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 2011 is now available on the following webpage:
As revealed from the figure below, the air masses reached Hong Kong in January 2011 predominantly from the north and northwest as the territory was under the influence of the winter monsoon most of the time.
Backward Trajectory of Air Mass reaching Hong Kong in January 2011
For Daily or Seasonal Backward Trajectory Maps, please visit the following webpages: