weather exam 1

chapters 1-4

Light year

The distance that light travels in one year (speed of light = 186,000 mi/s)

Orion Spur

The location of our solar system within the Sagittarius Arm of the Milky Way Galaxy

Nuclear fusion

Process where two hydrogen isotopes (deuterium and tritium) are forced together by the Sun's gravity to create helium and energy

Rotation

The spin of the earth about its axis; 1 rotation every 24 hours; influences diurnal (daily) rhythms

Axis

Imaginary line extending through the earth marking the center point of rotation

Axial tilt

The earth's axis is tilted 23.5° from vertical relative to the ecliptic plane; thought to result from a collision with a large body

Ecliptic plane

The orbital plane along which the earth revolves around the sun

Revolution

Movement of earth around the sun; takes 365.25 days along the ecliptic plane

Elliptical orbit

The earth's orbit is not a perfect circle but a slightly elongated ellipse, with the sun offset from center

Aphelion

Point in earth's orbit farthest from the sun (152 million km); reached around July 4th

Perihelion

Point in earth's orbit closest to the sun (147 million km); reached around January 4th

Insolation

Incoming solar radiation; energy received from the sun

Sphericity

Earth's shape, more accurately described as an oblate spheroid (wider than tall); affects the intensity of insolation via curvature

Oblate spheroid

A sphere flattened at the poles and bulging at the equator; the earth's actual shape

Beam spreading

When sunlight strikes at an angle, it spreads over a greater surface area and becomes less intense

Zenith angle (ZA)

Measures how far the sun's rays are from vertical (perpendicular to the surface); higher ZA = more beam spreading = weaker insolation

Beam depletion

Weakening of solar radiation as it passes through more atmosphere at high zenith angles (high latitudes, winter, morning/evening)

Solar declination

The latitude of the subsolar point (where zenith angle = 0); migrates throughout the year between 23.5°N and 23.5°S

Subsolar point

The point on earth where the sun is directly overhead (ZA = 0)

Summer solstice (NH)

~June 21; subsolar point at 23.5°N (Tropic of Cancer); Northern Hemisphere most angled toward sun

Winter solstice (NH)

~December 21; subsolar point at 23.5°S (Tropic of Capricorn); Northern Hemisphere least angled toward sun

Vernal/Autumnal equinox

~March 21 / September 21; subsolar point at the equator (0°); sun equally distributed between hemispheres

Circle of illumination

The dividing line between day and night on earth; bisects the earth unequally depending on season

Reason for the seasons

Combination of axial tilt, revolution, and earth's curvature, producing annual cycles in both intensity and duration of insolation

Arctic Circle

Latitude (66.5°) where true 24-hour days or nights begin to occur

Energy

The capacity to do work (i.e., move matter)

Kinetic energy

Energy of movement

Potential energy

Energy of possible movement (stored)

First Law of Thermodynamics

Energy can be stored, moved, and transformed, but the total amount of energy never changes

Second Law of Thermodynamics

Energy is conserved, but flows "downhill" from concentrated (hot) to dilute (cold) forms

Heat

Flow of kinetic energy between molecules or from one body/substance to another

Watt

Unit of power; rate of energy transfer (1 W = 1 J/s)

Conduction

Energy transmitted through direct contact between neighboring molecules; always flows hot to cold

Convection

Transfer of energy by the actual movement of heated material (fluid); redistributes energy from equator to poles and surface upward

Advection

Horizontally moving air (wind), as opposed to convection's vertical motion

Sensible heat

Heat you can feel; energy input causes a temperature change

Latent heat

Energy transferred during a phase change; not felt because there's no temperature change; stored in water vapor

Phase change energy rule

Change to a higher energy state (solid→gas) consumes energy from environment; change to lower energy state (gas→solid) releases energy to environment

Radiation

Energy transfer that does not require a medium; can travel through a vacuum

Electromagnetic radiation

A self-propagating transverse oscillating wave of electric and magnetic fields that moves energy through space; all matter emits it

Wavelength (λ)

The distance between wave crests or troughs

Frequency

The number of wavelengths passing a point per unit time; short wavelengths = high frequency, long wavelengths = low frequency

Stefan-Boltzmann Law

E = σT⁴; the hotter an object, the more radiation it emits (T in Kelvin)

Wien's Law

λpeak = 2898/T; the hotter an object, the shorter the wavelength of peak emission (T in Kelvin)

Shortwave radiation

Radiation emitted by the sun (< 4 microns), mostly visible light with some UV and near-infrared

Longwave radiation

Radiation emitted by the (cooler) earth (> 4 microns), in the infrared spectrum

Reflection

Radiation is redirected away from an object or medium

Transmission

Radiation passes through an object/medium unaltered

Absorption

Object/medium takes on radiative energy, causing it to heat up

Emission

Object re-emits energy after absorbing it

Scattering

A type of reflection where incident radiation is redirected in all directions

Albedo (α)

The fraction of total incoming shortwave radiation that is reflected or scattered away; brighter surfaces have higher albedo

Rayleigh scattering

Scattering that occurs when particles are much smaller than the radiation's wavelength (e.g., gas molecules vs. visible light); shorter wavelengths scatter more, making the sky blue

Why sunsets are red

At low sun angles, blues/greens are scattered out of view over the longer atmospheric path, while reds pass through to reach our eyes

Refraction

Change in direction of energy propagation when passing through an interface between two media of different density

Dispersion

Occurs when shorter wavelengths are refracted more than longer wavelengths (e.g., in a rainbow)

Net radiation (Rnet)

The balance of energy in minus energy out: Rnet = SWin − SWout + LWin − LWout

Positive Rnet

Gaining more energy than losing; temperature increases

Negative Rnet

Losing more energy than gaining; temperature decreases

Global radiation balance

Globally, Rnet = 0 (340 W/m² SW in − 100 W/m² SW reflected − 240 W/m² LW out = 0)

Greenhouse effect

Natural phenomenon where SW radiation passes freely through the atmosphere, but greenhouse gases absorb outgoing LW radiation and re-emit some of it back toward the surface, warming the planet (~33°C warmer than without it)

Greenhouse gases

Gases that selectively absorb longwave radiation, including water vapor, carbon dioxide, and methane

Selective absorbers

Greenhouse gases that only absorb specific wavelengths (via molecular transitions), letting visible light pass but absorbing much of the infrared

Eunice Foote

Scientist who in 1856 used glass cylinders with CO2 and other gases to show that increased CO2 could raise Earth's atmospheric temperature

John Tyndall

Scientist whose experiments showed water vapor and CO2 effectively absorb and emit infrared radiation

Energy surplus (equator)

The equator gains more radiative energy than it loses

Energy deficit (poles)

The poles lose more radiative energy than they gain

Atmospheric rivers (ARs)

Narrow corridors of concentrated water vapor transport responsible for over 90% of poleward water vapor movement

Diurnal temperature lag

The ~3-hour lag between peak insolation (solar noon) and the daily maximum temperature

Annual temperature lag

The ~1-month lag between the summer solstice (peak insolation) and the warmest time of year

Energy partitioning

Division of surface energy between sensible heating (warming air via conduction/convection) and latent heating (evaporating water)

Scientific Method

Process by which scientists work together to develop an accurate, reliable, consistent, and objective representation of the world

Hypothesis

An educated guess regarding the answer to a question; must be testable

Prediction

A statement about what you expect to happen when you test your hypothesis; should logically follow from the hypothesis

Experiment

The procedure taken to obtain data to test a hypothesis; can be active (e.g., a model) or passive (collecting data from an ongoing event)

Scientific Conclusion

Evaluation of a hypothesis based on analysis; not final, as new information can revise or disprove it

SI Units

The International System of measurement; combines a unit (what is measured) with a prefix (order of magnitude)

Kilo-

SI prefix meaning 10^3 (x1000)

Hecto-

SI prefix meaning 10^2 (x100)

Deci-

SI prefix meaning 10^-1 (x0.1)

Centi-

SI prefix meaning 10^-2 (x0.01)

Milli-

SI prefix meaning 10^-3 (x0.001)

Giga-

SI prefix meaning 10^9 (x1 billion)

Watt

Unit of power; the transfer of energy (J/s)

Geographic Grid

System allowing any location on Earth to be recorded using a latitude-longitude (coordinate) pair

Latitude

Measures angular distance north or south of the equator (0°); ranges from 0° to 90°N or 90°S

Parallels

Lines of latitude; run parallel to each other and encircle the globe like a belt

Longitude

Measures angular distance east or west of the prime meridian (0°, Greenwich, England); ranges from 0° to 180°E or 180°W

Meridians

Lines of longitude; converge at the poles rather than running parallel

International Date Line

Located at 180°E/W; crossing east to west moves time forward one day, crossing west to east moves it back one day

Prime Meridian

The 0° line of longitude, passing through Greenwich, England; reference point for UTC time

UTC

Coordinated Universal Time, measured at the prime meridian; other time zones are expressed as an offset from it

Isopleth

A line of constant value on a map, used to represent spatial patterns (e.g., elevation, temperature, pressure)

Contour Interval

The increment of value between two adjacent contour lines on a map

Gradient

The rate of change of a variable with distance; the strongest gradient runs perpendicular to the contours

Isotherm

An isopleth (line of constant value) used to map temperature

Isobar

An isopleth (line of constant value) used to map sea-level pressure

Isotach

An isopleth (line of constant value) used to map wind speed

Station Model

A symbolic diagram used on weather maps to represent multiple weather variables at a single location

Wind Barb

Symbol on a station model representing wind speed; short barb = 5 kt, long barb = 10 kt, triangle flag = 50 kt