Hadley cell influence on 7Be activity concentrations at Australian mainland IMS radionuclide particulate stations

Beryllium-7 (7Be) daily data from the four International Monitoring System (IMS) radionuclide particulate stations on mainland Australia are analysed over the period 2001 to 2011. The analysis indicates that levels of 7Be in surface air at the stations follow annual cycles, with yearly peak activity concentrations occurring later at stations further south. The yearly peak migrates north-south at a rate of approximately 4.4° latitude per month. The change in phase of the 7Be annual cycle between the stations corresponds with the seasonal migration of the Southern Hemisphere Hadley cell across mainland Australia. The implication is that the changing position of the downward limb of the Southern Hemisphere Hadley cell regulates the phase of the annual cycle in 7Be activity concentrations in surface air in the Australian region.