Atmospheric Winds & Ocean Currents
Monday, June 22, 2026 9:12 AM
Atmospheric winds & ocean currents are responsible for redistribution of heat that affects weather, climate,
vegetation, soil, water, storage & many other systems. If there was no heat redistribution, tropical areas would
burn up & the polar areas would freeze over (more than they already do!) Earth has evolved a system for
equalizing unequal distribution of heat received on earth
- The tropics receive surplus’s of energy from the sun b/c of direct rays hitting the tropics, whereas the polar
areas receive less energy from the sun b/c of oblique rays that strike these high latitudes. Heat is
redistributed by oceanic currents & atmospheric winds, where atmospheric redistribution accounts for 80%
of heat redistribution & ocean currents 20%. Warm air travels toward the poles & cold air travels to the
equator, warm tropical water is funneled toward the poles & cold, polar water is funneled into the tropics
Atmospheric Pressure
- The atmosphere is over 600 miles thick in weight of air that presses on earth's surface. We’ve learned that
density of air (molecules in a given volume) is greatest near the surface & decreases w/ elevation. Above
16,400 ft, air pressure becomes so low it becomes hard to breathe, climbers wear oxygen masks & airplanes
must be pressurized to the air at one mile high in elevation, to protect passengers & crew.
○ Like every substance, air molecules do weigh something, it’s surprisingly heavy at sea level - its density is
about 1.2 oz per cubic foot! So, the air inside a room that’s 20ft L x 20ft W x 8 ft H weighs about
237lbs! BUT air doesn’t always weigh the same, atmospheric pressure is defined as the total weight of
air exerted on a surface; The downward force exerted by the weight of air
Measures of Atmospheric Pressure
- One measure of atmospheric pressure is obtained w/ a barometer, a glass tube w/ a height of 31'' & a tray of
mercury at the bottom. The average height at sea level is 29.9'' Hg (mercury) but pressure varies at the
surface. When mercury levels are high, it means air is pressing down hard on the tray of mercury, pushing it
up the barometer, indicating high pressure. When the mercury level is low, the air is only pressing down
lightly on the mercury in the tray, indicating low air pressure
○ In 1940, the US Weather Service adopted the Millibar as the standard unit of measurement, a direct
measure of force. Millibars are pressure units used on weather maps, at sea level there are 1,013 mb of
pressure on the surface
○ Pressure is also measured in lbs per square inch, where sea level pressure is about 14.7 lbs/sq
inch. Average weight is 14.7 lbs/sq inch, 29.9 inches of mercury, or 1,013 mb, this value varies from place
to place at any time & is only the average figure. Air pressure varies depending on differences in air
temperature, atmospheric conditions & elevation. At sea level, air pressure varies from low pressure of
980mb in center storm to a strong high pressure of about 1,050 mb on a clear winter day
○ When you hear the terms surface high & low pressure on the evening weather, they are referring to air
pressure at sea level. High & low pressure areas exist in the atmosphere b/c of temperature differences
at the surface of the earth
Temperature & Pressure
- When air is heated, air molecules vibrate & expand in all directions, colliding & pushing further apart. This
reduces the amount of air molecules in a given area & causes reduction in pressure. As temperature
increases, the air pressure decreases
○ It’s important to understand differential heating of the surface; earth’s surface doesn’t heat
uniformly. For example, grass doesn't get as hot as asphalt, shallow section’s of air above the ground is
heated, directly due to the heat transfer processes of radiation & conduction. Air over asphalt becomes
warmer than the air above grass, air molecules above asphalt begin to vibrate the most, expand outward
& a pocket of lower pressure builds over the asphalt. The air becomes so light (if heated enough),
compared to surrounding air over the grass, it floats upward & heat is transferred via process of
convection
○ When air is cooled, molecules crowd closer together, increasing air pressure in a given space. As
temperature decreases, air pressure increases & air becomes heavy. Wherever air is colder & heavier
than the surrounding air, it sinks. This is how you bring a hot air balloon down! Unequal heating of
different parts of the earth's surface brings temp gradients (changes in temperature) that produce
pressure gradients (changes in pressure)
Pressure Gradient Force
- A pressure gradient where changes in pressure across a horizontal surface are caused by differential heating.
This variation of surface heating creates the planetary circulation of winds & ocean currents. Where a
pressure gradient exists, air molecules move from a high to a low pressure area’s. When air moves down a
pressure gradient, it becomes "wind". Wind is nature's attempt to even out distributions of air pressure all
over the earth, slow or quick, wind always begins in the same way w/ a difference in air pressure.
Isobars
- Pressure differences shown on weather maps by lines called isobars, connect places w/ the same pressure
○ An isobar is a line of constant atmospheric pressure & drawn at regular intervals (usually every 4
millibars). Spacing indicates the intensity of pressure differences. If they are far apart, the gradient
(change in pressure) is slight, reflecting a gradual difference in pressure. If the isobars are close together,
the gradient is steep, indicating there is a sharp difference in air pressure. The steeper the pressure
gradient, the stronger the wind blows. Air flows from high to low pressure & the pressure gradient
determines the force of the wind. Wind blows at a speed that increases w/ steepness of the pressure
gradient, causing windy weather.
Sea & Land Breezes
- This example of wind & pressure gradient generally blow in opposite directions on a daily basis. During the
day near the coast, a breeze flowing from the sea is called a "sea breeze." The land warms up quickly during
the day, air above it heats, expands & rises; this creates low pressure over the land. There is higher pressure
over the cooler water & air flows from the cooler surface to the warmer surface. Land consequently cools
from onshore flows of the wind, land heats & cools faster than water. At night, air over land cools off faster
than over the ocean, this produces high pressure over cooler land & low pressure over warmer ocean, winds
blow from land toward the sea in a land breeze
The Santa Ana
- This condition comes from the same pressure conditions as the land breeze, but larger in scale. The Santa
Ana is a hot, dry, easterly wind that sweeps from high deserts of the Great Basin & into coastal SoCal.
Although Santa Ana winds happen any time of year, they are most common during fall when the Basin desert
area begins cooling off. They're called Santa Ana's here b/c of the Santa Ana Canyon, these winds pass
through locally
- High pressure develops over the Basin due to cooling of the land surface. The air begins to blow from high to
low pressure near the coasts, local mountain terrain also plays a major role in bringing the Santa Ana's to the
coast. The orientation of these mountains (San Gabriel & San Bernardino) force the desert air upward & back
downward over the mountains. This dry, desert air descends about 4,000 ft. in altitude causing the air to
warm. It’s typical during autumn in Santa Ana for beach city temps to be in the 90's while desert locales are
in the 70's
- Winds often blow w/ strong gusts b/c the funneling of the air through mountains pass speeds w/ the flow of
the air. These winds are hot, dry & often causing fires. B/c of all the dust & pollen blowing in from other
areas, allergies often an effect of Santa Ana winds. On the brighter side, Santa Ana's blow smoggy air out to
sea & this layer of smog can be seen offshore
Monsoons
- Monsoons are large scale equivalents of sea & land breeze phenomenon; a monsoon is a winter & summer
reversal of winds. They are produced by changes in pressure systems that result from, changes in temps over
the surface (land or water). While they occur along many tropical coastlines, the Asian monsoon is the best
known
- During the summer, land warms faster than ocean & low pressure develops over the land. Water is cooler
than land, so higher pressure builds over the Indian Ocean. Air blows from high to low pressure (humid),
warm air moves from the ocean to the continent. Clouds & heavy rain result from humid air being brought
from the continent to its mountains. In India, 85% of the rain occurs during the summer months June-
September.
- During the winter, land loses its heat rapidly & it becomes cooler than the water. High pressure forms over
cooler land & lower pressure sits over the warmer Indian Ocean. Dry air blows from land to the ocean & the
winter months are the driest in South Asia.
Wind Direction Influences
- The Coriolis Effect
○ W/o earth's rotation, wind flows directly from high to low - down pressure gradient. Winds blowing over
larger distances of surface don’t blow in a straight line (from high to low pressure zones) b/c earth
rotates beneath these winds aka The Coriolis Effect
§ The deflective turn associated w/ earth's rotation (named after French physics prof Gaspard de
Coriolis, 1835) these winds are called "geostrophic winds"
- B/c earth rotates, objects moving freely/quickly over large enough distance’s near earth’s surface (like ocean
currents & winds) appear turning to the right in the Northern Hemisphere & left in the Southern Hemisphere
- Deflection
○ Deflection (0%) at the equator & the greatest at the poles is 100% since the speed of rotation on earth’s
surface varies from the equator to the poles. It’s faster (1,000+ mph) at the equator to 0 mph. Every time
soldiers fire an artillery shell or scientists shoot a missile, this deflection is accounted for & gunners use
computers to determine the percentage displacement to ensure missiles reach their targets. If looking
down in the direction of flow, in the northern hemisphere deflection is to the right. In the southern
hemisphere, the deflection is to the left
- The Coriolis affects higher altitude winds (since they blow stronger than winds slowed by friction near the
surface). Upper elevation winds called "jet streams" (aka "geostrophic winds") are caused by pressure of
gradient force & the Coriolis effect. Higher in the atmosphere above 5,000 ft, wind can travel fastest w/ the
least surface friction. Geostrophic winds don’t flow directly from high to low; they flow parallel to the isobars
- Watch this animation on the Coriolis effect Link
- The 2nd factor that influences the direction of wind is:
○ Friction
§ In addition to gradient force, consider the effects of friction on surface winds. There is friction
between the atmosphere & earth’s surface. Friction is determined by the roughness of the
surface, the smoother the surface (an ice-covered portion of Antarctica) the less friction is
forested in mountain areas. Wind flows faster over smooth surfaces, they slows near the
surface at -4000ft b/c of friction. The Coriolis reduces deflected winds that move from high to
low pressure, not directly, it crosses the isobars
§ This phenomenon produces an outflow of air around high grounds & an inflow of air around
low grounds near the surface. Meteorologists use the terms cyclones & anticyclones to refer to
these low & high pressures
- Cyclones & Anticyclones
○ Earth's rotation & changing surface temps produce changing patterns of pressure in the lower
troposphere. There is a horizontal & vertical movement associated w/ these pressure centers, they
bring changes in weather as they form & dissipate. Cyclones (aka depressions) refer to low
pressure systems, as air moves toward a low, it can’t go into the ground, it rises, though horizontal
winds are stronger than vertical winds. Air flow patterns around a low spiral in/upward, once it
rises to about 3 miles high, the air diverges away from the low pressure area
○ Cyclones are areas of light atmosphere, higher temps force air to rise since warmer air weighs less
(it‘s lighter & buoyant); this is not the only cause of a low pressure area. As the air rises, then cools,
clouds form & precipitation may occur. A cyclone is associated w/ rainy, often stormy unstable
weather (rain/snow/clouds). When meteorologists report the barometer is falling, this means that
pressure is falling & cloudy, rainy weather is on its way. Anticyclones are high pressure systems, as
winds surface & spread out of a high, to replace this laterally spreading air, the air from above
slowly descends. Air flow patterns around a high are outward & downward, highs are areas of
heavy atmosphere. Cooler air sinks or descends air & compresses as it approaches the surface of
the earth; the compression of air makes it warmer & drier. Highs are therefore associated w/ clear
weather & a rising barometer indicate’s nice weather
§ These highs & lows are typically large features of the atmosphere, covering 600 miles in
diameter or more. The atmosphere at any time contains a large number of these pressure
systems, they form, disappear, change size, shape, speed of motion, direction & never exactly
repeat themselves.
Monday, June 22, 2026 9:12 AM
Atmospheric winds & ocean currents are responsible for redistribution of heat that affects weather, climate,
vegetation, soil, water, storage & many other systems. If there was no heat redistribution, tropical areas would
burn up & the polar areas would freeze over (more than they already do!) Earth has evolved a system for
equalizing unequal distribution of heat received on earth
- The tropics receive surplus’s of energy from the sun b/c of direct rays hitting the tropics, whereas the polar
areas receive less energy from the sun b/c of oblique rays that strike these high latitudes. Heat is
redistributed by oceanic currents & atmospheric winds, where atmospheric redistribution accounts for 80%
of heat redistribution & ocean currents 20%. Warm air travels toward the poles & cold air travels to the
equator, warm tropical water is funneled toward the poles & cold, polar water is funneled into the tropics
Atmospheric Pressure
- The atmosphere is over 600 miles thick in weight of air that presses on earth's surface. We’ve learned that
density of air (molecules in a given volume) is greatest near the surface & decreases w/ elevation. Above
16,400 ft, air pressure becomes so low it becomes hard to breathe, climbers wear oxygen masks & airplanes
must be pressurized to the air at one mile high in elevation, to protect passengers & crew.
○ Like every substance, air molecules do weigh something, it’s surprisingly heavy at sea level - its density is
about 1.2 oz per cubic foot! So, the air inside a room that’s 20ft L x 20ft W x 8 ft H weighs about
237lbs! BUT air doesn’t always weigh the same, atmospheric pressure is defined as the total weight of
air exerted on a surface; The downward force exerted by the weight of air
Measures of Atmospheric Pressure
- One measure of atmospheric pressure is obtained w/ a barometer, a glass tube w/ a height of 31'' & a tray of
mercury at the bottom. The average height at sea level is 29.9'' Hg (mercury) but pressure varies at the
surface. When mercury levels are high, it means air is pressing down hard on the tray of mercury, pushing it
up the barometer, indicating high pressure. When the mercury level is low, the air is only pressing down
lightly on the mercury in the tray, indicating low air pressure
○ In 1940, the US Weather Service adopted the Millibar as the standard unit of measurement, a direct
measure of force. Millibars are pressure units used on weather maps, at sea level there are 1,013 mb of
pressure on the surface
○ Pressure is also measured in lbs per square inch, where sea level pressure is about 14.7 lbs/sq
inch. Average weight is 14.7 lbs/sq inch, 29.9 inches of mercury, or 1,013 mb, this value varies from place
to place at any time & is only the average figure. Air pressure varies depending on differences in air
temperature, atmospheric conditions & elevation. At sea level, air pressure varies from low pressure of
980mb in center storm to a strong high pressure of about 1,050 mb on a clear winter day
○ When you hear the terms surface high & low pressure on the evening weather, they are referring to air
pressure at sea level. High & low pressure areas exist in the atmosphere b/c of temperature differences
at the surface of the earth
Temperature & Pressure
- When air is heated, air molecules vibrate & expand in all directions, colliding & pushing further apart. This
reduces the amount of air molecules in a given area & causes reduction in pressure. As temperature
increases, the air pressure decreases
○ It’s important to understand differential heating of the surface; earth’s surface doesn’t heat
uniformly. For example, grass doesn't get as hot as asphalt, shallow section’s of air above the ground is
heated, directly due to the heat transfer processes of radiation & conduction. Air over asphalt becomes
warmer than the air above grass, air molecules above asphalt begin to vibrate the most, expand outward
& a pocket of lower pressure builds over the asphalt. The air becomes so light (if heated enough),
compared to surrounding air over the grass, it floats upward & heat is transferred via process of
convection
○ When air is cooled, molecules crowd closer together, increasing air pressure in a given space. As
temperature decreases, air pressure increases & air becomes heavy. Wherever air is colder & heavier
than the surrounding air, it sinks. This is how you bring a hot air balloon down! Unequal heating of
different parts of the earth's surface brings temp gradients (changes in temperature) that produce
pressure gradients (changes in pressure)
Pressure Gradient Force
- A pressure gradient where changes in pressure across a horizontal surface are caused by differential heating.
This variation of surface heating creates the planetary circulation of winds & ocean currents. Where a
pressure gradient exists, air molecules move from a high to a low pressure area’s. When air moves down a
pressure gradient, it becomes "wind". Wind is nature's attempt to even out distributions of air pressure all
over the earth, slow or quick, wind always begins in the same way w/ a difference in air pressure.
Isobars
- Pressure differences shown on weather maps by lines called isobars, connect places w/ the same pressure
○ An isobar is a line of constant atmospheric pressure & drawn at regular intervals (usually every 4
millibars). Spacing indicates the intensity of pressure differences. If they are far apart, the gradient
(change in pressure) is slight, reflecting a gradual difference in pressure. If the isobars are close together,
the gradient is steep, indicating there is a sharp difference in air pressure. The steeper the pressure
gradient, the stronger the wind blows. Air flows from high to low pressure & the pressure gradient
determines the force of the wind. Wind blows at a speed that increases w/ steepness of the pressure
gradient, causing windy weather.
Sea & Land Breezes
- This example of wind & pressure gradient generally blow in opposite directions on a daily basis. During the
day near the coast, a breeze flowing from the sea is called a "sea breeze." The land warms up quickly during
the day, air above it heats, expands & rises; this creates low pressure over the land. There is higher pressure
over the cooler water & air flows from the cooler surface to the warmer surface. Land consequently cools
from onshore flows of the wind, land heats & cools faster than water. At night, air over land cools off faster
than over the ocean, this produces high pressure over cooler land & low pressure over warmer ocean, winds
blow from land toward the sea in a land breeze
The Santa Ana
- This condition comes from the same pressure conditions as the land breeze, but larger in scale. The Santa
Ana is a hot, dry, easterly wind that sweeps from high deserts of the Great Basin & into coastal SoCal.
Although Santa Ana winds happen any time of year, they are most common during fall when the Basin desert
area begins cooling off. They're called Santa Ana's here b/c of the Santa Ana Canyon, these winds pass
through locally
- High pressure develops over the Basin due to cooling of the land surface. The air begins to blow from high to
low pressure near the coasts, local mountain terrain also plays a major role in bringing the Santa Ana's to the
coast. The orientation of these mountains (San Gabriel & San Bernardino) force the desert air upward & back
downward over the mountains. This dry, desert air descends about 4,000 ft. in altitude causing the air to
warm. It’s typical during autumn in Santa Ana for beach city temps to be in the 90's while desert locales are
in the 70's
- Winds often blow w/ strong gusts b/c the funneling of the air through mountains pass speeds w/ the flow of
the air. These winds are hot, dry & often causing fires. B/c of all the dust & pollen blowing in from other
areas, allergies often an effect of Santa Ana winds. On the brighter side, Santa Ana's blow smoggy air out to
sea & this layer of smog can be seen offshore
Monsoons
- Monsoons are large scale equivalents of sea & land breeze phenomenon; a monsoon is a winter & summer
reversal of winds. They are produced by changes in pressure systems that result from, changes in temps over
the surface (land or water). While they occur along many tropical coastlines, the Asian monsoon is the best
known
- During the summer, land warms faster than ocean & low pressure develops over the land. Water is cooler
than land, so higher pressure builds over the Indian Ocean. Air blows from high to low pressure (humid),
warm air moves from the ocean to the continent. Clouds & heavy rain result from humid air being brought
from the continent to its mountains. In India, 85% of the rain occurs during the summer months June-
September.
- During the winter, land loses its heat rapidly & it becomes cooler than the water. High pressure forms over
cooler land & lower pressure sits over the warmer Indian Ocean. Dry air blows from land to the ocean & the
winter months are the driest in South Asia.
Wind Direction Influences
- The Coriolis Effect
○ W/o earth's rotation, wind flows directly from high to low - down pressure gradient. Winds blowing over
larger distances of surface don’t blow in a straight line (from high to low pressure zones) b/c earth
rotates beneath these winds aka The Coriolis Effect
§ The deflective turn associated w/ earth's rotation (named after French physics prof Gaspard de
Coriolis, 1835) these winds are called "geostrophic winds"
- B/c earth rotates, objects moving freely/quickly over large enough distance’s near earth’s surface (like ocean
currents & winds) appear turning to the right in the Northern Hemisphere & left in the Southern Hemisphere
- Deflection
○ Deflection (0%) at the equator & the greatest at the poles is 100% since the speed of rotation on earth’s
surface varies from the equator to the poles. It’s faster (1,000+ mph) at the equator to 0 mph. Every time
soldiers fire an artillery shell or scientists shoot a missile, this deflection is accounted for & gunners use
computers to determine the percentage displacement to ensure missiles reach their targets. If looking
down in the direction of flow, in the northern hemisphere deflection is to the right. In the southern
hemisphere, the deflection is to the left
- The Coriolis affects higher altitude winds (since they blow stronger than winds slowed by friction near the
surface). Upper elevation winds called "jet streams" (aka "geostrophic winds") are caused by pressure of
gradient force & the Coriolis effect. Higher in the atmosphere above 5,000 ft, wind can travel fastest w/ the
least surface friction. Geostrophic winds don’t flow directly from high to low; they flow parallel to the isobars
- Watch this animation on the Coriolis effect Link
- The 2nd factor that influences the direction of wind is:
○ Friction
§ In addition to gradient force, consider the effects of friction on surface winds. There is friction
between the atmosphere & earth’s surface. Friction is determined by the roughness of the
surface, the smoother the surface (an ice-covered portion of Antarctica) the less friction is
forested in mountain areas. Wind flows faster over smooth surfaces, they slows near the
surface at -4000ft b/c of friction. The Coriolis reduces deflected winds that move from high to
low pressure, not directly, it crosses the isobars
§ This phenomenon produces an outflow of air around high grounds & an inflow of air around
low grounds near the surface. Meteorologists use the terms cyclones & anticyclones to refer to
these low & high pressures
- Cyclones & Anticyclones
○ Earth's rotation & changing surface temps produce changing patterns of pressure in the lower
troposphere. There is a horizontal & vertical movement associated w/ these pressure centers, they
bring changes in weather as they form & dissipate. Cyclones (aka depressions) refer to low
pressure systems, as air moves toward a low, it can’t go into the ground, it rises, though horizontal
winds are stronger than vertical winds. Air flow patterns around a low spiral in/upward, once it
rises to about 3 miles high, the air diverges away from the low pressure area
○ Cyclones are areas of light atmosphere, higher temps force air to rise since warmer air weighs less
(it‘s lighter & buoyant); this is not the only cause of a low pressure area. As the air rises, then cools,
clouds form & precipitation may occur. A cyclone is associated w/ rainy, often stormy unstable
weather (rain/snow/clouds). When meteorologists report the barometer is falling, this means that
pressure is falling & cloudy, rainy weather is on its way. Anticyclones are high pressure systems, as
winds surface & spread out of a high, to replace this laterally spreading air, the air from above
slowly descends. Air flow patterns around a high are outward & downward, highs are areas of
heavy atmosphere. Cooler air sinks or descends air & compresses as it approaches the surface of
the earth; the compression of air makes it warmer & drier. Highs are therefore associated w/ clear
weather & a rising barometer indicate’s nice weather
§ These highs & lows are typically large features of the atmosphere, covering 600 miles in
diameter or more. The atmosphere at any time contains a large number of these pressure
systems, they form, disappear, change size, shape, speed of motion, direction & never exactly
repeat themselves.
