The brainy people tell me that Cyclones are powered by “latent heat” yet despite an exhaustive couple of minutes googling, I find I still don’t really understand a) what latent heat is and b) how it powers cyclones

latent heat spread across the surface of land or oceans

during the day a house will absorb latent heat, and will lose this latent heat at night

someone else will explain it better

http://www.kidsgeo.com/geography-for-kids/0071-latent-heat.php

CrazyNeutrino said:

latent heat spread across the surface of land or oceans

during the day a house will absorb latent heat, and will lose this latent heat at night

someone else will explain it better

That’s not latent heat at all because supposedly latent heat doesn’t invokve a change in temperature

50 years ago latent was described as the heat released or absorbed when a substance changes state.
So when a liquid changes state to a gas it requires energy to do so, it takes this energy from it’s surroundings in the form of heat, ie latent or hidden heat.

Dropbear said:

CrazyNeutrino said:

latent heat spread across the surface of land or oceans

during the day a house will absorb latent heat, and will lose this latent heat at night

someone else will explain it better

That’s not latent heat at all because supposedly latent heat doesn’t invokve a change in temperature

latent heat is energy released or absorbed from evaporation, the change n state releases energy

Dropbear said:

CrazyNeutrino said:

latent heat spread across the surface of land or oceans

during the day a house will absorb latent heat, and will lose this latent heat at night

someone else will explain it better

That’s not latent heat at all because supposedly latent heat doesn’t invokve a change in temperature

Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. An example is a state of matter change, meaning a phase transition, such as ice melting or water boiling.

or a house absorbing or losing energy

from
http://en.wikipedia.org/wiki/Latent_heat

http://en.wikipedia.org/wiki/Latent_heat

Ok so how does that relate to cyclones ?

A good example is a gas bottle.
The bottle will sit there quite happily when closed with a liquid phase and a gas phase above it, the system will be in equliberium (however there is some interaction at the interface with gas condensing and liquid evapourating constantly but that is not important today).
When you open a valve the vapour pressure drops and allows liquid to evapourate, but it cant do that without energy so it takes it from it’s surroundings and the bottle get cold while theis is happening.
When you turn off the valve the gass/liquid in the bottle returns to equliberim although the interface will now be a bit lower.

• Ok so how does that relate to cyclones ?

Hot water?

Dropbear said:

Ok so how does that relate to cyclones ?

I’m not sure it does.
It certainly doesn’t involve latent during sea water evapouration, that is achieved via direct input of energy/heat from the sun. Maybe up higher in the condensation phase some latent heat may be involved, I’ll have to think about it.

Peak Warming Man said:

Dropbear said:

Ok so how does that relate to cyclones ?

I’m not sure it does.
It certainly doesn’t involve latent during sea water evapouration, that is achieved via direct input of energy/heat from the sun. Maybe up higher in the condensation phase some latent heat may be involved, I’ll have to think about it.

iirc its to do with the warm air in thunderstorms pushing the latent heat up higher than normal

stumpy_seahorse said:

Peak Warming Man said:

Dropbear said:

Ok so how does that relate to cyclones ?

I’m not sure it does.
It certainly doesn’t involve latent during sea water evapouration, that is achieved via direct input of energy/heat from the sun. Maybe up higher in the condensation phase some latent heat may be involved, I’ll have to think about it.

iirc its to do with the warm air in thunderstorms pushing the latent heat up higher than normal

the process of convection

CrazyNeutrino said:

stumpy_seahorse said:

Peak Warming Man said:

I’m not sure it does.
It certainly doesn’t involve latent during sea water evapouration, that is achieved via direct input of energy/heat from the sun. Maybe up higher in the condensation phase some latent heat may be involved, I’ll have to think about it.

iirc its to do with the warm air in thunderstorms pushing the latent heat up higher than normal

the process of convection

how far does heat from the sun penetrate land

how far does heat of the sun penetrate oceans

CrazyNeutrino said:

Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. An example is a state of matter change, meaning a phase transition, such as ice melting or water boiling.

or a house absorbing or losing energy

from
http://en.wikipedia.org/wiki/Latent_heat

http://en.wikipedia.org/wiki/Latent_heat

When a house absorbs or loses energy it changes temperature, so it isn’t latent heat.

Dropbear said:

Ok so how does that relate to cyclones ?

First, some definitions. “Cyclone” is a general name for a low pressure system. A tropical cyclone, also known as a typhoon, hurricane, or cyclonic storm, is a cyclone with high winds, a spiral pattern of thunderstorms, and heavy rainfall. An anticyclone is a high pressure system. An atmospheric low pressure system is always caused by rising air; conversely, a high pressure system is always caused by descending air.

A TC forms when a low pressure system moves to an area of ocean with a warm surface. The warm water evaporates, and in changing state absorbing heat from the surrounding air and water. As the moist air rises, it cools through adiabatic cooling, and the water condenses out, releasing the latent energy it absorbed when it evaporated. Because the air has risen, the region it previously occupied has a lower pressure than it had, so surrounding air moves in to fill the gap, and is subject to Coriolis forces as it does, so (in the southern hemisphere) the winds in a TC are clockwise (as are all winds in a southern-hemisphere cyclone. In a southern hemisphere anticyclone winds are always anticlockwise. In the northern hemisphere, these directions are reversed.)

If enough energy is available, the pressure in the centre of the TC can drop significantly, which causes the incoming winds to increase in speed and strength, often to the point of becoming destructive. When a TC crosses onto land, it loses access to the warm water that powered it, so dissipates, first into a tropical storm, then into a simple low pressure system, although it can still deliver a large amount of rain.

This is a brief summary of a complex storm system. Have a look at http://en.wikipedia.org/wiki/Tropical_cyclone#Physics_and_energetics for a deeper discussion on how they’re powered, and the Formation section for some more detailed information on the above.

The Rev Dodgson said:

CrazyNeutrino said:

Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. An example is a state of matter change, meaning a phase transition, such as ice melting or water boiling.

or a house absorbing or losing energy

from
http://en.wikipedia.org/wiki/Latent_heat

http://en.wikipedia.org/wiki/Latent_heat

When a house absorbs or loses energy it changes temperature, so it isn’t latent heat.

hows that different to an ocean absorbing or losing heat?

btm said:

Dropbear said:

Ok so how does that relate to cyclones ?

First, some definitions. “Cyclone” is a general name for a low pressure system. A tropical cyclone, also known as a typhoon, hurricane, or cyclonic storm, is a cyclone with high winds, a spiral pattern of thunderstorms, and heavy rainfall.

Except in Australia where “cyclone” = “tropical cyclone”.

btm said:

Dropbear said:

Ok so how does that relate to cyclones ?

First, some definitions. “Cyclone” is a general name for a low pressure system. A tropical cyclone, also known as a typhoon, hurricane, or cyclonic storm, is a cyclone with high winds, a spiral pattern of thunderstorms, and heavy rainfall. An anticyclone is a high pressure system. An atmospheric low pressure system is always caused by rising air; conversely, a high pressure system is always caused by descending air.

A TC forms when a low pressure system moves to an area of ocean with a warm surface. The warm water evaporates, and in changing state absorbing heat from the surrounding air and water. As the moist air rises, it cools through adiabatic cooling, and the water condenses out, releasing the latent energy it absorbed when it evaporated. Because the air has risen, the region it previously occupied has a lower pressure than it had, so surrounding air moves in to fill the gap, and is subject to Coriolis forces as it does, so (in the southern hemisphere) the winds in a TC are clockwise (as are all winds in a southern-hemisphere cyclone. In a southern hemisphere anticyclone winds are always anticlockwise. In the northern hemisphere, these directions are reversed.)

If enough energy is available, the pressure in the centre of the TC can drop significantly, which causes the incoming winds to increase in speed and strength, often to the point of becoming destructive. When a TC crosses onto land, it loses access to the warm water that powered it, so dissipates, first into a tropical storm, then into a simple low pressure system, although it can still deliver a large amount of rain.

This is a brief summary of a complex storm system. Have a look at http://en.wikipedia.org/wiki/Tropical_cyclone#Physics_and_energetics for a deeper discussion on how they’re powered, and the Formation section for some more detailed information on the above.

So basically you are saying that the low pressure is what generates the latent heat effect as in the gas bottle example.
Fair enough, I guess it would be very fuzzy given no closed system but yeah.

CrazyNeutrino said:

The Rev Dodgson said:

CrazyNeutrino said:

Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. An example is a state of matter change, meaning a phase transition, such as ice melting or water boiling.

or a house absorbing or losing energy

from
http://en.wikipedia.org/wiki/Latent_heat

http://en.wikipedia.org/wiki/Latent_heat

When a house absorbs or loses energy it changes temperature, so it isn’t latent heat.

hows that different to an ocean absorbing or losing heat?

Houses don’t usually evaporate or condense.

OCDC said:

CrazyNeutrino said:

The Rev Dodgson said:

When a house absorbs or loses energy it changes temperature, so it isn’t latent heat.

hows that different to an ocean absorbing or losing heat?

Houses don’t usually evaporate or condense.

so on a 40 degree day a house is absorbing sun all day, and on really hot days standing in a room there is still heat felt coming from the ceiling at 12 o’clock at night

so what sort of heat is that?

CrazyNeutrino said:

OCDC said:

CrazyNeutrino said:

hows that different to an ocean absorbing or losing heat?

Houses don’t usually evaporate or condense.

so on a 40 degree day a house is absorbing sun all day, and on really hot days standing in a room there is still heat felt coming from the ceiling at 12 o’clock at night

so what sort of heat is that?

Radiation.

If the ceiling changed state, without changing temperature, that would be latent heat.

CrazyNeutrino said:

OCDC said:

CrazyNeutrino said:

hows that different to an ocean absorbing or losing heat?

Houses don’t usually evaporate or condense.

so on a 40 degree day a house is absorbing sun all day, and on really hot days standing in a room there is still heat felt coming from the ceiling at 12 o’clock at night

so what sort of heat is that?

Latent heat is absorbed or released by a change of state, and the materials in a house don’t change state due to weather conditions, even at 100^oC. Housing materials like brick can absorb and store heat, and release it later: exactly how much it can store is called the material’s heat capacity. See http://en.wikipedia.org/wiki/Heat_capacity

CrazyNeutrino said:

OCDC said:

CrazyNeutrino said:

hows that different to an ocean absorbing or losing heat?

Houses don’t usually evaporate or condense.

so on a 40 degree day a house is absorbing sun all day, and on really hot days standing in a room there is still heat felt coming from the ceiling at 12 o’clock at night

so what sort of heat is that?

Radiated heat.

sibeen said:

CrazyNeutrino said:

OCDC said:

Houses don’t usually evaporate or condense.

so on a 40 degree day a house is absorbing sun all day, and on really hot days standing in a room there is still heat felt coming from the ceiling at 12 o’clock at night

so what sort of heat is that?

Radiated heat.

Although there is probably also some convection.

sibeen said:

sibeen said:

CrazyNeutrino said:

so on a 40 degree day a house is absorbing sun all day, and on really hot days standing in a room there is still heat felt coming from the ceiling at 12 o’clock at night

so what sort of heat is that?

Radiated heat.

Although there is probably also some convection.

…and if you lent against the wall or ceiling they’d probably be some conduction.

sibeen said:

sibeen said:

sibeen said:

Radiated heat.

Although there is probably also some convection.

…and if you lent against the wall or ceiling they’d probably be some conduction.

*there’d

OCDC said:

sibeen said:

sibeen said:

Although there is probably also some convection.

…and if you lent against the wall or ceiling they’d probably be some conduction.

*there’d

I was using the imperfect Subjunctive pluperfect form.

sibeen said:

OCDC said:

sibeen said:

…and if you lent against the wall or ceiling they’d probably be some conduction.

*there’d

I was using the imperfect Subjunctive pluperfect form.

You were using the Law of Recursive Pedantry.

btm said:

CrazyNeutrino said:

OCDC said:

Houses don’t usually evaporate or condense.

so on a 40 degree day a house is absorbing sun all day, and on really hot days standing in a room there is still heat felt coming from the ceiling at 12 o’clock at night

so what sort of heat is that?

Latent heat is absorbed or released by a change of state, and the materials in a house don’t change state due to weather conditions, even at 100^oC. Housing materials like brick can absorb and store heat, and release it later: exactly how much it can store is called the material’s heat capacity. See http://en.wikipedia.org/wiki/Heat_capacity

o,k I understand it a bit better now, thanks

Thanks Billy

http://en.wikipedia.org/wiki/Tropical_cyclone

tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. Depending on its location and strength, a tropical cyclone is referred to by names such as hurricane (/ˈhʌrɨkən/ or /ˈhʌrɨkeɪn/), typhoon /taɪˈfuːn/, tropical storm, cyclonic storm, tropical depression, and simply cyclone.

Tropical cyclones typically form over large bodies of relatively warm water. They derive their energy through the evaporation of water from the ocean surface, which ultimately recondenses into clouds and rain when moist air rises and cools to saturation. This energy source differs from that of mid-latitude cyclonic storms, such as nor’easters and European windstorms, which are fueled primarily by horizontal temperature contrasts. The strong rotating winds of a tropical cyclone are a result of the conservation of angular momentum imparted by the Earth’s rotation as air flows inwards toward the axis of rotation. As a result, they rarely form within 5° of the equator. Tropical cyclones are typically between 100 and 4,000 km (62 and 2,485 mi) in diameter.

Tropical refers to the geographical origin of these systems, which form almost exclusively over tropical seas. Cyclone refers to their cyclonic nature, with wind blowing counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The opposite direction of circulation is due to the Coriolis effect.

>Latent heat is absorbed or released by a change of state, and the materials in a house don’t change state due to weather conditions..”

Excepting a few things like the moisture changes in and of the building, and there’re the occupants of a building, that both radiate heat and shift it via evaporation from their bodies to the surrounds.

Generally I see evaporative cooling (like PWM’s gas cylinder example) as taking some mass of whatever volume, you expand it and the energy is distributed over a larger volume.

Have NFI of how much water expands when evaporated, but if you take a cup of water at 24C and expand it to 500x the volume, then the temperature of an equivalent single glass/volume of air from that expanded mass would be much less, well, each’d be 1/500th the energy, I suppose, maybe, possibly, possibly not.

transition said:

>Latent heat is absorbed or released by a change of state, and the materials in a house don’t change state due to weather conditions..”

Excepting a few things like the moisture changes in and of the building, and there’re the occupants of a building, that both radiate heat and shift it via evaporation from their bodies to the surrounds.

Generally I see evaporative cooling (like PWM’s gas cylinder example) as taking some mass of whatever volume, you expand it and the energy is distributed over a larger volume.

Have NFI of how much water expands when evaporated, but if you take a cup of water at 24C and expand it to 500x the volume, then the temperature of an equivalent single glass/volume of air from that expanded mass would be much less, well, each’d be 1/500th the energy, I suppose, maybe, possibly, possibly not.

PV=nRT

And P1V1 over T1 = P2 V2 over T2.
I was a sponge.

Peak Warming Man said:

And P1V1 over T1 = P2 V2 over T2.
I was a sponge.

Yes PT1.

Dropbear said:

The brainy people tell me that Cyclones are powered by “latent heat” yet despite an exhaustive couple of minutes googling, I find I still don’t really understand a) what latent heat is and b) how it powers cyclones

Do find for latent heat on this page http://www.abc.net.au/news/2011-02-01/tropical-cyclones-explained/1926870

Not there?

latent heat, characteristic amount of energy absorbed or released by a substance during a change in its physical state that occurs without changing its temperature.

Then re-examine the above link and the first line of text says:

Cyclones form with a combination of very warm sea surface temperatures and the right type of outflow. Imagine a tall chimney where all the energy comes into the base and gets sucked up to the top.

> The brainy people tell me that Cyclones are powered by “latent heat” yet despite an exhaustive couple of minutes googling, > I find I still don’t really understand a) what latent heat is and b) how it powers cyclones

There are some good answers above and some terrible answers. When water condenses from a gas to a liquid it releases energy in the form of heat. That’s called latent heat.

As a side note, consider boiling water in a jug. The latent heat is the heat input from the heating coil between the start of first boiling and the end of boiling dry. If it wasn’t for latent heat, the water would boil away very quickly after it started. There’s quite a lot of heat required to boil water, 2257 kJ/kg. This is more than for most other liquids. http://www.engineeringtoolbox.com/fluids-evaporation-latent-heat-d_147.html

Let’s start with an updraft. As the gaseous water vapour condenses into cloud droplets at the cloud base it releases heat. This heats the air immediately surrounding the cloud droplets. Heating air reduces its density, making it want to rise. this causes the updraft to intensify and the cloud to gain height. If there’s a lot of gaseous water vapour below the cloud then there’s a lot of heat generated as the gas condenses to liquid. The result can be a cumulo-nimbus cloud, a thunderstorm. To summarise so far, the latent heat of water, released as the water condenses from a gas to a solid, powers thunderstorms.

Now consider this happening over a warm ocean. The water from the warm ocean is evaporating, and this feeds gaseous water vapour into the air above. The gas condenses to cloud droplets releasing latent heat in the process. This makes the air containing the cloud droplets less dense and intensifies convection which makes more cloud. In a cyclone there’s so much water evaporating from the warm ocean that the cloud becomes enormous, and the Coriolis forces (due to the Earth’s rotation) give it a spin that turns it into a tropical cyclone. As the cyclone grows it sucks in more air laden with gaseous water vapour from outside the core releasing more latent heat as it condenses causing more convection and more cloud.

mollwollfumble said:

> The brainy people tell me that Cyclones are powered by “latent heat” yet despite an exhaustive couple of minutes googling, > I find I still don’t really understand a) what latent heat is and b) how it powers cyclones

There are some good answers above and some terrible answers. When water condenses from a gas to a liquid it releases energy in the form of heat. That’s called latent heat.

As a side note, consider boiling water in a jug. The latent heat is the heat input from the heating coil between the start of first boiling and the end of boiling dry. If it wasn’t for latent heat, the water would boil away very quickly after it started. There’s quite a lot of heat required to boil water, 2257 kJ/kg. This is more than for most other liquids. http://www.engineeringtoolbox.com/fluids-evaporation-latent-heat-d_147.html

Let’s start with an updraft. As the gaseous water vapour condenses into cloud droplets at the cloud base it releases heat. This heats the air immediately surrounding the cloud droplets. Heating air reduces its density, making it want to rise. this causes the updraft to intensify and the cloud to gain height. If there’s a lot of gaseous water vapour below the cloud then there’s a lot of heat generated as the gas condenses to liquid. The result can be a cumulo-nimbus cloud, a thunderstorm. To summarise so far, the latent heat of water, released as the water condenses from a gas to a solid, powers thunderstorms.

Now consider this happening over a warm ocean. The water from the warm ocean is evaporating, and this feeds gaseous water vapour into the air above. The gas condenses to cloud droplets releasing latent heat in the process. This makes the air containing the cloud droplets less dense and intensifies convection which makes more cloud. In a cyclone there’s so much water evaporating from the warm ocean that the cloud becomes enormous, and the Coriolis forces (due to the Earth’s rotation) give it a spin that turns it into a tropical cyclone. As the cyclone grows it sucks in more air laden with gaseous water vapour from outside the core releasing more latent heat as it condenses causing more convection and more cloud.

At the risk of confusing you, I can explain why the latent heat of evaporation of water is so large. Water is a polar molecule, with one side positively charged and the other side negatively charged. The latent heat of evaporation of water is the energy needed to pry the positively charged side of one water molecule away from the negatively charged side of an adjacent water molecule.

In this context, the cyclone is powered by the electrostatic attraction between water molecules. As water molecules that have been separated in a gas come together as liquid, the electrostatic attraction between them speeds them towards one another and this extra kinetic energy is transferred to adjacent air molecules as heat, known as latent heat.

mollwollfumble said:

mollwollfumble said:

> The brainy people tell me that Cyclones are powered by “latent heat” yet despite an exhaustive couple of minutes googling, > I find I still don’t really understand a) what latent heat is and b) how it powers cyclones

There are some good answers above and some terrible answers. When water condenses from a gas to a liquid it releases energy in the form of heat. That’s called latent heat.

As a side note, consider boiling water in a jug. The latent heat is the heat input from the heating coil between the start of first boiling and the end of boiling dry. If it wasn’t for latent heat, the water would boil away very quickly after it started. There’s quite a lot of heat required to boil water, 2257 kJ/kg. This is more than for most other liquids. http://www.engineeringtoolbox.com/fluids-evaporation-latent-heat-d_147.html

Let’s start with an updraft. As the gaseous water vapour condenses into cloud droplets at the cloud base it releases heat. This heats the air immediately surrounding the cloud droplets. Heating air reduces its density, making it want to rise. this causes the updraft to intensify and the cloud to gain height. If there’s a lot of gaseous water vapour below the cloud then there’s a lot of heat generated as the gas condenses to liquid. The result can be a cumulo-nimbus cloud, a thunderstorm. To summarise so far, the latent heat of water, released as the water condenses from a gas to a solid, powers thunderstorms.

Now consider this happening over a warm ocean. The water from the warm ocean is evaporating, and this feeds gaseous water vapour into the air above. The gas condenses to cloud droplets releasing latent heat in the process. This makes the air containing the cloud droplets less dense and intensifies convection which makes more cloud. In a cyclone there’s so much water evaporating from the warm ocean that the cloud becomes enormous, and the Coriolis forces (due to the Earth’s rotation) give it a spin that turns it into a tropical cyclone. As the cyclone grows it sucks in more air laden with gaseous water vapour from outside the core releasing more latent heat as it condenses causing more convection and more cloud.

At the risk of confusing you, I can explain why the latent heat of evaporation of water is so large. Water is a polar molecule, with one side positively charged and the other side negatively charged. The latent heat of evaporation of water is the energy needed to pry the positively charged side of one water molecule away from the negatively charged side of an adjacent water molecule.

In this context, the cyclone is powered by the electrostatic attraction between water molecules. As water molecules that have been separated in a gas come together as liquid, the electrostatic attraction between them speeds them towards one another and this extra kinetic energy is transferred to adjacent air molecules as heat, known as latent heat.

Follow on question. The latent heat from what process powers the cyclonic storm that is Jupiter’s red spot?

mollwollfumble said:

Follow on question. The latent heat from what process powers the cyclonic storm that is Jupiter’s red spot?

Gravitational collapse?

http://en.wikipedia.org/wiki/List_of_tropical_cyclone_records

Warmest Eye 30°C (86°F) at 700 hPa October 1973 Typhoon Nora in west Pacific Basin

What’s the average temp of a cyclone eye?

Divine Angel said:

http://en.wikipedia.org/wiki/List_of_tropical_cyclone_records

Warmest Eye 30°C (86°F) at 700 hPa October 1973 Typhoon Nora in west Pacific Basin

What’s the average temp of a cyclone eye?

do not form unless the sea-surface temperature is above 26.5°C, …

mollwollfumble said:

Follow on question. The latent heat from what process powers the cyclonic storm that is Jupiter’s red spot?

This article from 1976 in Scientific American on The Meteorology of Jupiter is well worth a long read. From that I infer that the Great Red Spot is ALSO driven by the latent heat of water. The deepest and thickest clouds of Jupiter are of water and reach down to a base 105 km below the top of Jupiter’s troposphere where the pressure is 5 bar and the temperature is a balmy 10 degrees Celsius.

poikilotherm said:

http://www.kidsgeo.com/geography-for-kids/0071-latent-heat.php

errk that was terrible…