13 June 2024
Secondary Eyewall Forms in Wind Shear

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Secondary eyewall formation (SEF) is a common phenomenon in intense tropical cyclones (TCs), occurring in about 80% of cases. SEF can significantly impact TC intensity, making it challenging to predict TC intensity. This study uses idealized simulations to investigate the formation of secondary eyewalls in TCs under different upper- and lower-layer vertical wind shear conditions. The results show that SEF can occur in both upper- and lower-layer vertical wind shear, and the characteristics of SEF vary depending on the shear conditions.

Secondary Eyewall Formation in Tropical Cyclones



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Introduction

Tropical cyclones (TCs) are among the most powerful and destructive natural phenomena on Earth. They can cause widespread damage and loss of life, particularly when they make landfall. One of the most fascinating and challenging aspects of TCs is the formation of **secondary eyewalls**.

What is **Secondary Eyewall Formation**?

**Secondary eyewall formation** (SEF) is a process in which a new eyewall forms outside the primary eyewall of a TC. This can lead to a period of increased intensity, as the two eyewalls compete for energy. However, SEF can also lead to a weakening of the TC, as the new eyewall can steal energy from the primary eyewall.

The Role of **Vertical Wind Shear**

**Vertical wind shear** is a measure of the difference in wind speed and direction between different levels of the atmosphere. It is a key factor in determining whether or not SEF will occur. In general, SEF is more likely to occur when there is strong **vertical wind shear**.

**Upper-Layer and Lower-Layer Vertical Wind Shear**

In a recent study, researchers investigated the characteristics of SEF in both **upper-layer** and **lower-layer vertical wind shear**. They found that SEF was only present in **upper-layer vertical wind shear** at a relatively low shear height. Fake SEF was present in **upper-layer vertical wind shear** at a relatively high shear height and in **lower-layer vertical wind shear**.

The Importance of Stratiform Clouds

The researchers also found that broad stratiform clouds were located in the downwind sector of principal rainbands before **SEF**. Active convection was produced on the inner side of the stratiform clouds, leading to the final SEF.

Implications for TC Intensity Forecasting

The findings of this study have important implications for TC intensity forecasting. By better understanding the role of **vertical wind shear** in SEF, forecasters can better predict when SEF is likely to occur and how it will affect the intensity of the TC.

Wrapping Up

**Secondary eyewall formation** is a complex and challenging phenomenon that can have a significant impact on the intensity of tropical cyclones. By better understanding the role of **vertical wind shear** in SEF, scientists can improve their ability to forecast TC intensity and help to protect lives and property.

FAQ’s

1. What is Secondary Eyewall Formation (SEF)?

SEF is a process in which a new eyewall forms outside the primary eyewall of a tropical cyclone (TC). This can lead to a period of increased intensity, as the two eyewalls compete for energy, or a weakening of the TC, as the new eyewall can steal energy from the primary eyewall.

2. What is the Role of Vertical Wind Shear in SEF?

Vertical wind shear is a measure of the difference in wind speed and direction between different levels of the atmosphere. It is a key factor in determining whether or not SEF will occur. In general, SEF is more likely to occur when there is strong vertical wind shear.

3. What are Upper-Layer and Lower-Layer Vertical Wind Shear?

Upper-layer vertical wind shear is the difference in wind speed and direction between the upper and lower levels of the atmosphere, while lower-layer vertical wind shear is the difference in wind speed and direction between the lower and middle levels of the atmosphere.

4. What is the Importance of Stratiform Clouds in SEF?

Broad stratiform clouds are often located in the downwind sector of principal rainbands before SEF. Active convection is produced on the inner side of the stratiform clouds, leading to the final SEF.

5. How do the Findings of this Study Affect TC Intensity Forecasting?

The findings of this study have important implications for TC intensity forecasting. By better understanding the role of vertical wind shear in SEF, forecasters can better predict when SEF is likely to occur and how it will affect the intensity of the TC, helping to protect lives and property.

Links to additional Resources:

https://journals.ametsoc.org/view/journals/atsc/48/12/JCLI-D-19-0031.1.xml https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JD033324 https://link.springer.com/article/10.1007/s00382-021-05802-9

Related Wikipedia Articles

Topics: Secondary eyewall formation (SEF), Tropical cyclones, Vertical wind shear

Tropical cyclone
A tropical cyclone is a rapidly rotating storm system with a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its location and strength, a tropical cyclone is called a hurricane (), typhoon (), tropical storm,...
Read more: Tropical cyclone

Wind shear
Wind shear (or windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizontal wind shear. Vertical wind shear is a change in wind speed or direction...
Read more: Wind shear

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