Chapter 2 (Part I): Air Temperature Flashcards

Air Temperature and Solar Radiation

• Chapter 2 (part I): Air Temperature

  • Topics include:
  • Basics on Energy, Heat, Temperature, and Solar Radiation
  • Factors Affecting Air Temperature
  • Earth-Sun Relations

• Heat and Energy

  • Energy is the ability to do work. Examples include mechanical, chemical, nuclear, thermal, and electrical energy.
  • Kinetic Energy vs. Potential Energy
  • Heat energy (i.e., thermal energy) – is the total kinetic energy in an object.
  • Note: this reflects a simplified thermodynamics view as presented in the material.
  • Units of energy: calorie, joule or BTU
  • Heat energy ALWAYS moves from higher temperatures to lower temperatures.

• Heat and Energy (definitions)

  • Energy types include: mechanical, chemical, nuclear, thermal, electrical
  • Kinetic energy vs potential energy distinction
  • Heat energy = total kinetic energy in a substance/object (as defined here)
  • Temperature units: °C, °F ext{ or } K

• Heat transfer: three modes

  • Convection
  • Conduction
  • Radiation
  • These modes are fundamental for understanding weather and climate processes.

• Convection and radiation in weather and climate

  • They play important roles in atmospheric processes.
  • Weather example often discussed: sea breeze and land breeze
  • Sea breeze (typical pattern):
  • Cooler water vs warmer land creates pressure differences.
  • Air moves from sea to land during daytime alongshore due to heating of land.
  • Land breeze (typical pattern):
  • At night, land cools faster than sea, reversing the flow to/from land and sea.
  • The figure shows sea/land breeze situations with surface pressure changes (e.g., values around 988 mb, 992 mb, etc.).

• Temperature

  • Temperature is the measure of the average kinetic energy in a substance.
  • Common units: °C, °F ext{ or } K
  • When temperatures increase, molecules move faster and the substance expands.
  • For air, heated air tends to rise while cold air descends (convection with vertical motions).
  • Temperature conversions are part of this topic (conversion between scales).

• Solar Radiation

  • Solar radiation is the ultimate source of energy that drives our weather.

• The Electromagnetic Spectrum

  • The spectrum includes: Gamma ray, Ultraviolet, Visible, X-ray, Infrared, Microwave, Radio
  • Typical emphasis in introductory meteorology: visible light and its role in heating and optical properties of surfaces.

• Visible Light (41% of solar radiation)

  • Visible light is a portion of the spectrum and accounts for approximately 41 ext{%} of solar radiation reaching Earth.
  • The wavelength range for visible light is roughly from ext{approximately } 400 ext{ to } 700 ext{ nm}.
  • Other spectral categories shown (ultraviolet, gamma, X-rays, infrared, radar, FM/AM, etc.) illustrate the full spectrum.
  • A spectral scale is presented showing wavelength vs. electromagnetic type.

• Solar Radiation • Intro concepts

  • Solar radiation is the primary energy source for weather systems.
  • As solar radiation enters Earth’s atmosphere, it can be reflected, scattered, or absorbed.

• Absorption, Reflection, Scattering (Albedo concepts)

  • A diagram summarizes how incoming solar radiation is partitioned among various processes.
  • Absorbed by air molecules and dust: around 14 ext{%}
  • Direct radiation to surfaces: a portion reaches the surface directly
  • Clouds influence reflection/scattering; dust can scatter or absorb
  • Diffuse radiation accounts for scattered light that reaches surfaces from multiple directions
  • Approximate overall albedo (reflected or scattered) is about 30 ext{%}.

• Albedo (Reflectance) concepts

  • Albedo = % of sunlight reflected off a surface
  • Surface albedo values:
  • City: 10 ext{-}15 ext{%}
  • Grass: 15 ext{-}25 ext{%}
  • Bare sand: 30 ext{-}60 ext{%}
  • Oceans: 5 ext{%}
  • Clouds: 50 ext{-}55 ext{%}
  • Forest: 5 ext{%}
  • Snow: 80 ext{-}90 ext{%}

• Reflectance (in percent) of various surfaces in the spectral range of solar reflection

  • Surface types and ranges:
  • Wet soil: 10 ext{-}30 ext{%}
  • Dry sand: 35 ext{-}45 ext{%}
  • Dry soil: 25 ext{-}45 ext{%}
  • Grass: 15 ext{-}25 ext{%}
  • Forest: 10 ext{-}20 ext{%}
  • Snow (Clean, Dry): 75 ext{-}95 ext{%}
  • Snow (Wet, Dirty): 25 ext{-}75 ext{%}
  • Water surface (Sun angle > 25°): range around 25 ext{-}70 ext{%}

• Solar Radiation: absorbed vs reflected/scattered

  • About 30 ext{%} of incoming solar radiation is reflected or scattered (albedo) on a global average.
  • Solar energy absorption:
  • About 50 ext{%} is absorbed by the Earth's surface.
  • About 15 ext{%} is absorbed by the atmosphere.
  • The remainder accounts for reflected energy or other fates of solar radiation.

• Terrestrial Radiation

  • After solar radiation is absorbed by Earth's surface, Earth radiates energy back to space as heat.
  • Terrestrial radiation and greenhouse gases (e.g., water vapor, carbon dioxide) are responsible for maintaining temperatures on Earth.

• Shortwave (insolation) vs. Longwave radiation

  • Shortwave radiation refers to solar radiation reaching Earth.
  • Longwave radiation refers to thermal radiation emitted by Earth (terrestrial radiation).
  • Clouds can reflect or scatter shortwave radiation; atmospheric processes emit longwave radiation.
  • The atmospheric system includes cloud reflection, scattering, and surface/atmosphere emissions.

• Factors affecting actual air temperature

  • Actual air temperature varies due to:
  • Latitude
  • Time of year
  • Time of day
  • Cloud cover
  • Slope aspect
  • Proximity to water
  • Altitude
  • Surface cover

• Earth-Sun Relations (latitude and time of year)

  • Our solar system is heliocentric (sun-centered).
  • Earth’s diameter ≈ 7{,}900 ext{ miles} vs Sun’s diameter ≈ 864{,}000 ext{ miles}.
  • Earth is not a perfect sphere.
  • Four main principles: Revolution, Rotation, Plane of the Ecliptic, Tilt of the Earth.

• Revolution

  • The Earth revolves around the Sun in an elliptical orbit: 365.25 ext{ days} (often written as 365 ¼ days).
  • Aphelion (farthest from the Sun): on or about July 4th at 94.5 imes 10^{6} ext{ miles}.
  • Perihelion (closest to the Sun): on or about January 3rd at 91.5 imes 10^{6} ext{ miles}.
  • Earth’s revolution does NOT by itself cause the seasons; Earth receives ~7% more solar radiation in January than in some other months.

• Rotation

  • Earth rotates on its axis once every 24 ext{ hours}.
  • This rotation creates day and night.
  • At any moment, half of the Earth is in darkness and half is in light.
  • The boundary of light is the circle of illumination.

• Plane of the Ecliptic

  • The plane in which Earth revolves around the Sun is called the plane of the ecliptic.
  • It is defined by the Sun-Earth orbital geometry.

• Tilt of the Earth

  • The Earth maintains a tilt of about 23.5^ ext{o} relative to the plane of the ecliptic.

• Seasons

  • Seasons are primarily controlled by the Earth's tilt, though the four principles influence them.
  • Equinox: when the Sun strikes the Equator directly; all latitudes have roughly 12 ext{ hours} of light and darkness.
  • Solstice: when the Sun is at its maximum axial tilt relative to the Equator (±23.5°).
  • Northern Hemisphere specifics:
    • Summer Solstice: Sun strikes the Tropic of Cancer (23.5^ ext{o} ext{N}) on about June 21st or 22nd; the North Pole experiences 24 hours of daylight; the Equator ~12 hours; the Antarctic Circle ~0 hours.
    • Winter Solstice: Sun strikes the Tropic of Capricorn (23.5^ ext{o} ext{S}) on about December 21st or 22nd; the Arctic Circle experiences 0 hours of daylight; the Equator ~12 hours; the Antarctic Circle ~24 hours.

• The Seasons on Earth (summary graphic)

  • Autumnal Equinox: first day of Autumn in the Northern Hemisphere.
  • Vernal (Spring) Equinox: first day of Spring in the Northern Hemisphere.
  • Summer Solstice: first day of Summer in the Northern Hemisphere.
  • Winter Solstice: first day of Winter in the Northern Hemisphere.
  • The illustrative diagram shows the angular tilt of the axis (~23.5°) and the seasonal positions.

• Example context

  • El Segundo, CA – January 1992 (following eruption of Mt. Pinatubo in June 1991) [note: volcanic eruption context linked to climate effects mentioned in the material].

• Quick reference to key numbers

  • Earth diameter: 7{,}900 ext{ miles}
  • Sun diameter: 864{,}000 ext{ miles} (approx. 8.64 imes 10^{5} ext{ miles})
  • Earth–Sun distance variations:
  • Aphelion: 94.5 imes 10^{6} ext{ miles} (around July 4)
  • Perihelion: 91.5 imes 10^{6} ext{ miles} (around January 3)
  • Tilt: 23.5^ ext{o}
  • Orbit period: 365.25 ext{ days}
  • Seasons are a function of tilt plus orbital geometry, with solstices and equinoxes marking key transitions.

• Connections to foundational principles and real-world relevance

  • Understanding energy types and heat transfer underpins meteorology and climate science.
  • Solar radiation and albedo influence surface temperatures, climate zones, and weather patterns.
  • The Earth’s rotation and tilt drive diurnal cycles and seasonal changes, affecting daylight hours and insolation distribution.
  • Greenhouse gases and terrestrial radiation explain why Earth remains warm enough to sustain life (greenhouse effect).
  • Volcanic eruptions (e.g., Mt. Pinatubo) can inject aerosols into the atmosphere, reflecting sunlight and temporarily cooling global temperatures, illustrating the sensitivity of climate to atmospheric composition.

• Summary takeaways

  • Weather and climate are governed by energy transfer processes (conduction, convection, radiation).
  • The Sun is the ultimate energy source; its energy interacts with the atmosphere, surface, and clouds via reflection, absorption, and scattering.
  • Surface properties (albedo) strongly influence the amount of solar energy absorbed vs reflected, thereby impacting local and regional temperatures.
  • The Earth–Sun geometry (revolution, rotation, plane of the ecliptic, tilt) shapes seasonal patterns and day-length variations across latitudes.

• Notable equations / LaTeX references

  • Orbital period representation: T = 365.25 ext{ days}
  • Distances during aphelion/perihelion: d{ ext{ap}} = 94.5 imes 10^{6} ext{ miles}, \ d{ ext{pe}} = 91.5 imes 10^{6} ext{ miles}
  • Tilt angle: heta = 23.5^ ext{o}
  • Surface albedo values are given as percentages (e.g., ext{Albedo}
    ightarrow 0.30 ext{ (30%)} for a typical surface).