NRL Chemical/Dynamical Model of the Middle Atmosphere (CHEM2D)

CHEM2D is a two-dimensional, zonally-averaged model of the Earth's Atmosphere. The model uses the Transformed Eulerian Mean (TEM) formulation of the zonally averaged equations of motion on a sphere. In the TEM formulation a residual meridional circulation is defined which takes into account wave induced motion of isentropic surfaces. This results in a simpler set of equations for the zonal-mean state. All of the wave forcing now appears as a flux divergence term in the zonal momentum equation. The thermodynamic equation is forced by diabatic heating only. The residual meridional circulation is a good approximation for the mean mass motion in the atmosphere. Thus the mean motion of chemical constituents in the atmosphere consists of advective transport by the residual meridional circulation.

The model calculates the distribution of up to 58 chemically active trace constituents. This is accomplished by using a fully implicit Newton-Raphson iterative scheme which makes no assumptions about the relative lifetimes of different chemical families. Current studies with this chemical package include a study of the seasonal variation of H₂O and CH₄ and a study of the transport of thermospheric NO into the middle atmosphere and its dependence upon vertical and horizontal mixing (as parameterized by K_zz and K_yy).

The CHEM2D model is a useful tool for studying the interactions between dynamics, radiative heating, and photochemistry in the middle atmosphere that produce inter-annual variations in important constituents such as ozone. Recent modifications to CHEM2D include realistic, fully interactive representations of the quasi-biennial oscillation (QBO) and semi-annual oscillation (SAO) in equatorial stratospheric winds, and allowing for observed, spectrally dependent variations in solar ultraviolet (UV) irradiance. These modifications now make it possible to study interactions between solar UV variability (on 11-year and 27-day time scales) and other dynamical sources of inter-annual variability (e.g., the QBO) that may help to explain the link between observed solar variability and long-term changes in the Earth's climate.

Contact: John McCormack (Code7646)

Publications

• Bacmeister, J. T., M. R. Schoeberl, M. E. Summers, J. R. Rosenfield, and X. Zhu, Descent of long-lived trace gases in the winter polar vortex, J. Geophys. Res., 100, 11669-11684, 1995.
  
• Summers, M. E., D. E. Siskind, J. T. Bacmeister, R. R. Conway, S. Zasadil, and D. F. Strobel, The seasonal variation of middle atmospheric CH4 and H2O with a new chemical-dynamical model, J. Geophys. Res.,, 102, 3503, 1997.
  
• Siskind, D. E., J. T. Bacmeister, M. E. Summers, and J. M. Russell III Two dimensional model calculations of nitric oxide transport in the middle atmosphere and comparison with HALOE data, J. Geophys. Res., 102, 3527, 1997.
  
• Bacmeister, J. T., D. E. Siskind, M. E. Summers and S. D. Eckermann, Age-of-Air in a zonally-averaged, two-dimensional model, J. Geophys. Res., 103, 11, 263-11,288, 1998.
  
• McCormack, J. P., and D. E. Siskind, Simulations of the quasi-biennial oscillation and its effect on stratospheric H2O, CH4, and age of air with an interactive two-dimensional model, J. Geophys. Res.,107 (D22), 4625, doi: 10.1029/2002JD002141, 2002.
  
• Ridal, M. and D. E. Siskind, A two-dimensional simulation of the isotopic composition of water vapor and methane in the upper atmosphere, J. Geophys. Res., 107, (D24), 4807, doi:10.1029/2002JD002215, 2002.
  
• Siskind, D. E., S. D. Eckermann, J.P. McCormack, J. M. Alexander, and J. T. Bacmeister, Hemispheric differences in the temperature of the summertime stratosphere and mesosphere, J. Geophys. Res.,108 (D2), doi: 10.1029/2002JD002095, 2003.
  
• McCormack, J.P., The influence of the 11-year solar cycle on the quasi-biennial oscillation, Geophys. Res. Lett., 30, doi:10.1029/2003GL018314, 2003.