Ground-based retrieval of continental and marine warm cloud microphysics

Abstract

A technique for retrieving warm cloud microphysics using synergistic ground based remote sensing instruments is presented. The SYRSOC (SYnergistic Remote Sensing Of Cloud) technique utilises a K_<i>a</i>-band Doppler cloud RADAR, a LIDAR (or ceilometer) and a multichannel microwave radiometer. SYRSOC retrieves the main microphysical parameters such as cloud droplet number concentration (CDNC), droplets effective radius (<i>r</i>_eff), cloud liquid water content (LWC), and the departure from adiabatic conditions within the cloud. Two retrievals are presented for continental and marine stratocumulus advected over the Mace Head Atmospheric Research Station. Whilst the continental case exhibited high CDCN (<span style="border-top: 1px solid #000; color: #000;"><i>N</i></span> = 382 cm⁻³; 10th-to-90th percentile [9.4–842.4] cm⁻³) and small mean effective radius (<span style="border-top: 1px solid #000; color: #000;"><i>r</i>_eff</span> = 4.3; 10th-to-90th percentile [2.9–6.5] μm), the marine case showed low CDNC and large mean effective radius (<span style="border-top: 1px solid #000; color: #000;"><i>N</i></span> = 25 cm⁻³, 10th-to-90th percentile [1.5–69] cm⁻³; <span style="border-top: 1px solid #000; color: #000;"><i>r</i>_eff</span> = 28.4 μm, 10th-to-90th percentile [11.2–42.7] μm) as expected since continental air at this location is typically more polluted than marine air. The mean LWC was comparable for the two cases (continental: 0.19 g m⁻³; marine: 0.16 g m⁻³) but the 10th–90th percentile range was wider in marine air (continental: 0.11–0.22 g m⁻³; marine: 0.01–0.38 g m⁻³). The calculated algorithm uncertainty for the continental and marine case for each variable was, respectively, &sigma;_<i>N</i> = 161.58 cm⁻³ and 12.2 cm⁻³, &sigma;_{<i>r</i>_eff} = 0.86 μm and 5.6 μm, &sigma;_LWC = 0.03 g m⁻³ and 0.04 g m⁻³. The retrieved CDNC are compared to the cloud condensation nuclei concentrations and the best agreement is achieved for a supersaturation of 0.1% in the continental case and between 0.1%–0.75% for the marine stratocumulus. The retrieved <i>r</i>_eff at the top of the clouds are compared to the MODIS satellite <i>r</i>_eff: 7 μm (MODIS) vs. 6.2 μm (SYRSOC) and 16.3 μm (MODIS) vs. 17 μm (SYRSOC) for continental and marine cases, respectively. The combined analysis of the CDNC and the <i>r</i>_eff, for the marine case shows that the drizzle modifies the droplet size distribution and <span style="border-top: 1px solid #000; color: #000;"><i>r</i>_eff</span> especially if compared to <i>r</i>_eff^MOD. The study of the cloud subadiabaticity and the LWC shows the general sub-adiabatic character of both clouds with more pronounced departure from adiabatic conditions in the continental case than in the marine.