, moist Continental tropicalcTSubtropical desertsWarm, dry Maritime polarmPMidlatitude oceansCool, moist(winter) Continental polarcPNorthern continental interiors Cold, dry (winter) Continental articcARegions near north poleVery cold and dry Continental antarticcAARegions near south poleVery cold and dry

TYPICAL AIR MASSES

NORTH AMERICAN AIR MASSES Strong influence on North American weather 1.Continental Polar (cP) Tongues of cold dry air; periodically extend S,E producing cold temperatures and clear skies 2. Continental Artic (cA) When moving southward: severe cold wave 3. Maritime Polar (mP) Unstable in winter: heavy precipitation over coastal ranges 4. Maritime Tropical (mT) Moves northward bringing moist unstable air: thunderstorms 5. Continental Tropical (cT) Does not move widely, influence weather conditions over source region

FRONTS Transition zone between two air masses of different characteristics COLD FRONT Transition zone where a cold air mass invades a warmer air mass Colder air mass remains in contact with ground (because is denser) It forces warm air mass to rise If warm air is unstable: thunderstorms

WARM FRONT Transition zone where a warm air moves into a region of colder air Cold air remains in contact with ground (denser) It forces warm air mass to rise If warm air is stable: Steady precipitation If warm air is unstable: thunderstorms

OCCLUDED FRONT When a cold front overtakes a warm front (cold fronts move at a faster rate than warm fronts) STATIONARY FRONT A front that is not moving. Masses are not strong enough to replace each other

TRAVELING CYCLONES AND ANTICYCLONES Air spirals inward and upward condensation, precipitation Air spirals outward and downward condensation cannot occur CYCLONES ANTICYCLONES TYPES OF CYCLONES: 1.Wave cyclones (middle and high latitudes, ~1000km or 600miles) 2.Tropical cyclones (hurricanes, typhoons) 3.Tornado

WAVE CYCLONES The wave cyclone forms, intensify and dissolves along the polar front Two anticyclones, one with warm air, and the other with cold polar air are in contact in the polar front. FORMATION A.Early stage: Wave formation in the polar front Cold air southward, warm air northward B. Open stage: Wave is deepened and intensified C. Occluded stage: Cold front overtakes warm front (occluded front) Precipitation is intensified D. Dissolving stage: The cold front is reestablished

HOW DOES A WAVE CYCLONE AFFECT WEATHER?

TROPICAL CYCLONES: HURRICANES TROPICAL AND EQUATORIAL WEATHER SYSTEMS Weak upper level winds Air masses have similar characteristics (warm, moist) Air masses move slowly NO fronts and wave cyclones Intense convectional activity Hurricanes are tropical cyclones with winds greater than 74 mi/hr. They circulate: counterclockwise in Northern Hemisphere clockwise in Southern Hemisphere

HOW ARE HURRICANES FORMED? Thunderstorms + Ocean heat and moisture (ocean temps warmer than 26.5°C or 81°F) + High relative humidity in middle and upper troposphere + Low wind shear (change of wind speed with elevation, storms grow vertically)

STAGES OF DEVELOPMENT 1. TROPICAL DEPRESSION A low pressure is formed in the center of the thunderstorm group (winds 23-39mph) 2. TROPICAL STORM Tropical depression intensifies (39-73 mph). It is assigned a name at this time. Strom is more circular in shape 3. HURRICANE Tropical storm becomes a hurricane when wind speed reaches 74mph A pronounced rotation develops around the central core

HOW IS THE RELATIONSHIP WITH EL NIÑO? More tropical storms and hurricanes in Eastern Pacific Decrease in Atlantic, Gulf of Mexico and Caribbean sea

THE GLOBAL CLIMATE WEATHER CLIMATE The condition of atmosphere at any particular time and place. It’s always changing The synthesis of weather, the average weather of a region over a period of time Weather surface map, June 30 th 2005 Annual average precipitation

CLIMATE CLASSIFICATION 1. LOW LATITUDE CLIMATES 2. MIDLATITUDE CLIMATES 3. HIGH LATITUDE CLIMATES Influence of cT, mT, mE air masses Equatorial low pressure and subtropical high pressure belts, ITCZ Tropical cyclones Interaction of mT and cP air masses (polar front) Wave cyclones Influence of cP and cA air masses (Northern Hemisphere), mP and cAA air masses (Southern Hemisphere) Influence of cP and cA air masses (Northern Hemisphere), mP and cAA air masses (Southern Hemisphere)

LOW LATITUDE CLIMATES 1.Wet EquatorialWet Equatorial 2.Monsoon and trade-wind coastMonsoon and trade-wind coast 3.Wet-dry tropicalWet-dry tropical 4.Dry tropicalDry tropical CLIMATEPATTERNSFACTORS WET EQUATORIALHeavy precipitation, uniform temperature all months ITCZ, mE, mT air masses MONSOON TRADE WIND COAST Heavy precipitation and warm temperatures, with annual cycle mE and mT brought by trade winds; summer: ITCZ closer, winter: high pressure. Monsoon patterns (India) WET-DRY TROPICALVery dry and warm in winter, very wet and cold in summer ITCZ proximity DRY TROPICALVery low rainfall and high temperatures Subtropical high pressure cells (adiabatic warming) HIGH ELEVATIONCold climate (higher: colder), annual cycle Orographic rainfall; ITCZ influence

MIDLATITUDE CLIMATES 1.Dry subtropicalDry subtropical 2.Moist subtropicalMoist subtropical 3.MediterraneanMediterranean 4.Marine west-coastMarine west-coast 5.Dry midlatitudeDry midlatitude 6.Moist continentalMoist continental CLIMATEPATTERNSFACTORS DRY SUBTROPICALLow precipitation, great annual temperature cycle Subtropical highs (25°-35°) MOIST SUBTROPICALAbundant rainfall on eastern side of continents all year Summer: flow of warm/moist air from oceans (mT) Winter: wave cyclones MEDITERRANEANWet winter and very dry summerPoleward movement of high pressure cells during summer(cT dominates) MARINE WEST COASTPrecipitation all months, max in winter. Small annual range temp Westerlies bring mP air masses. Orographic effect. Summer: subtropical high pressure poleward DRY MIDLATITUDEVery low precipitationRain shadow of mountains. Summer: convection rainfall MOIST CONTINENTALPrecipitation all year, max in summer. Strong annual cycle of temp Polar front (cP,mP,mT interaction). Summer: mT, winter: cP,cA