Events

Solar eclipses occurred on February 16 and August 11 of 1999. When the Sun is obscured or partly obscured, the calibration of the TOMS measurement is compromised. For this reason, data covering the region of the eclipses are excluded from the Level-2 (orbital) and Level-3 (map) data products.

Elevated values of Aerosol Index (AI) starting July 23, 1999 in North America are associated with Canadian Forest Fires. This may cause small underestimation of total column ozone amount in the vicinity of these fires. This map also shows dust emanating from Northern Africa and smoke from biomass burning in Southern Africa. The impact of dust and smoke on ozone derived from EP/TOMS measurements is described in Section 6.1 of the TOMS data User's Guide.

The eruption of Soufriere Hills Volcano on Monserat (lat, Lon) on July 21, 1999 caused a slight elevation in the Aerosol Index (AI) reported on the EP/TOMS Level-2 data product (not readily apparent in Level-3). The effect is small and does not lead to any data rejection from the Level-3 product, nor to any significant error in the total column ozone amounts.

Select to learn more about this image. During spring, some data were being rejected by the EP/TOMS algorithm in the vicinity of the North Pole. This was the result of air masses of very high total ozone amounts but with unusually low ozone concentration in the upper stratosphere. This situation was more prevalent in spring of 1999 than in previous years. This might possibly be associated with the two stratospheric warmings that occurred this Spring. Missing data in the TOMS Level-3 map products near the North Pole on April 25, for example, are the result of this type of data rejection. The white hole in the map is where the missing data is.

For more details on the TOMS profile mixing scheme, please refer to the algorithm section of the TOMS data User's Guide.

The eruption of Shishaldin (54.76 N, 163.97 W) on April 19. 1999 produced an ash cloud visible in the TOMS aerosol index (AI) over the Alaskan peninsula. Some of the TOMS ozone retrievals in this region are rejected for contamination due to the sulfur dioxide cloud produced by the eruption.