Grass temperature to be measured in northern part of New Territories

The Hong Kong Observatory has installed an automatic grass temperature measurement system at Ta Kwu Ling to monitor grass surface temperatures in the northern part of the New Territories. From today (December 1) real-time data from the system between 5pm and 8am the following morning, updated every 10 minutes, will be available on the following webpage:

http://www.weather.gov.hk/wxinfo/ts/display_element_gr_e.htm

During winter nights and under clear skies, the ground surface is cooled rapidly by radiating heat off to space. The air temperature near the ground will also fall and when the grass temperature drops below zero degrees Celsius, hoar frost will form by direct sublimation of water vapour onto the grass surface. This phenomenon typically occurs over open terrain on a day with clear skies and calm winds. Frost in the urban areas is rare, although on average it occurs once every two years in the northern part of the New Territories.

The public and farmers can make use of the grass temperature information to take necessary precautionary measures against frost damage to vegetation.