Is there a fourth meridional cell in the general circulation of the atmosphere?

Weihong Qian
Beijing University
12:30 pm October 16 in Room 2155

The three-cell model for the atmospheric circulation including the Hadley, Ferrel and Polar cells in each of two hemispheres has been accepted and used in climate study for a long time. According to the principle for conservation of angular momentum, a decrease in rotation radius will cause an increase in westerly velocity aloft for the Polar cell so that it cannot cross as many latitudes as the Hadley cell does in the lower latitudes because the distance between the tropospheric air particle and the earth's rotating axis reduces more rapidly poleward beyond the latitude of 60. Using three different global reanalysis products and one climate model simulation from the historical and future runs, we are able to show that there might be a fourth cell in each of two high latitudes. The analyses of meridional section streamline (MSS) and meridional-mass stream function (MSF) provided some evidences to support the existence of the fourth cells. The intensity and location of the fourth cell vary with season, and in some months it becomes invisible. Further, due to the elevated topography, the Antarctic cell is much weaker than the Arctic cell. This poses a challenge to the climate and meteorological community to verify the discovery with stronger observational basis, improved modelling capacity, and better assimilation over high latitudes.