Interpretation of mid-stratospheric Arctic ozone measurements using a photochemical box-model

In this study measurements of mid-stratospheric Arctic ozone are compared w ith model simulations. The measurements obtained at Spitsbergen (79 degrees N, 12 degrees E) by ground based millimeter-wave radiometry exhibit large day to day variabilities as well as periods with low ozone. To interpret th ese measurements, calculations were made using the new photochemical box-tr ajectory model BRAPHO, with air parcel trajectories calculated from analyze d wind fields. Using a relatively simple approach, the model reproduces the observed ozone variability well, including inter-annual variations. The ex planation for the observed ozone behavior is that at these altitudes ozone is determined by what we call 'dynamically controlled photochemistry'. This means that the photochemical evolution of the ozone volume mixing ratio is mainly controlled by the atmospheric dynamics, in particular the solar zen ith angle the air parcel has experienced.