New technologies improve typhoon forecasts
This year has offered an unusual number of opportunities for Japanese typhoon forecasters to test and evaluate their skills and abilities, as powerful storms pummeled the nation.
Despite all the advanced technologies available, it is still difficult to predict when a typhoon will form, where it is going and how strong it will be.
Researchers and forecasters are racing to apply state-of-the-art equipment, from high-performance radars to supercomputers, to improve typhoon forecasting. On Aug. 22, forecasters at the Meteorological Research Institute in Tsukuba, Ibaraki Prefecture, had a superb opportunity to improve their understanding of the physics that controls ferocious storms, as Typhoon No. 9 passed near the lab, which is affiliated with the Japan Meteorological Agency.
A cutting-edge radar at the institute captured clear images of how one cumulonimbus cloud after another grew to towering heights and then shrank and disappeared in several seconds.
Images of typhoons provided by weather satellites generally show the eye of the storm surrounded by the eyewall, a huge vertical wall of clouds, which is then encircled by what is called a “spiral rainband,” a band of clouds radiating outward. But little is known about what actually happens inside a typhoon, said Toru Adachi, a researcher at the institute.
It was the first time that images were captured of how the eyewall changed its form like a creature. The feat was made possible by a phased array radar, which can scan the entire cloud quickly from top to bottom. The sophisticated radar makes it possible to monitor detailed changes in the cloud every 30 seconds. Conventional weather radars can only be used to get the whole picture of a cloud in cycles of five to 10 minutes.
Images caught by the institute’s radar show that when the typhoon, which was headed north, slightly changed its track eastward, a band of clouds crumbled a little. This suggests that something happened at that time to weaken the intensity of the storm. The accumulated effects of such small changes determine the intensity and direction of the typhoon.
Researchers at the institute are using the new data obtained to improve the accuracy of their typhoon forecasts.
The diameter of a typhoon can exceed 1,000km. But inside such a gargantuan storm, numerous small phenomena on a scale of less than 1km occur. Analyzing all these small events requires so much computing power that they are not factored into current forecasts of typhoon intensity.
Junshi Ito and others at the Meteorological Research Institute have worked with the University of Tokyo to use the K supercomputer at the Riken Advanced Institute for Computational Science to simulate these small phenomena inside two typhoons.
To simulate the events, the researchers divided the atmosphere into small units, each of which was 100 meters in horizontal length and had one-sixtieth of the total vertical length. They made detailed calculations of changes that occurred during a 10-hour period in two typhoons with central pressures of 920 and 950 hectopascals, respectively.
In both cases, they observed different types of relatively small vortexes inside and outside an area that was a dozen or so kilometers from the center.
The project is aimed at figuring out how these vortexes affect the maximum intensity of typhoon winds and the locations of the strongest winds.
It is difficult to observe typhoons directly when they are offshore. Estimates of the maximum wind speeds of typhoons by the Japan Meteorological Agency tend to be smaller than those made by the U.S. military, according to Kazuhisa Tsuboki, a professor at the Nagoya University Hydrospheric Atmospheric Research Center.
Because it carried out direct observations of typhoons using aircraft until the late 1980s, the U.S. military has a large accumulation of useful data and therefore is able to make more accurate estimates of wind strength.
Nagoya University plans to start observations of typhoons using aircraft in fiscal 2017 jointly with the University of the Ryukyus and the National Taiwan University. During the three years through fiscal 2019, they will fly aircraft close to the centers of typhoons once or twice annually, dropping recording instruments into the storms to measure temperature, humidity and wind speed and direction.
Special microscopes will also be dropped to take pictures of the insides of upper layers of clouds. Clouds affect the intensity of typhoons by absorbing heat from the sun and radiating heat into outer space.
The data gathered will be used in computer models to make accurate simulations of how typhoons develop.
Typhoons and the sea
Nagoya University and the Meteorological Research Institute will also try to develop theories about the relationship between typhoons and the sea. The temperature of seawater is a major factor determining the intensity of typhoons. When the surface of the sea is stirred or sucked up, causing cooler water to rise from deeper parts, typhoons weaken.
The Meteorological Agency’s typhoon forecasts currently ignore this effect.
The effects caused by sprays created by strong winds, and salt that is swirled up from the surface, also cannot be ignored, according to researchers. Sprays evaporate and are absorbed into updrafts near the eyewall. When they are cooled high in the sky, they condense into droplets of fog and rain, radiating heat in the process. This heat makes the eyewall bigger and thereby makes the typhoon stronger.
The effects of aerosols, or fine particles of salt and other substances, were estimated by a group of U.S. researchers after Hurricane Katrina caused devastating damage in the U.S. in 2005.
Aerosols serve as cores that create clouds. If there are a large number of aerosols in a typhoon, the clouds inside the spiral rainband increase, curbing the development of the storm.
Tsuboki and others at Nagoya University plan to use drones to observe sprays and aerosols in approaching typhoons.