GEOG 2050 Seasons and Solar Radiation Flashcards

Chapter 3 of GEOG 2050

Meteorological Seasonality

Changes in temperature of precipitation over the years

Astronomical Seasonality

Changes in the positions of the sun and stars in the sky through the year

Plane of the ecliptic

flat plane that the orbital paths of the planets trace

Parallel axis

Points to Polaris (North Star)

Subsolar point

• Single point at which Sun’s rays are perpendicular to Earth’s surface at or near noon (between 23.5 N and S)

  • Latitude of the subsolar point is always 90 degrees away from circle of illumination, (line separating night from day)

  • Point determines solar altitude (angle of the Sun above the horizon)

  • Solar altitude determines intercity of noontime sun

  • Subsolar point migrates between the Tropics of Cancer (23.5 N) and Capricorn (23.5 S) 

  • Latitude of the subsolar point is called the solar declination

Axial tilt

23.5 is the latitude of the tropics (Cancer and Capricorn)

December Solstice

• 12/21

• Subsolar point at the Tropic of Capricorn 

• Winter solstice

• Shortest day of the year in the Northern Hemisphere

  • Days get longer after this until the June solstice

March Equinox

• 3/20

• Subsolar point crosses equator

• Spring equinox

June Solstice

• 6/21

• Subsolar point at the Tropic of Cancer

• Summer solstice

• Longest day of the year in the Northern Hemisphere

  • Days get shorter after the June solstice until we reach the December solstice

September Equinox

• 9/22

• Subsolar point crosses equator

• Fall equinox

Equinoxes

• All locations on Earth have 12 hours of day and night

• Sun is above equator

Temperature

average kinetic movement of atoms and molecules of a substance

Heat-index temperature

• temperature perceived by people as a result of high atmospheric humidity coupled with high air temps

Molecules

• move quickly in objects with high temps and relatively slowly in objects with low temps

• when molecules are no longer moving, a point of 0 kelvins, or absolute zero is reached

Water temperature scales

• freezes at 0°C (32°F)

• boils at 100°C (212°F).

Converting C to F

• °F = (1.8 × °C) + 32   ->quick way is to double and add 30

Converting F to C

• °C = (°F − 32)/1.8  -> quick way is to subtract 30 and divide by 2

Heat

• The internal energy transferred between materials or systems due to their temp differences

• If you touch something and feel it is hot it means that the object has more energy than you and vice versa

• The kinetic energy of molecular movement can be felt as heat

• Heat moves through

  • conduction

  • convection

  • radiation

Conduction

• Process by which energy is transferred through a substance or between objects in direct contact (touching)

  • In conduction, heat always flows from objects of higher temp to objects of lower temp

Convection

• The transfer of heat through movement of mass within a fluid (liquid or gas)

Radiation

• Process by which wave energy travels through the vacuum of space or through a physical medium such as air or water

Surface temperature patterns

• Difference between the average max, and average min temps over a year at a location is its annual temperature range or seasonality 

• Average annual temp at any given location is controlled mainly by elevation and latitude

Elevation influence

• In the troposphere temp decreases with altitude

• Mountains are always cooler than surrounding lowland regions

Latitude Influence

• Temperature generally decreases away from the equator as sunlight becomes more diffuse

• Lower surface temps and greater annual range at higher latitudes 

Why the difference

• Four main factors:

  • Specific heat of water

  • Evaporation of water

  • Mixing of water

  • Transparency of water

Heat Capacity

• The amount of heat that must be absorbed to change the temperature of an object

• Due to heat capacity, generally, continents become warmer in summer than oceans at the same latitude

• In winter continents become colder than oceans

Specific Heat

• Heat required to raise temperature of any object or material by a given amount (a measure of heat capacity)

• Water’s specific heat is higher than those of most materials that make up landmasses… continental effect results mainly from this difference

Evaporation

• cools water and prevents it from becoming warmer … land heats up more in sunlight than oceans do.

Ocean-atmosphere Heat Transfer

• Warm ocean currents (ex the Gulf Stream) from the tropics carry heat towards the poles

  • At higher latitudes some of their heat is transferred to the atmosphere (ex British Isles)

  • Warm ocean currents raise average annual temperature and reduce annual temperature range

  • Cold currents influence temperature less

Prevailing Wind

• Prevailing wind is from the west, so west coasts have maritime climates and east coasts have continental climates

• Pattern is strongest at midlatitudes and weakened in the Southern Hemisphere, polar regions, and tropics

Radiant Energy

• Energy that is propagated in the form of electromagnetic waves (ex visible light and heat)

  • All forms of radiation have both electrical and magnetic properties… referred to as electromagnetic energy

    • Electromagnetic waves travel at light speed

Photons and Wavelengths

• All matter emits photons (packets of energy) of electromagnetic radiation

• Photons travel in waves, and the distance between the peaks of two waves is the wavelength

• Longer wavelengths have less energy than shorter wavelengths

The Electromagnetic Spectrum (EMS)

the hotter something is, the shorter its wavelengths are

Longwave and Shortwave Radiation

• Objects with higher temperatures emit photons at shorter wavelengths and at a higher rate than objects with lower temps

• Earth emits energy at a lower rate than the sun

• All radiation emitted by Earth is longwave radiation (LWR)

• Most solar radiation is shortwave radiation (SWR)

Infrared and Visible Radiation

• Most solar radiation is in visible wavelengths

• Earth mainly emits infrared radiation

• Most solar UV radiation is absorbed by ozone in the stratosphere

• Clouds and aerosols help determine how much UV radiation reached Earth

• UV radiation is subdivided depending on its wavelength: UV-A, UV-B, and UV-C

Visible Radiation: Light

• 44% of solar radiation is in visible wavelengths

• When all visible light colors are combined, they blend into white

• Black (true darkness) is the absence of all light

Infrared Radiation (IR)

• IR has wavelengths longer than visible radiation

• Earth absorbs shortwave solar radiation and re-emits it as infrared radiation

Insolation

• Incoming Solar Radiation:

  • The fraction of the Sun’s energy that Earth intercepts

    • Insolation is transmitted, scattered, reflected, refracted, and absorbed as it travels through the atmosphere

Transmission

• The unimpeded movement of electromagnetic energy through a medium such as air, water, or glass

• The atmosphere absorbs UV and IR wavelengths but transmits visible wavelengths

• Glass transmits visible light but absorbs UV wavelengths

Scattering

• The process of redirecting solar radiation in random directions as it strikes physical matter

• Scattering creates diffuse light

Reflection

the process of returning a portion of the radiation striking a surface in the general direction from which it came

Albedo

• Reflectivity of a surface, given as the % of incoming radiation that it reflects

• Lighter-colored surfaces have a higher albedo than darker surfaces

• The albedo of Earth, taken as a whole, is 30%

• Surfaces with low albedo absorb more insolation than do objects with higher albedo

  • High albedo = snow

  • Low albedo = asphalt

• Earth does not emit light but only reflects it

• Earth is visible from space because it reflects sunlight

Refraction

• The process of redirecting solar radiation as it passes from one medium to another

  • If refraction is strong enough, it can separate visible light

The Urban Heat Island

• An urbanized region may become warmer than surrounding rural areas 

  • Cities have low albedos

  • City materials retain absorbed heat energy and radiate it

  • Cities lake water for evaporation (cooling)

The Great Balancing Act

• Temperature of Earth’s surface and atmosphere is the result of a balance between incoming and outgoing energy

The Greenhouse Effect

• The process by which the atmosphere is warmed as greenhouse gases and clouds absorb and counter-radiate heat

  • Without any greenhouse gases, Earth’s lower atmosphere would be much colder (inhospitable to most life) but humans have modified the greenhouse effect by adding greenhouse gasses to the atmosphere

The Global Heat Engine

• At most latitudes, there is either a surplus or a deficit of heat

• Heat from tropics is advected (horizontal movement of energy: AKA the wind) poleward by the atmosphere and the oceans

• Heat is transferred to the atmosphere through radiation

• The movement of heat from low to high latitudes and low to high altitudes as a result of heating differences

  • Almost all atmospheric movement (ex wind, tornadoes, etc) is the result of heating inequalities across latitude and altitude