1. How can I get the meteorological information which I need?

In order to provide the general public with good-quality meteorological services, the Central Weather Bureau (CWB) offers multiple channels for the general public to conveniently retrieve the most-recent meteorological information. Based on individual practices, you can acquire different kinds of CWB meteorological data and products through the following ways:

  • Weather forecast inquiry system: dial 166 (Mandarin) or 167 (local dialects or English);
  • Consulting hot lines: dial 02-23491234 (for weather) or 02-23491168 (for earthquakes), the CWB will have experts to explain for you;
  • WWW: connect to the CWB network at: http://www.cwb.gov.tw and/or subscribe our e-paper;
  • Fax On Demand system: use facsimile machine and dial 020303166 (Mandarin only) to get up-to-date meteorological information;
  • Other alternatives: radio/TV broadcasts and newspapers.

2. Will typhoon invasion cease attendance at school or work, where could I get the information?

Currently, the decision on whether to cease classes or work in the nation during typhoon invasion rests with the authorities of municipalities and county/city governments, and the voice inquiry line is 020300166 (Mandarin only). The decision-making will be in accordance with the relevant regulation enacted by the Executive Yuan, which sets a threshold for reference that when an area is to be covered by a typhoon's radius within 4 hours and have sustained wind speed of Beaufort scale 7 or greater or gusts with Beaufort scale 10 or greater predicted by the CWB.

3. When will the CWB issue a sea warning for typhoon?

A sea warning will be issued when the typhoon's radius of sustained winds of 34 knots or greater is anticipated to touch the 100 km sea area of Taiwan in 24 hours; and then be renewed every 3 hours. The 24-hour lead time is tried to allow navigating or operating vessels to have sufficient time to escape to shelters or to take other precautionary measures. Meanwhile, the public should avoid seashore activities during typhoon warning period to prevent surge-induced accidents. The schematic outline of typhoon sea warning is shown over the right:

The Schematic Outline of Typhoon Sea Warning 24-hr forcast typhoon position

4. When will the CWB issue a land warning for typhoon?

A land warning will be issued if the typhoon's radius of sustained winds of 34 knots or greater is going to hit the land of Taiwan, Penghu, Kinmen, and Matsu in 18 hours. The land warning will also be reissued every 3 hours while the typhoon center is located every hour. The 18-hour lead time is set to allow all the safety actions to get ready. During typhoon strikes, the public should refer directly to the latest typhoon information issued by the CWB and not believe or spread rumors. The schematic outline of typhoon land warning is shown at the right:

The Schematic Outline of Typhoon Sea Warning 18-hr forcast typhoon position

5. What does it mean by a typhoon landfall?

When a typhoon's eye (the typhoon center) crosses a land mass from the sea area is called a typhoon landfall. It is not applicable if only part of the typhoon's radius (exclusive of the eye) moves over the land. Although due to typhoon's various structures, a relatively different distribution of strong wind and rainfall appears along its radius of hundreds of kilometers, a much stronger wind force usually comes up near the center which brings about the most serious destruction. But anyway, prevention measures should be well-taken against typhoon severe damage, whether it is going to make landfall or not whenever it approaches.

6. What does it mean by a 60 percent probability of precipitation?@

The Probability of Precipitation (POP) is the percentage of precipitation likelihood (with rainfall amount 0.1 mm or above) in a specific time interval of an area estimated upon various meteorological data. For instance, if the POP forecast for Taipei City is 60%, it indicates 60 percent of chance that Taipei City will get rain. It has no explicit correlation with rainy period, size of the area, and rain amount. The figure below shows a comparison between the POP forecasts (in %) made by the CWB and actual precipitation frequencies (%) for Taipei from 2002 to 2006. Take the 60% precipitation forecast for example, about 58.6 out of 100 times of forecast hit, which indicates very close forecasts.

Comparison between CWB POP Forecasts for Taipei and Actual Precipitation Frequencies from 2002 to 2006

7.What is the difference between an earthquake's "magnitude" and "intensity"?

Magnitude is a terminology used as measuring the energy released at the source of an earthquake, represented by a real number. Intensity is the one that describes the strength of ground shaking or effects on human bodies at a certain location produced by an earthquake. It is related to the acceleration of ground motion. For now, a seismograph can record ground acceleration well so that intensity is determined by the range of maximum ground acceleration and ranked by an integer. The definition of the ranks varies from country to country. The CWB adopts an intensity table of 0 to 7 levels which is similar to the Japanese:

Earthquake Intensity Table by Central Weather Bureau, Ministry of Transportation and Communications, Promulgated and Revised on August 1, 2000

Intensity Scale 0
Range of Ground Acceleration Below 0.8 gal
Effects on People Not felt.
Effects indoors
 
Effects outdoors  

 

Intensity Scale 1
Range of Ground Acceleration 0.8 gal ~ < 2.5 gal
Effects on People Felt only by a few persons at rest.
Effects indoors
 
Effects outdoors  

 

Intensity Scale 2
Range of Ground Acceleration 2.5 gal ~ < 8 gal
Effects on People Felt by many persons, some awakened.
Effects indoors
Hanging lamps, lanterns and etc. vibrate slightly.
Effects outdoors Standing motor cars vibrate slightly similar to being passed by a truck while short duration.

 

Intensity Scale 3
Range of Ground Acceleration 8 gal ~ < 25 gal
Effects on People Felt by nearly everyone, a few frightened.
Effects indoors
Buildings rock slightly. Dishes, windows, doors make disturbing sound. Hanging objects vibrate.
Effects outdoors Standing motor cars vibrate obviously. Electric wires sway gently.

 

Intensity Scale 4
Range of Ground Acceleration 25 gal ~ < 80 gal
Effects on People Many people frightened. Some look for safe places. Nearly everyone awakened.
Effects indoors
Buildings rock noticeably. Unstable objects toppled over. Heavy furniture move. May cause slight damage.
Effects outdoors Felt by drivers. Electric wires sway obviously. Felt by walking persons.

 

Intensity Scale 5
Range of Ground Acceleration 80 gal ~ < 250 gal
Effects on People Nearly everyone considerably frightened.
Effects indoors
Walls cracked. Heavy furniture maybe overturned.
Effects outdoors Noticeably felt by drivers. Some chimneys and monumental archway toppled over.

 

Intensity Scale 6
Range of Ground Acceleration 250 gal ~ < 400 gal
Effects on People People are not easy to stand up.
Effects indoors
Damage slight in some buildings. Heavy furniture overturned. Windows bent.
Effects outdoors Driving unstably. Sands and clays spurt into the air.

 

Intensity Scale 7
Range of Ground Acceleration 400 gal or higher
Effects on People People move difficultly due to severe rocking.
Effects indoors
Damage great in some buildings or collapse. Most furniture move or fall down.
Effects outdoors Landslides, faults, rails bent, underground lines broken.

Note: 1gal=1cm/sec2

8. Are earthquakes predictable?

Earthquake prediction involves descriptions of the accurate time for an earthquake, the accurate place of occurrence, magnitude, and either intensity or devastation it may cause. Lots of scientists and professionals around the world are putting great effort on this issue. At present, techniques of earthquake prediction are still in development and being tested. It is expected that an applicable technique could be achieved soon.

Although the development of accurate prediction technique for earthquakes is still being underway, evaluation of potential disasters caused by strong earthquakes is getting more efficient which is attributed to more earthquake information having being collected. This includes (1) where destruction may occur; (2) the possibility of destruction; and (3) how serious the destruction may be resulted from. Such evaluation study helps promote the efficiency of relieving victims in earthquake-induced disasters and reducing the loss of properties. It is considered the best progress in the development program of earthquake prediction to date.

9. How many earthquakes in Taiwan every year?

Mad-dog WavesLying on the Pacific seismic belt, Taiwan is one of the places in the world where earthquakes occur frequently and some of them are strong ones. According to the data of 1991~ 2006 from the CWB, there were approximate 18500 earthquakes per year on average in the Taiwan area, and about 1000 of them were felt by people.

The most earthquakes occurred in the year 1999, mainly due to the effect of the 921 Chi-Chi earthquake. A total of 49,919 earthquakes have been detected during that year, and 3,228 of them were felt. According to the official statistics, there were 96 destructive earthquakes in Taiwan since 1900. The seismicity of Taiwan is divided into three categories (see the graph below):

  • The West Seismic Belt: It mainly covers western Taiwan, being parallel to the axis of the island of Taiwan. Earthquakes occur in this belt due to plate collision. The shallow earthquakes (about 10 km or a little more) are associated with the faults in the crust. Since a high density population and lots of high rises over the area, once a strong earthquake occurs along this belt, it may cause much severer damage.
  • The East Seismic Belt: Earthquakes in this belt are caused by the collision between the Philippine sea plate and the European-Asian plate. The seismicity is the most active in the Taiwan region. The south end of this belt is almost linked with the Philippine seismic belt, then extending northward around Taitung, Chenggong, Hualien up to Yilan, where connected with the circum-Pacific seismic belt. The hypocenters may be as deep as about 300 km in both southern area and to the north of Hualien in this belt as a result of the subduing plate.
  • The Northeast Seismic Belt: This belt is associated with the plate extension of Okinawa Trough, and covers from the upstream region of Lanyang River through Yilan to Okinawa. Earthquakes in this belt are shallow and sometimes accompanied by volcanoes and geothermal activities.

10. What is so-called "Mad-dog Waves"?

The vocabulary "Mad-dog Waves" is not a professional term in wave theory. It is just a colloquial expression by the public. Although its definition is not explicit, a more suitable way of this statement should be fierce waves that suddenly attack people on the seashore taking activities for pleasure and cause accidents. Three possible reasons may cause "Mad-dog Waves" through a synthetic analysis:

  • When the wind pushes offshore waves and swell moving toward the coast, they get to resonate with inshore waves and produce high waves;
  • When the offshore swell moves onto the continental shelf, it becomes slow, which makes the amplitude of the wave gets larger as a result of wave compression. And as the high wave crest approaches the coast, it forms high waves;
  • When the offshore swell spreads to the coast interacting with a change of inshore current, it often generates big swell and propels to the coast quickly. When it moves closer hitting inshore waves, it generates high waves near breakwaters.

The most frequent activities in the "Mad-dog Waves" accidents are playing and fishing in the coast, which account for 79%. The most occurrences are in May to June and October to next January and in locations of Keelung, Yilan, Kaohsiung, and Pingtung areas.

11. Does the Central Weather Bureau keep track of the air quality in major cities of Taiwan? / Where can I find information about duststorm related fallout in Taiwan?

Air quality monitoring in Taiwan is conducted by the Environmental Protection Administration (EPA). For current air quality, you can browse the EPA web site (http://taqm.epa.gov.tw/taqm/en/) or refer to http://web.epa.gov.tw/en/ for related information, including duststorm activities.