Atmospheric Vortex Engine

Frequently Asked Questions



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1. The Atmosphere

1.1 How does pressure in the atmosphere change with vertical elevation?

The pressure in the atmosphere decreases with height. Pressure is essentially the weight per unit area of the overlying air. Pressure decreases from approximately 101 kPa at the earth's surface to 10 kPa at the 16 km level.

1.2 How does temperature in the atmosphere change with vertical elevation?

The temperature in the lower part of the atmosphere (the troposphere) decreases as elevation increases.  The average temperature decreases from 15°C at the bottom of the atmosphere to -60°C at the top of the troposphere. The lower part of the atmosphere in which temperature decreases with height is called the troposphere. The height of the troposphere ranges from 18 km in the tropics to 12 km near the poles. The rate of temperature decrease with height is called the lapse rate. The lapse rate of the standard (average mid latitude) troposphere is 6.5°C/km. Lapse rate can vary widely. A layer within which temperature increases with height is called an inversion.

The layer of air above the troposphere where the temperature increases with height is called the stratosphere. The temperature increase in the stratosphere is caused by the absorption of ultra violet solar radiation mainly by ozone.

1.3 How is the atmosphere heated and cooled?

The atmosphere is heated from the bottom because it is transparent to short wave solar radiation. The troposphere is cooled by long wave infrared radiation to space. The earth's surface and the atmosphere both emit infrared radiation. The atmosphere is opaque to infrared radiation. Most of the infrared radiation emitted by the earth's surface is absorbed in the lower troposphere and then carried upward by convection. Heat is carried from the earth's surface to the lower troposphere by sensible heat, latent heat and by radiation. The heat is then carried upward by convection. Within the troposphere heat is transported upward mainly by convection. Infrared radiation to space cools the troposphere by 1 to 3°C per day. For more information on the earth's energy budget refer to entropy budget reference figures.

About 30% of the solar radiation is reflected directly back to space as short wave solar radiation either by the atmosphere, by clouds, or by the earth's surface. Reflected solar radiation does not affect on the earth's energy budget.

1.4 What is the relative importance of vertical versus horizontal heat transport?

The troposphere is comparable in thickness to the skin of an apple. The distance from the equator to the pole is 10,000 km while the maximum height of the troposphere is 20 km; a width-to-height ratio of 500:1. Vertical heat transport is more important than horizontal heat transport, but the wind blows mainly in the horizontal direction because of the large width to height ratio.

1.5 What is convection?

Heat can be transported by radiation, conduction or convection. Low temperature bodies like the earth's surface and the atmosphere emit infrared radiation.  Infrared radiation is ineffective in transmitting heat upward in the atmosphere because infrared radiation is absorbed by the atmosphere, mainly by water vapor and carbon dioxide.  Conduction is the primary heat transport process in solids. In a gas heated from the bottom the contribution of conduction is negligible compared to the contribution of convection.  Heat convection is heat transport resulting from change of position of warm and cold fluid masses.  In the troposphere heat is transported upward by convection by the upflow of warmed air and the downflow of cooled air.

1.6 What is sensible heat?

Sensible heat is the heat required to increase the temperature of a substance. The sensible heat of air is 1 kJ/(kg °C).  The sensible heat of water is 4.2 kJ/(kg °C)

1.7 What is latent heat?

Latent heat is the heat required to change water from the liquid phase to the gaseous phase. Vaporization can occur without change in temperature.  For air-water mixtures, the temperature at which vaporization occurs depends on the vapor pressure of the water vapor. Vaporization occurs at 100°C at a vapor pressure of 100 kPa and at 18°C at a vapor pressure of 2 kPa.

Latent heat is much larger than sensible heat. The latent heat of water is 2500 kJ/kg while the sensible heat of water is 4.2 kJ/(kg °C).  600 times more heat is required to vaporize water than is required to raise its temperature by 1°C.  Or alternatively, another way of looking at this is that during condensation of water vapor into liquid, 600 times more heat is released compared to the amount of heat released when liquid water temperature is reduced by 1°C.

When water vapour in a rising air parcel condenses into liquid, latent heat is released. This has important implications for an atmospheric vortex engine since the release of latent heat can further increase the buoyancy of the air.

1.8 What is buoyancy? What is stability?

An air mass is buoyant when its density is less than the density of the ambient air within which it resides. An air mass with the potential of becoming buoyant when it is raised is unstable. Non-buoyant air can have the potential of becoming buoyant if the release of latent heat causes its decrease in temperature with height to be less than the ambient lapse rate.

1.9 What happens to the temperature of an unmixed rising mass of warm air?

If there is no condensation the temperature of the parcel decreases by 9.75°C/km. If the air is saturated and there is condensation the temperature decreases by 3 to 7°C/km. The decrease in temperature is less for saturated air because the condensation of water vapor releases latent heat.

1.10 What is entrainment?

Entrainment is the mixing of ambient air in a mass of buoyant rising air. Entrainment of colder ambient air into a warm rising updraft reduces the buoyancy of the updraft.

1.11 How does mixing of ambient air affect updrafts?

Mixing reduces the temperature of updrafts. The temperature of updrafts is rarely more than a few degrees more than that of the ambient air because mixing increases with temperature difference. Mixing of dry ambient air with air containing condensed water has a very strong cooling effect on the updraft because of the re-evaporation of the condensed water.

1.12 What are clouds?

Clouds form when the water vapor content of air condenses. The flat bottom of fair weather cumulus clouds is the lifting condensation level.

1.13 How much solar radiation reaches the earth's surface?

The solar constant, the average solar energy received at the top of the atmosphere is 342 W/m2 of which 168 W/m2 is absorbed by the earth's surface. 40 W/m2 is radiated directly back to space as infrared radiation from the earth's surface. Of the remaining 128 W/m2, 78 W/m2 is transferred to the atmosphere as latent heat, 24 W/m2 as sensible heat, and 26 W/m2 is infrared radiation absorbed in the lower atmosphere. This total of 128 W/m2 is then carried upward by convection. For more details see Fig 1 of: entropy budget reference figures.

1.14 What is subsidence?

Subsidence is the slow descent of air from the upper troposphere. As the air descends, heat of compression increases its temperature. Air from near the top of the troposphere has the potential of becoming much warmer than the air at the bottom of the atmosphere when brought down to the surface. Compressing air from 20 kPa to 100 kPa without cooling increases its temperature from -60°C to +60°C. Without cooling the resulting buoyancy would inhibit subsidence. Infrared radiation to space cools the subsiding air by 1 to 3°C per day thereby limiting the temperature increase of the subsiding air.

Atmospheric convection is an unsymmetrical process. Air brought up quickly from the bottom to the top of the troposphere can have a temperature close to that of the ambient air at the top of the troposphere. Air brought down quickly from the top of the troposphere would have a much higher temperature than the ambient air at the bottom of the atmosphere. Consequently atmospheric convection consists mainly of fast updrafts and slow subsidence. The updrafts rise time is in the order of one hour while the subsidence time is about a month.

Fast subsidence warms up the troposphere therefore subsidence tends to occur where the air is coolest and easiest to compress. The subsidence time from the top to the bottom of the troposphere must be about 30 days to allow time for the subsiding air to emit the heat of compression to space.

For additional information on subsidence see: Subsidence required to replace radiative heat loss with work of compression. 

1.15 What is CAPE?

CAPE is Convective Available Potential Energy. A mass of buoyant air rising without friction accelerates upward. CAPE is the kinetic energy that would be produced by the force of buoyancy in frictionless flow. CAPE can be positive or negative; unstable air has positive CAPE, stable air has negative CAPE. The CAPE of continental air on warm days can exceed 4000 J/kg. The CAPE of maritime tropical air is typically between 800 and 1800 J/kg. A CAPE of 1800 J/kg corresponds to a velocity of 60 m/s. Updraft velocities rarely exceed 5 m/s because updraft reach a terminal velocity where velocity is limited by friction.

1.16 What is Coriolis Force?

The Coriolis force is an apparent force caused by motion relative to a rotating reference frame. Please refer to the following links for more information regarding Coriolis forces.

http://en.wikipedia.org/wiki/Coriolis_effect
http://www.rasmussen.edu/articles/learning-about-the-coriolis-force.asp

In most physical systems the magnitude of the Coriolis forces are small compared to other forces acting, therefore examples of Coriolis forces occuring in everyday life are relatively rare. The effect of Coriolis forces can be visualized in Foucault’s Pendulum. Coriolis forces also play an important role in large-scale meterological systems due to the rotation of the earth about its axis.
Coriolis force is a fictitious force and would not exist in an absolute frame of reference. The effect of Coriolis force on convective vortex can be explained using the circulation concept. Circulation approach is discussed at: Role of circulation in convective vortices 

1.17 What role does the Coriolis force play in meteorology?

Winds approaching a localized low pressure region will tend to be deflected around the region by the Coriolis force instead of flowing directly towards the region. In the northern hemisphere, winds tend to be deflected in a counter-clockwise direction around a low pressure cell. In the southern hemisphere, winds tends to be deflected in a clockwise direction around a low pressure cell. This deflection is also referred to as the “cyclonic” direction.


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