Photographs of the July 1999 Fires Near the Southern Great Plains Site

Discussion

During the AOS Annual Maintenance visit in July, field burning was observed frequently. Discussions with several local residents provide us with some understanding of the phenomenon. The field burning occurs several times a year, just after the harvest of one crop and before the planting of the next. Most years have three crop cycles in this part of Oklahoma, so there are usually three "burning seasons". Burning is usually done to destroy weeds, weed seeds, and undesirable co-existing plants (e.g., "cheat" grass), to reduce vegetation height along the roads, and to remove the hard straw that is left after harvesting the wheat (this is difficult to completely plow under). The duration of a typical burning season is often 3-6 weeks, or until all the farmers in the region have planted their next crop. Burning was observed to be more prevalent west of Interstate 35, presumably because the generally wetter conditions in the eastern part of the state mean substantially more trees in and around the fields and a greater chance of igniting a forest fire.

During July 1999, several well-defined aerosol plumes were sampled by the Aerosol Observing System (AOS). Aerosol light scattering values increased by several times over normal values, and aerosol light absorption usually increased by over an order of magnitude. Single-scattering albedos dropped into the 0.6-0.7 range.

Large smoke plume rising to the WSW of the ARM Southern Great Plains site. Over the course of several minutes, a cloud could be seen forming at the highest point of the plume. Wind is from the south, so this plume would probably not have impacted ARM measurements.

Smoke rising from a field just north of the ARM SGP site. Southerly winds blew this smoke away from the site.

Close-up views of a burned field along the road leading to the ARM site from Salt Fork. Both the field and surrounding ditches were burned.

Large fire burning approximately 7 miles directly south of the ARM site. Southerly winds brought this smoke plume over the site.

Large field fire right next to the ARM site. 60-m tower (and AOS stack in one photo) can be seen in the foreground.