Ridges are elongated high-pressure areas in the atmosphere, bringing clear skies and stable weather. They appear as "U" or "V" shapes on weather maps and influence airflow, causing clockwise winds in the Northern Hemisphere. Ridges can block weather systems and lead to prolonged dry or warm conditions.
What is Coriolis effect?
The Coriolis effect is the deflection of moving objects due to Earth's rotation. In the Northern Hemisphere, objects deflect right, while in the Southern Hemisphere, they deflect left. This impacts global wind patterns, ocean currents, and weather systems like cyclones.
What are mid-level troposphere winds?
Mid-level troposphere winds are winds found at altitudes of about 10,000 to 20,000 feet above sea level. These winds, typically in the 700-500 hPa pressure levels, guide weather systems like cyclones and fronts. They often consist of westerlies and play a key role in storm development.
Does WD split over Himalayas?
Western Disturbances (WD) often split over the Himalayas due to the region's complex terrain. The northern branch moves towards the Tibetan Plateau, while the southern branch can descend into the plains. This splitting affects precipitation patterns in North India and adjoining areas.
What is HPA unit?
HPA (hectopascal) is a unit of pressure commonly used in meteorology. One hPa equals 100 pascals or 1 millibar, making it suitable for measuring atmospheric pressure. Standard sea-level pressure is about 1013 hPa.
What are shear zones?
A shear zone is an area in the atmosphere where wind speeds change abruptly with height or direction. It typically occurs between different layers of the atmosphere, like between the lower and upper troposphere. Shear zones can intensify storms or create turbulence in the atmosphere.
What are convergence?
Convergence occurs when two air masses or winds meet and are forced to rise. This upward movement of air leads to cloud formation and can enhance precipitation. It typically happens near low-pressure systems or at the boundaries of different air masses.
What are divergence?
Divergence occurs when air moves away from a central point, usually in the upper atmosphere. It leads to sinking air at the surface, contributing to clear skies and fair weather. Divergence is important in the development of high-pressure systems.
What is a trough?
A trough is an elongated area of low pressure in the atmosphere, typically associated with unsettled weather. It causes air to rise, leading to cloud formation and precipitation. On weather maps, troughs appear as "U" or "V" shapes, often indicating stormy conditions.
How do we classify a system as Low Pressure, Depression, etc.?
Here are the classifications of weather systems with hPa values and corresponding wind speeds in both knots and km/h:
Low Pressure:
- **Pressure**:1006 hPa
- **Wind Speed**: Generally light to moderate (17 knots or 31 km/h).
Well Marked Low Pressure:
- **Pressure**: 1004 hPa
- **Wind Speed**: Generally light to moderate (17 knots or 31 km/h).
Depression:
- **Pressure**: 1003 hPa
- **Wind Speed**:Generally light to moderate (17 -27 knots or 31 - 49 km/h).
Deep Depression:
- **Pressure**: 1001 hPa
- **Wind Speed**: 28 to 33 knots (60 to 61 km/h).
Cyclone:
- **Pressure**: 1000 -995 hPa
- **Wind Speed**: 34 to 47 knots (62 to 88 km/h).
Severe Cyclone:
- **Pressure**: Below 995 hPa
- **Wind Speed**: 48 to 63 knots (89 to 117 km/h).
Severe Cyclone:
- **Pressure**: Below 995 hPa
- **Wind Speed**: 48 to 63 knots (89 to 117 km/h).
Very Severe Cyclone:
- **Pressure**: Below 995 hPa
- **Wind Speed**:64 to 89 knots (118 to 166 km/h).
Extremly Very Severe Cyclone:
- **Pressure**: Below 995 hPa
- **Wind Speed**: 90 to 119 knots (167 to 221 km/h).
*These values help determine the intensity and potential danger of each weather system.*
When does a coastal station start experiencing bad weather associated with a Cyclone?
Coasts come under the influence of bad weather in the form of heavy rain, gale winds (exceeding 65 kmph) when the cyclone moves closer to the coast within 200km. Heavy rainfall generally commences about 9-12 hours before cyclone landfall. Gale force winds commence about 6-9 hours in advance of cyclone landfall. Maximum storm surge may appear at or near the landfall time.
In which direction of a storm the surge will appear?
The on-shore wind gives rise to storm surge. Thus, the forward right sector of a storm gives rise to storm surge.
What is surge?
A surge refers to an abnormal rise in sea level caused by strong winds and low pressure, often during a tropical cyclone. This results in coastal flooding, especially when combined with high tide. It can cause severe damage to infrastructure and coastal areas.
What is landfall of a cyclone?
Landfall occurs when a tropical cyclone's center moves across the coast, causing peak storm surge, strong winds, and heavy rains. A direct hit involves similar effects but the storm's center remains offshore.
What is the size of a tropical cyclone over the north Indian Ocean?
The size of a Tropical Cyclone over Indian seas varies from 50-100 km radius to 2000 km with an average of 300–600 km.
What is the "eye"? How is it formed and maintained? What is the "eye-wall"? What are "spiral bands"?
- The "eye" of a cyclone is a calm, clear center surrounded by the most intense part of the storm. It forms when the central low-pressure area causes air to rise, creating a calm space at the center.
- The "eye-wall" is a ring of tall, intense thunderstorms surrounding the eye, where the strongest winds and heaviest rains occur.
- "Spiral bands" are curved rain bands of clouds that spiral inward toward the cyclone’s center, bringing heavy rainfall and winds. These bands extend outward and contribute to the storm's overall structure.
What is the wind structure in a cyclone?
The ideal wind and cloud distribution in a cyclone is shown in the following figure. The band of maximum winds may vary between 10 and 150 km. In this belt, speed decreases rapidly towards the eye of the cyclone. But it decreases slowly and in an irregular fashion outward from the eye wall.
How do cyclones form and intensify?
Tropical cyclogenesis requires warm ocean waters of at least 26.5°C to fuel the cyclone's heat engine. The atmosphere must cool rapidly with height to support moist convection, which is essential for cyclone development. A minimum distance of 500 km from the equator is necessary to provide sufficient Coriolis force for maintaining low pressure. Pre-existing near-surface disturbances with sufficient vorticity and low vertical wind shear (less than 10 m/s) are crucial for cyclone formation. Despite favorable conditions, not all disturbances develop into cyclones, but these criteria are well-suited for the north Indian Ocean.
What is the role of easterly wave on cyclogenesis in the north Indian Ocean?
Lower tropospheric westward traveling disturbances, known as easterly waves, serve as seedling circulations for many tropical cyclones, moving west in trade wind flow with a period of 3-4 days and a wavelength of 2000-2500 km. The relationship between the number of these waves and tropical cyclone activity over the north Indian Ocean each year is unknown.
What is the annual frequency of Cyclones over the Indian Seas? What is its intraannual variation?
The average annual frequency of tropical cyclones in the north Indian Ocean (Bay of Bengal and Arabian Sea) is about 5 (about 5-6 % of the Global annual average) and in the globe is about 80. The frequency is more in the Bay of Bengal than in the Arabian Sea, the ratio being 4:1. The monthly frequency of tropical cyclones in the north Indian Ocean display a bi-modal characteristic with a primary peak in November and secondary peak in May. The months of May-June and October-November are known to produce cyclones of severe intensity. Tropical cyclones developing during the monsoon months (July to September) are generally not so intense.
How many cyclones cross different coastal states of India?
The frequency of severe cyclonic storms is maximum for Andhra Pradesh, while that of cyclone is maximum for Orissa. Considering the west coast, Gujarat is most vulnerable.
When does a coastal station start experiencing bad weather associated with a Cyclone?
Coasts come under the influence of bad weather in the form of heavy rain, gale winds (exceeding 65 kmph) when the cyclone moves closer to the coast within 200km. Heavy rainfall generally commences about 9-12 hours before cyclone landfall. Gale force winds commence about 6-9 hours in advance of cyclone landfall. Maximum storm surge may appear at or near the landfall time.
In which direction of a storm the surge will appear?
The on-shore wind gives rise to storm surge. Thus, the forward right sector of a storm gives rise to storm surge.
What is surge?
A surge refers to an abnormal rise in sea level caused by strong winds and low pressure, often during a tropical cyclone. This results in coastal flooding, especially when combined with high tide. It can cause severe damage to infrastructure and coastal areas.
What is landfall of a cyclone?
Landfall occurs when a tropical cyclone's center moves across the coast, causing peak storm surge, strong winds, and heavy rains. A direct hit involves similar effects but the storm's center remains offshore.
What is the size of a tropical cyclone over the north Indian Ocean?
The size of a Tropical Cyclone over Indian seas varies from 50-100 km radius to 2000 km with an average of 300–600 km.
What is the "eye"? How is it formed and maintained? What is the "eye-wall"? What are "spiral bands"?
- The "eye" of a cyclone is a calm, clear center surrounded by the most intense part of the storm. It forms when the central low-pressure area causes air to rise, creating a calm space at the center.
- The "eye-wall" is a ring of tall, intense thunderstorms surrounding the eye, where the strongest winds and heaviest rains occur.
- "Spiral bands" are curved rain bands of clouds that spiral inward toward the cyclone’s center, bringing heavy rainfall and winds. These bands extend outward and contribute to the storm's overall structure.
What is the wind structure in a cyclone?
The ideal wind and cloud distribution in a cyclone is shown in the following figure. The band of maximum winds may vary between 10 and 150 km. In this belt, speed decreases rapidly towards the eye of the cyclone. But it decreases slowly and in an irregular fashion outward from the eye wall.
How do cyclones form and intensify?
Tropical cyclogenesis requires warm ocean waters of at least 26.5°C to fuel the cyclone's heat engine. The atmosphere must cool rapidly with height to support moist convection, which is essential for cyclone development. A minimum distance of 500 km from the equator is necessary to provide sufficient Coriolis force for maintaining low pressure. Pre-existing near-surface disturbances with sufficient vorticity and low vertical wind shear (less than 10 m/s) are crucial for cyclone formation. Despite favorable conditions, not all disturbances develop into cyclones, but these criteria are well-suited for the north Indian Ocean.
What is the role of easterly wave on cyclogenesis in the north Indian Ocean?
Lower tropospheric westward traveling disturbances, known as easterly waves, serve as seedling circulations for many tropical cyclones, moving west in trade wind flow with a period of 3-4 days and a wavelength of 2000-2500 km. The relationship between the number of these waves and tropical cyclone activity over the north Indian Ocean each year is unknown.
What is the annual frequency of Cyclones over the Indian Seas? What is its intraannual variation?
The average annual frequency of tropical cyclones in the north Indian Ocean (Bay of Bengal and Arabian Sea) is about 5 (about 5-6 % of the Global annual average) and in the globe is about 80. The frequency is more in the Bay of Bengal than in the Arabian Sea, the ratio being 4:1. The monthly frequency of tropical cyclones in the north Indian Ocean display a bi-modal characteristic with a primary peak in November and secondary peak in May. The months of May-June and October-November are known to produce cyclones of severe intensity. Tropical cyclones developing during the monsoon months (July to September) are generally not so intense.
How many cyclones cross different coastal states of India?
The frequency of severe cyclonic storms is maximum for Andhra Pradesh, while that of cyclone is maximum for Orissa. Considering the west coast, Gujarat is most vulnerable.
What is MJO (Madden-Julian Oscillation)?
The Madden-Julian Oscillation (MJO) is a tropical atmospheric disturbance that moves eastward, influencing rainfall and convection. It has two phases: enhanced convection (increased rainfall) and suppressed convection (dry conditions). The MJO affects weather patterns, including monsoons and cyclone development.
What is ITCZ (Intertropical Convergence Zone)?
The ITCZ is a region near the equator where the trade winds from both the northern and southern hemispheres converge. This causes warm, moist air to rise, leading to frequent cloud formation and heavy rainfall. It plays a key role in tropical weather systems.
What is the Pull Effect?
The Pull Effect refers to the phenomenon where a low-pressure area, such as a cyclone, "pulls" surrounding air toward it. This causes an influx of moist air, increasing wind speeds and contributing to the development and intensification of the storm.
What is the Pacific Ridge & Arabian Ridge?
The Pacific Ridge is a high-pressure system over the Pacific Ocean, influencing the weather in the western Pacific region. The Arabian Ridge is a high-pressure system over the Arabian Sea and surrounding areas, affecting weather patterns over the Indian subcontinent and the Arabian Peninsula.
What is IOD (Indian Ocean Dipole)?
The Indian Ocean Dipole (IOD) is a climate phenomenon where sea surface temperatures in the western and eastern parts of the Indian Ocean differ. Positive IOD leads to warmer temperatures in the western Indian Ocean, while negative IOD causes cooler temperatures, both affecting regional rainfall patterns and monsoon behavior.
What is El Niño and La Niña?
El Niño is the warming of sea surface temperatures in the central and eastern Pacific Ocean, leading to global weather disruptions like droughts, floods, and altered storm patterns. La Niña is the opposite, with cooler-than-average temperatures in the Pacific, causing different but similarly disruptive weather patterns globally.