Weather Radar Detected the Hill Fire on New Year's Day

The weather radar is primarily used to detect raindrops in the air, but on occasions can also capture other phenomenon. In the afternoon of 1 January 2008, under very dry conditions, hill fire broke out over Castle Peak and became rather extensive. A plume of smoke was seen emerging from the hill and spreading towards Chek Lap Kok under the background northeasterly wind (Figure 1).

While there is no rain in the vicinity of Hong Kong that day, the airport weather radar at Tai Lam Chung detected rather strong signals which resemble rain echoes. On the radar display (Figure 2), the radar echoes appear as a wedge shape area between Castle Peak and Chek Lap Kok.

The weather radar could detect the hill fire because the smoke was dense and extensive, bringing small particles which reflect the microwave emitted by the radar, similar to what raindrops do. Such phenomenon was seldom seen on weather radars before and the hill fire on the New Year's Day captured by the airport weather radar was indeed a rare and special observation.

Figure 1: Smoke seen to emerge from Castle Peak at about 4:35 p.m. on 1 January 2008. The photo was captured by Mr. CH Chow, duty Weather Observer at Chek Lap Kok.

Figure 2: Radar image of the airport weather radar showing smoke plume emerging from Castle Peak at 4:38 p.m. on 1 January 2008