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Optical filters near infrared show power of Typhoon Haima

Super Typhoon Haima brought dramatic storm conditions to the Philippines and China in mid-October, and NASA were able to track its progress using optical filters near infrared to detect the likely power of the storm cell.

Communities in the northern Philippines were badly hit by the storm, while the city of Hong Kong went into lockdown as the typhoon made its second landfall in China. NASA satellite data showed why it was so powerful, with optical filters near infrared allowing the NASA-NOAA Suomi NPP satellite’s Visible Infrared Imaging Radiometer Suite to picture not only the visual storm, but also the temperatures in the clouds.

Observing the storm with longwave pass filters

On October 18th, infrared analysis showed that the coldest temperatures in the typhoon, around the eyewall, reached -53 degrees Celsius (220 Kelvin). NASA described this as an indication of “very powerful thunderstorms with the capability to generate very heavy rainfall”.

Longwave pass filters allow for optical imaging near infrared, by blocking out the shorter wavelengths of visible and ultraviolet light. This allows for thermal imaging of objects – including very large formations like Super Typhoon Haima – to detect features that relate specifically to temperature, rather than to characteristics that can be seen in the visible light spectrum.

Predicting trends using optical filters

This is in spite of the fact that the storm was downgraded from ‘super typhoon’ to ‘typhoon’ status after evidence that its most powerful centre was decreasing in ferocity. “Microwave imagery continues to show concentric eyewalls and an apparent eyewall replacement cycle,” the Joint Typhoon Warning Centre stated. “The eyewall replacement as well as interaction with land has contributed to the recent weakening trend.”

An area extending some 60 miles outwards from the centre of the storm was classified as experiencing typhoon-strength winds at that time, while an area of 205 miles radius was battered by tropical storm force winds.

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