Aerosol impacts on drizzle properties in warm clouds from ARM Mobile Facility maritime and continental deployments

摘要

We have extensively evaluated the response of cloud base drizzle rate (R_(cb); mmd~(-1)) in warm clouds to liquid water path (LWP; gm~(-2)) and to cloud condensation nuclei (CCN) number concentration (N_(CCN); cm~(-3)), an aerosol proxy. This evaluation is based on a 19month long data set of Doppler radar, lidar, microwave radiometers, and aerosol observing systems from the Atmospheric Radiation Measurement (ARM) Mobile Facility deployments at the Azores and in Germany. Assuming 0.55% supersaturation to calculate NCCN, we found a power law R_(cb) = (0.0015±0.0009)?LWP~((1.68±0.05)) N_(CCN)~((0.66±0.08)), indicating that R_(cb) decreases by a factor of 2–3 as N_(CCN) increases from 200 to 1000 cm~(-3) for fixed LWP. Additionally, the precipitation susceptibility to N_(CCN) ranges between 0.5 and 0.9, in agreement with values from simulations and aircraft measurements. Surprisingly, the susceptibility of the probability of precipitation from our analysis is much higher than that from CloudSat estimates but agrees well with simulations from a multiscale high-resolution aerosol-climate model. Although scale issues are not completely resolved in the intercomparisons, our results are encouraging, suggesting that it is possible for multiscale models to accurately simulate the response of LWP to aerosol perturbations.