Thanks for your note. The smoke continues over Texas and other parts of the United States. Smoke from Mexico has reached as far north as Canada. Here is a status report that I have prepared. Please feel free to post on your web site. The report includes some very nice web sites.

Forrest M. Mims III

Significant Smoke from Widespread Fires in Mexico and Central America

Forrest M. Mims III
Sun Photometer Atmospheric Network
Goddard Space Flight Center Rapid Aerosol Response Team (member)

1. Introduction

Since early May very significant smoke from major agricultural and forest fires in southern Mexico and Central America has regularly arrived over Texas and periodically arrived over the other Gulf States, California and several Midwest and Southeast States. On 13 May 1998, NOAA's Automated Biomass Burning Algorithm (ABBA) identified 450 fires in Southern Mexico and Central America.

The highest concentration of fires and smoke appear to be in Mexico's states of Oaxaxa and Chiapas. Fires are also present in the Mexican states of Yucatan, Campeche, and Tabasco and the Central American countries of Honduras,Guatamala, Nicaragua and Costa Rica. Elaine Prins has posted annotated imagery of these fires on the web at:

2. Comparison of Texas and Burning Season in Brazil

The effect of the smoke on optical depth and UV-B closely resembles "typical" day during burning season in Brazil. Conditions near Seguin, Texas (29.6N, 97.9W), on 14 May 1998 were exceeded on only 2 of 12 days at Cuiaba, Brazil, in 1995 and 5 of 15 days at Alta Floresta, Brazil, in 1997.

3. Effects on the Population

On 12 May Texas placed 53 counties on a health advisory due to the smoke. On some days aircraft have been restricted to instrument flight rules (e.g. 14 May). Visibility in and near Seguin, Texas, was reduced to about 2 kilometers the afternoon of 14 May. At least one AirLife helicopter flight in San Antonio was canceled on 14 May due to poor visibility. The smoke event dominates virtually all news reports originating from Central Texas. Television news has provided extensive coverage, including imagery of the skylines of San Antonio and Houston obscured by thick smoke. Callers to area radio talk shows and television news programs have discussed various health problems, especially asthma, exacerbated by the smoke. Tourists vacationing in San Antonio and interviewed for television news programs have expressed strong displeasure.

3. Measured Atmospheric Effects in Texas

The optical density of the smoke near Seguin in South-Central Texas has caused atmospheric effects that closely resemble those in Central Brazil during the burning seasons of 1995 and 1997. The smoke is considerably more dense and widespread than that from 7 major forest fires that I measured for NASA during the fall of 1996 in California, Nevada, Montana and Wyoming. At solar noon on 14 May, the solar UV-B index measured with a Solar Light 501 Biometer was about 10% of the model clear sky value. Photosynthetic radiation measured with a Licor Quantum Sensor was 58.5% of the expected clear sky value. The normal polarization of the sky was essentially absent. The cloud-free aerosol optical depth on 14 May was by far the highest measured at this site since measurements were begun in 1988. The AOT shortly after solar noon at four wavelengths was:

Wavelength       AOT
376 nm  5.18 (ultraviolet-A)
540 nm   4.15 (green)
680 nm   3.24 (red)
1020 nm  1.36 (near-infrared)

4. Satellite Imagery

NASA's EarthProbe TOMS ozone satellite has provided excellent images of the smoke clouds. While these images lack the high resolution of GOES-8 images (see below), they ignore clouds and clearly show the optical depth of the smoke. These images are acquired once each day before local solar noon. They could be of significant practical value to health and environmental authorities as they clearly show the distribution of aerosols. Jay Herman of NASA's Goddard Space Flight Center has posted a series of daily TOMS images showing the smoke event at:

NOAA's GOES-8 images show the precise location of the major fires, dense smoke plumes and streams of smoke transported at various times to all the Gulf States and into the Midwest. Elaine Prins has posted a series of annotated GOES images showing the smoke event:

The Operational Significant Event Imagery support team of NOAA's Satellite Analysis Branch posts significant events at:

Smoke images posted by this team for 13 May 1998 include: (The previous image is from the AVHRR) Other GOES-8 images are also on the web. Especially good are the images at:

5. Conclusion

This smoke event could be of long duration as there is now no prediction of significant rain in the affected regions. Additional reports will be issued if conditions warrant. A formal paper on this very significant event is in preparation.

(Note: From 19 May to 3 June I am scheduled to teach a class in Hawaii and do calibrations at Mauna Loa Observatory. In my absence, the 501 Biometer will provide daily UV-B data. UV-B is an excellent indicator of the presence of smoke.)