Weather, Climate and Atmosphere

• The text introduces the topic of weather, climate, and the atmosphere
• It is lecture one, focusing on understanding the fundamentals
• The lecture is created by Mohammed M. Shahata in the Physics Department, Faculty of Science, Minia University
• The second semester of the academic year 2025

Overview of the Atmosphere

• Meteorology is the study of atmospheric phenomena, with a focus on weather and atmospheric conditions, and weather forecasting
• The atmosphere is composed of:
• 78% Nitrogen (N2)
• 21% Oxygen (O2)
• Trace gases Ar, CO2, H2O which are small amounts but vital to climate and life.

Importance of the Atmosphere

• Protection: Shields the Earth from harmful ultraviolet radiation from the sun
• Climate Regulation: Maintains Earth's temperature within a range that supports life
• Support of Life: Enables the water cycle and provides essential gases for life forms

Vertical Structure of the Atmosphere

• Troposphere: Where weather occurs; temperature decreases with altitude
• Stratosphere: Contains the ozone layer; temperature increases with altitude
• Mesosphere: Temperature decreases with altitude; meteors burn up
• Thermosphere: Temperature increases with altitude; location of the ionosphere
• Exosphere: The outermost layer where the atmosphere fades into space

The Ionosphere

• Location and Definition: Part of Earth's upper atmosphere, starting about 60 km above the surface and extending into the thermosphere
• Not a distinct layer but a region that overlaps with the mesosphere and thermosphere
• Characteristics: Contains a high concentration of ions and free electrons, formed by solar radiation and cosmic rays ionizing atoms and molecules
• Functions and Importance: Plays a crucial role in the electricity of the atmosphere and forms the inner edge of the magnetosphere.
• Critical for long-distance radio communications as it reflects radio waves back to Earth

Atmospheric Pressure and Density

• Atmospheric Pressure Defined: The weight of the air above us pressing down on Earth's surface
• Relationship to Atmospheric Density: Pressure and density are higher at lower altitudes due to Earth's gravity
• Pressure Changes: Decreases with altitude due to lower air density

Atmospheric Layers

• Layers of the atmosphere based on temperature, composition, and electrical properties

Carbon Dioxide and Greenhouse Gases

• Role of CO2: Absorbs and emits infrared radiation, heating the Earth
• Greenhouse Effect: Essential for maintaining the Earth's energy balance
• Historical Increase in CO2: Significant rise observed since 1958, contributing to global warming
• Unit of Measurement: CO2 concentration in the atmosphere
• Typically measured in parts per million (ppm)
• Denotes the number of CO2 molecules per million molecules of air

Carbon Cycle

• Carbon travels between the atmosphere, marine and terrestrial environments
• It can be removed from the atmosphere by means of chemical weathering and photosynthesis
• Release of carbon into the atmosphere is caused by means of volcanic activity, repiration, dissolution and fuel combustion

Weather vs. Climate

• Weather Defined: Short-term conditions of the atmosphere (minutes to weeks), including daily changes in temperature, humidity, precipitation, clouds, visibility, and wind
• Climate Defined: Average weather conditions for a specific location over a long period, typically 30 years or more
• Temporal Scale: Weather is short-term, climate is long-term
• Variability: Weather changes rapidly and can vary greatly in short periods; climate is relatively stable
• Measurement: Weather is what you get; climate is what you expect

Major Atmospheric Components

• Major atmospheric components of planets and the sun are listed in the table