Quantifying the aerosol/cloud-mediated radiative effect at a global scale requires simultaneous satellite retrievals of cloud condensation nuclei (CCN) concentrations and cloud base updraft velocities (W b ). Hitherto, the inability to do so has been a major cause of high uncertainty regarding anthropogenic aerosol/cloud-mediated radiative forcing. This can be addressed by the emerging capability of estimating CCN and W b of boundary layer convective clouds from an operational polar orbiting weather satellite. Our methodology uses such clouds as an effective analog for CCN chambers. The cloud base supersaturation (S) is determined by W b and the satellite-retrieved cloud base drop concentrations (N db ), which is the same as CCN(S). Validation against ground-based CCN instruments at Oklahoma, at Manaus, and onboard a ship in the northeast Pacific showed a retrieval accuracy of ±25% to ±30% for individual satellite overpasses. The methodology is presently limited to boundary layer not raining convective clouds of at least 1 km depth that are not obscured by upper layer clouds, including semitransparent cirrus. The limitation for small solar backscattering angles of <25°restricts the satellite coverage to ∼25% of the world area in a single day. (1) states that the uncertainty in aerosol/cloud interactions dominates the uncertainty about the degree of influence that human activities have on climate. Because clouds form in ascending air currents, whereas cloud droplets nucleate on aerosols that serve as cloud condensation nuclei (CCN), we need accurate measurements of both updrafts and CCN supersaturation (S) spectra before we can disentangle aerosol effects on cloud radiative forcing (CRF) from dynamical effects. Need for Global Measurements of Cloud Base Updrafts and CCN(S)Tackling the global change problems as identified by the IPCC requires that these quantities be measured on a global scale. However, satellites have not been able to measure updraft speed of the air that forms the clouds or the concentrations of aerosols that are capable of forming cloud drops, which are ingested into the clouds as they grow. Lack of such fundamental quantities has greatly hindered our capability of disentangling the effects of meteorology and anthropogenic aerosol emissions on cloud properties (2). This situation is starting to change with our recently developed methodology to retrieve updrafts at cloud base (3, 4) using the Visible/Infrared Imager Radiometer Suite (VIIRS) instrument onboard the Suomi National Polar-orbiting Partnership (NPP) satellite. This satellite is sun-synchronous, with an overpass time near 13:30 solar time.Missing such fundamental quantities as CCN(S) and cloud base updraft W b has been preventing us from disentangling the effects of aerosols from atmospheric dynamics (i.e., meteorology). Their absence also has limited our ability to validate the hypothesized impacts of added aerosols on a large range of phenomena, including (i) maintaining full cloud cover in marine stratocumulus, thus incurring a str...

The number of activated cloud condensation nuclei (CCN) into cloud drops at the base of convective clouds (N a ) is retrieved based on the high-resolution (375 m) satellite retrievals of vertical profiles of convective cloud drop effective radius (r e ). The maximum cloud base supersaturation (S) is calculated when N a is combined with radar-measured updraft and yields CCN(S), which was validated well against ground-based CCN measurements during the conditions of well-mixed boundary layer over the U.S. Department of Energy's Atmospheric System Research Southern Great Plains site. Satellite retrieving N a is a new capability, which is one essential component of simultaneous measurements of cloud microstructure and CCN from space by using clouds as natural CCN chambers. This has to be complemented by a methodology for satellite estimates of cloud base updraft, which is yet to be developed and demonstrated. In the mean time, the retrieved N a can be used for the assimilation of the combined CCN and updraft effects on clouds in models. The Motivation for Satellite Retrievals of Cloud Base Drop ConcentrationsDisentangling the effects of aerosols and meteorology on cloud radiative effects is a major challenge that impedes us from quantifying the aerosol cloud-mediated climate forcing and therefore constitutes the largest source of uncertainty in anthropogenic climate forcing . This disentanglement requires simultaneous measurements of cloud condensation nuclei (CCN) and cloud microphysical and dynamical properties from space, as envisioned by the CHASER (Clouds, Hazards, and Aerosols Survey for Earth Researchers) satellite mission Rennó et al., 2013]. The main idea of CHASER is using the base of convective clouds as CCN chambers. Measuring both the number concentrations of activated CCN into cloud drops at cloud base (N a ) and the updraft speed there (W b ) yields the vapor supersaturation (S) that the CCN particles are exposed to. Therefore, in fact, N a is the number concentration of CCN activated at S, i.e., CCN(S). This study represents a step toward the goal of satellite retrievals of CCN(S).Until now, satellite-retrieved cloud drop number concentrations (N d ) were based on vertically integrated cloud properties, such as liquid water path and optical depth [e.g., Szczodrak et al., 2001;Bennartz, 2007]. Therefore, the retrieved N d had to assume spatial homogeneity of the clouds, which is valid for layer much more than convective clouds. Furthermore, the mixing of the cloud with ambient air as it grows above its base dilutes N d to much smaller values than N a .Retrieving N a has become possible with the recent launch of the Suomi NPP (National Polar-Orbiting Partnership) satellite. The imager of the VIIRS (Visible Infrared Imaging Radiometer Suite) makes it possible by its breakthrough resolution of wave bands that allows retrieving cloud microstructure with the methodology that was developed by Rosenfeld et al. [2013]. The satellite resolution is 375 m at nadir, with little degradation across the swat...