3 MAIN INGREDIENTS

The Weather Recipe

What causes weather?

Weather is not a set of random acts of nature, it is a response to the unequal heating of Earth’s atmosphere.

Ingredient #1: Atmospheric Pressure

Weight of the column of air above a location.

Measured in millibars or inches of mercury.

Influenced by heat.Changes continually.Low P indicates

unstable air, cloudiness and storms.

Hi P indicated fair weather and clear skies.

Ingredient #2: Moisture

Vapor form of water has the most influence on weather.

Varies with height, latitude, longitude, and time.

Tropics = 4%Tropopause = 3 ppmExpressed as relative

humidity.Effects weather due

to energy content.

Ingredient #3: Heat

Fuels the weather machine.

Determined by the speed of molecules within a substance.

Transferred by radiation, convection, and conduction.

Temperature is a measure of the amount of heat.

Earth’s Heat Budget

Effect of Earth’s Motions

The atmosphere swaddles a rotating, revolving planet.

Tilted axis (23.5 deg.) causes seasonal changes.

Coreolis ForcePressure gradient

forceFriction

Pressure Gradient Force

Air flows from regions of higher pressure to those of lower pressure.

This difference is called a pressure gradient and drives the wind direction and speed.

Because of the coreolis effect air does not flow directly toward low pressure areas but is instead deflected.

Air Masses

A large body of air that has properties similar to the part of the Earth’s surface over which it develops.

CloudsClouds

Masses of small water droplets or tiny ice crystals that float in the air.

Three main types are cirrus, cumulus, and stratus.

Other clouds are a mixture of these three main types.

Cloud Types

Cirrus

High altitude clouds

Thin wisp like strands

Indicate an approaching front and a change in the weather

Cumulus

Puffy or cotton like in appearance

Form as a warm air mass rises into cooler air

May produce heavy rain, lightning, severe and strong winds, hail, and even tornadoes

Stratus

Strato- means “layer-like” or “sheet-like.”

Low-lying, dull-colored clouds that form in layers or sheets.

Usually bring drizzling rain or light-falling snow.

More detailed types of clouds

Types of Precipitation

RainRain SleetSleet

SnoSnoww

HailHail

Air Masses

A large body of air that has properties similar to the part of the Earth’s surface over which it develops.

Air Mass Map

Fronts

A boundary between two air masses of different density, moisture, or temperature.

Cold Front

Cold fronts occur when heavy cold air pushes lighter warm air upwards.

Cumulus clouds form and usually grow into thunderstorms

Temperatures drop anywhere from 5 degrees to 15. Winds become gusty and erratic.

Rain, snow, sleet, and hail can occur with a cold front.

Cold Front

Warm Frontthe leading edge of an advancing mass of warm air

The warm front symbol on a weather map marks the warm-cold boundary at the earth's surface. The circles on the red line point in the direction the warm air is moving.

As the warm air rises the water vapor condenses into clouds that can produce rain, snow, sleet or freezing rain, often all four.

Warm Front

Occluded front

Often, in the later stages of a storm's life cycle, a frontal occlusion occurs.

Frontal occlusions occur when storms redevelop farther back into the cold air. In most cases, storms begin to weaken after a frontal occlusion occurs

Occluded Front

Stationary Front

Rainbows

Rainbows are optical illusions and that cause a spectrum of light to appear in the sky when the Sun shines onto droplets of moisture in the atmosphere.

They take the form of a multicolored arc, with red on the outer part of the arch and violet on the inner section of the arch.

Contrails

The condensation trail left behind jet aircrafts

Contrails form when hot humid air from jet exhaust mixes with environmental air of low pressure and low temperature

Halos

Mostly caused by ice crystals in cold cirrus clouds located high (5–10 km, or 3–6 miles) in the upper troposphere

Light is reflected and refracted by the ice crystals and may split up into colors because of dispersion, similar to the rainbow.

Global Air Circulation

Heat and moisture are distributed over the earth’s surface by vertical currents that form six large convection currents at different latitudes.

Called Hadley cells, the direction of airflow and the ascent and descent of air masses in these cells determines earth’s general climatic zones.

The uneven distribution of heat and moisture over the planet’s surface leads to the formation of different biomes.

Global Air Circulation Patterns

Ocean Currents

The oceans absorb heat from the air circulation patterns.

The majority of the heat is absorbed near the tropics.

This heat plus differences in water density create warm and cold ocean currents.

These currents, driven by winds and the earth’s rotation, redistribute heat received from the sun from one place to another and thus influence climate and vegetation.

Ocean Currents

Normal Conditions

El NiñoEl Niño occurs when a change in the direction of tropical winds warms coastal surface water, suppresses upwellings, and alters much of the earth’s weather.

El Niño

La Niña•As El Niño conditions begin to right themselves (return to normal).

•The trade winds and upwelling become unusually strong

•ocean surface cools far below normal

•causes widespread climate disruptions that often have the opposite effect of those caused by El Niño

El Niño v. La Niña

La Niña

Key Points

The surface of the earth is heated unevenly due to the angle the sun’s rays strike the earth

Rotation of the earth deflects air masses setting up global air circulation patterns

Properties of air, water and land affect global air circulation.

The oceans absorb heat from air circulation creating warm and cold ocean currents.

Ocean currents redistribute heat from one place to another and thus influence climate and vegetation (biomes)

Thermohaline

large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes.