The world's highest recorded air temperature is officially recognized by the World Meteorological Organization as 134°F (57.6°C) recorded at Death Valley, California, USA on 10 July 1913.

Note that this is in recorded history. Higher temperatures have occurred, of course, at different times during the 4.55 billion years of Earth's history.

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El Azizia, Libya, held this record for 90 years, after recording a temperature of 136°F (58°C) on 13 September 1922. It was coincidentally also on 13 September of 2012 that this record was stripped by the World Meteorological Organization after a team of experts determined that there were enough questions surrounding this measurement that this temperature probably did not occur.

The temperature had been suspect in atmospheric science circles for a number of reasons. One being that the time of year is inconsistent with such a high reading. Also, the type and exposure of the measuring instruments cast doubt on the accuracy of the data. However, other temperatures in the same general area approach that maximum, especially in the cloudless southern Sahara, far from the moderating effects of water. Several links are provided below for more information on this process.

Other Earth Temperature Highs:

The modern, most reliably recorded air temperature in the world was 129.2°F (54.0°C) at Death Valley on 30 June 2013.

The highest naturally occurring temperature (at Earth's core) is higher than the melting point of iron and is estimated to be approximately 5000°C.

The highest temperature ever created in a laboratory experiment: Scientists, using the Z machine, have produced plasma at temperatures of more than 2 billion degrees Kelvin (3.6 billion degrees F) at Sandia National Laboratories, located near Albuquerque New Mexico.

Dasht-e Lut, a desert in southeastern Iran, was identified as having the hottest surface temperature (not air temperature) of 70.7 degrees C (159 degrees F) This was only during the years of study in 2004 and 2005 by MODIS, which is a satellite remote sensor, mounted on NASA satellites Aqua and Terra.

Caveats to the Above:

Modern measuring methods, instruments, and techniques are more sophisticated and standardized today. Example: The World Meteorological Organization, recommends that air temperatures be measured at a height of 1.25 to 2 meters (which is approximately 4 feet, 1.2 inches to 6 feet, 6.7 inches) above ground level.

The most likely places on Earth for record high temperatures are in depressions in desert regions, especially in areas below sea level. The Dallol (Danakil) Depression in Africa (Ethiopia), Death Valley in USA, and the area around Lake Eyre in Australia are likely candidates. However, the Gobi Desert's temperatures, while far from any ocean, are mitigated by altitude. The Dallol Depression had a weather station for a short while (only a few years). It was run by a mining company, and wasn't there long enough to measure an extreme maximum to beat the Libyan record. It did however, measure very high mean average temperatures while it operated.

The thing to remember about very hot places is that data is sparse. This is because very few people with high levels of technology stay in these places for long. The environment of the Dallol Depression is hostile to human life. 135

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The instrument, most commonly used in science, is a barometer.

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The word, Barometer, is derived from baro, meaning weight or pressure, and meter, meaning measuring device.

Barometers can be either analog or digital. The traditional analog barometer is known as an aneroid barometer. These are the round chrome or brass type that you would normally see on the bridge of a ship, many times accompanied by clock, temperature, and/or humidity gauge.

For an accurate and reliable aneroid barometer, you should expect to pay $249.00 or more. For aneroid barometers, accuracy and reliability will wane incrementally below that price. The cost of scientific instruments, including barometers, are directly tied to accuracy and reliability. In some cases, however, as you go up in price, accuracy will remain stable but quality of materials and craftsmanship will drive the price upwards (i.e. use of thick solid brass or chrome).

Digital barometers emulate the results achieved from an aneroid barometer (sometimes called a "nautical barometer). Their accuracy varies wildly and is not necessarily tied to price. For example, the barometers, in even the most reasonably priced (under $100.00) La Crosse Weather Stations, are exemplary performers. Anecdotal observations over many years show that the La Crosse variance from NIST traceable, accurate weather stations has been minimal (±.01). Other inexpensive manufacturer's products have nowhere near this steady and predictable tolerance. And many are as much as .06-.10 or 2-3mb off after initial calibration.

All barometers are not the same. Most have elevation limitations. With the Weems & Plath barometers, specific elevations are designated by each individual product. So, be sure to probe for this information before you buy. Some barometers can be upgraded for high elevation use. But this is relatively expensive, and generally for those barometers to be used in terrain of 5,000ft.

Digital barometers can have the same limitations. Again, be careful when you purchase. We are not aware of any low cost digital that will function correctly over 5,000-6,000 ft elevation. For high altitudes, or if you're a stickler for accuracy, you must consider the Davis, RainWise, WeatherHawk, or Columbia Weather Systems. Do not rely on any barometer above 5,000-6,000 ft for mission critical or safety applications, unless you are absolutely certain of its well defined and guaranteed specifications. Remember that as you begin to challenge the stated limitations of any scientific device, your inaccuracies will almost certainly increase as you approach the stated threshold. For example, a stated 6,000 ft elevation limit may function perfectly well up to 4,000 ft. Then, possibly a gradual fall-off in accuracy between 4,000-5,000ft. But then a rapid and possibly logarithmic increase in error percentage over 5,000ft. This is just an example and not meant to be a basis for calculating decreasing accuracy in any scientific instrument.

The original analog barometer was the water ball. This instrument featured a glass reservoir at its bottom that fed into a narrowing tube that protruded upwards. As atmospheric pressure increased, the water was driven upwards into the tube, to indicate fair or improving weather conditions. Conversely, as the air pressure dropped, the water level in the tube fell, to indicate a change to more inclement weather. As the water level fell even lower in the tube, it became a more urgent indicator of impending foul weather.

The instrument that measures humidity is called a hygrometer.

A hygrometer is an instrument that measures relative humidity in the air. One common kind of hygrometer is a psychrometer, a device that measures the temperature of a wet bulb and a dry bulb simultaneously. The wet bulb should be cooler (if it's above freezing), because water evaporates from the bulb, taking energy with it. If the air is more humid, the evaporation is slower, so the bulb is closer to the dry bulb's temperature. A comparison of the wet and dry bulb temperature using a Psychrometric Chart indicates the relative humidity of the air.

Hygrometers can be combined with other systems as the sensor to regulate humidity. The resulting instrument may be called a humidistat or hygristor, which function somewhat like a thermostat adding or subtracting moisture, not heat, to the air. Types of Hygrometers include:

• a dry bulb thermometer and a wet bulb thermometer with a Psychrometric chart

• A hygrograph which gives a continuous record of the humidity value using human hair, on a graph

• A hygristor using lithium chloride is used to find out the humidity values at different altitudes. Hygristor's resistance varies with the humidity and this principle is used to find out the humidity.

• A humidity indicator card (HIC) is a card on which a moisture-sensitive chemical is impregnated such that it will change color as the humidity changes

In term of units; humidity can be expressed by

• Absolute humidity: total moisture/volume of air

• Relative humidity: total moisture/saturated moisture

• Specific humidity: total moisture/weight of dry air

In term of method, Various equipment can be used to measure water content direct or indirectly.

• Direct measure by cooling the air down to condensation point.
• Indirect measure by measure air conductivity and related to presence of humidity. Infrared spectrometry is used to measure presence of moisture from IR absorption.

In term of equipment:

One device is known as a hygrometer. A hygrometer is used to measure humidity.

Not to be confused with the hydrometer which measures the specific gravity of liquids.

A Psychrometer is a type of Hygrometer. A psychrometer consists of two thermometers, one which is dry and one which is kept moist with distilled water on a sock or wick.

As an upgrade in technology there is the trace moisture sensor which is a phosphorous pentoxide (P205), a very hydrophilic material, the resistivity of which changes with the humidity, so it is used in electronic devices designed to make use of the property.

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Another tool that could be used is a Cyanometer, an instrument for measuring 'blueness', specifically the color intensity of blue sky. It is attributed to Horace-Bénédict de Saussure and Alexander von Humboldt. It consists of squares of paper dyed in graduated shades of blue and arranged in a color circle or square that can be held up and compared to the color of the sky. The blueness of the atmosphere indicates transparency and the amount of water vapor.

hygrometers and psychrometers

It is in the stratosphere, located 8 to 50km above sea level. The ozone layer surrounds the earth, meaning that it's wrapped around earth. The altitude varies with latitude as well, placing the stratosphere and the ozone layer closer to the Earth's surface over the poles.

The highest concentration of ozone is in the lower stratosphere, also called the tropopause, and the ozone here is called the ozone layer. Ozone is also found in the lower atmosphere, also called the troposphere, and the ozone here is one component of smog.

Ozone concentrations vary from near zero at extreme elevations (high in the exosphere), to a maximum (~9 ppm) at the bottom of the stratosphere, to zero again near Earth's surface (the troposphere ends here). So some ozone is found in every layer of the atmosphere (usually less than 1 ppm, except for the stratosphere).

When it is winter at one of the poles, there is no UV-C to make ozone, and since ozone decays with time, an "ozone hole" forms. The size of the hole depends on how many contaminants are present to accelerate the decay of ozone.
Ozone is concentrated at 20-40 km above earth with highest concentration 6-8 parts per million. It is present in the stratosphere of the earth's atmosphere.

Briefly:

CFCs and similar man-made gases break down the ozone in the stratosphere allowing in harmful ultraviolet radiation. The ozone hole happens mostly in Antarctica where four months of winter darkness create ideal conditions for the destruction.

Ozone is a protective layer in the upper atmosphere. It is formed, when oxygen molecules absorb short wavelength ultra violet radiations from the sun. Ozone is mostly destroyed by the free radicals in the atmosphere. When compounds like CFCs (chlorofluorocarbons) are released, they are dissociated by sunlight into chloride radicals. These radicals attack ozone, thereby decreasing its concentration. This results in hole in the ozone layer.

The hole in the ozone layer happens because the ozone in the stratosphere is destroyed by chlorine and bromine from halogen atoms. These atoms come from man-made halocarbon refrigerator gases (chlorofluorocarbons [CFCs], freons and halons) which are emitted at ground level but move up into the ozone layer. These gases all contain chlorine and bromine.

Ozone (O3) is formed when ultraviolet (UV) light strikes an oxygen molecule (O2), converting it into two oxygen ions (O). These oxygen ions (O) combine with other oxygen molecules (O2) to form ozone (O3). Later, another oxygen ion (O) will combine with the ozone molecule (O3) to form two oxygen molecules (O2). This is the natural ozone-oxygen cycle of the earth.

The ozone layer prevents the harmful ultraviolet B-waves (UV-B) from reaching the earth. Increased exposure to UV-B is thought to be responsible for increases in skin cancer, eye cataracts and damage to plants and plankton. Because of this the nations of the world in 1989 adopted the Montreal Protocol which bans production of CFCs, halons and other ozone-depleting chemicals.

The ozone hole happens during the spring in Antarctica (Sept to Dec). Polar Stratospheric Clouds (PSCs) form during the all-dark winter. When spring arrives and UV light appears again, crystals of ice and nitric acid in these clouds help to release the chlorine and bromine atoms from the halocarbon gases. These destroy the ozone. (A single chlorine atom can continue destroying ozone for up to two years, reacting with up to 100,000 ozone molecules.)

Because the concept of man made pollution doesn't cover all of what we see, another look at the issue is demanded. In the man induced theory, the depletion of ozone is due to release of man-made chemicals such as chlorofluorocarbon (CFC) compounds.

Over time these heavier then air chemicals work their way up into the upper stratosphere. CFC's break apart under UV radiation releasing chlorine atoms that would destroy ozone.

Assuming this man induced theory on the origin of the ozone hole is correct, the area most affected would be the mid-Latitude Northern Hemisphere where the industry and population centers in the U.S., Canada, Europe, India, Asia, Russia, China and Japan exist. This is precisely what is not happening! This area is where the least action occurs.

Instead, we are observing a substantial annual ozone hole in one area only, the Antarctic and then only during times of no sunlight (the polar winter). Once the sun returns, the hole disappears quickly. A substantially smaller hole (NASA calls this the dimple because it is so small) is also known to occur over the world's second cleanest area, the Arctic.

A second issue exists. The sun often generates explosions that produce bursts of high-energy protons. These are called Solar Proton Events. Ozone layer density on Earth can be dramatically affected by SPE's, which can locally decrease ozone content in the stratosphere up to 5%.

Some events that have caused serious dents in our levels of ozone levels can be measured using Nitrate Spike Signatures.

They show us large thinning of our ozone layer occurred prior to the creation of CFC's in September of 1859 and in July 1892.

Thirdly, There is growing evidence that ozone levels at the poles is directly connected to the strength of our magnetic fields. The ever weakening fields are believed to be assisting with the size and strength of the ozone hole. Projections for the hole, if tied to magnetic levels of the planet, are for an increasing hole, despite the banning of CFC's.

It is unfortunate that many confuse ozone depletion (which could be a man induced issue) with this natural event. Please see the related link below for a peer reviewed explanation of the natural event we refer to as the hole in the ozone layer;

Bad gases such as Carbon Dioxide and other fumes harm the Ozone layer. CFC (A fluorocarbon with chlorine; formerly used as a refrigerant and as a propellant in aerosol cans) is also the main problem in which the ozone has become thinner. It has been banned in 1966, but the effects are still slow.

The ozone hole is a natural event that occurs when it is winter at a pole. UV-C is required to replace ozone that is decayed (naturally or otherwise), and in winter at a pole, it gets no UV-C, so the ozone decays to very low levels. It also heals up towards spring, such that there is no ozone hole once UV-C from the Sun arrives.

See "How did the ozone hole occur?"

More information:

The "hole" in the ozone layer is not a hole in any real sense of the word, but a thinning of the amount of ozone in the atmosphere over the Antarctic during the end of the winter. This hole has been naturally occurring for centuries and is due, almost exclusively, to the lack of sunlight over this area during the long winter. A smaller, but similar situation occurs over the Arctic during the end of it's winter months. NASA refers to this thinning area as the dimple due to the small size when compared to the Antarctic's situation. Solar activity is also a known issue for the amount of ozone in our atmosphere. The largest known thinning of that we know of actually occurred in 1859 and is believed to have been caused by solar activity. CFC's are also having some contributory affect on the amount of thinning of the ozone.

Ozone depletion was observed to increase as emissions of halo-carbons increased.

Ozone is a protective layer in the upper atmosphere. It is formed when oxygen molecules absorb short wavelength ultra violet radiations from the sun. Ozone is mostly destroyed by free radicals in the atmosphere.

When compounds like CFCs (chlorofluorocarbons) and other halocarbons are released, they are dissociated by sunlight into chloride radicals. These radicals attack ozone, thereby decreasing its concentration. This results in a thinning of the ozone layer, and in polar regions, a hole.

The holes occur at the poles, and usually in Antarctica because of the extreme cold. During the winter polar stratospheric clouds form which are able to convert gases in the atmosphere into Cl (chlorine) and ClO (chlorine monoxide). When the sun arrives at the end of winter, that is the trigger to begin. This is why the hole is largest in spring.

The ozone hole occurs once a year at each pole. The southern polar hole is larger than the northern polar hole due the fact that the southern pole is much colder than the northern pole. The size of the hole is what is of concern and is caused by chlorofluorocarbons (CFCs) and halogens from human industry.

Ozone decays naturally with time. With the axial tilt that Earth has, once each year (local winter) each pole stops receiving the UV-C that turns some oxygen into ozone. So the ozone starts decaying, and a hole forms. The only ozone the pole gets at this time, diffuses in from areas that are still receiving UV-C. So the ozone would be exceedingly thin at this time. The presence of the polar jet stream prevents the ozone at the poles (during local winter) from being replenished as it is throughout the year otherwise.

Add contaminants to the mix, and the amount of ozone drastically decreases. Water vapor (natural and Man-sourced), chlorine (most commonly Man-sourced, carried by CFCs), and bromine (most commonly natural, but likely some Man-sourced, carried for example in halon) all have shown abilities in depleting ozone.

The concentration of ozone at any point is a balance of incident UV-C from the Sun (both making and destroying ozone), UV-B from the Sun (destroys ozone when absorbed), time, and compounds that can accelerate the decay of ozone.

The southern hole is larger because it is so much colder. It is cold enough to form something known as Polar Stratospheric Clouds (PSCs). These form a deposition site for the radicals in the atmosphere that are responsible for ozone depletion. These radicals can be recycled after use so that one molecule of contaminant (chlorine) is responsible for the destruction of several thousand molecules of ozone.

Air pressure decreases with an increase in altitude because the higher you are, the less air there is above weighing down upon you.

This is because air behaves much like water. If you are swimming, the deeper you dive, the greater you feel the pressure build, because there is more water above weighing down upon you.

It is the same with air. On top of a mountain, air pressure is lower because the column of air above you is shorter. At sea level, the column of air above is taller, increasing the air pressure.

In essence: More pressure is put on because there is more air above you.

The pressure at any given altitude in the atmosphere is equal to the weight of the air directly above that point. As altitude increases, the air becomes less dense because of the smaller amount of air above that altitude. There is a corresponding decrease in pressure with an increase in altitude. Eventually you reach a point without air, and the pressure decreases to zero. That is space.
Air, like everything on earth is subject to gravity - air pressure decreases at higher altitudes because it simply has less air pressing down on it from above
Atmospheric pressure is the result of the weight of air that's above you.

As altitude increases, the amount of air under you increases, and the

weight of the air on top of you decreases.

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Also air is compressible (this means that at sea level a fixed volume contains more air molecules than the same fixed volume taken higher up) so as you go up the weight does not decease as a straight line with altitude, it drops off more rapidly as a curve.
Air Pressure is the result of the weight of all the air above you. (Note - the function of gravity in this description.) As your altitude increases, the amount of air above you decreases.