World's largest earthquakes

How Tsunamis Occur

1000 killed in major tsunami after 8.9 Japan quake

A powerful tsunami spawned by the largest earthquake in Japan's recorded history slammed the eastern coast on Friday, sweeping away boats, cars, homes and people as widespread fires burned out of control. Authorities said at least 1000 people were killed. The magnitude 8.9 offshore quake was followedby at least 19 aftershocks, most of them of more than magnitude 6.0. Dozens of cities and villages along a 1,300-mile (2,100-kilometer) stretch of coastline were shaken by violent tremors that reached as far away as Tokyo, hundreds of miles (kilometers) from the epicenter. A utility company in northeastern Japan reported a fire in a turbine building of nuclear power plant. A tsunami warning was issued for the entire Pacific, including areas as far away as South America, the entire U.S. West Coast, Canada and Alaska. Japan's Fire and Disaster Management Agency said at least 1000 people were killed.

"The earthquake has caused major damage in broad areas in northern Japan," Prime Minister Naoto Kan said at a news conference.

Even for a country used to earthquakes, this one was of horrific proportions. It unleashed a 23-foot (7-meter) tsunami that swept boats, cars, buildings and tons of debris miles inland. Large fishing boats and other sea vessels rode high waves into the cities, slamming against overpasses. Upturned and partially submerged vehicles were seen bobbing in the water. Waves of muddy waters swept over farmland near the city of Sendai, carrying buildings, some on fire, inland as cars attempted to drive away. Sendai airport, north of Tokyo, was inundated with cars, trucks, buses and thick mud deposited over its runways. Fires spread through a section of the city, public broadcaster NHK reported.

The tsunami roared over embankments, washing cars, houses and farm equipment inland before reversing directions and carrying them out to sea. Flames shot from some of the houses, probably because of burst gas pipes.

"Our initial assessment indicates that there has already been enormous damage," Chief government spokesman Yukio Edano said. "We will make maximum relief effort based on that assessment."

Tropical Atlantic sees weaker trade winds and more rainfall

		IMAGE: Wind waves depend on wind speed and have long been logged by ship crews. A new ocean wind data corrected with wind-wave heights suggests a slow down of the southeast... Click here for more information.

Earth's global temperature has been rising gradually over the last decades, but the warming has not been the same everywhere. Scientists are therefore trying to pin down how the warming has affected regional climates because that is what really matters to people, and to adaptation and mitigation strategies. Their efforts, however, had hit a roadblock because the necessary observations of the winds over the oceans were biased.

Developing a new method to remove the bias, Hiroki Tokinaga and Shang-Ping Xie at the International Pacific Research Center, University of Hawaii at Manoa, found that their corrected observations show the trade winds in the tropical Atlantic have weakened and the pattern of ocean surface temperature has changed. As a result, the equatorial Amazon and the Guinea Coast are seeing more rainfall and the Sahel less. The findings are published online in the February 6, 2011, issue ofNature Geoscience.

The raw observations of winds over the ocean suggest that the winds have grown stronger during the last 60 years. The trend is, however, largely due to a change in the placement of the anemometers, the instruments measuring wind speed. Ships are the main source of wind data over the ocean, and ships have increased in height and so has the anemometer placement. Tokinaga and Xie corrected this wind bias using wind-wave heights. The tropical Atlantic has three major ship routes along which ships provide meteorological data. Applying their new correction technique to observations along these routes from 1950 to 2009 together with other observations, they found the trade winds in the tropical Atlantic had weakened significantly during this period.

Although ocean surface temperature in the tropical Atlantic has risen, the pattern has changed and with it the climate. The cold tongue of water that stretches out from the eastern tropical Atlantic coast has warmed more than the western part of the basin. At the same time, the weakened trade winds have resulted in less upwelling of cold water and nutrients in the eastern tropical Atlantic. These latter changes could impact marine life.

		IMAGE: This graphic shows changes over the last 60 years in the August marine-cloudiness and land-rainfall over the tropical Atlantic. Yellow to dark red indicates more cloudiness/rainfall; light blue to gray,... Click here for more information.

Accompanying these changes in wind and ocean temperature is a very significant increase in rainfall, not only over the ocean but also over adjacent land areas such as the equatorial coastal regions of the Amazon and the Guinea Coast. For example, the August rainfall at Ibadan, one of the largest cities in Nigeria, has increased by 79 mm/month from 1950 to 1998, which is a whopping 93% increase over the long-term average for 1900�. The study also suggests that the year-to-year variations of ocean temperature and rainfall have weakened during recent decades, implying fewer extreme events.

Tokinaga and Xie reason that the pattern of ocean warming and trade-wind changes are caused by the asymmetric reduction in surface solar radiation due to man-produced aerosols, the reduction affecting the Northern more than the Southern Hemisphere. If aerosol emissions decrease over the next decades, the tropical Atlantic climate may experience yet another shift as greenhouse gas forcing increases. Such a shift in the patterns of climate change (i.e., precipitation and sea level) will have important impacts on the socio-economics of regions surrounding the tropical Atlantic. For example, "If the year-to-year variability is to recover in the future, the resulting increase in climate extremes would add burdens to an ecosystem and to a society already stressed by global warming," said Tokinaga.

Historical observations of accurate winds are gravely lacking over the World's oceans. This new robust and physically consistent set of observations by the IPRC team is valuable for improving computer models and evaluating model projections of climate change under further global warming.