Project: GOME Evolution - Within the ESA GOME Evolution project, two different total column water vapor (TCWV) products are developed and applied to the satellite instruments GOME, SCIAMACHY, and GOME-2: 1. The "climate" product with focus on consistent time series of monthly means 2. The "advanced AMF algorithm" (A3) product with focus on accurate retrievals for individual pixels. The GOME Evolution project is funded by European Space Agency (ESA) under contract no. 4000110429 Summary: The "climate" water vapor product developed within ESA's "GOME-Evolution" project provides a consistent time series of monthly mean global maps of total column water vapor derived from the satellite instruments GOME, SCIAMACHY, and GOME-2 (Metop-A). Consistency amongst the different instruments (including cloud treatment) is substantially improved by (1) merging SCIAMACHY and GOME-2 observations to GOME pixel size, and (2) reducing the GOME-2 swath width to GOME/SCIAMACHY swath, thereby mimicking GOME-like observation conditions for all three sensors.