The temperature found at the upper limit of mesosphere is :

Question

Accepted Answer

The correct option is 3:

The correct option is 3: The temperature found at the upper limit of the mesosphere (known as the mesopause) is approximately $-100^{\circ}C$. The mesosphere is the third layer of the Earth's atmosphere, extending from about 50 km to 85 km above the surface. In this layer, the temperature decreases rapidly with increasing altitude because there is very little absorption of solar radiation. The mesopause, marking the transition to the thermosphere, is the coldest place in Earth's atmosphere. At this boundary, the atmosphere reaches its minimum temperature, typically ranging from $-90^{\circ}C$ to $-100^{\circ}C$ (or $-130^{\circ}F$), which is why $-100^{\circ}C$ is the accurate choice.

The incorrect option is 1: Option 1, $+80^{\circ}C$, is incorrect because this temperature is found at the upper limit of the stratosphere, known as the stratopause, where ozone absorption causes warming. The temperature trend in the mesosphere is the opposite: it decreases with height, reaching extreme cold at the top. An extremely high positive temperature like this is characteristic of an entirely different boundary layer in the atmosphere. The mesopause, as the coldest part of the atmosphere, cannot have a positive temperature.

The incorrect option is 2: Option 2, $-180^{\circ}C$, is incorrect because this temperature is significantly colder than the minimum temperature observed at the mesopause. While the mesopause is the coldest layer, temperatures generally do not drop as low as $-180^{\circ}C$. The lower boundary of the mesosphere (stratopause) is already around $0^{\circ}C$, and the drop over the mesosphere's altitude results in temperatures closer to $-100^{\circ}C$.

The incorrect option is 4: Option 4, $+100^{\circ}C$, is incorrect as temperatures in the mesosphere do not reach positive values. Temperatures this high (or much higher) are characteristic of the thermosphere, which lies above the mesopause, where atmospheric density is extremely low and molecules absorb high-energy solar radiation. The mesopause is a boundary between the cooling mesosphere and the warming thermosphere, and its temperature is profoundly negative.