Weather and Climate Study Notes

Weather and Climate

Key Concepts and Definitions

  • Weather

    • Definition: The state of the atmosphere at a specific place and time.

    • Characteristics: Air temperature, humidity, wind speed, cloud types, precipitation.

    • Variability: Weather can change rapidly and is dependent on several atmospheric factors.

  • Climate

    • Definition: The average of a region’s weather over a prolonged period, typically 30 years.

    • Characteristics: Changes slowly, determined by factors like the Sun's angle, cloud cover, and air pressure.

Atmospheric Moisture

  • Humidity

    • Definition: The amount of water vapor in the air.

    • Relative Humidity: The percentage of water vapor relative to the maximum capacity of air at a certain temperature.

    • Example: 80% humidity means air holds 80% of the total water it can at that temperature.

    • Dew Point: The temperature at which water vapor in the air begins to condense.

    • Example: When air cools to its dew point, water droplets form, visible as dew.

Cloud Formation

  • Clouds influence weather by insulation and precipitation.

Conditions for Cloud Formation

  1. Air reaches the dew point, which can happen in two ways:

    • Humidity increases while temperature remains constant (common in warm, humid areas).

    • Temperature decreases while humidity remains constant.

  2. Clouds form when water vapor condensates around nuclei (e.g., dust).

Types of Clouds

  • Classified based on altitude and precipitation characteristics:

    • High-Level Clouds (e.g., Cirrus, Cirrostratus, Cirrocumulus): Mainly ice crystals, indicate weather changes.

    • Middle-Level Clouds (e.g., Altocumulus, Altostratus): Can be made of both water droplets and ice.

    • Low-Level Clouds (e.g., Stratus, Stratocumulus, Nimbostratus): Predominantly water droplets, where Nimbostratus produces precipitation.

    • Cumulonimbus: Vertically developed clouds associated with thunderstorms.

Fog Types

  • Fog: A cloud at ground level, forms when humid air cools to its dew point.

    • Different Types of Fog:

    • Radiation Fog: Forms at night, skies clear, humidity high.

    • Advection Fog: Occurs with warm air moving over cool surfaces.

    • Steam Fog: Warm air over cooler water, creating vapor-like steam.

    • Upslope Fog: Humid air rises over a slope, cools, and condenses.

    • Valley Fog: Forms in valleys where cool air settles.

Precipitation

  • Definition: Important aspect of weather, falling liquid or solid water droplets from the clouds.

    • Types of Precipitation include: Rain, snow, drizzle, freezing rain, hail, and ice pellets.

    • Types of Precipitation Formation:

    1. Convective: Short-duration, intense.

    2. Stratiform: Extended duration, layered structure.

    3. Orographic: Moist air pushed over terrain causes cooling and precipitation.

Air Masses

  • Definition: Large bodies of air with uniform characteristics of temperature and humidity.

    • Source Region: Area where air mass acquires its properties.

    • Types of Air Masses in North America:

    • Maritime Tropical (mT): Moist, warm.

    • Continental Tropical (cT): Dry, warm.

    • Maritime Polar (mP): Moist, cold.

    • Continental Polar (cP): Dry, cold.

Weather Fronts

  • Definition: A boundary between two differing air masses.

    • Types of Fronts:

    • Cold Front: A cold front occurs when a mass of cold air advances towards a region occupied by warmer air. As the cold air pushes into the warmer air mass, it forces the warm air to rise rapidly, which can lead to the development of thunderstorms. Characterized by steep gradients, cold fronts are known for their quick and dramatic weather changes, often resulting in heavy precipitation, gusty winds, and even hail. The temperature drop can be significant behind the front as cooler air replaces the warmer air mass.

    • Warm Front: A warm front is formed when a mass of warm air moves into an area dominated by cooler air. The warm air gradually rises over the cooler air mass, leading to longer and more gradual weather transitions. This type of front typically brings steady rain or drizzle for extended periods, often accompanied by an increase in temperatures following the front’s passage. The cloud formations associated with warm fronts may include stratiform clouds and can result in widespread precipitation.

    • Occluded Front: An occluded front occurs when a cold front catches up to a warm front. This phenomenon typically leads to severe weather conditions as the warm air mass is lifted off the ground, resulting in intense storms. The mixing of cold and warm air can lead to the formation of complex storm systems, producing heavy rain and potentially severe thunderstorms as well as abrupt temperature changes. Occluded fronts are often associated with mid-latitude cyclones, which can bring a variety of weather patterns depending on the time of year.

    • Stationary Front: A stationary front forms when two air masses meet but neither advances. This lack of movement can result in prolonged weather conditions. Often associated with persistent clouds and rain, stationary fronts can linger for days, particularly in certain geographic areas. When a stationary front is present, the weather may consist of light to moderate rain or drizzle, along with cloudy skies, as the air masses combat for dominance without significant displacement.

    • Warm Front: Warm air slides over cold air, leading to longer transitions with gradual weather changes.

    • Occluded Front: When a cold front catches up to warm front, weather is severe.

    • Stationary Front: Little movement results in persistent weather conditions, often rain or drizzle.

Types of Extreme Weather

  • Thunderstorms: Worldwide, 14 million occur yearly. Categorized in stages:

    1. Cumulus Stage: Rising air forms cumulus clouds, accumulation of latent heat leads to instability.

    2. Mature Stage: Updrafts and downdrafts coexist; the storm is most intense.

    3. Dissipating Stage: Cloud weakens, stable downdrafts dominate.

  • Tornadoes: Average 770 annually in the US; characteristics include high wind speeds (average 177 kph).

  • Cyclones: Two main types: mid-latitude and tropical. Mid-latitude cyclones cause winter storms, while tropical cyclones are hurricanes originating in warm waters.

Climate vs. Weather

  • Meteorology: Study of atmospheric conditions and weather forecasting.

  • Climatology: Study of long-term atmospheric trends based on averages and patterns over decades to millennia.

Climate Change

  • Definition: A sustained change in climatic conditions over decades.

  • Global Warming: Specific increase in Earth’s average temperature.

  • Abrupt Climate Change: Rapid shifts over decades; under research.

Implications of Extreme Weather Events

  • Growing evidence suggests an increase in extreme weather events linked to climate change.

  • Human activity and population growth influence weather impact.

  • Meteorological tools: Weather balloons, satellites, and radar, etc., are essential for monitoring climate data.

Conclusion

  • Weather reflects short-term atmospheric conditions, while climate indicates long-term trends.

  • Extreme weather events, although rare, are affected by climatic changes and human influences.