"WIND: A GIFT or A WRATH"

PART-3

“As we know that Earth is not still, but it rotates on its axis and that too from West to East, hence, causing an impact on the Global Wind Currents. What happens actually is that hot air rises from the Equator and flows towards the North and South Poles but at around 30 degree latitudes near the tropics the hot air losses some steam and begins to cool. Due to this the cool air now sink back to Earth surface and in turn returns to the Equator forming a small loop or convection cell. This cell is called Hadley Cell because the person who found this was George Hadley. Similarly around the Polar Regions, both in North and South, the sinking cold air which had started moving towards the Equator gains some heat at around 60 degree latitude or sub-polar latitude. Due to this it starts rising up in the atmosphere and in turn returns back to the Poles forming another convection cell. This cell is known as Polar Cell and I suppose the reasons are obvious. Isn’t it amazing kids? Wait let me show you a picture.” Harshit shared a picture showing Hadley Cell and Polar Cell.

“Sir truly it’s amazing. It’s hard to believe. But what happens in the middle of Hadley Cell and Polar Cell?” Sarthak asked in amusement.

“Oh yes. Kids, the Hadley Cell and Polar Cell create yet another convection cell in between. It is a moderate temperature cell which follows the similar pattern as the other two cells. This cell is called Ferrel Cell named after William Ferrel who actually found it.”

“This is completely amazing. Thank you sir for sharing this information with us.” Vayu said. Rajiv was also feeling happy by the fact that his friends have actually spared time to teach all this.

“Wait, there is some more. Let me tell you some more amazing things. The rising up of the warm air takes place all along the Equator and not just at one point. This had caused some problems in the earlier times for the sailors. Since the hot air all along the Equator rises up and flows towards the 30 degree latitudes this made equatorial region devoid of any horizontal wind, making it difficult for the early sailors to carry their sails. Hence, this region got his name as DOLDRUMS. Doldrums are a state of inactivity or stagnation. Similarly at around 30 degree latitudes both in Northern and Southern Hemisphere, sailors find it difficult to travel because the air there sinks down making the area devoid of horizontal wind. In earlier days Spanish sailors used to transport horses to their colonies in the West Indies or America. But due to no horizontal wind around these latitudes their voyage prolonged severely. This resulted in the shortage of water supply for keeping their horses alive. Hence, they started throwing the dead or the dying horses down into the ocean. This incidence gave the name HORSE LATITUDE to this region. In similar way region around 60 degrees latitude also do not receive horizontal winds. No special name is given to them. It is just known as Sub-Polar Latitudes. Apart from these regions the rest of the Earth receives at least some sort of horizontal wind. So kids these are the Global Wind currents. Moreover the Earth’s weather moves with these currents. Interesting right?” Harshit said.

“Very interesting sir.” Both said in unison and looked towards each other in amusement. No one had taught this to them before. In school they only get to know what was printed in book.

“I am amazed Harshit you know so much.” David said jokingly. “But you forgot to explain one thing.”

“What? Really? What is that Mr. Intelligent?”

“About how do Coriolis force acts on the winds.”

“Oh! Yes. But I have left only 5 more minutes than I have to go.” Harshit said feeling sad.

“Doesn’t matter dude. I will explain it. It will take just 5 minutes.”

“Oh! Really? Let us see.”

“So kids it may seem that the winds flow from north to south and from south to north as shown in the earlier pictures but this is not the case as the Earth is not still. It is rotating along its axis. This is where Coriolis force comes into action. Due to the rotation of the Earth the Coriolis force causes the wind to deflect from its path. As told by Rajiv earlier in the Northern Hemisphere the Coriolis force causes the wind to turn to their right and in the Southern hemisphere it causes the wind to turn to their left. Hence, in the northern hemisphere, between 30 degree latitude and the equator coriolis force causes the wind to flow from North-East to South-West direction. Since these winds were very helpful for European Sailors to travel to new America hence, these winds got their name as Trade Winds because of the boost they provided for trade between Europe and America. And flowing in the northern hemisphere they were called as North Easterly Trade Winds because they start from North East Direction. Similarly in Southern Hemisphere they were known as South Easterly Trade Winds because they start from South East Direction and moves to North West Direction.

Now moving up between 30 degree and 60 degree latitude as we know that wind here flows from Horse Latitude to Sub-Polar latitude, these winds also deflect from their path towards Right side in Northern Hemisphere and towards Left side in Southern Hemisphere. But since the Coriolis force is greater in these regions it seems as if winds are coming from West directions and flowing to East direction. Hence, these winds are called Prevailing Westerlies. These are the winds which cover entire US and Canada. Hence, did you see why I said that we ourselves receive winds?”
“Oh! Yes Uncle now we understood.” Sarthak and Vayu said.

“Good. Now moving further up and coming to the Polar Regions. As we know here in these regions the wind flows from Poles towards the 60 degree latitude or Sub-Polar Latitude. These winds are also deflected by the Great Coriolis force. Since these winds flow from East to West hence, these are known as Polar Easterlies. I guess now you know why these are called as Polar Easterlies.”  

“Yes, because they are present at Polar Regions.” Sarthak said.

“Yes Sarthak. With this we finish the concept of Global Winds. Like Winds Oceans also form various currents and cells but that we will tell some other time. Your Harshit sir might be getting late. See Harshit I finished it in 5 minutes.” David said teasingly.

“Yeah! Yeah! Whatever. Ok Kids we hope you have learned something today that you can tell your other classmates moreover to your teacher also. Ha ha! Now I will take leave. It was nice meeting you all. Thank you Rajiv for putting me into this conference otherwise I would have missed it. Take care all of you.” Harshit said and logged out.

“This guy I tell you. He is always in hurry. Anyways children now I will also go. We will talk some other time.” David said.

“Thank you David for giving us your time.” Rajiv said.

“Thank you so much Sir. We learned a lot today.” Kids said

“Oh! No need to thank kids. And Rajiv now you have to tell them about other winds.”

“Yeah! Sure David. Bye. Take care. Give our love to family.”

“Sure brother. Bye.” With this David also logged out.

Sarthak and Vayu started discussing whatever they had learned.

“C’mon kids it’s getting late. We will go back. Sarthak you also come with us. I will drop you back after dinner. We will inform at your home. On the way I will tell you about Local and Seasonal Winds.”

“Yippeee! You will be having dinner with us. I will ask mom to cook your favourite dish.” Vayu said enthusiastically.

On the way back home Rajiv said, “Vayu remember last summer we went to Pondicherry. Can you tell Sarthak and me what change we noticed in the weather there?”

“Oh! Yes. I very well remember Dad. Sarthak you know what we found there, the days used to extremely hot but the nights were very cold.” Vayu said.

“Really? How come?” Sarthak asked in amusement.

“Sarthak this is because of Local Winds. These winds cover a small area and only flow during a particular period of day or year. Land Breeze and Sea Breeze are type of Local Winds.”

“But how are they formed Uncle?” Sarthak asked innocently.

“I am coming to that Sarthak. As we have learned the concept of convection today, the same applies here too. Only difference is that both land and sea absorb and transfer heat differently. As we know sun rays heat the land surface faster than the sea because in the case of sea the rays of the sun travels deep down under the sea and the heating starts from the sea bed but in case of land it only has to heat up the surface. So during Day time land heats up faster and becomes warmer than the sea. And according to the concept of convection the warm air on the land becomes lighter and rises up creating a low pressure area. On the other hand air is cool above the sea so it sinks down creating a high pressure area. As we know wind flows from high to low pressure hence, here also wind flows from Sea to Land. This is known as Sea Breeze because it flows from the sea.”

“What happens in the night Dad?” Vayu asked.

“During night reversal takes place. The sea becomes hot because of the heat it had absorbed the whole day and the land becomes cooler than sea. Hence, during the night the wind flows from Land to Sea. This is called Land Breeze.” Rajiv said and took the last turn to reach their home.

“There is yet another type of winds called Seasonal Winds. When these Sea and land breezes flow over a large regions and change directions with the seasons they cause Seasonal Winds. Our favourite monsoon season is caused because of the Seasonal Winds only.” Rajiv continued. By this time they had reached to their house.

“C’mon kids, you go inside. I will park the car and come.”