An estimate of the stratospheric contribution to springtime tropospheric ozone maxima using TOPSE measurements and beryllium-7 simulations

[1] Measurements of tropospheric ozone (O-3) between 30degreesN and 70degreesN show springtime maxima at remote locations. The contribution of seasonal changes in stratosphere troposphere exchange (STE) to these maxima was investigated using measurements from the Tropospheric Ozone Production about the Spring Equinox Experiment (TOPSE) campaign and the beryllium-7 (Be-7) distribution from a calculation driven by fields from the Goddard Earth Observing System Data Assimilation System (GEOS DAS). Comparison with TOPSE measurements revealed that upper tropospheric model-calculated Be-7 mixing ratios were reasonable (a change from previous calculations) but that lower tropospheric mixing ratios were too low most likely due to an overestimation of scavenging. Temporal fluctuations were well captured although their amplitudes were often underestimated. Analysis of O-3 measurements indicated that O-3 mixing ratios increased by 5-10% month(-1) for theta < 300 K (the underworld) and by 10-15% month(-1) for theta > 300 K (the tropospheric middleworld). Be-7 mixing ratios decreased with time for theta < 290 K and increased with time for theta > 300 K. Model-calculated middleworld increases of Be-7 were a factor of 2 less than measured increases. Be-7 with a stratospheric source (strat-Be-7) increased by 4.6-8.8% month(-1) along TOPSE flight paths within the tropospheric middleworld. Increases in strat-Be-7 were not seen along TOPSE flight paths in the underworld. Assuming changes in tropospheric O-3 with a stratospheric source are the same as changes in strat-Be-7 and that 50% of O-3 in the region of interest is produced in the stratosphere, changes in STE explain 20-60% of O-3 increases in the tropospheric middleworld and less than 33% of O-3 increases in the underworld.