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Polní laboratoř

NASA Satellite Sees Tropical Storm Yagi Just South of Japan

Tropical Storm Yagi is not expected to make landfall in Japan, but NASA satellite imagery showed that the storm was just south of the big island. NASA’s Aqua satellite passed over Tropical Storm Yagi on Tuesday, June 11 at 04:10 UTC (12:10 a.m. EDT/1:10 p.m. Japan local time) and the Moderate Resolution Imaging Spectroradiometer or MODIS instrument captured a visible image of the storm. The image showed that clouds associated with the northern fringes of the storm were draped over southeastern coastal Japan. The MODIS image also revealed that Yagi has a long “tail” or band of thunderstorms feeding into the center from the south. Multispectral satellite imagery shows tight bands of thunderstorms wrapping into the center of the storm, although the building of thunderstorms continues to weaken around the center. Vertical wind shear is starting to take a toll on Yagi, according to the Joint Typhoon Warning Center. Northwesterly wind shear has made a slight tilt to the system with the upper-level center displaced about 20 nautical miles east of the low-level center. When the lower and upper level centers of circulation are not “stacked,” a tropical cyclone begins weakening. At 09:00 UTC (5 a.m. EDT/6 p.m. Japan local time) Yagi had maximum sustained winds near 50 knots. Tropical storm force winds extend out 95 miles from the center, making the storm about 200 miles wide. Yagi was centered near 29.2 north and 136.9 east, about 307 miles west-northwest of Chichi Jima, Japan. Yagi was moving to the north-northeast at 17 knots. Yagi is kicking up seas with wave heights topping 21 feet, so the southeastern coast of Japan can expect rough seas until Yagi passes by. Yagi is forecast to turn to the southeast and move away from Japan over the next couple of days, where it is expected to weaken and dissipate.

NASA Sees Tropical Storm Yagi Spinning in Western Pacific Ocean

Tropical Storm Yagi developed over the weekend of June 8 and 9 in the Western North Pacific from Tropical Depression 03W and NASA satellites captured the storm coming together. NASA’s TRMM satellite measured rainfall rates within the storm and found the heaviest rain falling mostly south of the center. NASA and the Japanese Space Agency’s Tropical Rainfall Measuring Mission or TRMM satellite captured the rate rain was falling within Tropical Storm Yagi on June 10 at 8:19 a.m. EDT. The heaviest rain was falling south of the center around the center of circulation at as much as 1.2 inches (30.4 mm) per hour. On June 10, 2013 at 1500 UTC (11 a.m. EDT), Tropical Storm Yagi had maximum sustained winds near 45 knots (51.7 mph/83.3 kph), which is expected to be its peak wind speed. Yagi was located near 25.0 north and 135.2 east, about 344 nautical miles (396 miles/ 637.1 km) west of Iwo Jima, Japan. Yagi is moving to the northeast at 12 knots (13.8 mph/22.2 kph). According to the Joint Typhoon Warning Center, animated infrared imagery reveals a tightly wrapped low-level circulation center that is surrounded by shallow convection. Strong convection (rising air that forms thunderstorms) appears limited in the tropical storm. To the north of Yagi, vertical wind shear is moderate (between 15 and 20 knots/17.2 and 23.0/ 27.7 and 37.0 kph), and wind shear inhibits development of thunderstorms. Wind shear is a measure of how the speed and direction of winds change with altitude. Water vapor imagery shows that there is sinking air (subsidence) along the western edge of the storm, which is also inhibiting the development of thunderstorms. Sea surface temperatures remain warm enough to support Yagi, so the storm is expected to maintain strength for the next 24 hours as it moves northeast. Yagi is expected to dissipate south of Japan sometime before June 14.

NASA's 2013 HS3 Hurricane Mission to Delve into Saharan Dust

NASA's 2013 Hurricane and Severe Storms Sentinel or HS3 mission will investigate whether Saharan dust and its associated warm and dry air, known as the Saharan Air Layer or SAL, favors or suppresses the development of tropical cyclones in the Atlantic Ocean. The effects of Saharan dust on tropical cyclones is a controversial area of science. During the 2012 campaign, NASA's Global Hawk unmanned aircraft gathered valuable data on the dust layer that swirled around Tropical Storm Nadine for several days. The Saharan dust layer is composed of sand and other mineral particles that are swept up in air currents and whisked westward over the Atlantic Ocean. The extreme daytime heating of the Sahara creates instability in the lowest layer of the atmosphere, warming and drying the air near the surface and cooling and moistening the air near the top of the dust layer near 5 kilometers (16,500 feet). Once it exits the African coast, the dust-laden air moves over air that is cooler, and moister, and it's the temperature inversion of warm air over cold that prevents deep cloud development. This suppression of deep cloud formation along with the dry air within the dust layer is reasons why this Saharan air layer is sometimes thought to suppress tropical cyclone development. On the other hand, the southern boundary of this hot desert air essentially acts like a front whose attendant wind patterns are a major source of the African waves that are precursors to storm formation. NASA's Global Hawk flew five science missions into Tropical Storm/Hurricane Nadine, plus the transit flight circling around the east side of Hurricane Leslie. This is a composite of the ground tracks of the transit flight to NASA Wallops plus the five science flights. TD means Tropical Depression; TS means Tropical Storm. Credit: NASA Some Saharan dust has been known to make the journey across the Atlantic and to the U.S. east coast. But Saharan dust doesn't just cause sunrises to appear more reddish, the dust also impacts the development of clouds and precipitation. The dust particles can provide a surface for small cloud droplets and ice crystals to form within clouds. More dust particles means that a given amount of available water is spread onto more particles, creating large numbers of small drops and delaying the formation of larger raindrops. Those effects, coupled with the warm and dry air, have presented challenges to meteorologists who have been trying to understand the effect of Saharan dust on tropical cyclones.

HS3 addresses the controversial role of the Saharan Air Layer, or SAL, in tropical storm formation and intensification by taking measurements from three instruments on board the Global Hawk. These instruments include a cloud physics lidar which uses a laser to measure vertical profiles of dust; a dropsonde system that releases small instrumented packages from the aircraft that fall to the surface while measuring profiles of temperature, humidity, and winds; and an infrared sounder that measures temperature and humidity in clear-sky regions. On Sept. 11 and 12, during the 2012 HS3 mission, the NASA Global Hawk aircraft covered more than one million square kilometers (386,100 square miles) going back and forth over the storm in a gridded fashion in what's called a "lawnmower pattern." The SAL was present primarily during that first flight, and again on the flight from Sept. 14 to 15. "The SAL did not act to suppress development on Sept. 11 and 12, at least not in the sense of a direct intrusion into the storm circulation, but it is too early to say what role it might have played in other ways and in other flights," said Scott Braun, HS3 Principal Investigator, at NASA's Goddard Space Flight Center, Greenbelt, Md. "There is some evidence that it (the SAL) was getting into the storm circulation on Sept. 14 and 15, but the extent to which it impacted development is unclear." The dust data collected by the Global Hawk is important for scientific studies on the SAL. Other data was useful operationally to the National Hurricane Center (NHC), the entity that issues forecasts for tropical cyclones. The forecasters at the NHC used data from dropsondes released from the Global Hawk in the discussion of Nadine at 11 a.m. EDT on Sept. 20, "The current intensity is kept at 45 knots (51.7 mph/83.3 kmh)…is in good agreement with dropsonde data from the NASA global hawk aircraft and AMSU [satellite instrument] estimates."

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