The Living World
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Tropical Storms and General Atmospheric Circulation

Tropical storms are closely linked with the mechanisms of global atmospheric circulation. This relationship is especially visible when looking at the Hadley cell, the Coriolis effect and trade winds at the equator.

Extreme solar heating in the equatorial regions significantly increases ocean surface temperatures. As a result, warm, moisture-rich air rises, which creates a low-pressure area known as the Intertropical Convergence Zone (ITCZ). This zone is between two Hadley cells and bears the full brunt of the intense solar radiation.

A representation of Earth's atmospheric circulation cells, depicted as blue loops, demonstrating the movement of air masses. Starting from the left, the first cell, labelled "Polar cell", shows air sinking at 90°N latitude with high pressure and rising again around 60°N with low pressure. Next is the "Ferrel cell", which depicts air rising at 60°N with low pressure and sinking around 30°N with high pressure. Centred around the equator, marked as "ITCZ" (Intertropical Convergence Zone), is the "Hadley cell", which showcases air rising with low pressure and then sinking at 30°N and 30°S, both with high pressure. This pattern is mirrored for the southern hemisphere with another "Ferrel cell" and "Polar cell". The sun is illustrated shining brightly over the equator. The bottom axis denotes pressure ranging from high to low and latitude stretching from 90°N to 90°S.

Within the ITCZ, conditions are similar to those found in the ascending part of the Hadley cell. This results in the formation of thunderstorms, robust winds and heavy rainfall. At the same time, the opposite side of the Hadley circulation sees dry air descending, which creates a high-pressure zone at the surface.

The Coriolis Effect and Trade Winds

When there is a difference in atmospheric pressure, with one area having high pressure and another having low pressure, the air wants to balance things out. It is essentially seeking equilibrium. So, it moves from high-pressure areas to low-pressure areas.

This is where the trade winds and the Coriolis effect come into play. Now, when we’re close to the equator, the air movement is influenced by something called trade winds. These winds blow from the east to the west. So, if you’re standing at the equator and facing west, the wind would be blowing against your back.

A graphical depiction of Earth showcasing major wind patterns. The Earth is divided by dotted lines representing latitude, with the Equator distinctly marked. Above the equator, arrows labelled "Northeast Trade Winds" move from northeast to southwest, and above them are arrows denoting "Westerlies" moving from west to east. Below the equator, "Southeast Trade Winds" arrows move from southeast to northwest, and further south, another set of "Westerlies" arrows move from west to east. The North Pole and South Pole are labelled at the top and bottom respectively. The continents are faintly illustrated in beige against a blue ocean background.

  • Westerlies are prevailing winds that flow from the west towards the east, in the middle latitudes between 30 and 60 degrees latitude.

The trade winds combine with something called the Coriolis effect. Because the Earth is spinning, the winds don’t go straight from high to low pressure. Instead, they start to spin or rotate. North of the equator, this spin is counterclockwise, whereas, it’s clockwise south of the equator.

This rotation starts to become visible from about 5° latitude north and south of the equator. This spinning air, combined with the right temperature and moisture conditions, can start a tropical storm.

Impact of Climate Change on Tropical Storms

Climate change is expected to significantly impact the behaviour and distribution of tropical storms. Rising global temperatures are a major consequence of climate change. This could heat more of the world’s oceans to temperatures above 27°C, which is a crucial threshold for the formation of tropical storms.

This rise in ocean temperatures may cause tropical storms to become more common, including in regions previously untouched by such weather phenomena. Therefore, more areas in the world could find themselves experiencing the impacts of these storms.

Warmer conditions could also boost the intensity of these storms. Higher temperatures provide more energy for these storms, which makes them stronger and more destructive.

Therefore, on a warmer Earth, we may find ourselves dealing with more frequent and devastating tropical storms.

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