Thousands of fires have burned across Indonesia over the last few weeks.
This map shows the location of fires that have a high confidence* for being related to forest-clearing from September 7-17.
Weaker prevailing winds tend to blow the from the South or South East during this time of year, gently carrying smoke North from the fires further South.
Fires are an annual problem during the dry season, when forests in Indonesia are slashed and burned to clear the land for agriculture.
The chart shows daily fires observed throughout Indonesia by NASA's Terra and Aqua satellites.
Although it is illegal for companies in Indonesia to start forest or land fires, over a third of fires in Sumatra and Kalimantan from September 7 to 17 occurred within the pulp, palm oil or logging concessions that cover much of the land.
Fires on peat are of particular concern because they can be difficult to extinguish due to the depth and organic density of the soil. Some can burn for months or even years.
Between the 7th and 17th of September, 60 percent of the fires in Sumatra and Kalimantan were on carbon-rich peatlands, according to the World Resources Institute. The fires are set to burn off the vegetation but also burn roots and the peat soil itself.
NOTE: Average wind direction measured at Changi, Singapore, from March 2006 to August 2015.
*Classification employed by WRI. Identifies fires with a Brightness value ≥330 Kelvin and a Confidence value ≥ 30% using NASA’s Active Fire Data.
Graphics by Simon Scarr, Wen Foo, and Jessica Wang
Sources: NASA; World Resources Institute, Global Forest Watch Fires; Windfinder