seasonal atmospheric feedbacks

• Main Authors: S. -y. Lee, C. J. Poulsen
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2008
• Subjects: Sion; aleutian low
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.629.4101; http://www.earth.lsa.umich.edu/paleoclimate/pdfs/lee_poulsen2008.pdf

Abstract. Pleistocene benthic δ18O records exhibit strong spectral power at ∼41 kyr, indicating that global ice vol-ume has been modulated by Earth’s axial tilt. This fea-ture, and weak spectral power in the precessional band, has been attributed to the influence of obliquity on mean annual and seasonal insolation gradients at high latitudes. In this study, we use a coupled ocean-atmosphere general circula-tion model to quantify changes in continental snowfall asso-ciated with mean annual and seasonal insolation forcing due to a change in obliquity. Our model results indicate that in-solation changes associated with a decrease in obliquity am-plify continental snowfall in three ways: (1) Local reductions in air temperature enhance precipitation as snowfall. (2) An intensification of the winter meridional insolation gradient strengthens zonal circulation (e.g. the Aleutian low), pro-moting greater vapor transport from ocean to land and snow precipitation. (3) An increase in the summer meridional in-solation gradient enhances summer eddy activity, increasing vapor transport to high-latitude regions. In our experiments, a decrease in obliquity leads to an annual snowfall increase of 25.0 cm; just over one-half of this response (14.1 cm) is attributed to seasonal changes in insolation. Our results in-dicate that the role of insolation gradients is important in amplifying the relatively weak insolation forcing due to a change in obliquity. Nonetheless, the total snowfall response to obliquity is similar to that due to a shift in Earth’s preces-sion, suggesting that obliquity forcing alone can not account for the spectral characteristics of the ice-volume record.