Cloud droplet number concentration (N_d) is a key variable for understanding aerosol-cloud interactions and their climate effects. Aqua MODIS has provided one of the longest satellite records of cloud microphysical properties since 2002, but its reliability for recent trend analysis has been challenged by an unexpected global ocean N_d increase after 2022. We first show that this apparent increase is largely not a physical signal, but an artifact associated with Aqua’s orbital drift after entering free-drift mode. Changes in viewing geometry and solar illumination altered MODIS cloud retrievals and introduced artificial N_d biases, leading to a misleading reversal of the long-term declining tendency in global ocean N_d. Comparison with orbitally stable Suomi-NPP VIIRS observations confirms that the post-2022 MODIS increase is not reproduced by VIIRS and cannot be readily explained by changes in aerosol, meteorological, or precipitation conditions.

Building on this diagnosis, we further develop a MODIS-VIIRS bridging approach to construct a long-term, VIIRS-consistent global ocean N_d record. Rather than extending the record with drift-affected MODIS observations after 2022, we use the MODIS–VIIRS overlap period to place the pre-drift MODIS retrievals onto a VIIRS-consistent scale, and then continue the time series with VIIRS observations. This approach retains the historical continuity provided by the MODIS record while avoiding the artificial post-2022 drift signal. The resulting dataset captures major spatial and temporal features of marine N_d, including decreasing N_d over Northern Hemisphere mid-latitude oceans and relatively stable conditions over the Southern Ocean.

Together, these results highlight the importance of diagnosing satellite orbital artifacts before interpreting climate trends, and provide a more reliable observational basis for aerosol–cloud interaction studies and climate model evaluation.