3. What do you understand by storm surge? How does a storm storm surge get formed? Discuss.
तूफ़ानी उछाल से आप क्या समझते हैं? तूफानी लहर कैसे बनती है? चर्चा करें।
Demand of the question:
It expects candidates to write their understanding about storm surge. It also expects to write the mechanism of formation of storm surge.
Storm Surge is an abnormal rise of sea level as the tropical cyclone crosses the coast. The storms produce strong winds that push the water into shore, which might lead to flooding.
Storm surge depends on intensity of the cyclone (Maximum winds and lowest pressure associated with it and Coastal bathymetry (shallower coastline generates surges of greater heights). Following is the way of formation of cyclone:
- When a cyclone is in deep ocean waters, the circulating wind pushes the ocean surface to create a vertically circulating column of water, where the surge is barely visible.
- However, as the storm moves closer to the shore, the water which is being pushed downwards by the wind cannot move any lower, so the water forces itself from the sides towards land, causing a storm surge wave.
- Although low pressure also contributes to the surge, its influence is very small, i.e., around 5%.
- Whenever a cyclone moves near coastal areas, storm surges are the biggest and most common threat to life and property.
- This phenomenon is commonly found in low-pressure systems, and the severity of the storm surge wave depends on the tides, shallowness of the water in the area, and the angle at which the water is to the cyclone.
Following are some factors which determine the intensity of storm surge:
- Strength and Size of the Storm: During a cyclone, the water level rises to form storm surges, where the strength and speed of the winds are the highest. Usually, the largest surges occur in the direction of where the wind is blowing. Due to the rotation of the earth, the surge occurs towards the right side of the cyclone in the northern hemisphere, and towards the left side in the southern hemisphere.
- Atmospheric Pressure: The force exerted by the atmospheric pressure is a smaller factor in the formation of a storm surge.
- Bottom Conditions Near Shore: Another minor factor determining the strength of a surge is whether the coastal slope is steep or shallow, and rough or smooth. A shallow and smooth ocean floor near the coast can dramatically enhance the speed and power of the storm surge, while a steep climb with rough obstructions can slow and sometimes even stop a storm surge. A wider shore will have a higher surge than a narrower shore.
- Distance from Storm Centre to Shore: For a storm surge to achieve maximum potency, the distance between the eye of the storm and the shore should neither be too close nor too far. If the distance is less, the surge cannot gather enough velocity to gain power. However, if the storm is too far, the surge will lose its gathered energy by the time it reaches the shore.
- Tides: The gravitational force of the sun and moon cause low and high tides. If the storm surge occurs during a low tide, the intensity will be significantly reduced. However, a storm surge during high tide will cause a storm tide capable of heavy destruction.
- Freshwater: Usually, before a storm reaches land, most coastal areas receive heavy rainfall, causing water levels to rise. This is especially true in areas that have a river delta, causing bigger and stronger storm surges.
- Shape and Angle of Coast to the Storm: A shore with a convex shape will have a lower surge as compared to a concave shore. Also, if the storm is moving parallel to the shore, it will cause lower and weaker storm surges as compared to a storm moving perpendicular to the coast.
- Sea Waves: When waves break onto the beach, they may collect into pools, eventually making it easier for the surge to overcome the friction of the beach, and move even further inland.
A storm surge should not be misunderstood as seiche, as Storm surge is the unusual rise in the water levels generated by a storm over and above the predicted astronomical tide. The term seiche can be defined as a wave on the surface of a lake or landlocked bay; caused by atmospheric or seismic disturbances.
Storm surge as high as 15 to 20 ft. may occur when all the factors contributing to storm surge are maximum. This storm tide inundates low lying coastal areas which have far reaching consequences apart from flooding. Hence, necessary precaution if taken will ensure the minimal loss of environment human life in the surrounding area.