Cumulus Humilis Aerosol Processing Study (CHAPS)
Summer 2007 ASP Field Campaign

Graphic: CHAPS map The primary goal of the CHAPS campaign is to characterize and contrast freshly emitted aerosols above, within and below fields of cumulus humilis (or fair-weather cumulus). These observations will be used to examine the aerosol optical properties and cloud nucleating properties from both below-cloud and above-cloud, and how they differ downwind of a mid-size city relative to similar aerosols in air less affected by emissions. (Large image)


Scientists from across the country will be combining resources to study the interactions of aerosols on clouds and of clouds on aerosols. Aerosol mass spectrometers and other state-of-science instruments from these institutions will be onboard the DOE Gulfstream-1 aircraft to make in situ cloud microphysical and aerosol observations while an airborne LIDAR provides look-down information on these same clouds from NASA's Beech King Air 200. The scientific goals of the campaign are intended to reduce uncertainties associated with the understanding of cloud/aerosol interactions (e.g., indirect effects, whereby anthropogenic aerosols are thought to change the cloud droplet spectra with associated changes to cloud brightness and precipitation efficiency).

The ASP CHAPS campaign will be conducted in the vicinity of Oklahoma City, OK between June 1 and June 30, 2007. The project is designed to examine the influence of anthropogenic aerosols from a mid-size urban area on the microphysics of cumuliform clouds, and the effects of these clouds on urban aerosols that pass through fields of fair weather cumulus (FWC). The resulting observations will be used to address a number of basic scientific issues, and also to evaluate the representation of cumulus cloud/aerosol processes within climate models. See additional information discussed on the Science Goals Project Overview.

There will be three measurement platforms for CHAPS

  • The DOE Gulfstream-1 Research Aircraft, under the command of (509) 376-6176 will make a number of in situ cloud observations. Our primary point of contact for this aspect of CHAPS is
    (509) 372-6134.
  • The NASA Langley Research Center Beech King Air 200 twin engine turboprop aircraft, with (757) 864-5373, (757) 864-9443, and (757) 864-1406 will deploy a High Spectral Resolution Lidar to provide profiles of aerosol backscatter and extinction in the vicinity of clouds. See a description of the HSRL System.
  • Observations from a surface site just north of Oklahoma City will be used to continuously characterize aerosol and chemical features within the boundary layer. (509) 372-6140 is the principal investigator for the ground site.

For additional contact information, see the list of Field Participants.

Please check our Calendar of Activities frequently for updates and revisions, and notify or if you'd like to receive an e-mail for any such updates.

Airborne Platforms

We anticipate having the King Air carry out 'scouting' missions to identify the Oklahoma Plume and to make remote observations of these fields of clouds and aerosols, while the G-1 makes in situ observations of similar quantities. A 'typical' flight day will have the King Air take off from our base of operations in Ponca City, Oklahoma, scout out the plume and relay this information to the G-1 flight team who will then proceed to make the in situ observations while the King Air continues sampling overhead.

Aerosol sampling by the G-1 will involve measurements made from both a counterflow virtual impactor (CVI) and an isokinetic probe. See Instruments on each Inlet and the Key Scientists. In addition to measuring aerosol size, scattering and absorption, we will have a PTR-MS and Aerodyne Aerosol Mass Spectrometer (AMS) onboard. The PTR-MS will be sampling continuously from its own inlet. The AMS will be connected to a valve system that will allow the scientists on board to manually alternate aerosol composition measurements from either the CVI or the isokinetic probe. See our most recent Floor Plan for this dual-measurement approach. Note that this plan will be undergoing revisions as we start to put instruments on the aircraft so check frequently for updates. Contact with questions.

We have a number of Protocol and Flight Plans for the G-1 and similar Protocols and Flight Plans for the King Air. The information will be filed with DOE and the FAA and is summarized below.

  • Our first flight plan is designed to test the instruments and will consist of a series of stacked transects, with the lowest being in the mid-boundary layer and the highest being in the free troposphere, above cloud top.
  • Our 'basic' plume sampling strategy will consist of a set of below-cloud, within-cloud and above-cloud transects, with at least two sets of such Three-Layer Transects done at varying distances downwind of Oklahoma City. This flight will place the G-1 in both regional background air and within the urban plume of Oklahoma City, allowing us to contrast the influence of this aerosol plume on the clouds, and of the clouds on the aerosols. A similar flight plan is anticipated for cloud-free conditions. It differs from the cloudy plan in that the sampling altitudes are defined as a function of depth within of the convective boundary layer, rather than below-, within- and above clouds, and in having more downwind transects (since there is no need for in-cloud transects).
  • We anticipate working with scientists from the concurrent CLASIC Campaign to make in situ cloud microphysics observations with the G-1 while the ER-2 aircraft makes lidar observations of similar properties from greater altitudes. An aircraft instrument intercomparison flight is also planned with the CLASIC aircraft.
  • Another joint CHAPS-CLASIC aircraft experiment will involve sampling by the G-1 with the CLASIC aircraft concurrent with a flyover of NASA's 'A-Train' Satellites.
  • As time and resources allow, we also hope to carry out a cloud microphysics studies away from urban areas, within a few hundred kilometers of Ponca City.

The King Air flights will normally occur at a constant altitude of about 28,000 ft to facilitate optimum performance of the High Spectral Resolution Lidar (HSRL). This altitude enables this lidar system to measure aerosol profiles extending between the surface and about 23,000 ft above ground level. Since clouds attenuate the laser beams, the King Air may fly at a slightly lower altitude (24000-28000 ft) in order to avoid any clouds that may be present in this altitude range.

Ground Platform

The collection of meteorological and aerosol data will occur at a ground site (approximately 35º 44' 04" N, 97º 28' 49.4" W) just north of Edmond, Oklahoma. Mr. Bob Brentlinger, who is developing part of his farm as Brentlinger Industrial Park, has agreed to allow us to locate our equipment on his property for the campaign. The area is rural, but within a few miles of the Oklahoma City urban area.

At this site, PNNL will provide radiosonde launches (up to five per day when the G-1 flies) and particle characteristics from a passive cavity aerosol spectrometer probe (PCASP), a particle/soot absorption photometer (PSAP), nephelometer, and condensation particle counter. Argonne National Laboratory will provide radar measurements of the winds above the surface and profiles of aerosol backscatter from a micropulse lidar. Participants from Visidyne plan to operate a Sun and Aureole Measurement (SAM) sensor to measure cloud optical properties at the site, and Scot Martin's group from Harvard will operate their mass spectrometer.

PNNL is also planning to operate a Total Sky Imager at a nearby location, due to the requirement for internet access for the instrument.


This experiment will be the first ASP campaign to follow after the official release of the ASP Data Policy. Our team will work with this policy during and after the campaign, making the observations available within the time frame described therein. It is also expected that 'first look results' from the campaign will be available shortly after each flight. While always important, it will be particularly critical for this study because of the nature of the sampling and because so many new technologies are to be deployed on the aircraft. The sampling challenges for this campaign stem from the relatively high speed of the G-1 platform (~100m/s / 200 kts) and relatively small size of the cumulus clouds (observations from the ARM Southern Great Plains site show that the mean cloud chord length is ~ 1km,or 0.6 nautical miles, Berg and Kassianov, 2007) resulting in expected in-cloud sampling times of the order of 10 seconds. Our first flights will be focused on verifying that the instruments can detect a 'real' sample under these conditions.

CHAPS/CLASIC Interaction

Scientists from both CHAPS and CLASIC are interested in cloud microphysics. The CHAPS participants have, as their goal, to better understand how aerosols affect the internal cloud aerosol composition and associated optical properties, while the CLASIC scientists are interested in learning how changes in land use affects clouds through changes to surface heating and associated dynamics. Both campaigns will be making measurements of cloud water concentration, droplet size distributions, and the optical properties of aerosols in the vicinity of clouds. The CHAPS scientists will be measuring aerosol composition and related chemistry measurements, while the CLASIC team will have a more complete array of radiometric systems on their aircraft.

As a result, many of the observations made by the CHAPS aircraft (the G-1 and NASA King Air) will complement observations made by the CLASIC aircraft, and vice versa. The CHAPS/G-1 will focus on in situ observations of cloud properties, as will the CLASIC Twin Otter aircraft. The CHAPS King Air, flying NASA's HSRL, will focus on remote measurements of cloud albedo and effective droplet size that will compliment observations to be made by the CLASIC ER-2 flyovers. By having the ASP/CHAPS campaign and ARM/CLASIC campaign co-located in Oklahoma, scientists from both campaigns can use a suite of observations from the other to extrapolate their results to broader geographical areas.

With the exception of the CLASIC/ER-2 aircraft, all planes will be based in Ponca City, OK. Although the main sampling area for the G-1 will be near Oklahoma City, and the sampling area for the CLASIC aircraft is much broader, we are anticipating that many of the CLASIC aircraft will fly through the Oklahoma City region, often at times concurrent with the G-1 missions. In addition, aircraft from both CHAPS and CLASIC will be flying in a coordinated pattern to evaluate satellite observations from the NASA "A-Train" flyovers. To assure that these, and other opportunities for cross-program information exchange have merit, at least one, and possibly two, aircraft intercomparisons are planned. These are tentatively scheduled for the first and last days of the CHAPS/CLASIC campaign.


Lead Scientists