Outflow from Beijing: 1998 – 2008

Using the NASA Goddard Kinematic Trajectory model, I have examined flow out of the Beijing region during the month of August from 1998 – 2008 in an effort to put this year’s outflow (see earlier post) in context.  You will find PDF files on the project website summarizing the distribution of the outflow.  The contours indicate the number of parcel-quarter days found in each grid box.  Here’s a link to the outflow from Beijing in the Boundary Layer (< 2.5 km) and  another in the Lower Free Troposphere (2.5 – 5.0 km).

More details of the model: 

NCEP data from 1998 – 2001 are once daily; from 2002 – 2005 are twice daily; from 2006 – 2008 are four times daily.

Beijing box is 5 deg. lat by 8 deg. lon centered on 38.5 N, 115.5 E, with parcels every 0.5 deg. lat. and 0.5 deg. lon.

Gridded map in PDF files runs from 25 N ot 50 N and 105 E to 150 E, with a 1 deg. lat. by 1.5 deg. latitude grid cell.

Observations:

In the boundary layer, flow from China to Japan from 1999 – 2002 was relatively weak, with few areas of Japan experiencing much influence from air over Beijing.  In 1998, however, much of Honshu and all of Kyushu were influenced by Beijing air.  In particular, Northern and Southern Honshu and Kyushu saw substantial flows from Beijing.  In the lower free troposphere, when flows to Japan are strong (1998, 2000, 2003, 2006, 2007), Northern Honshu sees the most air from Beijing.

In the lower free troposphere, 1999, 2000, 2001, 2003, 2005, and 2008 are years with relatively weaker influences in Hokkaido from Beijing.  In the boundary layer, the weaker years are 1999, 2000, 2001, and 2008.  Thus, analysis of this summer’s pollution data need take into account the fact that outflow from China to Japan was relatively weak compared to previous years within the last decade.