We had learnt about the Variations in Tropopause in our earlier post. These variations are quite perceptable and abrupt in certain latitudes. In this lesson, we shall understand about the breaks in the Tropopause.
FIRST BREAK
When we say breaks or folds, we mean to say that in these places we can observe a clear or distinct change in the temperature. These changes in temperature would also result in change in thickness of the tropopause. The breaks in the tropopause are because of three cells called the Hadley, Farrell and Polar cells.
The first of these breaks would be found around 40 degrees of latitude. In this break, the warm air circulating from the equator meets the cooler air circulating from mid latitudes. This temperature difference in the troposphere creates a height change of the tropopause.
Due to this break come on we can call the tropopause between the Equator and 35 or 40 degrees of latitude as Tropical Tropopause. In terms of pressure levels, tropical tropopause is found at 100 HPa levels. This is the tropopause which you can find prevalent across India, since our country falls between equator to 40 degrees north. The height of tropical tropopause is approximately 16 to 16.5 kilometres above the earth surface.
SECOND BREAK
The second tropopause break is found around 55 to 60 degree latitude where cool polar air meets warm tropical air. Middle Tropopause is found between the Tropical and Polar Tropopause due to this break. In terms of pressure levels, Mid Tropopause is found at 200 hPa levels.
At times, this break could affect parts of North India above 23 degree latitude in winters. The average height of this tropopause is around 11.5 Kilometres. The average temperature could be around -45 degree centigrade. Sub-tropical Jet Steam can be found at the southern end of Mid Tropopause.
THIRD BREAK
The last of the tropopause breaks occurs at even greater latitudes and is evident mainly in the Northern hemisphere and in winter. At this break, very cold Arctic air meets the comparatively less colder polar air. At this latitude also there is a distinct change in the tropopause.
Due to this break, the tropopause beyond 60 degrees is called as the polar tropopause. In terms of pressure levels, Polar Tropopause is found at 300 HPa levels. We may observe Polar Front Jet-stream at the southern end of polar tropopause.
JET STREAMS AND CAT
The height of tropopause does tell us a few other things. As a result of very low densities in the upper atmosphere, the upper winds tend to be very strong and in some cases form narrow bands. These winds near the tropopause are called Jet Streams.
Jet streams can be beneficial if our flight is in the same direction as that of the jet stream while it can be a challenge if our flight is in the opposite direction. These jet streams is likely to cause significant turbulence. We call this Clear Air Turbulence, or CAT.
In our next post, we shall learn about Stratosphere and Stratopause which is the next layer in the atmosphere. The study of stratosphere is just for understanding since stratospheric flights are conducted mostly by Airforce and other Military Aviators.