Number of lightning strokes detected over the Hong Kong territory today and for the past three days

Points to Note:

• The image shows cloud-to-ground or cloud-to-cloud lightning strokes as detected by the Lightning Location Network over the Pearl River Estuary. The lightning records are updated at 5-minute intervals. An alert message is given on the top left only for cloud-to-ground lightning. The message will pop up on the display whenever lightning is detected in the past 5 minutes in the 15 km range from a location specified by user under the "Set alert option". The alert region can also be one of the four system-predefined regions (Click here to view the predefined regions). Also, when "Area Statistics" is selected, the number of lightning strokes detected within the area dragged by the mouse will be calculated.

• Cloud-to-cloud lightning strokes are those detected strokes that did not reach the ground. As such, they might not affect people or facilities on the ground. However, it should be noted that they may sometimes precede cloud-to-ground strokes. The location as shown depicts roughly the starting point of the discharge from one cloud to the other.

• This page is best viewed with 1280 x 1024 resolution by Microsoft Internet Explorer 6.0, Netscape Communicator 7.0, Firefox 1.0, or above. If the above interactive map cannot be displayed properly, you can click here to view the latest lightning location picture immediately.

• A number of geographical reference overlays can be added to the lightning location map. These overlays include landmarks, swimming pools, peaks of Hong Kong, and municipal names of the Guangdong province (Map information of Hong Kong is provided by the Lands Department of Hong Kong and the Guangdong municipal information is provided by the Guangdong Meteorological Bureau). These references will be displayed only when the scale of the map is suitably chosen. For example, landmarks of Hong Kong will be displayed only when the proportion of the Hong Kong territory in the map is sufficiently large. Similarly, municipal names of Guangdong will be shown only when the map is selected to cover part of the Guangdong province.

• This webpage can be selected to display radar images overlaid with lightning location information. The images were taken at 12-minute intervals and the rainfall rates estimated from radar data are represented by different colours. Since the measurements of radar and lightning location system differ in both time and space, the location of lightning may not correlate exactly with that of rain area in the radar image. For details about the radar images, please refer to the main pages of Weather Radar Image.

• The network comprises six stations jointly established by the Hong Kong Observatory, the Guangdong Meteorological Bureau and the Macao Meteorological and Geophysical Bureau. The stations are located at Chung Hom Kok, Tsim Bei Tsui, Sha Tau Kok, Taipa in Macao, Sanshui and Huidong in Guangdong. (Click here to see the location of these stations)

• The accuracy in determining the location of cloud-to-ground lightning strokes is 500 m within the network when all stations are operative. The lightning detection efficiency, i.e. the probability that a stroke with peak current greater than a certain level can be detected by the network, is estimated to be around 90 %. The location accuracy and detection efficiency will be reduced when the lightning stroke occurs outside of the network or when not all of the stations are operative.

• There is no guarantee that all occurred lightning strokes can be detected and false detection of lightning strokes cannot be ruled out completely. As it takes time for communication and computation, there is normally a delay of a few minutes in the display of data. Other factors, including interruption to telecommunications services and power supply, can also affect the reliability and availability of any lightning information.

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