Earth Systems Exam 2

Components of the general circulation

7:
- Subtropical highs
- trade winds
- Intertropical convergence zone
- westerlies
- polar highs
- polar easterlies
- polar front

Factors influencing atmospheric pressure

- density: higher density \= particles collide more frequently, increasing pressure
- temperature: warmer particles more faster \= increasing pressure

Atmospheric pressure is approx \_______ per square inch near sea level

14 lbs

Dynamic influences on air pressure:

- Strongly descending air \= dynamic high
- Very cold surface conditions \= thermal high
- Strongly ascending air \= a dynamic low
- Very warm surface conditions \= a thermal low
- Dynamic influences work in tandem with influences from density to affect air pressure

Lines of Pressure

isobars

Pressure is measured with a

barometer

Mapping pressure with isobars

- Typical units are millibars or inches of mercury
- Contour pressure values reduced to sea level
- Shows highs and lows, ridges and troughs

wind is \_________ air movement

horizontal movement
- vertical \= (small scale) updrafts/downdrafts, (large scale) ascents/ subsidences

Origin of Wind

- Uneven heating of Earth's surface creates temperature and pressure gradients
- blows from high to low pressure

Direction of wind results from

pressure gradient

Forces that govern the wind:

- pressure gradient force
- Coriolis effect
-friction

Pressure gradient force

- Characterized by wind moving from high to low pressure
- winds blow at right angles to isobars

Coriolis effect

- turns wind right in the North, left in the South
- affects wind direction (not speed)

Friction

wind is slowed by Earth's surface because of friction (doesn't affect upper levels)
- friction layer extends only to 1000 meters

Force balances

- geostrophic balance
- frictional balance

Geostrophic balance

- balance between pressure gradient force and coriolis force
- winds blow parallel to isobars

Frictional Balance

- Winds blow slightly towards low pressure and slightly away from high pressure
- Winds slowed by friction weaken Coriolis, \= pressure gradient force stronger and turns the winds

Anticyclones and Cyclones

distinct wind-flow patterns develop around high and low pressure centers
- shaped by pressure gradient, Coriolis effect, and friction
- 8 circulation patterns; 4 in each hemisphere

Vertical motions

- Surface convergence and low pressure indicate rising motion (cyclone); Rising motion \= clouds and storms
- Surface divergence and high pressure indicate sinking motion (anticyclone); sinking motion \= sunny skies

Tighter pressure gradients (isobars closer together) indicate

faster wind speeds
(winds are gentle on av)

Hadley Cell

one semipermanent convective cell near the equator

\____ latitudinal wind belts per hemisphere

3

Subtropical highs

- Persistent zones of high pressure near 30° latitude in both hemispheres
- Result from descending air in Hadley cells
- Subsidence is common over these regions
- Regions of world's major deserts
- No wind, horse latitudes

Trade winds

- diverge from subtropic highs
- between 25N-25S latitude
- easterly winds: southeasterly in South, northeasterly in North
- most reliable winds
- "winds of commerce"
- don't produce rain unless forced to rise (produce tremendous precipitation and storm conditions)

Intertropical Convergence Zone (ITCZ)

- zone of convergence for NE and SE trades near equ
- more pronounced over land
- doldrums
- feeble and erratic winds
- warm

Weather of the ITCZ

- feeble and erratic winds
- warm surface conditions with high rainfall
- instability and air ascends in thunderstorm updrafts
- energy into upper atmosphere

Westerlies

- form on poleward sides of subtropic highs
- wind system of midlatitudes
- 2 cores of high winds; jet streams

Rossby waves

- when jet streams curve as high-altitude westerlies flow north and south
- 3-7 Rossby waves in either jet stream
- separates polar and tropical air
- strong short term variability of weather in midlatitudes

Polar Highs

- Thermal highs that develop over poles from extensive cold conditions
- Winds are anticyclonic; strong subsidence
- Arctic desert

Polar easterlies

- regions North of 60N and South of 60S
- winds blow easterly
- cold and dry

Polar Front

- low pressure area between polar high and westerlies
- air mass conflict between warm westerlies and cold polar easterlies
- rising motion and precipitation
- polar jet stream position typically coincident with the polar front

Vertical Patterns of the General Circulation

- at the surface, alt E and W bands of wind

Buoyancy

the ability or tendency to float in water or air or some other fluid

Stable air

parcel is negatively buoyant, will not rise without an external force

Unstable air

parcel is positively buoyant, will rise without an external force

Adiabatic Processes

- Dry adiabatic lapse rate: 10°C/1000m (5.5°F/1000ft)
- Lifting condensation level (LCL)
- Saturated adiabatic lapse rate: ~6°C/1000m (3.3°F/1000ft)
- Parcel lapse rates versus environmental lapse rate

Water

most widespread substance on Earth's surface
- 70% of earths surface area
- essential for all life

hydrologic cycle (water cycle)

circulation of earth's water supply
- liquid water evaporates into air, condenses into liquid (solid state), and returns as precipitation
- stored in water bodies, soil, clouds, water vapor, biosphere, and ice

Properties of water

Liquidity
- exists as a liquid found in most places
Ice expansion
- expands when freezes, less dense than liquid (ice floats in water)
Surface tension
- polarity and cohesion \= high surface tension
Capillarity
- water's adhesion allows it to "stick" to other substances, moving upward when confined
Solvent ability
- dissolves almost any substance (water in nature is almost always impure)
Specific heat capacity
- absorbs enormous amounts of energy w small increase in temp

Phase changes of water

condensation: gas to liquid
evaporation: liquid to gas
freezing: liquid to solid
melting: solid to liquid
sublimation: solid to gas/gas to solid
(latent heat required for each process as a source of atmospheric energy)

Latent heat in the atmosphere

evaporation \= cooling process bc latent heat energy is stored in water vapor
- reduces temp of remaining liquid
condensation \= warming process as latent heat is released back into the atmosphere
- energy transferred by air masses and winds play a role in stability of atmosphere and power of storms

Water vapor content of air

- warm air \= hold more water vapor
- higher the temp \= higher the max vapor pressure
- air reaches max VP \= saturation
- rate of evaporation is more rapid in "dry" air w little water vapor, rate slow when air gets closer to saturation

If air is in motion, as wind or vertical turbulence, water vapor is dispersed and ...

rate of evaporation rises

Evapotranspiration

combined process of water vapor entering atmosphere from land sources
- small amount of evapor comes from land
- mostly from plants, minor from soil and other inanimate sources
- plants give up moisture through their leaves as transpiration

potential evapotranspiration

amount that could occur if group in that location were always wet
- rates of evapotrans and precipitation \= location is wet or dry
- annual precipitation is \> evapotrans, water surpluses accumulate on ground d
- annual potential evapotrans is \> than actual precipitation, no water is available for storage in soil/plants

Humidity

The amount of water vapor in the air

Vapor Pressure

contribution of water vapor to total atmospheric pressure

Relative humidity

how close the air is to saturation

Saturation point

The maximum amount of water vapor in the air at a given temperature
- dependent on temp

Dew point

The temperature at which saturation occurs in the air
- dependent on water vapor present
- high dew point \= abundant atmospheric moisture
- only be \= or less than air temp

supercooled water

Liquid water can persist at temp colder than 0 degrees C w/out a nuclei

Significance of adiabatic temperature changes

- Hypothetical parcel of air moving up and over a mountain range, assuming no evaporation
- Unsaturated air rises up windward side, cools at dry adiabatic rate
- Once lifting condensation level is reached, air cools at saturated adiabatic rate as condensation forms a cloud
- Once air reaches over summit, it descends down leeward side
- Air then warms at dry adiabatic rate, becoming drier and warmer than when it started at some elevation

Visual Determination of Stability

- Cloud pattern in the sky is indicative of sir stability
- Unstable air associated with distinct updrafts, vertical air currents, and vertical clouds (Especially cumulus clouds)
- Horizontal developed clouds characteristic of stable that is forced to rise
- Cloudless skies indicate stable air that is immobile

Characteristics of Stable air

- non buoyant; remains immobile unless forces to rise
- If clouds develop \= flat (stratiform) but can be thin or thick
- if precipitation occurs \= drizzly or light rain

Characteristics of Unstable air

- buoyant; rises w/out outside force
- if clouds develop \= puffy and have vertical development (cumuliform)
- if precipitation occurs \= showery/downpour

3 primary cloud forms

- cirrus
- stratus
- cumulus

10 types of clouds, divided into \_____ families by attitude

4
- high clouds above 6km
- mid clouds 2-6km
- low clouds below 2km
- clouds of vert development grow upward from low bases to 18 km (cumulonimbus clouds\= thunderstorm)

Dew

- usually from terrestrial radiation leaving and surface cooling
- moisture condensation on surfaces that have been cooled to saturation

Frost

- when air temp lowers to saturation pt (when lower than 0 degrees C)

Collision/coalescence

tiny cloud drops collide and merge to form larger drops

Bergeron Process

process that process ice crystals
- ice crystals attract vapor, supercooled drops evaporate to replenish the vapor
- fall as snow or rain

Types of Precipitation

- rain: liquid water
- snow: clouds ice crystals
- sleet: snow melted and frozen again before hitting land, ice pellets
- glaze (freezing rain): water falls as liquid, freezes to surfaces
- hail: strong updrafts are required

4 types of atmospheric lifting

- convergent
- convectional
- orographic
- frontal

Global Distribution of Precipitation

- high precipitation \= tropics
- low precipitation \= deserts and poles

Regions of High Annual Precipitation

- ITCZ and trade-wind uplift (warm, moist winds, forced orographic uplift, heavy rainfall)
- Tropical monsoon regions (winds divert from "normal" pattern in monsoon areas)
- Coastal areas in westerlies (frequent onshore westerly winds, storminess and mountain barriers)

Regions of Low Annual Precipitation

- areas of subtropical highs
- interiors of continents
- high latitude regions

Acid Rain

- deposition of wet/dry acidic materials from atmosphere onto Earth's surface
- pollutants in precipitation

Measuring acidity

pH scale
- lower the number, more acidic
- 7 is neutral
- from acidity to alkalinity

Damage from Acid Precipitation

major damage to aquatic ecosystems and forests
- acid precipitation, travels far from source (can cause many issues)

Action to reduce acid precipitation

- Title IV of 1990 Clean Air Act Amendment
- in 1991, Canada and USA signed the bilateral Air Quality Agreement

Convergence and low pressure indicate \_________.

rising motion

Divergence and high pressure indicate \__________.

sinking motion

Rising motion results in \_______.

clouds and storms

Sinking motion results in \________.

sunny skies

Tight pressure gradients (isobars close together) indicate \_______.

faster wind speeds

Seasonal reversal of winds

sea to land movement \= onshore flow in summer, offshore in winter

Monsoons

develop due to shifts in positions of ITCZ and unequal heating of land and water

Localized Wind Systems

- sea/land breezes
- valley/mountain breezes
- Katabatic winds
- Foehn/Chinook Winds
- Santa Ana winds

Sea/Land breezes

Sea breezes (day) \= winds blow from sea to land (thermal low over land, thermal high over sea)
Land Breezes (night) \= winds blow from land to sea (thermal high over land, low over sea)

Valley/Mountain breezes

valley \= Upslope winds out of valley; mountain top (during day) heats faster than valley, creating a thermal low at mountain top
Mountain \= winds blow from mountain to valley, downslope; mountain top cools faster at night, creating thermal high at top

Katabatic winds

- cold winds that originate from cold upland areas, bora winds
- winds descend quickly down mountain, can be destructive

Foehn/Chinook Winds

- High pressure on windward side of mountain, low pressure on leeward side
- Warm downslope winds
Santa Ana winds

Santa Ana winds

develop out of stationary high pressure in interior western US
- winds diverges clockwise out of high , bringing dry, warm northerly, or easterly winds to coast
- high speed, temp and dryness (ideal for wildfires)

El Nino-Southern Oscillation (ENSO)

episodic atmospheric and oceanic event of the equatorial pacific ocean
- warming of easter equator Pacific water and subsequent switching of the high and low air pressure patterns
- occurs every 2-7 years
- changes global pressure, wind, and precipitation
- more frequent in last century

Other Multiyear Atmospheric and Oceanic Cycles (teleconnections)

-Pacific decadal oscillation (PDO)
-North Atlantic Oscillation (NAO) & Arctic Oscillation (AO)

Winds \_____ with height, pressure \______ with height

increase, decreases

Air Mass Classification

2 letter system
lower case \= moisture content
- c - continental, dry
- m - maritime, humid
Uppercase \= source region
- P - polar
- T - tropical
- A - arctic
- E - equatorial

Properties of an air mass

- Large (diameter \> 1600 km)
- Uniform horizontal properties
- Recognizable entity; travel as one

Fronts

A boundary between two different air masses
- clash over midlatitudes between polar and tropical air masses

4 types of fronts

Cold - cold air advancing
Warm - warm air advancing
Stationary - no advance of air masses
Occluded - cold air overtakes warm air

Regardless which air mass is advancing, cooler denser air will force warmer lighter air \____

aloft

Cold front

- protruding "nose" of cold air
- faster than warm fronts
- lift warm air ahead of cold fronts
- blue lines w triangles pointing in direction of frontal motion

Warm front

- gentle slope of warm air rising above cool air
- slow cloud formation and precipitation
- red line w semicircles pointing in direction of warm air motion

Midlatitude disturbances

midlatitude cyclones

Tropical disturbances

easterly waves and hurricanes

Midlatitude Cyclones

- Exist between 35-70 degrees latitude
- 1600 km in size
- Central pressure between 990 to 1000 mb
- converging counterclockwise circulation in N hemisphere
- westward tilt w increasing elevation in N hemisphere
- steered by jet stream

Occlusions (occluded front)

- cold front catches warm front, removing the energy of storm (the warm air)
- mark the end of the cyclone's life
Marked as a purple line with alternating triangles and half circles in direction of advancing cold air

Occurrence and distribution of cyclones

- 6-15 exist worldwide
- more during winter
- move more poleward in summer

Midlatitude anticyclones

- high pressure system
- wind flow is clockwise
- slower than cyclones
- follow behind cyclone's cold front

Easterly waves

MINOR TROPICAL DISTURBANCE
- little cyclone circulation
- oriented N-S
- convergence behind wave, divergence ahead of wave
- can intensify to tropical cyclones