BARROW

Trends

AOD anomaly data for the NOAA/CMDL Arctic baseline station at Barrow, Alaska, U.S.A., are generally available over the period of record for months during which solar irradiance measurements are possible (usually from February or March through October). The most prominent features of the record are increases in AOD following the volcanic eruptions of El Chichón (Mexico, 1982) and Pinatubo (Philippines, 1991). The El Chichón event produced a larger impact at Barrow than at the NOAA/CMDL monitoring sites in the Southern Hemisphere. AOD anomalies reached a maximum of 0.18 in June 1983 and then decayed to background levels over ~3 years. Evidence of the Pinatubo eruption appeared in April 1992 (data were missing for September through March) and reached a maximum of 0.20 in May 1992. In addition to the effects of these volcanoes, the record also shows an annual cycle with a maximum AOD in spring. This annual maximum is associated with the presence of Arctic haze, a phenomenon thought to result from particulate emissions from high-latitude anthropogenic sources.

When the seasonal cycle and the effects of the volcanoes are subtracted, the collective AOD anomaly record from Barrow does not show any significant trend. However, Bodhaine and Dutton (1993) have found a statistically significant decrease since 1982 in AOD measurements during March-April, when the Arctic haze is most evident at Barrow.

Barrow
Alaska, U.S.A.
Arctic coastal seashore
71° 19' N, 156° 36' W
11 m above MSL

Barrow Optical Depth Graph

• Monthly aerosol optical depth anomalies at Barrow