By using computer model analyses, the past 72-hour backward trajectory of the air mass reaching Hong Kong is estimated by the Observatory on a daily basis. The daily trajectories are compiled into the Monthly Backward Trajectory Map. The Monthly Map for January 2010 is now available on the following webpage: http://www.weather.gov.hk/wxinfo/trajectory/trajectoryMonthly_e.shtml
As revealed from the Monthly Map in the figure below, most of the air mass reaching Hong Kong in January 2010 followed a route along the coast of the southeastern part of China.
Backward Trajectory of Air Mass reaching Hong Kong in January 2010
For other Daily or Seasonal Backward Trajectory Maps, please visit the following webpages: