How important is Dvorak Technique to measure tropical cyclone

In the past years, the world as well as India too has witnessed so many destructive cyclones. India faced hits by cyclone Fani (2019), Vayu (2019), Nisarga (2020), Amphan (2020), Gulab (2021), Yaas (2021), Tauktae (2021), Asani (2022), and very recently 'Sitrang' passed on

To save millions of lives and to take preventive measures against piles of devastation technology is immensely helpful to gauge tropical cyclone intensity. Thus, Dvorak Technique is a great discovery to forecast local meteorology and recognize cloud patterns for assessing the intensity of tropical storms.

Dvorak Technique was primarily developed in the year of 1969 and it was modified to accelerate the accuracy of forecasting tropical cyclones in 1973. This technology was set up by American meteorologist Vernon Francis Dvorak. Using satellite pictures of tropical cyclones within the North West Pacific Ocean he created this method which is now being used worldwide to analyze tropical cyclones. But unfortunately this year on 19th September he left us forever.

Several organizations around the world use this way from the very beginning to predict the power of the storm. In 1959, the establishment of the Meteorological Satellite Section of the US refers to the setup of the National Environmental Satellite, Data, and Information Service’s Satellite Analysis Branch. This branch is somehow responsible for doing Dvorak Technique to fix the vehemence of tropical cyclones. A Division under the National Oceanic and Atmospheric Administration, the National Hurricane Center’s Tropical Analysis and Forecast Branch created in 1967 use Dvorak intensity numbers for tropical cyclones and their precursors.

A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce havoc, rain, and strength. In the name of the cyclone, “Tropical” signifies the geographical origin of the system which exclusively forms almost over tropical seas. This kind of storm is mostly seen in the Pacific Ocean, Atlantic Ocean, Indian Ocean, Caribbean Sea, the Gulf of Mexico, and sometimes in the Bay of Bengal and the Arabian Sea. These tropical cyclones have different names like Hurricanes, Typhoons, Tropical storms, Tropical cyclones, and Tropical Depression among others.

Initially, Dvorak Technique calculates the vigor and consequences of tropical storms and depressions based solely on infrared satellite images which are also called infrared lights. Infrared light is electromagnetic radiation with wavelengths longer than those visible light. It is therefore invisible to the human eye. This technique compares these invisible images with some estimated visible patterns to forecast cyclonic impacts.

This method as it was originally conceived involved patterns matching cloud features with the development and decay model. But it went through advancement between the years 1970 and 1980. Calculations of cloud features become dominant in defining a cyclone’s intensity and the central pressure of the low-pressure area. A low-pressure area is a place where atmospheric pressure is lower than that of surrounding locations. This kind of area indicates cloudy windy weather with possible rain or storms while high pressure signifies lighter winds and clear skies. The formation of a low-pressure area is known as cyclogenesis which refers to the form of a cyclone. These kinds of cyclones consist of a roughly circular area of mostly calm weather at the center and this is called the “eye” of the cyclone. Typically it is 30-65 kilometers in diameter and surrounded by an “eye wall”. An eyewall is a ring of towering thunderstorms where the most severe weather and highest winds occur. Dvorak Technology uses the cloud-top temperatures within the eyewall and contrasts them with the warm temperatures within the eye itself via the use of infrared satellite images. This leads to a more objective assessment of the strength of tropical cyclones with eyes.

Due to human analysts, there are some subjective biases since sometimes tropical cyclones’ pattern fluctuates. To resolve this problem higher-resolution satellite imagery, more powerful computers, and automated techniques are being used to get a more reliable estimation. A new wind-pressure relationship in the North-West Pacific Ocean was thus devised by Atkinson and Holliday in 1975, and modified in 1977. Still keeping some subjectivity within the process, the Development of the objective Dvorak Technique began in 1998, and by 2004 a new modified Dvorak Technique was set up.

There is another method to foretell tropical cyclones which is the Saffir-Simpson Hurricane Wind Scale. It was developed by Herbert Saffir, a civil engineer, and Bob Simpson of the US National Hurricane Center. Despite the presence of this technology, the Dvorak Technique is very popular and fruit-bearing. But this method doesn’t correctly diagnose cyclonic intensity for storms like subtropical storm “Andrea” since it only applies to tropical cyclones.

Nowadays there are advanced model guidance, animations, artificial intelligence, machine learning, and modern satellite technology to help a high rate to evaluate more objectivity towards taking precautions. No doubt Dvorak Technique is a great discovery in this field.

In the past years, the world as well as India too has witnessed so many destructive cyclones. India faced hits by cyclone Fani (2019), Vayu (2019), Nisarga (2020), Amphan (2020), Gulab (2021), Yaas (2021), Tauktae (2021), Asani (2022), and very recently ‘Sitrang’ passed on. To take precautions against these fatal natural calamities this technology immensely helps. And in the future, it’ll give an objective message to forecast upcoming tropical cyclones Mandous (named by UAE), Mocha (named by Yemen), Biparjoy (named by Bangladesh), Tej (named by India), Hamoon (named by Iran) and so on.

Tuhin Sajjad SK

is a science graduate with honours in mathematics. Tuhin is a passionate Science Communicator. He writes poetry, flash fiction, docu-drama and features to communicate sci-tech.

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