The Science Experts » Weather

How are Hurricanes Classified?

Admin — Wed, 30 Mar 2011 02:37:29 +0000

Hurricane Fran

Hurricanes are classified on the Saffir/Simpson Hurricane Damage-Potential scale. This scale assigns a number from 1 to 5 based on the potential disaster the winds and storm surge of the hurricane may cause. The scale was developed by Herbert Saffir and Robert Simpson in 1971. It’s primarily used today for allowing disaster agencies to prepare for imminent storms and for general public awareness.

The following is a link to the National Weather Service’s Hurricane Wind Scale Summary Table. In a nutshell, the categories mean:

Category 1 – Winds: 74 to 95 mph. Storm surge: 4 to 5 feet above normal. Damage primarily to trees and unanchored mobile homes. Some coastal flooding.

Category 2 – Winds: 96 to 110 mph. Storm surge: 6 to 8 feet. Some damage to roofs, doors, windows, trees and shrubbery; flooding damage to piers.

Category 3 – Winds: 111 to 130 mph. Storm surge: 9 to 12 feet. Some structural damage; large trees blown down; flooding near shoreline and possibly inland; mobile homes destroyed.

Category 4 – Winds: 131 to 155 mph. Storm surge: 13 to 18 feet. Extensive damage to doors and windows; major damage to lower floors near shore; terrain may be flooded well inland.

Category 5 – Winds: in excess of 155 mph. Storm surge: more than 18 feet. Complete roof failure and some building failures; massive evacuation. Flooding causes major damage to lower floors of all shoreline buildings.

Source: http://www.sptimes.com/2007/04/15/Weather/How_hurricanes_are_cl.shtml.

How is visibility determined in weather reports?

Dan — Thu, 16 Sep 2010 01:13:25 +0000

One way would be for two people communicating wirelessly to start in a wide-open area and start walking until they could no longer see each other. Of course this is ridiculous. The way it’s usually done, by airports and such, is by looking at predetermined landmarks of known distances. Daytime visibility is defined as the distance in which is is possible to see and identify, with the naked eye, “a prominent dark object against the sky at the horizon.”Nighttime visibility is the distance at which it’s possible to see a known light source at “moderate density.” But a more accurate way airports measure visibility is by using a transmissiometer, which is a narrow light beam focused on a photoelectric cell 250 feet away. If the cell receives all of the light, visibility would be considered unlimited. If it receives none of the light, visibility would be considered “less than 250 feet.” Any variation in between would be calculated accordingly.

Source: The New York Times Book of Science Questions and Answers.

What is Doppler Radar?

Admin — Thu, 12 Aug 2010 07:13:24 +0000

What does Doppler radar mean and how is it different from other radar?

RADAR, an acronym for Radio Detection and Ranging, operates by transmitting a wave and recording the time it takes that wave to bounce off of an object and return to the source. Since we know the speed the transmitted wave is traveling, we can calculate the distance of the object.

Doppler radar operates on the same principle, but it also detects an objects motion by measuring the frequency shift between the outgoing wave and the returning wave. An object moving toward the radar would increase the returning wave’s frequency while an object moving away from the radar decreases the wave’s frequency. For weather purposes, this provides important information about the speed and direction of winds within thunderstorms.

Source: USA Today, Ask the Weather Experts. Posted by admin for the best selling toys of 2008 at Atomic Elephant Science & Toy Co.