Climate and Society Exam 2

Climate patterns in North America

- Average pressure at sea level is 1013 mbar. - Wind direction around a high-pressure cell in the NH is always clockwise: Eastern US receive warm, moist air from the low latitudes in the summer. - Wind direction around a low-pressure cell in the NH is always counter- clockwise: - Eastern US receive dry, cold air from the high latitudes in the winter.

Normal State of the Pacific

- East-west SST - upwelling - Thermocline depth - Sea surface height - Surface pressure - trade winds Normal Pacific pattern. Equatorial winds push warm water pool toward west. Cold water upwells along South American coast.

Real Time Ocean Observations

- Moorings - ARGO floats (uses profiling floats to observe temperature) - XBT (thermograph) - Satellite

Oceanographic and climatic effects of La Niña

- SSTs off Peru drop below normal - trade winds are stronger - SSTs in the western tropical Pacific are warmer than usual - very dry conditions appear over coastal areas of Peru and Chile - rainfall and flooding increase in Thailand, Myanmar and India: abnormally heavy monsoons in India and Southeast Asia - cold and wet winter in western Canada and northwestern US

El Niño and Birds

- bird droppings (guano) are rich in phosphate and nitrate and guano is therefore harvested for fertilizers - it is a $1.4 billion industry - El Niño causes strong mortalities among guano birds El Niño causes devastating short term effects on bird populations but birds could always recover - guano-producing seabirds decreased as the catches of Peruvian anchovy increased - but: birds lose the competition with fishermen, not enough food left for birds

Coastal upwelling off Peru-Chile

- deeper colder nutrient rich water rises up from beneath to replace the water that was pushed away - warmer surface water moves offshore - surface winds push surface water away from an area

Collapse of the Peruvian anchovy catch in response to El Niño and overestimated yields

- predominance of the anchovy is based on extreme variability of the environmental conditions - at the beginning of the event fish approached the shore and got caught more often - fish started migrating deeper in the water column and southwards - a change in fishing strategy from day to night time fishing decreased the stocks - total biomass decreased from 5.8 million tons in May 1997 to 1.2 million tons in September 1998 -most fish cannot regulate their body temperature - during El Niño years cold water fish migrate as far north as Alaska

Oceanographic and climatic effects of El Niño

- reduced Peruvian upwelling, and increasing SSTs by several °C - south-western US and typically dry regions of Peru and Ecuador experience high rainfall - Indonesia, Australia and the Philippines experience drought - El Niño years are associated with less intense hurricane years in the Atlantic - northern US and Canada typically experience warmer than usual winters

Food impacts of the warm/positive phase El Niño

- the 1982-83 El Niño led to a 90-95% reduction in Southern California kelp beds - the 1997-98 El Niño also caused massive kelp losses - low nutrient tropical waters reduce the recovery success

Marine ecosystem along the coast of Ecuador and Peru - El Niño

- warm, nutrient-poor surface waters brought by El Niño can sustain few phytoplankton - fish, sea lions, and other sea animals must dive deeper in search of food - sea birds scatter across the ocean and abandon their young

Surface ocean currents

- water moves slower than air - during this longer period earth rotates farther out from under the water than from under the wind - slower-moving water appears to be deflected to a greater degree than the overlying air

Ekman spiral

- wind-driven surface water pushes on water below it - the next deeper layer moves more slowly than the surface layer and it is deflected to the right (NH) or left (SH) of the surface-layer direction - the average net flow of the entire spiral is at a right angle to the direction of the wind - the dragging of waters by wind is called Ekman transport

equatorial upwelling

-Surface seawater diverges and moves apart - Deeper seawater (cooler, nutrient replaces surface water - Upwelling - High biological productivity

Diverging surface seawater, equatorial upwelling

-Surface seawater diverges and moves apart - Deeper seawater (cooler, nutrient-rich) replaces surface water - Upwelling - High biological productivity

Temperature decrease w height in the troposphere

1) Solar (radiative) heating at Earth surface 2) Atmospheric convection: warm/moist air rises, cool/dry air sinks 3) Decreasing pressure with altitude Troposphere's gases absorb very little of the incoming solar radiation. But the ground absorbs this radiation and then heats the tropospheric air by conduction and convection. Since this heating is most effective near the ground, the temperature in the troposphere gradually decreases with increasing altitude until the tropopause is reached.

Consider a rising parcel of air, but this time it has water vapor (typically 0.5% by weight)

1. Air parcel rises... starts to cool 2. Follows DRY ADIABATIC lapse rate until condensation (cloud) 3. condensation --> release of latent heat of condensation inside of parcel 4. Warming in parcel offsets cooling due to expansion, so 5. Rising parcel no longer follows dry adiabatic lapse rate of -10 K/km, but follows the MOIST ADIABATIC lapse rate of -6 K/km - this parcel cools more slowly and keeps rising! Tropical atmosphere follows MOIST adiabatic lapse rate Polar atmosphere follows DRY adiabatic lapse rate

ENSO - ocean-atmosphere coupling

1. Western Pacific sea surface temperature 2. Western Pacific atmospheric convection 3. Easterly surface winds 4. Easterly surface ocean currents

Coral bleaching

16% of the world's coral reefs suffered severe bleaching from the unusually strong 1998 El Niño event - water temperature increases, prolonged temperature stress takes place - bleached coral covered in filamentous algae

Strongest El Niños on record

1982, 1997, 2015/2016

La Niña Conditions

A cooling of the water in the equatorial Pacific, which occurs at irregular intervals, and is associated with widespread changes in weather patterns complementary to those of El Niño, but less extensive and damaging in their effects. Warm water is further west than usual

Movements in the atmosphere

Air (wind) always moves from regions of high pressure to low. Cool dense air, higher surface pressure. Warm less dense air, lower surface pressure.

The atmosphere in convective motion

Air holding H2O is less dense than air full of O2 and N2 • Warm air can hold more water vapor • Warm, moist air (less dense) rises • Cool, dry air (more dense) sinks • Land gains and loses heat more quickly than water • horizontally flowing air is wind, note that air flowing aloft moves in opposite direction to air flowing at the surface

El Niño

An irregularly occurring and complex series of climatic changes affecting the equatorial Pacific region and beyond every few years, characterized by the appearance of unusually warm, nutrient-poor water off northern Peru and Ecuador - Rain floods in western South America - Droughts in Indonesia, Africa and Australia -Increased ocean surface height in the eastern equatorial Pacific during El Niño

Coriolis effect

At the equator a parcel of air moves at the same speed as the rotating Earth. A northward blowing wind displaces the parcel from the equator. Earth's circumference becomes progressively smaller with latitude. Because there is little friction between atmosphere and ground, the parcel will move eastward at a speed greater than the eastward speed of Earth's surface at this higher latitude the air parcel is displaced to the east relative to the Earth's surface An air parcel moving from low to high latitudes in the NH will be deflected to the right of the direction of the air motion. An air parcel moving in the SH will be deflected to the left of the direction of the air motion.

Subtropics

Between the trade wind regions lie the subtropics - regions of divergence and subsidence, where sunny weather with little clouds and no rain prevails. Most of the earth's desert regions are found near 20-30 degree north and south of the equator.

Walker

British mathematician, director general of observations for India (formed after monsoon failure of 1877- worst famine in Indian history) Arrived in 1904, shortly after huge famine caused by drought Goal to predict Indian Monsoon Found that many global climate variations, including Monsoon rains in India, were correlated with the Southern Oscillation (i.e. the atmospheric component of ENSO)

Greenhouse effect

CO2, and other gases in the atmosphere trap heat, keeping the earth warm The sun has short wavelength

Climate

Climate is the common weather condition averaged over a long period of time (typically 30 years or more)

Consistent temperature patterns between ocean basins and coast lines

Coastal upwelling: example Monterey Bay Upwelling areas are areas of very high productivity Colder surface temperatures in upwelling areas

The earth rotates

Convection Cell model: Heating at the equator and cooling at the poles produce a single large convection cell in each hemisphere on a non-rotating, water covered model Earth. BUT The earth's circumference is larger at the equator than it is at the poles Yet all parts of the earth complete one rotation in 24 hrs. So the parts of the earth that are "fatter" have to travel faster This gives rise to the Coriolis effect

Geostrophic flow in the Northern Hemisphere

Counter-clockwise around low pressure cells Clockwise around high pressure cells

Forecast Initialization Procedures

Data assimilation --> initial conditions (t=t0) --> ocean and atmosphere model --> forecast

Ocean atmosphere coupling

Decreased ocean surface height along the North, Central and South American coast during La Niña

Phase changes of water

Direction - going to lower energy phase (vapor, liquid, ice) --> heat is released (warms air) e.g. rain, ice formation Going to higher energy phase (ice--> liquid-->vapor), heat is absorbed e.g. ice-melting, evaporation

Greater Pressure vs. Ocean Temperature

Doesn't directly alter water temperature. Pressure shifts the freezing, boiling and maximum density points. The temperature at which boiling and freezing occur will only hold true at sea level At a lower pressure (higher altitude), water will boil at a lower temperature. At higher pressures water will boil at a higher temperature Atmospheric pressure does not affect the temperature of the water itself, but only its ability to become vapor, thus shifting the boiling to the left or right.

Is the water warmer on the west coast of america or east coast?

East coast

How ENSO impacts people

Effective management of climate related risks (opportunities) for improved: • Agricultural production - Stocking, cropping calendar, crop selection, irrigation, insurance, livestock/trade • Water resource management - Dynamic reservoir operation, power generation, pricing/insurance • Food security - Local, provincial, regional scales • Public health - Warning, vaccine supply/distribution, surveillance measures,... • Natural resource management - Forests/fire, fisheries, water/air quality • Infrastructure development

Effects of La Niña

Effects of La Niña are often opposite to those of El Niño but typically not as devastating

El Niño and La Niña

El Niño and La Niña are officially defined as sustained sea surface temperature and atmospheric pressure anomalies across the central tropical Pacific Ocean - El Niño occurs approximately every 3-7 years - once developed, El Niño usually lasts for ~1 year but can last as long as 18 months - La Niña often but not always follows El Niño, it can last up to 2 years - ENSO (El Niño/Southern Oscillation) is a period of anomalous weather conditions centered in the tropical Pacific: perturbation of the ocean-atmosphere climate system

ENSO State tend to oscillate

Equatorial ocean dynamics Key observations by Klaus Wyrtki in 1970's El Niño is preceded by a transfer of warm water from west to east. This transfer is thought to trigger a warm event. What triggers the movement of water? - In cold phase, waters cold (and low) in east, warm (and high) in west. - Warm water from west sloshes back and overshoots equilibrium - positive feedbacks set off El Niño conditions.

Gyres

Gyres are areas of downwelling and very low productivity Subtropical gyres - North Pacific - South Pacific - North Atlantic - South Atlantic - Indian Ocean If there were no continents, surface currents would follow the major wind belts.... instead we have GYRES

Pressure fields like a topo map

High pressure wants to move to low pressure in the most direct way. If the Earth didn't rotate - air would flow H --> L.

Hurricane

Hurricanes ride the trade winds from east to west The air circulates counterclockwise around the low pressure cell. Hurricanes are fed by the evaporation over warm water: heat energy liberated from the condensing vapor increases the velocity. The very high rate of condensation associated with warm, moist rising air produce high precipitation rates. When they move over cold water or land, they run out of energy

Change in Stratosphere

In the stratosphere, the temperature remains isothermal until about 20 km. The temperature actually begins to increase with altitude. The reason for this temperature fluctuation is that ozone absorbs the uvb radiation in the lower atmosphere. Higher in the atmosphere, however, normal diatomic oxygen absorbs the uvc radiation.

Trade wind belts

In the tropics, on both sides of the equator, lies a wide region where winds blow from east to west (easterlies) with a slight equatorward tilt. This region is named the trade wind belt, because of the steadiness of the air flow here.

Southern Oscillation

Irregularly periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean, affecting the climate of much of the tropics and subtropics. Hadley and Walker winds vary in phase: Hadley Cell Circulation = energy (heat) transport is perpendicular to equator Walker Cell (ENSO) = Energy heat transport is parallel to the equator when Hadley cell is strong, so is the Walker circulation

Warm and strong western boundary currents

Kuroshio, East Australian Current, Gulf Stream, Brazil Current, Agulhas Current

Thermoclines

Layers of water with different temperatures can lie on top of each other without mixing because differing densities. When the upper water layers warm in the summer months, they become separated from deep water by a transition zone known as a thermocline. In a thermocline, the temperature decreases rapidly with small increases in depth. This phenomenon linking temperature change with depth is called temperature stratification. Temperature stratification occurs in most bodies of water from small ponds to oceans, but thermoclines are primarily found in the larger bodies of water.

Moisture affects air stability

MOIST PARCEL rising in warm environment --> unstable, keeps rising after 3km DRY PARCEL rising in warm environment --> stable, starts sinking around 2km

Planetary vorticity

Maximum spin at the north pole, slight spin above equator. No spin on the equator

Adiabatic compression of a gas

No temperature exchanged with the environment When an ideal gas is compressed adiabatically (Q=0), work is done on it and its temperature increases; in an adiabatic expansion, the gas does work and its temperature drops. Adiabatic compressions actually occur in the cylinders of a car, where the compressions of the gas-air mixture take place so quickly that there is no time for the mixture to exchange heat with its environment.

Tropical surface and subsurface temperatures

Normal atmospheric conditions in the tropical Pacific: humid conditions in Indonesia and dry conditions near South America

Midlatitude westerlies

North and south of the trade wind belt (in the Northern and Southern Hemispheres, respectively) lie regions where winds tend to blow from west to east (westerlies), and are therefore referred to as the westerly wind belts. Here the winds are highly variable and unsteady, especially so during winter.

Upper surface ocean

Only the very upper surface ocean layer is moved by winds

Ideal Gas Law

PV = nRT P = pressure in atmospheres V = volume in liters n = number of moles R = gas constant T = temperature in Kelvin Ideal gas molecules do not attract or repel each other. Only interaction = elastic collision impact with each other or with the walls of the container. Ideal gas molecules themselves take up no volume. The gas takes up volume since the molecules expand into a large region of space

Polar easterlies

Poleward from the westerly wind belt, winds with a generally easterly component prevail. The air here is cold, dry and stable, especially during winter, and is accompanied by subsidence from above

Trade winds

Prevailing winds that blow northeast from 30 degrees north latitude to the equator and that blow southeast from 30 degrees south latitude to the equator

Coriolis Key

Regardless of whether the object (air, water, wind) is traveling N, S, E, W: Its travel will be to the right of its initial trajectory in the N. Hemisphere, and to the left in the S. Hemisphere To the right or left assumes the viewer's perspective is in the direction of travel. The magnitude of the Coriolis effect increases with increasing latitude and decreases with the north/southward speed of the moving object. The Coriolis effect is an apparent force that only appears against a rotating frame of reference.

SSTs and SST anomalies

SST anomaly= SST (obs) - SST(average) SST = sea surface temperature SST anomaly = relative to the average state

ENSO Predictions

Snapshots of current conditions are not very useful. People need advance warning, and for their region. Models skillfully predict ENSO 6-9 months into the future. This ability has saved many millions of lives.

Seasonal temperature changes are also determined by the specific heat capacity of water, rocks and soils

Specific heat capacity is a measure of the heat required to raise the temperature of a substance by 1 Kelvin - in comparison to soil and rocks, water changes its temperature the least for a given amount of heat added or removed Water vs. Sand, with the same amount of heat in the material, water has a smaller temperature rise, sand has a larger temperature rise

Storm Surge

Storm surge is a pile of water that forms because of the lower pressure Water is also pushed by winds to the leading NW edge of the storm

Monsoonal climate

Summer= rain season, due to strong solar radiation, hot land surface (low pressure), and cooler ocean (high pressure) Winter = dry season, due to weak solar radiation, cold land surface (high pressure), warmer ocean (low pressure)

Western boundary currents

Surface ocean currents are faster, narrower, and deeper on the western side of an ocean basin. These are known as western boundary currents. Surface Ocean Currents help redistribute warm water to the poles and cold water to the equator

Franklin-Folger map

The Franklin-Folger map (1769) of the Gulf Stream encouraged captains to sail within the Gulf Stream en route to Europe and return via the trade winds belt and follow the Gulf Stream north again to Philadelphia and New York City. Franklin took measurements of sea-surface temperatures during his crossings of the Atlantic, thereby developing a navigation technique based on the location of the warm Gulf Stream waters.

Oceanic Niño Index (ONI)

The ONI is based on SST departures from average in the Niño 3.4 region, and is a principal measure for monitoring, assessing, and predicting ENSO. El Niño: characterized by a positive ONI greater than or equal to +0.5°C. La Niña: characterized by a negative ONI less than or equal to -0.5°C. By historical standards, to be classified as a full-fledged El Niño or La Niña episode, these thresholds must be exceeded for a period of at least 5 consecutive overlapping 3-month seasons, with consistent atmospheric features. These anomalies must also be forecasted to persist for 3 consecutive months. The most recent ONI value (November 2018- January 2019) is +0.8.

Walker Circulation

The Walker circulation is the result of a difference in surface pressure and temperature over the western and eastern tropical Pacific Ocean. Normally, the tropical western Pacific is warm and wet with a low pressure system, and the cool and dry eastern Pacific lie under a high pressure system. This creates a pressure gradient from east to west and causes surface air to move east to west, from high pressure in the eastern Pacific to low pressure in the western Pacific. Higher up in the atmosphere, west-to-east winds complete the circulation. - Trade winds bring moist surface air to the west - Dry air returns to the east and sinks as it cools - Moist air rises and becomes drier as it feeds rain

Polar front

The convergence zone between polar easterlies and midlatitude westerlies is referred to as the polar front. It separates the cold (and dry) polar air from the relatively warm (and more humid) midlatitude air.

Conduction

The direct transfer of heat from one substance to another substance that it is touching. Heat flows from the warmer to the cooler object until they're both at the same temperature.

Initial signs of El Niño

The first signs of an El Niño are: 1. Rise in air pressure over the Indian Ocean, Indonesia, and Australia 2. Fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean 3. Trade winds in the south Pacific weaken or head east 4. Warm air rises near Peru, causing rain in the deserts 5. Warm water spreads from the west Pacific and the Indian Ocean to the east Pacific. It takes the rain with it, causing rainfall in normally dry areas and extensive drought in eastern areas.

General Description of ENSO Processes

The key is to appreciate how odd the normal state is - The easterly trades drive westward currents, bringing the cold waters of the Peru Current from the South American coast. - The Coriolis effect turns westward surface currents poleward, causing divergence and upwelling. - The trade winds push the warm upper layer waters poleward as well as westward, pulling the thermocline to the surface in the east. All of this leads to the strong E-W temperature gradient. - All are due to the easterly winds, but the easterly winds are also due to temperature contrasts along the equator. Thus, there are positive feedbacks to reinforce both El Niño and La Niña phases.

Connecting El Niño and the SO (ENSO)

The link between SO and El Niño was made convincingly by Bjerknes Made extensive use of data gathered during 1957 (strong El Niño year) Realized that unusual events separated by half the circumference of Earth could be linked together as parts of a huge coupled phenomenon ENSO- involving both the ocean and the atmosphere.

Troposphere

The lowest layer of Earth's atmosphere All "weather" takes place in the troposphere

Why does ENSO State tend to oscillate

The oscillation is made possible due to the asymmetry between eastward and westward oceanic motions. Rossby waves move westwards north and south of the equator and gain momentum from wind stress at the surface layer. Trade wind relaxation allows formation of a relatively fast eastward motion called an equatorial Kelvin wave. Time scale: <1 yr for the Kelvin wave to shift the warm pool eastward (once trade winds relax); 2 yrs for the Rossby waves to return the warm pool to the west

lapse rate

The rate at which temperature decreases with an increase in altitude. Earth's surface lost heat to the atmosphere when water is evaporated from oceans to the atmosphere

Rotation of the Gyres

The rotation of the gyres in the NH is clockwise and in the SH anti-clockwise. eastern and western boundary currents are not wind-driven but provide continuity of flow Ekman transport causes accumulation of water at the center of the circular flow pattern that results in an elevated convergence Cyclonic wind --> upwelling with surface divergence, water rising towards the sea surface Anticyclonic wind --> downwelling with the water going towards the thermocline

Subtropical Gyres

The subtropical gyres are centered around 30 degrees N/S

Intertropical Convergence Zone (ITCZ)

The trade winds from the Northern and Southern Hemispheres converge into a narrow belt close to the equator, nowadays generally referred to as the Intertropical Convergence Zone (ITCZ). The convergence of the trade winds results in rising motion of the colliding air masses (to obey the law of mass continuity).

Radiation

The transfer of energy by electromagnetic waves, such as light and microwaves Conduction and convection require matter to transfer heat. Radiation doesn't rely any contact between the heat source and the heated object.

Convection

The transfer of heat by the movement of a fluid When warmer areas of liquid or gas rise to cooler areas in the liquid or gas. Cooler liquid or gas replace the warmer areas which have risen higher.

Wind Driven Summary

Upper ocean circulation results from wind stress on sea surface. Ekman transport of surface water by wind stress pusheswater to the right of wind direction (in NH). This piling up of water creates sea-surface hills/valleys (pressure gradients). Geostrophic flow occurs at right angles to pressure gradient.

Atmosphere

Very good convector Hot air rises and cool air falls to take its place

Temperature controls water vapor saturation in air

Warm air holds A LOT more water than cold air. Saturation water vapor content increases exponentially with temperature

El Niño Condition

Warm water pool approaches South American coast. Absence of cold upwelling increases warming.

Ocean temperature decreases with depth/greater pressure

Water = very poor conductor of heat, it has a great capacity to hold energy. Takes a lot of energy to raise the temperature of water, but once the temperature is raised, the heat energy is dissipated very slowly When sunlight hits, it heats the top layers. The sunlight is transmitted only enough to heat lower levels a little. In the ocean, most of the light energy is absorbed in the top 50 cm. At 2 meters depth, 98% of the energy has been absorbed and transformed into heat. Since water has a high capacity to hold on to heat - once heated it stays hot for a time, seasonal changes in ocean temperatures lag about 2 months behind land temperatures. Heat is transferred to lower levels of lakes, ponds, and oceans largely by the circulation of the body of water. Water circulation is caused by the movement of water molecules between areas of different densities. Since water near the surface is less dense than water near the bottom, the water circulates, bringing the solar-heated water of the surface down into the body of water and heating the lower levels. The water near the surface and warmed by the Sun is less dense than water near the bottom, because density of water changes as the temperature of the water changes. The lower the temperature of water, the higher the density of that water

Vorticity

Water flowing towards the equator: Lower planetary vorticity Eastern boundary currents are broad and shallow - mass spread out Water flowing towards higher latitudes: Greater planetary vorticity Western boundary currents are deep and narrow - mass concentrated in a smaller volume

The addition of water vapor decrease air density

Water vapor is a relatively light gas when compared to diatomic Oxygen and diatomic Nitrogen. Thus, when water vapor increases, the amount of Oxygen and Nitrogen decrease per unit volume and thus density decreases because mass is decreasing.

Weather

Weather is defined as the conditions of the atmosphere at a given time and place.

Thermocline

a layer in a large body of water, such as a lake, that sharply separates regions differing in temperature, so that the temperature gradient across the layer is abrupt. Located right below the surface of the ocean, epipelagic zone

Southern Oscillation Index

a measure of the Southern Oscillation calculated using the difference in air pressure between Tahiti and Darwin SOL = Tahiti SLP - Darwin SLP Tahiti and Darwin are at opposite ends of the SO's seesaw. Both Darwin and Tahiti have an appreciable seasonal cycle of mean sea level pressure (MSLP).

Heat Transfer

conduction in solids, convection of fluids and radiation through anything Atmosphere = poor conductor, good convection Very good radiation properties

latent heat of fusion and vaporization

describe the heat required to change the state of H2O without changing the temperature

Geostrophic current

horizontal pressure gradients are deflected by the Coriolis effect.

ocean-atmosphere coupling

increased ocean surface height in the eastern equatorial Pacific during El Niño decreased ocean surface height along the North, Central and South American coast during La Niña

specific heat

of all naturally occurring earth materials, water changes its temperature the least for the addition or removal of a given amount of heat ® this is the result of the extensive hydrogen bonding and the large latent heat of fusion and vaporization

Wind systems are modified by

seasonal temperature changes in the mid latitudes the distribution of land masses the difference in heat capacity of land and water: smaller heat capacity of land: land heats up in the summer and ocean keeps warmer in the winter transfer of heat between surface and deep ocean; land does not transfer heat like that large landmasses over the mid latitudes in the NH cause high and low pressure cells to change their position with the seasons

Pressure gradient

the amount of pressure change occurring over a given distance

Seasonally reversed wind patterns create the Asian monsoons

wet summer monsoon: air rises above the continents and attracts moist air from the oceans, condensation over land creates rain dry winter monsoon: a high pressure cell forms over land and attracts cool, dry air from central Asia

ENSO and Global Warming

• Instrumental climate records are too short (100-200 years). • Longer records of past climate change (paleoclimate): - Glaciers - tree rings - corals - lake and ocean sediments Looking for longer than instrumental records

Tropical cyclones (hurricanes)

• Large rotating masses of tropical low pressure • Cyclonic flow = around low pressure (CC in NH) • Intensity due to added power from condensation Typhoons = Pacific, Hurricanes = Atlantic, Cyclones = Indian Ocean