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Conclusions

Our findings of a SVC occurrence frequency of  centered near 10 km confirm the existence of SVC at northern midlatitudes. Comparing these findings with the climatological results from the SAGE II instrument, which unlike other instruments such as HIRS, is very sensitive to optically thin cirrus (), we find excellent agreement with Wang et al. [1996] zonal average cirrus cloud occurences at 44 ° N. The high altitudinal resolution of the lidar measurements show that the mean thickness of a SVC event is less than 1 km with the distribution skewed towards much thinner layers ( are less than 0.4 km) and that cirrus cloud tops often occur at the tropopause. With nearly 2300 hours of measurements, this is the most extensive lidar study of cirrus available. These results help provide detailed cirrus climatological information that is needed to accurately model the effect of these clouds on the radiation budget.

Acknowledgements: This work was supported by Snecma and the Université Paris 6 under grant #940480. The authors also gratefully acknowledge the technical support team at OHP.