Abstract. The distribution of 7Be during the TOPSE period was simulated using a global model driven by data from the Goddard Earth Observing System Data Assimilation System (GEOS-3 DAS). Temporal changes in the stratospheric component of tropospheric air were analyzed using model output and 7Be measurements. Comparison of model-calculated 7Be concentrations in the lower and upper troposphere with measurements revealed that cross tropopause exchange of 7Be was overestimated by only 10-25%. This bias is much less than what was seen in calculations with a different vertical grid driven by earlier versions of the GEOS DAS. The location and timing of fluctuations in 7Be concentrations were well captured by the model even during constant altitude portions of TOPSE flights. The amplitudes of the fluctuations were often underestimated. Within the TOPSE region (100°-60°W, 40°-80°N), 55-60% of 7Be in the model troposphere had a stratospheric source. No significant temporal trend is evident in observed or model-calculated 7Be concentrations. Model-calculated mean tropospheric 7Be concentrations increased by 2.9% per month in the southern portion of the TOPSE region. The stratospheric component in this region increased by only 0.6% per month. Analysis of the 7Be budget shows that seasonal increases in STE and scavenging contribute to this increase. Tropospheric O3 increases resulting from this increase are likely to be less than 1% per month. Model-calculated mean tropospheric 7Be concentrations increased by 1.6% per month in the northern portion of the TOPSE region. Analysis of the 7Be budget showed that seasonal increases in STE did not contribute to this increase.