Editorial 1 : Understand the Indian Ocean and you’ll understand much about earth
Context
The Indian Ocean is critical today to understand the earth’s overall ocean response to increasing greenhouse gases and global warming.
Home to the deadliest storms
- The Indian Ocean is famous for its dramatic monsoon winds and the bountiful rain it brings to the Indian subcontinent.
- More than a billion people depend on the moisture it supplies to quench their thirst, to replenish fisheries, and to produce food and energy.
- The warm summer months are characterised by the rapid warming of the Arabian Sea and the Bay of Bengal as well as the southern tropical Indian Ocean.
- The winds begin to turn around from a land-to-ocean direction during winter to an ocean-to-land direction as summer commences.
- The scorching heat on the subcontinent also comes with the threat of pre-monsoon cyclones.
- The North Indian Ocean doesn’t generate as many cyclones as the Pacific or the Atlantic Oceans, but the numbers and their rapid intensification have been growing ominously.
- The relatively small North Indian Ocean ensures cyclones don’t grow into the sort of hot powerhouses hurricanes and typhoons can be.
- But also the developing countries along the rim of South Asia, East Africa, and West Asia are sitting ducks in their path. Thus, cyclones tend to be the deadliest storms by mortality.
- The warm ocean supports fisheries, big and small, and fish such as anchovies, mackerel, sardines, and tuna.
- Tourists also flock to popular beaches and the corals from Lakshadweep to the Andaman-Nicobar Islands, all the way down to Reunion Island off Madagascar.
A unique configuration
- The northern boundary of the Indian Ocean is closed off by the Asian landmass, minus tiny connections to the Persian Gulf and the Red Sea.
- The southern Indian Ocean is also different from the other oceans thanks to two oceanic tunnels that connect it to the Pacific and the Southern Oceans.
- Through the first tunnel — the Indonesian seas — the Pacific Ocean dumps up to 20 million cubic metres of water every second into the eastern Indian Ocean.
- These waters also transport a substantial amount of heat. They stay mostly in the top 500 m and move through the Indian Ocean towards Madagascar.
- The Pacific waters, called the Indonesian Throughflow, wander around the Indian Ocean and affect the circulation, temperature, and salinities.
- The other tunnel connects the Indian Ocean to the Southern Ocean with two-way traffic.
- Colder, saltier and thus heavier waters flow into the Indian Ocean from the Southern Ocean below a depth of about 1 km.
- Due to the closed northern boundary, the waters slowly mix upward, and with the waters coming from the Pacific. The waters in the top 1 km eventually exit to the south.
- The mix of heat and water masses in the Indian Ocean confer some mighty abilities to affect the uptake of heat in the world’s oceans.
The little ocean that could
- The Indian Ocean is a warm bathtub despite the underwater tunnels because it is heavily influenced by the Pacific Ocean through an atmospheric bridge as well.
- The atmospheric circulation, dominated by a massive centre of rainfall over the Maritime Continent, creates mostly sinking air over the Indian Ocean.
- With global warming, the Pacific has been dumping some additional heat in the Indian Ocean. The cold water coming in from the Southern Ocean is also not as cold as before.
- Marine heat waves are also a major concern now for corals and fisheries.
- The warming Indian Ocean is affecting the wind circulation in a way that’s also affecting the amount of heat the Pacific is able to take up.
- The Pacific Ocean takes up heat in its cold, eastern tropical region, and this is crucial to determine the rate of global warming. The Indian Ocean is thus playing a role in how well the Pacific can control global warming.
- This is why, despite being the smallest tropical ocean, the Indian Ocean’s influence has become impossible to understate.
- Recall that the oceans take up over 90% of the additional heat more greenhouse gases in the atmosphere are trapping.
A hand in human evolution
- Indian Ocean may have played a role in the evolution of our ancestors as well.
- Until about three million years ago, Australia and New Guinea were well south of the equator and the Indian Ocean was directly connected to the Pacific Ocean.
- And this Indo-Pacific Ocean was in a warm state known as a ‘permanent El Niño’ — a state that was associated with permanently plentiful rain and lush green forests over East Africa. Today, this part of Africa is arid.
- The northward drift of Australia and New Guinea, which is still ongoing, separated the Indian and the Pacific Oceans around three million years ago.
- As a result, the eastern Pacific Ocean became cooler and the El Niño went from a permanent state to an episodic one, like the ones we’ve been seeing.
- This transition aridified East Africa, turning its rainforests into grasslands and savannahs.
- Researchers have also hypothesised that these changes forced our ancestors, such as chimpanzees and gorillas, to move farther and run faster.
- In the rainforests, they had an abundance of food and hiding places and didn’t have to.
Conclusion
The storied history of our neighbourhood ocean is thus a worthy thing to celebrate — and study — on World Oceans Day.
Editorial 2 : Heat: how it animates engines and global warming
Introduction
Understanding the microscopic and macroscopic characteristics of heat has been crucial for metallurgy and materials science, mining, refineries, and a large variety of chemical reactions, among other areas.
What is heat?
- In the microscope scheme, an object’s temperature is the average kinetic energy of its constituent particles.
- When two bodies at different temperatures come in contact, the temperature of the cooler one will rise and vice versa; heat here is the amount of thermal energy the bodies have exchanged to effect this temperature change.
- Macroscopically, heat is dealt with as a form of energy with specific characteristics, understood using the tools of thermodynamics and statistical mechanics, among other fields.
- A medium can absorb heat at one location and dissipate it at another — a possibility that forms the basis of many modern technologies, including thermal and nuclear power plants and air conditioning.
- Engineers have developed ways to convert heat into mechanical energy, paving the way for machines like the internal combustion engine.
How is heat used?
- The best way to understand heat is through a study on internal combustion engines (ICEs) and thermal power plants.
- An ICE converts heat to (mechanical) work, and in this sense is a practical application of a theoretical entity called the Carnot cycle.
- This cycle describes the maximum thermodynamic efficiency an engine converting heat to work can have.
- The engine has four components: a hot reservoir (a system with more heat), a cold reservoir (a system with less heat), an ideal gas in between (through which heat moves from the hot to the cold reservoirs), and a piston adjacent to the ideal gas.
- Each cycle has four steps. In the first step (isothermal expansion), the ideal gas is insulated from the cold reservoir and is exposed to the hot reservoir. Heat moves from the hot reservoir — generated by, say, the combustion of petrol — to the ideal gas. The gas particles are heated up and the gas expands, pushing on the piston.
- In the second step (isentropic expansion), the gas continues to expand even as it is insulated from both reservoirs, pushing the piston. Its temperature doesn’t change due to the insulation but it loses some energy against the piston.
- The expansion causes it to cool down as well. In these two steps, the piston has done work on its surroundings.
- In the third step (isothermal compression), the gas is exposed to the cold reservoir and deposits its leftover heat there. This time, the piston moves downwards.
- In the fourth and final step (isentropic compression), the gas is insulated from the reservoirs while the piston continues its downward motion. This act compresses the gas and warms it up again, and the cycle can begin all over again. In the last two steps, the surroundings are said to have done work on the piston.
- Similarly, in a thermal power plant, the main components are boiler, turbine, generator, condenser, and of course pumps. The ideal form of this system is the Rankine cycle, which also plays out in four steps.
- In the first (isentropic compression), a pump compresses the water to a high pressure.
- In the second (heat addition), the water is pumped to the boiler. Here, the water is heated from an energy source — like burning coal or nuclear fission — while the high pressure is maintained, turning the liquid into a saturated vapour.
- In the third step (isentropic expansion), the pressurised vapour is pumped to the turbine, where it expands to release heat and its pressure drops.
- The expansion drives the turbine’s blades, which then produce power through a generator. The cooled vapour is pumped to the condenser in the final step (heat removal), where it is condensed at a fixed pressure back to a saturated liquid form (that is, just about to vaporise).
- The condenser is functionally a heat exchanger, where a coolant like cold water takes heat away from the vapour.
How is heat related to work?
- Heat and work have the same physical dimensions. However, not all types of heat can translate to work.
- For example, if a system does work while also falling out of thermal equilibrium, it will lose some energy in the process.
- This can happen in an ICE if, say, the machine isn’t well-lubricated and the piston’s movement against the walls of the combustion chamber experiences friction.
- Such loss of ‘useful heat’ is closely related to the concept of entropy, which represents a sort of disorderliness in a system such that the corresponding heat cannot contribute to useful work.
- Likewise, when a system does work without losing or gaining heat energy — as in the isentropic expansion and compression steps of the Carnot cycle — the process is said to be adiabatic. Completely adiabatic processes are reversible.
- The various components of ICEs and thermal power plants are designed to maximise the amount of work and minimise entropy changes and other energy leaks.
Applications of heat
- Heat also has a starring role in Heating, Ventilation, and Air-Conditioning (HVAC) systems.
- Many cold countries generate and transport heat to homes and offices from centralised facilities, while individual homes also use electric heaters — which convert electric energy to heat energy by passing an electric current through a resistor — to keep people warm.
- Of late, many experts have articulated a ‘right to air-conditioning’ for the people of low- and middle-income countries suffering debilitating heat.
- Heat engines like ICEs and steam engines use the Carnot cycle. Heat pumps, which are air-conditioners that warm the air instead of cooling it, use the reverse Carnot cycle.
- Similarly, air-conditioners that are used to cool large spaces, like halls, and the insides of cars use the reverse Rankine cycle. Other cycles, depending on the heat-transporting medium and the desired operating conditions, include the Brayton, gas-generator, regenerative, Siemens, and Stirling cycles.
Conclusion
- The world is responding to climate change on two fronts: mitigation and adaptation.
- Vis-à-vis climate mitigation, researchers around the world are devising new ways to produce heat energy for various applications without involving the combustion of fossil fuels and/or finding ways to reduce emissions from existing technologies — while policymakers are finding new ways to incentivise the uptake of these solutions.
