Stratosphere (14-50 Kms): Stratosphere is a layer above the Tropopause extending up to 50 Kms above the surface. It is comparatively lesser turbulent than Troposphere. It has several stratified layers in it, with temperature gradually increasing from lower level to higher level of the stratosphere. This layer consists of mainly ozone, oxygen and nitrogen. Ozone layer is found in this region between 20-40 Kms above the Earth's surface. In this region it can be seen in the ranges of 2 to 8 parts per million. If the entire ozone was to be compressed to the pressure of the air above sea level the thickness would come up to 3 millimeters.
The temperature goes as high as -2˚C at the top in contrast to -85˚C at the bottom of stratosphere. Let us see the reasons behind gradual increase in temperature from bottom of the layer to the top. Before that, it is fundamental to understand that the ozone in this part of the atmosphere absorbs the Sun's higher frequency radiation in the wavelength of 200-300 nm which can be potentially damaging to the life on Earth. Ozone is pale blue, highly poisonous gas with a strong odor and it is an irritating, corrosive, colorless gas with a smell something like burning electrical wiring. It is formed when an electric spark is passed through oxygen. The presence of ozone causes a detectable odor near electrical machinery. In fact, ozone is easily produced by any high-voltage electrical arc ( Tesla coils, arc welders, as well as photo-copiers, laser printers, CRT-tubes as used in TV and PC-sets, etc). Ozone is chemically much more active than ordinary oxygen and is a better oxidizing agent.
1A : The Ozone in the top of the stratosphere interacts directly with the incoming UV-B and UV-C to break down in to oxygen molecule and oxygen atom. O3 ↔ O + O2
1B : The Oxygen in the top of the stratosphere interacts directly with the incoming UV-B and UV-C to break down in to two oxygen atoms. O2 + ℎνuv → 2O
2. The oxygen molecules and individual atoms further combine to form ozone. O + O2 ↔ O3
All the above processes go on simultaneously occur simultaneously in the layers between 20-40 Kms range of stratosphere.
Further, this region of the atmosphere is studied by sending huge air balloons also called high-altitude balloons or weather balloons. These can be used to study atmospheric conditions up to a height of 38 kms(Highest height reached by a weather balloon- BU60-1 was 53kms). This high-altitude balloons is used in the core of the PROJECT LOON by Google.
Stratopause (50-55 kms): This forms the end of stratosphere and occurs just below the Mesosphere. It has thickness of about 5 kms. The temperature reaches up to -2˚C to -15˚C in this region. The pressure is 1/1000 of the pressure at the sea level.
Mesosphere(50-100 kms): This is the layer of atmosphere between Stratopause and the Mesopause. The temperature again starts to gradually fall in this region and reaches up to -100˚C near the mesopause. This is supposedly the most unknown region of the atmosphere; it is also called Ignorosphere (as we are mostly ignorant about the layer). It is unknown to scientific analysis as this region is too high for the high-altitude air balloons to reach and too low for the satellites to orbit(due to the drag).
In spite of the reason above, observations shows that:
1. Mesosphere is the coldest of all the regions of the atmosphere, with temperatures touching -100˚C at the mesopause which is below the minimum temperature ever recorded at Antarctica.
2. Many meteoroids falling in to the atmosphere are burnt up in this region in to dust particles or the like. This can be seen as a beautiful sight; Meteor Shower, when large groups of meteors enter the atmosphere at the same interval of time and get
burnt in the mesosphere region.
3. For reasons unknown, there are lightenings and Noctilucent clouds(which are usually frozen clouds) in this region which are different from the lightenings and the clouds of the troposphere.
The temperature goes as high as -2˚C at the top in contrast to -85˚C at the bottom of stratosphere. Let us see the reasons behind gradual increase in temperature from bottom of the layer to the top. Before that, it is fundamental to understand that the ozone in this part of the atmosphere absorbs the Sun's higher frequency radiation in the wavelength of 200-300 nm which can be potentially damaging to the life on Earth. Ozone is pale blue, highly poisonous gas with a strong odor and it is an irritating, corrosive, colorless gas with a smell something like burning electrical wiring. It is formed when an electric spark is passed through oxygen. The presence of ozone causes a detectable odor near electrical machinery. In fact, ozone is easily produced by any high-voltage electrical arc ( Tesla coils, arc welders, as well as photo-copiers, laser printers, CRT-tubes as used in TV and PC-sets, etc). Ozone is chemically much more active than ordinary oxygen and is a better oxidizing agent.
1A : The Ozone in the top of the stratosphere interacts directly with the incoming UV-B and UV-C to break down in to oxygen molecule and oxygen atom. O3 ↔ O + O2
1B : The Oxygen in the top of the stratosphere interacts directly with the incoming UV-B and UV-C to break down in to two oxygen atoms. O2 + ℎνuv → 2O
2. The oxygen molecules and individual atoms further combine to form ozone. O + O2 ↔ O3
All the above processes go on simultaneously occur simultaneously in the layers between 20-40 Kms range of stratosphere.
What happens with CFCs?
Usually, the CFC are inert. Due to their inertness they diffuse as it is to higher levels of atmosphere up to stratosphere. Here, the UV radiation of wavelength 180-220 nm causes them to decompose. And the chlorine atoms formed as a result of decomposition use up the ozone molecules as well as monoatomic oxygen to form chlorine compounds and oxygen. This hinders the formation occurrence of O + O2 ↔ O3 therefore indirectly reducing the volume of ozone in the stratosphere.
Unlike Troposphere, there are no clouds or dust particles or lightenings or rain in this layer. Clouds occur very rarely above the Antarctica region and these clouds are called 'Mother of pearls' or 'Nacreous clouds'. If you can recollect, we have discussed in earlier blogs that the Earth rotates on its own axis from west to east(Counter-Clockwise). The jets traveling in the stratosphere take advantage of this rotatory motion when they have to travel from West to East. That extra push due to Earth's rotation helps the Jets to save on fuel besides decreasing the travel time.CFCl3 → CFCl22 + Cl
CF2Cl2 → CF2Cl + ClCl + O3→ ClO + O2
ClO + O → Cl + O2
O3 + O → 2O2
Further, this region of the atmosphere is studied by sending huge air balloons also called high-altitude balloons or weather balloons. These can be used to study atmospheric conditions up to a height of 38 kms(Highest height reached by a weather balloon- BU60-1 was 53kms). This high-altitude balloons is used in the core of the PROJECT LOON by Google.
Stratopause (50-55 kms): This forms the end of stratosphere and occurs just below the Mesosphere. It has thickness of about 5 kms. The temperature reaches up to -2˚C to -15˚C in this region. The pressure is 1/1000 of the pressure at the sea level.
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| Mesosphere |
Mesosphere(50-100 kms): This is the layer of atmosphere between Stratopause and the Mesopause. The temperature again starts to gradually fall in this region and reaches up to -100˚C near the mesopause. This is supposedly the most unknown region of the atmosphere; it is also called Ignorosphere (as we are mostly ignorant about the layer). It is unknown to scientific analysis as this region is too high for the high-altitude air balloons to reach and too low for the satellites to orbit(due to the drag).
In spite of the reason above, observations shows that:
1. Mesosphere is the coldest of all the regions of the atmosphere, with temperatures touching -100˚C at the mesopause which is below the minimum temperature ever recorded at Antarctica.
2. Many meteoroids falling in to the atmosphere are burnt up in this region in to dust particles or the like. This can be seen as a beautiful sight; Meteor Shower, when large groups of meteors enter the atmosphere at the same interval of time and get
burnt in the mesosphere region.
3. For reasons unknown, there are lightenings and Noctilucent clouds(which are usually frozen clouds) in this region which are different from the lightenings and the clouds of the troposphere.
 |
| Night clouds or Noctilucent clouds |
But why is mesosphere the coolest?
Well, the mesosphere is at 55 kms to 100 kms and is mostly empty i.e., it does't have significant amount of gas molecules. Reason#1: Due to the absence of gas molecules, the extent of heat absorbed by the molecules is negligible. Of the gas molecules present, CO2 dominates. Reason#2: This is how it goes: CO2 molecules move around in space -> They collide with other molecules of gases(CO2 or other) -> They get excited -> After excitation, they eventually reach their ground state(de-excitation) after a while -> During this de-excitation, they emit radiation(photons) -> This radiation in the form of photons, travel up in space, away from the mesosphere -> Since radiation is traveling 'away' from the mesosphere, it makes the mesosphere cool. Both Reason#1 and Reason#2 are responsible for the decreasing temperatures in mesosphere as we travel away from the earth's surface.
Mesopause(100-105 kms) : This layer, similar to a any other 'pause' layer like tropopause or stratopause, is an intermediate layer. It is the layer sandwiched between thermosphere and mesosphere. An interesting feature is that, the summer temperatures in mesopause are lower than the winter temperatures. This is called the Mesopause Anomaly. The reason although needs us to dig deeper in to the subject. One more important thing to be noted is that the same CO2 which heats up the Earth in the Troposphere(due to Green-House effect) cools the mesosphere-mesopause due to what is called as Radiative Cooling effect. Scientists say that with increasing CO2 content on Earth, the troposphere gets hotter and at the same time, the mesosphere shall be getting colder. Although the magnitude of temperature raising(in Troposphere) and falling(in Mesosphere) might not be proportional.
Thermosphere(105 kms - 1,90,000 kms) : This is the final layer of Earth's atmosphere. This extends from the end of Mesopause to outer space, where earth's gravitation will not be felt. Thermosphere is divided in to two sub-layers: Ionosphere and Exosphere.
Ionosphere(90-1000 kms): This layer actually extends from 90 kms(mesosphere) to about 1000 kms. This layer gets extremely hot as we travel away from the surface of the Earth. The upper part of this layer is ionized by the Sun i.e., this layer is so hot that the molecules present in this layer are broken apart by sun's radiation in to ions and electrons. This is how it goes: Molecules are present in this layer -> Dangerous radiations of all frequencies reach this layer from the Sun -> The photons of this radiations are absorbed by the electrons in the molecules and get loose from the molecule -> As the electron leaves the molecule, the molecule becomes an ion -> This process happens in bulk masses all over the Ionosphere resulting in monoatomic particles(ions and electrons). Although ionosphere comprises of large number of ions and electrons, the charge is balanced as there are equal number of ions as that of ions. It is to be noted that Ionization(splitting of a molecule in to monoatomic particles) happens during the day time i.e., in presence of sun's radiation. At night time, the reverse process can happen in the absence of such radiation. However, in the upper layers of Ionosphere the ions and electrons are always present due to the high temperatures. The temperatures of this layer just keeps increasing as you go up.
Ionosphere is of significant use to humans as they help in transmission of radio waves; the ions present especially in the top most layers of Ionosphere reflect the high frequency(HF) radio waves transmitted from Earth, back to Earth and thus enable communication. This goes like this: HF waves are transmitted in to space -> They reach the ionosphere and the electrons of this layer strongly reflect the waves -> Due to the reflection, the waves are thus transmitted back to Earth. The waves are transmitted from Earth in such an angle that the waves are reflected to the desired location. Further, Ionosphere is the stage for one more important event : The Auroras - Click to understand Auroras and the reason for their formation and so on.
Exosphere(1000-1,90,000 kms): Exosphere has two parts. The lower part called Exobase extending up to several thousand kilometers and the upper part, the Exosphere extending as high as 1,90,000 kms(Roughly half the distance to the moon). This layer being a part of Thermosphere has temperature continuously raising up and in most cases cannot be specified. Exosphere is the transitional phase between atmosphere and the interplanetary space.
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