Mixed-phase cloud radiative forcing during M-PACE: estimates from surface-based remote sensors
Authors
Chuck N. Long (deceased) — NOAA- Earth System Research Laboratory
Surabi Menon — Lawrence Berkeley National Laboratory
William D. Collins — Lawrence Berkeley National Laboratory
Gijs de Boer — University of Colorado
Category
Radiation
Description
An example of measured and retrieved mixed-phase cloud properties from M-PACE. Included (from top to bottom) are lidar aerosol backscatter cross-section, lidar depolarization ratio, millimeter cloud radar reflectivity, retrieved liquid (left) and ice (right) water content profiles, and retrieved liquid (left) and ice (right) effective particle sizes.
The influence of clouds on the surface radiative budget is an important component in understanding how changes in cloud cover may influence future climate states. In the Arctic, mixed-phase stratiform clouds are commonly observed and have been shown to be among the most radiatively influential structures. Previous efforts detailing the radiative forcing of mixed-phase clouds have demonstrated importance of the liquid water component in governing both long and shortwave radiation. Radiative forcing from these cloud structures is positive (net increase in energy into the surface) for much of the year, due to low sun angles and a dominance of longwave effects. During Arctic summer, these clouds impart negative cloud forcing due to their high shortwave albedo.
Estimates of cloud radiative forcing are obtainable from surface radiometric measurements, when available. At sites that do not offer such measurements, estimates of cloud radiative forcing can be obtained using a radiative transfer model initiated with conditions measured by remote sensors. In this study, we utilize a suite of ground-based remote sensors, including radar, lidar, and microwave radiometers, along with a state-of-the-art set of retrieval algorithms and radiative transfer models. These tools are used to estimate surface radiative forcing from mixed-phase clouds observed over Barrow, Alaska, during the 2004 Mixed-Phase Arctic Clouds Experiment (M-PACE). An overview of retrievals will be provided along with an analysis of model-calculated and measured surface radiative fluxes. Finally, an overview of cloud radiative forcing will be provided, along with a sensitivity analysis covering the most uncertain aspects of the retrievals.
