Topic – changes in critical geographical features (including water bodies and ice-caps) and in flora and fauna and the effects of such changes.
1) What do you understand by tropospheric and stratospheric polar vortex? How is it related to deep freeze in USA?(250 words)
Why this question
Parts of USA are expected to remain colder than Antarctica in the days to come. It is important for us to understand what will cause this deep freeze.
Key demand of the question
The question expects us to first explain what polar vortex is and examine the role that it would play in the deep freeze in USA.
Structure of the answer
Introduction – Highlight the news that weather reports have predicted deep freeze in USA .
- Explain what is a polar vortex. Thereafter, explain what are tropospheric and stratospheric polar vortex
- One exists in the lowest layer of the atmosphere, the troposphere, which is where we live and where the weather happens. The other exists in the second-lowest, called the stratosphere, which is a shroud of thin air that gets warmer at higher altitudes.
- The low-level vortex in the troposphere is a large mass of brutally cold air and swirling winds coiled around omnipresent polar low pressure. The year-round cold temperature causes air to condense and shrink in size, which creates a vacuum effect that draws air inward.
The tropospheric polar vortex is the one that affects our weather. Most of the time, its harsh conditions are out of reach. But every so often, lobes of it pinch off from the main flow and crash south. This can lash the Lower 48 with piercing shots of cold, intense bouts of storminess and bitter wind chills well below zero.
- stratospheric polar vortex lives above and separate from the troposphere. It is much more compact than its tropospheric cousin. It forms in a similar way but is smoother and maintains a much sharper edge. That is because there is very little mixing with the air below it. With lots of rotational energy, this counterclockwise gyre can speed with little to slow it down.
- Explain their impact on weather – Most of the time, the stratospheric polar vortex has little impact on our weather. The two layers of the atmosphere remain largely disconnected. Once in a while, the stratospheric vortex gets disrupted – a sudden stratospheric warming event. When this happens, the vortex can split and affect the weather below it. It can cause kinks in the jet stream so that, instead of flowing west to east, there are a lot of dips and ridges. And the waves in the jet stream can disrupt the lower (tropospheric) polar vortex, break off a lobe and force it south causing extreme chill in parts of USA.
Conclusion – Summarize your answer by focussing on the impact of polar vortex.