The Importance of the Oceans and Topography in Climate Simulations

The climate of the Earth's atmosphere is largely driven by forcing from the underlying surface, of which 71% is covered by the oceans. Thus, any simulations of present or future climate must be able to represent the land surface topography and the world oceans in a realistic way to be useful.

Also, the oceans and mountains are important in simulating what we call "storm tracks". Storm tracks (Fig. 1) are the climatological "signature" representing the frequency and strength of the regular passage of cyclonic disturbances. These disturbances are generally responsible for bringing weather that can be a minor nuisance in our day, such as rain or snow showers, or the severe weather that can cause the loss of life and property. These low pressures are also a significant mechanism for the poleward transport of heat, momentum, and water vapor out of the tropics. These actions are necessary for maintaining the structure of our current general circulation and climate.

Then, natural variations, as well as global or regional climate change, will be reflected by changes in the storm tracks. Wilson et al. (2010) note; "As the climate changes, the ocean dynamics will change, but the land and mountains remain unchanged over millennia. Therefore in order to understand how the shape of the storm tracks will evolve, it is crucial to understand the relative impact of ocean dynamics and orography, as well as their interactions..."

Four different model "worlds" were constructed by Wilson et al. (2010) using a coupled ocean-atmosphere general circulation model. A model control run was performed with realistic topography and a fully dynamic ocean (Fig. 1). Then, a typical modeling strategy was used to produce three other runs. This strategy involves using extreme and unrealistic parameterizations in order to isolate the impact of certain factors. A scenario was developed in which all land topography was leveled to 1 meter in height and the ocean was a 30 meter "slab" which does not move. Then a scenario with mountains, but a slab ocean was developed, and finally a scenario without mountains, but a fully dynamic ocean was implemented.

Wilson et al. (2010) show that storm tracks are a feature that is inherent in our atmosphere as these were found in the model run even without mountains and topography. In the model runs that included a dynamic ocean, the effect was to push the storm tracks poleward. The impact of the mountains was to reduce storm activity on their leeward side. The two forcings combined result in distinct Atlantic and Pacific storm tracks rather than just one long track in the Northern Hemisphere.

Changes in climate will alter the storm tracks through changes in the frequency and intensity of the cyclones that comprise it. This would have an impact on the changes in frequency and intensity of related phenomena such as blocking anticyclones. Blocking anticyclones are implicated in contributing to the European and Russian heat waves of 2003 and 2010, respectively. Such events are also implicated in severe winter cold across all continents. Thus, in order to discuss possible future scenarios for the climate or even the occurrence and severity of extreme events, any models used to generate these would need to include interactive ocean dynamics. And as Wilson et al. (2010) point out; "Increased resolution is needed is needed in coupled climate models to adequately address the role of ocean dynamics."