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Analysing Typhoons for Future Use
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Analysing Typhoons for Future Use

NASA's Tropical Rainfall Measuring Mission (TRMM) satellite captured a typhoon in mid-growth on the third of December 2012. At that time, the typhoon, codenamed Bopha was a category 3 storm, and was still intensifying, growing towards a category 4 as it headed for the Philippines . It made landfall 18 hours later.

What made this particular typhoon special was TRMM. The satellite was able to capture in full 3D, the development of the storm as it grew over this 18 hour period, and was able to measure in unprecedented detail, the precise structures the typhoon developed, and how it developed them as it crossed the open water.

Whilst current virtual environments are nowhere near large enough to make use of a full-size typhoon as a weather system, this kind of data is excellent in the fight to understand precisely how they form, and what factors guide their development. The scope of our environments are growing in pace with developments in computing capability and interface development, so there will come a time when we are ready to implement these things outside of dedicated weather simulations.

Of course, that particular area of VR research – the weather simulator – is where such data will be useful the earliest. As we gather more information on what makes a typhoon tick, so we are able to more accurately predict their course and size in simulation, and save many lives.

TRMM's main advantage is its radar system, which is the most sensitive anyone has ever used to date. The radar system is best compared to a high-definition camera with a flash that reveals vertical structure. The TRMM radar has 5 km (3.1 mile) horizontal resolution and 250 meter(820 foot) vertical resolution, giving a three dimensional image of every cloud that contained particles the size of raindrops, and every chunk of ice large enough to fall out of its cloud.

In this particular case, TRMM managed to discern that Bopha's main engine consisted of two hot towers simultaneously reaching a 15.5 km (9.6 mile) altitude on the northeast side of the eyewall where the storm's forward motion is added to the counter-clockwise winds circling under the eyewall. TRMM studies have suggested that even a single hot tower exceeding a 14.5 km (9 mile) height may be sufficient to indicate intensification is on-going. At the base of the hot towers, radar reflectivity exceeded 45 dBZ indicating heavy rainfall (as shown in deep red in the image).
As a third indicator, the TRMM radar saw a double eyewall, two concentric rings of intensity storm cells exceeding a 12 km (7.4 miles) altitude. Yellows and greens indicate locations inside of the typhoon's clouds where updrafts were lifting precipitation-size ice between 9 and 12 km (5.5 and 7.4 miles) above the ocean. Concentric eyewalls are generally evidence of an eyewall replacement cycle, which can be associated rapid intensification.

Fourth, the TRMM Lightning Imaging system (LIS) saw two lightning flashes in the inner edge of one of the eyewall hot towers. Lightning flashes are relatively rare in eyewalls, even in the eyewalls of intensifying tropical cyclones. Lightning tends to occur where updrafts are strong enough to suspend in mid-air a mix of supercooled water and grauple or hail-sized chunks of ice. Such large chunks of ice can only form when updrafts repeatedly "bob" ice particles up and down through a lower cloud layer with liquid water droplets and then a higher cloud layer cold enough to promote freezing.
In addition to lightning, radar, and passive microwave observations, the TRMM satellite also simultaneously observes cloud-top temperatures, which provide a fifth indicator that the inner-core energy-conversion machinery of Super-typhoon Bopha was working in overdrive. Specifically, the coldest cloud tops were observed with extremely cold temperatures below -90C (-130F), which indicates Bopha was extracting a great deal of energy from the ocean surface and converting it into kinetic energy of strong updrafts that where punching through the troposphere (the bottom layer of the atmosphere that usually contains weather) and into the transition zone between troposphere and stratosphere.
As a bonus, the TRMM-observed cloud-top temperatures clearly illustrate how the circling winds of the tropical cyclone can act as a "containment vessel" preventing at least some of the energy released in hot towers from rapidly dissipating harmlessly far from the cyclone's inner core. Specifically, the cloud-top temperatures show gravity waves propagating around the eyewall instead of spreading away from the inner core like ripples in a pond. The observed gravity waves have their wave crests perpendicular to their direction of motion and the wave crests are seen to be oriented radially, i.e., perpendicular to the wind circling the eye. The gravity waves are seen in the upper left of the image as alternating bands of gray and pink.

Even without any further processing, the satellite has gathered enough data that Bopha could be recreated in its entirety as an interactive simulation itself, allowing research up close and personal, to each of the structures driving the storm's growth, as they unfolded over many hours. This alone would be a worthy simulation to explore, regardless of the other benefits of this new class of weather imaging system.

With each new typhoon TRMM locates and analyses, we gain more valuable data to help unravel the mysteries of these storms – and of course, volumetric data straight from the satellite sensor systems that is open-source and usable as raw, to create violent weather systems in our own environments with minimal processing.

References

NASA's TRMM Satellite Provides 3-D Analyzation of Super-typhoon Bopha: "Full Catastrophe"

Staff Comments

 


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