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The northern annular mode in summer and its relation to solar activity variations in the GISS ModelE

Publication ,  Journal Article
Lee, JN; Hameed, S; Shindell, DT
Published in: Journal of Atmospheric and Solar-Terrestrial Physics
March 1, 2008

The northern annular mode (NAM) has been successfully used in several studies to understand the variability of the winter atmosphere and its modulation by solar activity. The variability of summer circulation can also be described by the leading empirical orthogonal function (EOF) of geopotential heights. We compare the annular modes of the summer geopotential heights in the northern hemisphere stratosphere and troposphere in the Goddard Institute for Space Studies (GISS) ModelE with those in the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. In the stratosphere, the summer NAM obtained from NCEP/NCAR reanalysis as well as from the ModelE simulations has the same sign throughout the northern hemisphere, but shows greater variability at low latitudes. The patterns in both analyses are consistent with the interpretation that low NAM conditions represent an enhancement of the seasonal difference between the summer and the annual averages of geopotential height, temperature and velocity distributions, while the reverse holds for high NAM conditions. Composite analysis of high and low NAM cases in both model and observation suggests that the summer stratosphere is more "summer-like" when the solar activity is near a maximum. This means that the zonal easterly wind flow is stronger and the temperature is higher than normal. Thus increased irradiance favors a low summer NAM. A quantitative comparison of the anti-correlation between the NAM and the solar forcing is presented in the model and in the observation, both of which show lower/higher NAM index in solar maximum/minimum conditions. The temperature fluctuations in simulated solar minimum conditions are greater than in solar maximum throughout the summer stratosphere. The summer NAM in the troposphere obtained from NCEP/NCAR reanalysis has a dipolar zonal structure with maximum variability over the Asian monsoon region. The corresponding EOF in ModelE has a qualitatively similar structure but with less variability in the Asian monsoon region which is displaced eastward of its observed position. In both the NCEP/NCAR reanalysis and the GCM the negative anomalies associated with the NAM in the Euro-Atlantic and Aleutian island regions are enhanced in the solar minimum conditions, though the results are not statistically significant. © 2007 Elsevier Ltd. All rights reserved.

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Published In

Journal of Atmospheric and Solar-Terrestrial Physics

DOI

ISSN

1364-6826

Publication Date

March 1, 2008

Volume

70

Issue

5

Start / End Page

730 / 741

Related Subject Headings

  • Meteorology & Atmospheric Sciences
  • 5109 Space sciences
  • 5101 Astronomical sciences
  • 0401 Atmospheric Sciences
  • 0201 Astronomical and Space Sciences
 

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Lee, J. N., Hameed, S., & Shindell, D. T. (2008). The northern annular mode in summer and its relation to solar activity variations in the GISS ModelE. Journal of Atmospheric and Solar-Terrestrial Physics, 70(5), 730–741. https://doi.org/10.1016/j.jastp.2007.10.012
Lee, J. N., S. Hameed, and D. T. Shindell. “The northern annular mode in summer and its relation to solar activity variations in the GISS ModelE.” Journal of Atmospheric and Solar-Terrestrial Physics 70, no. 5 (March 1, 2008): 730–41. https://doi.org/10.1016/j.jastp.2007.10.012.
Lee JN, Hameed S, Shindell DT. The northern annular mode in summer and its relation to solar activity variations in the GISS ModelE. Journal of Atmospheric and Solar-Terrestrial Physics. 2008 Mar 1;70(5):730–41.
Lee, J. N., et al. “The northern annular mode in summer and its relation to solar activity variations in the GISS ModelE.” Journal of Atmospheric and Solar-Terrestrial Physics, vol. 70, no. 5, Mar. 2008, pp. 730–41. Scopus, doi:10.1016/j.jastp.2007.10.012.
Lee JN, Hameed S, Shindell DT. The northern annular mode in summer and its relation to solar activity variations in the GISS ModelE. Journal of Atmospheric and Solar-Terrestrial Physics. 2008 Mar 1;70(5):730–741.
Journal cover image

Published In

Journal of Atmospheric and Solar-Terrestrial Physics

DOI

ISSN

1364-6826

Publication Date

March 1, 2008

Volume

70

Issue

5

Start / End Page

730 / 741

Related Subject Headings

  • Meteorology & Atmospheric Sciences
  • 5109 Space sciences
  • 5101 Astronomical sciences
  • 0401 Atmospheric Sciences
  • 0201 Astronomical and Space Sciences