What is air pressure, and how do pressure differences and Earth's rotation create wind?
Explain how temperature affects air pressure and density, how wind blows from high to low pressure, the Coriolis effect, and local winds such as land and sea breezes (Virginia 2018 Earth Science SOL ES.8).
A SOL-level answer on air pressure and wind for the Virginia Earth Science EOC: how temperature controls air density and pressure, why wind blows from high to low pressure, the difference between rising low-pressure systems (stormy) and sinking high-pressure systems (fair), the Coriolis effect, and land and sea breezes, with worked exam questions.
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What this topic is asking
Virginia Earth Science SOL standard ES.8 asks you to explain air pressure and wind: how temperature changes air density and pressure, why wind blows from high to low pressure, the contrast between high-pressure (fair) and low-pressure (stormy) systems, the Coriolis effect, and local winds like sea breezes. The EOC tests this with pressure-system items (what weather a high or low brings), wind-direction items, and the classic sea-breeze and land-breeze reasoning. It builds on the energy transfer from the start of the module.
Air pressure and temperature
How wind forms
High- and low-pressure systems
This high-versus-low contrast is one of the most tested forecasting ideas: lows are stormy, highs are fair.
The Coriolis effect
Because Earth rotates, moving air does not travel in a straight line from high to low pressure; it is deflected by the Coriolis effect, to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This is why large weather systems and global winds curve and why winds spiral into a low and out of a high rather than flowing straight.
Local winds: sea and land breezes
Try this
Q1. State the direction wind blows relative to pressure, and what makes it stronger. [2]
- Cue. Wind blows from high pressure to low pressure; a greater pressure difference (steeper gradient, closer isobars) makes it stronger.
Q2. Explain what kind of weather a low-pressure system usually brings and why. [2]
- Cue. A low has rising air that cools and condenses, forming clouds and precipitation, so it brings cloudy, stormy weather.
Exam-style practice questions
Practice questions written in the style of VDOE exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
VA Earth Science SOL 2023 (style)1 marksIn which direction does wind blow? (A) from low pressure to high pressure. (B) from high pressure to low pressure. (C) only from north to south. (D) randomly with no pattern.Show worked answer →
A 1-point multiple-choice item on wind.
The correct answer is B. Wind is air moving from areas of higher pressure to areas of lower pressure, trying to equalize the difference (then deflected by the Coriolis effect). It does not flow from low to high (A), is not fixed north to south (C), and is not random (D); the bigger the pressure difference, the stronger the wind.
The test rewards the rule: wind blows from high pressure to low pressure.
VA Earth Science SOL 2024 (style)2 marksOn a sunny afternoon at the beach, a cool breeze blows from the ocean toward the land. (a) Explain why a sea breeze forms during the day. (b) Explain how the breeze reverses at night to become a land breeze.Show worked answer →
A 2-point item on local winds.
(a) 1 point: during the day the land heats faster than the water, so the air over the land warms, becomes less dense and rises (low pressure), and cooler, denser air from over the ocean (higher pressure) flows in to replace it: a sea breeze (from sea to land).
(b) 1 point: at night the land cools faster than the water, so now the air over the water is warmer and rises while cooler air over the land sinks and flows out toward the sea: a land breeze (from land to sea).
Markers reward the daytime land-heats-faster, air-rises, sea-breeze-in explanation in (a) and the reversed nighttime situation in (b).
Related dot points
- Describe the composition and layers of the atmosphere and explain how energy is transferred by radiation, conduction and convection, including the greenhouse effect (Virginia 2018 Earth Science SOL ES.8).
A SOL-level answer on the atmosphere for the Virginia Earth Science EOC: the composition (mostly nitrogen and oxygen), the layers (troposphere, stratosphere with the ozone layer, mesosphere, thermosphere), and the three ways energy moves (radiation, conduction, convection) plus the greenhouse effect, with worked exam questions.
- Explain humidity, relative humidity and dew point, describe how clouds form when air cools to saturation, and identify the main cloud types and forms of precipitation (Virginia 2018 Earth Science SOL ES.8 and ES.9).
A SOL-level answer on atmospheric moisture for the Virginia Earth Science EOC: humidity and relative humidity, the dew point and saturation, how clouds form when rising air cools and condenses on nuclei, the main cloud types (cumulus, stratus, cirrus), and the forms of precipitation, with worked exam questions.
- Describe air masses and the weather at cold, warm, stationary and occluded fronts, and explain how thunderstorms, hurricanes and tornadoes form (Virginia 2018 Earth Science SOL ES.9).
A SOL-level answer on weather systems for the Virginia Earth Science EOC: how air masses get their properties from their source region, the weather at cold, warm, stationary and occluded fronts, and how thunderstorms, hurricanes and tornadoes form, including their hazards in Virginia, with worked exam questions.
- Interpret weather maps, including isobars, front symbols, and the station model (temperature, dewpoint, pressure, wind, sky cover), and use them to forecast (Virginia 2018 Earth Science SOL ES.1 and ES.9).
A SOL-level answer on weather maps for the Virginia Earth Science EOC: reading isobars and what close isobars mean, the symbols for cold, warm, stationary and occluded fronts, how to decode a station model (temperature, dewpoint, pressure, wind direction and speed, sky cover), and using maps to forecast, with worked exam questions.
- Explain surface currents (driven by wind and deflected by the Coriolis effect into gyres), deep density-driven circulation, and upwelling, and describe how currents transfer heat and affect climate (Virginia 2018 Earth Science SOL ES.10).
A SOL-level answer on ocean currents for the Virginia Earth Science EOC: wind-driven surface currents and gyres, the Coriolis effect, the difference between warm and cold currents, deep density-driven (thermohaline) circulation, upwelling and marine productivity, and how the Gulf Stream affects climate, with worked exam questions.
Sources & how we know this
- 2018 Science Standards of Learning (Earth Science) — Virginia Department of Education (2018)
- SOL Practice Items (All Subjects) — Virginia Department of Education (2024)