AEROSOL

Goals: The focus of the Aerosol IOP is primarily on the effect of boundary layer aerosol loading on clear-sky radiation fields. A secondary emphasis is to examine the effect of aerosol loading on overcast cloud microphysics and the effect of the microphysics on cloud optical properties. Specific issues include:

• Better vertical resolutions of aerosol in the boundary layer starting at 500 feet above the surface
• Support of CART Raman lidar and Micropulsed lidar profiles
• In-situ measurements for comparing lidar thin-cloud and radar microphysical retrievals
• Comparison of UAV upwelling radiation above in-situ measurement area with aircraft downwelling radiation below the clouds

Activity Summary

The Aerosol IOP was highlighted by the Gulfstream-1 aircraft flying clear-sky aerosol missions over the Central Facility to study the effect of aerosol loading on clear sky radiation fields, with weather particularly favorable for these flights during the first and third weeks of the IOP. A secondary but important goal of this IOP was to fly cloudy-sky missions over the Central Facility to study the effect of aerosol loading on cloud microphysics, and the effect of the microphysics on cloud optical properties. The Gulfstream obtained aerosol data in support of some of the UAV IOP clear-sky missions, the LANDSAT overpass of September 27, and in situ cloud microphysical data in support of the UAV IOP under cloudy sky conditions. The aerosol data collected by the Gulfstream is also of critical importance to the Shortwave IOP's radiometric measurements. Another key IOP priority was to use the collected aerosol data to support algorithm development for MPL and Raman lidar aerosol profiles.

The clear-sky experiment examined the effect of aerosol loading on clear sky radiation fields, and involved obtaining vertical profiles of aerosol microphysical and optical properties under clear sky conditions. Flights in support of this experiment involved passes over the Central Facility as low as 500 ft. AGL, with stepped legs up to about 17,000 ft. and spirals back down to 500 ft. Flights for this experiment were centered approximately on solar noon. Optimal conditions for this experiment were either clear skies or skies with minimal cloud cover (e.g., fair weather cumulus). Flights were made directly over the Central Facility for best coincidence with surface aerosol (AOS) and radiometric (variety of platforms) measurements.

The overcast-sky experiment addressed the issue of aerosol loading on cloud microphysics and the effect of variations of the microphysics on cloud optical properties. Flights measured the vertical distribution of cloud microphysical properties (e.g., droplet number density, size distribution, and liquid water content). The objective was to examine the relationship between the pre- or below cloud aerosol number concentrations, CCN spectra and the cloud droplet number concentration. Optimal clouds for these experiments were warm (liquid water) stratus or stratus with imbedded stratocumulus. Flights were conducted during daylight hours, centered on mid-day, and were coupled with UAV IOP flights to obtain cloud radiative properties whenever possible. Flight tracks consisted of vertical soundings through cloud layers and extended legs above, below, and in clouds.

The Gulfstream payload for aerosols included instruments for measuring aerosol number concentrations and size distributions, aerosol light scattering coefficient at three wavelengths, aerosol backscatter, aerosol absorption, CN concentrations and the CCN activation spectra.

Clear-sky Gulfstream flights were conducted on September 15, 18, 21, 25, 27 (in support of LANDSAT), 28, 29 (coordinated with the Altus/Twin Otter clear-flux profiling), 30 (wingtip-to-wingtip flight with the King Air for wind and water vapor sensor calibrations), and October 1 and 4 (both coordinated with the Altus and/or Twin Otter clear-sky flux profiling). Cloudy sky flights were conducted on September 21, 24, and 25. The cloudy sky flights were coordinated with flights of the UAV IOP aircraft as possible.

Critical ARM ground-based instrumentation included the AOS, Raman lidar, MPL, RSS, MFRSR, and a guest Cimel sunphotometer. The AOS data provided the local microphysical environment at the surface, while the MFRSR, RSS, and Cimel sunphotometer provided column-integrated optical depths. Vertical profiles of microphysical properties were specified by the Raman lidar and MPL, and by the Gulfstream aircraft.

Timeline

Campaign Data Sets