Studying the vertical variation of cloud droplet effective radius using ship and space‐borne remote sensing data

The albedo of marine stratocumuli depends upon cloud liquid water content, droplet effective radius ( r e ), and how these parameters vary with height. Using satellite data and shipborne data from the East Pacific Investigation of Climate (EPIC) Stratocumulus Study, this study investigates the cloud r e vertical variation for drizzling and nondrizzling clouds. Visible/near‐infrared retrievals from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) are used to estimate the vertical profile of r e . MODIS r e observations and collocated shipborne scanning C‐band precipitation radar data show that r e generally increases with height in nondrizzling clouds, consistent with aircraft observations. It is found that in clouds with precipitation rates greater than a few hundredths of a mm h −1 the vertical gradient of r e is significantly less than that in nondrizzling clouds and can become negative when the drizzle is heavier than approximately 0.1 mm h −1 . High values of r e at drizzling cloud base are consistent with estimates of the ratio of liquid water in the drizzle drops to that in the cloud droplets. C‐band derived cloud base precipitation rates are found to be better correlated with r e at cloud base than with r e at cloud top, suggesting that passive remote sensing may be useful for drizzle detection.