Atmospheric Layers

Layers of the Atmosphere

• The atmosphere is divided into four layers based on temperature structure: Thermosphere, Mesosphere, Stratosphere, and Troposphere.
• The height of each layer is defined as:
  • Thermosphere: 84.9 km ≤ H
  • Mesosphere: 47 km ≤ H ≤ 84.9 km
  • Stratosphere: 11 km ≤ H ≤ 47 km
  • Troposphere: 0 km ≤ H ≤ 11 km
• Almost all clouds and weather occur in the Troposphere.

Boundaries of the Layers

• The top limits of the bottom three layers are named:
  • Mesopause: H = 84.9 km
  • Stratopause: H = 47 km
  • Tropopause: H = 11 km
• The Tropopause height varies with latitude:
  • Lower (around 8 km) near the Earth's poles
  • Higher (around 18 km) near the equator
  • Average height in mid-latitudes: around 11 km, with seasonal variations (lower in winter, higher in summer)

Temperature Maxima

• Three relative maxima of temperature occur in the atmosphere due to absorption of solar radiation:
  • Ultraviolet light absorption by ozone near the Stratopause
  • Visible light absorption at the ground
  • Absorption of most other radiation in the Thermosphere

Atmospheric Boundary Layer (ABL)

• The bottom 0.3 to 3 km of the Troposphere is called the Atmospheric Boundary Layer (ABL)
• The ABL is often turbulent and varies in thickness in space and time
• It is affected by the Earth's surface, which:
  • Slows the wind due to surface drag
  • Warms the air during daytime and cools it at night
  • Changes in moisture and pollutant concentration
• Most of human life is spent in the ABL

Time Zones

• Each town had its own local time before the 1800s, with noon being when the sun was highest in the sky.
• Railroad companies created standard time zones in the 1800s to enable precise schedules, and it was eventually adopted worldwide.

Calculating Time Zones

• The Earth makes one complete revolution in one day, covering 360° of longitude.
• Each hour of elapsed time spans 15° of longitude, resulting in each time zone spanning approximately 15° of longitude.
• This means neighboring time zones are usually 1 hour different from each other.

Time Zone Characteristics

• All clocks within a time zone are set to the same time.
• Time-zone boundaries are sometimes modified to follow political or geographic boundaries for commercial purposes.

Coordinated Universal Time (UTC)

• UTC is the time zone at the prime meridian, also known as Greenwich Mean Time (GMT) and Zulu time (Z).
• The prime meridian is in the middle of the UTC time zone, spreading 7.5° on each side.
• UTC is the official time used in meteorology for coordinating simultaneous weather observations worldwide.

International Time Zones

• Time zones are designated by letters A-Z, with Z being at Greenwich.
• East of the UTC zone, local time zones (A, B, C, ...) are ahead of Greenwich time, while west of the UTC zone, local time zones (N, O, P, ...) are behind.
• Each zone can have multiple local names, depending on the countries it spans.

Examples of Time Zones

• Most of western Europe is in the Alpha (A) zone, also known as Central Europe Time (CET) or Middle European Time (MET).
• North America has 8 time zones, designated by letters P to W.

International Date Line

• The international date line is near 180° longitude in the middle of the Pacific Ocean.
• When traveling east to west across the date line, you lose a day, while traveling west to east, you gain a day.