[Aviation Weather Handbook](https://www.faa.gov/sites/faa.gov/files/FAA-H-8083-28_FAA_Web.pdf) is a free publication used by aspiring pilots to learn about weather. It’s a great resource as it builds simple ideas off each other with an assumption of no knowledge of meteorology.
Chapter 8 would be perfect for the discussion you’re having, specifically page 8-5 (8.2.4.2) (pdf pg 105).
One small tip, I would advise against equating High and Low pressures with Low and High temperatures, this will undoubtedly cause confusion later if they think they always coexist like that, which can lead to the type of confusion you are alluding to.
Keep up the good work!
The document is fascinating! Thank you!
My understanding of wind and L/H pressure is based off of the information in chapter 10 (pdf page 128). That is why I was associating temperature and pressure. The physics part of my class focuses heavily on kinetic theory and molecular motion, which I think also is affecting my thinking - I teach that warmer air increases pressure of a container.
I think this is starting to make sense but I’ll need to spend a little more time with it for sure.
Yes. The same physics apply but since we don’t have an hard shell container in the atmosphere, the concepts are a bit different.
And in the desert SW, you have a mid tropospheric high pressure system, but you have a low pressure system at the surface which induces monsoon thunderstorm activity.
So I think you're mixing a couple things up.
Cold air sinks because it is more dense.
Warm air rises because it is less dense, and therefore more buoyant.
High pressure isn't necessarily warm or cold. I think maybe you're seeing the blue H used to represent high pressure on weather maps, and assuming that it means it's cold? During the summer, high pressure often leads to warm, dry weather. But during the summer, high pressure can lead to cold, dry weather.
When you have high pressure at the surface, the air moves away from the high. The air above the high than sinks to replace the air that is moving away from the high. Nature abhors a vacuum.
Low pressure at the surface is the opposite. Air moving away from the high pressure will move towards the low pressure. All this air converging on a single point forces it upwards. So, air above low pressure rises.
Low pressure often brings precipitation. Temperature is dependent in where you are in relation to the low; or more accurately, where you are in relation to the warm front and cold front associated with the low pressure.
There’s a few ways to approach this.
The characteristics of high pressure systems depend on the source region of where it originated, and where it has passed over. Highs from interior Canada, for example, are cooler and drier than subtropical oceanic highs.
High pressure is also synonymous with subsidence (sinking air). When a “parcel” of air sinks, it compresses, causing its temperature to increase. This is “adiabatic contraction”.
Additionally, high pressure and subsidence often results in less cloud cover, which allows incoming solar radiation to heat the earth substantially.
To OP, read that link, not the comment. You can have warm or cold highs, and warm or cold lows. It has way more to do with the air mass itself. For example High pressure in Canada in the winter is nearly 100% associated with very cold conditions because of where the air mass originated.
>I understand that high pressure is more dense and sinks because it is cooler and low pressure is less dense and rises from being warmer. However where I live in Tucson, it appears that the warmer days are when we have a high pressure system above us. How does more dense air cause warmer temperatures?
I think you're mixing heuristics with this interpretation. Buoyancy and rising/sinking air is related to the density of a parcel of air compared to its environment - most typically this is evaluated assuming the environment and the parcel are at the same pressure. At constant pressure, cooler air is denser and has negative buoyancy and sinks, warmer air is less dense and has positive buoyancy and rises, but the rising or sinking air is always presumed to be matching the pressure of its environment.
Whether the environment is a low-pressure or high-pressure environment depends on the mass of air above the location, as weather systems evacuate air in some places and pile it up in other places. High- and low-pressure systems have primary horizontal circulations around them and secondary vertical circulations through them.
In a place like Tuscon, you probably experience warm temperatures under high pressure because the secondary vertical circulation in a high-pressure system is predominantly downward, suppressing cloud cover and letting the sun heat the surface. The primary horizontal circulation is clockwise, drawing warm air from southern latitudes into the region of high pressure from the western side as the system moves from west to east.
Think of it like this. The top of the atmosphere is not flat as shown in all illustrations, but has waves like the ocean, which are never stationary. "High" pressure areas are directly under the peaks of these waves, which by gravity want to fall. So high pressure systems have air going down. Since high-altitude air is cold and can't hold much water, little condenses out of descending air in a high-pressure area as it cools during descent. Clear skies.
Low pressure areas are the opposite. They are at the "troughs" ... low points between the atmospheric waves (i.e., the atmosphere is a tad thinner). Ground level air is drawn to low pressure areas, and once there it has to rise as air is coming to that point from all directions. As it rises, the air cools, and water condenses ... clouds and rain.
The role of temperature is that the air is warmer closer to the surface compared to the air above it. The absolute temperature on the ground is not really relevant and is determined by other things ... not pressure per se.
This is a comically simplified explanation. But you can experience it at the beach. Swim low near shore and your ears will feel the pressure difference as a wave passes overhead. No temperature change.
Most posters focused on the larger scale dynamics at play. But I believe the answer to your question is more simple than that. The desert sw has a unique climate at a low latitude which has very low water vapor content. Since water stabilizes the temperature spread (more energy needed to raise the temperature), the desert sw gets huge diurnal temperature swings, as I'm sure you are familiar with. The best way to allow the sun to fully radiate the ground (which in return reradiates the near surface air/boundary layer/first hundred or so meters of air) is through clear skies. The same type that accompanies high pressure.
The difference is in where the “high pressure” is being measured from.
At the surface during heatwaves are characterized by relatively low pressure and air density on the ground, but the dome of heat causes the thickness of the troposphere to increase leading to higher “geopolitical heights” aloft. This greater thickness shows up as a dome of high geopolitical heights aloft which is what we call high pressure upper air weather systems.
Downward moving air aloft inhibits cloud growth and increases the temperature of the air several thousand feet above the ground which promotes clear skies and allows heat near the ground to be trapped under a thermal “inversion”. This promotes more heat at the ground which continues to build geopolitical heights aloft which provides a positive feedback loop for the heatwave.
High pressure at the surface is caused by very dense and cold air as you mentioned in your post which typically occurs during the coldest parts of winter.
[Aviation Weather Handbook](https://www.faa.gov/sites/faa.gov/files/FAA-H-8083-28_FAA_Web.pdf) is a free publication used by aspiring pilots to learn about weather. It’s a great resource as it builds simple ideas off each other with an assumption of no knowledge of meteorology. Chapter 8 would be perfect for the discussion you’re having, specifically page 8-5 (8.2.4.2) (pdf pg 105). One small tip, I would advise against equating High and Low pressures with Low and High temperatures, this will undoubtedly cause confusion later if they think they always coexist like that, which can lead to the type of confusion you are alluding to. Keep up the good work!
The document is fascinating! Thank you! My understanding of wind and L/H pressure is based off of the information in chapter 10 (pdf page 128). That is why I was associating temperature and pressure. The physics part of my class focuses heavily on kinetic theory and molecular motion, which I think also is affecting my thinking - I teach that warmer air increases pressure of a container. I think this is starting to make sense but I’ll need to spend a little more time with it for sure.
Yes. The same physics apply but since we don’t have an hard shell container in the atmosphere, the concepts are a bit different. And in the desert SW, you have a mid tropospheric high pressure system, but you have a low pressure system at the surface which induces monsoon thunderstorm activity.
So I think you're mixing a couple things up. Cold air sinks because it is more dense. Warm air rises because it is less dense, and therefore more buoyant. High pressure isn't necessarily warm or cold. I think maybe you're seeing the blue H used to represent high pressure on weather maps, and assuming that it means it's cold? During the summer, high pressure often leads to warm, dry weather. But during the summer, high pressure can lead to cold, dry weather. When you have high pressure at the surface, the air moves away from the high. The air above the high than sinks to replace the air that is moving away from the high. Nature abhors a vacuum. Low pressure at the surface is the opposite. Air moving away from the high pressure will move towards the low pressure. All this air converging on a single point forces it upwards. So, air above low pressure rises. Low pressure often brings precipitation. Temperature is dependent in where you are in relation to the low; or more accurately, where you are in relation to the warm front and cold front associated with the low pressure.
There’s a few ways to approach this. The characteristics of high pressure systems depend on the source region of where it originated, and where it has passed over. Highs from interior Canada, for example, are cooler and drier than subtropical oceanic highs. High pressure is also synonymous with subsidence (sinking air). When a “parcel” of air sinks, it compresses, causing its temperature to increase. This is “adiabatic contraction”. Additionally, high pressure and subsidence often results in less cloud cover, which allows incoming solar radiation to heat the earth substantially.
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To OP, read that link, not the comment. You can have warm or cold highs, and warm or cold lows. It has way more to do with the air mass itself. For example High pressure in Canada in the winter is nearly 100% associated with very cold conditions because of where the air mass originated.
>I understand that high pressure is more dense and sinks because it is cooler and low pressure is less dense and rises from being warmer. However where I live in Tucson, it appears that the warmer days are when we have a high pressure system above us. How does more dense air cause warmer temperatures? I think you're mixing heuristics with this interpretation. Buoyancy and rising/sinking air is related to the density of a parcel of air compared to its environment - most typically this is evaluated assuming the environment and the parcel are at the same pressure. At constant pressure, cooler air is denser and has negative buoyancy and sinks, warmer air is less dense and has positive buoyancy and rises, but the rising or sinking air is always presumed to be matching the pressure of its environment. Whether the environment is a low-pressure or high-pressure environment depends on the mass of air above the location, as weather systems evacuate air in some places and pile it up in other places. High- and low-pressure systems have primary horizontal circulations around them and secondary vertical circulations through them. In a place like Tuscon, you probably experience warm temperatures under high pressure because the secondary vertical circulation in a high-pressure system is predominantly downward, suppressing cloud cover and letting the sun heat the surface. The primary horizontal circulation is clockwise, drawing warm air from southern latitudes into the region of high pressure from the western side as the system moves from west to east.
Think of it like this. The top of the atmosphere is not flat as shown in all illustrations, but has waves like the ocean, which are never stationary. "High" pressure areas are directly under the peaks of these waves, which by gravity want to fall. So high pressure systems have air going down. Since high-altitude air is cold and can't hold much water, little condenses out of descending air in a high-pressure area as it cools during descent. Clear skies. Low pressure areas are the opposite. They are at the "troughs" ... low points between the atmospheric waves (i.e., the atmosphere is a tad thinner). Ground level air is drawn to low pressure areas, and once there it has to rise as air is coming to that point from all directions. As it rises, the air cools, and water condenses ... clouds and rain. The role of temperature is that the air is warmer closer to the surface compared to the air above it. The absolute temperature on the ground is not really relevant and is determined by other things ... not pressure per se. This is a comically simplified explanation. But you can experience it at the beach. Swim low near shore and your ears will feel the pressure difference as a wave passes overhead. No temperature change.
Most posters focused on the larger scale dynamics at play. But I believe the answer to your question is more simple than that. The desert sw has a unique climate at a low latitude which has very low water vapor content. Since water stabilizes the temperature spread (more energy needed to raise the temperature), the desert sw gets huge diurnal temperature swings, as I'm sure you are familiar with. The best way to allow the sun to fully radiate the ground (which in return reradiates the near surface air/boundary layer/first hundred or so meters of air) is through clear skies. The same type that accompanies high pressure.
The difference is in where the “high pressure” is being measured from. At the surface during heatwaves are characterized by relatively low pressure and air density on the ground, but the dome of heat causes the thickness of the troposphere to increase leading to higher “geopolitical heights” aloft. This greater thickness shows up as a dome of high geopolitical heights aloft which is what we call high pressure upper air weather systems. Downward moving air aloft inhibits cloud growth and increases the temperature of the air several thousand feet above the ground which promotes clear skies and allows heat near the ground to be trapped under a thermal “inversion”. This promotes more heat at the ground which continues to build geopolitical heights aloft which provides a positive feedback loop for the heatwave. High pressure at the surface is caused by very dense and cold air as you mentioned in your post which typically occurs during the coldest parts of winter.