General Knowledge - World Geography - Discussion

Ionosphere and exosphere are the parts of the thermosphere. So, thermosphere and exosphere are included in the Ionosphere.

Is the ionosphere the topmost layer?

The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation.

http://en.wikipedia.org/wiki/Ionosphere

The ionosphere is a shell of electrons and electrically charged atoms and molecules that surrounds the Earth, stretching from a height of about 50 km to more than 1000 km. It owes its existence primarily to ultraviolet radiation from the Sun.

Because ionosphere and exosphere are parts of thermosphere.

I think option (b) is the correct answer because there is five distinct layers of atmosphere i.e. troposphere, stratosphere, mesosphere, thermosphere and exosphere. So basically ionosphere is the only part of thermosphere because the dynamics of the thermosphere are dominated by atmospheric tides which are driven by the very significant diurnal heating. Atmospheric tides dissipate collision between the neutral gas and the ionospheric plasma.

I don't think mesosphere includes the answer.

Answer should be thermosphere only.

The ionosphere is a region of the atmosphere that is ionized by solar radiation. It is responsible for auroras. During daytime hours, it stretches from 50 to 1, 000 km and includes the mesosphere, thermosphere, and parts of the exosphere.

However, ionization in the mesosphere largely ceases during the night, so auroras are normally seen only in the thermosphere and lower exosphere.

Ionosphere and exosphere are part of thermosphere itself. So the question should be reconsidered.