The Heat Budget Of The Earth
The balance of incoming heat absorbed by the Earth and outgoing heat escaping the Earth in the form of radiation is perfect. If they were not balanced, Earth would become either warmer or cooler with each passing year. The Earth's heat budget is the balance between incoming and outgoing heat.
• 35 percent of the total incoming solar radiation entering the earth's atmosphere is scattered by dust particles (6 percent), reflected by clouds (27 percent), and reflected by the ground surface (2 percent), 51 percent is received by the earth's surface (received as direct radiation), and 14 percent is absorbed by atmospheric gases (ozone, oxygen, etc.) and waded back into space.
• Direct solar radiation accounts for 34% of the solar energy received by the earth, while diffuse day light accounts for 17%. The heat budget of the atmosphere is made up of 48% solar radiation, with 14% coming from shortwave incoming solar radiation and 34% coming from outgoing long-wave terrestrial radiation.
• After receiving energy from the sun, the earth radiates energy through long-waves from its surface into the atmosphere. Because it aids in the heating of the lower atmosphere, terrestrial radiation is also known as "effective radiation."
• Twenty-three percent of the energy gained by the earth from the sun is lost as direct long-wave outgoing terrestrial radiation, of which six percent is absorbed by the atmosphere and seventeen percent goes directly to space.
• Convection and turbulence consume about 9% of terrestrial energy, while evaporation consumes 19%, which is added to the atmosphere as latent heat of condensation. As a result, the total energy received by the atmosphere from the sun (14% ) and the earth (34% ) is reduced to 48%, which is reradiated to space in some way.
Latitudinal Heat Balance
• The tropics are much warmer than the poles, which is the most basic observed global characteristic of the atmosphere. This is a straightforward result of the earth's geometry. At the equator, annual averaged solar radiation per unit area of the earth's surface is much higher than at the poles.
• Because the Polar Regions are covered in ice and snow, much of the incoming radiation is reflected back to space, the difference arises. Another fact is that tropical regions receive more energy from the sun than they emit back to space, whereas high latitudes receive more energy from the sun than they emit back to space.
Temperature Inversion
• A temperature inversion occurs when a layer of cool air at the surface is overlain by a layer of warmer air, reversing the normal behavior of temperature in the troposphere (the region of the atmosphere closest to the Earth's surface). (Under normal circumstances, air temperature drops as one rises.)
• Cloud formation, precipitation, and visibility are all influenced by inversions. The upward movement of air from the layers below is slowed by an inversion. As a result, convection caused by below-inversion heating is limited to levels below the inversion. Dust, smoke, and other air pollutants are also limited in their spread. Convective clouds cannot grow high enough to produce showers in areas where there is a significant low-level inversion.
There Are Four Kinds Of Inversions: Ground, Turbulence, Subsidence, And Frontal.
• When air is cooled by contact with a colder surface until it becomes cooler than the overlying atmosphere, a ground inversion develops; this happens most often on clear nights, when the ground cools rapidly due to radiation. Fog can form when the temperature of the surface air falls below the dew point.
• The magnitude of ground inversions is greatly influenced by topography. If the terrain is hilly or rolling, the cold air formed on the higher land surfaces drains into the hollows, resulting in a larger and thicker inversion above low ground and little or no inversion above higher elevations.
• When quiescent air overlies turbulent air, a turbulence inversion occurs. Vertical mixing within the turbulent layer transports heat downward and cools the upper layer. The unmixed air above does not cool, and it eventually becomes warmer than the air below, resulting in an inversion.
• When a large layer of air descends, it creates a subsidence inversion. As a result of the increased atmospheric pressure, the layer is compressed and heated, and the temperature lapse rate is reduced. When an air mass sinks low enough, the air at higher elevations becomes warmer than the air at lower elevations, resulting in a temperature inversion.
• In the winter, subsidence inversions are common over the northern continents and the subtropical oceans; these regions have subsiding air due to their proximity to large high-pressure centers.
• When a cold air mass undercuts a warm air mass and lifts it aloft, a frontal inversion occurs; the front between the two air masses then has warm air above and cold air below.
• Other inversions have a nearly horizontal slope, whereas this one has a noticeable slope. Furthermore, humidity levels may be high, and clouds may be present just above it.
Atmospheric Pressure And Circulation
• The force per unit area exerted against a surface by the weight of the air above that surface is known as atmospheric pressure. The pressure at point "X" in the diagram below rises as the weight of the air above it rises. The same is true for decreasing pressure, where the pressure at point "X" falls as the weight of the air above it falls.
• In terms of air molecules, as the number of molecules above a surface rises, there are more molecules to exert a force on that surface, and the pressure rises as a result. The opposite is also true: a decrease in the number of air molecules above a surface results in a reduction in pressure. Because atmospheric pressure is measured with a device known as a "barometer," atmospheric pressure is also known as barometric pressure.
• Pressure is measured in inches of mercury (“Hg”) in aviation and television weather reports, but meteorologists use millibars (mb), the unit of pressure used on weather maps.
Pressure Gradient Force
• Air flow is from higher density regions to lower density regions, or from high to low pressure or down the barometric slope, which can be represented by a line drawn at right angles to the isobars.
• The steepness of the pressure gradient or rate of pressure change indicates the rate of air flow, or wind velocity. When the gradient is steep, the air flow is quick, and when it isn't, the wind is also quick.
• Gradients and winds are weak when isobars are far apart. A "pressure gradient" is the difference in pressure measured over a given distance. The “pressure gradient force” is the result of the pressure gradient, which is a net force that is directed from high to low pressure.
Coriolis Force
• When air is set in motion by the pressure gradient force, it deviates from its intended path, as seen by an observer on the ground. The apparent deflection is caused by the earth's rotation and is known as the "Coriolis force."
• The Coriolis force deflects air to the right as it moves from high to low pressure in the northern hemisphere. The Coriolis force deflects air moving from high to low pressure to the left in the southern hemisphere. The amount of deflection produced by air is proportional to both its speed and its latitude.
• As a result, slow-moving winds will be deflected only slightly, while stronger winds will be deflected significantly. Winds blowing closer to the poles will also be deflected more than winds blowing closer to the equator at the same speed. At the equator, the Coriolis force is zero.
Geostrophic Wind
• Geostrophic winds are those that are balanced by the Coriolis and Pressure Gradient forces. Because of the pressure gradient force, an air parcel that is initially at rest will move from high pressure to low pressure (PGF).
• In the northern hemisphere, however, the Coriolis force deflects that air parcel to the right as it begins to move (to the left on the southern hemisphere). The deflection increases as the wind speed rises until the Coriolis force equals the pressure gradient force. The wind will be blowing parallel to the isobars at this point. The wind is referred to as geostrophic when this happens.
• Winds in nature are rarely perfectly geostrophic, but the winds in the upper troposphere can be fairly close. This is because winds are only truly geostrophic when the isobars are straight and no other forces are acting on them — and these conditions don't occur very often in nature.
Frictional Force
• Because the Coriolis force and the pressure gradient force are equal, geostrophic wind blows parallel to the isobars. However, it's important to remember that wind isn't always geostrophic, especially near the surface. The air blowing just above the Earth's surface is subjected to frictional drag. This friction can change the direction of the wind and cause it to slow down, preventing it from blowing as fast as the wind above.
• In fact, the amount of friction applied is directly proportional to the terrain conditions. A calm ocean surface, for example, is relatively smooth, so the wind blowing over it does not move any features up, down, or around. Hills and forests, on the other hand, cause the wind to slow down and/or change direction much more.
• Surface features have less impact on the wind as we climb higher, until the wind is truly geostrophic. The top of the boundary (or friction) layer is considered this level. The height of the boundary layer varies depending on the terrain, wind, and temperature profile vertically.
• The height of the boundary layer is also affected by the time of day and the season of the year. The boundary layer, on the other hand, usually exists from the surface to about 1-2 km above it. The wind's direction and velocity are both affected by the frictional force.
Tri-Cellular Meridional Model
• This model proposes a three-cell model of meridional atmospheric circulation, also known as tri-cellular meridional atmospheric circulation, in which cellular air circulation is believed to exist at each meridian (longitude).
• Surface winds blow from high pressure areas to low pressure areas, but air circulation in the upper atmosphere is generally in the opposite direction of surface winds. In the northern hemisphere, each meridian has three air circulation cells:
1. Hadley cell
2. Ferrel cell
3. Polar cell
1. Hadley Cell
• Tropical cell is also known as Hadley cell, after G. Hadley, who discovered this thermally induced cell in both hemispheres in 1735. The winds ascend upward after being heated by the extreme heat at the equator. After condensation, these ascending warm and moist winds release latent heat, causing the winds to rise even higher, reaching a height of 8 to 12 kilometers in the troposphere over the equator, where they diverge northward and southward, or poleward.
• Trade winds are surface winds that blow from subtropical high pressure belts to equatorial low pressure belts to replace ascending air at the equator. Antitrade refers to upper air that moves in the opposite direction of surface winds (trade winds). The subtropical high pressure belt is caused by upper air antitrades that descend near 30°-35° latitudes.
• After descending near 30°-35° latitudes, these antitrades blow back towards the equator, where they are heated and ascend once more. As a result, a complete meridional air circulation cell is formed. Between the equator and 30° latitudes, this is known as the tropical meridional cell.
2. Ferrel Cell
• circulation of air Surface winds, known as westerlies, blow from the subtropical high pressure belt to the subpolar low pressure belt (60°-65°) between 30° and 60° latitudes. Winds ascend near 60°-65° latitudes and then diverge in opposite directions once they reach the upper troposphere (poleward and equator-ward).
• To reinforce the subtropical high pressure belt, these winds (which diverge equatorward) descend near horse latitudes (30°-35° latitudes). These winds then blow poleward as surface westerlies after descending, forming a complete cell. Temperate cyclones, migratory extra-tropical cyclones, and anticyclones are all known to disrupt the regularity and continuity of the westerlies.
3. POLAR Cell
• The atmospheric circulation between 60° and the poles is referred to as the polar cell. Polar easterlies blow cold winds from polar high pressure areas to the sub-polar or mid-latitude low pressure belt. Due to Coriolis force, the general direction of surface polar winds becomes easterly (east to west).
• Near 60°-65° latitudes, these polar cold winds converge with warm westerlies to form the polar front or mid-latitude front, which serves as the origin point for temperate cyclones. At the subpolar low pressure belt, the winds ascend due to the earth's rotation, and after reaching the middle troposphere, they turn poleward and equatorward. At the poles, the poleward upper air descends, reinforcing the polar high pressure. As a result, a complete polar cell is created.
Doldrums
• The "doldrums" is a nautical term for the belt around the Earth near the equator where sailing ships can become stuck in windless waters. The intertropical convergence zone (ITCZ), a belt of converging winds and rising air encircling Earth near the Equator, contains the doldrums, also known as equatorial calms, which are equatorial regions of light ocean currents and winds.
Horse Latitudes
• About 30 degrees north and south of the equator are the horse latitudes. Winds diverge in this part of the subtropics, flowing either toward the poles (known as the prevailing westerlies) or toward the equator (known as the equatorial winds) (known as the trade winds).
• An area of high pressure is responsible for the diverging winds, which is characterized by calm winds, sunny skies, and little or no precipitation. The term is said to have originated from ships sailing to the New World becoming stranded for days or even weeks when they came across areas of high pressure and calm winds.
• As part of their cargo, many of these ships brought horses to the Americas. Due to a lack of wind, crews were unable to sail and resupply, and they frequently ran out of drinking water. To save water, these ships' sailors would occasionally throw the horses they were transporting overboard. As a result, the term "horse latitudes" was coined.
Roaring 40s; Furious 50s; Shrieking Or Screaming 60s
• The roaring forties, furious fifties, and screaming sixties are nicknames for the Southern Ocean's latitudes. The strong westerly winds in these areas are well-known. The lack of land, combined with the monotony of water, has given these winds such strength.
• ‘Below 40 degrees south, there is no law, and below 50 degrees south, there is no God,' says an old sailor. The ferocious storms that rage over these areas are exemplified by this.
• Waves can grow to be as tall as a six-story building. For sailors travelling from Europe to the East, the roaring forties were a major plus. These winds could greatly increase SPEED, which was extremely advantageous in the Age of Sail. We now primarily sail here because it is extremely exciting and adventurous!
Moisture In The Atmosphere
• Despite the fact that water vapor makes up a tiny fraction of the total atmosphere, accounting for less than 2% of the total mass, it is the single most important component of the air in terms of weather and climate.
• Near sea level, the proportions of most of the gaseous constituents that make up the atmosphere are relatively constant from place to place on the earth's surface. Water vapor, in particular, is a highly variable substance, ranging from nearly zero to nearly 5%.
This variation in water vapor content in the atmosphere, both in terms of place and time, is significant for at least four reasons:
1. The amount of that gas in a given mass of air indicates the potential capacity of the atmosphere for precipitation, one of the two most important climatic elements.
2. Water vapor is a regulator of the rate of heat loss from the earth, and thus has a significant impact on temperature phenomena, due to its absorptive effects on terrestrial radiation.
3. The amount of latent or potential energy stored up in the atmosphere for the origin and growth of storms increases as the amount of water vapor increases; as a result, it frequently determines whether an air mass will be stable or unstable.
4. The amount of water vapor in the atmosphere has an impact on the rate of cooling, or the sensible temperature, of the human body.
ABSOLUTE HUMIDITY- Absolute humidity refers to the total amount of water vapor contained in a given volume of air, expressed in weight of water vapor per unit volume.
SPECIFIC HUMIDITY- Specific humidity refers to the total amount of water vapor measured in grams per kilogram of air.
RELATIVE HUMIDITY- Relative humidity is always expressed as a percentage, fraction, or ratio. It compares the amount of water vapor actually present in the air (absolute humidity) to the maximum that could be contained at the given temperature and pressure under saturation conditions (Humidity Capacity)
• The Dew Point temperature is the temperature at which air becomes saturated. The relative humidity of saturated air is 100 percent (or is equal to 1). Condensation occurs only when the air is super saturated, that is, when the Relative Humidity exceeds 100%. (or is more than 1).