Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
WIND AND PRESSURE (Chapter 5 Book) • Wind is the movement of air, generally is horizontal •Air tends to move from high to low pressure H L 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): 2 1 L 3 H L 4 L H L L H H L L H 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 H F L 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 ACTUAL SURFACE WINDS AND PRESSURE PATTERNS (Figure 5.14 Book, very important for climate processes) 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 THE ITCZ AND MONSOON CIRCULATION •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) Monsoon: •Movement of ITCZ •Change in pressure pattern Monsoon (in Asia) •Summer Monsoon: WET Warm, humid air comes from Indian Ocean and southwest Pacific •Winter Monsoon: DRY Dry, continental air from north ACTUAL SURFACE WINDS AND PRESSURE PATTERNS HIGHER LATITUDES : •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 High) permanent anticyclone (South Polar 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 oceanatmosphere 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 WHAT IS EL NIÑO? EL NIÑO CONDITIONS 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 (1982-83 and 1997-98 were the last extreme events) WINDS ALOFT How does air move at higher elevations? The gradient force INCREASES with altitude How does pressure changes with elevation? stronger winds 800mb colder warmer 850mb H4 800mb 850mb H L H3 900mb H2 900mb Low Height L H 950mb H POLE (90°) L 950mb High Height H1 Sea level 30° latitude 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 Height (of pressure): HIGH in WARMER air LOW in COLDER air Figure 5.17, Page 139 ROSSBY WAVES •Undulations of upper air westerlies Formation: 1. Waves arise in the Polar Front 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 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 27th 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 mass Symbol Source region Properties Maritime equatorial mE warm oceans in equatorial region warm, very moist Maritime Tropical mT warm oceans in tropical region Warm, moist Continental tropical cT Subtropical deserts Warm, dry Maritime polar mP Midlatitude oceans Cool, moist(winter) Continental polar cP Northern continental interiors Cold, dry (winter) Continental artic cA Regions near north pole Very cold and dry Continental antartic cAA Regions near south pole Very 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 CYCLONES Air spirals inward and upward condensation, precipitation ANTICYCLONES Air spirals outward and downward condensation cannot occur TYPES OF CYCLONES: 1. 2. 3. Wave cyclones (middle and high latitudes, ~1000km or 600miles) Tropical cyclones (hurricanes, typhoons) Tornado WAVE CYCLONES The wave cyclone forms, intensify and dissolves along the polar front FORMATION Two anticyclones, one with warm air, and the other with cold polar air are in contact in the polar front. 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 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 TROPICAL CYCLONES: HURRICANES • • 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 The condition of atmosphere at any particular time and place. It’s always changing Weather surface map, June 30th 2005 CLIMATE The synthesis of weather, the average weather of a region over a period of time Annual average precipitation CLIMATE CLASSIFICATION 1. LOW LATITUDE CLIMATES • Influence of cT, mT, mE air masses • Equatorial low pressure and subtropical high pressure belts, ITCZ • Tropical cyclones 2. MIDLATITUDE CLIMATES • Interaction of mT and cP air masses (polar front) •Wave cyclones 3. HIGH LATITUDE CLIMATES • Influence of cP and cA air masses (Northern Hemisphere), mP and cAA air masses (Southern Hemisphere) LOW LATITUDE CLIMATES 1. 2. 3. 4. Wet Equatorial Monsoon and trade-wind coast Wet-dry tropical Dry tropical CLIMATE PATTERNS FACTORS WET EQUATORIAL Heavy 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 TROPICAL Very dry and warm in winter, very wet and cold in summer ITCZ proximity DRY TROPICAL Very low rainfall and high temperatures Subtropical high pressure cells (adiabatic warming) HIGH ELEVATION Cold climate (higher: colder), annual cycle Orographic rainfall; ITCZ influence MIDLATITUDE CLIMATES 1. 2. 3. 4. 5. 6. Dry subtropical Moist subtropical Mediterranean Marine west-coast Dry midlatitude Moist continental CLIMATE PATTERNS FACTORS DRY SUBTROPICAL Low precipitation, great annual temperature cycle Subtropical highs (25°-35°) MOIST SUBTROPICAL Abundant rainfall on eastern side of continents all year Summer: flow of warm/moist air from oceans (mT) Winter: wave cyclones MEDITERRANEAN Wet winter and very dry summer Poleward movement of high pressure cells during summer(cT dominates) MARINE WEST COAST Precipitation all months, max in winter. Small annual range temp Westerlies bring mP air masses. Orographic effect. Summer: subtropical high pressure poleward DRY MIDLATITUDE Very low precipitation Rain shadow of mountains. Summer: convection rainfall MOIST CONTINENTAL Precipitation all year, max in summer. Strong annual cycle of temp Polar front (cP,mP,mT interaction). Summer: mT, winter: cP,cA