C H A P T E R
N ° 11
Space Weather and the Earth’s atmospheric layers
The Earth’s atmosphere includes several atmospheric layers: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Each of these atmospheric layers interact with incoming space radiation differently. In today’s article, we will, therefore, explore these atmospheric layers to get a better understanding of their relation to space weather.
Image Credit: NOAA: Cartoon illustrating the atmospheric layers of Earth.
The troposphere
The troposphere is at an altitude of approximately 10 to 15 km above Earth. It is the Earth’s first atmospheric layer and the place we live and breathe. It is, additionally, the place where weather conditions such as rain, snow, and cloudy days are created. At the top of the troposphere before the next atmospheric layer named the stratosphere is the ‘tropopause’. It is above this region, we find airplanes. Between the tropopause and the stratosphere is where most aviation is located due to the jet streams. Jet streams are relatively narrow bands of strong wind.
During times when there are little to no Earth-directed solar activities, or when the Earth-directed solar activity is weak, no consequences can be felt within the troposphere. However, during space weather events causing things such as strong, severe, or extreme geomagnetic storms, Solar Energetic Particles (SEPs) have the potential to reach the troposphere. When it does, it increases the risk of radiation exposure to planes, pilots, and crew members onboard airplanes flying transatlantic routes or at higher altitudes.
Image Credit: FlightDeckFriend: Cartoon illustrating the first atmospheric layer of Earth named ‘troposphere’.
The stratosphere
The stratosphere is the atmospheric layer one step above the troposphere. It spans from and altitude of approximately 6-20 km to 50 km above Earth’s surface. This layer holds approximately 19 percent of the atmosphere’s gases. Within the stratosphere we find the ozone layer. This layer absorbs a portion of the incoming radiation from the Sun, preventing it from reaching the planet’s surface. The stratosphere, thus, has the ability to absorb the portion of UV-light named UVB. UVB is a kind of ultraviolet light originating from the Sun and sun lamps. This ability is important to reduce the risk of things such as skin cancer. Furthermore, the temperatures within this atmospheric layer increases with increasing height and the boundary between the stratosphere and the third atmospheric layer is called the ‘stratopause’. The stratosphere is the place where weather balloons can be found.
Image Credit: FlightDeckFriend: Cartoon illustrating the second atmospheric layer of Earth named ‘stratosphere’.
The mesosphere
The mesosphere is the thirds atmospheric layer, spanning from an altitude of approximately 50 km to 85 km. In contrast to the stratosphere, here the temperatures decrease with increasing height, consequently making the top part of the mesosphere the coldest (~ -90oC/-130oF) region within all the atmospheric layers of Earth. The mesosphere is the region sounding rockets are launched into. Sounding rockets are used for proving the upper atmospheric region and for space research. They are also used as a platform to test or prove prototypes of new components or subsystems intended for use in launch vehicles and satellites. Additionally, the mesosphere is the atmospheric region where most meteors occur and burns up. Following the mesosphere, before the thermosphere, is the mesopause. This is the boundary between the mesosphere and the thermosphere (the fourth atmospheric layer).
Image Credit: FlightDeckFriend: Cartoon illustrating the third atmospheric layer of Earth named ‘mesosphere’.
The thermosphere and ionosphere
The thermosphere is an atmospheric layer spanning from an altitude of approximately 85 km to 500 km and is where aurora borealis (northern lights) and aurora australis (the southern lights) occur. The thermosphere has been given its name due to the high temperatures found in the region – ‘thermos’ meaning ‘hot’. Here, atmospheric processes are highly dependent on the activities happening on the Sun. Within the thermosphere is the ionosphere, ranging from an altitude of approximately 60 km to 1000 km. Under normal circumstances (i.e., when there is no space weather impact) this region is able to absorb UV, X-ray, and cosmic rays. The ionosphere is, thus, an important atmospheric layer for a society’s technological systems.
However, as mentioned, the thermosphere and, thus, the ionosphere are both dependent on the Sun’s activity cycle. For example, severe and extreme Earth-directed solar activity can change the density of the ionosphere and make it thicker. Solar activities such as solar flares are intense in UV and X-ray and can, therefore, change the composition of the ionosphere on the sunlit side of Earth during a solar flare event.
Within the ionosphere is a layer named the ‘D-region’. This region is the lowest layer of the Earth’s ionosphere (~60 km to 90 km altitude) and covers the mesosphere and lower thermosphere regions of the Earth’s atmosphere. Solar activities such as solar flares can thicken this region, enabling the ionosphere to bend the path of radio waves or scatter them completely, consequently causing things such as loss of Global Positioning System (GPS) signal or communication.
The ionosphere and the D-region are very complex environments, especially during severe and extreme space weather events. Furthermore, it is very difficult to measure the ionosphere. Satellites cannot stay in the ionosphere, as it is too dense and would make the satellites re-enter the atmosphere, consequently causing them to burn up or land on terrestrial infrastructures. This means, that measurements are made by radar or rockets. However, these are difficult to move. We, therefore, only know a lot about the ionosphere at those locations and not around the whole globe. We can measure the ionosphere, but we cannot measure or see all the small and fine structures, which makes a lot of things remain unknown.
Although there is still much to learn about the ionosphere, scientists have found that this region is exposed to ionizing radiation and is able to conduct electrical currents which gets intensified during space weather events such as geomagnetic storms. This creates issues for things such as satellites, telecommunication, and Global Positioning System (GPS).
Image Credit: FlightDeckFriend: Cartoon illustrating the fourth atmospheric layer of Earth named ‘thermosphere’.
The exosphere
The exosphere is the outermost layer of the atmosphere and starts where the thermopause ends. It extends from an altitude of approximately 600 km to 10.000 km above Earth. In this layer, atoms and molecules escape into outer space, and satellites orbit the Earth. It is the atmospheric layer where the radiation exposure levels are the highest, due to the lack of protection from the Earth’s magnetosphere, as the exosphere extends beyond that. In this atmospheric region, bursts of plasma from solar activities such as solar flares can increase the radiation levels for a short amount of time.
Image Credit: FlightDeckFriend: Cartoon illustrating the fifth atmospheric layer of Earth named ‘exosphere’.
Source
NOA (2024): https://www.noaa.gov/jetstream/atmosphere/layers-of-atmosphere
Met Office (n.d.): https://www.metoffice.gov.uk/weather/learn-about/space-weather/glossary
NOA (2023): https://www.noaa.gov/jetstream/global/jet-stream
Indian Space Research Organisation, Department of Space (n.d.): https://www.isro.gov.in/soundingRockets.html
Center for Science Education (UCAR) (n.d.): https://scied.ucar.edu/learning-zone/atmosphere/mesosphere
A.P. Mitra D. Phil et al. (1978): The De-region of the ionosphere. ELSEVIER. Endeavour. Vol. 2, Issue 1. Pp. 12-21. DOI: https://doi.org/10.1016/0160-9327(78)90028-5
Carine Briand et al., (2022): Role of hard X-ray emission in ionospheric D-layer disturbances during solar flares. Springer Open. Earth, Planets and Space. Vol. 74, Article No. 41. DOI: https://doi.org/10.1186/s40623-022-01598-2
