Higher and Higher: WACCM Tracks Chemistry and Climate from Ground to Thermosphere

Historically, climate models have been relatively simple, tackling important physical and radiative processes in the troposphere rather than attempting to replicate the Earth system as a whole. This was due in part to the inherent complexity of the Earth system and its feedbacks, and also to the fact that the computing power needed to run more extensive models was not available. With petascale computing (1,000 trillion floating point operations processed per second) a near reality, processing times are less of an obstacle today.Historically, climate models have been relatively simple, tackling important physical and radiative processes in the troposphere rather than attempting to replicate the Earth system as a whole. WACCM’s capabilities represent a major advance in climate models. Likewise, modeling capabilities and scientific understanding have advanced. These evolutionary steps have led to the development of more complex models, which have a greater number of system components and can simulate a larger range of phenomena in the natural system. WACCM⎯the Whole Atmosphere Community Climate Model⎯is one such a model.

WACCM simulates Earth-atmosphere interactions from the troposphere (the lowest portion of the atmosphere, starting at Earth’s surface) up to the lower thermosphere at 140 kilometers. In addition to its ability to represent interactions between the major physical elements of the natural system⎯atmosphere, oceans, land⎯WACCM has an atmospheric chemistry component that can simulate the transport and photochemistry of trace species throughout the atmosphere.

WACCM’s capabilities represent a major advance in climate models. WACCM is one of only a few models able to simulate atmospheric physics, the transport of chemical species (for example, ozone, methane, water vapor, etc.), and the combined effect[ of atmospheric chemistry and physics on climate variability between the troposphere and upper atmosphere. Scientists have gained a greater appreciation of the importance of the physical and chemical interactions between different atmospheric regions, and learned that changes in the propagation of planetary waves into the stratosphere (due to natural or anthropogenic factors) likely play a role in tropospheric climate variability.

As of 2008, WACCM has become the latest addition to the Community Climate System Model suite. In addition to ongoing use by community members and in work being done for the World Meteorological Organization Ozone Assessment program, future WACCM modeling runs will be included in the Fifth Assessment Report for the Intergovernmental Panel on Climate Change. Projected applications of the model for scientific studies include the following:

  • Investigate interactions between stratospheric dynamics and chemistry to clarify the role of natural and anthropogenic variability in ozone depletion during the last 20 years and into the 21st century.
  • Investigate the effects of solar variability on the middle and upper atmosphere on time scales ranging from the solar rotation period (about 25 days) to the 11-year solar cycle.
  • Study processes controlling the stratosphere/troposphere exchange of mass and minor constituents.
  • Interpret observations from NASA and NSF programs: Upper Atmosphere Research Satellite (UARS), Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED), Earth Observing System (EOS) (High Resolution Dynamics Limb Sounder (HIRDLS)), and the Coupling, Energetics and Dynamics of Atmospheric Regions (CEDAR).
  • Investigate the effects of coupling between the stratosphere and the troposphere on climate variability.
  • Understand whether stratospheric ozone and temperature changes induced by the 11-year solar cycle play a role in observed correlations between the solar cycle and tropospheric and lower stratospheric temperature and geopotential patterns.
  • Study physical and chemical processes in the vicinity of the mesopause, in particular changes associated with increasing CO2 concentrations.