TROPOPAUSE: CHARACTERISTICS, CHEMICAL COMPOSITION AND FUNCTIONS - ENVIRONMENT - 2024

The tropopause is an intermediate transition zone between two layers of the Earth's atmosphere. It is located between the lower layer of the atmosphere, called the troposphere, and the layer above it, the stratosphere.

The Earth's atmosphere has been divided into several layers. These layers are called "spheres" and the transition zones between the layers are called "pauses." According to its chemical composition and temperature variation, the layers of the atmosphere are the troposphere, stratosphere, mesosphere, thermosphere and exosphere.

Figure 1. Layers and transition zones of the Earth's atmosphere. Source: Josell7 The troposphere extends from the surface of the Earth up to 10 km in height. The stratosphere ranges from 10 km to 50 km in height. The mesosphere ranges from 50 km to 80 km in height. The thermosphere from 80 km to 500 km, and the exosphere from 500 km to 10,000 km in height. The latter is the limit with interplanetary space.

Tropopause characteristics

The tropopause is a region with very particular characteristics that have recently motivated its scientific study in greater detail. Being the zone of transition of properties between the troposphere and the stratosphere, it is opportune to briefly indicate the characteristics of these two layers.

The troposphere is the active layer where the meteorological phenomena that originate the climate occur, such as winds, rains, electrical storms and hurricanes. The temperature in this layer decreases with altitude.

In the stratosphere, temperature increases with altitude due to the effect of chemical reactions that give off heat (exothermic). Ozone is primarily involved, absorbing high-energy ultraviolet (UV) radiation from the sun.

The tropopause is the boundary between these two gaseous layers that have very different properties of temperature, chemical composition and general dynamics. The characteristics of the tropopause are briefly listed below.

Height

The height at which the tropopause is located above the Earth's surface is variable. It changes with latitude, with the season, and with the time of day.

The tropopause is located at an average height of 7 to 10 km in the regions of the Earth's poles, and between 16 to 18 km high in the areas of the tropics, around the equator.

In this way, the polar tropopause is warmer and is closer to the earth's surface, while the equatorial-tropical tropopause is cooler and is higher.

At the equator, the Sun's rays strike the Earth's surface perpendicularly, causing great surface heating. This heat from the earth's surface is absorbed by the air of the troposphere, which expands in this equatorial-tropical zone and increases the distance to the tropopause.

Through various scientific studies it has been determined that the global height of the tropopause has increased in recent years. It is believed that this increase could be due to the increase in greenhouse gases (GHG), the reduction of the ozone layer in the stratosphere, and the cooling of this layer.

Changes in the height of the tropopause are evidence of warming of the troposphere, called global warming.

The tropopause as a zone of calm

The tropopause constitutes a zone of relative calm, since the meteorological phenomena that originate the climate occur below this zone, in the troposphere. However, recent studies report that the tropopause presents a particular dynamic.

Temperature

In the tropopause zone the temperature remains constant, it does not decrease with height (as in the troposphere) nor does it increase with height (as in the stratosphere). The tropopause temperature is about -55 ^° C.

Discontinuity zone

The tropopause is not a continuous zone; there are breaks in this region in the areas of tropical latitudes and mid-latitudes of the Earth's northern and southern hemispheres.

Moisture storage and transport area

The tropopause acts as a large reservoir for moisture in the troposphere, and has the function of transporting water vapor into the stratosphere.

Formation of cirrus clouds

The tropopause is the region where cirrus-like clouds form, a type of tall, white clouds made up of ice crystals. They are shaped like filaments in narrow, fine bands, similar to hair curls.

Figure 2. Cirrus clouds. Source: Pixabay.com

Cirrus clouds reflect sunlight and trap the heat that the Earth emits outwards. It is not known exactly if the net balance of cirrus clouds is cooling or warming of the planet.

The appearance of cirrus clouds indicates a change in weather with low temperatures and rain within the next 24 hours.

Chemical composition of the tropopause

The tropopause represents a zone of abrupt change between the chemical composition of the troposphere and that of the stratosphere. It contains gases that come from both layers.

In the tropopause are gases from the troposphere, such as water vapor and carbon monoxide (CO). There is also ozone (O ₃), a gas that comes from the stratosphere.

Very interesting chemical reactions occur in the tropopause. Scientists are trying to study these chemical changes to get a more complete explanation of the phenomenon of global warming.

How is the tropopause studied?

To study the tropopause, samples of its gas mixture must be taken. This sampling at altitudes of up to 18 km above the earth's surface presents many difficulties.

Only a few aircraft can reach these heights. NASA has three very sophisticated aircraft equipped with special equipment to carry out these studies. These are the ER-2, DC-8 and WB-57 aircraft.

These three aircraft, coupled with a support infrastructure with satellites and radars, on-site detection equipment and remote detection, fulfill the so-called TC4 mission for its acronym in English: Tropical Composition, Clouds and Climate Coupling Experiment.

Features

The tropopause has important functions in the transport of water vapor from the troposphere to the stratosphere. It also functions as a zone for mixing gases of tropospheric origin (water vapor, carbon monoxide) with gases from the stratosphere (ozone).

The tropopause is recently being studied as an indicator of global warming of the planet and of phenomena that determine general atmospheric chemistry.

References

1. Newton, R., Vaughan, G., Hintsa, E. et al. (2018) Observations of ozone-poor air in the tropical tropopause layer. Atmospheric Chemistry and Physics. 18: 5157-5171 doi: 10.5194 / acp-18-5157-2018
2. Biernat, K., Keyser, D. and Bosart, LF (2017). Linkages Between the Great Arctic Cyclone of August 2012 and Tropopause Polar Vortices. American Geophysical Union, Fall Meeting 2017, abstract # A43D-2478.
3. Werner, B. (2017) Probing the subtropical lowermost stratosphere and the tropical upper troposphere and tropopause layer for inorganic bromine. Atmospheric Chemistry and Physics. 17 (2): 1161-1186. doi: 10.5194 / acp-17-1161-2017
4. Jensen, EJ, Pfister, L., Jordan, DE, Bui, TV, Ueyama, R. and Singh. HB (2017). The NASA Airborne Tropical Tropopause Experiment: High-Altitude Aircraft Measurements in the Tropical Western Pacific. AMS 100. Journals on line. BAMS. doi: 10.1175 / BAMS-D-14-00263.1
5. Jensen, EJ, Kärcher, B., Ueyama, R., Pfister, L., Bui, TV et all. (2018). Heterogeneous Ice Nucleation in the Tropical Tropopause Layer. Journal of Geographical Research: Atmosphere. 123 (21): 12,210-12,227.