The clear‐sky aerosol direct radiative effect (DRE) was estimated at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) and Tropical Western Pacific (TWP) sites. The NASA Langley Fu‐Liou radiation model was used with observed inputs including aerosol vertical extinction profile from the Raman lidar; spectral aerosol optical depth (AOD), single‐scattering albedo and asymmetry factor from Aerosol Robotic Network; temperature and water vapor profiles from radiosondes; and surface shortwave (SW) spectral albedo from radiometers. A radiative closure experiment was conducted for clear‐sky conditions. The mean differences of modeled and observed surface downwelling SW total fluxes were 1 W m−2 at SGP and 2 W m−2 at TWP, which are within observational uncertainty. At SGP, the estimated annual mean clear‐sky aerosol DRE is −3.00 W m−2 at the top of atmosphere (TOA) and −6.85 W m−2 at the surface. The strongest aerosol DRE of −4.81 (−10.77) W m−2 at the TOA (surface) are in the summer when AODs are largest. The weakest aerosol DRE of −1.28 (−2.77) W m−2 at the TOA (surface) are in November–January when AODs and single‐scattering albedos are lowest. At TWP, the annual mean clear‐sky DRE is −2.82 W m−2 at the TOA and −10.34 W m−2 at the surface. The strongest aerosol DRE of −5.95 (−22.20) W m−2 at the TOA (surface) are in November (October) due to the biomass burning season’s peak. The weakest aerosol DRE of −0.96 (−4.16) W m−2 at the TOA (surface) are in March (April) when AODs are smallest.

Ice cloud column optical depths from the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite and ground‐based Raman lidars (RLs) at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) and Tropical Western Pacific (TWP) sites are compared for 8 and 4 years, respectively. The cloudy mean ice cloud column optical depths from CALIPSO Version 4 data product with a horizontal resolution of 5 km are 78% (63%) larger than those from the RLs with a resolution of 10 min/30 m at SGP (TWP) for collocated transparent profiles. The main difference at SGP is caused by the lidar ratio that for CALIPSO is related to its treatment of the multiple scattering factor. The main difference at TWP is caused by the averaging resolution. Large differences in the optical depth distribution between the CALIPSO and RL are found for small optical depths at both sites, which are due to optically very thin clouds only detectable by the RLs. The differences in ice cloud column optical depth distributions and their mean values between the CALIPSO and RL can largely be reconciled over both sites after accounting for the averaging resolutions, lidar ratios along with the CALIPSO multiple scattering factor treatment, sensitivity to optically very thin ice clouds, and definition of transparent profiles. This work also examines in detail the lidar ratios that are directly observed by the RLs, which does not support the temperature‐dependent parameterizations of ice cloud lidar ratio and multiple scattering factor used in CALIPSO's Version 4 data product.

Optically very thin ice clouds from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and ground-based Raman lidars (RL) at the atmospheric radiation measurement (ARM) sites of the Southern Great Plains (SGP) and Tropical Western Pacific (TWP) are analyzed. The optically very thin ice clouds, with ice cloud column optical depths below 0.01, are about 23% of the transparent ice-cloudy profiles from the RL, compared to 4–7% from CALIPSO. The majority (66–76%) of optically very thin ice clouds from the RLs are found to be adjacent to ice clouds with ice cloud column optical depths greater than 0.01. The temporal structure of RL-observed optically very thin ice clouds indicates a clear sky–cloud continuum. Global cloudiness estimates from CALIPSO observations leveraged with high-sensitivity RL observations suggest that CALIPSO may underestimate the global cloud fraction when considering optically very thin ice clouds.

All‐sky aerosol direct radiative effect (DRE) was estimated for the first time at the Atmospheric Radiation Measurement Southern Great Plains site using multiyear ground‐based observations. The NASA Langley Fu‐Liou radiation model was employed. Observed inputs for the radiation model include aerosol and cloud vertical extinction profile from Raman lidar; spectral aerosol optical depth, single‐scattering albedo, and asymmetry factor from Aerosol Robotic Network; cloud water content profiles from radars; temperature and water vapor profiles from radiosondes; and surface shortwave spectral albedo from radiometers. A cloudy‐sky radiative closure experiment was performed. The relative mean differences between modeled and observed surface downwelling shortwave total fluxes were 6% (7%) for transparent (opaque) cloudy‐skies. The estimated annual mean all‐sky aerosol DRE is −2.13±0.54 W m−2 at the top of atmosphere (TOA) and −5.95±0.87 W m−2 at the surface, compared to −3.00±0.58 W m−2 and −6.85±1.00 W m−2, respectively, under clear‐sky conditions. The seasonal cycle of all‐sky aerosol DRE is similar to that of the clear‐sky, except with secondary influences of the clouds: The cloud radiative effect is strongest (most negative) in the spring, which reduces the all‐sky aerosol DRE. The relative uncertainties in all‐sky aerosol DRE due to measurement errors are generally comparable to those in clear‐sky conditions except for the aerosol single‐scattering albedo. The TOA all‐sky aerosol DRE relative uncertainty due to aerosol single‐scattering albedo uncertainty is larger than that in clear‐sky, leading to a larger total relative uncertainty. The measurement errors in cloud properties have small effects on the all‐sky aerosol DRE.