Towards satellite retrieval of CCN by using clouds as CCN chambers

 

Author

Daniel Rosenfeld — The Hebrew University of Jerusalem

Category

Warm Low Clouds and Interactions with Aerosol

Description

An overview of the closure of CCN and cloud base properties by combined satellite and cloud base measurements. Satellite retrieved drop concentrations (see methodology in the upper right box) are combined with SGP radar measured updrafts, and yield CCN(SS). This is validated against the measured CCN at the SGP, shown in the lower right box.
The ambiguity between the roles of meteorology and aerosols on cloud properties is the main hindrance in quantifying the aerosol cloud-mediated effects on the global energy budget. Disentangling of the respective roles would be achievable if we could measure independently the CCN and updrafts. Here we show advancements towards this goal by using clouds as natural CCN chambers (Rosenfeld et al., 2012). The specific steps for doing that have been already done are: 1. Satellite retrieval of the number concentrations of activated CCN into drop at convective cloud base (Na) over the SGP. 2. Retrieving the maximum supersaturation at cloud base (SS) by combining Na with SGP radar measured cloud base updraft (Wb). This yields CCN(SS), which is validated against SGP measured CCN. 3. Developing satellite based method for retrieving updraft speeds of thermals, by relating the SGP-lidar measured thermal updraft speed to the temperature difference between satellite-retrieved ground skin temperature and 2 m air temperature, as measured at the SGP (Zheng et al., 2014). 4. Satellite retrieving cloud base temperature and validating against SGP cielometer and sounding (Zhu et al., 2014). The next steps in progress: 5. Developing satellite based method for retrieving convective cloud base updraft speeds (Wb) as done and validated for thermals. 6. Combine the satellite retrieved Na and Wb for obtaining satellite retrieved CCN(SS), and validate against SGP measured CCN(SS). Our satellite retrievals (Rosenfeld et al., 2013) are based on the NPP/VIIRS Imager, which provides breakthrough resolution of 375 at nadir, thus allowing resolving the small convective clouds at the top of the boundary layer. This will allow a global application of the methodology developed here. References: Rosenfeld D. et al., 2012: The scientific basis for a satellite mission to retrieve CCN concentrations and their impacts on convective clouds. Atmos. Meas. Tech., 5, 2039–2055, 2012 Rosenfeld, D. et al., 2013: High resolution (375 m) cloud microstructure as seen from the NPP/VIIRS Satellite imager, Atmos. Chem. Phys. Discuss., 13, 29845-29894. Zheng Y., D. Rosenfeld, Z. Li, 2014: Retrieving updraft speeds of thermals by observed surface temperatures and winds. Submitted to JGR. Zhu Y., D. Rosenfeld, X. Yu, G. Liu, J. Dai, X. Xu, 2014: Satellite retrieval of convective cloud base temperature based on the NPP/VIIRS Imager. Submitted to J. Geophys. Res., 2014.

Lead PI

Daniel Rosenfeld — The Hebrew University of Jerusalem