Evaluation of Cloud Microphysical Properties Derived From MODIS and Himawari‐8 Using In Situ Aircraft Measurements Over the Southern Ocean

Abstract

Cloud microphysical properties from aircraft measurements during the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study are used to evaluate the cloud products from the geostationary satellite Himawari-8 (H-8) and the polar-orbiting satellite the Moderate Resolution Imaging Spectroradiometer (MODIS). Compared to the in situ aircraft observations when aircraft flew horizontally near cloud tops, the cloud droplet effective radius (r e ) and number concentration (N d ) from H-8 (MODIS) are 33% (26%-31%) and 2% (9-13%) larger. Both the H-8 and MODIS retrievals behave similarly for liquid-only and mixed-phase low-level clouds, indicating the weak sensitivity of the satellite cloud retrieval performance to cloud phase. The r e and N d of the cloud profiles from aircraft measurements were also used to compare with the satellite product. It shows that H-8 r e and N d agree better with aircraft measurements when considering only the in situ data acquired in the upper portions (highest 20%) of the clouds. Roughly, the r e overestimation by H-8 decreases from 18% to 3% when considering the upper portions of clouds compared to all cloud layer averages, except for one case with drizzles appeared. In addition, the performance of MODIS r e and N d is highly dependent on the wavelengths the retrieval method uses. The droplet r e retrievals using wavelength of 1.6 μm have much larger biases than that using the other two channels. The potential effects of the cloud vertical variation and the photon penetration depth, the cloud heterogeneity, the cloud droplet size spectra, and the drizzle on satellite retrievals have also been discussed. is a co-corresponding author with Chuanfeng Zhao Key Points:• Himawari-8 (MODIS) cloud product overestimates r e near cloud top by 33% (26-31%) over Southern Ocean • Himawari8 r e and N d agree better with aircraft measurements when considering only the in situ data acquired in the upper portions of clouds • The performance of MODIS retrievals depends on the wavelength, with larger biases at 1.6 μm than 2.1 and 3.7 μm

Coalescence Scavenging Drives Droplet Number Concentration in Southern Ocean Low Clouds

“…For the precipitation sink term, the cloud thickness (h) is estimated from nearby sawtooth legs, where cloud top and cloud base are defined as the highest and lowest altitude with liquid water content (LWC) > 0.03 g m −3 , following Wood et al (2011). The results of our analysis are not sensitive to reducing this LWC threshold to a lower value (e.g., 0.005 g m −3 as in L. Zhao et al, 2020). In a few cases, multilayer clouds were present and the top and bottom were chosen to span over the levels that were consistent with the radar and lidar boundaries observed during the below cloud leg.…”

Evaluation of MODIS and Himawari‐8 Low Clouds Retrievals Over the Southern Ocean With In Situ Measurements From the SOCRATES Campaign

“…Based on results from other regions, one expects that satellite retrievals for these relatively spatially homogenous clouds should work well (e.g., Painemal and Zuidema, 2011;hereafter PZ11). In section 5, we discuss conditional sampling issues and how results obtained here related to previous evaluation studies over the Pacific and over the SO (e.g., A18;Zhao et al, 2020) in more detail.…”

Evaluation of MODIS and Himawari-8 Low Clouds Retrievals over the Southern Ocean with In Situ Measurements from the SOCRATES Campaign

“…Very recently, Zhao et al (2020), hereafter Z20, evaluated MODIS and Himawari-8 re using SOCRATES measurements for a subset of the flights that we have analyzed. Their results differ from ours in several key respects.…”