In-depth Weather Notes

Understanding Weather

• Weather is defined as the state of the atmosphere at a specific point in time.
• Parameters to describe weather include:
  • Temperature
  • Precipitation
  • Humidity
  • Wind speed
  • Cloudiness
  • Sunlight intensity

Convection

• Convection: Heat transfer due to bulk movement of molecules within fluids (gases, liquids).
  • Emerges from fluids warmed from below.
  • Rising parcels of fluid cool at higher elevations.
  • An efficient way to transfer heat.
  • Essential for storm formation, ocean circulation, and plate tectonics.

Thunderstorms

• Thunderstorms develop from atmospheric convection:
  • Warm, moist air rises, cools, and condenses releasing heat.
  • Further cooling can lead to freezing, releasing additional heat.
  • Storms organize into intense circulation; precipitation occurs as condensed water rains out.
  • Can persist as long as warm, moist air is available.

Tropical Weather

• Characterized by two main seasons:
  • Wet Season: Dominated by convection and thunderstorms.
  • Dry Season
• Key weather systems include:
  • Inter-Tropical Convergence Zone (ITCZ)
  • Monsoons
  • Tropical Cyclones

Inter-Tropical Convergence Zone (ITCZ)

• A band of thunderstorms encircling the Earth, forming where the sun is overhead.
• Position influences local rainfall patterns:
  • Shifts north and south with seasons (farthest north during Northern Hemisphere summer, and vice versa).
  • Affects mid-tropics with two rainy seasons; surrounding regions receive one.

Monsoons

• Caused by land-sea temperature differences:
  • Heating of land creates a low-pressure zone, drawing in moist ocean air.
  • Enhanced by geographical features (e.g., mountain ranges).
  • Cycle reverses in winter, leading to dry conditions.

Tropical Cyclones

• Form from clusters of thunderstorms in warm sea conditions (>$26°C$).
• Requires:
  • Warm ocean water
  • Low shear winds
  • Ability to organize into a low-pressure system.
• Naming conventions vary by region:
  • Hurricanes: Atlantic, Eastern Pacific
  • Typhoons: Western Pacific
  • Cyclones: Indian Ocean

Extra-Tropical Weather

• Dominated by high and low-pressure systems:
  • High pressure from descending winds; low pressure from rising air.
  • Air movement creates pressure gradients influencing weather patterns.
• High pressure typically leads to clear, sunny weather; low pressure results in cloudiness and storms.

Front Formation

• Fronts are boundaries between air masses:
  • Warm Fronts: Warm air rises over cooler air, leading to gradual temperature increases and light rain.
  • Cold Fronts: Cold air forces warm air upwards, resulting in heavy precipitation and strong winds.
  • Occluded Fronts: Form when a cold front overtakes a warm front, lifting warm air to create intense precipitation.

Extreme Weather

• Defined as unexpected, unpredictable, severe, or unseasonal weather.
  • Includes storms (tropical cyclones, tornadoes) and extreme temperature events (heat waves, cold waves).

Tornado Formation

• Developed through:
  1. Shear winds creating horizontally rotating air.
  2. Updrafts catching spinning air and bending it vertical.
  3. Formation of a super-cell thunderstorm capable of producing tornadoes.
• Tornadoes are short-lived yet can be extremely intense; capable of causing localized severe damage.

Local Weather Effects

• Local geographical features also influence weather:
  • Orographic Precipitation: Moist air rises over mountains, cools, and precipitates, leaving a dry rain shadow on the leeward side.
  • Sea Breezes: Generated by temperature contrasts between land and ocean, moving air from ocean to land.
  • Katabatic Winds: Cold, dense air flowing downhill from high elevations; strongest in valleys and over glaciers. These winds can reach over $300 ext{ km/h}$.