Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 1:23 PM GMT on March 17, 2011
Favorable winds blowing at 10 - 20 mph out of the northwest continue over Tokyo, Japan today, and these winds will take radiation particles emitted by the stricken Fukushima nuclear plant immediately out to sea, without lingering over Japan. The northwesterly winds are blowing in response to the clockwise flow of air around a high pressure system approaching Japan from the southwest. Since high pressure systems are regions of sinking air, the radiation will stay close to the ocean surface over the next day or two as the air spirals clockwise over the Pacific.
Figure 1. Surface weather map for 8am EDT today, taken from the 6-hour forecast from this morning's 6 UTC run of the GFS model. A high pressure system to the southwest of Japan, in combination with a low pressure system to the northeast are driving strong northwesterly surface winds over the country. Image is from our wundermap with the "Model" layer turned on. The lines are sea-level pressure (blue contours, 4 mb interval) and 1000 to 500 mb thickness (yellow contours, 60 m interval). Thickness is a measure of the temperature of the lower atmosphere, and a thickness of 5400 meters is usually close to where the dividing line between rain and snow occurs.
As the high pressure system moves northeastwards and passes just east of Japan on Saturday, winds will gradually shift to the west and then southwest, keeping the radiation from the Fukushima plant blowing out to sea. As the winds shift to southwesterly, the sinking air over Japan will be replaced by rising air, and radioactive emissions will begin being lifted high in the atmosphere. Since there is less friction aloft, and the high speed winds of jet stream increase as the air moves higher in the atmosphere, this radiation will undergo long-range transport. Latest trajectory runs using NOAA's HYSPLIT model (Figures 2 - 4) show that radioactivity emitted today and Friday could wind up over Alaska and eastern Siberia after five days, and radioactive particles emitted on Saturday could make it to Hawaii and California by late next week. I've made trajectory plots for the next three days assuming two possible release altitudes--a surface-based release near 10 meters, which should be the predominant altitude in the current situation, and a higher release altitude of 300 meters, which might occur if there is an explosion and major fire. However, the 5-day trek to Hawaii and California is 4000 - 5000 miles, and a tremendous amount of dispersion and dilution of the radioactive plume will occur. Given the current levels of radiation being emitted, any radioactivity reaching Hawaii or the U.S. may be difficult to detect, and will not be a threat to human health. Keep in mind also that the most dangerous radionuclide to human health in the radioactive plume--Iodine-131--has a half life of eight days, so will be reduced by at least 30% after 5 days of travel time.
The next period of onshore winds that will blow radioactivity inland over Japan will occur beginning on Saturday night (U.S. time), continuing through Sunday morning, according to the latest run of the GFS model. The latest HYSPLIT trajectories show that regions of Japan north of the disaster site would be most at risk of receiving radioactive fallout on Saturday night. On Sunday and Monday, an approaching low pressure system is expected to bring considerable rain to Japan, and it is uncertain at this time what direction the wind might blow during this rain storm.
Figure 2. Five-day forecast movement of plumes of radioactive air emitted at 10 meters altitude (red line) and 300 meters (blue line) at 18 UTC (2pm EDT) Thursday, March 17, 2011 from the Fukushima Daiichi nuclear plant. The plumes initially spiral clockwise around the high pressure system to the southwest of Japan and stay near the surface. By Saturday, though, the plumes get caught in a southwesterly flow of air in advance of an approaching low pressure system. Ascending air lifts the plumes to high altitudes, where winds are stronger and rapid long-range transport occurs. Images created using NOAA's HYSPLIT trajectory model.
Figure 3. Five-day forecast movement of plumes of radioactive air emitted at 10 meters altitude (red line) and 300 meters (blue line) at 18 UTC (2pm EDT) Friday, March 18, 2011 from the Fukushima Daiichi nuclear plant. The plumes get caught in a southwesterly flow of air in advance of an approaching low pressure system. The plume emitted near the surface (red line) stays trapped near the surface for 4 days then lifted to 2 km, but the plume emitted at 300 meters is lifted to 5 km altitude after 2 1/2 days by the rising air associated with the approaching low pressure system. Images created using NOAA's HYSPLIT trajectory model.
Figure 4. Five-day forecast movement of plumes of radioactive air emitted at 10 meters altitude (red line) and 300 meters (blue line) at 18 UTC (2pm EDT) Saturday, March 18, 2011 from the Fukushima Daiichi nuclear plant. The plumes get caught in a southwesterly flow of air in advance of an approaching low pressure system and lifted to 4 - 5 km altitude. The plume emitted at 10 meters (red line) ends up getting caught in the clockwise circulation of air around a high pressure system situated north of Hawaii, and spirals down towards the surface in the high's sinking air. The plume emitted at higher altitudes (blue line) ends up escaping this high and making it over California at high altitude, getting caught in the southwesterly flow around a low pressure system predicted to affect California next week. Images created using NOAA's HYSPLIT trajectory model.
Seven-day weather forecast for Sendai near the Fukushima nuclear plant
The Austrian Weather Service is running trajectory models for Japan.
Current radar loops from the Japan Meteorological Agency
Mumbai hits its hottest temperature of all-time
The temperature in Mumbai (formerly Bombay), India skyrocketed to an all-time high of 107°F (41.6°C) yesterday, March 16, at the downtown Colaba observatory. Records at the observatory go back to 1847, which may be the longest time series of temperature observations at any location in Asia. Mumbai's previous all-time record temperature was 105°F (40.6°C) recorded on April 19, 1955. Mumbai's Santacruz Airport, located in the suburbs several miles inland, did not set an all-time high yesterday, hitting 41.3°C (all-time record: 42.2°C on April 14, 1952.) The record heat yesterday was due to an unusually hot and dry northeasterly flow of air from the center of India that kept the usual cooling sea breeze from establishing itself along the coast. Hot weather continued in Mumbai today, with the mercury hitting 102°F (39°C.) Thanks go to weather records researcher Maximiliano Herrera for supplying these statistics for me.
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