Effect of volcanoes on the vertical temperature profile

Changes in the vertical temperature profile may be an important diagnostic for detection of anthropogenic temperature change. It is therefore interesting to ask how volcanic eruptions affect upper air temperatures, and what effect volcanic eruptions may have had on trends in the vertical temperature profile. Comparison of the temperature responses to aerosol forcing from the Agung, El Chichon and Pinatubo volcanic eruptions shows the expected stratospheric warming, with a maximum at 50 mb in the tropics, and a predominantly cooling effect in the troposphere with a maximum in the middle or upper troposphere. While the stratospheric warming effects of all three are similar in the tropics, the tropospheric cooling is much greater after Pinatubo, with a significant effect on the temperature difference between the upper and lower tropical troposphere. Nevertheless, trends for 1979-1998 calculated with and without data from the three years after Pinatubo and El Chichon are similar, suggesting that the direct effects of volcanic eruptions are not a major cause of recent trends in tropospheric lapse rates. We will also compare the observations to GCM simulations of the effects of the Pinatubo eruption.