Comprehensive Notes on Atmospheric Phenomenon: Winds and Global Circulation

Winds: Movement of air relative to the Earth's surface, influenced by various forces.
Air in Motion: Primarily horizontal movement (advection) is considered.
Uneven Heating: Leads to pressure differences, driving wind (differential heating).
Wind Representation:
- $u$ : West-East direction (x-axis)
- $v$ : North-South direction (y-axis)
- $w$ : Upward-Downward direction (vertical component)
Directional Wind: Air moves from high to low pressure areas.
Major Forces Affecting Wind: Pressure gradient force, centrifugal force, Coriolis force, and turbulent drag.
Advection: Horizontal movement of air from warmer to colder areas.

Definition: Change in pressure over a given distance.
Denotation: $pg = \frac{\Delta p}{\Delta x}$
Mechanism: Air moves from high to low pressure, creating a force.
Meteorological Practice: Focus is on the pressure gradient rather than computing the force directly.
Distance Relationship: Closer distance between pressure differences results in a higher force.

Apparent Force: Arises from the inertia of winds moving on a curve.
Direction: Outward from the center of the curve, opposite to the centripetal force.
Curved Path: Created by an imbalance between inward and outward forces.

Definition: Force due to the Earth's rotation.
Effect: Deflects wind direction.
Action: Perpendicular to the direction of motion.
Hemispheric Differences:
- Northern Hemisphere: Deflection to the right.
- Southern Hemisphere: Deflection to the left.
Equation: $m \cdot 2 \cdot u \cdot \Omega \cdot sin(\phi)$
Latitude Dependence: Zero at the equator, maximum at polar regions.
Cyclone Movement: Explains why cyclones generally move towards polar regions and do not cross the equator.

Definition: Force that slows down winds due to resistance from the Earth's surface or objects.
Mechanism: Objects like grass, trees, and buildings block and decelerate winds.
Atmospheric Boundary Layer (ABL): Lower part of the troposphere (approximately 0.3 meters to 3 kilometers) where turbulent movement occurs.
ABL Effect: Slower air movement near the surface, faster movement higher in the ABL, leading to mixing and heat exchange, affecting air temperature.

Geostrophic Balance: Balance between the pressure gradient force and the Coriolis force.
Geostrophic Wind: Wind resulting from geostrophic balance, usually parallel to isobars (lines of constant pressure).
Isobars: Lines of constant pressure.
Inference: Wind direction and intensity can be inferred from pressure lines (isobars).
Northern Hemisphere: Low pressure area to the left, high pressure area to the right.

Definition: Wind flowing along curved isobars or curved pressure lines.
Forces Involved: Pressure gradient force, Coriolis force, and centrifugal force.
Centrifugal Force Role: Arises because air is flowing on a curved path, acting in the same direction as the Coriolis force and opposite to the pressure gradient force.

Forces Involved: Pressure gradient force, Coriolis force, and frictional drag force (turbulent drag).
Effect: Wind shear, turbulence, and convective turbulence cause drag, resulting in slower wind speeds in the ABL compared to geostrophic winds.
Cross-Isobar Flow: Causes air to cross isobars towards low-pressure areas.

Definition: Average global winds, representing the average wind speed and direction over a long period.
Purpose of Averaging: To remove short-term fluctuations.
Driving Force: Uneven heating (differential heating) of the Earth's surface by the sun.
Solar Radiation: Maximum at the equator, minimum at the poles due to the Earth's curvature.

Assumptions: Earth is entirely covered with water, no seasons, sun always directly over the equator, no Coriolis force.
Dominant Force: Pressure gradient force.
Heat Distribution: Heat moves from hot (equator) to cold (poles).
Reflection vs. Absorption: Areas with snow reflect radiation, while areas without snow absorb it, distributing heat.
Hadley Cell: Circulation from hot to cold, representing a single-cell model.

Explanation: Allows for the effects of excitation and breaks the large Hadley cell into multiple cells.
Cells Present:
- Hadley Cell: Extends from the equator to 30 degrees North.
- Ferrel Cell: Extends from 30 degrees North to 60 degrees North.
- Polar Cell: Circulates cold air near the poles.
Pressure Belts: Low-pressure belt along the equator, high-pressure system at 30 degrees North, low-pressure system between 30 to 60 degrees, and high-pressure system at the top.
Wind Patterns: Subtropical highs bring easterly winds to tropical areas; westerly winds from 30 to 60 degrees North; trade winds from 0 to 30 degrees.
Doldrums/Intertropical Convergence Zone (ITCZ): Belt of low-pressure system along the Equator.