Typhoon Rammasun

Typhoon Rammasun

Typhoon Rammasun became a named storm on May 7, 2008. The storm system formed well away from the coastal areas of the Philippines, and reached Category 4 strength by May 10, making it a Super Typhoon. The typhoon weakened and fell apart over the next few days without ever making landfall.

This data visualization of the storm shows observations from the QuikSCAT satellite on May 10 at 6:12 p.m. local time (9:12 UTC), when Rammasun was near its peak strength. At this time, Rammasun had peak winds around 230 kilometers per hour (145 miles per hour, or roughly 125 knots). The image depicts wind speed in color and wind direction with small barbs. White barbs point to areas of heavy rain.

QuikSCAT measurements of the wind strength of Typhoon Rammasan and other tropical cyclones can be slower than actual wind speeds. QuikSCAT’s scatterometer sends pulses of microwave energy through the atmosphere to the ocean surface and measures the energy that bounces back from the wind-roughened surface. The energy of the microwave pulses changes depending on wind speed and direction.

To relate the radar signal to actual wind speed, scientists compare measurements taken from buoys and other ground stations to data the satellite acquired at the same time and place. Because the high wind speeds generated by cyclones are rare, scientists do not have corresponding ground information to know how to translate data from the satellite for wind speeds above 50 knots (about 93 km/hr or 58 mph).

Also, the unusually heavy rain found in a cyclone distorts the microwave pulses in a number of ways, making a conversion to exact wind speed difficult. Instead, the scatterometer provides a nice picture of the relative wind speeds within the storm and shows wind direction.

NASA image courtesy of David Long, Brigham Young University, on the QuikSCAT Science Team, and the Jet Propulsion Laboratory. Caption by Jesse Allen.